Chemical engineering education

http://cee.che.ufl.edu/ ( Journal Site )
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Material Information

Title:
Chemical engineering education
Alternate Title:
CEE
Abbreviated Title:
Chem. eng. educ.
Physical Description:
v. : ill. ; 22-28 cm.
Language:
English
Creator:
American Society for Engineering Education -- Chemical Engineering Division
Publisher:
Chemical Engineering Division, American Society for Engineering Education
Place of Publication:
Storrs, Conn
Publication Date:
Frequency:
quarterly[1962-]
annual[ former 1960-1961]
quarterly
regular

Subjects

Subjects / Keywords:
Chemical engineering -- Study and teaching -- Periodicals   ( lcsh )
Genre:
periodical   ( marcgt )
serial   ( sobekcm )

Notes

Citation/Reference:
Chemical abstracts
Additional Physical Form:
Also issued online.
Dates or Sequential Designation:
1960-June 1964 ; v. 1, no. 1 (Oct. 1965)-
Numbering Peculiarities:
Publication suspended briefly: issue designated v. 1, no. 4 (June 1966) published Nov. 1967.
General Note:
Title from cover.
General Note:
Place of publication varies: Rochester, N.Y., 1965-1967; Gainesville, Fla., 1968-

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
oclc - 01151209
lccn - 70013732
issn - 0009-2479
Classification:
lcc - TP165 .C18
ddc - 660/.2/071
System ID:
AA00000383:00126

Full Text














Ilelen C. Hollein,


A WARD LECTURE



M Features:














0 Special Features ...



Northeastern University






















Each year
Chemical Engineering Education
publishes
a special fall issue devoted
to graduate education.
It includes
0 articles on graduate courses and research,
written by professors at various universities, and
0 ads describing the university graduate programs.

Anyone interested in contributing
to the editorial content of the
1995 fall issue should write to CEE,
indicating the subject of the contribution
and the tentative date it will be submitted.


Deadline is June 15, 1995


CALL FOR PAPERS


FALL 1995

GRADUATE EDUCATION ISSUE OF

CHEMICAL ENGINEERING EDUCATION













EDITORIAL AND BUSINESS ADDRESS:
Chemical Engineering Education
Department of Chemical Engineering
University of Florida
Gainesville, FL 32611
PHONE and FAX: 904-392-0861
e-mail: cee@che.ufl.edu

EDITOR
Ray W. Fahien
ASSOCIATE EDITOR
T. J. Anderson
CONSULTING EDITOR
Mack Tyner
MANAGING EDITOR
Carole Yocum
PROBLEM EDITORS
James O. Wilkes and Mark A. Burns
University of Michigan
LEARNING IN INDUSTRY EDITOR
William J. Koros
University of Texas, Austin
PUBLICATIONS BOARD

CHAIRMAN *
E. Dendy Sloan, Jr.
Colorado School of Mines

PAST CHAIRMEN *
Gary Poehlein
Georgia Institute of Technology
Klaus Timmerhaus
University of Colorado

MEMBERS
Anthony T. DiBenedetto
University of Connecticut
Thomas F. Edgar
University of Texas at Austin
Richard M. Felder
North Carolina State University
Bruce A. Finlayson
University of Washington
H. Scott Fogler
University of Michigan
J. David Hellums
Rice University
Angelo J. Perna
New Jersey Institute ri T, ,,..... ., v
Stanley I Sandler
University of Delaware
Richard C. Seagrave
Iowa State University
M. Sami Selim
Colorado School of Mines
James E. Stice
University of Texas at Austin
Phillip C. Wankat
Purdue University
Donald R. Woods
McMaster University



Spring 1995


Chemical Engineering Education


Volume 29


Number 2


Spring 1995


EDUCATOR
66 Helen C. Hollein, of Manhattan College, C. Stewart Slater

DEPARTMENT
70 Northeastern University, Ralph A. Buonopane

AWARD LECTURE
76 Computer-Aided Design and Operation of Batch Processes,
G. V. Reklaitis

LABORATORY
86 Bioseparation via Cross-Flow Membrane Filtration,
Helen C. Hollein, C. Stewart Slater, Rita L. D'Aquino, Annmarie L. Witt

CLASSROOM
94 Exorcising Maxwell's Demon: Entropy, Information, and Computing,
B. G. Kyle
96 An Ancient Method for Cooling Water Explained by Mass and Heat
Transfer, J. Ignacio Zubizarreta, Gabriel Pinto
106 Determining Residence Time Distributions in Complex Process Systems:
A Simple Method, Paul D. Gossen, G. Ravi Sriniwas, F. Joseph Schork
134 Terse Words in Tight Margins, Robert R. Hudgins

RANDOM THOUGHTS
102 Just Another Day at the Office, Richard M. Felder

LEARNING IN INDUSTRY
112 WPI Projects Globalize Engineering Education in the Pacific Rim,
Y.H. Ma, L. Schachterle, J.F. Zeugner

LABORATORY
116 Unsteady-State Heat Transfer from a Steam-Heated Coil to a Tank of
Water, Peter Rice
120 Polymer Processing: For the Undergraduate Unit Operations Laboratory,
Ajit V. Pendse, John R. Collier

CURRICULUM
126 A Course on Tissue Engineering, Susan L. Ishaug, Antonios G. Mikos

CLASS AND HOME PROBLEMS
130 Problems on Fluids in Motion and at Rest, A.R. Konak
93, 111, 125 Book Reviews

100 ASEE Annual Meeting: ChE Division Program

104 Letters to the Editor: Why Do You Belong to ASEE?
133 Letter to the Editor
136 Books Received


CHEMICAL ENGINEERING EDUCATION (ISSN 0009-2479) is published quarterly by the Chemical Engineering
Division, American Society for Engineering Education, and is edited at the University of Florida. Correspondence
regarding editorial matter, circulation, and changes of address should be sent to CEE, Chemical Engineering Department,
University of Florida, Gainesville, FL 32611-2022. Copyright 1995 by the Chemical Engineering Division, American
Society for Engineering Education. The statements and opinions expressed in this periodical are those of the writers and
not necessarily those of the ChE Division, ASEE, which body assumes no responsibility for them. Defective copies replaced
if notified within 120 days of publication. Write for information on subscription costs and for back copy costs and
availability. POSTMASTER: Send address changes to CEE, Chemical Engineering Department., University of Florida,
Gainesville, FL 32611.


















HELEN C. HOLLEIN

of Manhattan College



Connie's evolution from ballerina
through high school dreamer to college
professor.


n 1982, The Quadranilc i Nlan- -: --
hattan College's student ne\'s-
paper) published an article prto-
claiming, "Engineering Goes Co-
ed." It heralded the arn.ial ot three
women faculty members t[o the
School of Engineering, one of whom
is the subject of this paper. The college had become coeducational
and had admitted women students nine years earlier (a few women
engineers graduated from Manhattan prior to 1973 through a coop-
erative program with neighboring College of Mount Saint Vincent).
Helen Conway Hollein, or Connie as she is known to her friends,
family, and colleagues, joined the chemical engineering faculty at
MC in 1982 and has since become a role model for female engi-
neering students at Manhattan College as well as for other women
across the country. She is currently Professor of Chemical Engi-
neering, Chair of the ChE Department, Director of the Interdisci-
plinary Biotechnology Program, and one of four women who teach
engineering at MC. She is also a licensed professional engineer in
New Jersey. Connie was MC's first woman engineer to be pro-
moted to associate professor in 1988 and to professor in 1994. In
1989, she became the first woman at Manhattan to head an engi-
neering department (she is one of only four women who currently
chair U.S. ChE departments).

THE MANHATTAN YEARS
Teaching at Manhattan College means developing a research
program with the help of undergraduate students plus an occa-
@ Copyright ChE Division ofASEE 1995


I
e*


sional master's student, while teaching three to four
classes each semester. Connie says that the best advice
she received as a new faculty member dealing with
these challenges was "to land on your feet and running."
In her first year at Manhattan she did just that, with an
Excellence in Teaching Award from the Tau Beta Pi
student chapter and an NSF grant from the Engineering
Research Initiation Program. The chemical engineering
seniors seconded her teaching award with a "Rookie of
the Year" award at our annual chemical engineering
banquet. Rumor has it that the seniors used to go to the
local "watering hole" for "Connie's keg" after process
Chemical Engineering Education


S= educator


C. STEWART SLATER
Manhattan College
Riverdale, NY 10471












As to her philosophy of teaching, Connie says that the _
most important qualities in teaching are to be
organized, to know your material, to respect
your students, and to grade fairly.


control exams. Some students referred to her as the "female
Famularo,"-a double-edged compliment since Jack Famularo had
a reputation as a great teacher but a really tough so-and-so.
In subsequent years, Connie was recognized with teaching awards
from the students in 1986 and again in 1989, and in 1987 she
received a Trustees Award from Manhattan College as the outstand-
ing engineering faculty member. This award honored her teaching
and scholarly activities, which included external funding of ap-
proximately $450,000 for her first five years at the College. She also
received national recognition with a Ralph R. Teetor Educational
Award from the Society of Automotive Engineers in 1984.
Connie is a popular teacher, and her teaching evaluations are
always outstanding. Her favorite courses to teach are "anything
during the senior year," including the senior laboratory courses,
biochemical engineering, transport phenomena, advanced mass trans-
fer, process control, and polymer engineering. She has also taught a
graduate-level biochemical engineering course, the introductory mass
transfer course (junior year), and engineering materials lecture and
laboratory courses (sophomore year).
As to her philosophy of teaching, Connie says that the most
important qualities in teaching are to be organized, to know your
material, to respect your students, and to grade fairly. She gives
students the rules on their first day, e.g., what material will be
covered, how grades will be determined, when major assignments
are due, what are the late penalties, and what is the material's value
to their engineering future. To make the subject matter more rel-
evant, she supplements the text with current literature, such as
issues of chemical engineering journals on process control or ar-
ticles from news magazines on biotechnology. Connie says, "Joe
Reynolds hired me and impressed upon me the importance that
the College places on teaching and research. He is our top-rated
teacher and publishes with Louis Theodore on environmental man-
agement." When she asked Br. Conrad Burris, FSC (former ChE
Department Chair and Dean Emeritus of Engineering) about grad-
ing practices at Manhattan, he told her, "Teachers don't fail stu-
dents, they fail themselves."
After completing her dissertation on "Separation of Proteins via
pH Parametric Pumping with Electric Field," Connie published
several papers related to that body of research in addition to writing
a handbook chapter on parametric pumping. At MC, she chose to
focus on biological separations instead of continuing as a parametric
pumper. She received NSF and NIH grants to work on protein
separations using ion exchange chromatography and a grant from
the New York State Science and Technology Foundation to study
commercial applications of high performance liquid chromatogra-
phy for bioseparations. She also received an NSF grant under the
Spring 1995


The 1984 Manhattan College faculty. Standing (left
to right) are Jamie Chua, Joseph Reynolds, Paul
Marnell, Br. Conrad Burris, Jack Famularo, Stewart
Slater, Connie Hollein, and Fred Zenz. Connie's
husband, Leo, is seated with the other spouses.


Instrumentation and Laboratory Improvement Program
to develop a biochemical engineering laboratory. Each
year, she involves two or three students in her research
and laboratory development efforts, and many of her
students are coauthors of papers and presentations.
When I came to Manhattan College in 1983, Connie
and I began a collaborative effort in research and
laboratory development that has been mutually benefi-
cial. My research expertise is in the area of membrane
separation processes, so we agreed to work on several
joint projects involving use of membrane processes
for biological separations. Our joint efforts include
projects on purification and concentration of proteins
and enzymes using several ultrafiltration systems and
cell harvesting studies using microfiltration. I worked
with her to develop the biochemical engineering
laboratory, helping with downstream separation ex-
periments while she focused on fermentation experi-
ments. We also worked together on several NSF grants
to develop an advanced separation process laboratory
for our students and to conduct an NSF-sponsored
workshop on membrane separation processes for chemi-
cal engineering faculty.
When Br. Burris retired from full-time teaching in
1989, Connie was the unanimous choice of the ChE
faculty to succeed him as Department Chair. She had
already proved her administrative talents as chair of
the Fischbach Lecture Series, chair of the School of
Engineering Curriculum Committee, president of the
Manhattan College Chapter of Sigma Xi, and vice
chairman of the Council for Faculty Affairs. In addi-
tion, she had served as a key player in a 1989 team
effort that resulted in New York State approval to
67










grant an interdisciplinary master's degree in bio-
technology. Development of the new program was
both a curricular challenge and a nightmare of
campus politics because it involved three depart-
ments (biology, chemistry, and chemical engineer-
ing) and the science departments are cooperative ven-
tures between Manhattan College and the College of p
Mount Saint Vincent.
Her first task as departmental administrator was to
lead us through a successful ABET accreditation in
1990. When asked what she likes most about being
chairperson, Connie says it is the fact that her second
and final term will end in 1997. She is looking for-
ward to spending more time on her true loves of
teaching and undergraduate research. She finds that
her greatest job satisfaction comes from seeing stu-
dents who worked on her biochemical engineering
projects succeed in the food, pharmaceutical, and Ral
biotech industries. Wi
exp
Connie is active in ASEE and AIChE and has Enh
presented papers and chaired sessions in both organi-
zations. She has served as a director of ASEE's Chemical
Engineering Division, and as Secretary-Treasurer and news-
letter editor of the Women in Engineering Division. She is
also active in the Division of Experimentation and Labora-
tory-Oriented Studies. She previously served as chairman of
AIChE's Group 4, Education, and is currently a member
of the Admissions Committee. Connie is a senior member of
the Society of Women Engineers and served as moderator
of MC's student section from 1984 to 1988. Under her
leadership, the section inaugurated our annual "Engineering
Awareness Day" (a high school outreach program) in 1986
and won two national awards: the Corning Glass Works
Career Guidance Award in 1987, and an Outstanding
Activities Award in 1988. She has also served on a number
of NSF review panels.

THE EARLY YEARS
Connie was born in Fort Bragg, North Carolina, to Lt.
Arthur Conway Faris and his wife Helen, and is the oldest of
five children, all seventh-generation Americans of Scotch-
English descent. Ancestors of all four grandparents fought in
the Continental Army during the Revolutionary War. Her
Faris ancestors immigrated from Scotland to Ireland during
the religious persecutions of 1680-1683, and from Ireland to
West Virginia in 1763. Her other paternal ancestors, the
Houstons, immigrated from Scotland to Virginia in 1652.
Her maternal ancestors were early English settlers, one branch
settling in the Massachusetts Bay Colony around 1630 and
the other arriving in the colonies in the early 1700s.
With the exception of a short period between wars (1947
to 1951) when she lived on a farm near Maryville, Missouri,
Connie and her family moved from one army base to another
68


ph Buonopane, Nilufer Dural, Connie Hollein, and John
ncek (left to right) operate a hand-held reverse osmosis
eriment during an NSF-sponsored Undergraduate Faculty
lancement Workshop at Manhattan College (1991).

as her father progressed through the ranks to colonel. She
did all of the typical "girl things," such as taking dance and
piano lessons, and she advanced to Curved Bar in scouting
(highest rank in the Girl Scouts). She attended a total of
fourteen different schools prior to graduating from Douglas
MacArthur High School in San Antonio, Texas, in 1961.
Her father maintained his permanent military residence in
South Carolina, so Connie took advantage of in-state tuition
costs and enrolled at the University of South Carolina after
graduating from high school. She started college as a double
major in chemistry and mathematics. In the 1960s, engineer-
ing students at Carolina were required to complete one-year
courses in calculus, chemistry, and physics before becoming
eligible to enroll in the College of Engineering. At the end of
her freshman year, when her male counterparts were apply-
ing for admission to engineering, some of them told her that
since she had the requisite grades, she should also apply.
Connie remembers, "I had asked my father about studying
engineering (before entering college), but he told me that it
was a man's field. So I made an appointment with the dean
of engineering and asked him if girls were allowed to study
engineering. He laughed and said that there weren't any
regulations against it, but he was somewhat skeptical about
my chances to graduate." Three years later, Connie became
the first female chemical engineer to graduate from USC and
was only their third woman engineering graduate (less than
0.1% of the engineering graduates at that time were women).
Connie's high school and college yearbooks reveal that
her administrative talents surfaced at an early age. In high
school she was business manager of the yearbook and
president of the Pep Club, while in college she was pres-
ident of the AIChE student chapter, corresponding secretary
Chemical Engineering Education










of the AIChE Southern Regional Student Conference, and a
member of Alpha Order, USC's honor society for women
leaders. Her innate talents as a teacher must also have
been evident, even in high school, because the senior proph-
esy foretold that she would become a high school math
teacher in New England.
During her junior year as USC, Connie qualified for mem-
bership in Tau Beta Pi, but discovered, to her astonishment,
that the national engineering honor society did not admit
women. She received a Woman's Badge from the society in
1964, an honor that some women refused because they wanted
equal recognition or none at all. Tau Beta Pi initiated the first
women in 1969, becoming one of the last honor societies to
do so. Wearers of the Woman's
Badge were offered full member-
ship at that time, and Connie was
one of 97 women (out of total of
619) who accepted the offer.
In the 1960s, girls had to wear
skirts to class, which presented a
problem when it came time to take
the unit operations laboratory course
in a two-story facility with open
grates between the first and second
floors. After lobbying at every pos-
sible level, Connie finally got per-
mission from the president of the
university to wear pants in the labo- T Holn-
The Holleins-Kath
ratory. Permission included the con- and Leo-at Mary'
edition that she leave and reenter the the Universitj
dormitory in skirts. These incidents
at USC, plus the notoriety resulting from three newspaper
interviews and several television news reports, made Connie
realize that her choice of major was a bit unusual.
Connie's first exposure to research occurred during the
summer between her second and third years at USC when
she worked on an NSF undergraduate research grant super-
vised by Milton Davis. This was followed a year later by her
senior thesis under the direction of Joseph Gibbons (cur-
rently Associate Dean of Engineering at USC). She also
gained engineering experience with summer internships at
Cardinal Chemical Company in South Carolina and the U.S.
Navy in Washington, DC.
As graduation approached, Connie's professors encour-
aged her to apply to graduate school, but she decided to
accept an engineering position with Exxon Research and
Engineering Company in Florham Park, New Jersey. She
liked the idea of working at the Exxon site, where she would
be their fourth woman engineer, instead of working for some
other companies which interviewed her where she would be
the first. Also, the women in the northern states were stereo-
typed as being more assertive or liberated than "southern
belles," so she felt that New Jersey would be a more support-
Spring 1995


y, M
s 19
rof]


ive environment for a female professional.
At Exxon, Connie met her future husband, Leo Hollein.
They were married and in due time became the proud par-
ents of three children. Their oldest daughter, Mary, followed
in her mother's footsteps and is currently a senior engineer at
Exxon, having previously worked as a nuclear engineer at
the Savannah River Plant in South Carolina. Mary earned a
bachelor's degree in mechanical engineering from the Uni-
versity of Pennsylvania and a master's degree in chemical
engineering from Manhattan College. Their second child,
Kathleen, completed a baccalaureate degree in sociology at
Jersey City State College, and an associate degree in early
childhood education at Teikyo Post University. Their son,
Michael, is a student at the Uni-
versity of Colorado, where he is
majoring in skiing and minoring
in chemical engineering.
During her two years at Exxon,
Connie worked on a number of
projects in the Chemicals Division.
After Title VII passed into law,
she became the first woman
engineer at ER&E to go on a
field assignment. This assignment
was associated with a project
aimed at improving product qual-
ity in the isophorone/
like, Connie, Mary, dihydroisophorone distillation unit
88 graduation from at Bayway Refinery (Bayway,
Pennsylvania. New Jersey). Connie had previ-
ously worked on a p-xylene li-
censing proposal that would have resulted in a three-month
field assignment at a pilot facility in Connecticut, but a
male colleague went on that assignment because women
simply did not work in chemical plants in those days. Some
thirty years later, her daughter goes on short trips to refiner-
ies in Canada, England, Greece, and the U.S. on a routine
basis and is looking forward to a three-year assignment at
Fawley Refinery in England.
While she was expecting her first child in 1967, Connie
agonized over the problems of balancing engineering with
family life and decided to change professions. It was
clear that to advance in her career at Exxon, she would
have to travel much as her daughter does today, and she
didn't see how that would be possible with young children.
She completed the required educational credits for second-
ary certification in physical sciences and mathematics at
Fairleigh Dickinson University and found a position teach-
ing chemistry and physics at Livingston High School in
suburban New Jersey. In the next two years, she discovered
that she truly loved teaching.
In 1969, Connie resigned from her teaching position to
Continued on page 75.
69










1 ~department


Chemical Engineering at...


Northeastern University, Huntington Avenue entrance.

RALPH A. BUONOPANE
Northeastern University Boston, MA 02115-5096

he history of Northeastern University is the history of
cooperative education in the United States. In 1896 the
Boston Young Men's Christian Association (YMCA) pro-
posed that an educational institution should be responsible to the
needs and demands of the local community. Boston was a grow-
ing coastal city at that time; its land area was expanding inland
through the filling of hundreds of acres of tidewater lands and its
population was expanding through the arrival of new citizens
immigrating mainly from Eastern Europe.
Although Boston was already a center for advanced education
by the 1890s (Boston College, Boston University, MIT, Radcliffe
& Wellesley had been added to the existing Harvard and Tufts
Colleges prior to this time), a college education was available
only to those fortunate enough by heritage to be able to afford the
luxury of an advanced education. Thus, in 1896 the Directors of
the Boston YMCA established, "with an eraser and two sticks of
chalk," an "Evening Institute for Young Men" to merge, coordi-
nate, organize, and improve the lectures and classes that had
developed during the first forty years of the Association's exist-
ence.
On October 3, 1898, the Boston YMCA established an
"Evening School of Law," the first school of the educational
units that were destined to become Northeastern University. The
"Automobile School" in 1903 and the "Evening Polytechnic
School" in 1904 were added to address the needs of the rapidly
changing community.
Copyrght ChE Division ofASEE 1995


Northeastern





University



By 1909 the Boston YMCA began addressing the needs
of younger boys in the growing Boston area by forming
the "Association Day School," which provided a college
preparatory program, and the "Co-Operative Engineering
School," a day program providing young men of New
England an opportunity to attend a technical school where
both theory and practice are correlated while part of their
educational expenses were earned through cooperative
learning experiences. The Chemical Engineering Depart-
ment was one of the original four day programs estab-
lished as the "Co-Operative Engineering School" in 1909.
Today, Northeastern University is a private urban co-
educational nonsectarian university offering cooperative
educational programs in seven full-time basic undergradu-
ate colleges. It is a modern, comprehensive urban univer-
sity with nine graduate schools, part-time evening degree
programs, and a Division of Continuing Education offer-
ing certificate and professional programs.
The main campus is located on fifty-five acres in the
heart of the Back Bay (the bay that was filled) section of
Boston. Near the center of the campus, which was the site
of the "Huntington Avenue American League Base Ball
Grounds" where the first World Series was played in
1903, there is now a life-sized bronze statute of Cy Young
on the pitcher's mound poised to pitch to a batter. At the
western edge of the campus are the world-renowned Bos-
ton Museum of Fine Arts, the Isabella Stewart Gardner
Museum, and the Longwood Medical Area (New England
Baptist Hospital-1903, Harvard Medical School-1906, New
England Deaconess Hospital-1907, Peter Bent Brigham
Hospital-1913, and Children's Hospital-1914). At the north-
ern boundary lies Fenway Park, home of the Boston Red
Sox, and the Fenway section of John Olmstead's "Emer-


Chemical Engineering Education












"Huntington Avenue American League Base Ball" grounds in 1903,
scene of the first World Series game (below). Lower photograph is of
Snell Engineering Center, located today about where the grand-
stand behind
home plate
was, and the
photograph
on the right
shows the
statue of
Cy Young
that today
stands on the
site of the
1903 pitchers
.mound.


aid Necklace" of green space which threads through Boston.
At the northeastern edge stands Symphony Hall, the New
England Conservatory of Music, and the Christian Science
Mother Church. To the east lies Copley Square, surrounded
by the old and the new of Boston's major cultural/convention
area; the original landmarks (Boston Public Library, Trinity
Episcopal Church, and Copley Plaza and Ritz Carlton hotels)
are intermingled with the new landmarks (John Hancock
Tower, the Marriott and Westin hotels, and Copley Place).
In the southeastern corner of the University is the oldest
multiple-use sports arena and artificial ice rink in the world-
the Boston Arena, built in 1910. It was the first home of the
Boston Bruins and was the site of the first Boston Celtics
home game before the Boston Garden was built. Renamed
Matthews Arena in 1977 after its purchase by Northeastern
University, the late Boston Celtics Captain, Reggie Lewis,
played all his collegiate basketball for the Northeastern Hus-
kies there. The southern edge of the campus is bordered by the
Northeast Corridor Amtrak line and the T Commuter Rail
lines to the southwestern suburbs.
Thus, with the realistic goals of the founders of Northeast-
ern University having been fulfilled, the location of the Uni-
versity continues to offer its students, faculty, and staff unique
opportunities for interaction with the athletic, cultural, educa-
tional, medical, and religious institutions of the city. The
campus now distinctly extends beyond the space and bounds
of the single building shared by the YMCA and the College of
Engineering in 1909. The College of Engineering now has
office and laboratory facilities in four buildings, with primary
locations near the center of campus in the Dana Research
Center (1967) and the Snell Engineering Center (1984). The
Egan Engineering/Science Research Center, presently under
construction next to Dana and Snell, is expected to be com-
Spring 1995


pleted in 1996. In addition to having offices and laboratories
in the Snell Engineering Center, the Chemical Engineering
Department also has offices and laboratories in Mugar Hall.
Chemical Engineering started with one student in 1909
when tuition was $100 a year (including YMCA member-
ship), rooms were $1.50 a week, and board was from $3.50 to
$5.00 a week. Cooperative work assignments paid from $5.00-
6.00 a week for thirty weeks. By 1917, there were two faculty:
Wm. F. Odom (also coach of the varsity baseball team) and
Samuel A.S. Strahan, the first department head. It was operat-
ing under the considerations that "a rapidly growing demand
has arisen for men who possess, in addition to skilled chemi-
cal knowledge, the training and ability for the efficient control
of plants and processes, economical utilization of power, the
conversion of factory by-products into marketable commodi-
ties, and the adaption and design of mechanical appliances to
carry out chemical reactions on a large scale. The curricu-
lum was defined such that chemical engineers "must be able










to consider propositions, processes, and plans from the com-
bined viewpoints of the chemist and the engineer [and that
their] training should of necessity be very broad, combining
that of both of the above named professions." The coopera-
tive plan of education then required that the men work in
pairs, alternating one-week periods between the employing
firm and the school.
The courses of study for chemical engineering included
the traditional mathematics, physics, chemistry, and English
courses, with descriptive geometry, mechanical engineering
drawing, applied mechanics, practi-
cal electricity, thermodynamics, elec-
trical engineering, heat engineering,
and the metallurgy of iron required ... in 1896 the
as engineering courses. The chemis- Boston YMCA es
try courses taken then were qualita- an eraser ani
tive and quantitative analysis, organic chalk," an "Ev
chemistry, and industrial chemistry for Young M
There was also a senior professional coo
course, Chemical Engineering! coordinate,
improve the
Over the ensuing years the curricu- classes hat h
lum and the cooperative work em- te
ployment assignments followed the during theirs
natural changes slowly taking place the Association
in chemical engineering education [and] on Octol
and industry. During those early years established an '
the University experimentally of Law," the fii
changed the four-year alternating pro- educational u
gram of one-week periods of coop- destined 1
erative work and school to programs Northeasten
with two-, and then five-week peri-
ods before developing a five-year,
ten-week term calendar in 1918 after World War I to accom-
modate the demands of the industrial sector for longer peri-
ods. In each year after the freshman year the students alter-
nated school and work periods in two ten-week terms and
one five-week term; the summer was divided into two five-
week terms with a two-week "shutdown" between terms.
The fifth year of the plan was the middle, or "Middler," year
which was sandwiched between the typical freshman-sopho-
more and junior-senior years. The emergence of distinct
principles of chemical engineering that incorporated the con-
cepts of unit operations became the chemical engineering
educational standard.
As the United States prospered between world wars, North-
eastern College was renamed Northeastern University of the
Boston YMCA in 1922, and then in 1935 became indepen-
dent of the YMCA as Northeastern University. Chester P.
Baker, one of "Pop" Strahan's students, graduated in 1920,
became an instructor in 1921, and was appointed as the
second chairman in 1939. Together with John C. Morgan,
who joined the faculty in 1930, Baker guided the department
through many years of change in the profession. Industrial


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chemistry was replaced with physical chemistry, and reac-
tion kinetics and unit operations were expanded to form the
nucleus of the unique chemical engineering disciplinary
courses.
When Baker requested an accreditation visit from AIChE
in 1939, the inspector turned down the request, indicating
"among other things, a need for a larger unit operations
laboratory that would have a two-story area of at least a
thousand square feet." A new building, housing the Biology
and Chemical Engineering Departments, was constructed in
1941 as a result. It not only included the
thousand square feet of two-story area,
but also a stock room, a machine shop, a
ectors of the travelling crane for installing equipment,
ilished, "with floor drains, three underground water
to sticks of sumps, gas, water, electricity (DC), and
ng Institute steam. Ralph A. Troupe joined the fac-
Sulty in 1940, and John C. Morgan was
put in charge of the unit operations labo-
nize, and ratory in 1941. In 1942 the department
tures and applied for and received its first accredi-
developed station, only the third in New England
rty years of (after MIT and Yale).
existence .... With the United States fully engaged
3, 1898, lit] in World War II, the first six women
ening School students matriculated in May, 1943, at
schooll of the the now coeducational Northeastern Uni-
s that were versity. The only engineering student
become among those first six women was Lillian
university. Kolodiz. In her first chemical engineer-
ing course with C.P. Baker, she was asked
if she wanted to be a good engineer. Her
"yes" response resulted in C.P. (Chemical Pure) Baker in-
forming the class that she "would have to learn how to drink
and swear because she couldn't be a good engineer unless
she could do those things." Lillian Kolodiz Stone graduated
with a BS in Chemical Engineering in 1946 after completing
the demanding requirements of the accelerated continuous
36-month wartime program. In 1992, Lillian K. Stone, Chief
of the Energy Facilities Division, Office of Environmental
Affairs at the United States Department of the Interior re-
ceived the Federal Environmental Engineering of 1992 Award
from the Secretary of the Interior Department.
Although little appeared to change in the chemical engi-
neering curriculum during the years between 1943 and 1950,
the nature of a cooperative education program requires that
current chemical engineering practices be continually inte-
grated into academic courses. Additional courses in Ameri-
can and world literature, modern democracy, economics,
and psychology became required, and courses such as phi-
losophy, art, music, or history had to be elected.
While the United States engaged in the Korean conflict,
the Cold War, and the space race in the late 50s and early
Chemical Engineering Education











Evolution of a U. O. lab


60s, Northeastern University was expanding and the chemi-
cal engineering department was developing a graduate coop-
erative program to add to its successful and growing under-
graduate program. Joining Professors Baker, Morgan, and
Troupe in 1960 was Charles S. Keevil, who was the Chemi-
cal Engineering Chair at Bucknell before World War II.
Three recent graduates of the department, John G. Miserlis
('53), Bernard M. Goodwin ('56), and Richard R. Stewart
('60), also were serving as instructors at that time. "Sam"
Keevil was instrumental in forming the graduate masters
program, which started in 1960 with one student. In 1961,
Bernard M. Goodwin was appointed as an assistant profes-
sor to introduce the new "transport phenomena" approach to
chemical engineering into the Northeastern University pro-
grams. Also that year, two cooperative graduate teaching
assistants, Ralph A. Buonopane and Frederick C. Heron
alternated their unit operations laboratory teaching assign-
ments with graduate classes while six other graduate stu-
dents alternated classes with assignments in industry. Thus,
the first graduate cooperative program in chemical engineer-
ing was established.
In 1962, "Doctor" Troupe became the third chemical engi-
neering department chairman when "Bone Dry" Baker re-
tired. As both the undergraduate and graduate programs
continued to grow, the department hired another young as-
sistant professor in 1964, John A. Williams.
A full-time doctoral program leading to the PhD degree
was established in 1964 with four doctoral students who had
received masters degrees from the department. In 1965, the
University adopted a new five-year academic calendar which
operated with four 13-week quarters alternating between
school and cooperative work assignments. Once again, the
University responded to industry's call for students to spend
Spring 1995


a longer continuous period of time on cooperative work
assignments. Although the quarter plan had proven success-
ful for the undergraduate programs, the graduate programs
shifted to full- and part-time operation without coop by
1920.
In 1967 the first PhD was awarded to Ralph A. Buonopane,
who had been appointed an assistant professor in the depart-
ment in 1966 to address the need for additional faculty to
handle the growing number of undergraduate students (which
had reached more than two hundred upperclass students by
1965). By the end of the 60s, as the University withstood the
years of civil and student unrest, including a two-week clos-
ing in May 1970, the number of undergraduate chemical
engineering students reached more than three hundred. In
1971 and '72, the department granted the largest number of
BS degrees in the U.S.: 103 in '71 and 73 in '72.
Faculty changes in the 70s were made slowly and cau-
tiously, while the number of graduate teaching assistants
grew. In 1982, Ralph Troupe retired and Elisabeth Drake,
became the fourth chairperson of the department, and in
1986, the fifth and current chairperson, Ralph A. Buonopane,
was appointed. During these years, three new faculty were
added to the department: Ronald J. Willey in 1983, Scott T.
McMillan in 1987, and Donald L. Wise in 1987. When
McMillan left in 1989 to start his own business, Gilda A.
Barabino was hired to become the seventh faculty member
in the present department. The current faculty members and
their research areas of interest follow.
Gilda Barabino, the newest faculty member, teaches ki-
netics, biochemical engineering fundamentals, and polymer
science. Her research specialties are in the areas of bio-fluid
mechanics, bio-reactors, and sickle cell disease. She was the
73


The first laboratory (above, 935) was in a two-story
YMCA building. The double-effect evaporator is shown
in the center photograph with Lilian Kolodiz, first female
ChE student. At far right is the double-effect evaporator
todaywith the departmentfacultyexaminingthemodern
computer control instrumentation.










recipient of the 1994 ASEE Dow Outstanding New Faculty
Award for the New England Section and is the DiPietro
Assistant Professor of Chemical Engineering.
Ralph Buonopane, the Department Chairman, teaches
chemical engineering calculations and directs development
of the chemical engineering laboratory. His research inter-
ests are in the area of developing novel process heat transfer
equipment. He is a Fellow of AIChE, is active in ASEE and
AIChE at the local and national levels, is involved in town
government, and plays softball in his local community.
Bernie Goodwin, with the longest service in our depart-
ment, teaches calculations computation lab, thermodynam-
ics, separations processes, and engineering problem solving
with applications software. His research interests are in the
areas of computational thermodynamics and kinetics. He has
edited the AIChEMI Modular Instruction Series in Thermo-
dynamics.
Dick Stewart, a former Northeastern University varsity
basketball player, teaches momentum transport, heat trans-
port, chemical process control, and engineering problem
solving and computation. His research interests are in the
area of process control, and he is about to complete a text-
book in that area.
Ron Willey, an avid "lunchtime basketball" player, teaches
experimental methods, chemical process safety, and engi-
neering design and graphics. His research work in the area of
catalysis is specialized in the development of high surface
area aerogels.
John Williams, a registered professional engineer, teaches
the senior process design courses and economics. His stu-
dents have received national awards in three of the last four
years of the AIChE Student Design Contests.
Don Wise, a Vice President at Dynatech R&D before
coming to Northeastern, teaches chemical process pollution
control. He is the Director of the Center for Biotechnology
Engineering and conducts research in the areas of controlled
release materials and biological reactions for pollution con-
trol and waste minimization. He has edited five handbooks
in these areas and is the Cabot Corporation Professor of
Chemical Engineering.
Today, the department currently has about 130 upperclass
chemical engineering students, with approximately 31%
women, 7% international, and 8% minority students. In the
past decade, the department has granted 326 bachelor's de-
grees, 95 master's, and 10 doctorates.
The curriculum today includes traditional calculus, phys-
ics, chemistry, and English courses, with engineering design
and computer applications, taken in the freshman year; chemi-
cal engineering calculations, organic chemistry, and differ-
ential equations are required in the sophomore year; chemi-
cal engineering thermodynamics, momentum transfer, and
physical chemistry are the middle year courses; experimen-
74


tal methods (unit operations laboratory), heat transport, sepa-
rations processes, and economics are the junior-year courses;
and the senior year includes process design, process control,
three chemical engineering electives, an engineering elec-
tive in another department, and an advanced chemistry elec-
tive. To complete the non-engineering requirements, six so-
cial science/humanities courses (including macroeconomics)
and a technical writing course to satisfy the University
upperclass writing requirement are taken. The three current
chemical engineering electives are chemical process pollu-
tion control, chemical process safety, and mass transfer op-
erations.
All of the chemical engineering courses incorporate the
most current practices used in academia and industry by
emphasizing relevant problems and using current problem-
solving techniques. The chemical engineering laboratory,
named the Baker Laboratory in 1972, has been upgraded to
include modern data acquisition and control equipment on
most of the experiments. A large double-effect evaporator
system, a 450-gallon agitated mixer unit, and a 10-foot, 7-
tray distillation column are equipped for remote computer
control. All experiments now include the use of modem
electronic process sensors and remote computer data acqui-
sition hardware and software.
By combining their classroom and laboratory experiences
with cooperative work assignments, our chemical engineer-
ing students possess, as in the words of our founders, "... in
addition to skilled chemical knowledge, the training and
ability for the efficient control of plants and processes, eco-
nomical utilization of power [energy], the conversion of
factory by-products into marketable commodities [pollution
prevention], and the adaption and design of mechanical
appliances [chemical process equipment] to carry out chemi-
cal [and biochemical] reactions on a large scale." Today,
130 undergraduate students are "co-operating with [fifty-
six]firms in connection with the Chemical Engineering course
and [the program] could have more [102 firms], had we
sufficient students to supply the demand. A demand greater
than the supply exists today, as it did in 1917 when "42 men"
were assigned at "seven" companies.
As Northeastern University prepares to celebrate its Cen-
tennial Anniversary in 1998, cooperative education in chemi-
cal engineering is firmly established and progressing to meet
the challenges of the next century. A 1973 alumnus of our
department, Albert Sacco, Jr., is scheduled to be a Payload
Specialist aboard the Space Shuttle Columbia (STS-73) on
the second Microgravity Laboratory (USML-2) in late Sep-
tember, 1995. With the information and communications
ages already in place, we are incorporating new methods of
delivering chemical engineering education while our stu-
dents are experiencing cooperative work assignments in the
newly re-engineered workplaces of our industry. The future
belongs to the chemical engineer! O
Chemical Engineering Education










EDUCATOR: Helen Hollein
Continued from page 69.


accompany her husband on an assignment to Argentina. The
period from 1969 to 1976 included relocations to England,
Singapore, and Belgium, plus the birth of her other two
children. Connie says that her favorite assignment was
Singapore, where she substituted as a mathematics teacher at
the American high school and enjoyed the local culture in
her spare time.

GRADUATE STUDIES
By 1976, Leo had advanced to a stage in his career where
the overseas assignments could be expected to be fewer in
number, so Connie bought a calculator and blue jeans and
went back to school. Her initial goal was to earn a master's
degree so that she could teach chemistry in a junior college,
but she later decided to stay at New Jersey Institute of
Technology and complete her doctoral degree in chemical
engineering. The next six years were not easy, but she got
through them with the help of her husband who was in-
volved in shared parenting long before the Yuppies made it
popular. Leo remembers the worst semester as the fall term
of 1978 when Connie had classes four nights a week and he
was the primary caretaker for their three children.
When she started work on her master's thesis in 1977,
Connie decided to work on a molecular spectroscopy
project with William Snyder. The project was not associated
with any grants and she was working alone, which was
perfect at the time because she had young children (ages 3,
7, and 10) and needed a flexible research schedule. She
completed her thesis and published two papers with Dr.
Snyder. She also taught physical chemistry and general chem-
istry during her stint at NJIT.
For her doctoral research, Connie chose to work for Hung-
Tsung Chen in a more high-pressure environment. He had
NSF-funded research projects on polymerization and para-
metric pumping and offered her a new project where the idea
was to modify an electrophoresis column for separation of
proteins via parametric pumping. She joined a research group
of close to thirty students, most of them from Taiwan, and
the faculty at NJIT teasingly observed that she "had joined
the Chinese Army." She also started telling people that her
name was Helen because "Hai Lin" sounded much better in
Chinese than Connie. For the next three years, Connie's
morning greeting when she entered the lab was, "Speak
English!" Her fellow researchers usually cooperated.
Connie profited from Dr. Chen's mentorship in many of
the traditional ways. He invited senior people in their field,
like Phil Wankat, Norm Sweed, and Frank Hill, to give
seminars at NJIT, introduced all of the students, and invited
the senior students to dinner with the speakers. Doctoral
candidates also edited papers prior to publication, and helped


prepare NSF proposals and reports. Dr. Chen was a prolific
publisher, and took his senior doctoral students with him to
AIChE meetings to present their work. The first paper on her
doctoral research was presented at the 2nd World Congress
of Chemical Engineering in 1981.
Connie had completed most of her research by the spring
of 1981 and was coauthor on several papers with her advisor
before he was killed in an automobile accident in 1981. She
feels she was fortunate in that a key paper on her research
was completed the day before he died and it was later ac-
cepted for publication in I&EC Fundamentals. This proved
that her work was publishable so that she could complete her
parametric pumping research and graduate instead of start-
ing on a new topic with another advisor. Thus, her disserta-
tion was completed in 1982 with Ching-Rong Huang as her
advisor and Frank Hill as an external consultant.

WOMEN'S ISSUES
Connie frequently gives lectures to women's groups and
female high school students. In 1989 she spoke about
women's issues as part of a panel at an Electro-89 conven-
tion in New York's Javits Convention Center. The panel
discussions were quoted in The New York Times and The
Chicago Tribune (April 1989) under the title "Difficulties
for Women Engineers." She is quoted as saying, "Things
haven't changed that much for women in engineering in
recent years." She also said that it is still difficult for women
engineers who have children and advised young women not
to take seven years off the job as she had done. She reports
that, "After that article was printed, one of our female gradu-
ates called me to dispute my comments. She had recently
resigned from an engineering position to stay home with her
son, and assumed it would be easy to find another position
when the time came to do so."
Connie says, "Conditions have improved for women engi-
neers in industry and academia in the last thirty years, but it
is still difficult for young women to balance a career with
family life. Many women professionals postpone having
children until they are settled in their careers, or even indefi-
nitely. One of our female graduates recently left engineering
to teach high school so that she could have more time for her
family, and several others have called me because they are
considering similar moves. Women are allowed to work in
plant environments in the U.S. and other English-speaking
countries, but another ChE alumna was recently denied a
plant assignment in Italy because the affiliate would not
accept a woman engineer. Since our undergraduate classes
[in chemical engineering] are close to 50% women, our
women engineers are clueless to problems of this type until
they go to work in the "real world." 0


Spring 1995










Award Lecture...




COMPUTER-AIDED

DESIGN AND OPERATION

OF BATCH PROCESSES


G.V. Rex Reklaitis is
Professor and Head of
the School of Chemical
Engineering at Purdue
University. He received
his BS from the Illinois
Institute of Technology
('65) and his PhD from
Stanford University
('69). Following a year as NSF Postdoctoral
Fellow at the Institut fur Operations Research
and Elektronische Datenverarbeitung in
Zurich, Switzerland, he joined the faculty at
Purdue, where he was appointed full profes-
sor in 1980 and served as Assistant Dean of
Engineering for Graduate Education and Re-
search from 1985 to 1988. He was named
Head of the School in 1987.
Rex's PhD thesis, with Douglass Wilde,
addressed theoretical and algorithmic issues
in nonlinear programming, in general, and
geometric programming, in particular. He ini-
tiated work on the computational component
of this theme during his postdoctoral year.
The nonlinear optimization thread continued
at Purdue, where he developed an interdisci-
plinary course that led to the book Engineer-
ing Optimization. During his initial years of
teaching the process design courses at Purdue,
he noted the consistent difficulties that stu-
dents had in specifying and solving basic
process material and energy balances. This
spurred the development of a suitable frame-
work and led to teaching the associated course
and the publication of the text Introduction
to Material and Energy Balances. More re-
cent educational interests include the
codevelopment of video- and computer-
graphics-based simulated industrial labora-
tory modules and the initiation of a team-
taught course on computer-integrated pro-
cess operations.

Copyright ChE Division ofASEE 1995


G.V. REKLAITIS
Purdue University West Lafayette, IN 47907

his article describes, at a conceptual level, the basic operational and
design decisions that arise in batch chemical processing and will sum-
marize the approaches that have been developed to employ computing
technology to facilitate these decision processes. It is not a comprehensive
treatment of the available literature either from the perspective of problem
formulations or solution methods; rather, the aim is simply to convey the
richness of the domain, present the nature of some of the research issues that
must be addressed, and sketch out a few of the successes that have been
attained to date, all from an unapologetically personal perspective. The reader
interested in more detailed technical reviews is invited to consult other refer-
ences131] and the additional sources cited therein.
Batch chemical processing has been practiced by the chemical engineering
profession for many decades; indeed, it precedes the birth of our discipline by
centuries. It had long been neglected in process systems engineering research,
perhaps, because it was viewed as but a temporary expedient in the transition
to an automated modern continuous process. But the venerable batch process
has received increased attention within the last decade or two because of the
growing emphasis on high value-added products, notably in the food, pharma-
ceutical, polymers, agricultural chemicals, and specialty chemicals domains.
Batch operations are typically employed when 1) the production volume of a
product is too low to justify a dedicated plant (typically less than 1000 tons per
year), 2) the complexity of the processing steps is too high and production
scale too low to justify research and development expenditures sufficient to
fully develop reaction engineering, physical properties, and engineering scaleup
information, and 3) a high degree of flexibility is required to accommodate
continual changes in product slate, grades, and demands. The batch plant, in
fact, is now often viewed as the CPI version of the modern flexible manufac-
turing facility of the future-a remarkable rehabilitation of an old workhorse!
Unfortunately, that rehabilitation is not yet complete within chemical engi-
neering professional training, as evidenced by the minimal coverage of batch
operations in the typical undergraduate curriculum.

BATCH PROCESS FEATURES
What makes a batch process different? There is, of course, the obvious
difference that batch operations are inherently non-steady-state and, thus,
require the explicit consideration of time and, therefore, of the dynamics of the
processing steps. Additional fundamental differences exist, however. The manu-


Chemical Engineering Education











facture of all chemical products involves three key elements: a process or
recipe that describes the set of chemical and physical steps required to
make product, a plant that consists of the set of equipment within which
these steps are executed, and a market that defines the amounts, timing,
and qualities of the product required.
A distinguishing feature of continuous operations is the one-to-one
correspondence between the recipe steps and the plant equipment items.
In the continuous case, the flowsheet is the physical realization of the
recipe and its structure remains fixed in time. In batch plants, the structure
of the recipe and the plant equipment network structure are in general
distinct. Moreover, the equipment configuration may change each time a
different product is made. Thus, in the batch case there exists an additional
engineering decision level: the assignment of recipe steps to equipment
items over specific intervals of time. These assignment decisions are
inherently discrete in nature, introducing a combinatorial aspect not nor-
mally present in the continuous process case.
To aid in our further exploration of the implications of the above
distinctions, we will first review some basic terminology. A recipe is a
network of tasks that must be executed to produce a product. Each task
consists of a sequence of chemical/physical steps which are executed in
the same vessel (see Figure 1). Each step or subtask is described by a
processing time, a size factor that defines the capacity required per unit
amount of task output; and input/output ratios that describe the propor-
tions in which inputs must be supplied and outputs are generated. A
production line is a set of equipment assigned to each task of a given
recipe. Assuming that the identity of a batch is preserved in the production
line, then the batch size will be the amount of final product made in one
batch. If the production line is used to produce a series of identical
batches, it is often convenient to operate the line in a cyclic fashion. The
cycle time is then the time between the completion of batches. A Gantt
chart is an equipment occupation diagram in which time is the ordinate
and the abscissa has an entry for each equipment item. A campaign is a
time interval during which one or more production lines are dedicated to
making a specific set of products.
Figure 2a shows a Gantt chart for a serial four-task recipe in which a
distinct unit is assigned to each task. Note that the transfer of a task
output to the next task in the recipe is denoted by an arrow. The cycle time
is 6, corresponding to the maximum of the processing times of the four
tasks of the recipe. As is typical, several of the units are idle for a
considerable portion of the time, but at least one is continuously engaged
and becomes cycle time limiting. In this illustration the campaign consists
of three batches.
As noted earlier, a characteristic feature of batch production is the need
to specify an assignment of units to tasks. In general, this assignment need
not be one-to-one; rather, multiple tasks can be assigned to the same unit
and multiple units can be assigned to execute the same task. For the recipe
of Figure 2, task 4 can be executed in two different units (U1 and U4).
Since these two units are inefficiently used in the one-to-one assignment
shown in Figure 2a, an improvement in equipment utilization can be
achieved by assigning U1 to execute both the first and fourth task, as
shown in Figure 2b, thereby releasing U4 for other uses.
This multiple task assignment can be viewed as a form of recycle since
the batch revisits a previously used unit. Of course, since the two tasks are
Spring 1995


temporarily displaced and there is no mixing of
task 1 and task 4 materials, this does not consti-
tute a recycle in the usual continuous sense. Im-
provements can also be achieved by assigning
multiple units to a task that is performance limit-
ing. If a unit assigned to a task is batch size
limiting, then assigning another unit which al-
lows the batch at that task to be split and pro-
cessed in parallel (parallel unit in-phase) will
allow an increase in the batch size. (A set of in-
phase units assigned to a task is called a


Figure 1. Recipe, tasks, and subtasks


Task 1 Task 2 Task 3 Task 4

Time 2 6 4 3
Units U1 U2 U3 U1, U4

a) One-to-one
ul Assignment
U2
U3
U4

--me

b) Multiple Task Assignment


U2
U3

time
Figure 2. One-to-one and many-to-one
task to unit assignments











group.)Alternatively, if the task is cycle time limiting, then
adding another unit and alternating the processing of batches
at that task (parallel unit out-of-phase) will effectively re-
duce the task processing and thus the cycle time. As shown
in Figure 3, the addition of a second U2 unit out-of-phase
reduces the cycle time to 4.
Based on the nature of the product recipes and the allow-
able task/unit assignments, batch operations can be roughly
classified into three basic types: the multiproduct plant, the
multipurpose plant under campaign mode, and the general
multipurpose plant. The classical multiproduct plant is
employed for a set of products whose recipe structure is the
same (or nearly so), the production line employs fixed many-
to-one unit/task assignments, the line is operated cyclically,
and multiple products are accommodated through serial cam-
paigns. It should be noted that the special case of the
multiproduct plant, which occurs when campaigns are re-
duced to single batches, is sometimes referred to as a
flowshop. The multipurpose plant under campaign op-
eration is appropriate for products with dissimilar recipe
structures, allows many-to-many unit/task assignments, and
employs multiple campaigns involving one or more produc-
tion lines, each operated cyclically. Finally, the general
multipurpose plant is a multipurpose plant operated with
no defined production lines; rather, production occurs in an
periodic fashion involving many-to-many unit/task assign-
ments on an individual batch basis.
The distinction between these operational types is illus-
trated in Figure 4. Two products, A and B, are to be pro-
duced, each involving a two-step recipe. Three multipurpose
units are available, each capable of accommodating all four
tasks. Figure 4a shows a production line in which Ul is
assigned to task Al, and U2 and U3 are assigned out-of-
phase to task A2. If the same unit/task assignments were
employed for product B, we would have a multiproduct


operation. In Figure 4b, a different assignment is selected for
product B (Ul and U2 are assigned to BI, and U3 to B2).
Both lines operate in campaign style with their own charac-
teristic cycle times. For instance, a campaign of four batches
of A might be followed by a campaign of three batches of B,
followed by another campaign of six batches of A, etc., as
required to meet specific product orders.
In Figure 4c, production is in the general multipurpose
mode, with tasks assigned to units in a flexible fashion, no
clearly defined production line, and certainly no cyclic
patterns of batch completion. Note that as a result of the
imposition of a cyclic production pattern, the equipment
utilization in the campaign mode (as evident from the idle
time gaps) is in general not as efficient as the utilization
obtained when that constraint is relaxed. But if cross-con-
tamination is a consideration, the flexible, acyclic operation
would require more frequent equipment clean-out than in the
regular campaign mode where clean-outs may only be re-
quired between campaigns.
As noted by Lucet, et al.,141 the multiproduct mode typi-
cally is employed for larger volume products (300 to 700 t/y)
with similar recipes, such as might be the case with a plant
that produces a family of grades of the same product. The
multipurpose mode is prevalent in facilities which produce a
large number of products of smaller volume (30 to 300 t/y).
The campaign form of the multipurpose plant is used when
product purity requirements are stringent (such as in phar-
maceuticals production) for reasons of operational simplic-
ity, or to facilitate batch consistency. The general form al-
lows more effective use of capital equipment at the cost of
operating complexity and additional change-over costs.

THE SCHEDULING PROBLEM
A key problem that arises in batch operations is schedul-
ing of the plant to meet specified product requirements.


Task 1 Task 2 Task 3 Task 4


Time 2 6 4 3
Units U1 U2A,U2B U3 U1, U4


Product A Campaign


A Recipe

Multipurpose
Equipment U1,U2,U3

Product B Campaign

B Recipe
B Recipe


Al Al Al Al
A2 A2
A2 A2+


Time
B1 B1
B1 B1
B2 B 82B2 B2
$ f f


Al
B1


General
Multipurpose
Operation


Al


A2 A2 B1 B2


B2 B1 B1 B2 Al
A2 Al 2 All A2
Chemical Engineering Educatio


B A A B A B

Chemical Engineering Education


Figure 3. (Above) One-to-many task to unit assign-
ments

Figure 4 (right) Multipurpose plant operation










Specifically, given the mode of operation, the product
orders, the product recipes, the number and capacity of
the various types of existing equipment, the list of equip-
ment types allowed for assignment to each task, any limita-
tions on shared resources (such as utilities or
manpower), and any operating or safety
restrictions, the scheduling problem is to de- ... the ve
termine the order in which tasks use equip- process
ment and resources and the detailed timing of increase
the execution of all tasks so as to optimize within th
plant performance. or two b
The scheduling problem involves three growing
closely linked elements: assignment of units high vi
and resources to tasks, sequencing of the tasks products,
assigned to specific units, and determination food, ph
of the start and stop times for the execution of pol
all tasks. For instance, given two reactors (Ul
and U2) and six product batches (A through chem
F) which need to be processed, the assignment special
step might involve allocating A through C to do
Ul, and D through F to U2. The sequencing
step would involve determining the processing order on each
unit (e.g., first B, then C, and then A on Ul), while the
timing step would assign specific start and stop times for
each batch on each unit. The above problem elements are
shared by scheduling problems arising in a wide range
of applications, from machine shops to transportation
systems to classroom assignments. Not surprisingly, a large
literature (dating to the early 1950s) exists in the operations
research domain on solution approaches to scheduling prob-
lems. The batch processing related literature began its growth
only in the mid-1970s.
Note that in the above example, the assignment compo-
nent at root involves binary decisions (assign Ul to task A,
or not) as does the sequencing component (position A first in
the sequence, or not). The timing component can be a dis-
crete decision problem, or not, depending on whether time is
treated as a continuum or is divided into individual time
quanta. It is the binary decisions that provide the challenge
to scheduling problem solution. Indeed, theoretical worst-
case (computational complexity) analysis has shown that
even the conceptually simplest forms of scheduling prob-
lems (those involving only sequencing considerations, such
as the sequencing of jobs on a single machine with set-up
costs that are dependent on the job order) can exhibit expo-
nential growth in computational effort with increasing prob-
lem size (e.g., number of jobs).
Fortunately, recent research experience has shown that
through creative problem representation, clever exploitation
of problem specific structure, and effective algorithm de-
sign, practical problems can be solved before "hitting the
wall" of exponential growth. The key to effective solution of
scheduling problems (and thus the essence of the challenge
Spring 1995


to research) has been the detailed exploitation of problem
structure. Indeed, as will be shown in the subsequent discus-
sion, tailored approaches have been proposed for each of the
types of operating modes, taking advantage of the occur-
rence of specific resource constraints types,
inventory characteristics, and cost structures.
able batch
received THE PRELIMINARY
mention DESIGN PROBLEM
ist decade While the scheduling problem focuses on
use of the effective use of existing production resources
is to meet product requirements, the design
phasis on
problem involves determination of what the
a-added optimal level of those production resources
ably in the should be. Thus, given the mode of opera-
aceutical, tion, the product orders, the product recipes,
,ricultural the list of equipment types allowed for as-
!s, and signment to each task, any limitations on
chemicals shared resources (such as utilities or man-
inpower), and any operating or safety restric-
tions, the preliminary design problem is to
determine the required number and capacity


of the various types of equipment, the order in which tasks
use equipment and resources, and the timing of the execu-
tion of all tasks so as to optimize plant annualized cost.
Note that the principal difference between the earlier defi-
nition of the scheduling problem and the above statement of
the design problem lies in the relaxation of the equipment
number and capacity from the status of problem parameters
to optimization variables. Indeed, since how the plant is
scheduled will determine its capacity, the design problem
can be viewed as an upper-level decision problem which has
imbedded in it the scheduling problem. Thus, to solve the
former, we must necessarily also solve the latter. Of course,
there are differences in the time scales that must be consid-
ered; at the design stage product demands are not known
at the level of individual orders, and instead might be
aggregated at quarterly, seasonal, or annual requirements.
Moreover, because of differences in the degree of certainty
of the demand requirements (longer range forecasts in the
design case versus concrete orders in the scheduling case)
the scheduling subproblem solutions required in the design
case may be less rigorous.
In principle, in defining the design problem one should
also include the choice of mode of operation as one of the
design optimization variables. After all, mode selection (e.g.,
cyclic vs. acyclic, multiproduct vs. multipurpose) is at root
dictated by economic considerations such as cost of inven-
tory, change-overs, complexity (measured in labor and auto-
mation costs), and off-spec production. Indeed, since the
general multipurpose operational mode can be viewed to
encompass the other two limiting modes as special cases, the
mode-specific design problems can in principle be subsumed
by that of the general multipurpose plant. The direct optimi-


ner
has
ede
e ]a
ecai
em,

note

;, ag
ical
trcl
maj










zation over operational mode proves impractical-first, be-
cause all of the mode-dependent costs are difficult to quan-
tify, and second, because more effective solution methods
can and have been devised for mode-specific formulations.
In the next few sections, we will briefly visit some ap-
proaches to the scheduling and design problems for each of
the three types of operating modes. For simplicity, we will
confine the discussion to recipe descriptions in which size
factors and input/output ratios are known constants, and task
processing times are constant or known functions of the
batch size. Demands will be assumed to be deterministic.

THE MULTIPRODUCT PLANT
This operating mode was the first to be addressed in the
literature[51 and continues to receive the greatest attention. It
has been investigated both in the campaign form and in the
limiting flowshop form.
In the campaign form, if the equipment groups used out-
of-phase for a given task are equivalent, the scheduling
problem reduces to the straightforward determination of the
maximum product batch size and minimum cycle time for
each product. Determination of the campaign lengths is made
by solving a linear programming planning model if the
change-over times and costs between campaigns are inde-
pendent of product order. If change-overs are sequence de-
pendent, then the resulting sequencing problem can be trans-
formed and solved as a traveling salesman problem (TSP).[6]
If unequal, out-of-phase groups are allowed and task times
are dependent on the batch size, then cyclic operation is
possible with different batch sizes and cycle times, depend-
ing upon the path that a batch takes.[7] The problem can be
posed as a mixed integer nonlinear programming problem
(MINLP) and solved via decomposition methods.
In the flowshop form, the same recipe structure is used for
all products; thus the equipment network is fixed and,
in addition, batches are scheduled individually rather than
in campaigns. A variety of approximate and rigorous
branch-and-bound approaches to this problem have been
proposed for various types of network structures."81 Approxi-
mate approaches typically divided the problem into a se-
quencing subproblem and a completion time computation
problem.9-ll Rigorous approaches to problems with serial
and with parallel network structures have used reformula-
tion to TSP problem forms and specialized branch-and-bound
solution methods."2,'13 This work is notable not only because
of the efficient optimal solutions which are obtained, but
also because of the bounds on attainable schedule perfor-
mance that are provided if the solution process must be
terminated before the optimum is reached.
The design problem has principally been attacked in its
campaign form, beginning with the seminal paper by Spar-
row, et al.[14] If for each task only out-of-phase parallel units
of equal size are allowed, then assuming constant processing
80


times and no sequence dependent change-over losses, the
capital cost minimization problem is simply stated as:
Minimize

mmj{ajVj aI

subject to


where


V. 2B. S.. for all products i and tasks/units j
T >t.. /m. for all tasks j and each product i

SQiTi /Bi ViMn J J J


denotes size of the unit assigned to task j
batch size of product i
cycle time
number of out-of-phase units assigned to task j
available production time in hours per year
annual demand for product i
processing time
size factor for task j of product i


The power law expression in the objective function is simply
a correlated cost function for equipment assigned to task j.
Note that in this model the scheduling constraints consist
only of (2) and (3). The former family of constraints, which
define the cycle times for each product, derive their simple
structure from the fact that each unit is assigned a unique
task. Constraint (3) merely insures that the total plant utiliza-
tion time assigned to each product does not exceed the total
available production time. There are no explicit restrictions
on the number of campaigns into which the production of
any given product is divided, no cost of inventory of finished
products, and no explicit consideration of the costs (in time
or money) of transitioning from one product to another.
These more detailed production planning considerations are
all essentially lumped into the specification of the produc-
tion horizon H.
The presence of the integer variables mj makes the above
formulation an MINLP, whose solution requires use of some
form of partial enumeration strategy. The additional restric-
tion of the Vj variables to a discrete set of "standard" sizes
increases the combinatorial dimension of the problem.
One approximate approach to such combinatorial problems
is to relax the discrete value restrictions on the variables,
solve the resulting continuous nonlinear programming prob-
lem (which in this case can be shown to have a unique
optimal solution), and then round the solution up to the
nearest discrete value. Given the structure of the above
model, rounding up always leads to a feasible solution, but
one which is usually not cost-optimal. Thus, some round-up/
Chemical Engineering Education










round-down trade-offs must be explored in either heuris-
tic"151 or rigorous (branch-and-bound) form. The above prob-
lem has been extended to include semicontinuous equip-
ment, batch-size-dependent processing times, and in-phase
units while preserving the unique optimum property of the
relaxed problem.[16'
The above formulation implicitly assumes that a batch
retains its identity in processing: the batch volume/mass
simply expands or contracts from task to task, as determined
by the Sj. But in practice, it may be advantageous to store a
large batch from, say, a long duration fermentation task, and
then to process it in several smaller batches in a successor
task (centrifugation, filtration, etc.). Furthermore, it is pos-
sible that the intermediates produced as outputs of one or
more tasks must be combined as ingredients to a successor
task (e.g., tasks 1 and 2 in Figure 1). These batch splitting
and mixing possibilities require introduction of suitably
sized intermediate storage. Storage decouples the production
line into trains, which have their own characteristic batch
sizes and cycle times, but which are linked through material
balances. The minimum required size of such storage facili-
ties can be determined as a periodic function of the up-
and down-stream train parameters.[17] But the joint determi-
nation of the optimal locations in the recipe network for
such intermediate storage, the sizing of such storage, and
the sizing of the process units, requires solution of an
augmented MINLP. This expanded problem is challenging
even in the single-product case""8 because of its dimension-
ality and the presence of many local optima in the underly-
ing relaxed problem.
An interesting review of alternative MINLP formula-
tions of the multiproduct design problem in its various
forms is given by Ravemark and Rippin.1~91 Suffice it to
note that much computational research remains to derive
efficient solution methods to the large-scale MINLP prob-


CAMPAIGN 1


product B


CAMPAIGN 2


I HORIZON
Figure 5. Multipurpose plant: operation modes
Spring 1995


lems that arise when batch mixing, splitting, intermediate
storage, campaign change-over, and product inventory costs
are considered.

THE MULTIPURPOSE PLANT:
CAMPAIGN OPERATION
This mode of operation extends the multiproduct mode by
allowing the reassignment of equipment to tasks as dictated
by the specific recipe requirements of the individual prod-
ucts. Since not all available equipment may be required by a
given product, parallel production of compatible products
can also be considered. But once configured, the resulting
production lines are operated in a cyclic fashion. As illus-
trated in Figure 5, decisions must be made on grouping of
products for parallel production in the same campaign (e.g.,
products A and B in campaign 1), assignment of the avail-
able equipment among the products in the campaign (seven
of the units to product A and only three to product B), and
detailed configuration and scheduling of the production lines.
Thus, the overall scheduling problem for this form of multi-
purpose plant inherently involves three decision levels: plan-
ning of campaigns, formation of campaigns, and scheduling
of the production lines.
Mauderli and Rippin[20' were the first to consider this
problem, focusing particularly on the campaign formation
problem. They used enumerative techniques to generate and
evaluate alternative single-product production lines. The more
efficient of these single-product lines were then combined in
an enumerative fashion, aided by an LP screening proce-
dure, to identify a set of dominant multiproduct campaigns.
For instance, campaign 1 of Figure 5 would be considered
dominant if the combined rate of production of A and B is
higher than the average production rate obtained if A and B
are produced sequentially, each using its own optimally
configured single-product line.
Recognizing the limitations of the heuristic enumeration
approach, Wellons and Reklaitis[21] developed rigorous
MINLP formulations for all three of the decision levels and
solved them using decomposition-based mathematical pro-
gramming techniques. A key feature of that work was the
use of the Noninferior Set Estimation method to sequentially
generate dominant campaigns starting with the set of opti-
mized single-product campaigns. Using this approach, cam-
paigns yielding production rates as much as 20% higher than
those obtained in the earlier work could be generated. Given
a set of dominant campaigns, the production planning prob-
lem could then be posed and solved as a multi-time period
MILP that selects the dominant campaigns and determines
their optimal sequence and duration so as to meet production
requirements while maximizing net profit.
The key limitation of both these approaches is the require-
ment of first determining a set of dominant campaigns. As
the number of products increases, the computational burden
81


product A


product A


product C










associated with this step grows explosively, yet at the production planning
level most of these campaigns will never be selected. Thus, a more effective
strategy is to form campaigns as and when they are required for specific
production needs. This strategy is exploited in Tsirukis, et al.,r22] to address a
more general form of the problem, which also considers the assignment and
use of constrained resources (such as utilities and operators) and product
demands expressed in the form of orders with specified product amounts and
due dates. The key decision variables of the Tsirukis, et al., formulation are
the structural variables
Xomegk which take on the value 1 if task m of order o is processed by unit
type e of equipment group g in campaign k, and 0 otherwise
and the usual continuous variables describing the batch sizes, cycle times,
campaign lengths, and production amounts. The number of batches produced
in each campaign are integer, but for integer values sufficiently large, can be
treated as continuous. Whether defined using a cost-based or a performance-
based objective function (e.g., minimize total order tardiness), the formula-
tion is a large-scale MINLP, whose solution requires some form of problem
structure dependent decomposition. In the present instance this is accom-
plished by a hierarchical decomposition involving two decision levels: an
upper-level relaxation called the campaign formation subproblem (CFS) and
a reduced dimensionality lower-level problem called the equipment and
resources assignment problem (ERAS).
The role of the CFS subproblem is simply to assign orders to campaigns. In
this problem, the equipment of a given type is considered to be a continu-
ously divisible resource of constrained availability. A key feature of this
subproblem is that it can be proven to be a proper relaxation of the original
MINLP problem and thus will yield lower bound estimates of its solution.
Since the number of campaigns required (K) is not known a priori, K is
treated as an outer iteration variable that is adjusted, as shown in Figure 6.
The role of the ERAS subproblem is to convert the campaign information to
specific task and equipment assignments. Since it is a reduced dimensionality
form of the original MINLP, it will yield an upper bound estimate of the
solution of the original problem. Furthermore, it is interesting to note that by
virtue of the underlying campaign structure, the ERAS subproblem really
consists of a set of individual campaign assignment problems. Since the
individual campaign problems decouple, they can be solved in parallel.
As is typical in decomposition approaches, the two levels must be solved
recursively until the difference between the upper and lower bound estimates
is sufficiently reduced, as also shown in Figure 6. It should be noted, how-
ever, that due to the nonconvexity of the ERAS subproblems, convergence to
the global optimum can not be guaranteed. An approach to obtaining the
global solution of the ERAs problem as been proposed and tested[231 using
feature extraction methods.
Finally, the grass-roots and retrofit design forms of the campaigned multi-
purpose plant can be treated using strategies similar to those for the underly-
ing scheduling problem. The grass-roots design problem differs principally in
that order information is typically not available and thus the design is tar-
geted toward meeting annual production requirements, somewhat simplify-
ing the campaign planning level. Also, at the grass-roots design level,
resource constraints are normally not treated. The number and sizes of
the equipment, however, become unknowns which must be determined. As
shown in Papageorgaki, et al.,[24] the resulting MINLP problem can again be
solved via a hierarchical decomposition strategy. The retrofit problem is
82


positioned somewhat between the grass-roots
design and the scheduling case in that some
of the equipment items exist and others may
need to be added. In general, the problem must
be posed with an annualized net profit objec-
tive function, which accounts for the additional
revenue produced by the retrofit and is
nonconvex. Details of the retrofitting problem
under the restriction that all groups assigned to
a given task are identical can be found in
Papageorgaki, et al.125-261

GENERAL MULTIPURPOSE PLANT
If production requirements of individual prod-
ucts are small and cross-contamination risks
low, then it is advantageous to relax the stric-
tures of the campaign production mode and to
allow product tasks to be executed in an
acyclic fashion as needed to meet specific or-
der deadlines. The equipment utilization and
resource utilization time profiles thus will
appear as shown in Figure 7. Note that mul-
tiple tasks of different products are assigned
to a given unit and no periodic resource
utilization structure is evident over time. The
key challenge in formulating a scheduling
model for this mode is to construct sets of
constraints that insure that at each point in time
in the production horizon each item of equip-
ment is assigned to a single task and that the
utilization level of each resource shared by the
simultaneously active tasks does not exceed


Figure 6. Multipurpose plant schedul-
ing problem decomposition.
Chemical Engineering Education










the available supply.
The classical approach to this problem was proposed in
the early days of mathematical programming research127"281
and was subsequently elaborated in the resource constrained
scheduling context by Pritsker, et al.,[291 and others. The
modeling device employed is to discretize time in
some suitable fashion, to introduce assignment variables
specific to each time interval, and then to write for each
time period a constraint set that would insure resource re-
strictions were not exceeded. This approach was first ap-
plied in the context of the multipurpose batch plant by Sargent
and coworkers.130'311
If time is subdivided into suitably small uniform time
quanta, then a zero-one decision variable can be defined for
each quantum:
W,, which takes on the value 1 if task i is performed in unit j
in time quantum t, and 0 otherwise
Typical resource constraints might, for instance, take the
form

Wt <1, for each j and t

indicating that in time interval t, unit j can be assigned to at
most one task. Similarly, one can write mass balance con-
straints on the material resulting from a given task i, which
expresses the fact that the material available at the start of an
interval, plus that produced over the interval, minus that


U1

U2

U3


A2 B1 82

B1 B2 Al

B2 Al A2
S[IIrn Im


time


Resource
Level


Availability
Profile



B2 B A
B2


I ' I ' I ' ' I ..
Figure 7. General multipurpose plant schedule structure.






c

Data-related: I I I I 11 I I 1111 1
Model-related:

Figure 8. Uniform and nonuniform time discretization.
Spring 1995


consumed, must be equal to what is available to the next
time interval. Assuming fixed task processing times, re-
source utilization amounts, and size factors, it is possible to
express all of the necessary constraints as linear functions of
the 0-1 and continuous variables (batch sizes, material
amounts, etc.). The resulting scheduling problem can thus be
posed as a mixed integer linear program.
In general, the MILPs will be quite large. For instance,
with 25 time intervals, 20 tasks, and only 4 unit choices
allowed per task, the 0-1 variables will number 2000. With
ten equipment items, the number of constraints of the above
form alone would be 250. Because of this, solution using
off-the-shelf MILP solvers is not efficient or reliable, be-
yond problems of perhaps 100 to 200 0-1 variables. As noted
in Pekny, et al.,[321 it is possible to formulate the MILP
constraints in alternative ways, some of which provide tighter
relaxations and therefore lend themselves to more effective
solution than others. Moreover, as shown in that work, it is
critically important to develop solution methods that fully
exploit the structure and data of these types of problems. A
number of alternative uniform discretization (UDM) formu-
lations have been recently proposed,""'36' with various means
of representing key problem features such as sequence de-
pendent change-over times and losses.
Collectively, these various UDM formulations offer the
advantages of accommodating complex recipe structures,
treating alternative intermediate storage policies and limita-
tions as well as handling multiple task-unit assignments,
partial equipment connectivity, and batch/lot size selection.
But all UDM forms share a common limitation-namely,
approximation of the underlying problem that results
from the use of time discretization. In order to rigorously
model the processing events that will take place, the size
of the time quantum must be chosen to equal the shortest
duration event. For instance, if task processing times range
from 10 hours to 1/4 hour, the latter value must be chosen
for the discretization. If the scheduling horizon is 100 hours,
a problem with 400 intervals is created. On the other hand, if
a much coarser interval is selected, the schedule obtained
may be quite slack, reducing considerably the value of the
entire optimization exercise. To address this limitation,
Zentner[371 proposed the notion of using nonuniform repre-
sentations of time.
The motivation for nonuniform continuous time modeling
(NUCM) is illustrated in Figure 8. The chart shows an avail-
ability profile of a required resource and several shaded
blocks representing tasks that require this resource. The
width of each block represents the task duration and the
height the level of the resource required. The UDM model
uses the fine discretization in order to insure that all events
are captured. Since the relevant events occur only at the
beginning and end of tasks and at discontinuities in the
resource profile, the problem data suggest that a much sparser,










nonuniform time representation might suffice. Specifically,
in Zentner's formulation a set of 0-1 variables is only used to
represent the sequence in which tasks are executed, and
continuous time variables are used to represent the start
times of these tasks. It could be shown that this approach
allowed significant reduction in the number of 0-1 variables,
especially for problems in which the processing time values
ranged widely. But for problem instances in which all task
durations are of unit length, the UDM formulation will still
yield problems with fewer 0-1 variables. Nonetheless, the
explicit sequencing variables of the NUCM formulation do
offer important advantages in treating sequence dependent
change-overs. The key limitation of Zentner's formulation,
namely that batch sizes must be specified, was removed in
Mockus and Reklaitis[381 at the price of introducing some
bilinear terms into the mixed integer formulation. An alter-
native nonlinear nonuniform formulation was reported in
Xueya and Sargentl391 but no computational comparisons
could yet be offered. While there is considerable scope for
further work in exploring representation, formulation, and
solution issues, it is clear that there is a role for both UDM
and NUCM type formulations in process scheduling.
As noted in Shah and Pantelides,[401 the design of the
general multipurpose plant can be in principle accommo-
dated within the scope of a UDM scheduling model by
allowing the processing unit capacities to be variables that
can take on any of a set of discrete values. An MILP formu-
lation of the design problem can thus be obtained and solved
to yield both the design and a suitable operating schedule.
The key difficulty underlying this approach, however, is that
the design specifications are normally defined for annual or
seasonal capacity, while the scheduling model of necessity
can only consider shorter time frames.
To address this difference between the capacity planning
and plant scheduling time scales, Subrahmanyam, et al.,r41]
proposed a decomposition strategy in which plant capacity
optimization is carried at the level of a Design Superproblem
while the verification of the operational feasibility of the
design is carried out at the detailed UDM scheduling level.
The Design Superproblem is an MILP that accommodates
demand changes over seasonal periods, but handles the sched-
uling constraints in an aggregate form. The design solution
is then used to create a series of scheduling problems that
cover the seasonal periods in sufficient detail to allow effec-
tive UDM solution. If one or more of these scheduling
problems prove to be infeasible, then the parameters of the
Design Superproblem must be modified and the design opti-
mization repeated. The particular feedback strategy employed
in this work focuses on identifying bottleneck resources and
suitably reducing their effective availability at the
Superproblem level. This hierarchical approach appears to
be an effective means of extending the size of UDM formu-
lations that can be treated in large-scale planning, design,
and scheduling applications in general.[421
84


CONCLUDING REMARKS
In this paper we have provided a highly personalized per-
spective on modeling and optimization approaches to deter-
ministic batch process scheduling and preliminary design prob-
lems. We have sought to highlight the inherently discrete and
combinatorial nature of these problems and the requirements
for careful formulation and rigorous solution strategies, tai-
lored to the specific features of the selected operating mode.
While the optimization problems that are encountered are typi-
cally large in dimensionality and their solution invariably very
computationally intense, application in the field is now gener-
ally feasible, although not yet with off-the-shelf technology.
Indeed, commercial software suitable for these problems is
limited to generic MILP solvers and rule-based systems. None-
theless, over the past decade, a methodological foundation has
been crafted that is rapidly leading to tools accessible to the
practicing engineer. The field in its present state continues to
offer excellent opportunities for academic research and indus-
trial application, most especially in close university-industry
research collaborations.
While the focus of this article has been on simplified, deter-
ministic batch process scheduling and preliminary design
problems, the range of research issues in batch process
systems engineering extend much beyond these confines. It
includes: treatment of uncertainty and variability at both the
operational and the design levels; physical layout of plant
equipment; dynamic simulation as well as control of plant
operations; heat integration and waste minimization, integra-
tion of monitoring, diagnosis, control, and scheduling levels;
synthesis of operating procedures, batch process hazard and
operability analysis; coordination of multiple plant sites; and
supply chain management.
Each of these issues itself constitutes an exciting area for
research and development of a computational nature. Indeed,
progress is being made today in each of these areas both at
Purdue and elsewhere. But a discussion of these development
must be deferred to other venues.

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11,357(1987)
11. Kuriyan, K., and G.V. Reklaitis, "Scheduling Network
Flowshops So As To Minimize Makespan," Computers &
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12. Pekny, J.F., and D.L. Miller, "An Exact Solution of the No-
Wait Flowshop Scheduling Problem with Comparison to Heu-
ristic Methods," Comput. Chem. Eng., 15, 741 (1991)
13. Gooding, W.B., J.F. Pekny, and P.S. McCroskey, "Enumera-
tive Approaches to Parallel Flowshop Scheduling via Prob-
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cal Engineering, West Lafayette, IN, CIPAc Report #93-2
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of Equipment Sizes for Multiproduct Batch Plants: Heuris-
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Dev., 14(3), (1975)
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16. Knopf, C., M. Okos, and G.V. Reklaitis, "Combined Design
and Scheduling of Regenerative Noncontinuous Processes,"
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17. Karimi, I., and G.V. Reklaitis, "Intermediate Storage in
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puter Aided Process Design -83, Westerberg and Chien (eds.),
CACHE Corp., 425 (1984)
18. Yeh, N.C., and G.V. Reklaitis, "Synthesis and Sizing of Batch/
Semicontinuous Processes: Single Product Plants," Comput-
ers & Chem. Eng., 11, 639 (1987)
19. Ravemark, D.E., and D.W.T. Rippin, "Predesigning a
Multiproduct Batch Plant by Mathematical Programming,"
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ries F, in press (1994)
20. Mauderli, A.M., and D.W.T. Rippin, "Production Planning
and Scheduling for Multipurpose Batch Chemical Plants,"
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pose Batch Chemical Plants: Part 1. Formation of Single
Product Campaigns; Part 2. Multiple-Product Campaign For-
mation and Production Planning," Ind. Eng. Chem. Res., 30,
671 (1991)
22. Tsirukis, A.G., S. Papageorgaki, and G.V. Reklaitis, "Sched-
uling of Multipurpose Batch Chemical Plants with Resource
Constraints," Ind. Eng. Chem. Res., 32, 3037 (1993)
23. Tsirukis, A.G., and G.V. Reklaitis, "Feature Extraction Algo-
rithms for Constrained Global Optimization: Part II. Batch
Process Scheduling Applications," special issue of Annals of
Operations Res., 42, 275 (1993)
24. Papageorgaki, S. and G.V. Reklaitis, "Optimal Design of
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2054 (1990)
25. Papageorgaki, S., and G.V. Reklaitis, "Retrofitting in General
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purpose Batch Chemical Plants," in Batch Processing Systems
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Springer Verlag, NATO ASI Series F, in press (1994)
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Res., 7, 621 (1959)
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29. Pritsker, A.A.B., L.J. Waters, and P.M. Wolfe, "Multiproject
Scheduling with Limited Resources: A Zero-One Programming
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30. Kondili, E., C.C. Pantelides, and R.W.H. Sargent, "A General
Algorithm for Short-Term Scheduling of Batch Operations: I.
M ILP Formulation," Comput. & Chem. Eng., 17, 211 (1993)
(Earlier version presented at PSE'88, Syndey, Australia)
31. Shah, N., C.C. Pantelides, and R.W. H. Sargent, "A General
Algorithm for Short-Term Scheduling of Batch Operations: II.
Computational Issues," Comp. & Chem Eng., 17, 224 (1993)
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33. Zentner, M.G., J.F. Pekny, G.V. Reklaitis, and J.N.D. Gupta,
"Practical Considerations in Using Model Based Optimization
for the Scheduling and Planning of Batch/Semicontinuous Pro-
cesses," J. Process Control, special issue on Batch Processing,
5(4), 259 (1994)
34. Pantelides, C.C., "Unified Frameworks for Optimal Process
Planning and Scheduling," in Foundations of Computer Aided
Process Operations, Rippin, Hale, and Davis (eds.), CACHE,
253 (1994)
35. Zentner, M.G., J.F. Pekny, D.L. Miller, and G.V. Reklaitis,
"RCSP++: A Scheduling System for the Chemical Process In-
dustry," Proceedings of Process Systems Engineering Sympo-
sium, Kyongju, Korea, May (1994)
36. Elkamel, A., "Scheduling of Process Operations Using Math-
ematical Programming Techniques: Towards a Prototype Deci-
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West Lafayette, IN (1993)
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tion for the Scheduling of Resource Constrained Batch Chemi-
cal Processes," in Batch Processing Systems Engineering,
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NATO ASI Series F, in press (1994)
38. Mockus, L., and G.V. Reklaitis, "Mathematical Programming
Formulation for Scheduling of Batch Operations Based on Non-
uniform Time Discretization," Paper No. 235d, AIChE Annual
Meeting, San Francisco, CA, November (1994)
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for Process Scheduling," paper presented at AIChE Annual
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Planning and Design of Batch Plants," Ind. Eng. Chem. Res.,
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225b, AIChE Annual Meeting, San Francisco, CA, November
(1994) 0


Spring 1995











Me 'a laboratory


BIOSEPARATION VIA


CROSS-FLOW MEMBRANE FILTRATION1


HELEN C. HOLLEIN, C. STEWART SLATER, RITA L.
Manhattan College Riverdale, NY 10471

Prior to the mid 1980s, most chemical engineering
programs focused their courses on petroleum-based
industries. Since that time, curricula have broadened
to include new and emerging technologies such as biochemi-
cal engineering, electronics processing, advanced materials,
and environmental applications. Manhattan College is one
of the institutions that has added elective courses and experi-
ments in biochemical engineering.[1'21 Fermentation experi-
ments that measure kinetics of cell growth and oxygen trans-
fer are complicated to run and require many hours to collect
data. A microfiltration experiment on cell harvesting from
yeast slurries can be used to simultaneously introduce bio-
chemical engineering principles and modern separation pro-
cesses. The equipment is relatively easy to operate and ex-
periments are not time-consuming.
Microporous membrane filtration, or microfiltration, is
one of a group of separation processes that depends on
pressure as the driving force for separation. In order of
increasing pore size and decreasing operating pressure, these
processes are reverse osmosis (RO), nanofiltration (NF),
ultrafiltration (UF), microfiltration (MF), and conventional
particulate filtration. Filtration processes can be operated in
a dead-end or flow-through mode with feed flowing perpen-
dicular to the filter surface, and in a cross-flow or tangential-
flow mode with feed flowing parallel to the filter. In recent
years, the authors have developed unique undergraduate in-
structional experiments in RO and UF.13-6] These experi-
ments use polymeric membranes as the filtration media and
are operated in a cross-flow mode. Configurations include
hollow fiber, spiral wound, and thin-channel systems. In
addition, a conventional plate and frame filter press is oper-
ated in our senior laboratory course. That system uses a cloth
filter and operates in a dead-end mode. New experiments in
microfiltration were recently added to the experimental se-
quence. The MF experiments use polymeric membranes and

I This paper is based on a publication in the 1994 ASEE Annual
Conference Proceedings.
2Address: ABB Lummus, Bloomfield, NJ 07003
Copyright ChE Division ofASEE 1995


D'AQUINO, ANNMARIE L. WITT2


tangential flow operation.
Membranes used for UF and MF are characterized as
porous. Other membrane processes such as reverse osmosis,
gas permeation, and pervaporation use nonporous membranes,
where transport occurs by a solution-diffusion mechanism.
Slater and co-workers have developed and reported on ex-
periments in gas permeation and pervaporation.17-101 MF ex-
periments with specific application to biochemical engineer-
ing have been discussed briefly in several publications"'5'111
and were presented in more detail in the 1994 ASEE Annual
Conference Proceedings.["21
Similar types of equipment may be used for MF and UF,
except that membranes with larger pore sizes are installed
for microporous separations. Pore sizes in microfiltration are
around 0.02 to 10 pm in diameter, as compared with 0.001
to 0.02 gm (300 to 300,000 Daltons) for ultrafiltration (ranges
vary slightly depending on source). The membranes are
made of either organic materials (polymers) or inorganic
materials (ceramics, metals, and glasses). MF processes are
suitable for retaining suspended solids and large colloidal
particles, while allowing passage of macromolecules like
proteins and enzymes. UF processes are designed to retain

Helen C. Hollein is Professor of Chemical Engineering, Chair of the ChE
Department, and Director of the Biotechnology Program at Manhattan
College. She earned her MS and DEngSci degrees in chemical engineer-
ing from the New Jersey Institute of Technology, and her BSChE from the
University of South Carolina. Her teaching and research interests are in
biochemical engineering and bioseparation processes.
C. Stewart Slater is Professor of Chemical Engineering at Manhattan
College. He received his PhD, MPh, MS, and BS degrees in chemical
engineering from Rutgers University. His research and teaching interests
are in separation and purification technology, membrane processes, and
biotechnology. He has had industrial experience with Procter & Gamble
Company.
Rita L. D'Aquino teaches mathematics and computers at a private school
while seeking admission to a doctoral program. She received her BS and
MS degrees in chemical engineering from Manhattan College and did
graduate research on membrane pervaporation processes. She previously
worked for Lever Brothers Company.
Annmarie L. Witt is a process engineer at ABB Lummus in Bloomfield,
New Jersey. She earned her BS and MS in chemical engineering from
Manhattan College. She developed several membrane process experi-
ments in conjunction with her senior honors project and completed an
advanced design project at the graduate level.


Chemical Engineering Education











macromolecules, while allowing inorganic salts and small
organic molecules to pass into the permeate stream.
Industrial applications of MF include clarification and
cold sterilization of beverages and pharmaceuticals. A popu-
lar example is the use of ceramic microfilters to process
"cold-filtered" beer. Other applications include a step in
production of ultrapure water for the semiconductor indus-
try, bacteriological analysis of fresh water, cell harvesting
from fermentation broths, recovery of precipitated heavy
metals from wastewater, and dewatering of latex emulsions.13-
151 Recent publications report that of the vari-
ous membrane processes, microfiltration and A mic
ultrafiltration have the biggest market. The
largest section of this market niche is hemo- experin
dialysis (artificial kidneys), followed by mi- harvesting
crofiltration in general, with ultrafiltration slurries c
much further behind. This technology is ex- simul
pected to replace diatomaceous earth filtra-
tion of foods and pharmaceuticals and possi- introduce
bly to make inroads into environmental ap- engineer
plications such as water and sewage treat- and mode
ment.[16-~71 Thus, MF experiments can be re- p
lated to various specialties within chemical
engineering, including food engineering, equipment
pharmaceutical or biochemical engineering, easy to
environmental engineering, and biomedical experim
engineering. time-c

SEPARATION PRINCIPLES
Principles of microfiltration are presented in books on the
subject.[3'14'18-20] This discussion is limited to theoretical as-
pects of the MF experiments covered in this paper. These
experiments concern harvesting of unwashed yeast cells from
a defined media containing only dextrose and salt. Cells
grown in fermentation experiments could also be used,
but the data would be less reproducible due to the presence
of other components in the media such as chemicals re-
quired for cell nutrition, fermentation products, cell debris,
and antifoam.
System performance may be defined in terms of permeate
flux, J, with dimensions of (volume/area-time), e.g., typical
units are (L/m2-h). Flux can be determined by measuring
each incremental volume of permeate, AV, collected in time
period, At, and dividing by surface area of the membrane.
AV/At (1)
J= (1)
surface area
Since MF is a pressure-driven separation process, it is
appropriate to measure effects of pressure on flux. In the
absence of any boundary layer effects, flux through porous
membranes is directly proportional to the applied pressure
gradient across the membrane, AP, and inversely propor-
tional to solution viscosity, rl, and membrane thickness, Ax.
The hydrodynamic resistance of the membrane, Rm, is in-
Spring 1995


versely related to the permeability coefficient, Lp.
L AP AP
J-= (2)
Ax i1R,

Values for Lp and Rm can be determined by running ex-
periments with purified (filtered, deionized, and distilled)
water and varying operating pressure in the retentate chan-
nel. Permeate is collected at atmospheric pressure. The per-
meability coefficient accounts for factors such as membrane
porosity, pore size distribution, and liquid viscosity.
Permeation of macromolecules through MF
tration membranes leads to concentration polariza-
on cell tion and possibly to subsequent fouling of the
membrane. Both of these phenomena can lead
om yeast to a drop in permeate flux. Concentration
e used to polarization is an increase in the solute con-
ously centration at the membrane (feed side) in
che l excess of bulk feed solution levels. This
"boundary layer" solute concentration is a
principles function of solute characteristics, cross-flow
separation velocity, and flux. Concentration polari-
. The nation is a reversible phenomena. On the other
relatively hand, fouling may or may not be reversible,
depending on its cause. When separating mi-
ate and croorganisms and cell debris from fermenta-
are not tion broths, a biological cake is formed while
mning. other components of the fermentation slurry
such as antifoam, macromolecules, and pre-
cipitates tend to foul the membrane. The net
result is a severe decline in permeate flux leading to de-
creased system throughput.
Based on conventional filtration theory, flux should be
directly proportional to pressure for a noncompressible cake,
but independent of pressure for a "perfectly compressible"
cake.1131 In the MF process for cell harvesting, increased
operating pressure tends to compact biomass on the mem-
brane surface and may also increase membrane fouling.
These phenomena can lead to decreased permeate flux at
higher operating pressures rather than increasing flux with
pressure as expected. In some cases, flux increases with
pressure up to some optimum operating condition, then de-
creases with further increases in pressure. In other cases, a
pressure-independent, steady-state flux is observed at higher
operating pressures.
Cross-flow filtration is designed to sweep the membrane
surface so as to decrease membrane fouling. In the case
where a buildup on the surface occurs due to cake formation,
the shearing action of the cross-flow velocity will tend to
remove previously deposited particles and return them to the
bulk feed stream. Cross membrane flow rate can be varied,
and its effect on flux measured experimentally. While the
cross-flow mode is a significant improvement over dead-end
filtration, permeate flux still decreases to some steady-state


rofil\
lent
ggfr
an b
tane
Sbio
ng p
rn S
sses
t is
per
ents
onsu










value or limiting flux, J_. Cake filtration models describing
actual system performance typically represent transport re-
sistance in terms of a series/resistance model. MF equations
usually include resistances to permeation through the mem-
brane and the biological cake, Rm and R, respectively.[13,21-241

S AP (3)
Sn(Rm +Rc)
In membrane separation processes, temperature effects on
flux generally follow the Arrhenius relationship, where Jo is
the flux at 250C, E, is the activation energy, R is the univer-
sal gas constant, and T is absolute temperature. Changes in
flux with temperature result from changes in solution viscos-
ity. Viscosity decreases as temperature increases, so water
permeability through the membrane subsequently increases.
This relationship can be shown to hold for a Newtonian fluid
like distilled water. Thus, for microfiltration runs with puri-
fied water, Arrhenius constants in the following equation
can be measured as a function of temperature.

J Jo-E(/RT) (4)

Fermentation broths containing suspended microorgan-
isms exhibit non-Newtonian behavior at higher concentra-
tions, so increased temperature tends to increase flux but not
in the same magnitude as observed for aqueous solutions. In
addition, higher process temperatures tend to improve filtra-
tion characteristics of the biological cake. Temperature ef-
fects can be measured in cell harvesting experiments, but the
results cannot be predicted directly from Eq. (4).
A relative measurement of system performance is the con-
centration factor, V, defined as the ratio of initial feed
volume to final retentate volume, Vo/Vf. Experimental val-
ues of v approaching 20 have been attained, with the upper
limit dependent on the patience of students doing the experi-
ment rather than system limitations. The final concentration,
Cf, that would be obtained if all of the cells stayed in suspen-
sion can be calculated from the initial concentration, Co, and
the concentration factor (Eq. 5), then compared with experi-
mental data. The final concentration of yeast cells in the
retentate may be used as an absolute measure of system
performance. Measured values up to 45.7 g/L were obtained
in these experimental studies. Yeast concentrations as high
as 80 g/L may be obtained in cross-flow systems.[13]
V
C, = Co 0 = Co (5)
Vf
A parameter used to describe continuous system perfor-
mance is recovery, which may be defined as the ratio of
permeate flow rate to feed flow rate, Q/Q,. Solute rejection
is another parameter that is used to measure performance in
RO and UF systems.'31 In all of the MF experiments on
concentration of yeast slurries, 100% of the solids were
rejected by the membrane. This was determined by measur-


ing the turbidity of the permeate which was the same as that
of the media without cells.

EXPERIMENTAL SYSTEM

Microfiltration Equipment
Two tangential flow systems were purchased from
Millipore Corporation: a Minitan acrylic ultrafiltration
system and a Pellicon cassette system. Both units include
a pump and a microfilter and support microfiltration or
ultrafiltration, depending on the type of membrane selected.
The effective filter area in the Minitan unit ranges from
0.0060 m2 to 0.0600 m2 (1 10 plates). The Pellicon system
is larger, with an effective filter area ranging from 0.0465 m2
for a single membrane packet, to 0.465 m2 (10 packets or 1
standard cassette), to a maximum of 4.65 m2 with multiple
cassettes. The Minitan system is recommended for process-
ing volumes between 0.1 L and 2.0 L, and the Pellicon
system for volumes between 2L and 200 L.
For harvesting of bacterial or yeast cells, Millipore recom-
mends a Durapore 0.45 gm membrane. Durapore is the
trademark for an anisotropic membrane made from the poly-
mer PVDF (polyvinylidene difluoride). These membranes
are surface treated so as to be hydrophilic. Manufacturers
give PVDF membranes different acronyms, according to
pore size (VVLP for 0.1 ntm, GVLP for 0.2 gm, HVLP for
0.45 pnm, and DVLP for 0.65 rnm). Bacterial cells are ap-
proximately 1-2 microns in size, and yeast cells 7-20 mi-
crons, so any of these membranes will retain whole cells.
Cell debris is somewhat smaller (around 0.4 microns), but
will generally be removed by HVLP membranes.
Membranes are available as individual sheets, plates, pack-


Figure 1. Minitan acrylic ultrafiltration system
(photograph courtesy of Millipore Corp.)
Chemical Engineering Education










ets, and cassettes. Maximum operating conditions for these
membranes are 100 psia, 500C, and pH 11. A Minitan plate
consists of two membranes bonded to a rectangular molded
plastic plate. Two plates (0.0120 m2) with retentate separa-
tors were used in the Minitan experiments to concentrate one
to two liters of yeast slurry. A Pellicon packet consists of
two membrane sheets bonded to a filtrate screen. Two pack-
ets (0.0930 m2) with retentate screens were used in the
Pellicon experiment shown in this paper to concentrate seven
liters of yeast slurry. Pellicon cassettes contain membranes
and filtrate screens stacked in fully bonded units and are
available in three sizes: 0.465 m2, 0.930 m2, and 1.395 m2.
Cassettes were used in prior experiments with yeast and
Streptomyces rimosus.
The Minitan system is shown in Figure 1. This system
includes a plate-and-frame filtration unit and a variable speed
pump. The pump is a standard reversible flow peristaltic
pump. The microfilter consists of upper and lower acrylic
manifolds with nylon adaptors, upper and lower stainless-
steel frames, a stainless-steel pressure gauge, and brass
torque nuts. Dimensions of the filter holder assembly (not
including membrane plates or mounting screws) are 11.4 cm
wide, 15.2 cm deep, and 7.6 cm high. Maximum operat-
ing pressure is 20 psi with silicone tubing or 40 psi with
Tygon tubing. Calibration curves of flow rates versus dial
settings were prepared for the pump and distributed for
use with the experiments. Operating instructions provided
by Millipore for assembling the equipment, installing the
membrane plates, and cleaning the membranes are well
written and easy to follow.
A process flow diagram for operating a tangential flow
microfilter is shown in Figure 2. In the batch concentration
mode, a yeast suspension is pumped from a well-mixed feed
tank into the microfilter, retentate is recycled to the feed
tank, and permeate is collected in another container. The
batch concentration mode was used to collect all of the
experimental data shown in this paper. Concentration in the


I Pump
Figure 2. Process flow diagram showing batch concentra-
tion (recycle) and continuous (single pass) modes:
TI=temperature indicator; PI=pressure indicator.
Spring 1995


feed tank increases throughout the batch run. The continu-
ous mode is the same except that the retentate makes a single
pass through the microfilter and is collected in a third con-
tainer (separate from the permeate or feed). The continuous
mode may be used to run experiments at constant feed con-
centrations. Prior to running each experiment, the membrane
is preconditioned by pumping media without cells, at the
temperature and pH of the feed slurry, through the unit in the
recycle or batch mode. The cleaning steps at the end of the
experiment are run in the single pass or continuous mode.
The Pellicon cassette system is similar to the Minitan unit
except for its larger scale. The microfilter contains upper and
lower acrylic manifolds, polypropylene fittings, stainless-
steel pressure gauges on the feed and retentate lines, and
bronze torque nuts. The upper and lower frames are made of
nylon-encapsulated stainless steel. Without membranes, the
filter holder assembly measures 26.0 cm wide, 18.1 cm
deep, and 19.7 cm high. The pump is a Procon positive
displacement pump with a maximum flow rate of 1 gpm. It is
fitted with rigid-wall polyethylene tubing that withstands
pressures up to 100 psi. This pump is recommended for 2 to
20 L batches. A larger Procon pump (4 gpm) and Masterflex
peristaltic pumps are also available. The Procon pump was
selected to provide the option of high-pressure operation
which is needed to concentrate mycelial organisms, but a
peristaltic pump can be used for harvesting yeast and bacte-
ria. The Pellicon microfilter and Procon pump are mounted
as a complete system on a polypropylene board.

Experimental Methods
Saccharomyces cerevisiae (Baker's yeast) was selected to
study microfiltration in biological systems. Fleischmann's
active dry yeast can be purchased in seven-gram packages at
any supermarket. A defined media consisting of distilled
water, 2.0 g/L dextrose, and a pinch of salt was adjusted to
pH 5.0 with 1 N HCI and used to precondition the mem-
branes prior to each run. Yeast was added to the dextrose
media for the experimental studies. Solution pH affects flux,
and pH of distilled water may be below 7; therefore, pH of
the yeast suspension must be measured and adjusted to some
set value. Actual concentrations of dextrose and sodium
chloride are not critical, but should be consistent between
experiments. To give the experiments more of an environ-
mental focus, Escherichia coli K 12 (a weakened laboratory
strain) could be used.
A sodium hypochlorite solution is recommended for clean-
ing and sanitizing the HVLP membranes between runs. Fresh
household bleach is diluted to 300 ppm, and pH is lowered to
the 6-8 range with 1 N HC1. Millipore recommends heating
the hypochlorite solution to 40-500C, but room temperature
cleaning is sufficient to remove the gel layer developed
during harvesting of yeast cells at low operating pressures. If
the membranes are heavily soiled (this occurs at increased
operating pressures), they should be removed from the sys-
89










tem and rinsed with distilled water to remove visible debris,
then reinstalled in the system and cleaned with heated hy-
pochlorite solution. Terg-A-Zyme enzymatic cleaner can be
used as a cleaning solution instead of diluted bleach solu-
tion, but the authors do not recommend this because it is
very difficult to remove the detergent from the membrane.
We have cleaned and reused the membranes in the Pellicon
system a number of times without any problems. The Minitan
system has silicone retentate separators between the
membrane plates, and the design of the separators is such
that they tend to deform and block the channels after clean-
ing with hypochlorite solution. The Minitan plates can be
cleaned and reused several times during one laboratory pe-
riod. The system must be cleaned and opened at the end
of each laboratory period, the membrane plates removed
and stored in distilled water, and the separators laid flat
to dry. If the separators are deformed after drying they have
to be replaced before the system can be sealed for the next
set of experiments.
Yeast concentrations were measured by optical density
using a DRT-100B turbidimeter manufactured by HF Scien-
tific Inc. Turbidity readings were converted to dry weight
per unit volume using a calibration curve. The turbidity
calibration curve is prepared by weighing out different
amounts of yeast solids, mixing with dextrose solution or
fermentation media in volumetric flasks, and measuring tur-
bidity. Turbidity readings become nonlinear, approaching a
constant value, at higher concentrations. For turbidity read-
ings above 1000 NTU (normal turbidity units) or approxi-
mately 1.6 g/L, samples must be diluted until readings are in
the linear range.

TYPICAL EXPERIMENTAL RESULTS
Prior to experimenting with the yeast slurry, students are
asked to determine the effects of transmembrane pressure
gradient and operating temperature on permeate flux for
purified water. Normal operating pressure for the Minitan
unit is approximately 2 psi. Using pure water with the reten-
tate tube completely closed, the transmembrane pressure
reaches 4 to 6 psi, depending on cross-flow rate. Water
fluxes are measured at 0.5 psi intervals within this range in
order to determine coefficients in Eq. (2). The Procon pump
on the Pellicon system produces higher transmembrane pres-
sures, e.g., approximately 10 psi for pure water with the
retentate tube fully open. In both systems, higher operating
pressures can be obtained when filtering cell slurries.
Initial studies with purified water are very important if
temperature will be used as a process variable in the yeast
experiments. Maximum operating temperature is 500C for
both the Minitan unit and the HVLP membrane. Operating at
temperatures above 500C will kill the microorganism. Thus,
we suggest that data be taken at room temperature, cooler
temperatures using an ice bath, and temperatures up to 400C


using a hot plate. The manufacturer states that prior to sys-
tem use, media must be circulated through the system in
order to precondition the membranes. This step also adjusts
the temperature of the Minitan unit. Water flux studies pro-
vide a method for determining whether the system has reached
the proper temperature, since a graph of the natural loga-
rithm (LN) of J versus 1/T should result in approximately the
same slope as a graph of LN (1 / r) versus 1/T. We ask the
students to graph their data and the literature values for 1 / 1,
then examine the slopes before continuing with the cell
harvesting studies. The high and low temperature runs must
be repeated if the experimental slope is not reasonable. Val-
ues of E, and Jo are calculated from these graphs using the
Arrhenius relationship in Eq. (4).
Each laboratory group is assigned one process variable for
investigation in the yeast experiments. Variables include
cross membrane flow rate, operating temperature, transmem-
brane pressure gradient, feed concentration, and solution
pH. Figure 3 shows typical experimental data for batch
concentration of one liter of yeast slurry in the Minitan
system. Initial concentrations were approximately 7.0 grams
of Fleischmann's dry yeast suspended in one liter of defined
media. The powdered yeast was not washed after rehydra-
tion. In cross-flow experiments with a polypropylene filter,
Redkar and Davis report that unwashed yeast results in an
accelerated initial flux decline and a significantly lower final
flux than washed yeast.[21] They attribute the poorer perfor-
mance for unwashed yeast to the presence of extracellular
proteins and other molecules or colloids, which foul the
membrane and increase cake resistance.
As shown in Figure 3, volume versus time data for dis-
tilled water is linear, but plots for the yeast slurry curve with
decreasing slopes as the membrane becomes caked with
solids and fouled with macromolecules. Porter plots graphs
of this type and refers to the permeate volume collected as
"volume processed" or "throughput."'131 Run 1, at room tem-


0.8


S0.6
I06 //
E
o-
0.4 -


0.2


00.
0.0 0.1


0.2
Time (h)


Run 33

0.3 0.4


Figure 3. Results of typical microfiltration experiments:
Water, T=220C, pump=48.6 L/h; Run 1, T=22"C, pump 48.6 L/h;
Run 2, T=3"C, pump = 48.6 L/h; Run 3, T=220C, pump=9.4 L/h.
Chemical Engineering Education











perature and a relatively high cross-flow rate, has the greatest
throughput per unit time of the three yeast runs shown. When
temperature is decreased (Run 2) or cross-flow rate is decreased
(Run 3), while keeping the other parameters constant, the time
required to concentrate the feed solution and collect a given
volume of permeate increases. Slopes from the volume versus
time curves are used to calculate flux (Eq. 1).
Most graphs of microfiltration data in the literature plot flux as
a function of time. Feed concentration increases with time in
batch concentration experiments; therefore, two variables (con-
centration and cross-flow rate) affect flux at a given point on the
time axis in Figure 4. Comparison of two runs at the same
temperature but different tangential flow rates verifies that the
higher flow rate in Run 1 results in improved system perfor-
mance. In both runs, permeate flux declines rapidly from the
initial water value (1030 L/m2-h), then levels out and approaches
a final value. At the higher cross-flow rate, the data exhibit a
1000


Figure 4. 48.6 uh
Effect of 800 IX
cross-flow 9.4 Uh
rate on flux in
yeast slurries: 600
Run 1, E A
T=22 C,
pump=48.6 L/h; 400
Run 3, A
T=22C, i
pump 9.4 L/h. I 20
200 I Z1
I
X z I

0
00 0.1 02 0.3 0.4
Time (h)

1000

Figure 5. Effect A
IT=22 c
of temperature soo
on flux in yeast T=3C
slurries:
Run 1, T=22C, 600
pump=48.6 L/h; ,
Run 2, A
T=3oC'
pump= 48.6 L/h. 400
A

200
*

0
1 2 3 4 5 6 7
Concentration Factor

Spring 1995


more gradual flux decline and approach a higher final
flux. Increased tangential flow is more effective in sweep-
ing accumulated solids from the boundary layer and ar-
resting growth of the yeast cake. Note that the flow rates
in the figures represent total output of the pump, including
retentate and permeate flow. Permeate flow decreases and
retentate flow increases as the run progresses, so tangen-
tial flow rate varies.
Figures 5 and 6 plot permeate flux as a function of
concentration factor w (Eq. 5). Since Co is the same for
the two runs graphed in each figure, only one variable
affects flux at a given point on the X axis when the data is
plotted in this manner. Comparison of two experiments
at the same tangential flow rate but at different tempera-
tures (Figure 5) verifies that the higher operating tempera-
ture in Run 1 leads to improved system performance. The
initial and final fluxes are higher at 220C than at 3C,
while the rates of flux decline are approximately equal.
Higher fluxes result from decreased solution viscosity at
higher temperatures and from improved filtration charac-
teristics for the biological cake. Note that the temperature
of the feed slurry must be measured for each run rather
than assuming that it is at a known value such as room
temperature, because the distilled water used for the me-
dia may be cold or hot.
All of the data shown in this paper was obtained by
running the Minitan and Pellicon systems at low pressure
(without a clamp on the retentate tube). Cell concentration
in the feed/retentate tank was measured at the beginning
and end of each run and at several intermediate points,
then compared with values calculated from Eq. (5). Mea-
sured concentrations follow the same trend as calculated
values, but the measured values are lower in magnitude.
This difference occurs because cells, proteins, and other
materials are retained by the membrane. Cellular material
is removed from the membranes at the end of each experi-
ment by flushing the system with distilled water. Proteins
and other fouling substances are then removed by cleaning
the system with hypochlorite solution. At higher operating
pressures there is a greater difference between measured
and calculated concentrations, and significantly more ma-
terial is removed from the membranes in both cleaning
steps. In order to obtain good experimental data, the stu-
dents must clean the membranes thoroughly between runs.
A comparison between the Minitan and Pellicon sys-
tems is shown in Figure 6 (next page). Both systems used
Durapore 0.45 nm PVDF membranes, and operating con-
ditions were comparable. Initial concentrations were ap-
proximately 3.5 g/L and feed temperatures were 23C in
both runs. Pump settings and membranes were selected so
that the tangential flow rate per effective membrane area
was approximately the same in both systems. This ratio
was 1050 L/h per square meter for the Minitan system
(Run 4) and 930 L/h per square meter for the Pellicon
91










system (Run 5). As shown in the figure, the Minitan system
has a more gradual flux decline and a slightly higher final
flux than the Pellicon system at comparable concentrations.
Prior work with Pellicon cassettes gave similar fluxes to
those obtained with Pellicon packets in this study. Differ-
ences between the flux values in Runs 4 and 5 may be
attributed to differences in channel designs of the Minitan
and Pellicon units, plus the higher operating pressure deliv-
ered by the Procon pump positive displacement pump in the
Pellicon system. The Minitan system was selected for ex-
periments in our senior laboratory course because this sys-
tem makes it possible to process given volumes of fluid
rapidly and thus generate more data during a single labora-
tory period. The larger Pellicon system may be preferred in
teaching laboratories that are organized so that students work
on an open-ended experiment for several weeks because of
its advantages with regards to cleaning and reuse of the
membranes.
Other student groups studied variations in operating pres-
sure. Although the manufacturer recommends against clamp-
ing the retentate tube to increase operating pressure in mi-
crofiltration experiments, this procedure is useful for teach-
ing purposes. Small increases in average transmembrane
pressure significantly increase water fluxes. Similarly, in-
creases in operating pressure tend to increase permeate fluxes
for cell suspensions, but higher pressures may show little or
no improvement. In experiments with the yeast slurry, oper-
ating pressures can be raised to any desired value (2 20 psi
in the Minitan system) by partially closing the retentate tube.
Pressures of 5 6 psi are high enough to demonstrate that
increased pressure tends to compact the biological cake and
increases membrane fouling, resulting in an accelerated flux
decline and decreased system throughput. Operating pres-
sures above 10 psi are not recommended by the authors
because the membranes become so heavily fouled that it is
very difficult to clean and reuse them.
S1200


1000


600

400

200 -

0
1 2 3


4 5 6 7 8
Concentration Factor


Effects of initial feed concentration and solution pH were
also examined. Flux values decrease as feed concentration
increases, which can be demonstrated in continuous (single-
pass) runs at different concentrations. Experiments run at 1.0
g/L and 7.0 g/L took approximately 25 minutes to process
twenty liters of feed and gave reasonable data. Solution pH
has less of an effect on system performance than the other
variables discussed above. A solution pH of 5.0 was selected
for yeast concentration experiments because this is a typical
value for yeast fermentation. The pH of the feed affects
binding characteristics of the membrane and solubility of
macromolecules, with both factors influencing membrane
fouling and steady-state fluxes. The Durapore PVDF mem-
brane has low protein-binding characteristics, so pH is not a
major factor in system operation. High or low pH values will
kill the cells and change filtration properties. Within the
middle pH range, flux appears to vary inversely with pH for
this membrane.

ACKNOWLEDGMENTS
This project was partially supported by the National Sci-
ence Foundation under Grant #USE-9054212. Equipment
and supplies were funded by Manhattan College.

REFERENCES
1. Hollein, H.C., C.S. Slater, S.G. Walsh, M.N. Venezia, and
A.A. Caruso, "A Unit Operations Approach to Biochemical
Engineering," 1989 An. Conf. Proc. of ASEE, Lincoln, NE,
256 (1989)
2. Hollein, H.C., C.S. Slater, N.J. Peill, V.C. Lanzon, and M.N.
Venezia, "Biochemical Engineering Laboratory Experiments
in Fermentation and Downstream Processing," 1987 Ann.
Conf. Proc. ofASEE, Reno, NV, 1605 (1987)
3. Slater, C.S., H.C. Hollein, P.P. Antonecchia, L.S. Mazzella,
and J.D. Paccione, "Laboratory Experiences in Membrane
Separation Processes," Int. J. ofEng. Ed., 5, 369 (1989)
4. Slater, C.S., and J.D. Paccione, "A Reverse Osmosis System
for an Advanced Separation Process Laboratory," Chem.
Eng. Ed., 21,138 (1987)
5. Slater, C.S., and H.C. Hollein, "Educational Initiatives in
Teaching Membrane Technology," Desalination, 90, 291
(1993)
6. Parkinson, G., "Hands-On Learning/The New Wave in ChE
Education," Chem. Eng., 45 (October, 1994)
7. Slater, C.S., J. Mencarini, and R. Coppola, "Development of
Experimental Methodology in Pervaporation: Part 2," Ann.
Conf. Proc. ASEE, Champaign, IL, 578 (1993)
8. Slater, C.S., and R. D'Aquino, "Development of Experimen-
tal Methodology in Pervaporation: Part 1," Ann. Conf. Proc.
ofASEE, Champaign, IL, 444 (1992)
9. Slater, C.S., C. Vega, and M. Boegel, "Experiments in Gas
Permeation Membrane Processes," Int. J. of Eng. Ed., 7,
368(1992)
10. Slater, C.S., "Education on Membrane Science and Technol-
ogy," in J.G. Crespo and K.W. Baddeker (eds.), Membrane
Processes in Separation and Purification, Kluwer Academic
Publishers, Dordrecht, The Netherlands, 479 (1994)
11. Davis, R.H., and D.S. Kompala, "Biotechnology Laboratory
Methods," Chem. Eng. Ed., 23, 182 (1989)
12. Hollein, H.C., C.S. Slater, R.L. D'Aquino, and A.L. Witt,
"Microfiltration: A Novel Experiment in Bioengineering,"
1994 Ann. Conf. Proc. of ASEE, Edmonton, Canada, 1966
Chemical Engineering Education


Figure 6. Comparison of operation of Minitan and Pellicon
systems: Run 4, Minitan, T=23C, pump=12.6 L/h; membrane
area=0.0120 m2, Vo=2L; Run 5, Pellicon, T=23C, pump=86.4 L/h,
membrane area=0.0930 m2, Vo=7 L.










(1994)
13. Porter, M.C., Handbook of Industrial Membrane Technol-
ogy, Noyes Publications, Park Ridge, NJ, Chap. 2 (1990)
14. Hanisch, W., "Cell Harvesting," in Membrane Separation in
Biotechnology (W.C. McGregor, ed.), Marcel Dekker, New
York, NY; Chap. 3 (1986)
15. Michaels, S.L., "Crossflow Microfilters: The Ins and Outs,"
Chem. Eng. 84 (January 1989)
16. Haggin, J., "Membrane Technology Has Achieved Success,
Yet Lags Potential," Chem. & Eng. News, 22 (October 1,
1990)
17. Baker, R.W., E.L. Cussler, W. Eykamp, W.J. Koros, R.L.
Reiley, and H. Strathmann, "Membrane Separation Sys-
tems: A Research Needs Assessment," U.S. Dept. of Energy,
Report 30133-H1, Vol. 2 (April 1990)
18. Ho, W.S., and K.K. Sirkar (eds.), Membrane Handbook, Van
Nostrand Reinhold, New York, NY; Chaps. 31-35 (1992)
19. Mulder, M., Basic Principles of Membrane Technology,
Kluwer Academic Publishers, Boston, MA (1991)
20. Wankat, P.C., Rate-Controlled Separations, Elsevier Ap-
plied Science, New York, NY; Chap. 12 (1990)
21. Redkar, S.G., and R.H. Davis, "Crossflow Microfiltration of
Yeast Suspensions in Tubular Filters," Biotech. Prog., 9,
625(1993)
22. Takahashi, K., N. Ohtomo, K. Ishii, and T. Yokota, "Cake
Formation and Spatial Partitioning in Batch Microfiltra-
tion of Yeast," J. of Chem. Eng. of Japan, 24, 372 (1991)
23. Tanaka, T., R. Kamimura, R. Fujiwara, and K. Nakanishi,
"Crossflow Filtration of Yeast Broth Cultivated in Molas-
ses," Biotech. and Bioengg., 43, 1094 (1994)
24. Tanaka, T., R. Kamimura, K. Itoh, K. Nakanishi, and R.
Matsuno, "Factors Affecting the Performance of Crossflow
Filtration of Yeast Cell Suspension," Biotech. and Bioengg.,
41, 617 (1993) 0


r book review


The Science of Polymer Molecules
by Richard H. Boyd and Paul J. Phillips
Cambridge University Press, 40 West 20th Street, New York,
NY 1011-4211; $79.95 (1994)

Reviewed by
Timothy A. Barbari
Johns Hopkins University

Although there are a number of excellent texts for under-
graduate courses in polymer science, they do not provide the
necessary depth for a graduate course in the subject. There
has long been a need for a graduate-level textbook that
presents polymer science from a rigorous, molecular ap-
proach. Professors Richard H. Boyd (University of Utah)
and Paul J. Phillips (University of Tennessee) address that
need with this book, The Science of Polymer Molecules. The
authors' intentions are clear from their own words in the
Preface:
We have taken the viewpoint that a textbook should
undertake to explain and develop the principles
selected and notjust present results. For most of the
subjects, we have proceeded from a very elementary
Spring 1995


starting point and presented in fair detail the steps.
The goal has been to arrive at a point where the
student can understand the principles and profitably
read the literature connected with that subject.
In reviewing this book, I decided to assess the extent to
which Boyd and Phillips achieved their goal. The book is
intended for graduate students in chemistry, chemical engi-
neering, and materials science, and a background in physical
chemistry and organic chemistry is assumed. According to
the authors, however, "Students from an entirely engineer-
ing background have been very successful in masatering the
subjects covered."
The book begins with a short chapter on polymerization
methods as a means of introducing polymer chemistry to the
student. Following the introduction, Chapters 2, 3, and 4
cover molecular weight distribution, molecular weight de-
termination, and polymerization kinetics, respectively. De-
pending on the topic, the authors provide considerable detail
by deriving many of the expressions that are simply stated in
most polymer textbooks. For example, in Chapter 2, the
"most probable" and Shultz-Zimm molecular weight distri-
bution functions are clearly derived. Chapter 3 discusses the
various methods of measuring molecular weight that appear
in any textbook on this subject. It appears that the authors are
most comfortable with light scattering given the amount of
space devoted to it.
The presentation of polymerization kinetics in Chapter 4 is
very similar to that in other introductory textbooks. One
important aspect of free radical polymerization that was not
treated here and which is not covered in other textbooks is
the composite molecular weight distribution. The instanta-
neous distribution only provides a snapshot of the polymer-
ization reaction. The effect of conversion on the instanta-
neous distribution and the integration to obtain the compos-
ite distribution are important from a practical point of view.
In addition, this material would demonstrate to students how
very broad distributions can occur in practice using the free
radical mechanism.
In Chapters 5 and 6, the authors do an excellent job of
establishing the fundamental principles necessary to under-
stand the properties and behavior of chain molecules. True
to their intentions, these chapters provide the detail for gradu-
ate students that is sorely lacking in many textbooks on
polymer science. Chapter 5 deals primarily with stereochemi-
cal configurations, tacticity, and their effects on molecular
shape. In Chapter 6, the authors discuss the statistics of
disordered chains and distribution functions for end-to-end
distances, particularly for the phantom chain.
Chapter 7 discusses the interacting bond model for obtain-
ing average properties of more realistic chains using com-
plex statistical methods. Many readers may find this chapter
somewhat tedious to read. The many references to contribu-
Continued on page 133.
93











Classroom


EXORCISING MAXWELL'S DEMON

Entropy, Information, and Computing


B. G. KYLE
Kansas State University Manhattan, KS 66506


In 1867, James Clerk Maxwell suggested that a sentient
being capable of observing molecular motions might be
able to bring about a violation of the second law of
thermodynamics through a systematic sorting of molecules.
Since then, this being-dubbed "Maxwell's demon" by Lord
Kelvin-has been an active topic of scientific inquiry and
speculation. Numerous variations of the demon have ap-
peared: some sentient, some automated, some sorting mol-
ecules to achieve a temperature difference, some trapping
molecules to achieve a pressure difference, and some tend-
ing an engine operating on a one-molecule working fluid.
Likewise, various concepts have been developed in order to
reconcile the demon's actions with the second law. Details
of these schemes and concepts can be found in a recent book
by Leff and Rex1" who have ably traced the demon's history
and have identified three epochs. These can be characterized
in terms of the dominant explanatory concept.
During the first epoch, discussions centering on Maxwell's
demon undoubtedly contributed to the much-needed shaping
and sharpening of statistical concepts as applied to the mo-
lecular description of matter. Toward the end of this epoch,
the consensus seemed to be that automated demons will not
function because their delicate mechanisms would be sub-
ject to Brownian motion. It was believed, however, that
sentient demons might pose a threat to the second law.
The second epoch began in 1929 with Szilard's121 demon-
assisted, one-molecule heat engine. Szilard believed it nec-
essary to introduce the concept of entropy of information in
order to prevent this engine from violating the second law.


Copyright ChE Division ofASEE 1995


Somewhat later, Brillouin131 elaborated on this concept and
proved that sorting demons could not beat the second law.
He showed that the entropy associated with the measure-
ments a demon would be required to make in order to enable
sorting would more than compensate for any entropy reduc-
tion brought about by sorting. The reason for this is that
photons of black-body radiation would fill the container and
it would not be possible for the demon to "see" the gas
molecules without the aid of a high-temperature torch.* The
torch is a source of entropy, identified by Brillouin as en-
tropy of information, which forces the net entropy change
for the isolated system, including the demon, to be positive
in conformance with the second law. Later, Denbigh[41 was
able to demonstrate the same result using a classical thermo-
dynamic analysis without recourse to the entropy of infor-
mation concept. At this point, only Szilard's engine seemed
to threaten the integrity of the second law, which apparently
could be ensured only through the concept of entropy of
information.
In the third and current epoch, the threat of Szilard's one-
molecule engine survives. As a rescuing concept, entropy of
information seems to have yielded to the idea of memory
erasure deriving from the application of thermodynamic ideas
to computing.15'61 Recently, these ideas were discussed in this
journal.[71
The object of the present work is to consistently apply the
methods of classical thermodynamics to show that Szilard's
engine does not threaten the second law. Also, it will be
shown that current ideas concerning the thermodynamics of
computing are unsound.

SZILARD'S ONE-MOLECULE HEAT ENGINE
In the years since its inception, Szilard's one-molecule
engine has undergone many modifications. But since the
working principle remains unchanged, the following account,
patterned after that of Reference 1, is given here. It is as-

* The inability to see objects in a black-body enclosure is well
illustrated by a color photograph of pots in a firing kiln found in
Reference 5.
Chemical Engineering Education


Benjamin G. Kyle is Professor of Chemical
Engineering at Kansas State University, where
he has enjoyed over thirty years of teaching.
He holds a BS from the Georgia Institute of
Technology and a PhD from the University of
Florida. He has not outgrown an early fascina-
tion with thermodynamics and is interested in
practically all aspects of the subject. He is the
author of a thermodynamics textbook published
by Prentice-Hall.













The object of the present work is to consistently apply the methods of classical thermodynamics
to show that Szilard's engine does not threaten the second law. Also, it will be shown that
current ideas concerning the thermodynamics of computing are unsound.


sumed that all moving parts are weightless and operate with-
out friction.
Step 1 A cylinder containing the one-molecule "gas" is
partitioned into halves by the insertion of a
partition.
Step 2 The demon determines which half contains the
molecule.
Step 3 The partition is replaced by a piston. Depending
on which half contains the molecule, the piston
is suitably connected to a load and the "gas" in
expanding moves the piston to the end of the
cylinder. Work is done and the "gas" receives
heat from a constant-temperature heat bath so
that its temperature remains constant. The "gas"
now has the same volume and temperature that
it had initially and the three-step cycle can be
repeated.
Szilard reasoned that the cycle would return the "gas" to
its original state with no net entropy change, but that the heat
bath would have transferred a quantity of heat to the "gas"
equal to the work done in Step 3, and therefore it would have
suffered a negative entropy change. In order to ensure that
the entropy change of the universe not be negative, Szilard
proposed the existence of an entropy of information which
would be positive and large enough to offset the negative
entropy change of the heat bath. It appears that Szilard was
the first to quantify entropy of information and he is often
credited with originating information theory.
Aside from the obvious operating difficulties that are waved
away by invoking frictionless and weightless engine parts,
there are two troublesome aspects of Szilard's analysis: the
lack of significance of terms such as heat, entropy, and
temperature as applied to a one-molecule "gas," and incon-
sistency in the thermodynamic analysis. Statistical mechan-
ics tells us that heat, entropy, and temperature have meaning
only when applied to large collections of molecules and
therefore would lack significance when applied to a one-
molecule "gas." However disquieting this may be, stronger
grounds for rejecting Szilard's analysis can be found in the
failure to maintain a consistent state-specific approach ex-
pected of a legitimate thermodynamic analysis.
Szilard viewed the system macroscopically and identified
the terminal states in analyzing Step 3, but in analyzing Step
1 he switched to a microscopic perspective and abandoned
the state description. In Step 3 he reasoned that a quantity of
1/N mol of "gas" (assumed ideal) expands isothermally and
Spring 1995


doubles its volume doing work (1/N)RTln2(=kTln2) and
receiving an equal quantity of heat from the heat bath. For
Step 1 it is merely stated that a partition is inserted with no
consideration of the macroscopic ramifications. Because the
density of a real gas is uniform, the insertion of a partition
would only divide the gas into two identical halves. Not so
for a one-molecule gas! A description of Step 1 proper to a
thermodynamic analysis is that initially the "gas" occupies
the volume V with a pressure P while the state following the
insertion of the partition consists of the "gas" occupying a
volume V/2 at a pressure 2P with a vacuum in the remaining
volume V/2. Obviously, this change in state of an ideal gas
requires the expenditure of work. If the process were revers-
ible and isothermal, the work of compressing the "gas" from
V to V/2 in Step 1 would be kTln2. An equal quantity of heat
would be delivered to the heat bath. The result of the 3-step
cycle would be no net work performed and no net heat
transferred. Breaking even is the best that can be expected
with this cycle. As the insertion of a partition would result in
a macroscopic process that hardly qualifies as reversible, the
input work and, concomitantly, the heat rejected to the heat
bath would be expected to exceed kTln2 with the net result
of the cycle being the conversion of work into heat.

The most generous assessment of the one-molecule heat
engine would be the recognition of a contradiction in Step 1
where the insertion of a weightless partition, a seemingly
simple and inconsequential step, results in a change in state
requiring an input of work. But until this contradiction is
resolved, Szilard's thought experiment cannot be considered
a challenge to the second law and the contrivance of an
entropy of information is unnecessary.
The preceding argument takes its impetus from the state-
ment of Jauch and Bronr8' that "the idealizations in Szilard's
experiment are inadmissible" as "the gas violates the law of
Gay-Lussac because the gas is compressed to half its volume
without expenditure of energy." It is unfortunate that this
fatal flaw was identified in 1972 but seems to have been
ignored by later workers. The only exception seems to have
been an attempted rebuttal by Costa de Beauregard and
Tribus,29g but they offered arguments that can only be de-
scribed as oblique and bizarre.
In passing, it should be noted that had Szilard's analysis
been correct, the contrivance of an entropy of information
would have balanced the entropy but would not have saved
the second law in its most basic form. Unless heat dissipa-
Continued on page 119.











)


AN ANCIENT METHOD

FOR COOLING WATER

EXPLAINED BY

MASS AND HEAT TRANSFER


J. IGNACIO ZUBIZARRETA, GABRIEL PINTO
E.T.S.I. Industriales
Universidad Politgcnica de Madrid
28006 Madrid, Spain
Educators know that presenting real-life examples in
the classroom helps students to understand the prin-
ciples in engineering education. They are always on
the lookout for examples that will confirm textbook equa-
tions and principles'1-41 and for novel problems that will
stimulate student interest once students have mastered the
more routine skills in engineering.
In this paper we present an example in which the applica-
tion of basic concepts normally introduced in the sophomore
heat and material transfer class allow the quantitative expla-
nation of an ancient method of chilling water. The experi-
ment and exercise cover several important concepts in a
variety of topics, including material and heat balances, ther-
modynamics, psychrometry, differential equations, and nu-
merical methods. It shows how to put the concepts together
to analyze a familiar effect.
An earthenware pitcher with a spout and a handle (called a
botijo in Spanish) is a liquid container used for centuries in
Spain and other countries to chill drinking water. Most people
know that earthenware is a clay-based ceramic ware, or
pottery, that has not been fired to the point of vitrification
and is thus slightly porous and coarser than stoneware or
porcelain.'51 It was developed by people in ancient civiliza-
tions who found that clay could be mixed with water, shaped,
dried, and placed in a fire to harden.i61
With the advent of refrigeration, the use of this pottery
has diminished, but it is still used by some segments of
society, such as farmers and bricklayers who often do not
have a convenient source of cool drinking water. The botijo
is a familiar object in Spain not only because it keeps
water cold, but also because it provides a characteristic and
Copyright ChE Division ofASEE 1995


J. Ignacio Zubizarreta is a chemical engineering
professor at Polytechnical University of Madrid,
where he received his BSc (1972) and his PhD
(1991) degrees in Industrial Engineering. He
worked in industry for a number of years prior to
joining the faculty in 1991. His areas of interest
include process dynamics and control, environ-
mental engineering, and mathematical modeling.

Gabriel Pinto has been a professor in the depart-
ment of industrial chemical engineering of the
Polytechnical University of Madrid since 1986. He
obtained his BSc (1985) and his PhD (1990) de-
grees in chemistry at Complutense University. His
main research interests include optical character-
ization of polymers, electrical properties of poly-
mer composites, and applied spectroscopy.

enjoyable mineral flavor.
At the secondary level or in freshman chemistry and phys-
ics courses in Spain, when concepts such as evaporation and
heat transfer are studied, it is not unusual that the students
are asked why water contained in a botijo is cooled. The
answer could be that the porous ceramic material contains
dead-air spaces that have a very low thermal conductivity.
On the other hand, the water exudes through the pores and
evaporates into the air, and the energy required to sustain
the evaporation (e.g., the latent heat of vaporization of
the water) must come from the internal energy of the
liquid, which then must experience a temperature reduction.
But those answers are only a qualitative approach to this
particular problem of transpiration cooling. A more quanti-
tative answer follows.

EXPERIMENT
A summer day was simulated with an oven at 39.00C (in
this manner the external temperature can be maintained con-
stant). The measured relative humidity in the laboratory was
42% and the temperature was 27.50C. We poured 3.161 kg


Chemical Engineering Education


I


= classroom










of water at 39.0C into the botijo (placed previously in the
oven), immersed in it a long thermometer with an accuracy
of 0.1 C, and then measured the loss of water mass (due to
evaporation) by removing the entire jar from the oven and
weighing it (with an accuracy of 1 g) periodically. An as-
sumption is that the removal does not disturb the experiment
due to the slowness of the evaporation process and the high
heat content of the water. A photograph of the experimental
setup is shown in Figure 1.
We observed that the water temperature fell quickly (in
about seven hours) to about 240C, with a loss of mass of
about 400 g. About three days later, after an increase in the
water temperature (slow at first and abrupt near the end) the
water was completely evaporated, with an end temperature
of about 390C. It should be noted at this time that the point of
using this kind of jar in real life is to chill water on a warm
day, and it obviously is full for only a few hours before it is
drunk.

MASS AND HEAT TRANSFER MODEL
The botijo is modeled as a sphere of 0.10-m radius, as
shown in Figure 2. The volume occupied by the water is

V =(4 /3)iR3 (t/3)(3Rh2 -h3)

The water interior surface is


Figure 1. Photograph of the experimental device.
Spring 1995


In this paper we present
an example in which the application
of basic concepts normally introduced in the
sophomore heat and material transfer class allow
the quantitative explanation of an
ancient method of chilling water.


A= t(2Rh-h2)

and the wet exterior surface is
S = 27R(2 R h)
Given the fact that the density of the water is around the
unity, considering a V of 103 cm3 is equivalent to consider-
ing the mass of water in kilograms.
In the mass and heat transfer model that has been devel-
oped, the following assumptions have been made:
1. The earthenware pitcher is perfectly spherical.
2. The porous material is perfectly permeable to water and
permits formation of a stable and continuous film in the wet
outer surface. Thus, there is no additional resistance to the
mass transfer of water.
3. There is no loss of water by dripping or exuding.
4. The mass transfer coefficient at the outer surface and the
inner surface (free surface) is the same (simplifying the
mathematical treatment).
5. The surface of the liquid at the interface with air is at
constant temperature and is in equilibrium with the air.
6. The dry wall above the liquid is maintained at the oven
temperature of 39.0 OC and radiates to the inner surface of
liquid (at 0, = 24.2 C).


water interior surface, A




0s 0G h




R=0.10m
wet exterior
a_ surface, S


Figure 2. Sketch of the geometrical model taken for the
mass and heat transfer model where 0G, 6s, and 0L are the
air temperatures at the surface of the water and in the
water, respectively.










7. The overall heat transmission coefficient U lumps together
all the resistances of convection in the liquid and conduc-
tion in the liquid and through the wall.
8. The liquid is perfectly mixed.
9. The heat capacity of the pottery wall material is rather low
in comparison to the heat capacity of the water. Thus the
heat content of the jar is assumed negligible.
10. The shape factor of radiation between surfaces, f is
constant.
11. There is a total renovation of the air in the oven at every
moment.
12. The humidity and temperature of the air (in the oven and at
the laboratory) do not vary during the process.
13. The methods of measurement of mass and temperature are
sufficiently quick so as not to alter the process and its
results.

According to principles of mass and heat transfer given in
textbooks,t1710] the system of differential equations describ-
ing the physical situation is
dV
d= k'a(H, H) (1)
dt


VCp( = ha( S)

+feo[(273 + G)4 -(273 + e,)4]4R2 s)

-Ua(OL s)- (2)
t s j,- w -) (2)

Equation 1 expresses the water evaporation rate as a func-
tion of the mass transfer coefficient of the water (k'), the
total water surface (a=A+S) and the difference between the
saturation humidity of the air (Hs) (e.g., in the equilibrium
with wet-bulb or adiabatic saturation temperature), and the
actual air humidity (H). The values for humidities are ob-
tained by using a psychrometric chart[91 for 1 atm and in
accordance with the experimental conditions are:
H = 0.011 kg water/kg dry air
Hs = 0.018 kg water/kg dry air
By fitting the experimental evaporation data into Eq. 1 by
the least-squares method, a value for k' of 80 kg water/hm2
was obtained. There is very good agreement between this
obtained coefficient and values obtained in accordance with
Perry's Handbook.I"1
Equation 2 is a lumped analysis which expresses the ther-
mal variation of the liquid and corresponds to a balance
between heat transfer from the air to the water (thermal
convection over the surface A+S and thermal radiation by
the air in the chamber without water), the heat loss from the
liquid to the interphase liquid-vapor (measured by the over-
all heat transmission coefficient per unit area, U) and the
evaporation of liquid (measured by the latent heat of vapor-
98


ization, X,). The specific heat capacity of water is

Cp = 1.0 kcal/ kgK

According to Sherwood and Pigford,[~21 the values of hc
and k' are related by the expression

h= sLe2/3 (3)
k'
where
s = wet heat of air
Le = Lewis number for the air-water system

In our case, using Le = 1.15 and s = 0.24 kcal/kgK, hc /k'
results in a value of 0.26.
The value of 6G is 39.0C as measured, and the value of
Os is 24/20C, as shown in the psychrometric chart. For the
latent heat of vaporization of water we have taken the value

Mass transfer evolution
3500
3000 ------------- f
3000

3 2500

S2000/

1500

1000

500

0 --- --- -- --
0 1000 2000 3000 4000 5000
Time (min)

Figure 3. The mass of water evaporated vs. time, using
Eq. (4): experimental f; fitted -

I Temperature drop in liquid


U
r 10


a





0
0 1000 2000 3000
Time (min)


4000 5000


Figure 4. The temperature difference (39.0 C- L) vs.
time, using Eq. (5): experimental ; fitted -
Chemical Engineering Education










of 24.2'C, which is X, = 583 kcal/kg. The least-squares
method gives

feo=3.0510-8 kcal/hm2K4 and U = 22kcal/hm2K
These two values are of typical magnitudes. The Stefan-
Boltzmann constant is

a= 4.910-8 kcal/hm2K4
f is the shape factor of heat radiation, and e is the emissivity
of surface. These two latter values must be in the range
0-1, as found. On the other hand, the values of U given by
Perryt"' for similar systems are on the order of magnitude of
that obtained by regression.
By substituting the above values, Eqs. (1) and (2) reduce,
respectively, to

dV
--=0.56(A+S) (4)
dt

6.41 51S+(A+S)(840.2-220L)+583(dV
dOL dt (5)
dt V


RESULTS AND DISCUSSION
Both differential equations, together with the simultaneous
calculations of V, A, S, and h values (geometric parameters
dependent only upon the volume of water in the vessel) were
solved by numerical methods (algorithms of 4th-order Runge-
Kutta and Newton), giving the values of the mass of evapo-
rated water and the temperature drop of the liquid as func-
tions of time, as represented in Figures 3 and 4.
It can be seen in the figures that the agreement between
experimental data and the values obtained according to the
mass and heat transfer model is very good, with the excep-
tion of the last experimental value where several assump-
tions (such as Nos. 1 and 9) are no longer valid.

CONCLUDING REMARKS
We believe that practical applications of the type described
in this paper enhance students' understanding of the prin-
ciples of heat and mass transfer. We hope that using such a
novel system will also serve to make the international com-
munity aware of this ancient Spanish method of chilling
water.
In developing the model it was necessary to consider the
effect of radiation in heating the water in the jar. This is an
interesting aspect of the experiment that was not initially
expected and it fits well the experimental data.
The values of the regressed parameters obtained are rea-
sonable in terms of their physical significance, showing the
usefulness of this problem.
The number and variety of concepts used in modeling this
heat and mass transfer system that has been used for hun-


dreds of years produce an example of interdisciplinarity that
distinguishes chemical engineering.

NOMENCLATURE
a total external surface of the water; a = A + S (m2)
A water surface in contact with the air in the chamber
without water (m2)
C specific heat capacity (kcal/kg K)
f shape factor of heat radiation (adim.)
h height from the water to the top of the pottery (m)
h heat convection coefficient of air per unit area (kcal/hm2K)
H humidity of the air (kg/kg)
Hs saturation humidity (kg/kg)
k' mass transfer coefficient of the water (kg/hm2)
Le Lewis number (adim.)
r radius of the external surface of the water in contact with
the air (m)
R radius of the pottery (m)
s wet heat of air (kcal/kgK)
S external surface of the water in contact with the air (m2)
t time (h)
U overall heat transmission coefficient of water per unit area
(kcal/hm2K)
V volume or mass of water (kg)
Greek Symbols
E emissivity of surface (adim)
9G temperature of the air (C)
60 temperature in the inner of the water ("C)
Os temperature at the outer of the water (oC)
X heat of vaporization of water (kcal/kg)
0 Stefan-Boltzmann constant (kcal/hm2K4)

REFERENCES
1. Lippincott, W.T., ed., Essays in Physical Chemistry, Ameri-
can Chemical Society, Washington, DC (1988)
2. De Nevers, N., "A Simple Heat of Crystallization Experi-
ment," Chem. Eng. Ed., 25, 154 (1991)
3. Konak, A.R., "Magic Unveiled Through the Concept of Heat
and Its Transfer," Chem. Eng. Ed., 28, 180 (1994)
4. Van Wie, B.J., J.C. Poshusta, R.D. Greenlee, and R. A.
Brereton, "Fun Ways to Learn Fluid Mechanics and Heat
Transfer," Chem. Eng. Ed., 28, 188 (1994)
5. Schneider, S.J., Engineering Materials Handbook: Vol 4.
Ceramic and Glasses, ASM International, U.S.A. (1991)
6. Richerson, D., Ceramics Applications in Manufacturing, So-
ciety of Manufacturing Engineers, Dearborn, Michigan (1988)
7. McCabe, W.L., J.C. Smith, and P. Harriott, Unit Operations
of Chemical Engineering, 4th ed., McGraw-Hill, New York,
NY (1985)
8. Incropera, F.P., and D.P. de Witt, Fundamentals of Heat
and Mass Transfer, John Wiley, New York, NY (1990)
9. Moran, M.J., and H.N. Shapiro, Fundamentals of Engineer-
ing Thermodynamics, John Wiley, New York, NY (1993)
10. Welty, J.R., C.E. Wicks, and R.E. Wilson, Fundamentals of
Momentum, Heat and Mass Transfer, 3rd ed., John Wiley,
New York, NY (1984)
11. Perry, J.H., Chemical Engineers' Handbook, 5th ed.,
McGraw-Hill, New York, NY (1973)
12. Sherwood, T.K., R.L. Pigford, and C.R. Wilke, Mass Trans-
fer, McGraw-Hill, New York, NY (1975) J


Spring 1995










ASEE ANNUAL MEETING

Anaheim, California
June 25-28, 1995



Program: Chemical Engineering Division



FEATURE SESSION: Future Directions in Chemical Engineering Education

Edward L. Cussler Chemical Engineering: The Curriculum in 2020
The changes in the next 25 years will be societal rather than technical. Two such changes relate to
the fact that the university system can produce more chemical engineers than can find technical
jobs, and that the available jobs may be in non-traditional areas.

Richard M. Felder Current Issues and Future Directions in Engineering Education
Proponents for change call for attaching greater importance to teaching and movement away
from traditional lectures toward more active and cooperative learning. There is resistance among
those who believe the present system works. Both sides of the issue will be discussed.

Thomas F. Edgar Chemical Engineering Computing: Revolution or Evolution
Incremental changes in the use of computers have been observed, but it is unclear that this will
ever have an impact on the way courses are taught. The potential for a revolution that restructures
courses may lie with increased use of multimedia instruction and computer-based classroom
facilities.



ADDITIONAL SESSIONS

* Chemical Engineering Division Award Lecture
Stanley Middleman, University of California, San Diego; "Modeling Flows in Films, Jets, and Drops"

* Chemical Engineering Division Banquet
Speaker, Frank L. Lambert
Art Conservation Today-A Remarkable Combination of Science and Art

* Learning and Teaching Styles
A workshop by Richard M. Felder (sponsored by Educational Research and Methods Division)

* Incorporation of Biotechnology into Engineering Curricula
Session Sponsored by Biological and Agricultural Engineering Division


Chemical Engineering Education










REGULAR SESSIONS

* Innovative Uses of Computers in Undergraduate Chemical Engineering Education
3 Interactive Videodisc Case Studies in a Polymer Engineering Elective
3 Computer Simulations of Thin Film Growth
3 Animations, Simulations, and Other Learning Stimulations: An Electronic Laboratory Tour
3 Virtual Reality in Chemical Engineering Education
0 Process Dynamic Simulator for Dynamics and Control Demonstrations
3 Addressing the Variety of Learning Styles of Chemical Engineering Using Multimedia


* Novel Curriculum or Course Content
3 Can We Teach Engineering Design to Freshmen? (Or is it our last chance?)
3 Integration of Skills Development Across Engineering Programs
3 Fitting Statistics Into the Chemical Engineering Curriculum
( An "Open-Ended" Chemical Engineering Laboratory
3 The Video Laboratory Report: Enhancing Communication Skills in the Undergraduate Laboratory
3 The Selling of Unit Ops Laboratory


* Novel Education Programs
3 Teacher Institute for Science/Mathematics Education Through Engineering Experience
3 Introducing Freshman Students to Programming
3 Hands-On Approach to Foundations of Engineering
3 Introducing Chemical Engineering to Freshmen Through Measurement Oriented Studies in the Unit Operations
Laboratory
3 A New Approach to Introducing Freshmen Students to Chemical Engineering
3 An Interdisciplinary Approach to Engineering Design Education
3 A Different Approach to the First-Year Graduate Curriculum
3 Engineering Education and Research: TQM and R&D in Bioengineering


* What Works? Tips From Chemical Engineering Faculty
3 Introducing Freshman Engineering Students to Design
3 Modes of Contacting
3 Explaining Distillation Arrangements Through Gradual Evolution of Flowsheets
0 Students Coaching Students
( Making Statics Interesting


* Student Learning Assessment
How do (should) we determine our success in engineering education? What Measures and analyses are being tried?
Which work?
There will be a panel discussion on assessment of learning outcomes. Each panelist will speak for five minutes. A
discussion with audience participation willfollow.


* Education via Academic-Government-Industry Partnerships
3 Conducting Research, Development and Educational Programs in Partnership with the U.S. Department of Energy
3 The SCUREF Graduate Internship Program
3 A Practitioner-Educator Partnership for Teaching Engineering Design
0 The South-Central Environmental Resource Alliance (SERA)
3 Computerized Laboratory Course Material for Graduate Studies in Environmental Risk Assessment
3 The Design of a Skill-Based Course Focused on Student Outcomes: A Partnership Template


^_____________________________


Spring 1995











Random Thoughts...




JUST ANOTHER DAY AT THE OFFICE


RICHARD M. FIELDER
North Carolina State University Raleigh, NC 27695-7905


The scene is the conference room in a mythical chemi-
cal engineering department just before a faculty meet-
ing. Everyone is talking.
Andre: (the department chairman): "Okay, let's get started,
gang, or we'll never get out of here."
The noise slowly subsides.
Andre: "Now, our first order of business is the budget."
Everyone: (Loud chorus of grumbling.)
Andre: "All right, the next person who gives me grief is our
new laboratory safety inspector." (Everyone shuts
up instantly.) "I've got good news and bad news.
The bad news is that it's September 12 and we've
already exhausted our operating budget through
April. The good news is that I've got a plan."
Ed: "You're not planning to make us pay for our coffee
again, are you? The last department head tried that
and look what happened to him."
Andre: "No, it's even better than that-listen up! The hot
research topics these days are biotechnology and
microelectronics, right? I say we write a proposal to
genetically engineer a bug that produces ultrapure
silicon wafers from sand. I figure we should be able
to get a bundle for it from a couple of our industry
friends and then use what we get as matching money
for an even bigger bundle from the NSF. Bruce and
Gary, how about knocking out a proposal draft ...
just make sure you include about 30% release time
for each of you and enough to pay a secretary full
time."
Bruce: "No problem, as long as I can get three months
summer support, some lab renovation, and a laptop
... and a graduate student, of course.
Gary: "And I need a scanning microscope and summer
support and two graduate students oh, and I'll
also need money to go to the Annual Conference of
the ESGFPICED."
Andre: "The ESGFPICED?"
Gary: "Yeah, the Emotional Support Group for Physicists
in Chemical Engineering Departments we're
sharing our inner feelings in Hawaii this year, and
Copyright ChE Division ofASEE 1995


since Sheila is chairman. ."
Sheila: "Chairperson."
Gary: ". .. chairperson, I thought I should be there."
Andre: "Fine, as long as you don't charge too many leis to the
project. OK, so you and Bruce can ..."
Bill: "Wait a minute-you can't get the price of a bagel for
research this year that doesn't include polymers."
Andre: "SACRE BLEU, you're right OK, how about
a genetically engineered bug to produce ultrapure
silicon from a combined feedstock of sand and polypro-
pylene..."
Irving: "Make it molten sand and polypropylene, so we can get
some good non-Newtonian rheology in there."
Andre: "Right... now in the budget, don't forget to .."
Bill: ". put in summer support and an HPLC for me, and I
also need about three graduate students..."
Irving: "And I need a new rheometer and a REALLY good pair
of safety shoes, four graduate students to do some heavy
equipment lifting, and a workstation with a 287 GB hard
disk and a full-time computer repairman .."
Sheila: "Repairperson."
Irving: "... a full-time repairperson to maintain it."
Andre: "No problem. All right, Gary and Bruce and Bill and
Irving go ahead and .."
Hazel: "You can't be serious-you're going to try to get that
kind of money for a project that doesn't involve the
environment?"
Andre: "CARAMBA-how could I forget that? OK, Bruce, Gary,
Bill, Irving, and Hazel design a bug to produce silicon
from molten sand and recycled plastic things recovered
from the beach after Labor Day weekend. I don't know,
guys-this may be getting a little too..."
Hazel: "Piece of cake ... all I'll need is a little summer support,
money to attend the Fourth Annual Conference on Very
Important Environmental Stuff in Acapulco next year,
and five graduate students ... someone has to shovel all
that sand."
Al: "Just a cotton-pickin' minute here-I'm doing environ-
mental research too, and I also have the experience to
pitch this to industry once me and my six new
Chemical Engineering Education










graduate students hit up our industry friends I guar-
antee they'll sprain their wrists reaching for their
wallets."
Nigel: "Now see here, none of this will work unless you do
it at cryogenic temperatures, a field that I just hap-
pen to know more about than anyone else here ...
besides, I have much broader experience in the manu-
facturing ."
Sheila: (Clears her throat loudly.)
Nigel: "Excuse me, I have much broader experience in the
personufacturing industries than Al does, in addition
to which my British accent makes me sound ever so
much more intelligent."
Al: "Oh yeah-well maybe if we were talking about the
cryogenic production of bangers and mash your ex-
perience would be worth something, but we're deal-
ing with polymerization here and you don't know
jack. .."
Andre: "BOZHE MOI-will you guys knock it off already!
If we don't get serious about this we'll never ..."
Charlie: "HEY-what am I, chopped liver? I'm also
doing environmental research besides, if you
don't consider the homogeneous catalytic effects
of the impurities in beach sand and plastic things
you'll ."
Ed: "No way, Charlie-if anyone's gonna do any cataly-
sis on this project it's me and the seven graduate
students I need-besides, this project needs some-
one who knows how to do real surface science, and
also someone with outstanding diplomatic skills to
sell it to the NSF, and it just so happens that I.. ."
Paul: "Don't make me laugh, Ed-I'm the real surface
scientist here. You let me and eight graduate stu-
dents throw some surfactants into the pot and I could
get funding from your grandmother."
Ed: "I don't think so-my grandmother knows more
surface science than you do, and not only that..."
Sheila: "Nine graduate students and my own Cray to de-
velop an ASPEN simulation of the process and ex-
clusive rights to our best graduate student hacker as
project manager..."
Everyone: (Shouted in unison) "PERSONAGER!"
Sheila: ". .. as project personager, or I'm out of here!"
Stanley: "Look, you're all forgetting that we're an educa-
tional institution, not just a research factory."
Matt: "He's right-we need to get the undergraduates in-
volved. I know-we get about ten graduate students
to put the whole thing in the unit ops lab, then we
say that we're updating the lab to make it more
relevant to chemical engineering in the 21st century,
and then we go to our friends in industry and ..."


Walter: "You'd BETTER use undergraduates-last spring all
the new graduate students agreed to work for me when I
recruited them."
Everyone: (General uproar)
Andre: "BESAME MUCH, ENOUGH ALREADY! Okay, let's
see what we've got here-check me on this. We propose
to develop an undergraduate laboratory experiment on
the formulation of an ASPEN simulation of homoge-
neous and heterogeneous catalytic impurity effects on
the cryogenic biochemical generation of ultrapure sili-
con from molten sand and plastic things...
Hazel: "And its environmental implications."
Andre: ". and its environmental implications. Does that work
for everyone?"
Everyone: ("Sure, great, sounds good to me," etc.)
Ed: "I still don't think it's scientific enough-they'll get
proposals to do that from half the departments in the
country."
Andre: "We'll take our chances. Now, all that's left is to write
the proposal-we have a tight deadline to meet. I guess
Al and Nigel with all that industrial experience should
be able to..."
Al: "Gee, Andre, I'd like to, but I'm on the Conference
Room Scheduling Committee this year and I've got so
much to do, I really don't think I can free up the time."
Nigel: "And I'm chairing the Coffee Machine Cleaning and
Supply Committee and have much more to do than
Al ... I really think Bruce and Gary should do it, since
the heart of the project is their specialties."
Andre: "Okay, that seems reasonable..."


Ev


Bruce: "Just a minute, Andre-I'd love to do it, but I'm going to
be away from my office for three weeks and no one will
have a clue how to find me. I'm willing to let Gary cover
for me."
Gary: "Gee thanks, Bruce ... uhhh, Andre, normally I'd jump
at the chance, but unfortunately I'm also going to be
unavailable. It's a physicist thing-you wouldn't under-
stand."
Andre: "Hmmm. Well, how about..."
eryone: (Shout out excuses.)
Andre: (Disgustedly) "OY GEVALT, I don't believe you tur-
keys. SOMEONE has to write this proposal, otherwise
we'll have to go back to..."
Ollie: "Hold on-I have an idea. I'll assign the proposal to the
first-year graduate students as part of their project class."
Andre: "Sold-just make sure they get it done by Wednesday.
Okay, it's late now, so we'll postpone our discussion of
next year's faculty retreat in Paris which I'm working on
our industry friends to sponsor. Meeting adjourned."
(All get up and exit stage left.) 0


Spring 1995











letters


Why Do YOU Belong to ASEE?


The activities sponsored by the American Association of Engineering Educators (ASEE) are the principal
forum in North America for the discussion of issues related to our profession-engineering education.
The Chemical Engineering Division is one of the most active divisions in this professional society; it is
responsible for the Chemical Engineering Summer School, programming at the annual conference, and
the publication of this journal. The following letters give us a flavor of the diverse motives that exist for
joining a professional organization such as ASEE and the benefits that accrue from membership. We
strongly encourage our readers to consider expanding their involvement in ASEE.

To the Editor:


Early in my teaching career I joined ASEE and attended an
effective teaching workshop at the annual meeting at Penn
State. The techniques and ideas I learned at that workshop,
plus those learned at subsequent ASEE meetings, have been
invaluable to me over the past 20 years. At every ASEE
meeting I have attended I have learned something that im-
proves my teaching. In addition, the ASEE meetings have a
far different milieu than meetings that focus on research.
The atmosphere is one where kindred spirits spend time
discussing with one another how to be better teachers, ex-
changing ideas on education and how to solve problems they
face in the classroom and in their department.
The rewards from my association with ASEE have come
not only to me, but also to the students I have had in class.
I feel it would be a benefit if every chemical engineering
department would send at least one member to the annual
meeting who could share information and ideas on teaching
with their department colleagues.
Scott Fogler
Chemical Engineering
Division Chair, ASEE
The University of Michigan



To the Editor:
With this note I would like to suggest why ASEE and its
ChE Division are important to the professional development
of chemical engineering faculty and to urge wider participa-
tion in it.
Although most ChE faculty are actively engaged in both
teaching and research, our efforts to develop professional
competence and accomplishment in these two domains are
quite different. As a rule, we participate actively in the
AIChE as well as in other professional societies which focus
on specific areas of science and technology relevant to our
104


research interests. This is done, with the strong encourage-
ment of senior faculty and academic administrators, as a
means of rapid exchange of new technical developments,
intellectual stimulation, networking with peers, and general
professional growth. We similarly publish in research jour-
nals sponsored by these societies and by commercial scien-
tific publishers to record, disseminate, and seek validation of
our research results.
While the AIChE and the domain focused professional
societies have educational objectives within their mission
statements, few if any make the educational process a pri-
mary focus. Yet, the needs for and benefits of rapid dissemi-
nation, validation, and networking are every bit as real for
the teaching side of our professional life. Teaching compe-
tence cannot grow by just "doing" in isolation. We all need
to continuously improve our teaching skills by sharing with
each other alternative ways of capturing and presenting dif-
ficult concepts to students, novel ways of enhancing the
value of student-teacher contact time, and the lessons of
explorations of new instructional delivery technologies. A
forum for this purpose exists but too few of us participate
actively in it.
The ASEE exists precisely to provide an organized frame-
work for disseminating, validating, and learning best prac-
tices in engineering education, through publications, such as
CEE, through regular professional meetings, periodic fac-
ulty summer programs, and the work of its divisions and
committees. As an organization, it will be most effective and
relevant if all of the most creative, productive, and energetic
teachers of the engineering profession are among its active
members. I strongly encourage the brilliant young ChE fac-
ulty who are the future of our profession and the master
teachers-scholars who define its core to join in ASEE and its
ChE Division. Through our collective efforts we have an
opportunity to "re-engineer" the ChE Division into a model
of a vibrant community of engineering educators who will
Chemical Engineering Education










lead in the revitalization of the teaching component of our
professorial profession.
G. V. Reklaitis
Purdue University

To the Editor:
My original motivation to be a faculty member in chemi-
cal engineering was based on my perception that teaching
was the primary activity. This was a view I held as an
undergraduate and graduate student until the day I came to
The University of Texas at Austin as an Assistant Professor.
My perspective changed suddenly when I realized that class-
room teaching is only a part of the package. For all faculty
time is a precious resource that is divided among teaching,
research, department and university service, and professional
activities. However, our commitment to be an excellent
teacher should not take a back seat to efforts at being a
leading researcher. One of the ways to honor this commit-
ment is to be a member of ASEE and be a regular reader of
its publications as well as attend society meetings.
Staying up-to-date in areas I teach, such as process con-
trol, optimization, and modeling, requires a special effort
because of the new software that has appeared during the
past decade. Attendance at ASEE meetings, and especially
the ChE Summer School, has helped keep me current on
new software developments and innovative ideas in com-
puter-aided instruction. I view ASEE membership as inte-
gral to my success as an engineering educator-and I use the
term "educator" holistically.
In the future, due to economic forces, I believe that univer-
sities will be called upon to review their commitment to
education of all types (undergraduate, graduate, extension,
technical, individual), and membership in ASEE will be-
come even more important in this new environment.
Thomas F. Edgar
The University of Texas at Austin


To the Editor:
The Chemical Engineering Division of ASEE has been a
motive force in my career. I would like to take this opportu-
nity to recount some of my experiences. Perhaps like many
other faculty I have long been aware of some of the Division
activities, but until I became active in ASEE perhaps 15
years ago I was not fully aware that it was the Division that
sponsored them.
Chemical Engineering Education has always been my
favorite journal. It is the only journal I will routinely read
from cover to cover. Ray Fahien has done an outstanding job
improving the quality of the journal to the point where it is
the envy of most other ASEE divisions. We should be proud
of it.
Spring 1995


The 3M Lectureship was synonymous with outstanding
educators from my earliest recollections as a young faculty
member. I never really associated the award with ASEE
until recently when the sponsorship passed on temporarily to
the Chemical Engineering Division itself and now to Union
Carbide. Of more recent origin, the Corcoran and Martin
awards also reflect the Division's recognition of contribu-
tions to education.
I was never able to take advantage of the third major
activity sponsored by the Division until relatively recently
either. Nor did I realize that the Chemical Engineering Sum-
mer School, held every five years for essentially the past 50
years, was sponsored by the Division. I now regret that I did
not take advantage of the opportunity to attend earlier in my
career. It is a unique opportunity to focus on the teaching
part of our jobs.
We all have demands on our time going far beyond the
nominal 40-hour week. The ASEE deserves some portion of
every engineering educator's time. Perhaps only in retro-
spect can I see how important the ASEE can be. The activi-
ties cited above may be the major contributions of the Chemi-
cal Engineering Division, but don't forget the programming
at the ASEE Annual Meeting. What I have come to value
most are the recurrent sessions on improving teaching effec-
tiveness. The ASEE offers a needed complement to primary
research focus at other society meetings.
John C. Friedly
University of Rochester

To the Editor:
The twin emphasis on quality teaching and quality re-
search is one of the reasons why I enjoy my work in the
Chemical Engineering Department at the University of Wis-
consin. There is this belief that research goes hand in hand
with innovative graduate-level teaching; from there, suc-
cessful teaching experiments create material for moderniza-
tion of the undergraduate curriculum (this approach was
described as one of the Hougen Principles in an article by
R.B. Bird in a recent CEE article).
I joined the ASEE in the fall of 1993 to meet others with a
commitment to teaching excellence. Recently, I have been
organizing new research results in my area of research inter-
est (particulate fluid dynamics and high performance paral-
lel computing), accumulated over the past dozen years, into
topical modules for introductory graduate level courses and
advanced undergraduate electives. I believe that ASEE meet-
ings and journals are good places to learn about techniques
for introducing new materials. And of course, some years
down the road, I hope to reciprocate by dissemination of my
experience through ASEE meetings and publications.
Sangtae Kim
University of Wisconsin, Madison











M] "classroom


DETERMINING

RESIDENCE TIME DISTRIBUTIONS IN

COMPLEX PROCESS SYSTEMS

A Simple Method

PAUL D. GOSSEN,* G. RAVI SRINIWAS, F. JOSEPH SCHORK
Georgia Institute of Technology Atlanta, GA 30332-0100


n many chemical processing plants, liquid products pass
through multiple operations. These processes may in-
clude purification, reaction, filtering, blending, and other
unit operations. The operations may be batch, continuous, or
semicontinuous, and the overall processing may involve batch
and continuous units with intermediate storage. In mixed
batch and continuous units, batches may be dropped at vari-
ous times and average residence time calculated from steady
state conditions in the continuous component of the system
may be invalid. If component batches react in the continuous
part of the process, these properties will also be affected by
the RTD (residence time distribution) of the product in the
process. In addition, the approximation of complex flow
patterns in industrial reactors by combinations of simple
ideal reactors (e.g., tanks in series, etc.) can be accomplished
using the concepts of RTD. The reader can doubtless find
other applications where calculating the RTD of a complex
system becomes important.
Unless the system consists exclusively of well-mixed, con-
stant-volume tanks and plug-flow elements operating at steady
state, a rigorous solution to calculation of the RTD of the
systems can be formidable. The problem must be set up in
code (FORTRAN, etc.) for each specific flowsheet and is
greatly complicated if there are parallel units in the flow
system, or time-dependent flows. Alternatively, Nauman and
Buffham'1l suggest taking the Laplace transform of the RTD
of each vessel. Using the properties of Laplace transforms,
the RTD for two vessels in series is then the inverse Laplace
transform of the product of the transforms for the individual
vessels. Anderssen and White121 have proposed solution of
the RTD problem via Laguerre Functions.
The experimental determination of the RTD of an arbi-

'Address: E.I. DuPont de Nemours & Company, Louisville, KY


Paul Gossen received his BASc from the Univer-
sity of Waterloo, and his MEng and PhD from
McMaster University, all in chemical engineering.
He is currently with DuPont in the Polymer Prop-
erty Measurements Group of Central Research and
Development in Louisville, Kentucky, and special-
izes in the modeling, instrumentation, and control
of polymerization reactors.

G. Ravi Sriniwas received his BS from the Indian
Institute of Technology, Delhi, and his MS from
Georgia Tech, where he is currently a PhD stu-
dent. His research interests include nonlinear
control, nonlinear model identification, and model
predictive control.


F. Joseph Schork is an Associate Professor of
Chemical Engineering at the Georgia Institute of
Technology. He received his BS and MS degrees
from the University of Louisville, and his PhD from
the University of Wisconsin. His research interests
are in process control and polymerization. He is the
S coauthor of Control of Polymerization Reactors
(Marcel Dekker, 1993).

trary flow is the subject of a great deal of study. Bischoffl31
has used pulse inputs, while Kramers and Alberda1[4 apply
frequency response techniques, and Woodburn'5" and Gibilaro,
et al., 6] propose the use of pseudorandom binary inputs. Nor
is the concept of the moments of the RTD new. Nauman171
gives the equation for the unsteady-state evolution of the
first moment of the RTD. Nauman and Buffhaml]" introduce
the moments of the steady-state RTD and their relationship
to the mean and variance of the distribution, and Nauman181
gives the expression for the first three moments of the RTD
of the steady-state CSTR. The use of the moments of an
experimentally determined RTD to fit the parameters of a
flow model is the subject of a great number of papers, the


Copyright ChE Division ofASEE 1995


Chemical Engineering Education










more recent among them being Nauman and Buffham,111
Simandi, et al.,IO9 van Gelder and Westerterp,'o10 and Thijert,
et al. 11
This paper extends the work of Nauman17' by deriving the
ordinary differential equations describing the evolution of
the higher moments of the RTD of the unsteady-state CSTR.
In addition, it derives the expressions for the moments of the
RTD of a plug flow reactor. This allows the calculation of
the overall RTD of a processing system using the leading
moments of the RTD to characterize the RTD in much the
same way as the leading moments of the molecular weight
distribution of a polymer are used to characterize the mo-
lecular weight distribution of that polymer. Finally, the re-
sulting equations are implemented in MATLAB/
SIMULINK in a way that allows each process flow system
to be defined graphically.

MOMENT DESCRIPTION
OF THE RESIDENCE TIME DISTRIBUTION
We will define two basic types of vessels with which we
will construct a flow system by connecting vessels of these
two types in some combination of series and parallel. The
first type will be a stirred tank. While we will assume that
the contents of the tank are well mixed, we will not require
that the tank contents have constant volume. That is, flow
out does not have to equal flow in. Thus, the level in the tank
can vary between zero and a maximum volume (Vmx). Flow
out may be constant, may vary with liquid level in an open-



k-1
'f n
tn
Fin


Figure 1. Stirred tank (shown at the top) for the RTD
development. Note that liquid volume need not be con-
stant since inflow is not restricted to equal outflow. This
allows the analysis of the RTD during tank filling or
draining. In the plug flow vessel (shown at the bottom)
volume is constant and inflow and outflowmust be equal.
Spring 1995


We will define two basic types of
vessels with which we will construct a
flow system by connecting vessels of these
two types in some combination of series and parallel.
The first type will be a stirred tank .... The second
type of vessel will be the plug flow vessel.

loop manner, or may be controlled by some type of level
controller. The second type of vessel will be the plug flow
vessel. This vessel will have perfect radial mixing, no axial
mixing, and constant volume. Flow in will necessarily equal
flow out. Figure 1 shows the two types of vessels. Any other
vessel (such as a tank with dead volume) may be approxi-
mated as combinations of these two vessels, as in
Levenspiel.'12]
Consider the k-th vessel in a flow system to be a stirred
tank as shown in Figure 1. Define fnk(t) to be the volume
fraction at time t of the flow leaving vessel k which has a
total age (since entering the flow system) of T, where
nAx < T < (n + 1)AT and AT is a fixed increment of residence
time. A balance over fnk(t) for the stirred tank in Figure 1
yields

d[Vk ,
d[ = F in fnk-l(t) -F kut k(t)-V fk(t)-fnk-l(t)] ()

The generation term (last term on the right-hand side) occurs
because the fluid ages as it passes through the vessel. When
Eq. (1) is multiplied by (n)' and summed over all values of n,
the result is


d Vk (n f (t)

dt

F n (n)i fnk-1 (t)- F n)ifnk(t)-Vk ni[fk (t)-fk (t)]
n=O n=0 n=0
(2)

Defining X (t) as the i-th moment of the RTD, at time t,
leaving the k-th vessel,


?(t)=Y(n)fnk(t)
n=0
Eq. (2) then becomes


d[Vk,(t)
d[ t] =FkXk-l (t)-Fokut k(it)-V k (t)- (n)i fk- (t)
d n=2 J
(4)

Algebraic manipulation will yield the following for the final
term in Eq. (4):


Plug Flow Vessel k
k
Fout


f k-1

k l
In











Vkt)= (t) + X k(t) fori=l (5)
'n= (t)+2? k(t)+ (t) fori=2
n=2 nO I2
Thus, the RTD moment equations for the stirred tank
become


d Vk (t) k
1 -dt =Fn-I k(t)--Fokutkt)+ V 0 (t)
k(0)= 0
d[VkXk(t]
V Fk k- (t)- Fxkui (t) + Vk [Xk (t) + 2 k (t)]
dt in 2
2 (0)= 0


k-lk 6 -(t- 0)+ k-(t- ) fori=l
(n= )if -m (t)= -(t-I)+2~-l(t-0)+02 k-l(t-0) fori=2
(13)
Thus, the moments of the RTD for the plug flow vessel become
X k(t)= -l(t )+ k-l(t- ) (14)
S(t) =Xk-l(t -9)+29 -(t-9)+ 921k-l(t--) (15)


(6) Equations (14) and (15), along with Eqs. (8) through (10) where
appropriate, make up the moment characterization of the RTD of
the plug flow vessel. Notice once again that it is not necessary to
track the zeroth moment since this is always unity for a normalized
(7) distribution.


The initial conditions reflect the fact that at time equal
to zero, all fluid in all vessels is assumed to have zero
age. The values of the moments of the RTD of the inlet
stream to vessel k [ -l (t)] are the moments of the outlet
stream of vessel k-1. A stream entering the flow system
will have the following moments:

ok=0 (t)= 1 (8)
hX=O(t)=O i>1 (9)

his simply means that all material entering the system
has an age of zero. In addition, since fk(t) is defined to
be a volume fraction, it is normalized and the sum of all
fractions must equal unity

,0(t)= (n)0fnk(t)= 1 (10)
n=o
Thus, it is not necessary to track 4o(t). Equations (6)-
(10) define the first three moments of the RTD at the
outlet of the k-th vessel (if vessel k is a stirred tank).
Consider now the second type of vessel, the plug flow
vessel. It corresponds to a simple pipe, or other process-
ing unit in which there is no backmixing, as shown at
the bottom of Figure 1. Proceeding as before, it is pos-
sible to write a balance on fn(t) over the plug flow
vessel:
fnk (t)= fk (t ) (11)
where 0 is the residence time of the vessel, (V/F), and m
is an integer representing the number of RTD incre-
ments, AT, in 0. (If AT arbitrarily is set to one time unit,
then m = 0.) As before, Eq. (13) can be multiplied by (n)'
and summed over all n

(n)'ifk(t)= r(n) f (t 6) (12)
n=O n=0
The left-hand side of Eq. (12) is hx(t) (the i-th mo-
ment of the material leaving vessel k). Algebraic ma-
nipulation of the right-hand side results in


Once a set of moments is available, the RTD of the material
leaving the k-th vessel can be reconstructed in a number of ways.1131
The average residence time is the ratio of the first to zeroth mo-
ments
Xk(t)
ek(t)= X (t) (16)
Ak(t)
The variance of the RTD can be written as

F (t)2 (t) ( (t) 2 (17)

In many cases, measures of the mean (0) and variance (o) may
be enough to characterize the RTD. If desired, a log normal distri-
bution may be presumed1141


a(t)= 2n (t)(t 2


b X (t)
b(t) a(t)
2,-~


IMPLEMENTATION IN MATLAB
Equations (6), (7), (14), and (15) form a mathematical descrip-
tion of the RTD. As such, the set of equations, along with the
proper initial conditions, could be solved with any numerical inte-
grator in any standard language. We have chosen instead to exploit
the graphical programming capabilities of MATLAB, a math-
ematical analysis program marketed by The MathWorks of Natick,
Massachusetts, which runs under DOS Windows or Macintosh
System 7, as well as on various Unix workstations. A unique
feature of MATLAB is the SIMULINK subsystem. This is a
block-diagram oriented environment in which various dynamic
blocks are chosen from a library of dynamical elements and inter-
connected on the screen to form a dynamical system. The system
can then be simulated directly from the diagram with no additional
programming.
Most SIMULINK elements are transfer functions defined in the
Laplace or Z-transform domains. Blocks are available to input
systems of ordinary differential equations (ODEs) directly, but
only if the ODEs are linear.
Chemical Engineering Education


f(,t) = exp[-a(t)(n n b(t))2]
TVC 0. I1










Equations (6), (7), (14), and (15) are nonlinear for varying
liquid volumes or flowrates. To accommodate these nonlin-
ear ODEs within the SIMULINK framework, we have de-
veloped SIMULINK modules for the stirred tank and plug
flow vessel RTD. These are constructed of standard
SIMULINK elements (integrators, etc.) and supplied to the
user as dynamic blocks. The user then selects these elements
from a menu much as he or she would select a transfer
function block. The blocks are connected by arrows showing
the information flow, and the entire block diagram is simu-
lated by selecting the Simulation menu from SIMULINK.
We have found that the nonlinear blocks are directly por-
table from the Macintosh to the Windows version of
MATLAB. Plots of the time evolution of the moments can
be created directly from SIMULINK or from MATLAB.
The complete age distributions can be reconstructed from
the moments by assuming a log normal distribution. This is
easily done in MATLAB by means of a MATLAB function.

EXAMPLE
The use of the moment characterization and its implemen-
tation in MATLAB is best illustrated by an example. Con-
sider the system shown in Figure 2 which is composed of
two stirred tanks interconnected by a plug flow element. At
time zero, the first stirred tank (CSTR 1) contains 500 L of
material. The plug flow vessel (PFR) is initially empty, but
has a volume of 100 L when full. The second stirred vessel
(CSTR 2) has an initial liquid volume of 500 L.

At time zero, flow into CSTR 1 is begun at a constant 20
L/min. At the same time, flow out of CSTR 1 is begun, also


F0 Foutl
Flow Out


Flow In


1st Moment In


2nd Moment In


3rd Moment In

Clock
Clock


Fout


L1-


L2


L3


Fin


at 20 L/min. PFR begins to fill at a rate of 20 L/min, and
since its volume is 100 L, it is filled after five minutes, and
flow into CSTR 2 begins (also at 20 L/min). When flow into
CSTR 2 begins, flow out also begins at the same flowrate
(20 L/min).
Figure 2 is not only the schematic for the RTD problem in
question, it is also the SIMULINK "program" from which
the simulation is to be carried out. Figure 2 was constructed
by selecting the RTD stirred vessel and plug flow vessel
modules from a menu and connecting them with arrows
indicating information or material flows. The schematic also
contains standard SIMULINK elements such as the clock
and transport delay (used here to start outflow from PFR
after it is filled).

The first three moments of the material entering CSTR 1
are set to zero, indicating zero age at the inlet. The initial
volumes of CSTR 1 and 2 are set by double-clicking on the
icon and entering a value when it is requested. The volume
of the plug flow vessel (PFR) and its residence time are
entered in a similar manner. Both the inflow and outflow of
CSTR 1 are inputs. Their values are entered into the boxes at
the left end of the respective arrows. The outflow of CSTR 1
becomes the inflow of PFR. Likewise, the outflow of PFR
becomes the inflow of CSTR 2. This, however, is delayed
(via the standard Transport Delay block) to account for the
five minutes necessary to fill PFR. The RTD moments of the
material leaving CSTR 1 become the moments of the inlet
stream to PFR. Likewise, the moments of the outflow from
PFR become the moments of the inflow to CSTR 2. Finally,


the moments


Flow Out CSTR 2 D

--I Transport Delay


Flow Out


1st Moment


2nd Moment


3rd Moment


Volume




Time


cstr






CSTR 1


Figure 2. SIMULINK diagram of two stirred tanks connected by a plug flow
vessel. This is the diagram used to solve the Example. In it, Ln referes to the
n-th moment of the RTD of the material leaving the vessel shown; Fin and
Fout are the inlet and outlet flowrates, respectively, for a given vessel.
Spring 1995


V
Volume


12


L3


CSTR 2


the outflow from CSTR 2 characterize the
RTD of the system under the conditions
outlined above and can be sent to a
SIMULINK workspace for plotting versus
the time signal generated by the clock icon.
The simulation is begun from the Simula-
tion menu.
Figure 3 shows the time evolution of the
average and variance of the RTD of the
material leaving CSTR 2. The average resi-
dence time approaches a steady-state value
of 55 min, which can be calculated as the
sum of the nominal residence times of the
two CSTRs (25 min each) and the resi-
dence time of the plug flow vessel (5 min).
Figures 3, however, also shows the tran-
sient approach of the average residence time
to its final value, as well as showing the
variance of the RTD. The variance reaches
a steady-state value of about 1,257, which
gives a standard deviation (the square root
of the variance) of approximately 35 min.
Thus, although the average residence time
at steady state is 55 min, the standard de-

109


Ll L estr











aviation of 35 min indicates quite a broad distribution. This is
shown in Figure 4 where the steady-state moments from the
example have been used to form a log-normal distribution. It
may be seen that some elements of the fluid have residence
times as short as 5 min, while others remain in the system for
over 200 min.
The example was chosen for its simplicity to illustrate the
use of the moment characterization and SIMULINK simula-
tion. The level of complexity of problems which can be
handled by this method is limited only by the patience of the
user in developing the schematic and the computational speed
of the computer.

CONCLUSIONS
The moment characterization of the RTD of a complex
flow system allows the student to look at the effects of
multiple vessels, nonsteady-state flow, and nonideal flow
(where the nonideal vessel is approximated by a system of
ideal vessels). When the moment description of the RTD is
coupled with the graphical programming environment of the

100



0 50 100 150 200 250 300 350 400
Time (min.)

2000 -

10001

0
0 50 100 150 200 250 300 350 400
Time (min.)

Figure 3. MATLAB plot of the evolution of the average
residence time and the variance of the RTD as a function
of time. The average and variance are derived from the
moments of the RTD according to Eqs. (16) and (17), re-
spectively. Note the approach to steady state as the system
goes from startup to steady operation.


0.02


0.015


0.01


0.005


0 20 40 60 80 100 120 140 160 180 200
Residence Time (min)
Figure 4. MATLAB plot of the steady-state RTD for the
example. A log normal distribution has been used to re-
cover the complete RTD from its first two moments.

110


SIMULINK subsystem of the MATLAB mathematical pro-
gramming package, the overall RTD for complex systems of
vessels under the influence of transient flows can easily be
analyzed. The simplicity of implementation allows the student
to develop a conceptual understanding of RTD (in a visual,
rather than equation, form), both for classroom demonstration
and homework or project assignments.

NOMENCLATURE
f fraction of material leaving vessel k which has a total
residence time between (n 1)A and nAt
F.k flowrate into vessel k
in
Fk flowrate out of vessel k
out
t time
Vk volume of vessel k
Superscripts
k vessel number
Subscripts
i moment index
n residence time increment index
Greek Letters
AT increment in residence time
Ok average residence time of the material leaving vessel k
sk i-th moment of the residence time of the material leaving
vessel k
ok standard deviation of the RTD of the material leaving vessel
k
T residence time

REFERENCES
1. Nauman, E.B., and B.A. Buffham, Mixing in Continuous Flow
Systems, Wiley, New York, NY (1983)
2. Anderssen, A.S., and E.T. White, "The Analysis of Residence
Time Distribution Measurements Using Laguerre Functions,"
Can. J. Chem. Eng., 47, 288 (1969)
3. Bischoff, K.B., "The General Use of Imperfect Pulse Inputs to
Find Characteristics of Flow Systems," Can. J. Chem. Eng., 41,
129(1963)
4. Kramers, H., and G. Alberda, "Frequency Response Analysis of
Continuous Flow Systems," Chem. Eng. Sci., 2, 173 (1953)
5. Woodburn, E.T., R.P. King, and R.C. Everson, "Optimal Esti-
mation of Process Parameters Using Pseudo-Random Binary
Signals with Application to Mixing Inside a Packed Tower,"
Can. J. Chem. Eng., 47, 301 (1969)
6. Gibilaro, L.G., M.O. Stevens, and S.P. Waldram, "The Evalua-
tion of System Moments from Frequency Response Data," Chem.
Eng. Sci., 33, 1394 (1978)
7. Nauman, E.B., "Residence Time Distribution Theory for Un-
steady State Stirred Tank Reactors," Chem. Eng. Sci., 24, 1461
(1969)
8. Nauman, E.B., Chemical Reactor Design, Wiley, New York, NY
(1987)
9. Simandi, B., A. Balint, J. Sawinsky, "Application of the Method
of Attenuated Moments to the Evaluation of Curves for the
Residence-Time Distribution," Int. Chem. Eng., 28, 362 (1988)
10. van Gelder, Klaas B., and K. Roel Westerterp, "Residence Time
Distribution and Hold-Up in a Cocurrent Upflow Packed Bed
Reactor at Elevated Pressure," Chem. Eng. Tech., 13, 27 (1990)
11. Thijert, M.P.G., M.H. Oyevaar, W.J. Kuper, and K.R.
Westerterp, "Residence Time Distribution of the Gas Phase in
Chemical Engineering Education










a Mechanically Agitated Gas-Liquid Reactor," Chem. Eng.
Sci., 47, 3339 (1992)
12. Levenspiel, Octave, Chemical Reaction Engineering, 2nd ed.,
Wiley, New York, NY (1972)
13. Ray, W.H., "On the Mathematical Modeling of Polymeriza-
tion Reactors," J. Macromol. Sci.-Revs. Macromol. Chem.,
C8, 1 (1972)
14. Biesenberger, J.A., and D.H. Sebastian, Principles of Process
Engineering, Wiley, New York, NY (1983) 0



Book review


COULSON AND RICHARDSON'S
CHEMICAL ENGINEERING
Volume 6 (Design), Second Edition
by R. K. Sinnott
Pergamon Press Ltd., Oxford, UK; 954 pages, $48.00 (1993)
Reviewed by
John A. Williams
Northeastern University
This book well serves the principal purpose of the au-
thor-to provide an undergraduate textbook for the chemi-
cal process design course. Expansions made to the first
edition include an introductory presentation of process heat
integration (pinch analysis), a discussion of safety and loss
prevention, and a presentation of current (1992) costs related
to process evaluation and step-counting techniques for fixed
capital cost estimates.
The breadth of the treatment is impressive and includes
mechanical design of process equipment. An extensive list
of references, principally to sources in the UK and the USA,
is available at the end of each chapter if additional detail is
needed by the reader. The topics covered are discussed un-
der the following chapter headings:
Introduction to Design
Fundamentals of Material Balances
Fundamentals of Energy Balances
Flow-Sheeting
Piping and Instrumentation
Costing and Project Evaluation
Materials of Construction
Design Information and Data
Safety and Loss Prevention
Equipment Selection, Specification, and Design
Separation Columns (Distillation and Absorption)
Heat-Transfer Equipment
Mechanical Design of Process Equipment
General Site Considerations
The book is of very high quality both in preparation and in
presentation. A question that a chemical process design in-
Spring 1995


structor might ask upon reading this text is, "Could this book
be successfully used by students in my design course?"
Since there are many ways to present a course in chemical
process design, the answer to that question would not be an
unambiguous yes or no. Some considerations include the
following questions:
Is the volume self-sufficient?
Are the topics covered current to the practice of
process design?
Would process costs that are presented in pounds
sterling be accepted by the undergraduate audience in
the USA?
Does the library have resources to support access to
the extensive list of references cited as publications of
the IChemE (Institution of Chemical Engineers,
London)?
Is a sufficient supply of exercises provided for practice
in the application of design techniques?
The book is intended to be as self-sufficient as possible.
The author often refers to the earlier books of the Coulson
and Richardson series. For undergraduate programs that do
not use that series in foundation courses, the instructor could
prepare a list of equivalent references to alternate textbooks.
Current topics of design are covered in the revised edition.
Topics mentioned, but not examined in detail, are batch
processing and optimization. British standards and govern-
ment management procedures for loss prevention are most
frequently cited. Students in the USA will ask how those
standards differ from USA standards and regulations, and
the instructor should be prepared to answer.
The problem of converting costs from pounds sterling to
American dollars is covered in detail, with examples that can
be clearly understood by senior students.
A set of eight design projects is presented in Appendix G.
A model answer is available in the literature for one project.
There is no list of practice problems (exercises) at the end of
each chapter. Fully-solved exercises are included, however,
where appropriate to the presentation of topics in the book.
An experienced design instructor should have no trouble in
finding appropriate exercises and design projects from back-
ground. The lack of design exercises at the end of each
chapter could be a more serious impediment to an instructor
who wishes to rely entirely on the textbook as a source of
design problems for the student.
The strengths of this book are the outstanding quality of
writing, the consistent, successful effort to present technical
material in the context of the process design requirement,
and the breadth of coverage that results in a nearly self-
sufficient textbook. It is recommended for serious consider-
ation as a required textbook in an undergraduate process
design course. C











, learning in industry


This column provides examples of cases in which students have gained knowledge, insight, and
experience in the practice of chemical engineering while in an industrial setting. Summer interns and
coop assignments typify such experiences; however, reports of more unusual cases are also welcome.
Description of analytical tools used and the skills developed during the project should be emphasized.
These examples should stimulate innovative approaches to bring real world tools and experiences
back to campus for integration into the curriculum. Please submit manuscripts to Professor W. J.
Koros, Chemical Engineering Department, University of Texas, Austin, Texas 78712.



WPI PROJECTS


GLOBALIZE ENGINEERING EDUCATION

IN THE PACIFIC RIM


Y.H. MA, L. SCHACHTERLE, J.F. ZEUGNER
Worcester Polytechnic Institute Worcester, MA 01609


American trade to and from the Pacific Basin cur-
rently exceeds trade with any other region, and in
fact, by hosting a recent APEC Forum in Seattle,
the Clinton Administration publicly recognized the rapidly
growing importance of Asian markets to the U.S. Profes-
sional education with any stake in the future has to be linked
with Asia. The crucial question is "how"? Ideally, American
universities should prepare their engineers to be fully com-
petent both technically and socially in any part of the globe,
but the reality of mastering two such disparate and intensely
demanding disciplines as engineering and Asian language
and culture presents severe barriers to achieving this kind of
undergraduate training.

WPI'S PROJECT PROGRAM
Worcester Polytechnic Institute (WPI) addresses the prob-
lem of preparing engineers for global careers through a
project program. Since 1865, the faculty and students at WPI
(the nation's third oldest private technological university)
have been keenly aware of the educational value of projects;
working on real-world problems (often originated in indus-
try) provides students with the motivation and discipline that
are too often absent from passive classroom experiences.
Projects have become the cornerstone of an innovative edu-
cational program known as the "WPI Plan," which was
developed and implemented in the early 1970s. In addition
to course requirements and a final project in the humanities,
every student must complete two nine-credit-hour projects:
Copyright ChE Division ofASEE 1995


the first in the student's major field (the Major Qualifying
Project, or MQP), and the second on a topic relating society
and technology (the Interactive Qualifying Project, or IQP).
The experience gained from off-campus projects over the
past twenty years provides opportunities for WPI to apply
the project approach to globalization in engineering educa-
tion. Projects can be completed by a full-time commitment


Y.H. Ma received his BS from National Taiwan
University, his MS from Notre Dame, and his ScD
from MIT, all in chemical engineering. He has
taught at WPI since 1967 and served as Director
of the first off-campus internship center. His re-
search areas include adsorption and diffusion in
porous materials, separations, and inorganic mem-
branes for separation and membrane reactor ap-
plications.

Lance Schachterle is Professor of English at
WPI and has been head of WPI's international
and global programs. He helped set up the first
WPI residential project centers in Hong Kong,
Bangkok, and Taipei, and served for a decade as
coordinator of WPI's first international center in
London.


J.F. Zeugner is Professor of American Foriegn
Relations and Director of WPI's Asian Program.
He also has taught extensively in Japan and is
presently Bryant Drake Guest Professor at Kobe
College in Japan. He received his AB from Harvard
College, his MA and PhD from Florida State Uni-
versity (1968 and 1971).

Chemical Engineering Education










of one term of seven weeks, so students can obtain a concen-
trated two-month experience in a foreign country during one
of the five terms in the Institute's calendar (two in the
autumn, two in the spring, and one in the summer). The IQP,
with its emphasis on the importance of students becoming
aware of the relationship between technology and society,
forms the basis of the WPI global program.
IQPs, which in many cases are supported by professional
organizations, industry, and/or government, are usually open-
ended, real-world problems illustrating ways in which sci-
ence and technology affect societal structures and/or values.
Students thus learn very effectively the ambiguities and trade-
offs that characterize problem solving beyond the textbook
and introductory stage.

WPI'S GLOBAL PERSPECTIVE PROGRAM
The global economy, driven by technological innovations
and competition for financial, material, and human resources,
demands trans-national interdependence for scientists and
engineers who will be confronted as never before with prob-
lems whose solutions require not only technical knowledge
but also a knowledge of cultures other than their own. Yet,
ironically, the United States as a nation provides few oppor-
tunities and little encouragement to engineering and science
students to learn and understand other cultures, languages,
and nations.
To provide opportunities for all WPI students within the
usual four-year BS program and to allow students to learn
about working in cultures new to them, WPI faculty launched
the "Global Perspective Program" in 1989 with projects and
courses concentrating on global issues. Because all faculty
at WPI (engineering, science, management, humanities, and


social sciences) advise and co-advise IQP projects, students
are exposed to differing professional points of view and
often see engineering faculty as role models in terms of
concerns and analyses of social issues. This faculty commit-
ment to a flexible, project-based curriculum makes it
possible for WPI to send over two hundred undergraduate
students abroad every year (roughly one-third of each
graduating class). Unlike most international programs, WPI
minimizes the costs of study abroad by charging no extra
fees for the program, extending full financial aid as allow-
able by regulations, and securing highly competitive room-
and-board rates overseas. The Institute even waives on-
campus room-and-board fees when students are carrying out
their global projects.
Through a combination of reciprocal exchanges (where
undergraduate and graduate students can spend a defined
period of time at a partner university under a tuition waiver)
and residential project centers (where teams of students with
a full-time WPI faculty advisor in residence carry out
projects), WPI has created an extensive network of global
opportunities in Europe, Latin America, and Asia (see Fig-
ure 1). While the challenges of cultural and linguistic adjust-
ment are nowhere greater than in the Pacific Rim, WPI
recognized the enormous technical and financial growth and
potential in this region. Thus, with the help of alumni and
corporate contacts, we have established residential project
programs in Taiwan, Thailand, and Hong Kong, and are
exploring possible new sites in Viet Nam, Japan, and China.
Students who want to participate in one of these three
Asian residential project programs have to apply for admis-
sion to the program through the Global Program Office.
After a competitive selection process, groups of two to three


WPI
has established
off-campus programs in:
Bangkok, Thailand Moscow, Russia
Darmstadt, Germany Munich, Germany
Eindhoven, Holland Paris, France
Guayaquil, Ecuador San Francisco, CA
Hong Kong San Juan, Puerto Rico
Limerick, Ireland Stockholm, Sweden
Leuven, Belgium Taipei, Taiwan
London, England Venice, Italy
Monterrey, Mexico Washington, DC
Montreal, Canada Zurich, Switzerland


Yo-


Figure 1. WPI's off-campus centers.


Spring 1995










students are formed, either among the students themselves
or by the staff of the Global Program Office. Generally, one
or more students of Asian descent are paired with one or
more non-Asian students.
The WPI faculty who serve as on-site program coordina-
tors elicit project topics from participating industrial, gov-
ernmental, or educational project sponsors. Then, from these
topics, the student groups choose a project to work on.
During the term prior to their departure, the students must
take an independent study course designed specifically to
prepare them for their overseas experience. This preparation
involves a mix of three activities: academic, linguistic, and
cultural. All students must complete a formal project pro-
posal, to professional expectations, on the topic they will
work on full time while at the foreign residential site. Work-
ing from letters of intent supplied by the sponsors, the stu-
dents conduct a formal Literature Review (normally involv-
ing some direct telecommunications with the sponsors) as
well as laying out a Procedures section, a Budget, and a
Time Line for the proposed activity. In addition, depending
upon the students' backgrounds, they must devote attention
to gaining some linguistic proficiency for the country they
visit as well as some appreciation of its historical and cul-
tural background.

DEVELOPING THE
PROJECT PROGRAMS IN ASIA
Probably the most difficult task in the overseas project
program is developing a list of educationally sound projects
of interest to sponsors in each host country. Since this paper
focuses on WPI's programs in the Far East, we will describe
the procedure for project programs in Asia.
Establishing connections before the program begins is
especially urgent in the Far East. Through the assistance of
local WPI alumni and contacts arranged by one of the au-
thors (YHM), the Dean and Associate Dean of Undergradu-
ate Studies (LS) visited Hong Kong, Thailand, and Taiwan
in 1990 to investigate the feasibility of establishing project
programs in the Pacific Rim. A subsequent visit by the
first author, followed by a joint visit by both above
authors, established local contacts with professional societ-
ies, industries, government agencies and universities. (Sub-
sequently, another author [JFZ] was appointed Director of
WPI's Asian program.) Two local project coordinators were
also appointed: a chemistry professor at the Chulalongkorn
University became a WPI Adjunct Professor and the project
coordinator in Bangkok, and a chemical engineering pro-
fessor was named in Taiwan. Both appointees are WPI
alumni with a good understanding of WPI's programs. Their
superb service and supervision were indispensable to the
success of the project program.
Our concerns that few US students not of oriental descent
would be able to learn Chinese or Thai were assuaged by the


warm support we found along our alumni in these countries
and by the fact that English is widely used in professional
circles around the globe (especially in science and technol-
ogy). Further, the concepts of project-based education we
developed in Worcester were well received by the profes-
sionals we met. They shared our vision that American stu-
dents would most readily learn to do professional-level work
in a new culture through real-world projects with a bilingual
staff, rather than being relegated to passive language and
learning experiences in a classroom.
We faced several hurdles in the development of actual
projects. First, many Asian cultures have reservations about
undergraduate's capabilities, and second, substantive links
between industry and academia at the undergraduate level
have not been developed. But at all three sites, the services
and flexibility of alumni were crucial in addressing the ini-
tial risks of offering a project for students who need to show
more independence and maturity than their Asian counter-
parts. Nonprofit organizations in need of help at all levels,
university researchers, and joint Asian-American enterprises
were all most receptive to the project concept.

WRESTLING WITH
BANGKOK'S RECYCLING NEEDS
In 1993, a group of three students, supervised by WPI
chemistry faculty in Bangkok, undertook a project to exam-
ine the feasibility of recycling plastic, thus alleviating part of
a garbage disposal problem in the slum area of Klong Toey.
The students worked under the auspices of the Duang Prateep
Foundation, renowned for improving life in the slums of
Bangkok. The on-campus preparation work included exam-
ining different plastic recycling technologies and their eco-
nomics. From the preparative work, the students learned that
recycling programs are location-specific due to differences
in available resources, city government structures, and atti-
tudes of local citizens towards recycling.
Research for information on local environmental and
recycling issues led not only to the records kept in the
two major libraries, but also to interviews with key local
people with interests in the plastics recycling program
and to academic, industrial, governmental, and non-govern-
mental organizations.
The students offered three recommendations: first, educat-
ing the public about important environmental issues; second,
improving the separation of plastics wastes; and third, fos-
tering better cooperative government/industry interaction.
Specifically, the students urged changes that would provide
a monetary incentive to individuals for separating the wastes
prior to bringing them to the collection crews, thus improv-
ing the separation efficiency and maximizing the benefits
derived from the other two suggestions.
The recommendation report has been distributed to the
appropriate organizations in Thailand, including the faculty
Chemical Engineering Education










at the Chulalongkorn University, governmental agencies,
industrial groups, and non-governmental groups. WPI's
local coordinator is following up the responses to the
report and identifying opportunities for new projects in this
crucial area.

CHEMICAL PROCESS SAFETY IN TAIWAN
A second group of four students (one Chinese speaking
and three non-Chinese speaking) studied chemical process
safety in Taiwan. The Chemical Engineering Department of
the National Central University sponsored the project, and
one of its faculty served as the on-site supervisor working
with Professors Ma and Zeugner.
A by-product of the rapid economic growth experienced in
Taiwan over the past forty years is a lagging effort in the
areas of environmental legislation and industrial hygiene.
This project examined the impact of the discrepancy be-
tween industrial progress and environmental safety within
the framework of Chinese culture and specifically studied
the level of safety, environmental protection, and industrial
hygiene in the Taiwan chemical industry. The interactions
between chemical plants and the surrounding communities,
the employee and contractor attitudes, and the government/
industry interactions were examined, leading to the defini-
tion of the associated problems facing the Taiwan chemical
industry.
Prior to their departure for Taiwan, the students gathered
extensive information and background on commonly used
hazard identification and evaluation procedures. They also
visited a major US chemical company and discussed safety
practices with the company's safety officers. The knowledge
they gained served as the basis for a comparison of safety
practices in US and Taiwan chemical companies. In Taiwan,
the students (accompanied by a chemical engineering pro-
fessor who is also a leader in chemical process safety) vis-
ited six chemical companies. Each visit consisted of two to
three hours of interviews with safety management person-
nel, followed by a plant tour. These visits formed the basis
for their final analysis, which included the evaluation and
general discussion of each company's emergency response,
safety management, and training and safety review.
The students' analysis included the results of their study
on the community's attitude toward chemical industry safety.
They concluded that communities are more interested in
seeking financial settlements than they are in demanding
improvements in the chemical process safety. Facing the
pressure of financial settlements, the companies are begin-
ning to resist financial compensations and instead are reach-
ing out to the public to discuss the safety aspects of their
operations. Although Taiwan's central government is pro-
ceeding at a rapid pace to establish rules for chemical safety,
cooperation between the governmental regulatory agency
(Environmental Protection Administration) and the chemi-
Spring 1995


cal industry which they plan to regulate clearly needs
improvement. The students also suggested that Taiwan's
universities strive to offer broader curricula in the areas of
risk assessment techniques such as HAZOP, fault trees,
and checklists, along with education in engineering ethics.
Finally, they recommended the development of a set of
"Guiding Principles" and "Codes of Management Practices"
by the Petrochemical Industry Association of Taiwan
to provide guidance.

CONCLUSION
WPI's Global Project Program provides a two-month
project exposure to both technical and social issues in an
Asian setting. Working side by side with Asian profession-
als, living in Asian cities, and using local transit to commute
to work, all serve to challenge students to adjust quickly to
the demands of being productive in a new environment.
The students at each site found that they were functioning
not as guests, or even as consultants, but were more like full-
time employed residents. Obstacles such as difficulties in
data collection, confusion during interviews, and technical
incompatibility in word processing had to be overcome
quickly, even as the adjustments to different food, work
habits, values, and assumptions were being faced simulta-
neously-just as real professionals would have to do. Most
students found adjusting to the pace of a different culture
both exhilarating and exhausting. While learning a new
language to professional standards was not part of the
program expectations, students made the most of opportuni-
ties to learn to negotiate in a different culture. One young
woman, for example, celebrated her grounding in Asian
culture by concluding her experience with a solo train trip
from Beijing to Hong Kong.
The sponsoring agencies also reported benefits. Every
project must be fully documented to professional standards
by the end of the two-month stay. Agencies found the fresh
points-of-view of students helpful, especially on issues where
students could gather data that sources were reluctant to
share with professional peers. And sponsors soon discovered
that there were unexpected outcomes and payoffs in these
projects; undergraduate curiosity often prompted cross-de-
partmental and cross-agency communication that had not
been possible before.
Our program in the Pacific Rim is barely five years old,
and we await with intense interest its results. A social evening
two years ago brought together the first two dozen or so
students who had been our project pioneers in Asia. To a
person they testified that nothing else in their education had
been as meaningful as these projects that tested their ability
to decipher complex societal and technical issues in a culture
new to many of them. We look forward to their professional
success as they return (as many stated they would) to the
Pacific Rim to participate as professionals and as citizens. O











W laboratory


UNSTEADY-STATE HEAT TRANSFER

FROM A STEAM-HEATED COIL

TO A TANK OF WATER

PETER RICE
Loughborough University of Technology Loughborough, Leics., England LE11 3TU


As a response to the Finneston report1]1 that recom-
mended more practical, industry-related experience
in undergraduate degree courses, a series of experi-
ments related to industrial practice has been introduced for
first-year students. One such experiment, which can also be
used as an unsteady-state heat transfer experiment, is the
primary object of this paper.
At Loughborough students receive lectures on heat trans-
fer in the second semester of their first year at the university
(the first semester introduces fluid mechanics). These lec-
tures expand on and develop the university entrance ('A'-
level) examination syllabus in physics. With this course and
other experiments on heat transfer in the first-year labora-
tory, they thus receive a solid foundation in this subject.
The experiment consists of heating a tank of water with
an immersed steam-heated coil, a common chemical engi-
neering operation. The temperature of the water is measured
as it varies with time and, simultaneously, the condensate
formed is collected.
As a practical-experience experiment, it shows the use of
pressure reducing valves, steam traps, and strainers. The
strainer and the steam trap (a floating ball type) are
stripped down to show how they function, sketches are
drawn of the internalss," and the strainer and trap are reas-
sembled. Locking off the steam reducing valve and using
a "permit to work" are included in the procedure, similar
to industrial practice. Other types of disassembled steam
traps are on display by the rig. Postgraduates assist in super-
vising the undergraduates.

EQUIPMENT
Figure 1 is a line drawing of the steam lines. The coil
enters and leaves through the top of the tank. It consists of a
186-cm long, 1/2-in outside diameter copper pipe formed
into two complete vertical coils on a 16.5-cm diameter. The
coils are "open," with approximately 5 cm between loops.
Copyright ChE Diision ofASEE 1995


Peter Rice spent twenty-one years in industry
after leaving school at fifteen years of age. He
received his Master's degree from Cranfield and
his PhD from Loughborough (at age 40), where he
has spent the last twenty-five years as lecturer
and senior lecturer. His interests are in heat and
mass transfer, especially in food processing, and
with phase change also in physical property pre-
diction.

The equivalent surface area for heating is 0.073 m3, based on
outside diameter. The coil is approximately at the geometric
center of the tank, which has anl8-in square (47 cm square)
base by 15-in (38 cm) high. The tank is made isenthalpic by
having 4-cm thick expanded polystyrene sheets on all sides,
including the base and top. A mercury-filled thermometer
with a 6-in diameter dial was used to monitor the tempera-
ture change. The bulb of the thermometer was positioned at
the geometric center of the liquid in the tank.
PROCEDURE
We asked the students to add enough cold water to make
70 liters in the tank, which results in a beginning water
temperature of about 15 C. The main steam valve was
opened and steam passed through a by-pass to waste. This
clears any condensate present in the supply line. The steam
main pressure was 9 barg and was reduced to 1 barg through
the reducing valve. The steam was wet, so the pressure
reading could be used to estimate the steam temperature.
The steam pressure was read on a calibrated Bourdon
gauge. The valve allowing steam to the coil was opened and
the steam passed through a strainer, a sight glass, an elec-
tronic sensor for pressure, and then through the steam trap.
At this point the steam trap by-pass was open and the two-
way valve directed any condensate to waste.
When the water reached 25 C, the steam trap by-pass was
closed and the two-way valve was turned to direct the con-
densate into a preweighed drum. A stopwatch was also started
at this point. Then time was recorded at 5C-temperature
Chemical Engineering Education




























Figure 1. Flow diagram of the system.


intervals until the temperature reached 750C. At that time the
two-way valve was turned to again direct the condensate to
waste, the valve directing the steam to the coil was closed,
and the steam valve was turned and "locked off." The by-
pass valve was opened and the main steam supply valve was
then closed. The condensate collection drum was then
weighed and the amount of accumulated condensate was
found.
At this time, a "permit to work" was obtained from the
laboratory supervisor, who checked the equipment for safety
prior to issuing the permit. The steam trap and strainer were
stripped, sketches were made of their internal structures, and
the equipment was reassembled. The permit was counter-
signed to indicate safe completion of the work. The mass of
water heated was recorded from a calibrated sight glass
fixed on the side of the tank.

UNSTEADY-STATE MODELING
A simple heat balance at some time t gives

MC d =UA(T-T) (1)
P dt s
where
M mass of water being heated
Cp specific heat of water
A area of coil for heat transfer
T, steam temperature (set by steam pressure)
T water temperature at time t
U overall heat transfer coefficient
We note that since the steam side condensation coefficient
(of the order of 14,000 Wm-2K ') is so much greater than the
liquid side coefficient, we can assume that U is, essentially,
the liquid side coefficient.
Integration using the initial condition that at t=0, T=Ti, the
water temperature at the beginning of the experiment (25C
Spring 1995


The experiment consists
of heating a tank of
water with an immersed
steam-heated coil, a
common chemical
engineering operation.
The temperature of the
water is measured as it
varies with time and,
simultaneously, the
condensate formed
is collected.


in our case), gives an exponential temperature-time relation-
ship of
T = T -(T Ti) exp(-t ) (2)
or

t (n T -T i (3)
T -T
where
MC
T= p (3a)
UA
The time constant, t, describes the shape of the curve,
e.g., whether the temperature change is fast or slow. As will
be shown later, a reasonable fit of the data is obtained.
The heat loss, however, is by natural convection on the
liquid side, and noting that for natural convection
Nu= f(GrPr)0.25 (4)
where
Nu Nusselt number
Gr Grashof number
Pr Prandtl number
we set

U = U'(T T)025 (5)

The heat balance is then

MCdTU'A(T T)25 (6)
P dt s=(
which, on integration and using the initial condition that at
t=0, T=T,, as before, results in


t MC' 1 1
0.25 U'A (T T) (T Ti)2














T=Ts -
T=T 0.25U'At 1i
MCp) (T T)0251

As will be seen, a better fit of the data results by using Eq.
(8).
To describe the temperature variation with time, U and U'
have to be known. This is done by using the time at tempera-
ture T=60'C to evaluate U and U' and then using these
values to predict the rest of the curve. It is possible to carry
through a multi-regression and obtain values for U and U'
which minimizes the least squares deviations with the ex-
perimental points, but this is just an exercise in numerical
methods and does not give a better insight into the heat
transfer process.

APPLICATION TO THE EXPERIMENT
Two steam pressures (Case 1 and 2) were used: 1300C (1.7
barg) and 121.30C (1.07 barg). The corresponding masses of
water heated by the coil were 65 kg and 69 kg, respectively.
The mass of condensate collected in each case was 6.56 kg
and 6.8 kg, respectively. The initial (starting) temperature
was 250C, and the specific heat was taken as 4.19 kJ kg-iC'-
(a mean value over the present range of temperatures).

RESULTS AND DISCUSSION
The calculated values from the data for U, corresponding
to the two steam temperatures, were 5795.2 and 4303 Wm2C1,
respectively, while the values of U' were 2022 and 1455.2
Wm-2C-125, using the 600C experimental value. With these
values of U and U', the theoretical results presented in
Figure 2 were calculated. Both models give good fit to the


experimental data, with correlation coefficients of 0.9985
and 0.9990 with U, and 0.9994 and 0.9998 with U'AT0O25 for
the two cases. The U'AT0O25 model fit of the data is slightly
better, as can also be seen from Figure 2.
Although the use of steam-heated coils is a common
operation and is widely used in chemical engineering, there
is little information on their performance. Inglesant
and Storrow,131 reporting results on heat transfer using cool-
ing coils in tanks, suggest a value of 0.73 in place of
0.53 (Fraas21]) for C in the (Nu=C(GrPr)0.2) relationship
used to describe free convection from a horizontal cylinder.
Even using this value of C, the size of U is still consid-
erably less than the measured values, as one would expect
comparing a horizontal cylinder with a cylinder formed
into a vertical coil.

We reportl41 results for an 18-cm diameter, 1 -loop steam-
heated closed-loop coil (area of 0.061 m2) positioned simi-
larly to the present experiments, but with the loop cross-
section oriented horizontally. A value for U of 2325 Wm 2C'
was obtained by using steam at 120.30C.
The reason for this difference in heat-transfer coefficient
values is that within the tank confines, a strong recirculatory
flow is set up due to the convection currents. This causes an
enhanced free-convection type heat transfer. The two heat-
transfer coefficients corresponding to the two driving tem-
perature differences used in the experiments indicate differ-
ent enhancement factors (e.g., different recirculatory flows)
with the more intense recirculation created by the higher
steam temperature, as would be expected.
In the case of the results reported in [4], the recirculation is
less vigorous due to the coil orientation compared to the
present results. To complete the results for the laboratory
experiment, we calculate as follows:


70 -


U60

S50

4
| 40


30 *--


0 200 400 600 800
Time (s)


1,000 1,200 1,400 1.600


Case 1 Steam dryness =MCpAT/mhg =0.96,
where m is the mass of condensate collected and hfg
is the latent enthalpy (2174 kJ kg' at 1.7 barg)
Case 2 Steam dryness = 0.97 (hfg=2200 kJ
kg-' at 1.07 barg)

REFERENCES
1. "Engineering Our Future," Report of the
Committee of Inquiry into the Engineer-
ing Profession; Chairman Sir Montague
Finniston, FRS Cmnd 7794, Jan (1980)
2. Fraas, A.P., Heat Exchanger Design, 2nd
ed., Wiley-Interscience, New York, NY; 63
(1989)
3. Inglesant, H., and J.A. Storrow, "Heat
Transmission in Coils," Ind. Chem., 26 313
(1950)
4. Aird, R.J., and P. Rice, "Unsteady State
Heat Transfer from a Steam Heated Coil
to Water," Int. J. Mech. Eng. Ed., 18, 37
(1990) 0
Chemical Engineering Education


Ts=121.3 Ts=130
experiment U const. U prop T^.25 experiment U const. U prop. T^.25


Figure 2. Comparison of variation of measured and predicted
temperatures with time.


f I I I I i i


or
os
oo



rm
I (PI











Exorcising Maxwell's Demon
Continued from page 95.

tion is associated with the entropy of information, there
would still have been a complete conversion of heat into
work. Szilard offered no details concerning the manifesta-
tion of this entropy change.

THE THERMODYNAMICS OF COMPUTING
Despite the exposure by Jauch and Biron of the flaw in
Szilard's engine, work dedicated to saving the second law
has continued apace, with the computer now assuming the
role of savior. Instead of the "corrective" kln2 entropy units
being assigned to information acquisition, the idea has now
been advanced that these units of entropy must be assigned
to memory erasure.J5 This is purported to be the entropy
change accompanying the thermodynamically reversible era-
sure of one bit of information.[6] The argument proceeds by
stating that a measurement in the one-molecule heat engine
can be made reversibly (no creation of entropy) but after the
completion of a cycle the demon must reset its memory at a
cost of kln2 units of entropy increase in the surroundings due
to heat dissipation. As the work of Landauerr6' forms the
basis for this explanation, it will now be subjected to a
critical review.
Mixing ideas from thermodynamics, statistical mechanics,
and information theory, Landauer obtained an expression for
the minimum energy dissipation in a computer. His system
was an assembly of N bits, each of which could occupy
either a zero or a one state. He assumed each state to have
the same entropy and considered a restore-to-one operation
where the bits, initially randomized with regard to state,
were all set to one. Arguing that the number of states avail-
able to a bit had been reduced from two (either zero or one)
to one in the process, he reasoned that the entropy of each bit
would be reduced by kln2. He continued by stating that the
entropy decrease of a bit must be compensated by heat
dissipation to the surroundings of at least kln2. Despite
disclaiming a reliance on information theory, Landauer ob-
viously views the entropy change of kln2 per bit in this
context.
Landauer is not justified in assigning an entropy change to
the process of restore-to-one. Although he provides little
explanation, he seems to be applying methods of statistical
mechanics, not at the molecular level but to a system com-
prised of N macroscopic subsystems, the bits. Not only is
this procedure questionable, but the process considered has
no thermodynamic significance. Landauer's restore-to-one
process involves macroscopic subsystems, and his calcu-
lated entropy change is akin to that which might be imagined
to accompany rearrangement of pieces on a checkerboard.
As a macroscopic subsystem, each bit will exhibit a set of
intensive properties which will depend only on the state-
Spring 1995


determining intensive variables (e.g., temperature and mag-
netic-field strength) as specified by the phase rule. In terms
of intensive properties, each bit behaves as if it alone were
present and oblivious of the identity of its neighbors, as, for
example, would be the case for a collection of crystals.
Because Landauer set entropies equal for states zero and
one, there can be no thermodynamically significant entropy
change in going between any two spatial configurations of
zeros and ones. Of course, if the transition between states is
not carried out reversibly, as would be expected of a com-
puter, heat dissipation to the surroundings will account for
the necessary entropy increase of the universe.
Landauer seems to view kln2 as the information entropy
of a bit. But, as has been convincingly shown by Denbigh
and Denbigh,101 information entropy does not reduce to ther-
modynamic entropy. Landauer's association of heat dissipa-
tion with the kln2 term is therefore inadmissible.
For Landauer's assumption of equal entropies for states
zero and one, a legitimate thermodynamic analysis shows
that there would be no entropy change in the surroundings
from a thermodynamically reversible resetting of memory.
This would contribute no additional entropy changes to the
analysis of Szilard's engine, but as we have seen, none is
needed.

CONCLUSION
The one-molecule heat engine is a flawed thought experi-
ment and therefore cannot provide thermodynamic justifica-
tion for an entropy of information or an entropy of erasure.
Neither of these "entropies" is appropriate in an entropy
balance and neither is necessary to save the second law from
the assault of Maxwell's demon. With the demise of the one-
molecule heat engine, the long and laborious exorcism of
Maxwell's demon should be complete.

REFERENCES
1. Leff, H.S., and A.F. Rex, Maxwell's Demon: Entropy, Infor-
mation, Computing, Princeton University Press, Princeton
NJ (1990)
2. Szilard, L., Z.F. Physik, 53, 840 (1929) [and page 124 of
Reference 1]
3. Brillouin, L., J. Appl. Phys., 22, 334 (1951) [and page 134 of
Reference 1]
4. Denbigh, K.G., Chem. Brit., 17, 168 (1981) [and page 109 of
Reference 1]
5. Bennett, C.H., Sci. Am., 225(11), 108 (1987)
6. Landauer, R., IBM J. Res. Dev., 5, 183 (1961) [and page 188
of Reference 1]
7. Rastogi, S.J., Chem. Eng. Ed., 26(2), 78 (1992)
8. Jauch, J.M., and J.G. Baron, Helv. Phys. Acta, 45, 220
(1972) [and page 160 of Reference 1]
9. Costa de Beauregard, 0., and M. Tribus, Helv. Phys. Acta,
47, 238 (1974) [and page 173 of Reference 1]
10. Denbigh, K.G., and J.S. Denbigh, Entropy in Relation to
Incomplete Knowledge, Cambridge University Press, Cam-
bridge, UK (1985) O











=1 laboratory


POLYMER PROCESSING

For The Undergraduate Unit Operations Laboratory


AJIT V. PENDSE, JOHN R. COLLIER
Louisiana State University Baton Rouge, LA 70803


In recent years polymers have assumed a commanding
position in the chemical industry. According to a recent
survey in the 1994 Annual Technical Conference of the
Society of Plastics Engineers (SPE ANTEC), the volume of
plastics manufactured in 1993 approached 70 billion pounds.
With polymers playing an ever-greater role in industry, poly-
mer processing becomes an even more important component
in chemical engineering education.
Polymer processing is an engineering specialty concerned
with the operations carried out on polymeric materials or
systems to increase their utility.[',21 Typical industrial pro-
cessing operations include extrusion, blowing, injection mold-
ing, and reaction injection molding; each of these operations
can involve chemical reactions, flow, or a permanent change
in physical property.
The objectives of an experiment in polymer processing are
twofold: understanding the governing principles of the op-
eration, and appreciation of the process as applied in indus-
try. Two unit operation experiments involving polymer pro-
cessing have been developed and incorporated into the unit
operations laboratory curriculum at Louisiana State Univer-
sity. One, an experiment involving a single-screw extruder,
emphasizes the former, and the second, an experiment in-
volving an injection molding machine, primarily focuses on
the latter. A different approach was followed in developing

Ajit V. Pendse is a graduating doctoral student at
Louisiana State University. He received his
master's degree in chemical engineering from the
Indian Institute of Technology, Bombay, in 1989.
His research interests are in polymer processing,
S process development, and rheology.


John R. Collier is Professor of Chemical Engi-
neering at Louisiana State University. He received
his BS from South Dakota Tech in 1961, his MS
from the University of Illinois in 1962 and his PhD
from Case Western Reserve in 1966. His aca-
demic research involves polymer processing and
properties, and textile processing and properties.
Copyright ChE Division ofASEE 1995


the volume of plastics manufactured
in 1993 approached 70 billion pounds. With
polymers playing an ever-greater role in industry,
polymer processing becomes an even more
important component in chemical
engineering education.

each of the experiments according to the level and scope of
the students performing the experiments.
In the experiment for senior-level students that involves
extrusion through a capillary die, the students learn the op-
eration and principles of a single-screw extruder. They are
asked to determine the viscosity of a polymer melt (a non-
Newtonian fluid) from the experimental data of pressure
drop across the capillary tube and the corresponding flow
rate. They are asked to infer the relationship between pres-
sure drop and backmixing in the extruder. The emphasis is
on understanding the concept of viscous flow of a non-
Newtonian fluid. The students are also asked to observe the
die swell and attempt to correlate it with the operating condi-
tions. Since die swell is not well understood in the literature,
this demonstration generates an appreciation for the com-
plexity of the flow.
In the junior-level experiment, the students learn about the
controls and operation of a state-of-the-art injection molding
machine. They are asked to find the best operating condi-
tions for producing a part with the given material on the
injection molding machine. Emphasis is on the design of
optimal experimental planning, statistical variation of the
properties of the parts, and sensitivity of the product to
different sets of operation conditions.
Groups comprised of three students perform each of the
experiments and three periods of three hours each are allot-
ted. The students prepare a preliminary report after the first
meeting and then prepare and present a full report on the
experiment at the end. The report consists of a description of
the experiment's goal, the experimental plan, a description
of the apparatus, a discussion of the theory behind the ex-
periment, presentation of experimental data, a discussion of
Chemical Engineering Education










the results, and finally, any suggestions which might improve
the experiment and a discussion of the sources of error.

S EXPERIMENT 1: Extrusion

Apparatus
The extruder assembly (shown schematically in Figure 1)
consists of an extruder equipped with a motor and a die. The
extruder is a single-screw extruder, 3/4" in diameter with an
L/D ratio of 20, manufactured by Siescor. It is driven by a
3/4-HP DC motor manufactured by G.E.C. The motor is pro-
vided with a single reduction worm gear reducer, 321-c series.
The diagram also shows the points of measurement of tem-
perature and pressure.
Figure 2 shows the cross section of the capillary die used in
the experiment. The diameter of the capillary is 2 mm and the
length is 12.5 mm. A Dynisco TPT 232 transducer is used to
measure the pressure and temperature of the polymer melt.
A charge of pellets is put in the hopper and the unit is heated
up. The temperature profile, including the operating tempera-
ture for the die and the temperatures for zones 1 and 2 of the
extruder depends on the material of choice. Typical die tem-
perature for polypropylene (PP) and polyethylene (PE) are in
the range of 190-230 C and 150-200 C, respectively. The
screw is not rotated until the temperatures have been stable for
sixty minutes (called heat-soak). Zone 1 temperatures are
within 3 C of the melting temperature of the polymer. Zone
2 temperature is set between the zone 1 and the operating
temperature. The students are asked to find the melting points
for the material in a standard reference such as Polymer Hand-
book.3]
Theory
Shear stress for a Newtonian fluid is a linear function of
shear rate (-dV,/dy):
dv
trz =--7 (1)

In a plot of shear stress vs. shear rate, the slope of the resulting
straight line is equal to the viscosity (i) and only dependent
upon the temperature. For a non-Newtonian fluid, the shear
stress is a function of the shear rate, and the viscosity is
dependent upon both the temperature and the rate of shear.
Several mathematical models are applicable to describe the
stress and strain rate response (constitutive equations) of vis-
cous fluids. For the melt flow of a typical thermoplastic mate-
rial such as PP or PE, as is used in this experiment, the Power
Law model is the most suitable constitutive equation.[2] In
cylindrical coordinates, according to the model,
Sdv In"- dv
z dr dr2

The model contains two empirical constants: the consis-
Spring 1995


tency or modulus of viscosity, m, and the Power Law index,
n.[4] While m is a strong function of temperature, n varies
with shear rate-but for the range of the shear rates used in
this experiment n can be treated as a constant. The above
relation holds good at a given temperature. Notice that for
n=l the Power Law model reduces to Newton's Law (Eq. 1),
where m is the same as the viscosity of the fluid.
Experimental
Material
The material chosen for the following experiments was
Linear Low Density PE from DOW, type LLD 2. The re-
ported Melt Index (ASTM D1238) was 1.5. The melting
point from DSC analysis was determined to be 128'C. The
operating temperature range was from 1450C to 1750C for
the experiment.
Part 1 For this part of the experiment, the students are
asked to determine the values of m and n that best character-
ize the material chosen for extrusion (PP or PE). As men-
tioned above, n should be a constant and m a function of
temperature. Assuming that the cylindrical die on the dis-
charge end of the extruder may be approximated as a cylin-
der of uniform radius R and that the polymer melt maintains
a constant fluid density, a differential balance for the trans-
port of momentum yields





HOPPER
: _





DIE ZONE II ZONE I DRIVE

Figure 1. Schematic of the extruder assembly.

12.5 mm
I -- : Pressure Transducer

,r--
I/


S2mm







Figure 2. Schematic of the die.












Q = nrR3 (ApR n
S1+3n 2 mL

where
Q = volumetric flow rate of the extrudate
L = length of the cylinder
AP = pressure drop across the cylinder
The students are encouraged to refer to standard 1
books14'51 to gain an understanding of the shell balance t
nique. They are required to derive this relationship be
ning with a differential shell balance written in cylind
coordinates.
The data collected in the experiments should consi,
volumetric flow rates and polymer melt pressures for v
ing values of melt temperatures. When the extruder is c
ating at a steady state (stable pressure drop for a given 1
rate), the effects of the speed of screw rotation, the temp
tures at the various points in the units, and the pressure i
across the capillary should be made. The volumetric :
rate or mass flow rate can be determined by periodic
cutting off the extrudate and weighing the extrudate r
exiting between measured time intervals.
Equation 2 can also be expressed in terms of the
stress Tw and apparent strain rate y, which are express

ApR
tw 2L


74Q
7 R3
iR


respectively.
(3) Equation 2 can be alternatively written as
w = m n (6)
The data can now be used to determine the parameters n and
m by regressing the linearized form of the momentum equa-
tion.

Figure 3 shows a log-log plot of wall shear stress vs. strain
text-
rate for PE at different temperatures, and Table 1 shows the
ech-
values of the parameters m and n determined from the data.
:gin-
gin The data are then compared with that obtained from a com-
rical
mercial rheometer at Louisiana State University. A
Rheometric Advanced Capillary Extrusion Rheometer
st of (ACER) and a Bohlin CS VOR cone and plate rheometer
'ary- have been used for that purpose.
Iper-
flow Another important goal of this experiment is to highlight
,era- the difference between the results of the students' experi-
drop ment and the analysis from the commercial instruments. The
flow students learn that the L/D ratio is an important factor in the
ally accurate determination of viscosity through capillary rheom-
nass eters. A lower L/D ratio (6.25 for this experiment) results in
an incorrect higher viscosity as the flow is not fully devel-
oped. The students are expected to comment on the differ-
wall ences between the two results and to point out other possible
d as sources of error.

(4) Part 2 Another aspect of the experiment is to examine
the behavior of the screw extruder as a volumetric pump.
The amount of polymer melt delivered per rotation varies
with the operating conditions. The screw does not function
(5) as a constant discharge device. Data for pressure drop vs.


S5.3






0 5
i5 5.1
U)





4.8 -
. 1.8 1.9


1V
7


V
S v
r


2 2.1 2.2
log (Strain Rate,


Fr 145


155 v 165


2.3
1/S)


2.4 2.5


175


Figure 3. Wall stress vs. strain rate for a range of melt temperatures.
-1450C; E 1550C; V 1650C; V 175C


Chemical Engineering Education


TABLE 1
Values of n and m
as functions of
temperature

T OC n m (Pa S")
145 0.38 17200
155 0.47 10100
165 0.51 7420
175 0.53 6190










screw rpm at different temperatures is collected. Since the
polymer is virtually incompressible in the accessible operat-
ing range, a deviation from a straight line will provide a
measure of the degree of slippage and back-mixing in the
extruder. The data is then correlated with the operating con-
ditions. Figure 4 shows the results obtained from PE at
several operating temperatures.
To give the students an appreciation of the complex phe-
nomena of die swell, they are asked to determine the percent
increase in diameter. Only a qualitative comment on the
phenomena is expected, as further analysis is beyond the
scope of the unit operation experiment.
Comments
The temperature range in this experiment is intentionally
kept on the lower side of the typical operating temperatures,
primarily to observe a considerable difference in viscosity
with increasing temperature. Polystyrene would be a good
choice as an alternative material for the above experiment. It
is readily available and its hardening mechanism is governed
by vitrification rather than by crystallization. Rheological
properties would change differently as the glass transition
temperature is approached rather than as the melting point is
approached.
The students are graded on their ability to collect good
data, their application of theory to interpret results, their
understanding of the limitations of the experiment, and the
presentation of written and oral reports.


2.5E-07

() 2E-07

9 1.5E-07
a "
5 1E-07 *

5E-08

0 .. --
0 5 10 15 20
Screw rpm

Figure 4. Flow rate vs screw rpm: T-165C

Ejector Pins Die Screw Feeding Bin









Figure 5. Schematic of injection molding machine.
Spring 1995


EXPERIMENT 2: Injection Molding

Apparatus
The injection molding apparatus consists of a state-of-the-
art Allrounder 170 CMD fully hydraulic injection molding
machine manufactured by ARBURG. The machine consists
of a melt chamber with a screw that is capable of both rotary
and translator motions, a motor-drive assembly for the
screw, and a die that splits in two. The part of the die at the
screw end is stationary, and the other half is moved back
automatically to remove the part with the help of the ejector
pins. Figure 5 shows a schematic of the machine.
The polymer is fed from the bin. At the beginning of the
cycle the screw rotates and moves back, taking in a mea-
sured amount of the material. During the next phase of the
cycle the screw moves forward, building up the pressure,
and injects the melt into the die. The screw holds the pres-
sure for a preset holding time, and the material in the die is
then cooled for a preset cooling time. The mold opens and
the part is ejected out in the last phase of the cycle.
Even though the whole cycle is fully automatic, there are
over one hundred variables that can be set individually from
the control panel. The variables correspond to operating
conditions such as temperature and pressure, and the three
phases of the cycle-metering, injection, and cooling. In this
experiment, five of the most relevant variables are selected
for study. They are dosing volume, injection speed, injection
pressure, holding pressure time, and cooling time. To
maintain simplicity of experimental design and unifor-
mity among the experiments, all other variables are
kept constant.
Theory and Scope of the Experiment
As mentioned earlier, the goals and emphasis for
this experiment are different than the one on extrusion.
Since this experiment is designed for junior-level stu-
dents, the detailed mechanism of the injection molding
process (which involves nonlinear differential heat and
momentum transfer equations describing the fluid flow)
is beyond its scope. The goal is to educate the students
on the importance of good experimental planning when
there are a large number of variables present in a
process. They learn to isolate the significant variables
in the process.
The students have to understand the basic steps in-
volved in the injection molding operation and learn
how the machine is operated. They are asked to plan a
series of experiments to collect data that will enable
them to determine the set of variables that produces
the best part. They have to identify the effect of each
variable on the final product and assess the sensitivity
of each of the variables under study.
A "dogbone" shaped ASTM D638M 91-A standard
123











tensile test part is formed in the mold for this experiment.
The parts are analyzed using the following criteria:
1. Visual Inspection As is the practice in industry, the
part is scrutinized for the following defects:
Flash Extra material on the edge of molding which
has to be cut off
Bubbles Trapped air in the part
Surface Marks Marks of the flow lines on the surface that
damage the finish
Short Molding Incomplete sample
Shrinkage Indentation along the mold length
2. Weight of the sample
3. Tensile Strength The sample was tested on a tensile
testing machine (Instron 4301) to determine the yield strength
and the modulus of the sample. The gauge length was 50
mm, the grip length was 115 mm, and the crosshead speed
used was 500 mm/min according to the ASTM test men-
tioned above.
Experimental
Material Polypropylene HGZ 030 (manufactured by
Phillips) is used for this experiment. Its melting point was
determined to be 1680C using the DSC technique. The re-
ported melt index was 30, and the operating temperatures for
the barrel and the screw are fixed at 2000C.
Operating Conditions The following critical operating
conditions are selected for optimization:
1. Dosing Volume: Total volume (cc) of the material metered
in the barrel. The whole charge is injected in the mold.
2. Injection Pressure: The pressure (bars) that is generated by
the screw to charge the material in the mold.
3. Injection Speed: The volumetric speed (cc/s) at which the
screw charges the material. The barrel is divided into five
sections and the screw translational speed in each can be
controlled individually. In this experiment, only the speed


in the final section is allowed to vary; the speeds in the
other sections are kept constant.
4. Holding Time: The time (s) for which the pressure is
maintained by the screw at the mold after all the material is
charged.
5. Cooling Time: Total time (s) between the instant when the
charge is complete and when the part is ejected out of the
mold.
The students optimize the properties of the "dogbone"
sample by systematically varying the operating conditions.
The optimum sample is a complete sample with the least
defects requiring the shortest cycle time. The students are
required to select twenty samples for tensile test from the
samples that they visually analyze. A constraint on the num-
ber of the samples curbs haphazard runs and necessitates
careful planning of experiments. Of the twenty samples, five
must be made with identical conditions so that a statistical
deviation among the samples of the same batch and among
different sets can be compared.
A summary of the effects of the operating conditions on
the product is given in Table 2. The first column lists the
operating variable that was studied, and the second and third
columns describe, respectively, the effect of decreasing and
increasing the value of the variable on the sample.
Comments
Grading is based on the students' ability to plan the experi-
ments, to identify the effect of the operating conditions, their
interpretation of a large amount of data to arrive at the
optimum condition, and the general organization and pre-
sentation of their oral and written reports.
The experiment was carried out on a fully automatic as-
sembly, which is otherwise used for research work. A fre-
quent complaint from the students was the inability to make
a "bad" sample. A semiautomatic Newbury injection mold-
ing machine (Model H375-RS) is being considered for use
only in the undergraduate unit operations laboratory.


TABLE 2
Effect of Operating Conditions on the Properties of the Polypropylene Sample in the Injection Molding Machine


VARIABLE

Injection Speed


gLO
Sample weight is higher


HIGH

Sample weight is lowAer
Produces flash


Flow marks visible on the surface Increased minimum pressure required for molding
Injection Pressure Needs lower injection speed High injection speed is possible
Needs longer holding ume
Produces short shot
Dosing volume Produces short shot Produces Flash
Holding time Shorter cycle time Longer cycle time
Material shnnks back
Cooling Time Difficult to handle sample Longer cycle time
Deformation of sample as the sample remains soft


24 Chemical Engineering Education


I










ACKNOWLEDGMENTS
The authors would like to acknowledge the help of Minqui
Lu and Jeff Smith for their valuable suggestions during the
development of the experiments, and Rocky Chen and An-
drea Hailey for providing the data on the extruder experi-
ment.

REFERENCES
1. Crawford, R.J., Plastics Engineering, 2nd ed., Pergamon
Press, New York, NY (1987)
2. Progelhof, Richard C., and James L. Throne, Polymer Engi-
neering Principles: Properties, Processes, Tests for Design,
Hansen Publishers, New York (1993): McCrum, N.G., C.P.
Buckley, and C.B. Bucknall, Principles of Polymer Engi-
neering, Oxford University Press, Oxford, UK (1988)
3. Brandrup, J., and E.H. Immergut, Polymer Handbook, 3rd
ed., Wiley Interscience, New York (1989)
4. Bird, B.R., R.C. Armstrong, and O. Hassagar, Dynamics of
Polymeric Fluids, 2nd ed., Vol. I, Wiley-Interscience, New
York (1987)
5. Bird, R.B., W.E. Stewart, and E.N. Lightfoot, Transport
Phenomena, Wiley-International Edition (1960) 0



r =Mbook review



THE COMPLEAT CHEMICAL ENGINEER:
A Guide to Critical Thinking
by Robert B. Barat, Norbert Elliott
Kendall/Hunt Publishing Company, 111 Purina Drive, Dubuque,
IA 52001 (1993)

Reviewed by
Donald R. Woods
McMaster University

The main focus of this book is to improve critical thinking
and communication skills, especially in the context of
the senior laboratory. The book is founded on the four prin-
ciples that the authors describe in an essay for instructors:
take an interdisciplinary view, think critically, learn to
communicate effectively, and consider the impact of tech-
nology on society.
The authors produce a framework for introducing and
integrating these principles. The model that they use is one
of seeing the situation from four different points of view-
independent thought, intellectual breadth, cultural breadth,
and ethical awareness. They illustrate their application of the
model to the process of solving a mass and energy balance,
designing a process, and performing a laboratory experi-
ment. The seven-step strategy for doing the laboratory
(plan, execute, convert and integrate data, look for patterns,
reflect on the quality of the results, argue your results and
conclusions, and translate) is well illustrated by excerpts
Spring 1995


from various laboratory experiments. Although this is a
broad framework for thinking critically, few details are
given about how to actually do it. The premise is good; the
details are missing.
The topics address in the various chapters are:
Chapter 2, Interpreting the History of Chemical Engineer-
ing, introduces the heuristic of "particle, wave, field" and
asks us to apply these different viewpoints to a study of the
several historical decisions important to chemical engineers.
Chapter 3, Working in the Laboratory, describes the pur-
pose of experimentation, provides an 11-step strategy, lists
the usual safety regulations, gives seven very good guide-
lines for experimenting (e.g., penetrate the heart of the ex-
periment), gives checklists to troubleshoot experiments, dis-
cusses collaborative work, and provides assessment check-
lists. On the assessment forms that are given, I would have
liked to have seen the criteria given explicitly as well as
some items that assess critical thinking.
Chapter 4 on The Uses of Argument in Chemical Engi-
neering focuses more on error bars than on evidence, claims,
and qualifications. I would have liked more on the latter.
Chapter 5, Conducting the Literature Search, describes the
usual resources and strategies.
Chapter 6 on Ethics, gives a good but brief overview.
Some of the professional engineering association's Codes of
Ethics could have been given and applied to different cases.
The authors' tendency was to encourage the reader to create
his or her own code.
Chapter 7, Planning the Laboratory Environment, An Ar-
chitectural View, discusses the layout of a lab.
Engineers and the Environment, Chapter 8, uses a case
study to briefly illustrate the principles.
Communicating Information in Chemical Engineering,
Chapter 9, outlines the principles of writing to the audience,
and Chapter 10 describes the formats to use for different
types of reports and lecture notes. Chapter 11 illustrates how
to write lab reports and has a rich set of examples. The
marking of the communication is given. I would like to have
seen more assessment of critical thinking.
The last part of the book, "An Essay for Instructors,"
provides excellent suggestions about how to use the topics
and assignments in a variety of courses. The problems at the
end of each chapter are imaginative and illustrate the four
principles upon which the text is based. Some basic feed-
back forms are given; no index is given.
The book introduces a starting framework for indepen-
dence, breadth of viewpoint, and ethics. I wish there was
more explicit development of the themes. The book gives a
convenient collection of material on how to work in the
laboratory and how to write laboratory reports, but little is
given to develop critical thinking. 0











culum




A COURSE ON


TISSUE ENGINEERING


SUSAN L. ISHAUG, ANTONIOS G. MIKOS
Rice University Houston, TX 77251

Tissue engineering is a new and emerging interdisci-

plinary field that combines engineering, materials
science, and cellular biology knowledge to solve the
critical problems of tissue loss and organ failure. Approaches
involve using biological and synthetic materials, together
with mammalian cells, to create new tissues or biological
substitutes for functional replacement. Materials are used as
supportive matrices for functional cells, as necessary barri-
ers between transplanted cells and host tissues, or as stimu-
lants for a desired cellular response.
Chemical engineers are uniquely qualified to make sig-
nificant contributions to this new field since they can apply
the engineering principles of transport and reaction phenom-
ena to understand the biological processes occurring in the
human body. The undergraduate chemical engineering cur-
riculum requires courses in organic chemistry, which are
usually prerequisites for biochemistry and cellular biology
courses, and also offers electives in materials science and
engineering. This basic training gives chemical engineers an
advantage over other engineering disciplines in communi-
cating with life scientists and clinicians to investigate prob-
lems in medicine and to respond to challenges for new
technological developments.

Susan L. Ishaug is a chemical engineering gradu-
ate student at Rice University. She received her
BS from the University of Minnesota in 1991, and
her research interests focus on bone tissue engi-
neering with polymer/cell constructs.


Antonlos G. Mikos is T.N. Law Assistant Profes-
sor of Chemical Engineering and Bioengineering at
Rice University. He received his DiplEng in 1983
from the Aristotle University of Thessaloniki, Greece,
his PhD from Purdue University in 1988, both in
chemical engineering, and was a postdoctoral fel-
low at Massachusetts Institute of Technology and
Harvard Medical School during 1990-91. His re-
search interests are in tissue engineering and tar-
geted drug delivery.
Copyright ChE Division ofASEE 1995


Chemical engineers are uniquely qualified
to make significant contributions to this new field
since they can apply the engineering principles
of transport and reaction phenomena to
understand the biological processes
occurring in the human body


Engineering, materials science, and cellular biology are
distinct disciplines, and their courses do not usually cover a
specialized subject such as tissue engineering in sufficient
depth. This course aims to not only teach aspects of engi-
neering and cellular biology in the same semester, but also to
present them in such a way that the student learns the cellu-
lar phenomena involved in tissue development and growth
and gains an appreciation of the role of biochemical and
mechanical environment in regenerating tissues.
Classes are held in a traditional lecture format, but empha-
sis is placed on class discussions and question/answer
sessions. It is ultimately a design course in which students
use fundamental concepts and principles to develop ways
to regenerate tissues and methods to replace the function
of diseased organs. The three-credit-hour course meets
two days a week during the semester. It is offered as an
elective to graduate students of any discipline, but it appears
to be predominately of interest to science and engineering
majors. The course was first offered in the spring of 1993
and was attended by seventeen students, including two
students of the Baylor College of Medicine/Rice University
MD/PhD program.

COURSE CONTENT
The course content includes background information on
biomaterials, cell/tissue interactions with materials, tissue
development and growth, and new approaches to tissue re-
generation and replacement of function (see Table 1). We
devote approximately half of the semester to covering back-
ground information since this knowledge is essential for
discussing the design of biological substitutes.
In their natural environment, cells are surrounded by ex-
tracellular matrix (ECM). Biomaterials used in tissue-engi-
neering constructs are generally designed to simulate the
Chemical Engineering Education


MwCUrh~











environment experienced by cells and can therefore be
referred to as ECM analogs. In attempting to regenerate
tissues, some form of ECM is required to either organize
transplanted cells or recruit cells from the surrounding
tissue. We review the role of natural ECM found in the
body to inform the students of its importance in holding
together and compartmentalizing tissues. These ECM
molecules can be isolated and used in tissue-engineering
constructs, or synthetic materials can be manufactured
for the same purpose. A majority of these ECM analogs
are polymers of synthetic or biological origin; therefore,
we present a brief review of polymer chemistry, cover-
ing topics such as polymer chain types, kinetics, thermo-
dynamics, morphology, mechanical properties, synthe-
sis, and fabrication techniques. We also discuss the chemi-
cal structure and morphology of the most common syn-
thetic and natural polymers used in tissue engineering,
with emphasis on structure-property relationships.
The surface, biochemical, and mechanical environ-


TABLE 1
Course Outline

Extracellular Matrix Analogs (3 lectures)
Extracellular Matrix
Synthetic Polymers
Natural Polymers
Regulation of Cell Function (4 lectures)
Cell Adhesion
Cell-Biomaterial Interactions
Cell Migration
Cell Metabolism

Tissue Development and Growth (6 lectures)
Tissue Remodeling
Tissue Repair
Angiogenesis
Inflammatory Response
*Immunoprotection
Drug Delivery
Tissue Engineering Approaches (10 lectures)
Tissue Induction
1> Skin, Nerve, Esophagus, Blood Vessel
t> Tendon, Ligament, Bone
Cell Transplantation
> Skin, Cartilage, Bone
> Endothelium, Urothelium, Intestine, Nervous System
1> Liver, Kidney
Biohybrid Organs
> Liver
> Pancreas
Blood Substitutes
Gene Therapy
1> Cardiovascular System
> Other Systems
Tissue Engineering Products (2 lectures)
Patents
Regulations


Spring 1995


ment encountered by cells has a direct effect on their function and
thus determines the success of a cell-based therapy. The environ-
ment created by the materials used in tissue-engineering approaches
must be appropriate to promote the desired response from trans-
planted or recruited cells. In order to understand how the environ-
ment should be altered to achieve a desired cellular response, we
give lectures on the variety of factors that influence the function
and survival of cells, such as cellular adhesion, cell-biomaterial
interactions, and migration, as well as metabolism.
We present an example that demonstrates the importance of
cellular adhesion in anchorage-dependent mammalian cells which
need to adhere to a substrate in order to grow and retain their
phenotypic expression. The involvement of adhesion molecules
and cell-surface receptors in cellular phenomena suggests that
biomaterials used in tissue engineering should mimic their natural
counterparts, the ECM of the body. We discuss cellular adhesion,
with emphasis on the role of adhesive receptors and adhesion
recognition sequences. We also consider the engineering of intelli-
gent biomaterials with immobilized adhesion recognition sequences
for targeted cellular adhesion, using illustrated examples of the
effects of substratum chemistry on cellular physiology.
Cellular migration is also regulated by receptor/ligand adhesive
interactions. We review the mechanisms of cellular motility and
locomotion and discuss contact inhibition. We analyze the cellular
binding and trafficking processes and present mathematical mod-
els to better understand receptor-mediated cellular functions and
the effects of cytokines and growth factors on cellular migration.
Cellular adhesion, migration, and metabolism are all interre-
lated. The vascular and skeletal systems provide excellent ex-
amples of this interplay, and we discuss them along with the
influence of the biochemical and mechanical environment on cel-
lular metabolism. We cover the stress and strain effects on vascu-
lar gene expression as related to the production of therapeutic
molecules for vascular proliferative diseases. We also analyze the
mechanical load effects on osteoblast proliferation and migration
and the production of bone matrix proteins, which are all impor-
tant in the bone remodeling process.
Tissue development and growth is a complex process involving
many cells and components. Understanding the process of natural
tissue development and growth is necessary to appreciate the cel-
lular or mechanical components of the different tissue-engineering
approaches presented in later lectures. We teach tissue develop-
ment and growth processes in separate lectures that focus on tissue
remodeling, tissue repair, angiogenesis, inflammatory response,
immunoprotection, and drug delivery, all of which are described
below.
Dynamic processes occur constantly in healthy as well as in
injured tissue. Bone is an excellent example of a tissue that con-
tinuously remodels itself. In one lecture we discuss the steps
involved in bone remodeling so that students can understand the
role of the cellular, biochemical, and mechanical environments in
tissue remodeling. We devote another lecture to wound healing as
an example of tissue repair because this naturally occurring pro-
127










cess has been extensively studied and offers the chance to
observe the actual repair and regeneration of tissue. We
review in detail the roles of the cells and ECM components
involved in the different steps of wound healing.
Many metabolic organs, including the liver, are highly
vascularized. A high frequency of blood vessels throughout
the liver is necessary for the survival of the cells housed
within, as well as for their vascular, secretary, and metabolic
functions. Therefore, while creating a new construct to re-
generate such a vascularized organ, the mass transport prin-
ciples specific for nutrient diffusion and waste removal must
be considered. We address the need for angiogenesis (the
formation of new blood vessels) to occur within the con-
struct, as well as the angiogenic factors and inhibitors in-
volved in the vascularization mechanism.
The materials or cells used in organ regeneration or re-
placement devices may come in direct contact with blood or
tissues, and therefore they must be biocompatible. A com-
plete understanding of the immunological response to for-
eign materials or cells is necessary in order to develop a
system that is immunologically "invisible." We present a
review of immunology to teach the students about those
cells and other components involved in immune and inflam-
matory responses, including the chemical mediators of in-
flammation, phagocytosis, and foreign-body reaction. We
also outline methods for developing materials that do not
elicit an immune response.
Synthetic or natural biodegradable polymers used as cell
transplantation and tissue induction scaffolds can also serve
as controlled release systems to deliver bioactive molecules.
Many tissue-engineering scenarios require the local release
of angiogenic, growth, and differentiation factors to facili-
tate the development and growth of new organoids. There-
fore, we present drug delivery systems based on biodegrad-
able polymers, with emphasis on design parameters and
drug-release kinetics.
The next section of the course deals with case studies of
strategies for the creation of new tissues, including tissue
induction, cell transplantation, biohybrid organs, blood sub-
stitutes, and gene therapy. We give a brief overview of the
existing options to replace human tissue before each case
study, stressing their shortcomings and emphasizing the great
need for alternative methods.
Tissue induction techniques rely on the recruitment of
cells from the tissue surrounding the implant site into
biomaterial matrices. These matrices are designed to aid the
regeneration process by providing a suitable environment
for the organization and function of the recruited cells and
tissue. We examine the principles of tissue induction and
follow with illustrated examples of how this technique is
being explored to regenerate tissues. We cover practices for
regenerating skin, nerve, esophagus, and blood vessels in
128


one lecture, whereas those for tendon, ligament, and bone
are covered in another lecture.
Transplantation of isolated cells seeded onto polymer ma-
trices provides another method for regenerating organs and
tissues. These matrices serve the same purpose as those used
in tissue induction techniques, but may have to be designed
differently to accommodate the introduction of isolated cell
populations. We explore the material requirements of cell
transplantation scaffolds, along with case studies for regen-
erating skin, cartilage, bone, endothelium, urothelium, intes-
tine, nervous system, liver, and kidney.
Biohybrid organs may provide yet another means of re-
placing functions lost by diseased or injured organs. Biohybrid
organs are artificial systems that use cells donated by a
different person or animal for functional replacement of
metabolic organs. In these systems, the donor cells are iso-
lated from the host by semipermeable membranes which
allow for the passage of metabolites but not immunogenic
molecules. We analyze the function of biohybrid organs,
using chemical engineering principles such as mass trans-
port since multiple nutrient transport barriers exist between
the encapsulated cells and the host's blood vessel, all of
which take part in the overall diffusion limitation of the
devices. In one lecture we present the important membrane
parameters and other design parameters for cell immobiliza-
tion devices, such as intravascular stents, macrocapsules,
and microcapsules, whereas biohybrid liver and pancreas are
covered in separate lectures.
The prime function of the red blood cells is to transport
oxygen to various parts of the body. Blood substitutes are
bioartificial constructs designed to replace this function when
it is compromised. The development of blood substitutes
would be advantageous in circumventing the problems aris-
ing from the lack of blood donors, the transfer of blood-born
pathogens in transfusions, and long-term storage. We there-
fore cover the important criteria that must be considered in
the design of blood substitutes, along with methods to fabri-
cate blood substitutes and ways to assess their performance.
The advances of the growing field of genetic engineering
can be used in tissue engineering. Gene therapy may be
defined as the introduction of genetic material into cells to
alter selected cellular functions. This technique may be used
to deliver enzymes, proteins, or other compounds produced
by the genetically modified cells. One lecture focuses on
cardiovascular gene transfer and another concentrates on
gene transfer applied to other systems, including the blood-
clotting, hematopoietic, and hepatic systems.
A lecture on patents is appropriate since one should be
aware of the means of protecting intellectual property devel-
opments. We therefore discuss the patentability requirements
of an invention and the formal requirements of a patent,
along with giving examples of tissue-engineering patents.
Chemical Engineering Education










We conclude the course with an overview of the FDA
regulations for tissue-engineering product investigations. We
present the guidelines for human biological products and the
procedures for submitting an investigational new drug
application in order to give the students an appreciation
of the series of tests required to bring a tissue-
engineering product to market.

COURSE WORK
Students are graded on their participation in class discus-
sions, one in-class exam, and a group project. The project
requirements consist of a written paper and a thirty-minute
oral presentation. The students are divided into groups of
two or three and are allowed to choose an organ or tissue
which they investigate and for which they devise a tissue-
engineering strategy. The students are encouraged to use the
knowledge they gained in the course, together with past
engineering and scientific experience, to develop an innova-
tive method to regenerate an organ or improve an existing
method. In the spring of 1993, seven design project topics
were chosen by the class and involved strategies to regener-
ate the pancreas, kidney, bone marrow, intestine, breast,
blood vessel, and nerve.

RESOURCE MATERIAL
It is difficult to find just one textbook for this course since
it covers such a broad range of subjects. Most of the resource
material used is from research and review articles in journal
publications, proceedings, or books. Two excellent review
articles on tissue-engineering accomplishments, challenges,
and directions were recently published in Science.11'21 The
key chemical engineering principles involved in tissue engi-
neering (mass transport and materials synthesis and fabrica-
tion) are presented in a recent article in Chemical Engineer-
ing Progress.1" A few of the important journals that publish
articles related to tissue engineering include ASAIO Journal,
Annals of Biomedical Engineering, Biomaterials, Biotech-
nology and Bioengineering, Cell Transplantation, Diabetes,
Human Gene Therapy, Journal of Applied Biomaterials,
Journal of Biomechanical Engineering, Journal of Biome-
chanics, Journal of Orthopaedic Research, Journal of Bio-
medical Materials Research, Transplantation, and Trans-
plantation Proceedings. Surgical journals, such as Journal
of Bone and Joint Surgery, Journal of Craniofacial Surgery,
Journal of Pediatric Surgery, and Plastic and Reconstruc-
tive Surgery, also publish articles on tissue engineering.
Starting in January of 1995, a new journal, Tissue Engi-
neering, will be published. Also, Biotechnology and Bioengi-
neering has published two special-issue volumes14'51 that in-
clude only articles related to the subject. The Journal of
Biomechanical Engineering, as well, had a special issue
on tissue engineering.[6'
The Materials Research Society also published two sym-
Spring 1995


posium proceedings devoted to tissue-engineering topics.[7'81
Two additional proceedings publications [9,10] contain useful
articles-though most of them may now be outdated.
Currently, many organ regeneration and functional re-
placement methods are either in pre-clinical or clinical trials;
therefore, new information is constantly appearing in the
literature. We recommend performing literature searches to
uncover the most recent work in this new field before teach-
ing a similar class. An edited volume by Hay'"1 includes
useful review articles on ECM metabolism and regulation of
tissue development and growth, and a book by Lauffenburger
and Linderman"'21 is an excellent reference on receptor-
mediated cell function, including cell adhesion, migration,
and metabolism. A book by Fung"13] is a valuable reference
on cell and tissue mechanics and the role of mechanical
environment on tissue remodeling and repair, while a
handbook by Culver"141 presents the methods for gene trans-
fer and summarizes the most recent developments in gene
therapy for treating non-neoplastic disorders. Finally,
the conference proceedings of an annual continuing-
education course offered by Rice University"s51 may be a
helpful reference material.

REFERENCES
1. Langer, R., and J.P. Vacanti, "Tissue Engineering," Science,
260, 920 (1993)
2. Peppas, N.A., and R. Langer, "New Challenges in
Biomaterials," Science, 263, 1715 (1994)
3. Cima, L., and R. Langer, "Engineering Human Tissue,"
Chem Eng. Progr., 46, June (1993)
4. Hubbell, J.A., B.O. Palsson, and E.T. Papoutsakis (eds),
"Special Issue: Tissue Engineering and Cell Therapies: I,"
Biotechnol. Bioeng., 43, 541 (1994)
5. Hubbell, J.A., B.O. Palsson, and E.T. Papoutsakis (eds),
"Special Issue: Tissue Engineering and Cell Therapies: II,"
Biotechnol. Bioeng., 43, 683 (1994)
6. Heineken, F.G., and R. Skalak (eds), "Special Issue on Tis-
sue Engineering," J. Biomech. Eng., 113, 111 (1991)
7. Cima, L.G., and E.S. Ron (eds), "Tissue-Inducing
Biomaterials," MRS Symposium Proceedings, Vol. 252, Ma-
terials Research Society, Pittsburgh, PA (1992)
8. Mikos, A.G., R. Murphy, H. Bernstein, and N.A. Peppas
(eds), "Biomaterials for Drug and Cell Delivery," MRS Sym-
posium Proceedings, Vol. 331, Materials Research Society,
Pittsburgh, PA (1994)
9. Skalak, R., and C.F. Fox (eds), Tissue Engineering, Alan R.
Liss, New York, NY (1988)
10. Woo, S.L.-Y., and Y. Seguchi (eds), Tissue Engineering-1989,
The American Society of Mechanical Engineers, New York,
NY (1989)
11. Hay, E.D. (ed), Cell Biology ofExtracellular Matrix, 2nd ed.,
Plenum Press, New York, NY (1991)
12. Lauffenburger, D.A., and J.J. Linderman, Receptors: Mod-
els for Binding, Trafficking, and Signaling, Oxford Univer-
sity Press, New York, NY (1993)
13. Fung, Y.C., Biomechanics: Mechanical Properties of Living
Tissues, 2nd ed., Springer-Verlag, New York, NY (1993)
14. Culver, K.W., Gene Therapy: A Handbook for Physicians,
Mary Ann Liebert, New York, NY (1994)
15. Advances in Tissue Engineering, Conference Proceedings,
Rice University, Houston, TX (1994) O











W class and home problems


PROBLEMS ON

FLUIDS IN MOTION AND AT REST


A.R. KONAK
Southern Alberta Institute of Technology Calgary, Alberta, Canada T2M OL4


Engineering courses should not be presented as a dry
set of facts, experiments, and calculations; they should
have a context related to practical applications and
daily experiences in order to awaken the students' curiosity
and awareness. The following potpourri of classroom and
home problems, the second in a series,111 are short and meant
to be thought provoking. Mixed in with standard exercises,
they can provide variety and a better understanding of the
fundamentals of fluid flow, statics, and related phenomena.

(PROBLEMS

1. a) Why does a stream of water coming out of a tap get
progressively thinner? b) What is the relationship be-
tween the velocities at the exit of the tap and at a
distance, d, below the exit?
2. Explain why bacteria living in the air find life just as
"viscous" as people would find if they were living in a
viscous fluid-say, honey.
3. Why are golf balls dimpled and tennis balls smooth?
4. It is possible to suspend a table tennis ball or a golf ball
in the exhaust of a powerful vacuum cleaner, and the
ball will not escape the air stream on its own. Explain
why this situation is pretty stable.
5. The heart beats about 72 times a minute at rest. Over
two ounces (70 mL) of blood are pumped at an average
Copyright ChE Division ofASEE 1995


A. Riza Konak received his BSc and PhD de-
grees in chemical engineering from the University
of Birmingham (England). He started his career
as assistant professor, and then spent fifteen years
in industry, mostly in applied research and devel-
opment and engineering with a major oil and gas
company, before returning to academia. He cur-
rently teaches unit operations, process design,
simulation, and control.


pressure of 100 mm of mercury per beat. Estimate the
power developed by the heart. Is the result surprising?
6. Explain how blood would flow at much higher rates
than normal during a strenuous exercise without caus-
ing excessive blood pressure.
7. The blood pressure of a giraffe lying down is measured
at 120 mm of mercury. The blood pressure doubles
when the animal stands up. If the heart of a standing
giraffe is 1.8 m above the ground, what would be its
height? The specific gravity of mercury is 13.6. State
your assumptions.
8. A waiter brings you a cup of coffee. While he is putting
it down on the table he turns the cup around so that the
handle faces you. Did the coffee move with the cup, or
did it remain still?
9. In Florentine (Italy) in the seventeenth century, well
diggers observed that, in suction pumps, water would
not rise more than about 10 meters. In 1642 they came
to the famous Galileo for help, but he did not want to be
Chemical Engineering Education


The object of this column is to enhance our readers' collections of interesting and novel
problems in chemical engineering. Problems of the type that can be used to motivate the student
by presenting a particular principle in class, or in a new light, or that can be assigned as a novel
home problem, are requested, as well as those that are more traditional in nature and which
elucidate difficult concepts. Please submit them to Professor James O. Wilkes (e-mail:
wilkes@engin.umich.edu) or Mark A. Burns (e-mail: maburns@engin.umich.edu), Chemical
Engineering Department, University of Michigan, Ann Arbor, MI 48109-2136.










bothered with the problem and delegated it to his dis-
ciple, Toricelli. How did Toricelli explain the mystery?
10. An owner of a sailboat decides to check out the speed of
his boat by using an L-shaped tube. The horizontal leg
of the tube is immersed in water facing in the direction
of travel, while the four-meter long vertical leg is above
the water level. What is the maximum speed the owner
can measure? What improvements can you suggest?
11. Why does hydrogen travel twenty-two times faster than
carbon dioxide in a straight pipe of uniform cross sec-
tion at the same temperature, pressure, and mass flow
rate? You may assume ideal gas relationship holds for
both fluids.
12. A small boat is floating in a swimming pool. Which of
the following events raises the water level more in the
pool? a) A rock is dropped directly into the pool. b) The
same rock is placed in the boat.
13. In which of the following media is the velocity of sound
highest and lowest? Air, water, steel.
14. The velocity of sound is nearly the same in water and
mercury, although mercury is 13.6 times as dense as
water. Why?
15. Atmospheric air at room temperature (200C) is allowed
to enter an initially evacuated and insulated container.
Estimate the temperature of air in the container when it
is full.
16. A group of mountaineers reaches the top of a mountain
and discovers that water boils at 850C. What informa-
tion do they need to estimate their altitude? What is
their altitude?

SSOLUTIONS

1. a) Water coming out of a tap accelerates as it falls.
Since the volume of water is constant and is equal to
volume times the area, the cross-sectional area gets
smaller downstream.
b) Bernoulli's equation between the two points indi-
cated in Figure 1 yields

S2 P 2
+PI +z =-2 + +
pg 2g pg 2g 2
where P, = P2 = atmospheric pressure and cancel out
each other. Therefore we have
2 2
2 =v +2gd
It is interesting to note that this is the famous free fall
formula for a body falling a distance d = z, z2 under
the influence of gravity, with an initial velocity v, and
final velocity v2.
2. Let's take some typical numbers for the average size of
bacteria ~ 10-m, which is moving at -103m/s, say, in
Spring 1995


air whose kinematic viscosity is -10-5m2/s (the bacteria
might be floating in air like a bunch of very small dust
particles). The Reynolds number is

(10- m)(10-3m/s) =
10- m2 /s

Thus, although the air has very low viscosity, the bac-
teria would find life very viscous due to their size and
slow movements. As Shapiro points out,[21 it is more
meaningful to speak of a very viscous situation than of
a very viscous fluid.
3. Golf balls initially started out smooth, but it was dis-
covered, quite accidentally, that scarred balls went fur-
ther than the smooth ones. This discovery led to dimpled
golf balls. The classical explanation involves the bound-
ary layer around the ball that becomes turbulent for a
dimpled ball before it does for a smooth one. The
turbulent layer remains attached to the ball longer and
thus produces a smaller wake and a smaller drag. A
table tennis ball, on the other hand, goes slower and
roughening increases the friction drag. Shapiro[21 cov-
ers this phenomenon in great detail.
4. As soon as the ball strays out of the air stream, the air
flows faster on the opposite side where the streamlines
are straight; an increase in speed means a decrease in
pressure, as would be predicted by the Bernoulli's equa-
tion, and so the ball tends to move back into the air
stream.
5. The power developed by the heart is equal to the pres-
sure developed times the flow rate. Since 100 mm of
mercury = 13330 Pa

Power=(13330Pa)(70 x10-6 x 72/60m3 /s)=1.12W

or, say, 1 watt. This is a surprisingly low number and is
about 1% of the total power generated by the body.
6. During normal body function, the blood flow is,[31 say,
(70 mL / beat)(72 beats / min) = 5040 mL / min = 5 L / min
During an exercise the blood flow may be


Figure 1










(200 mL/ beat)(120 beats/ min)= 24000 mL/ min = 24 L / min
This is almost a five-fold increase. When blood flows
at a steady rate through long, smooth vessels, the flow
is laminar; turbulent flow is encountered under some
conditions, such as in the root of the aorta and at the
major arterial branches. The laminar flow is governed
by Poiseuille's law, which states that the rate of blood
flow is directly proportional to the fourth power of the
diameter of the vessels. In the body as a whole, about
two-thirds of the flow resistance to circulation is in the
small blood vessels with diameters that can range be-
tween 8 and 30 micrometers,141 but they have strong
vascular walls that allow the internal diameters to change
by as much as four-fold. From Poiseuille's equation we
can see that a four-fold increase in vessel diameter
theoretically could increase the flow by as much as
256-fold.
7. The additional pressure which the heart must over-
come when the animal is standing is 120 mm of mer-
cury, or
(120)(13.6/1)= 1632mm of water
or 1.6 m of water. Hence, the head of the giraffe is 1.6
m above its heart, assuming that the specific gravity of
blood is the same as water and is equal to one. Thus the
giraffe is
1.6+1.8 = 3.4m tall
8. The famous "no slip at the wall" principle of hydrody-
namics tells us that a very thin layer of coffee will
attach to the cup and will move with it; most of the
coffee, however, will remain stationary.
9. Toricelli figured out that water was not being pulled up
by the vacuum, but rather was being pushed up by the
local air pressure. When the pump lowered the air
pressure above the column of water, the normal air
outside the pump pushed down harder on the ground
water, forcing the water in the pipe upward. Toricelli
checked out his theory by using a column of mercury
and a bowl of mercury, and that led to his discovery of
the first barometer. Since the local air pressure is about
equal to 10 m of water (760 mm of mercury), a suction
pump will not raise water if the water level in the well
is more than about 10 m.
10. The device described is basically a Pitot tube. The
maximum velocity that can be measured is given by

v(max)= (2)(9.81m/s2)(4m)] =8.86m/s=32km/h

A Bourdon tube attached to the long leg would consid-
erably increase the range of velocity, also simplifying
the device. A Bourdon tube consists of a flattened tube,
shaped as a segment of a circle or spiral. The increased
pressure inside the tube straightens the tube a little.


The movement at the end of the tube is transmitted
through a linkage which causes a pointer to rotate, thus
giving an indication of pressure.
11. The mass flow rate of gas is
G= Aup
where
A = pipe cross-sectional area
u = average velocity of the gas
p = density of the gas
The ideal gas law is
SpRT
P=
M
where P, R, T, and M are pressure, gas constant, tem-
perature, and molar mass, respectively. Combining these
two equations gives
u=(GRT{ i)
AP )M)
Thus, the average velocity is inversely proportional to
the molar mass. Since respective molar masses of car-
bon dioxide and hydrogen are 44 and 2, hydrogen
travels 22 times faster.
12. Archimedes' principle states that an object that is to-
tally or partially immersed in a fluid is acted upon by a
buoyant force equal to the weight of fluid displaced.
When the rock falls to the bottom of the pool, the water
level rises in proportion to the volume of the rock.
When the same rock is placed in the boat, however, the
level rises higher because the buoyant force is greater;
that is, the amount of water displaced is larger than
before, causing the boat and the rock to float. Using
Archimedes' principle, it can be shown that the volume
of water displaced when the rock is in the boat is equal
to the volume of the rock times the relative density of
the rock (relative density being the density of rock
divided by the density of water).
13. The velocity of sound is highest in steel and lowest in
air. Generally, the more incompressible the medium,
the higher the sonic velocity. At room temperature the
approximate sonic velocities in air, water, and steel are
340, 1480, and 5100 m/s, respectively.
14. The sonic velocity is given by

E 1/2
LP
where E is the bulk modulus and p is the density of the
material. The E values of water and mercury are 2.13
and 28 GPa, respectively. Since mercury is 13.6 times
denser than water, the E/p ratios are about equal.
A similar situation arises with aluminum and steel. The
E values for aluminum and carbon steel at room tem-
perature are 69 and 207 GPa, respectively, while their
Chemical Engineering Education










densities are 2710 and 7860 kg/m3.[51 Thus, the sonic
velocity in steel is
112
207x109pa 5132m/s
7860kg/m3 5132m

and in aluminum is

S69xl 09pPa 1.s/2
2710kg/m3J =5046m/s

As mentioned in the solution to Problem 13 above, the
more incompressible the medium (the larger the E
value), the higher the sonic velocity. But the higher the
density of the medium, the lower the sonic velocity-
due, presumably, to the closely packed atomic struc-
ture of the medium. The examples cited above indicate
that one factor might work against the other for two
completely different materials.
15. The air inside the container is not in motion and hence
its total energy is in the form of internal energy. Once
the container is full, this internal energy is supplied by
the atmospheric air filling in the container. Therefore,
the internal energy of air in the container at the final
temperature T, equals the enthalpy of atmospheric air
at 200C. Or, in equation form

c T =c T.
vTf p air
R Rk
k-l k-1 air
or
T = kTai =1.4(20+273)=410.2 K=137.20C

Here, R is the gas constant and k is the ratio of specific
heats cv and c, at constant volume and constant pres-
sure, respectively. Thus, there is a considerable in-
crease in temperature under adiabatic conditions.
16. They need to know the vapor pressure of water at 85C
and the properties of standard atmosphere at different
heights. The vapor pressure of water at 85C is 57.81
kPa from the steam tables. This corresponds to about
4440 m height in the table which gives the properties
of the atmosphere (e.g., see Table A.3, The Properties
of U.S. Standard Atmosphere, in reference 6).

REFERENCES
1. Konak, A.R., "Magic Unveiled Through the Concept of Heat
and Its Transfer," Chem. Eng. Ed., 28(3), 180 (1994)
2. Shapiro, A.H., Shape and Flow, Heinemann (1981)
3. The American Medical Association, Home Medical Library,
'Your Heart," The Reader's Digest Association Inc. (1989)
4. Guyton, A.C., Textbook of Medical Physiology, W.B. Saunders
Co. (1991)
5. Callister, Jr., W.D., Materials Science and Engineering: An
Introduction, 3rd ed., John Wiley and Sons (1994)
6. Fox, R.W., and A.T. McDonald, Introduction to Fluid Me-
chanics, 4th ed., John Wiley and Sons (1992) O
Spring 1995


[] letter to the editor

To the Editor:
I appreciate the inclusion of appropriate quotations from
my book The Interpretation and Use of Rate Data. The Rate
Process Concept, revised printing, Hemisphere Publishing
Coprporation, Washington, DC (1979), in the excellent ar-
ticle by Shacham and Brauner in Chemical Engineering
Education, 29(1), p. 22. However, I wish to point out that the
ungrammatical phrase in the last sentence of their article,
namely, "data justifies," appeared correctly as "data justify"
in my book, page 309.
Stuart W. Churchill
Carl V.S. Patterson Prof. Emeritus
University of Pennsylvania


REVIEW: Polymer Molecules
Continued from page 93.
tions of one of the authors suggest some personal bias re-
garding the inclusion of this chapter. In fact, I found no
references to this material in the last two chapters. Although
I have no argument with the importance of the topics cov-
ered in Chapter 7, I suspect that most faculty members using
the book for a course will skip over this material unless their
research interests lie in this area. To the authors' credit, they
do state in the Preface that this chapter "can be studied or not
depending on the interests of the reader."
In the final two chapters, the authors apply the principles
established in Chapters 5 and 6 to two very important areas:
rubber elasticity in Chapter 8 and polymer solutions in Chap-
ter 9. Both of these areas typically receive a few pages each
in traditional undergraduate polymer science textbooks. In
these treatments, a simplistic physical description is fol-
lowed by the end result, an equation for students to apply in
problems at the end of the chapter. It is refreshing to see
more complete descriptions and detailed derivations in both
areas. For example, many textbooks are content to give the
expression for solvent activity from Flory-Huggins theory as
gospel for polymer solutions. In Chapter 9 the authors derive
the configurational entropy of mixing for Flory-Huggins
theory, discuss the limitations of the theory, and develop
newer treatments such as equations of state.
In summary, I recommend The Science of Polymer Mol-
ecules for consideration as a textbook for a graduate course
in polymer science or polymer physical chemistry. Problems
are included at the end of each chapter, evidence that the
authors were serious about writing a textbook for graduate
students in this area. With minor exceptions, The Science of
Polymer Molecules is presented in a reader-friendly manner
that will further motivate students with an interest in macro-
molecules and their behavior. 0











M classroom


TERSE WORDS

IN TIGHT MARGINS



ROBERT R. HUDGINS
University of Waterloo Waterloo, Ontario, Canada N2L 3G1


here does the undergraduate chemical engineer
encounter professional criticism? In the early un-
dergraduate years, most feedback either comes
indirectly through successful course examinations or directly
through the grading of assigned homework problems and lab
reports. Thus, on a day-to-day basis, guidance comes chiefly
in the margins of graded assignments and reports. It is there
that the terse comments, scribbled hurriedly by graders (e.g.,
teaching assistants and, more rarely, course instructors), be-
come the aspirant's routine source of evaluation and im-
provement. It therefore makes good sense to carefully con-
sider the nature of such commentary.
Let me begin with a typical smattering of critical com-
ments that I, for one, have been known to write in a paper's
margins.
Explain
Justify
Not so!
Omit
So what?
Vague
Comments like these are concise and arresting. They send
the author a quick diagnosis without providing detail. Or do
they? Perhaps graders just assume that the comments will be
regarded as useful corrections. Could the recipient also in-
terpret a given remark as a question that occurred to the
grader, or an exclamation, a form of encouragement, a pleas-
antry, or even an insult? Delivered aloud by a competent
actor, any one of the above comments could be made to fit
almost any of these categories; the spoken word can convey
levels of emotion that exceed by far the face value of a word
or phrase. But written in the margin of a graded report, hasty
words of judgment acquire levels of emotion supplied by the
reader. Some students may find them gruff, while others
may find the same words straightforward and direct. In any


Bob Hudgins holds degrees in chemical engi-
neering from the University of Toronto and
Princeton University. He teaches courses in
stoichiometry, unit operations,and reaction en-
gineering, and studies the periodic operation of
catalytic reactors.

case, different messages can be conveyed by critical re-
marks, depending on who reads them.
According to studies on personality differences, there are
distinct responses to criticism, depending on whether an
individual operates in a "thinking" or a "feeling" mode.11
Those who prefer to function in the thinking mode would
find such criticism candid and would tend to appreciate it,
while those who prefer feeling would hear it as gruff and
would respond with discomfort at its lack of compassion.
Criticism untempered by sympathy causes "feelers" to be-
come defensive; this impairs their learning rather than helps
it. At the same time, it is self-evident that to be useful,
criticism must be presented in a manner that makes it accept-
able to its audience. Therefore, to include as many different
personalities as possible in this audience, it is important to
satisfy both thinkers and feelers.
The following is a true story that shows the need for
sensitivity in offering criticism. Recently, I heard of an engi-
neering faculty that considered introducing a scheme in which
students could provide continuous anonymous feedback on
their instructors' teaching. The technology supporting the
scheme was in-house electronic mail. After much debate,
however, the proposal was abandoned because of concern
over its potential to hurt faculty members' feelings. In a
sense, this seems a surprising reason to drop an inherently
beneficial program. And yet, quite apart from the issue of
tactless wording, sensibilities can sometimes be bruised with


Copyright ChE Division ofASEE 1995


Chemical Engineering Education










unexpected ease. Even something as innocent as LAPSING
INTO UPPER CASE PRINT MAY PROVOKE AN ELEC-
TRONIC MAIL RESPONDENT TO COMPLAIN, "Why
are you shouting?" In a similar vein, it is not uncommon to
find people for whom a machine-written letter is inherently
less courteous than one written by hand, even though the
content is identical and the machine version might well be
more legible. The point is, criticism is often difficult to
accept, and the form in which it is offered may itself foster
resentment.
Appreciative comments, on the other hand, are hard to
misconstrue no matter how terse. We can all use a little
encouragement.
Excellent!
Original approach
Thorough analysis.

It seems that only when the grader finds fault does terse-
ness become a difficulty! This leads me to conclude that in
providing feedback, a grader can offer encouragement with
tombstone brevity. By contrast, however, negative criticism
often creates confusion and/or raises hackles unless it is
done sympathetically and thoroughly.
It is scarcely novel that one- or two-word comments are
sometimes far from self-explanatory. This is precisely the
problem a marker encounters in trying to second-guess an
answer submitted in point-form. It is why we sometimes
remind students to answer a question in complete sentences.
It is also why just about everyone has trouble understanding
how to complete business forms. I recall a joke about a
would-be employee filling out a job application form; seeing
the word "Sex" following by spaces preceded by the letters
M and F, the applicant uses the F to write "Frequently."
With such potential for misunderstanding lurking behind
suggested corrections, why do markers jot brief remarks on
an assignment or report in the first place? The reason for
brevity is the easy part: it's obvious that concise remarks
reflect narrow page margins and short times available for
writing. But the reasons for making the remarks are not
always so clear-cut, perhaps not even to the person offering
them. Even so, graders seem to be responding to at least
some intuitive educational objectives as they jot.
One objective in offering critical comment is to record
why a certain result has lost points according to a particular
grading scheme. Another is that to jot down a remark en-
gages the grader's highest motives in instructing the student
author to correct an error or omission. Indeed, a student
might hope that this were the main reason for all jotted
remarks. On occasion, however, such a noble motive may
become tarnished when an exasperated grader realizes that a
large fraction of the class has consistently made an "elemen-
tary" error. In that event, the marker may let slip an occa-
Spring 1995


... terse comments, scribbled hurriedly by
graders ..., become the aspirant's routine source
of evaluation and improvement. It therefore
makes good sense to carefully consider
the nature of such commentary.


sional "You jest!" or "Ridiculous!", or even "Arghh!" Such
comments, redolent of sarcasm, faithfully convey the grader's
anguish and frustration. At this stage, the marker's objective
has evolved into an unconscious one of ventilating disap-
pointment and annoyance. At the same time, only a very
secure student would dismiss these exclamations as the melt-
down of the grader, and not hear them as withering personal
criticism. Such a destructive approach as this is something
no grader can afford. For this reason, grading must be done
as a conscious and sympathetic activity.
Until now, I've given considerable space to difficulties
that can arise in correcting papers. Let's now turn our focus
to commentary that encourages. To illustrate the Joy of
Constructive Criticism, let me share a family anecdote. My
father once submitted an overlong essay to his professor.
The venerable gentleman evidently struggled a bit to get
through it, but even so withheld all graceless remarks such
as "Verbose!" Instead, he penned a constructive, under-
stated comment that remained with my father from that point
on: "Cultivate the art of brevity." Whether it was a freshly
minted thought or was written by the professor on half of
his students' essays is of no consequence. My dad learned
from it, enjoyed its lightheartedness, and chuckled about
it at odd moments even years later. In fact, my whole
family found this story quite charming. But now I think
I'm in danger of overselling my point by implying that a
few words of constructive criticism might even provide
amusement for posterity.
A lecturer I know holds periodic short quizzes in her
subject. In what started as a tongue-in-cheek gesture,
she "marks" her students' papers by stamping them with a
"happy face" whenever they get a perfect score. It seems
to be just the right touch. Her students haven't had the
opportunity to earn a happy face since their days in elemen-
tary school, so it's novel and makes gentle sport of the
seriousness of academe.
A while ago I attended a seminar given by a professor in
arts on the theme of university teachers' use of authority and
power. In her talk, she revealed that she now grades her
students' work in impermanent pencil, out of a sensitivity to
her own attitude toward criticism in her discipline as being
fleeting and subjective. (I hope lecturers in engineering will
not misconstrue this to mean that homework based on the
laws of conservation should be graded in ink.) What I hear
behind the seminar speaker's words is that the comments










written in the margin may sound needlessly absolute about
things that are often matters of the grader's own taste. The
same professor deliberately uses courteous forms such as
"Please" a great deal, along with phrases such as "I suggest
. or "Have you considered ... ?" A refreshingly light
touch indeed, compared with such thundering exclamations
as "So what!" and its ilk.
The light touch in correcting papers may also offer another
way of improving communication with students, but achiev-
ing this style may come at the cost of more time and effort to
compose appropriate phrases and write them down. Does
this just add one more unwelcome burden to the grader?
Maybe not, if the grader can "think smart." By this I mean
that a balance needs to be found between correcting every-
thing a student submits in a flurry of terse remarks and
simply pointing out a few important items for improvement
with enough grace that the student will appreciate and accept
the analysis.
While touching on the subject of thoroughness in marking,
let's suppose a grader does cover the margins of a paper with
all manner of meticulous corrections (goodness knows, an
occasional paper appears to deserve such treatment!). Is
such effort likely to benefit early undergraduates? I doubt it.
Thoroughness is more appropriate for the draft of a thesis,
rather than for an assignment, term paper, or lab report.
Technical errors need to be spotted, but I have found that
students tend to ignore large collections of comments on
minutiae. Learning good habits of problem solving and re-
porting takes time, so grading them needs to be viewed as
part of a long process. In my view, it's better strategy to
criticize a few points carefully than to try and correct many
shortcomings at once.
Is there any systematic way to improve the quality of
correcting papers to make it a more positive experience for
students and instructors? I am persuaded there is, but to
explain why, let me start with an important generalization.
Richard Felder has observed in these pages that the quality
of a student's experience in a university is strongly affected
by the kind of relationship that the individual has with mem-
bers of the teaching staff.[2] For this reason, I favor replacing
terse comments jotted in tight margins with face-to-face
discussions between students and their instructors. This may
mean, as it has for me, a greater use of the tutorial mode of
teaching at the expense of formal lecturing.
Yet, no matter what methods are used to teach, there is an
irreducible level of homework and laboratory reporting that
undergraduates have to submit. I'd therefore like to suggest
a few guidelines for jotting comments in margins. Unable to
itemize the steps as ABCs, I have dubbed them WXYZs
instead. They are:
W It's Worse if it's terse.
X X marks an error without providing details and


can be jotted quickly. Also, small x's seem more
respectful than large ones.
Y Yahoo is taboo. Courtesy is cool. Encourage-
ment is empowering.
Z Z-Z-Z (the cartoonist's symbol for sleep).
Indifference is the reaction to an excess of
criticism, especially if subjective. Zealous
graders beware.

By whatever method we graders conduct our art, students
will read and weigh our words of criticism. The pressures of
time may make terseness a temptation, but seldom a virtue.
Those of us who grade papers and reports would do well to
consider carefully the tone of our comments as we write
them in margins eagerly waiting to receive them.

ACKNOWLEDGMENTS
My thanks to colleagues John Peet and Maurice Allen
(Department of Chemical and Process Engineering, Univer-
sity of Canterbury, Christchurch, New Zealand) as well as to
Suzanne Shand (College of Education, Christchurch) for
their thoughtful comments. Special thanks go to Carol
Hudgins for discussion of the Myers Briggs Type Indicator
and for criticism of this article. No margins were ill-treated
during its preparation.

REFERENCES
1. Hirsch, S., and J. Kummerow, Life Types, Warner Books,
New York, NY (1989)
2. Felder, R.M., "What Matters in College," Chem. Eng. Ed.,
27(4), 194 (1993) O


Ffbooks received

Mass Spectrometric Study of the Vaporization of Oxide Systems, by
Stolyarova and Semenov; Wiley, 605 Third Avenue, New York,
NY 10158; 434 pages, $130 (1994)
Organometallics in Synthesis: A Manual, Schlosser (editor); Wiley,
605 Third Avenue, New York, NY 10158; 603 pages, $100 (1994)
Thermodynamics of Irreversible Processes: Applications to Diffu-
sion and Rheology, by Kuiken; Wiley, 605 Third Avenue, New
York, NY 10158; 425 pages, $54.95 (1994)
Progress in Inorganic Chemistry, Vol. 42., edited by Karlin; Wiley,
605 Third Avenue, New York, NY 10158; 606 pages, $125 (1994)
Principles of Plasma Discharges and Materials Processing, by
Lieberman and Lichtenberg; Wiley, 605 Third Avenue, New York,
NY 10158; 568 pages, $54.95 (1994)
The Chemistry of Organic Arsenic, Antimony and Bismuth Com-
pounds, by Patai; Wiley, 605 Third Avenue, New York, NY 10158;
962 pages, $425 (1994)
Tellurium-Containing Heterocycles, Vol. 53, by Detty and O'Rega;
Wiley, 605 Third Avenue, New York, NY 10158; 511 pages, $125
(1994)
Relaxation Phenomena in Condensed Matter, edited by Coffey;
Wiley, 605 Third Avenue, New York, NY 10158; 766 pages, $150
(1994)
Chemical Engineering Education













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A modern view of process control engineering in the age of new technology!


Process Dynamics, Modeling,


and Control


BABATUNDE A. OGUNNAIKE, ADJUNCT PROFESSOR, DEPARTMENT OF CHEMICAL
ENGINEERING, UNIVERSITY OF DELAWARE, AND W. HARMON RAY, STEENBOCK
PROFESSOR OF ENGINEERING, DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OF
WISCONSIN, MADISON
This text offers a modern view of process control in the context of today's tech-
nology. It provides the standard material in a coherent presentation and uses
a notation that is more consistent with the research literature in process con-
trol. Topics that are unique include a unified approach to model representations,
process model formation and process identification, multivariable control, statisti-
cal quality control, and model-based control. This book is designed to be used as
an introductory text for undergraduate courses in process dynamics and control.
In addition to chemical engineering courses, the text would also be suitable for
such courses taught in mechanical, nuclear, industrial, and metallurgical engi-
neering departments.


FEATURES:

* Provides a modern view of process control r Close to 500 review questions and over 200
engineering; topics include digital computer data problems are drawn from many areas of
acquisition, process monitoring, and process application and appear throughout the text.
control. More than 100 worked examples are also included.


* The text is logically organized; basic concepts are
presented to students and details of the most
advanced material are left to later chapters.
* Mathematical concepts are reviewed throughout
the text to assist engineers with limited
mathematical backgrounds.
* The text is designed to provide the theoretical
background for courses that include a laboratory.


* Appendices are provided that cover topics
including modern instrumentation capabilities,
complex variables and solution methods for
ordinary differential and difference equations,
Laplace transforms and z-transforms, matrix
methods and computer packages for computer-
aided control system design.


TABLE OF CONTENTS:
......................................................................................................................................................


PART I: Introduction
1. Introductory Concepts of Process Control
2. Introduction to Control System Implementation
PART II: Process Dynamics
3. Basic Elements of Dynamic Analysis
4. The Process Model
5. Dynamic Behavior of Linear Low Order-
Systems
6. Dynamic Behavior of Linear Higher Order-
Systems
7. Inverse-Response Systems
8. Time-Delay Systems
9. Frequency-Response Analysis
10. Nonlinear Systems
11. Stability
PART III: Process Modeling and
Identification
12. Theoretical Process Modeling
13. Process Identification: Empirical Process
Modeling


PART IV: Process Control
Part IVA: Single-Loop Control
14. Feedback Control Systems
15. Conventional Feedback Controller Design
16. Design of More Complex Control Structures
17. Controller Design for Processes with Difficult
Dynamics
18. Controller Design for Nonlinear Systems
19. Model-Based Control
Part IVB: Multivariable Process Control
20. Introduction to Multivariable Systems
21. Interaction Analysis and Multiple Single Loop
Design
22. Design of Multivariable Controllers
Part IVC: Computer Process Control
23. Introduction to Sampled-Data Systems
24. Tools of Discrete-Time Systems Analysis
25. Dynamic Analysis of Discrete-Time Systems
26. Design of Digital Controllers


PART V: Special Control Topics
27. Model Predictive Control
28. Statistical Process Control
29. Selected Topics in Advanced Process Control
30. Process Control System Synthesis Some
Case Studies
PART VI: Appendices
A. Control System Symbols used in Process and
Instrumentation Diagrams
B. Complex Variables, Differential Equations,
and Difference Equations
C. Laplace and z-Transformations
D. Review of Matrix Algebra
E. Computer-Aided Control System Design
Author Index
Subject Index
(Topics in Chemical Engineering)
1,296 pages; 446 illus.
509119-1 1994 $79.95


To ore or fo int -om topes rt



Price an puliato dat- s at sujc to chang


*




Full Text








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