Chemical engineering education

c e e a a c 0

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Education (CEE), a quarterly journal published by the Chemical Engineering Division of the
American Society for Engineering Education (ASEE).
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program, machine computation, special instructional programs, or give views and opinions on
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EDITORIAL AND BUSINESS ADDRESS:
Chemical Engineering Education
Department of Chemical Engineering
University of Florida
Gainesville, FL 32611
FAX 904-392-0861

EDITOR
Ray W. Fahien (904) 392-0857
ASSOCIATE EDITOR
T. J. Anderson (904) 392-2591
CONSULTING EDITOR
Mack Tyner
MANAGING EDITOR
Carole Yocum (904) 392-0861
PROBLEM EDITORS
James 0. Wilkes and Mark A. Burns
University of Michigan

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
George Burnet
Iowa State University
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
Carol M. McConica
Colorado State University
Angelo J. Perna
New Jersey Institute of Technology
Stanley I Sandier
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 1992

Chemical Engineering Education

Volume 26

Number 2

Spring 1992

AWARD LECTURE
104 Interfacial Transport Processes and Rheology: Structure
and Dynamics of Thin Liquid Films, Darsh T. Wasan

DEPARTMENT
58 The University of Toledo, Bruce E. Poling

EDUCATOR
62 George Burnet, of Iowa State University,
Janet Rohler Greisch

LABORATORY
66 Experimental Methods to Characterize and Control Liquid-
Liquid Processes, L.L. Tavlarides, C. Tsouris

72 Model Development and Validation: An Iterative Process,
G. W. Barton

94 Monitoring and Control of a Fed-Batch Fermentation,
Jose A. Teixeira, Maria L. Sousa,
Sebastao Feyo de Azevedo, Manuel Mota

98 A Systematic Approach for Long-Range Laboratory
Development, Bahman Ghorashi

STIRRED POTS
78 How a Clever Demon Nearly Blew Up the Second Law of
Thermodynamics, Sanjeev R. Rastogi

CLASS AND HOME PROBLEMS
82 Environmental Impact of Paper and Plastic Grocery Sacks:
A Mass Balance Problem with Multiple Recycle Loops,
D.T. Allen, N. Bakshani

CLASSROOM
88 Helping Students Develop a Critical Attitude Towards
Chemical Process Calculations, Noel de Nevers, J.D. Seader

RANDOM THOUGHTS
196 There's Nothing Wrong with the Raw Material,
Richard M. Felder

75,87, 102, 112 Book Reviews

CHEMICAL ENGINEERING EDUCATION (ISSN 0009-2479) is published quarterly by the
Chemical Engineering Division, American Societyfor 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. Copyright 1992 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.

THE UNIVERSITY OF TOLEDO

Steve LeBlanc with his
prize-winning fluidized bed
popcorn popper.

BRUCE E. POLING
The University of Toledo
Toledo, OH 43606

The most distinctive features of the Chemical Engineering Department
at the University of Toledo are its outstanding undergraduates (16 of the
160 undergraduates are National Merit Scholars) and the teaching quality
of the faculty (four of whom have won University "outstanding teacher"
awards). Also, as is the case with many departments, research activity has
increased dramatically in recent years, and the department now has active
research programs in surface phenomena, biomedical engineering, environ-
mental engineering, aircraft anti-icing and analysis, microgravity bubble
and droplet phenomena, resistojet performance, rarefied gas analysis of the
plume region, coal de-sulfurization, and polymer processing.

ABOUT TOLEDO ...
Many Americans know Toledo as the home of the
AAA baseball team, the "Mudhens," or perhaps as
the location of a professional golf tournament. But
this year, a number of engineering educators will
become acquainted with Toledo for a different rea-
son when the College of Engineering hosts the ASEE
National Convention.
Toledo itself is a blend of small-town flavor and
big-city attractions. After fighting traffic jams in
larger (as well as smaller) communities, one finds
it a pleasure to drive in Toledo-perhaps because
it has been allowed to expand uninhibited over a
large area of what was once Ohio farmland. The
Copyright ChE Division ofASEE 1992

Jim Lacksonen serves home-
made white-pine-needle tea to
his pulp and paper class.

nearly half-million population enjoys a variety of
shopping, cultural, and culinary opportunities, and
Toledo's location on Lake Erie provides numerous
recreational opportunities.
ABOUT THE UNIVERSITY...
The University of Toledo had its beginning in
1872 as The Toledo University of Arts and Trades,
and from 1884 to 1967 it was supported, in part, by
the city of Toledo. In 1967 it became part of the state
system, and it is currently Ohio's fastest growing
university, with an enrollment of approximately
25,000 students. In addition to engineering, the Uni-
versity has programs in arts and sciences, educa-
tion, nursing, law, business, and pharmacy, and is
Chemical Engineering Education

affiliated with the Medical College of Ohio. It also
has an affiliated community and technical college,
located approximately two miles from the main cam-
pus. In recent years the University has made a
concerted (and successful) effort to upgrade the qual-
ity of its student body; during the last two years, 92
National Merit Scholars have enrolled at the Uni-
versity of Toledo.

CHE, PAST AND PRESENT
Chemical engineering began in 1946 as a four-
year "Option in Chemical Engineering," part of the
curriculum in General Engineering. The BS chemi-
cal engineering program was begun in 1950 and has
been ABET/AIChE-accredited since 1964. There are
currently nine full-time faculty members, 160 un-
dergraduates (includes freshmen), and thirty gradu-
ate students.
Graduate work
was first offered in
1959, with the MS
program being au-
thorized in 1961
and the first MS
degree being
awarded in 1964.
A college-wide doc-
toral program was
begun in 1967, and
the first PhD was
Summer workshop students awarded in 1972.
test their solar collectors As the college con-
at Lake Erienues to grow,
tinues to grow,

Photo provided courtesy of The Blade, Tole
Ron Fournier and his rat get set to test the artificial pancre
Spring 1992

space is becoming scarce, and plans are now in
progress to construct a larger building that will pro-
vide 50% more space.
The quality of the department's graduates has
been high, but because the department is relatively
young and because it has primarily served only the
Toledo area in the past, the number of graduates per
year has not been large. This has changed at the
undergraduate level; enrollment has gone up and
has actually increased in quality, and the under-
graduate program now compares favorably with any
in the country. Although the graduate program is
new, the department nevertheless has active research
programs in several areas. For example, the Poly-
mer Institute does research in the areas of polymer
processing and in the development and testing
of new polymer materials for packaging house-
hold materials, foods, and beverages. The depart-
ment has also had extensive interactions with NASA-
Lewis, and as a result has research activities in the
areas of de-icing of aircraft, resistojet performance,
and microgravity research. New faculty that have
more recently joined the department have started
research programs in biomedical research, use of
high-sulfur coal, membrane separations, and super-
critical phenomena.

The past few years have seen a dramatic in-
crease in enrollment. Formerly, the student body
was largely made up of commuters. But the percent-
age of students from Toledo has steadily declined to
the point that last year only about 35% of the chemi-
cal engineering students were local citizens. This
change and the increased quality of our stu-
dents has been due in large part to two
programs: recruitment of National Merit
scholars by the university, and a summer
workshop for high school students, conducted
by our department.
For the past four years, The University
of Toledo has been remarkably successful in
aggressively recruiting National Merit
Scholars, and chemical engineering has
benefitted more than any other department
from this venture. Our department has more
National Merit Scholars than any other de-
partment on campus; sixteen of our 160
undergraduates are National Merit Schol-
ars. They are from all over Ohio and have
raised the quality and level of performance
of the other students in the program as well.
These students form a significant pool of
do. Ohio. talent, the likes of which one rarely finds in
eas. a single department.
59

The past few years have seen a dramatic increase in enrollment. Formerly, the student body was largely
made up of commuters. But the percentage of students from Toledo has steadily declined ... last year
only about 35% of the ChE students were local citizens. This has been due ... to two programs:
recruitment of National Merit scholars ... and a summer workshop for high school students ...

Class size demonstrates that enrollment in our
department is on the rise: 22 seniors, 32 juniors, and
56 sophomores. The increase can be attributed to a
number of factors such as the National Merit Scholar
program, but perhaps the most significant factor is a
summer workshop for high school students that our
department has conducted in one form or another
for the past four years. This past year the workshop
lasted three weeks, was attended by forty high school
students in their junior and senior years, and was
sponsored, in part, by NSF. The workshop consisted
of a variety of hands-on activities, including unit ops
experiments, independent "research" projects by
small groups of two to four students, and a "creativ-
ity" competition in which groups of four students
were asked to design and build a solar collector
(from readily available materials) that would be suit-
able for back-packing and could heat eight ounces of
water to 140F. (The closest any group got was
1390F-and then the sun went behind some clouds.)
Ostensibly, the purpose of the workshop is to
interest talented high school students in careers in
science and engineering. In fact, about half go into
chemical engineering, and of this half, about half go
to UT. We know of previous workshop attendees who
are now in chemical engineering at Cincinnati, Ohio
State, Vanderbilt, Michigan, and Northwestern-so
chemical engineering departments other than ours
have also profited from our efforts.
Even though the workshop is a lot of work, and
dealing with forty high school students of mixed
gender who are housed on a single floor of a college
dormitory presents problems not ordinarily encoun-
tered in chemical engineering, we feel the workshop
has been worthwhile because it has encouraged
talented young people to go into chemical engineer-
ing. Our workshop has been successful primarily
because of the unique talents of our academic co-
ordinator, Gale Mentzer, and the ability of several
of our faculty to relate to and work with that par-
ticular age group.

FACULTY: RESEARCH AND OTHER INTERESTS
Three of the faculty, Ken De Witt, Gary Bennett,
and Jim Lacksonen, have been in the department
since the early 1960s and have had considerable
60

influence in making the department what it is to-
day. Gary Bennett's area of expertise is environ-
mental engineering. He was featured in a 1979 ar-
ticle in Chemical Engineering Education and is prob-
ably best known for his service activities in the envi-
ronmental area, both through AIChE and as a
speaker to a variety of organizations. Ten times each
year he teaches a UT continuing education short
course on industrial wastewater pretreatment and
has won a number of AIChE awards, including the
Environmental Division's National Award in 1975
and the Environmental Division Award for service
to the Division in 1990. He serves as editor for Envi-
ronmental Progress and the Journal of Hazardous
Materials and enjoys spending his spare time with
his family at his cottage in Canada.
Ken De Witt has been the dominant force at the
graduate level, having taught transport phenomena
to all of the graduate students since joining the
department. During this time, Ken has supervised
over seventy graduate students and has developed
his status as a leading expert on de-icing and anti-
icing systems for aircraft. His research group has
been able to predict the three-dimensional ice build-
up and subsequent shedding from airplane compo-
nents. Active progress in microgravity bubble and
droplet phenomena, and in experimental testing and
rarefied gas analysis of resistojets, has been estab-
lished. Ken is one of the university's ten distinguished
research professors and has won a University Out-
standing Teacher Award. He is an avid golfer (time
permitting) and baseball fan, and has coached hun-
dreds of players on numerous baseball and basket-
ball teams over the years.
Ron Fournier is an avid Lake Erie sailor. On
calm days his interests focus on his research on
bioartificial organs and novel bioreactor systems. He
is currently working on the development of a
bioartificial pancreas for the treatment of diabetes
and (with Sasidhar Varanasi) on a novel pH-con-
trolled immobilized enzyme system for the simulta-
neous isomerization and fermentation of xylose.
Saleh Jabarin is a professor in the department
and also serves as the director of UT's Polymer Insti-
tute, which has an extensive collection of equipment
that is used in all aspects of polymer research. Saleh
Chemical Engineering Education

holds over twenty-five patents in the areas of poly-
mers, polymer properties, and the processing of poly-
mers to make containers for household products,
beverages, and foods. Approximately one-fourth of
the chemical engineering graduate students are cur-
rently housed in the Polymer Institute.
Jim Lacksonen is an accomplished watercolor
artist, is active in the Boy Scouts, and has interests
in fly-tying and foods from natural sources. In his
spare time he just happens to be one of the best
instructors on campus. Students routinely grade him
at 3.9 on a 4.0-scale, and he has also received an
Outstanding Teacher Award from the university.
His research interests include pulp and paper, and
reaction engineering, and he has recently filed a
patent application for an improved Kraft pulping
process. He is also working on a high temperature,
rapid glass-melting process in which recyclable glass
is made from waste fly ash and/or waste fiberglass.
His teaching effectiveness derives partly from his
enthusiasm and his ability to enhance his classroom
instruction with examples from his outside inter-
ests-like the time he made white-pine-needle tea
and served it to the students in his pulp and paper
class. He also serves as AIChE student-chapter ad-
visor, and in this role he regularly attends the re-

TABLE 1
Chemical Engineering Faculty
University of Toledo

Gary F. Bennett University of Michigan
environmental engineering

Kenneth J. De Witt Northwestern University
transport phenomena and applied mathematics

Ronald L. Fournier University of Toledo
biomedical engineering

Saleh Jabarin University of Massachusetts
polymer processing

James W. Lacksonen Ohio State University
reaction engineering, pulp and paper

Richard M. Lemert University of Texas
supercritical extraction

Steven E. LeBlanc University of Michigan
process control, computer applications

Bruce E. Poling University of Illinois
thermodynamics

Sasidhar Varanasi State University of New York, Buffalo
colloids and interfacial phenomena

Spring 1992

gional conferences, goes on field trips, and coordi-
nates outside speakers to talk to the students.
Steve LeBlanc is our computer expert and is
another recipient of the university's Outstanding
Teacher Award. Steve, along with Sasidhar Varanasi,
is doing research in the area of separation of SO2
from flue gas in coal-fired power plants by means of
a hollow-fiber absorption process. He is currently co-
authoring a book (with Scott Fogler, University of
Michigan) on open-ended design-type problems for
chemical engineers.
Rich Lemert joined our faculty last fall. His
research area is supercritical fluid science and tech-
nology, and his PhD research work was instrumen-
tal in Keith Johnston's winning AIChE's Colburn
Award in 1990.
Gale Mentzer, our academic coordinator, is re-
sponsible for advising students in the routine sched-
uling of classes, raising funds for and organizing our
summer workshop, and generally helping out with
the many tasks necessary for running a department
but which do not require chemical engineering train-
ing. With her background in English she often pro-
vides a refreshing point of view to a room full of
chemical engineers.
Bruce Poling, who serves as department chair-
man, has research interests in the thermodynamics
of reversible reactions, in the estimation and mea-
surement of physical properties, and in calculational
techniques for using equations of state to describe
liquid phase properties. He has used calorimetry to
measure equilibrium concentrations in a reversible
Diels-Alder reaction and has used conductivity to
characterize equilibrium concentrations in the car-
bon dioxide-ammonia-water system. He runs regu-
larly (but not rapidly) in an effort to maintain a
modest level of physical fitness.
Sasidhar Varanasi's research interests are in
the areas of surface phenomena, colloids, and mem-
branes. He is particularly interested in phenomena
associated with polyelectrolyte layers grafted onto
solid surfaces. Grafted polyelectrolytes can have a
profound effect on the stabilization of colloids, on
controlled drug release, and in selective separation
processes. The projects in which he is collaborating
with Ron Fournier and Steve LeBlanc represent ap-
plications of his membrane expertise.

If you would like to meet the above faculty mem-
bers, visit Toledo by attending the ASEE conven-
tion. We think Toledo is a nice place to be, are proud
of our department, and are pleased with the direc-
tion in which it is going. I

educator

GEORGE BURNET

of

Iowa State University

JANET ROHLER
GREISCH
Iowa State University
Ames, IA 50011-2150

T o demonstrate the
danger of powdered
materials in the vicinity
of a flame, a high school
chemistry teacher blew
some flour dust into a cof-
fee can heated with a
candle. The resulting ex-
plosion blew the can lid
into the air-and piqued
the interest of at least
one student in that cen-
tral Iowa classroom. To that student, George Bur-
net, the demonstration conveyed the excitement he
could find in a career in chemistry.
But instead, George seemed destined for engi-
neering. His father, grandfather, great-grandfather,
and great-great-grandfather were all civil engineers
named George. George V didn't break the tradition
entirely; he combined his interests and chose chemi-
cal engineering. One of his six children, son George
VI, became a mechanical engineer.
College confirmed his decision. "When I got to
O.R. Sweeney's senior industrial chemistry class at
Iowa State, I was really hooked," George recalls.
"His lectures convinced students that chemical engi-
neers could do anything."
Other chemical engineering faculty also influ-
enced the young engineering student. From the Uni-
versity of Minnesota, department head Sweeney had
attracted B.F. Ruth who developed the department's
unit operations course, became known as the father
of filtration theory, and ultimately supervised
George's MS program.
@ Copyright ChE Division ofASEE 1992

World War II inter-
rupted George's educa-
tion after two years into
which he had packed
three-fourths of the re-
quired courses plus
ROTC training. George
entered the chemical
warfare service, went
through the officer train-
ing program, was com-
missioned in the field ar-
S. G tillery, and served over-
seas in the China Burma
India theater. He re-
turned to Iowa State in
1947 to finish his under-
graduate work, earn the
MS in 1949, and complete his PhD with L.K. Arnold
in 1951. By that time he and his wife Betty, whom
he had married before going overseas, had three
children in their two-bedroom apartment in the tem-
porary student housing erected for returning ser-
vicemen and their families.
They were happy to move to Terre Haute, Indi-
ana, where George had accepted a position in Com-
mercial Solvents Corporation's central engineering
division. But five years later, when B.F. Ruth's death
opened a vacancy on Iowa State's chemical engineer-
ing faculty, George returned as associate professor
in charge of the unit operations course Ruth had
taught. He also accepted a half-time appointment at
the Ames Laboratory. "That proved to be a very
attractive arrangement," George recalls, "because it
involved work at an outstanding research facility
(almost like an industrial research environment)
coupled with teaching at a major university."

RESEARCH
George's research at Ames Lab centered around
high-temperature processing. In the early years he
Chemical Engineering Education

As department head, George decided he wanted to interact both with students just entering
the department and with those who were about to leave. So for the next seventeen years he taught one
section of the introductory materials and energy balance course to sophomores and
one section of the plant design course to seniors.

studied the fundamental properties of liquid metal
systems and their applications in heat transfer
and separation phenomena-areas of particular
interest to the Atomic Energy Commission which
managed the Ames Lab at that time. George and
his group studied ways to purify and use metals
until the time that support for such work related to
nuclear energy declined.
When the national labs began to look at energy
more broadly under the new Department of Energy,
George's interest turned to extremely pure, single
crystals of metals as large as three inches in diam-
eter and twelve to fifteen inches long. "We trans-
lated the skill we had in high-temperature systems
to techniques for growing these very large single
crystals for use in instruments and for measuring
properties of materials," George recalls. "We were
successful enough that the process became routine,
and Ames Lab created a Materials Research Center
that consolidated a number of activities such as this."
George then began looking for a new problem to
solve. Because of the oil crisis in the early 1970s,
fossil energy, including efficient use of coal, was a
candidate. While serving on graduate research com-
mittees in civil engineering, George had learned about
research to characterize fly ash and determine its
fundamental properties and reactions. In particular,
the civil engineering group studied the use of this
by-product of powdered coal combustion for soil sta-
bilization. "But from a chemical engineering stand-
point, I could see it as a raw material for processing
rather than for use in construction," George recalls.
Fly ash typically contains 35% alumina, 20-24%
iron oxide, and 1-1.5% titania, plus silica. "An ore
with a composition like that would be an attractive
raw material to mine," George says, "and millions
of tons of this waste product with a high and uni-
form quality are readily available in fixed locations."
Their search for ways to "mine" fly ash economically
led to the Ames lime-soda sinter process and to the
HiChlor process.
The lime-soda sinter process heats fly ash in the
presence of lime and a small amount of sodium car-
bonate to convert the alumina into soluble calcium
and sodium aluminates and the silica into an in-
soluble dicalcium silicate. Using a very dilute so-
dium carbonate solution to adjust pH, the research-
Spring 1992

George and his long-time associate Mike Murtha
developed this pilot plant size model of the
Ames lime-soda sinter process

ers learned they could extract 90% of the alumina in
very pure form, leaving a residue of dicalcium sili-
cate. "Portland cement is tricalcium silicate, so you
simply add more limestone, heat-and you have Port-
land cement," George points out. "You've used every-
thing," he adds. "There's nothing left but the squeal!"
The HiChlor process uses high temperature to
treat metal oxide with chlorine in the presence of
carbon to get a stream of gaseous metal chlorides
mixed with carbon oxides. "The carbon acts as an
oxygen getter and removes oxygen from the
reaction system so you get a mixture of metal
chlorides," George explains. "You condense and sepa-
rate these metal chlorides and get metals in the
form of halides."
By the late 1980s, George and his group had
thoroughly investigated both processes and patented
some aspects of them. "When people begin looking
for new capacity in the production of alumina, these
processes using indigenous raw materials are going
to be quite attractive," George predicts. Environ-
mental concerns may help fulfill his prediction.
TEACHING
Along with his research activities, George taught
both undergraduate and graduate unit operations,
as well as transport phenomena. And when Morton
63

Smutz (chemical engineering's successor to G.L.
Bridger, who replaced Sweeney) became an associ-
ate director at Ames Lab in 1961, George replaced
him as department head. The appointment also made
him Chief of the Ames Lab's Chemical Engineering
Division with its five research groups.
As department head, George decided he wanted
to interact both with students just entering the de-
partment and with those who were about to leave.

"That involvement [with AIChE] has been a very
satisfying and important part of my professional
life, largely because of the association it
provided with outstanding individuals ..."

So for the next seventeen years he taught one sec-
tion of the introductory materials and energy bal-
ance course to sophomores and one section of the
plant design course to seniors. "This served a good
purpose," George says. "I got to know students com-
ing in and could assess changes in their preparation,
and I was also able to see firsthand how these and
other engineering courses changed over those years."
George ventured into new territory when Iowa
State's chemical and nuclear engineering depart-
ments merged. "We occupied the same building; the
chair of nuclear engineering, Glenn Murphy, had
reached age sixty-five, and back then that meant
compulsory relinquishment of administrative duties,"
George says. "So he took over the Engineering Edu-
cation Projects Office, and I became head of the
Chemical Engineering and Nuclear Engineering De-
partment." George's work at Ames Lab had intro-
duced him to nuclear power, but he admits he was
"far from a nuclear engineer."
Iowa State's nuclear engineering program, like
most of the programs throughout the country at that
time, offered only a graduate degree. Most of the
undergraduate programs that did exist had emerged
from advanced-degree programs whose faculty came
from nuclear science disciplines such as physics and
metallurgy. So not only were there too few BS de-
gree graduates to meet industry's demand, but also
the graduates there were had learned little about
processes. George changed that at Iowa State. "We
had a lab that looked a lot like a chemical engineer-
ing unit operations lab where students learned heat
transfer, fluid flow, and process control," he says.
The program was accredited for the full term the
first time it was evaluated.
Eventually, chemical and nuclear engineering
separated, and a nuclear engineer again headed the

nuclear engineering department. Since Murphy had
recently died, the Engineering Education Projects
Office (EEPO) needed a new director, and George
took it on. "I thought of EEPO as a small ASEE," he
says, "doing many of the things right here in our
college that ASEE does nationally: things such as
enrichment of teaching, pedagogical development of
faculty, new teaching materials, foundation support
for experimental programs, new ideas, and innova-
tions in the area of engineering education."

EXTENSION, OUTREACH, AND SERVICE
Continuing education was one area that George
developed in EEPO. "As we began to work on im-
proving teaching, we found good resources on cam-
pus as well as outstanding individuals off campus
who had good, new ideas and perspectives on ways
to teach engineering," George says. At the same
time, distance-learning technologies evolved. "Over
the years it has become almost a way of life to bring
in satellite-transmitted short courses and confer-
ences taught by some of the leading investigators in
the country," he says. "It has also led to my interest
in the broader aspects of continuing education and
bit-by-bit to my present assignments in the college."
That present assignment-associate dean for out-
reach and external affairs-precludes most research
activity. Until going to an associate position at Ames
Lab two years ago, George had maintained an active
research program there, supervising twenty doctoral
and nearly fifty master's students, in addition to his
teaching and administration.
All of the above was in addition to George's other
activities. "I can still recall the telephone conversa-
tion in the early 1960s when George Bankoff, then
chairman of the AIChE Education and Accreditation
Committee, asked me if I would be an ad hoc visitor
for what was then ECPD." Burnet's accreditation
experience at the time had been limited to one visit
at ISU. "George Bankoff persuaded me that this
would be a useful thing to do, and I'm very glad that
he did," George says. "He also arranged for me to go
on a learning evaluation assignment with Jim
Knudsen as team chairman, and I couldn't have had
a better mentor-tutor. All this convinced me that
accreditation activities offered a good way to use my
discretionary time. I could see so many really good
things resulting from this work." Among them were
appointments to the ECPD (later ABET) Engineer-
ing Education and Accreditation Committee and later
to the chairmanship of that committee and to the
Board of Directors as an AIChE representative and
as a member of the executive committee.
Chemical Engineering Education

In 1965, shortly after O.R. Sweeney died, George
invited Eric Walker, shown here, to give the first
Sweeney Lecture at Iowa State.

"That involvement has been a very satisfying
and important part of my professional life, largely
because of the association it provided with outstand-
ing individuals in AIChE," George notes. "Much the
same thing could be said for my ASEE experience
with its strong interdisciplinary exposure and ideas
that were important to my work."
Ray Fahien, a colleague and friend in his early
years at Iowa State, sparked George's interest in
ASEE. "Ray said I should join, and I'm glad I did,"
George says. His first national meeting was at the
University of Kentucky. The president was Eric
Walker, who later was one of the founders of NAE
and president of Penn State. "With people like Ray
Fahien and Eric Walker to admire, I soon became
active in ASEE," George recalls. That activity in-
cluded serving as national president in 1976.
Another result of his ASEE activity was an invi-
tation to serve on an eighteen-member commission
established by the National Science Board to look at
precollege education in math, science, and technol-
ogy. Over a period of two years the commission held
Spring 1992

hearings around the country, listening to experts'
opinions about ways to strengthen precollege educa-
tion, visiting model programs, and writing a report,
"Educating Americans for the 21st Century," to ac-
company the Department of Education's report, "A
Nation at Risk." That report, which came out first,
dealt with broad aspects of precollege education. Its
extensive media and public attention set the stage
for the second report, which George remembers as
more focused, more action-oriented, and more spe-
cific in the kind of remedies it proposed.
One of the programs that grew out of those
recommendations was NSF's Science and Engineer-
ing Education Directorate, with its commitment to
precollege and undergraduate education. George
served on the advisory committee for that new direc-
torate for two years.

HONORS AND AWARDS
George's activities have garnered honors and
awards too numerous to list. He was named Anson
Marston Distinguished Professor at Iowa State; he
was elected a Fellow in AIChE, AAAS, and the Iowa
Academy of Science, and a Charter Fellow in ASEE
and ABET; he won AIChE's Founders Award, ASEE's
Lamme Medal and Collins Award, and ABET's Linton
E. Grinter Distinguished Service Award.
George has also served on many awards commit-
tees to provide others with the recognition they de-
serve. "Recognition of achievement is important un-
der all circumstances, whether in your family or
your profession," he asserts. "Serving on awards com-
mittees is another activity that has so many ben-
efits," he adds. "Just like ASEE and accreditation-
the doer soon becomes the benefactor, and not just in
terms of personal satisfaction. I benefit from reading
about achievements, accomplishments, what others
have done, and how they've done it. I've learned a lot
just from seeing what other people do and working
to emulate them."
Emulate them? The citation on George's AIChE
Founders Award describes a career others might
only dream of: "For being an outstanding teacher
and leader in engineering education, influencing edu-
cation both nationally and internationally, leading
an outstanding department of chemical engineering
in the production of graduates who have been major
contributors to progress in industry and in educa-
tion, and for his research work in applying chemis-
try, pyrometallurgy, and coal waste utilization"
George Burnet has had a career to make all his
engineering forebears, as well as that high school
chemistry teacher, proud. [

BMWl laboratory

EXPERIMENTAL METHODS

TO CHARACTERIZE AND CONTROL

LIQUID-LIQUID PROCESSES

L.L. TAVLARIDES, C. TSOURIS
Syracuse University
Syracuse, NY 13244

L iquid-liquid extraction is one of the most com-
mon separation processes. It is used to separate
the components of a homogeneous liquid mixture by
either a solvent or a reactive liquid solution. The two
liquid systems are immiscible or partially miscible,
and they are introduced into contacting equipment
where one of the two phases is dispersed into the
other. The desired compound is then transferred
from the feed to the solvent phase. The interfacial
area of mass transfer is increased by mechanical
agitation, and the mass transfer rate is determined
by the concentration driving force, the contact area
between the two phases, and the contact time. Fur-
ther processing of the solvent phase is required to
yield the desired component and to recover the sol-
vent. Applications of the extraction process can be
found in the petroleum industry, in hydrometal-
lurgy,I11 in waste treatment,121 in the nuclear indus-
try,131 and in biochemical separations.14]
Industrial-scale equipment for liquid-liquid ex-
traction includes column contractors and continuous-
flow stirred tanks. A number of different types of
column contractors are available, some of which per-
form in a comparable manner-making the selection
of the equipment type a difficult problem.I15 After
selection of the equipment, the next step is dimen-
sioning of the extractor. Column height and diam-
eter are determined in an empirical way and after a
series of experiments on pilot plant units. The col-
umn diameter, for given feed-flow rates, is selected
so that the continuous-phase superficial velocity is
50-60% of the maximum allowable determined at
flooding.[61 The column height is determined by the
summation of the theoretical height and the eddy-
diffusivity height. The former is calculated for plug
countercurrent flow and is a function of the column
Copyright ChE Div'mon ofASEE 1992

Lawrence L. Tavlarides is Professor of Chemi-
cal Engineering and former Chairman of the
Department of Chemical Engineering and Mate-
rials Science at Syracuse University. He received
his BS, MS, and PhD degrees in chemical engi-
neering at the University of Pittsburgh. His re-
search interests include multiphase transport,
extraction, mixing, reaction engineering, inor-
ganic membrane technology, and supercritical
extraction and wet oxidation.

SCostas Tsouris is a Cypriot native and re-
ceived his PhD from the Department of Chemi-
cal Engineering and Materials Science at Syra-
cuse University. He also holds a Masters de-
gree from Syracuse University and a Diploma
of Engineering from the Aristotle University of
Thessaloniki, Greece. He works in the area of
modeling and control of extraction columns.

diameter, whereas the latter is estimated by axial
mixing parameters. The axial-dispersion and the
tank-in-series-with-backflow models have been ap-
plied to column contractors since the 1960s.[7,81 The
dispersed-phase droplets are considered to have the
same size by both models, and mixing parameters
are considered constant throughout the column. Ex-
periments on two or more different-diameter col-
umns yield scale-up criteria which are used for the
design of larger industrial units.
An effort to reduce expensive experimentation
and overdesign problems led to a more detailed
analysis of the extraction process in column con-
tactors.'i9131 This approach is based on population
balances'14-161 and considers droplet processes of break-
age and coalescence. Nonuniform holdup profiles and
drop size distributions along column contractors have
been explained by this consideration. Population bal-
ance equations have also been applied for liquid
dispersions in stirred tanks'17-181 in studies on the
effect of droplet breakage and coalescence on the
drop size. Simulation techniques have also been in-
troduced'"921" to overcome the complexity of the popu-

Chemical Engineering Education

lation-balance equations.
The new trends in the modeling of dispersive
systems require more experimental information for
model evaluation and parameter estimation. This
article describes experimental techniques developed
over the last few years in our laboratories for the
acquisition of data such as interfacial kinetics, drop-
let size distributions, concentrations in both liquid
phases, and volume fraction of the dispersed phase.

EXPERIMENTS IN LIQUID DISPERSIONS
The Liquid Jet Recycle Reactor (LJRR)
The LJRR has been developedl2] for evaluating
interfacial kinetics for liquid-liquid systems. The ba-
sic idea of this technique is to contact the two phases
in a chamber under well-known hydrodynamic flow
conditions, such as the ones imposed by a laminar
liquid jet, for a short period of time, and monitor the
change in concentration in one of the two fluids
caused by mass transfer. The jet chamber appears in
Figure 1. The heavier fluid (aqueous) is introduced
into the jet chamber through the nozzle, forming a
liquid jet which flows concurrently with the second
fluid (organic) and leads to the receiver. The organic
phase is recycled, and its concentration is monitored
continuously. The nozzle consists of 2mm I.D. preci-
sion-bore glass tubing. A jet of 3.54cm length is
employed by this apparatus, with the flow rate
varying from 70 to 130 ml/min giving a contact
time in the order of 0.05s. The outer fluid flow
may vary from 40 to 100 ml/min. The jet chamber
has an inner diameter of 1.0cm, and the total vol-
ume of the organic phase is approximately 25ml. For
a constant diameter jet whose surface velocity is
proportional to the average velocity, the change in
organic phase concentration with time t is given by
the following relation

V n rb-Cb 4 D DOQ-PL
0 mCb-Co(t=0) +mD
where
Vo = volume of the organic phase
m = partition coefficient

Ca = bulk concentration in the aqueous phase

Co = bulk concentration in the organic phase

(1)

Cb (t = 0) = concentration in the organic phase at zero
time
Da, Do = diffusivities in aqueous and organic phases
Qa = aqueous phase volumetric flow rate

An effort to reduce expensive experimentation
and overdesign problems led to a more
detailed analysis of the extraction
process in column contractors.

to Spectrophotometer

Figure 1. Jet chamber of the LJ reactor.

L = length of the jet
p = ratio of the surface velocity to the average jet
velocity
The jet surface velocity is calculated by consider-
ing a completely relaxed liquid jet, i.e., no accelera-
tion is assumed, and then solving the Navier-Stokes
equations. The interfacial area between the jet and
the outer fluid is determined photographically. The
LJRR can be employed to obtain mass transfer coef-
ficients and diffusivities of solutes in liquids, to study
sorption phenomena, and to obtain kinetic data.[23,241
In the absence of external fields, diffusional cou-
pling, and homogeneous reactions, the conservation
equations for species j are written as follows:
Aqueous phase:

ac 2ca
u S =DJ 2 (2)
ax a 2
Organic phase:
C_. (2C3
aC a2 .
us J =DJ J (3)
ax ay2

Spring 1992

subject to normal penetration theory boundary con-
ditions
Cj(x,)= Cjb (4)

Cj(0,0)=Cj,b (5)

where us is the surface velocity, the subscript b re-
fers to the bulk phase, and i refers to either the
organic phase o or aqueous phase a. The x direction
is parallel to the jet surface velocity, and y is perpen-
dicular to the jet interface. The surface velocity is
given by
us =Uavg (6)
avg
where the proportionality constant is a function of
physical, geometrical, and operating properties.[221
The power and utility of the LJRR as an experimen-
tal technique rests largely in the ability to accu-
rately model the complex problem of mass transfer
across a free surface in two-phase flow using Eqs. (2)
and (3), which have received widespread attention
in one-dimensional unsteady state heat or mass
transfer problems. Eqs. (2) and (3) are coupled to-
gether through the interfacial fluxes by the conser-
vation of mass. For an interfacial reaction of n com-
ponents with arbitrary stoichiometry as represented
by the following equation
vC1 + v22 +... +nCn = 0 (7)
The conservation of mass requires that

v.D. =v.D (8)
1i ay j ay o

One additional boundary condition required for the
solution may be supplied by letting the interfacial
flux of a species to be equal to the rate of interfacial
reaction of the same species, or
ac.
D. a =R. (9)
y=0

The rate of reaction R, is, in general, a function of
interfacial concentrations of the reactants and prod-
ucts. The above problem can be solved analytically
for linear kinetic rate expressions. For arbitrary ki-
netics, a numerical solution is required.
Results from the Liquid Jet Recycle Reactor are
reproducible. The overall experimental error is less
than 6%, providing the accuracy required to dis-
criminate between similar models by using rigorous
statistical methods. Summarizing this configuration
of the LJRR permits accurate determination of the
interfacial area and a simple yet satisfactory ap-
proximation of the hydrodynamics; the short contact

times allow applications of the penetration theory
approach. The diffusional contributions can be readily
approximated or, if needed, a more rigorous numeri-
cal solution can be employed.
The Stirred Transfer Reactor
Another experimental technique which can pro-
vide mass transfer coefficients or interfacial kinetics
between two liquid phases is the stirred transfer
reactor. This reactor is a modified Lewis cell which
was designed by Landau and Chin[251 and further
modified by Demetropoulos.[261 It consists of a cylin-
drical compartment divided into upper and lower
sections (see Figure 2). Each section has its own
agitation unit. The heavier phase is contained in the
lower section and contacts the lighter phase through
an annular interface. The stirrers are housed in
a perforated shell in order to maintain the inter-
face quiescent at sufficiently high rotational
speeds. The fluids are pumped by the stirrers into
the shell, where vertical baffles direct the flow down-
wards or upwards and leave the shell in a radial
direction via circular perforations on the cylindrical
part. All wetted parts of the reactor are made of
either Teflon or glass.
The stirred transfer reactor, as well as the LJRR,
provides a known interfacial area for mass transfer
between the two phases. The stirred cell is valuable
for low surface tension systems when the liquid jet
fails. Disadvantages of the stirred transfer reactor
as compared to the liquid jet recycle reactor are the
complexity of the hydrodynamics and the accumula-
tion of surface active impurities during reaction.
Pure mass transfer of toluene in water and the ki-
netics of cobalt (II) extraction by D2EHPA (Di(2-
ethylhexyl) phosphoric acid) have been studied'271 in
the stirred transfer reactor.

Figure 2. Flow diagram for the Stirred Transfer Reactor
Chemical Engineering Education

Microphotographic Technique
Once the mass transfer coefficient or the interfa-
cial kinetic-rate expression is obtained, the total in-
terfacial area between the two liquid phases is re-
quired for the prediction of mass transfer or reaction
rate. For the estimation of the contact area, informa-
tion about the droplet size and the volume fraction of
the dispersed phase is needed. A microphotographic
technique for drop size measurements in liquid dis-
persions is described here. An optical probe[28] has
been developed for drop size distribution measure-
ments (see Figure 3). It consists of a microscope, a
camera, fiber-optics, and a microflash unit. The light
travels through fiber-optic light conduits to the focal
point 3-5mm away from a glass window which is
glued at the tip of a metal adapter. This adapter
holds the objective lens of the microscope. On the
other end of the microscope there exists an eyepiece
lens and an adapter to hold the camera. The focal
point of the microscope is located inside the disper-
sion, providing direct photographs of the droplets.
The droplet size is measured by a semiautomatic
particle analyzer (MOP-30, Carl Zeiss, Inc.) inter-
faced with an IBM PC. From the drop size distribu-
tion, the Sauter mean diameter, d32, defined by

d3 d
d32 2di

can be obtained. Then, the
transfer, a, is estimated by

specific area of mass

Figure 3. Microphotographic technique
Spring 1992

where 0 is the dispersed phase fraction. The rate of
mass transfer, M, defined by
M= KaAC (12)
where K is the mass transfer coefficient and AC the
driving force, can thus be calculated.

Laser Photometric Probe
The laser photometric probe has been developed
for concentration measurements in liquid disper-
sions[29,301 in order to study flow properties and mass
transfer coefficients. For example, one of the models
used to analyze extraction in column contractors is
the dispersion model which neglects the effect of
drop size distribution on the mass transfer perfor-
mance. For counter-current flow of both phases

ac,, 2c ac
S= DD _-2 u TK aAC (13)
at ah2 a Sh
where
a = continuous (c) and dispersed (d) phases
u = superficial velocity
C = concentration
h = column height
D = axial dispersion coefficient
The dispersion coefficient in both phases can be
estimated by tracer experiments at which a tracer is
introduced in the flow and the tracer concentration
is measured at various locations. Analysis of concen-
tration distributions yields the dispersion coefficients.
The laser probe consists of a two-
loop fiber-optic setup as shown in
Figure 4. The two fiber-optic bundles
Remote consist of 50pm fibers enclosed in a
'lash shuffer
trger stainless-steel tube of 4mm outer
diameter (O.D.). At the end of this
tube the two bundles are separately
adjusted in two small stainless-steel
| camera tubes of 0.7mm O.D., forming a
bdy forked device of 10mm in length. At
the tip of each prong, a rectangular
isosceles prism is located in such a
way to reflect the light by 900. The
experimental setup includes a laser
tube with a power supply, an elec-
tronic device, and a data-acquisi-
tion system. Laser light travels
SMcrolsh through the fiber optics and through
to Microflash
dnve unit the liquid medium between the two
prisms. The intensity of the light,
I, measured by an electronic device
69

Column wall

(Trifurcated BundleBranch)

0=

at the exit of the probe, is related to the initial
intensity, Io (at zero concentration), the concentra-
tion of the investigated species in the liquid, c, and
the traveling distance through the medium, x, by the
Lambert-Beer law
I= Iexp(-Ecx) (14)

where E is the molar absorption coefficient charac-
teristic for each species.
The laser photometric technique can be applied
for concentration measurements in liquid dispersions
after the separation of the two phases. In situ sepa-
ration and isokinetic withdrawal of droplets are
achieved by coalescence devices supported at the tip
of the fiber-optic probe.

Laser Capillary Spectrophotometric (LCS)
Technique
The LCS technique has been develop-
ed[31-331 for bivariate (size and concentra- ple
tion) distribution measurements. A bivari-
ate drop size-concentration distribution
f(v,c)dvdc represents the fraction of droplets beam
with volume between v and v + dv and con- splitter
centration between c and c + dc, and pro-
vides information about the dispersed-phase
IOmW
mixing. The effect of droplet mixing on re- HeNe
laser

E
SExpanded "X"
a ^? iro

Figure 4. Laser photometric probe

actions occurring in the dispersed phase has been
studied in a number of investigations.120,21,33-35] The
basic idea of the LCS technique is to force a repre-
sentative sample of drops through a glass capillary
by developing a pressure difference along the tube
(see Figure 5). As drops pass through the capillary,
they form cylindrical slugs. The optical device is
designed to measure drop size by difference of light
refraction between the two phases and drop concen-
tration by light absorbance of the solute in the drop.
A laser tube of appropriate wavelength is selected as
a light source. The laser beam is split into two rays
by using a beam splitter and a plane mirror, and the
rays pass through the center of the capillary. From
the measurement of the passage time (At2) of a slug

Figure 5. Optical system for the LCS technique

Figure 6. Experimental setup for the LCS technique
Chemical Engineering Education

data
Idoro
s -- oquisisition
I system

plug
plug to tonk

conical CA, time
entrance I v '

t^time

at one detector and its travel time (At,) between two
detectors in Figure 5, the velocity, u, and diameter,
d, of the drop can be calculated by

u=S/Ati (15)
Lp =uAt2 (16)
and

d= 3/2d2 Lp )13 (17)
c p
Here S is the distance between two detectors, d, the
capillary diameter and L, the length of the slug. The
width of each pulse is proportional to the drop vol-
ume and the intensity can be related to the concen-
tration of the light absorbing species. The experi-
mental setup is shown in Figure 6. A sample of the
dispersion is withdrawn continuously through the
capillary by a vacuum pump. After passing through
the capillary, the two laser rays are received by
photodiodes where they are translated into current.
This current is changed into voltage which is sampled
with a frequency of 50 KHz by and A/D converter

1 Multistage Column
2a Transmitting Ultrasonic Transducer
2b Receiver Ultrasonic Transducer
3 Dual VHF Switch Multiplexer
4 Pulse Generator
5 Digital Computer
5a Interface Card
6 Digital Programmable Oscilloscope

Figure 7. Ultrasonic technique
Spring 1992

(DASH-16, Metrabyte Co.). The LCS technique can
provide steady state as well as transient information
which can be processed for the description of droplet
interactions and mass-transfer characteristics.

Ultrasonic Technique
A noninvasive ultrasonic technique has been de-
veloped[36,371 for dispersed-phase volume fraction
measurements in stirred tanks. This information is
needed for the estimation of the interfacial area of
mass transfer as described by Eq. (11). Also, a re-
cently developed data-acquisition systeml381 made
the technique applicable for automatic on-line
multipoint measurements, as shown in Figure 7,
which can be used for the control of extraction col-
umns at safe operation below flooding. A pulse gen-
erator sends a series of square pulses to a transmit-
ting ultrasonic transducer through a dual multi-
plexer and to a digital oscilloscope for triggering.
The transducer is activated by the electric signal
and produces sound waves which pass through the
liquid dispersion. The signal is received by a receiver
transducer and is transmitted through the multi-
plexer to the oscilloscope where the travel time is
calculated. The travel time through the dispersion is
compared to the travel time through pure phases for
the calculation of the volume fraction of the dis-
persed phase. By considering sound refraction and
reflection on the droplet-continuous phase interface,
the dispersed-phase volume fraction is calculated
from the relation139,401
t*-t
^ (18)
gdtd -gctc
where gd and g, are explicit algebraic functions of
the sound velocity ratio. The ultrasonic technique
has been employed for process identification and
control of a multistage stirred column.1411 It has also
been successfully applied for low volume-fraction
measurements of water in oil.

SUMMARY
In summary, a number of experimental techniques
have been developed to study some properties and
parameters in liquid-liquid systems. Information ob-
tained by these techniques significantly helps our
efforts to understand and model fundamental pro-
cesses occurring in liquid-liquid extraction such as
droplet interactions, mass transfer phenomena, in-
terfacial kinetics, and phase flow patterns. The Liq-
uid Jet Recycle Reactor provides information about
microscopic phenomena of mass transfer and inter-
facial kinetic rates between the two liquids. Similar
Continued on page 86.

Laboratory

MODEL DEVELOPMENT AND VALIDATION

An Iterative Process

G. W. BARTON
University of Sydney
New South Wales 2006, Australia

A t the turn of the last century the prevailing view
in Western science and philosophy was that
mankind inhabited a "clockwork" universe, wound
up in some way by a Creator and unfurled according
to deterministic laws. We seemed to be free to ap-
proach certainty in cosmic modeling as closely as
time and diligent application allowed.
Since they are fed a steady diet of analysis, nu-
merical methods, and computer-based calculations,
today's chemical engineering undergraduates can be
excused if they too feel that modeling is an exact
science. However, for many students the worries
about the value of process modeling that begin to
surface in the undergraduate laboratory (where ex-
periments "fail to agree with the theory") are con-
firmed early in their working life. For them, model-
ing is of very limited value in the "real world" that
exists beyond the bounds of academia.
As we move toward the turn of this century,
however, one of the few certainties we can hold on to
is the increasing role computers will play in all of
our lives. For engineers, productivity pressure and
the need for quick answers mean that there will be
increased reliance on software modeling packages
with which they may have had only limited experi-
ence. For some, the result could be a blind accep-
tance of someone else's model predictions.
The way forward, of course, embodies neither
complete rejection of, nor blind obedience to, process

Geoff Barton completed both his BE (Chem)
and PhD at the University of Sydney, Australia.
After working in nuclear energy and mineral pro-
cessing research establishments for several
years, he returned to the University of Sydney"'
Chemical Engineering Department, where he is
currently an associate professor. His teaching
and research interests are primarily in the area of
j process systems engineering.
Copynght ChE Dilsion ofASEE 1992

modeling. An important challenge is for engineering
departments to foster in their graduates a more re-
alistic (and critical) attitude toward process model-
ing. One approach to this challenge is to present
projects which are structured to include the follow-
ing three phases:
1. Development of an initial model from first principles
2. Collection of experimental data against which the
model predictions can be compared
3. Modification of the original model in light of any
significant disagreement with the experimental data
The first of these steps is familiar to all engineer-
ing students, but the idea of model validation as a
possibly iterative process involving data collection
and model refinement seems to get little attention in
most curricula.
While part of an existing undergraduate labora-
tory could be used, my preference is to employ every-
day examples with which the student is familiar but
for which no analysis is available. Such projects can
well form part of an existing laboratory course, re-
placing some of the more structured experiments.
Given the need for both analytic and experimental
work (as well as the iterative nature of the process)
it is best to conduct such projects through a whole
semester.
It should be pointed out, however, that the role of
the supervisor in such projects is crucial. I make no
attempt to lead a student to the "correct" answer; I
merely act as a technical sounding board for their
ideas. This can be quite trying for both parties-
particularly in the early stages of the project.
EXAMPLE PROJECT
I have frequently explained chemical engineering
to the uninitiated in terms of the unit operations
involved in making a cup of coffee: the size reduction
of the beans; extraction of soluble coffee; separation
of the coffee from the spent beans; mixing the coffee
with milk; and heat transfer as the coffee cools.
Even this everyday task can provide a whole range
of simple student modeling projects. The one I de-
scribe here is the cooling of a cup of coffee, using the
Chemical Engineering Education

results obtained by a student whom I have code-
named John.

Stage 1: Initial Model Development
The key point in this stage is that the student has
to develop his/her own model-the necessary analy-
sis should not be available in a text or paper. Based
upon undergraduate heat and mass transfer theory
and a reasonable set of assumptions, John's first
model consisted of just one equation: an unsteady-
state energy balance on the coffee (see Figure 1)

(C*M)dT/dt = Qi

(i = 1,...,5)

Even at this stage John was beginning to appre-
ciate the joy of model development. His model con-
tained parameters (such as the thermal conductivity
of ceramic material and the emissivity of glazed
surfaces) for which the literature gave quite variable
values. The temperature dependence of the gaseous
physical properties (such as the diffusivity of water
vapor in air) seemed to be important. He was faced
with heat transfer modes (for example, natural con-
vection) that had received scant attention in lec-
tures. All such problems, however, could be over-
come with a certain amount of literature review,
discussion, and engineering judgement.
Solution of the initial model prior to any experi-
mentation gave rise to mixed emotions. On the posi-
tive side, both the time scale of the temperature
changes and the amount of water evaporated seemed
realistic. On the downside, however, the results gave
rise to some concern. In particular, the predicted
results showed that evaporative heat losses were
dominant, particularly at high water temperatures.
The model calculated this heat transfer component
(Q4) by first calculating the amount of mass transfer
using a heat and mass transfer analogy, Sh = a.Nu,
Radiation from liquid surface (Q3)
Evaporation (Q4)
Convection from liquid
surface (Q5)

COFFEE (M grams)

CERAMIC CUP

Radiation from
wall (Q2)

Convection from
wall (Q1)

INSULATED BASE

Figure 1. Heat transfer modes considered.
Spring 1992

to give the mass transfer coefficient (contained in
the Sherwood number). Unfortunately, predicted val-
ues of a varied from being essentially constant
(around 0.9) to being highly temperature dependent
(reaching values around 3 when the water tempera-
ture is high). The time was obviously right for some
experimental work!

Stage 2: Experimental Results
A major reason for using projects such as this one
is that the student can readily design, build, and run
an appropriate piece of experimental equipment.
John's rig consisted quite simply of a digital balance,
a couple of thermometers, an electric kettle, and
several sheets of cardboard that formed a draft
excluder. An attempt was made to alter the rela-
tive importance of the various heat transfer modes
by restricting the evaporative losses (using an annu-
lar, acrylic ring floated on the surface) and using
cups with different aspect ratios (H/D values of 1.07
to 0.74). The experimental results showed that at
low water temperatures (below 800C) the mass trans-
fer rates measured were in good agreement with
those predicted assuming a simple heat and mass
transfer analogy with an essentially constant a
factor (see Figure 2), although in some runs, at
higher water temperatures there was some evi-
dence of mass transfer rate enhancement due to

- Key
SExperimental re
Model (no enha
Model enhancec

0.8 -

results
cement)
:ment) /

0.2 -

0S

I I

U
30 40 50 60 70 80 90
Water temperature (deg C)

Figure 2. Comparison of experimental and predicted
(with and without mass-transfer enhancement)
evaporation rates.

vapor condensation as predicted by Hills and
Szekely.ll Without experimentation, there was no
way of knowing whether mass transfer rate enhance-
ment would, in fact, occur.
The experimental temperature profiles clearly
showed that neglecting the heat capacity of the cup
was a gross simplification since the water tempera-
ture measured "immediately" after its addition to
the cup was in the range of 80-900C. Using this
measured value as the initial temperature of the
liquid in the cup, and assuming no mass transfer
enhancement, gave predicted temperature profiles
that were in reasonable agreement with the experi-
mental results (see Figure 3).
It is worth noting that a sensitivity analysis in-
volving likely variations in the assumed model pa-
rameters (such as the thermal conductivity of the
cup) was easy to perform and really should be part of
any model-development program. However, my ob-
servation to John that values quoted for such pa-
rameters should only be regarded as representative,
and that a variation of +20% was probably conserva-
tive, was initially treated as bordering on heresy
(could Perry be wrong?). However, in this case it
turned out that the original model could not be res-
cued simply by adjusting poorly known parameters.
At this stage, therefore, it did seem that the major
deficiency in the original model was in neglecting
the heat capacity of the cup.

Stage 3: Model Modification
To improve the accuracy of the model, the student
is forced to modify the original model. It should be
pointed out that, in general, any number of model
modifications are possible, varying both in the
amount of additional model complexity and the ex-
tent of model improvement. The skill is in deciding,
based on engineering judgement and the available
results, which is the most fruitful option. Here, the
most obvious modification was to include the heat
capacity of the cup in the model. Assuming negli-
gible resistance to heat transfer between the coffee
and the cup, the transient one-dimensional conduc-
tion equation was used to calculate the temperature
profile in the cup as a function of time and position
(by now John was getting adventurous!). This equa-
tion was solved by a finite difference method using
four internal node points. The results showed that it
only took on the order of 30-s for the cup to heat up
(from room temperature) and the coffee to cool down.
This meant that the average rate of change in the
temperature of the coffee over this period was about
25-350C/min, showing how difficult it was to obtain
an "initial" measured temperature for the coffee in

100

] Key
S Experimental results
Initial model
80 --- Modified model

60

40
I I --
-^~~~-^' .--

20 40 60
Time (mins)

80 100 120

Figure 3. Comparison of experimental and predicted
temperature profiles.

the original model.
Once the heat capacity of the cup was taken into
account, there was good agreement between the ex-
perimental and model temperature profiles, as shown
for example in Figure 3. The modified model was not
perfect. It was, however, a validated engineering
model, capable of explaining the available experi-
mental data and providing a predictive tool for cases
where such data were unavailable.

CONCLUSIONS
The frontiers of science will never be in any real
danger from such projects-but that is not the aim of
the exercise. Using the skills acquired as part of
their training, students learn not only that they can
accurately model an unfamiliar (from an engineer-
ing-analysis point of view) process, but also, and
more importantly, that developing an acceptably ac-
curate model (even for a "simple" process) is an it-
erative procedure involving analysis, validation
against experimental data, and model refinement.
The development of such validated models is as close
to absolute certainty as engineering gets.
So-you are interested but feel your students
need more of a challenge? How about a project in-
volving the transient behavior of a distributed pa-
rameter system, with simultaneous heat and mass
transfer, time varying physical properties, and com-
Chemical Engineering Education

plex (but poorly known) kinetics? Consider baking a
potato. Bon Appetit!

REFERENCES
1. Hills, A., and J. Szekely, "Notes on Vaporization into Much
Colder Surroundings," Chem. Eng. Sci., 19, 79 (1964) C1

book review

CHEMICAL PROCESS SAFETY:
FUNDAMENTALS WITH APPLICATIONS
by Daniel A. Crowl and Joseph F. Louvar
Prentice-Hall, Englewood Cliffs, NJ 07632; 426+
pages, $49.00 (1990)

Reviewed by
J. Reed Welker
University of Arkansas

One of the areas of study frequently missing from the
chemical engineer's undergraduate education in the United
States is safety and loss prevention. It also happens that
safety is one of the areas that practicing engineers all need
to have in their repertoire. Chemical Process Safety is the
first text designed for undergraduate study, and its mes-
sage can be incorporated into the curriculum by faculty
who do not have any specialized background in safety. I
have used it as the text for classes in chemical process
safety and find it to be an excellent basis for such a course.
Like any other teacher, I have incorporated other material
into my course and provided a background flavored by my
own experience, but that in no way detracts from the text.
Chapter 1 introduces the subject with some statistics
and a little background on relative risks and our percep-
tion of them. That seems particularly important because
we seldom hear the word "chemical" in the news without
an adjective like hazardous or dangerous preceding it.
There is also a summary of three significant accidents: the
cyclohexane explosion at Flixborough, England; the methyl
isocyanate release at Bhopal, India; and the 2, 3, 7, 8-
tetrachlorodibenzoparadioxin release at Sevesco, Italy.
Chapter 2 provides a brief background in toxicology. It
covers the importance of dose versus response, and details
the routes of entry into the body for toxic materials. The
definitions for various traditional and legal values of expo-
sure levels are provided, along with a brief background in
the analysis of probability curves for assessing response.
Probit analysis is shown to be useful for interpolating (and
sometimes extrapolating) toxicology data.
Industrial hygiene is covered in Chapter 3. Methods of
estimating exposure are presented and some control tech-
niques are discussed. There are some inconsistencies in
some of the methods described (for example, vapor emis-
sion during drum filling assumes that the air space in a
drum is saturated with vapor, but a calculation is still
made for the evaporation rate from the liquid surface), but
the methods presented are useful for preliminary esti-
Spring 1992

mates of ventilation requirements.
Chapter 4 is a review of source models used to estimate
the input rates for atmospheric dispersion models. It is
primarily a review of fluid mechanics because most source
models presume the release originates at a broken pipe or
from an orifice in a pipe or vessel. Liquid, compressible
fluid, and two-phase fluid flow are all considered, as are
vaporization rates from open liquid pools. These methods
provide realistic source rates providing the orifice can be
well characterized.
The fifth chapter uses the source rates to determine the
size of plume that might be formed by a leaking gas or by a
vapor from a volatile liquid spill. The dispersion models
presented are far from the most sophisticated models avail-
able today, but they are appropriate for the level of under-
standing of students with little or no knowledge in disper-
sion. They provide a basic understanding of the process
and methods used for estimation of the extent of potential
danger for toxic or flammable vapors following a release.
Chapter 6 begins the discussion of fires and explosions.
The flammability characteristics of liquids and vapors are
presented, including the fundamental concepts of flamma-
bility limits, minimum oxygen concentration, and flash
point. The often-overlooked area of dust explosions is cov-
ered in detail, including a description of the equipment
used for testing dusts for explosion potential. Methods for
estimating the potential for damage from explosions, based
on the idea of TNT equivalence, are discussed.
Once the potential for explosions and fires has been
presented, methods are discussed for preventing them.
Chapter 7 discusses inerting and purging, static electric-
ity and its control, explosion-proof equipment, and venti-
lation as methods of prevention of fires and explosions.
The section on static electricity and its control seems par-
ticularly hard for students to grasp, partly because it is so
highly summarized and partly because it is foreign to
chemical engineers. However, static electricity is impor-
tant to cover because it is not well understood by chemical
engineers and because prevention of static buildup is es-
sential to plant safety.
Chapters 8 and 9 cover the design of relief systems.
They include not only the philosophy behind relief sys-
tems, but also methods of determining relief sizes. Meth-
ods are included for liquids, gases, and two-phase flow.
Simplified methods using DIERS results for venting react-
ing systems are presented, along with the latest NFPA
methods for deflagration venting.
Hazard identification and safety reviews are presented
in Chapter 10. The quantitative assessment of risk, using
probability analysis and fault trees is covered in Chapter
11. These relatively simple procedures are valuable in
identifying and correcting potential safety problems in
plants, but are seldom covered in undergraduate courses.
The text concludes with chapters on accident investiga-
tions (Chapter 12) and case histories (Chapter 13). These
are particularly useful to the teacher who does not have a
broad background in safety because they provide some
real-life illustrations of determining what went wrong,
Continued on page 112.

Random Thoughts...

THERE'S NOTHING WRONG

WITH THE

RAW MATERIAL

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

n the Institute Lecture I was privileged to deliver
at the Los Angeles AIChE meeting last Novem-
ber, I spoke about the quality of American students.
I reviewed the dismal statistical and anecdotal evi-
dence that many of them cannot read or write any-
where near their grade levels, know little math and
less science, and can't find anyplace in the world on
a map. I might have added that far too many of them
are also without dreams or ideals: their ambition
goes as far as getting through school, landing a high-
paying job, and buying the large-screen television
with HBO and MTV that will meet their educational
and cultural needs for the rest of their lives.
Teaching these young people in college can be a
pretty joyless experience. Intellectual curiosity, cre-
ative thinking, and excitement over ideas simply
don't show up, in or out of class. Most students won't
offer ideas or respond to questions because they don't
want to risk being wrong, and they almost never ask
questions themselves except the ever-popular "Are
we responsible for this on the test?"
In Los Angeles I speculated on the causes of this
situation and concluded that while a variety of socio-
logical factors have played a part, the American
precollege educational system must accept the prin-
cipal burden of responsibility. I also cited some evi-
dence that the problems only become visible at the
fourth- or fifth-grade level and get progressively
worse through high school.
Not long ago I got some first-hand evidence sup-
porting the latter observation. As part of the NCSU-
Wake County Scientist-Teacher Partnership, I vis-

Richard M. Felder is Hoechst Celanese Pro-
fessor of Chemical Engineering at North Caro-
hna State University. He received his BChE
from City College of CUNY and his PhD from
Princeton. He has presented courses on
chemical engineering principles, reactor de-
sign, process optmization, and effective teach-
ing to various American and foreign industries
and institutions. He is coauthor of the text
Elementary Principles of Chemical Processes
(Wiley, 1986).

ited a fourth-grade class in a rural community out-
side of Raleigh. I spoke a little about what scientists
and engineers do, ran some chemistry demonstra-
tions, had the students do some experiments on de-
tection of acids, and talked about acid rain.
It was a remarkable experience-I couldn't hold
those kids back. Early in the class I divided them
into groups of four and gave each group two small
closed vials containing colorless liquids, one labeled
"H" (which contained water) and one labeled "V" (for
vinegar). Before I gave them the vials I told them we
would do some experiments to figure out which one
was acid and which was just water. As soon as they
got the vials, they took off. They shook them, sniffed
them, held them up to the light. One child saw that
one of the liquids was somewhat thick and bubbly
when she shook it and the other behaved more like
water, and she guessed that the first one was the
acid. Another student in the same group looked at
the second vial and said "Yeah, I bet that H stands
for H20." Someone in another group detected a faint
aroma coming from one of the vials, saw the V on it,
and said "This one's vinegar-hey, is vinegar an
acid?" I hadn't opened my mouth yet!
The whole class went like that. The children flailed

Copyvrght ChE Division of ASEE 1992

Chemical Engineering Education

Polls show that Americans are willing to invest more in the future of our children and our
country.. .but our "education president" and many of our other elected representatives don't want to
hear about it. However, if we follow their lead and persist in limiting ourselves to
solutions that cost little or nothing, we will get little or nothing in return.

their hands in the air after every question I asked,
hoping I would call on them. They debated vigor-
ously about the experiments they were performing
and came up with possible interpretations that hadn't
occurred to me. They asked questions about acids
(including "If I poured some of that on his head,
would it go all the way through to his feet?"), and
acid rain, and what scientists do. They asked if they
could do more experiments. When I finished they
swarmed around me, showing me work they had
done in class, asking more questions. They told me
they wanted to be chemists, physicists, veterinar-
ians. Not one mentioned anything about getting an
engineering degree followed by an M.B.A. and start-
ing off at $50,000 a year.

I left the classroom exhilarated and remained
charged up for the rest of the day. I conclude that no
matter what's wrong with our educational process,
there's nothing wrong with the raw material. But I
also keep thinking that in two or three years, maybe
fewer, the lights will start to go out in those bright
eyes, and by the time they get through high school
most of those excited, curious kids will have become
classroom zombies. What a shameful, inexcusable
loss, both for them and for society!
Interest in educational reform is at a high level at
the moment as SAT scores continue to decline and
U.S. students continue to get trounced by European
and Asian students in science and math tests. How-
ever, the commonly proposed remedy is to go "back
to basics," which to most people means increased
drilling in elementary reading, math, and science.
Let's find out what they need to know on the SAT's
and shovel it into them. If they can't do multiplica-
tion when we give them fifteen repetitive problems a
week, then let's give them fifty. Let's hit them with
more and more drill on vocabulary and "science facts"
and get them to repeat the words and facts often
enough to be sure they can do it on the California
Achievement Test. They're not learning enough in
five and a half-hour days and nine-month academic
years? OK, let's do the same old stuff but keep them
in school six hours every day for eleven months-
that should do it!

It won't, of course. Neither will "freedom-of-choice"
schemes that let those who can afford it send their
children to better schools, overcrowding those schools
and leaving the others as dumping grounds for the
underprivileged. What might do it is attracting large
numbers of our best and brightest young people to
join the woefully inadequate number of inspired edu-
cators out there now at considerable personal sacri-
fice. Meeting this goal requires above all paying
teachers a decent salary, reducing their class sizes,
removing their nonteaching responsibilities, and
empowering them to take an active role in determin-
ing academic policies and procedures. We must also
find ways to provide all of our schools with the
resources they need to do their job effectively-mod-
ern instructional materials, laboratories, computers,
multimedia facilities, and in-service training on how
to make classrooms exciting centers of learning and
creativity. Industry-school and university-school part-
nerships can play vital roles in these efforts.
There can be little doubt that all of these steps
would move things in the right direction. Unfor-
tunately, they all cost money-much more than
loading on more drill and cramming in more facts,
which may be economical but won't accomplish any-
thing useful. Equally unfortunately, finding the
necessary money will among other things probably
require-forgive me- raising taxes, while providing
a mechanism for assuring that the money goes
where it's needed and not into creating additional
layers of administration.
Polls show that Americans are willing to in-
vest more in the future of our children and our
country, which expenditures on education represent,
but our "education president" and many of our other
elected representatives don't want to hear about it.
However, if we follow their lead and persist in
limiting ourselves to solutions that cost little or
nothing, we will get little or nothing in return. We
will still be complaining about student quality in
the next century, and the lights will still be going
out in our children's eyes. I hope we are unwilling to
let that happen.
J

Spring 1992

stirred pots)

HOW A CLEVER DEMON

NEARLY BLEW UP

THE SECOND LAW OF THERMODYNAMICS

SANJEEV R. RASTOGI
University of Delaware
Newark, DE 19716

The best you can do is break even.
... first law of thermodynamics

You can't even break even.
. second law of thermodynamics

Heat can not pass from a cooler body to
a hotter body without some other process
occurring.
... second law of thermodynamics

The entropy, or disorder, of the universe
as a whole cannot be made to decrease.
... second law of thermodynamics

s all this really true? In 1871, the Scottish physi-
cist James Clerk Maxwell suggested that a crea-
ture small enough to see and handle individual mole-
cules might be exempt from the second law of thermo-
dynamics. This creature soon came to be called
"Maxwell's demon" because of its far-reaching sub-
versive effects on the nature of things.
In the years since, theorists have spent countless
hours trying to save the second law. Nearly all their
proposals have been flawed. Flaws often arose be-
cause the workers had been misled by advances in
other fields of physics; many thought (incorrectly)
that various limitations imposed by quantum theory
invalidated Maxwell's demon.
The real reason why Maxwell's demon cannot vio-
late the second law has been uncovered only re-
cently. It is a very unexpected result of a very differ-
ent line of research-research on the energy require-
ments of computers. It is an information-based ap-
proach which involves keeping track of the informa-
tion that the devil requires, including the way it
Copyright ChE Division, ASEE 1992

stores and erases that information.

MAXWELL'S DEMON
To quote Maxwell:[11
One of the best established facts in thermodynamics is
that it is impossible in a system enclosed in an envelope
which permits neither change of volume nor passage of
heat, and in which temperature and pressure are
everywhere the same, to produce any inequality of
temperature or pressure without the expenditure of
work. This is the second law of thermodynamics, and it
is undoubtedly true as long as we can deal with bodies
only in mass, and have no power of perceiving or han-
dling the separate molecules of which they are made
up. But if we can conceive a being whose faculties are so
sharpened that he can follow every molecule in his
course, such a being, whose attributes are still as essen-
tially finite as our own, would be able to do what is
presently impossible for us. For we have seen that
molecules in a vessel full of air at uniform temperature
are moving with velocities that are by no means uni-
form, though the mean velocity of any great number of
them, arbitrarily selected, is almost exactly uniform.
Now let us suppose that a vessel is divided into two
portions, A and B, by a division in which there is a
small hole, and that a being, who can see the individual
molecules, opens and closes this hole, so as to allow
only the swifter molecules to pass from A to B, and only
the slower ones to pass from B to A. He will thus,
without expenditure of work, raise the temperature of
B and lower that of A, in a contradiction to the second
law of thermodynamics.
The "being" soon came to be known as Maxwell's
demon.12-41 Such a demon, if it existed, would abolish
the need for energy sources such as oil, uranium,
and sunlight. Machines of all kinds could be oper-
ated without batteries, fuel tanks, or power cords.

Sanjeev Rastogi received his Bachelor's in
chemical engineering from the University of
Bombay in 1990, and is presently a first-year
graduate student at the University of Delaware.
His research interests center around the com- ~
puter simulation of concentrated polymer solu-
tions using Brownian dynamics. He is also in-
terested in the isotropic-nematic phase transi-
tion in liquid crystal polymers.

Chemical Engineering Education

For example, the demon would be able to run a
steam engine continuously, without fuel, by keeping
the engine's boiler perpetually hot and its condenser
perpetually cold.
Maxwell offered no definitive refutation of the
demon, beyond saying that we lack its ability to see
and handle individual molecules. This is not a com-
pletely satisfying exorcism of the demon because it
leaves open the question of whether a being able to
see and handle molecules (if such a being did exist)
could violate the second law.

OTHER DEMONS
Since Maxwell's day, numerous versions of the
demon have been proposed. One of the simplest
creates a pressure difference (rather than a
temperature difference) by allowing all molecules,
fast or slow, to pass from B to A, but preventing
them from passing from A to B. Eventually most
of the molecules will be concentrated in A, and
a partial vacuum will be created in B. This demon
is, if anything, more plausible than Maxwell's origi-
nal demon, since it would not need to be able to
think or see.
Like Maxwell's original demon, the "pressure de-
mon" could be a source of limitless power for ma-
chines. For example, pneumatic drills of the kind
used to cut holes in the streets generally run on
compressed air from a tank kept full by a gasoline
powered compressor.
This demon is like a one-way valve for molecules
and could be visualized as a simple inanimate
device-a miniature spring-loaded trap door. Imag-
ine that the door opens to the left. If the demon
works as it is supposed to, then every time a mole-
cule from the room on the right strikes the door,
the door swings open and the molecule passes into
the room on the left. When the molecule from the
left strikes the door, however, the door slams
shut, trapping the molecule. Eventually all the
molecules are trapped on the left and the demon
has compressed the gas (reducing its entropy) with-
out doing any work.
However, this trapdoor demon is flawed. First of
all, the spring holding the door shut must be rather
weak. The work of opening the door against the
spring's force must be comparable to the aver-
age kinetic energy of the gas molecules. In 1912,
Marian Smoluchowskil5i pointed out that since the
door is repeatedly struck by molecules it will eventu-
ally acquire its own kinetic energy of random mo-
tion, i.e., heat energy. The door's energy of random
motion will be about the same as that of the mol-
Spring 1992

In the years since, theorists have spent
countless hours trying to save the second law.
Nearly all their proposals have been flawed.
Flaws often arose because the workers
had been misled by advances in
other fields of physics...

ecule striking it, and so the door will jiggle on its
hinges and swing open and shut, alternately bounc-
ing against its jamb and swinging open against the
force of the spring.
When the door is open, it obviously cannot func-
tion as a one-way valve since molecules can pass
freely in both directions. One might still hope that
the door would act as an inefficient demon, trapping
at least a small excess of gas on the left-but it
cannot do even that. Any tendency the door has to
act as a one-way valve, opening to let a molecule go
from right to left, is exactly counteracted by its ten-
dency to do the reverse-to slam shut in front of a
molecule that has wandered in front of it, actively
pushing the molecule from the room on the left to
the one on the right (aided by the force of the spring).
The two processes-a molecule pushing its way
past the door from right to left, and the door pushing
a molecule from left to right-are mechanical re-
verses of each other. In an environment at constant
temperature and pressure, both processes would take
place equally often, and the ability of the trapdoor to
act as a one-way valve would be exactly zero. There-
fore, it cannot work as a demon.
THE SZILARD ENGINE
Even though a simple mechanical demon cannot
work, perhaps an intelligent one can. Indeed, some
time after Maxwell had described the demon, many
investigators came to believe that intelligence was a
critical property that enabled the demon to operate.
In a paper in 1914, Smoluchowski[6J remarked, "As
far as we know today, there is no automatic, perma-
nently effective perpetual motion machine, in spite
of molecular fluctuations, but such a device might,
perhaps, function regularly if it were appropriately
operated by intelligent beings."
This apparent ability of intelligent beings to vio-
late the second law called into question the accepted
belief that such beings obeyed the same laws as
other systems. In 1929, the physicist Leo Szilard, in
his paper "On the Decrease of Entropy in a Thermo-
dynamic System by the Intervention of Intelligent
Beings,"[7] attempted to escape from this predica-
ment by arguing that the act of measurement, by
79

which the demon determines the molecule's speed
(or, in Szilard's version of the apparatus, determines
which side of the partition it is on) is necessarily
accompanied by an entropy increase sufficient to
compensate the entropy decrease obtained later by
exploiting the result of the measurement.
Szilard considered a demon that differed in sev-
eral ways from Maxwell's and it has since come to
be called the Szilard engine. The engine described
here is a slightly modified version by Bennetl21 of
the original Szilard engine. The engine's main
component is a cylinder in which there is a single
molecule in random thermal motion. Each end of
the cylinder is blocked by a piston, and a thin,
movable partition can be inserted into the middle of
the cylinder to trap the molecule in one half of the
cylinder (see Figure 1).
The engine's cycle consists of six steps. In the first
step the partition is inserted, trapping the molecule
on one side or the other. Szilard argued that
the work necessary to insert the partition can be
made negligibly small.
In the next step the demon determines in which
half of the apparatus the molecule has been trapped.
The devil's memory has three possible states: a blank
state to signify that no measurement has been made,
and L to signify that the molecule has been observed
in the left half of the apparatus, and an R to signify
that the molecule has been observed in the right
half. When the measurement is made, the memory
switches from the blank state to one of the other two.
The third step, which is similar to a compression
stroke, depends on the knowledge gained during the
preceding step. The piston on the side that does not
contain the molecule is pushed in until it touches the
partition. As the piston is compressing empty space,
this compression stroke requires no work. The mole-
cule which is trapped on the other side of the parti-
tion cannot resist the piston's movement.
In the fourth step the partition is removed, allow-
ing the molecule to collide with the piston that has
just been advanced. The molecule's collision exerts a
pressure on the face of the piston.
In the fifth step, which is similar to a power stroke,
the pressure of the molecule drives the piston back-
wards to its original position, doing work on it. The
energy the molecule gives to the piston is replaced
by heat conducted through the cylinder walls from
the environment (so the first law of thermodynamics
is not violated). The molecule thus continues at the
same average speed. The effect of the power stroke is
therefore to convert heat from the surroundings into

PARTITION WHICH THE DEVIL
CAN MOVE UP AND DOWN

Figure 1. The Szilard Engine
mechanical work done on the piston.
In the sixth step the engine erases its memory,
returning it to the blank state. The engine now has
exactly the same configuration that it had at the
beginning of the cycle.
Overall, the six steps seem to have converted heat
from the surroundings into work, while returning
both the gas and the engine to the same state they
were in at the beginning. If no other change has
occurred during the cycle of operation, the entropy of
the universe as a whole has been lowered. In prin-
ciple, this cycle can be repeated as often as the
experimenter wants, leading to an arbitrarily large
violation of the second law.
Szilard postulated that the act of measurement,
in which the molecule's position is determined, brings
about an increase in energy sufficient to compensate
for the decrease in entropy brought about during the
power stroke. Szilard was slightly vague about
the nature and location of this entropy increase,
but a widely held interpretation of the situation,
ever since his paper appeared, has been that mea-
surement is inevitably an irreversible process,
attended by an increase in entropy of the universe as
a whole by at least k ln2 per bit of information
acquired by measurement.

OVERPOWERING THE DEMON
To defeat Maxwell's demon, recourse to a totally
different line of approach had to be taken: the thermo-
dynamic cost of computation in digital computers.
According to Bennet,I81 the usual digital computer
performs operations that seem to throw away infor-
mation about the computer's history, leaving the
machine in a state where the immediate predecessor
is ambiguous. Such operations include erasure
or overwriting of data, and entry into a portion
of the program addressed by several different
transfer instructions. In other words, the typical
computer is logically an irreversible or entropy-
Chemical Engineering Education

generating process and produces a great deal of waste
heat, enough to require elaborate cooling strategies
in some computers.
Landauer[9] showed that the fundamental source
of dissipation was the erasure of information. For
example, logic circuits have the property of being
noninvertible, i.e., from the output of a logic circuit
one cannot always reconstruct the input. Landauer
asserted that the logical noninvertibility translates
into physical irreversibility and hence a loss of use-
ful energy. He imagined an abstract phase space,
with one coordinate being the information content of
a logic device. Prior to an erasure operation, for
example, the device can have two states (0 or 1).
Afterward it can have only one-the standard state
of an erased bit. Consequently, the extent of occu-
pied space in the logical coordinate is reduced by
two, and the occupied volume must expand in the
other coordinates. These coordinates represent things
like thermal vibrations in whatever physical system
the logic device is implemented. Excitation of ther-
mal vibrations means heat is generated.
According to Zurek,110] reversible computation can
be accomplished only by using computer memory to
keep track of the exact path from the input to the
output. This is based on the observation that thermo-
dynamic irreversibility is inevitable only in the pres-
ence of logically irreversible operations. If several
input states lead to the same output, the loss of
information in such a many-to-one mapping makes
it impossible to reversibly "backtrack" the machin-
ery of the computer. To allow reversible operation
the computer must retain this additional informa-
tion (i.e., the history of all logically irreversible steps)
at least temporarily, and it must retain at the end of
the computation at least enough information to as-
sure unambiguous backtracking. Thus, reversible
computation can be achieved only at the expense of
filling up computer memory with historical records,
aptly named "garbage."
Now, consider the operating cycle of Szilard's
engine. The last step in which the engine's memory
is reset to a blank state is logically irreversible
because it compresses two states of the machine's
memory ("the molecule is on the left" and "the
molecule is on the right") into one ("the molecule's
position has yet not been measured"). The demon
cannot reset its memory without adding a bit to
the environment.
Landauerll11 has shown that the energy needed to
erase a bit is precisely kT ln2. This converts all the
work that had been gained during the power stroke
to heat. So the demon cannot violate the second law
Spring 1992

because it must forget the results of the earlier ob-
servations in order to observe a molecule.
Consider a case where the demon has a very large
memory and simply remembers the results of all its
measurements. There would be no logically irrevers-
ible step, and the engine would convert one bit's
worth of heat into work-seemingly jeopardizing the
second law. The point to note here is that the cycle is
not a true cycle. Every time around, the demon's
memory, initially blank, would acquire another ran-
dom bit. The correct thermodynamic interpretation
of the situation would be to say that the demon
increases the entropy of its memory in order to de-
crease the entropy of its environment. Here useless
information about the outcomes of past measure-
ments piles up. The process uses the devil's memory
as a zero-entropy reservoir. To make the process
truly cyclic, the memory has to be periodically erased,
and the cost of erasure must be subtracted to calcu-
late the actual amount of useful work extracted.
Caves1121 suggests that a Maxwell demon may be
able to extract work by waiting for rare thermal
fluctuations. His system consists of a number of
Szilard engines coupled together. The trick lies in
briefing the demon, which must be told to extract
work from the engine only when the storage of infor-
mation can be handled economically. In the extreme
case, for example, the demon might be told to not
extract work except when the N molecules in the N
containers are on the left-hand side of their respec-
tive partitions. Then, the work the demon can ar-
range to be produced is NkT ln2. The state can be
represented by only a single bit, the erasure of which
will require only the expenditure of kT ln2.
This led Caves to conclude that Maxwell's demon
could indeed extract work by waiting for thermo-
dynamic fluctuations that are, by definition, rare.
Thus it would appear that the second law has a
modest loophole. This result (that the demon could
win occasionally) was disproved before Caves' paper
appeared in print.
The trouble was that the demon had to carry
additional bits of memory to show whether or not it
decided to use a particular configuration. Otherwise
it could get caught in a loop: looking at a set of boxes,
rejecting that configuration, storing no information,
then not knowing whether it had checked that con-
figuration, looking at it again, and so on. To avoid
getting caught in such a loop, the demon ends up
with a memory filled with a string of essentially
random digits distinguishing between the useful
arrangements and the rejected arrangements. There
is no compact form of expressing this information.
Continued on page 86.

I class and home problems

The object of this column is to enhance our readers' collection 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 Professors James 0. Wilkes and Mark A. Burns, Chemical Engineer-
ing Department, University of Michigan, Ann Arbor, MI 48109-2136.

ENVIRONMENTAL IMPACT OF

PAPER AND PLASTIC GROCERY SACKS

A Mass Balance Problem with Multiple Recycle Loops

D. T. ALLEN, N. BAKSHANI
University of California
Los Angeles, CA 90024

Environmental issues are becoming increasingly
important in the design of chemical processes
and chemical products. Incorporating these issues
into an already crowded chemical engineering cur-
riculum is a challenge. One way to address this
challenge is to develop entire courses dedicated to
environmental issues. An alternative strategy is to
develop homework and design problems that can be
used in existing chemical engineering courses, illus-
trating both fundamental engineering principles and
environmental issues
For the past year we have been developing such
problems for the chemical engineering curriculum.
One of the problems developed for the mass and
energy balances course is given below. The problem
illustrates the concept of recycle, a topic normally

N. Bakshani is a research fellow in the Chemical
Engineering Department, University of California,
Los Angeles. He holds a BS and MS in metallurgi-
cal engineering from New Mexico Institute of Tech-
nology and a PhD in applied earth sciences from
Stanford University. Current interests include the
process engineering tools required for pollution
tries.

David Allen is an associate professor of chemi-
cal engineering at the University of California, Los
Angeles. He received his BS degree, with distinc-
tion, from Cornell University (1979) and his MS
and PhD degrees from California Institute of Tech-
nology (1981 and 1983). He has also held visiting
appointments at the California Institute of Tech-
nology and the Department of Energy.

covered in a mass and energy balance course, and
the problem exposes students to the issue of product
life-cycle analysis. Specifically, the problem compares
paper and plastic grocery sacks based on energy
requirements and environmental impacts. The prob-
lem is divided into five sections:
1. Background material
2. A problem statement
3. Open-ended questions for discussion
4. A solution
5. References and suggestions for further reading
Sections 1-3 and 5 can be distributed to the
students as a homework assignment. The prob-
lem solution takes between two and three hours for
most students.
BACKGROUND
At the supermarket checkout stand, consumers
are asked to choose whether their purchases should
be placed in unbleached paper grocery sacks or in
polyethylene grocery bags. Many consumers make
their choice based on their perception of the relative
environmental impacts of these two products.
The analysis framework for this problem will be
the mass flow diagram shown in Figure 1. For the
problem, we can simplify Figure 1 considerably. First,
consider the recycle loops. Almost all recycled gro-
cery sacks are returned to the raw material formula-
tion stage, so we can ignore the product recycle and
remanufacture loops. This simplification leads to the
mass flow diagram shown in Figure 2 (and Figure 3).
Copyright ChE Division ofASEE 1992
Chemical Engineering Education

These two figures define our life-cycle analysis frame-
work for comparing paper and plastic grocery sacks.
In the figures we have listed the air emissions
generated per unit of production for both plastic and
paper grocery sacks. Before a quantitative compari-
son between the two products can be made, however,

energy

energy

energy

energy

we must consider how the products are used. Al-
though both are designed to have a capacity of 1/6
barrel, fewer groceries are generally placed in plas-
tic sacks than in paper sacks, even if the practice of
double-bagging (one sack inside the other), used in
some stores, is taken into account. There is no gen-
eral agreement on the num-
energy ber of plastic grocery sacks

needed to hold the volume of
product groceries usually held by a pa-
disposal per sack. Reported values
range from 1.2 to 3. In this
atmos problem we will use a value of
2.0 plastic grocery sacks re-
quired to replace a paper gro-
cery sack.

Figure 1. The life cycle for manufactured goods: an analysis template

BASIS 1000 Ibs of Polyethylene (PE) Sacks
since weight o PE sack 0 2632 oz Energy.185 Btu per sack (combined raw material acquisition and product disposal)
1000 lbs PE sacks = 60,790 sacks

Energy: 464 Btu per sack

nasources r.aw materilas materials manufacture. product manufacture. product
acquisition product use disposal

Almos Emissions 00146 oz per sack

Recycle

Atmospheric Emissions 00045 oz per sack (combined raw material acaulstion ard product d postal)
Figure 2. The life cycle for manufactured goods: polyethylene (PE) grocery sacks
(Source: Franklin Associates, Ltd.-see suggestions for further reading.)

BASIS # of Paper sacks = 60,790/2
or 30,395 sacks
weight of 1 paper sack = 2.144 oz

Atmospheric Emissions: 0 0510 oz. per sack (combined raw material acquisition and product disposal)
Figure 3. The life cycle for manufactured goods: paper grocery sacks
(Source: Franklin Associates, Ltd.-see suggestions for further reading.)
Spring 1992

PROBLEM STATEMENT

a) Using the data in Figures 2
and 3, determine the amount
of energy required and the
quantity of air pollutants re-
leased per 1,000 lb of produc-
tion of plastic sacks. Also de-
termine the amount of energy
required and the quantity of
air pollutants released for the
quantity of paper sacks
capable of carrying the same
volume of groceries as the
1,000 lb of polyethylene sacks.
Both the air emissions and the
amount of energy required are
functions of the recycle rate,
so perform your calculations
at three recycle rates, 0%
recycled, 50% recycled, and
100% recycled.
b) Plot the results of part a)
for both types of sacks. Com-
pare the energy requirements
and atmospheric emissions
of the paper and plastic gro-
cery sacks as a function of re-
cycle rate.
c) Based on your results, dis-
cuss the relative environmen-
tal impacts of the two prod-
ucts. Note that in part b) of
the problem, you compared the
quantity of air emissions re-
leased. As shown in Table 1,
the qualitative characteristics

of the air emissions due to paper sacks are different
than those due to plastic sacks. In your discussion
you should consider whether or not it is valid to
compare directly the mass of atmospheric emissions
due to the two products.
d) The material and energy requirements of the
plastic sacks are primarily satisfied using petroleum,
a non-renewable resource. In contrast, the paper
sacks rely on petroleum only to a limited extent and
only for generating a small fraction of the manufac-
turing energy requirements.'11 Most of the energy
requirements of pulp and paper manufacturing are
met by burning wood chips.
Compare the amount of petroleum required for
the manufacture of two plastic sacks
to the amount of petroleum neces-
sary to provide 10% of the energy
required in the manufacture of one Profile c
paper sack. Assume 0% recycle, and
that 1.2 lb of petroleum is required
to manufacture 1 lb of polyethylene.
The higher heating value of petro- .A m.np, nr.
leum is 20,000 BTU/lb.

Questions for Discussion
1) Is 100% recycle really feasible for
the products being analyzed or for
any consumer products? Consider at
least two points in your analysis: con-
taminants on or within the sacks,
and mechanical wear and tear of the
grocery sacks.

2) In this problem you have con-
sidered only two choices for deliv-
ery of groceries: paper sacks and
plastic sacks. Can you suggest other
alternatives?

SOLUTION
a) The energy requirements and to-
tal atmospheric pollutants for both
paper and polyethylene (PE) grocery
sacks, extracted from Figures 2 and
3 of the problem statement, are listed
in Table 2. All values pertaining to
PE sacks are based on 1,000 lbs of
product, or 60,790 PE sacks. Values
for the paper sacks are based on
60,790/2 = 30,395 sacks, the number
required to hold an equivalent vol-
ume of groceries.
b) The data from part (a) are plotted
in Figures 4 and 5. These figures
84

Particulates
Nitrogen Oxide
Hydrocarbons
Sullur Oxides
Carbon Monoxide
Aldehydes
Other Organics
Odorous Sulfur
Ammonia
Hydrogen Fluoride
Lead

show the effect of recycle rate on energy require-
ments and atmospheric pollutants. At 0% recycle,
PE sacks (on an equal-use basis, two PE sacks per
paper sack) require approximately 20% less energy
than paper sacks. However, as the recycle rate in-
creases, this difference in energy requirement de-
creases linearly. At recycle rates above 80% there
appears to be no significant difference in energy
requirements for PE and paper sacks. Therefore, on
the basis of energy alone, paper sacks would be
considered competitive with PE sacks, at high (>80%)
recycle rates.
The plot for total atmospheric emissions shows
a similar declining difference between the prod-
ucts, with increasing recycle rates. At 0% recycle,

TABLE 1
if Atmospheric Emissions for Paper and Plastic
Grocery Sacks
rSource: Franklin Associates, Ltd. I
AL;P___Then, P.llun.rai l Per .ie ilb _

F.r.raoioni fr 1 Paper Sack
0- Recjclng I,)! I-ecdunp

Emissions for 2 Polyethylene Sacks
0% Recycling 100% Recycling

2.8 x 104
8 0 x 10
3.9 x 104
10.6 x 10'
6.5 x 10'
0.1 x 10
0.2 x 104
0.0
0.0

0.0

0 8 x 104
2.1 x 104
5.8 x 10'
2.6 x 10"
0.7 x 10'
0.0
0.0

0.0

0.0

0.8 x 104
1.7 x 104
3.2 x 10.
2.7 x 10"
0.6 x 10 '
0.0
0.0

0.0

0.0

24.6 x 104
9.2 x 104
4.9 x 10 '
13 6 x 10'
7.0 x 10-'
0.1x 104
0.3 x 10'
4.5 x 104
0.0

0.0

Merc ury
Chlorine

TABLE 2
Energy Requirements and Atmospheric Emissions
for Paper and Plastic Sacks

0" Recycle
Energy Atmospheric
Requ red Polutants
I MI BTU' Ib-

Polyethylene
60,790 sacks

Paper
30.395 sacks

49.5 195.0

50'1 Rectle
Energy Atmosphenc
Required Pollutants
INMM BTUi lbs

33.8 64.0

38.5 146.5

100% Reecle
Energy Atmosphenc
Required Polutants
I MM BTU, lb.

28.2 55.6

27.5 98.0

Chemical Engineering Education

on. lit.;

total atmospheric emissions are 60-70% lower for
PE sacks; this difference gradually declines to 40%
at 100% recycle.
c) PE sacks generate lower amounts of atmospheric
emissions at all recycle rates-a fact that may be
significant if there are no qualitative differences be-
tween the emissions. However, the emission compo-
sition data of Table 1 show both quantitative and
possible qualitative differences in the emissions as-
signed to PE and paper. In the case of paper sacks,
the amount of particulates, nitrogen oxides, and sul-
fur oxides is higher than for PE. As might be ex-
pected, higher levels of hydrocarbon emission are
assigned to PE sacks. These hydrocarbons are also
very likely to be qualitatively different from the hy-
drocarbon emissions generated by paper-sack pro-
duction. It would be difficult to assess the respective
environmental impacts of the hydrocarbon emissions
without a much more detailed description of the
emissions. Also, lack of emission data from other
sources within the life cycle (i.e., incineration and
emissions from landfills) makes the comparison of
PE and paper sacks incomplete and any comprehen-

so0
Polyethylene Sacks
---- Paper Sacks

a 40

| 30
aLJ
W

0 20 40 60 80 100
Recycling Rate
Figure 4. Energy requirements for grocery sacks.
Basis: 60,970 polyethylene sacks, 30,395 paper sacks.

200

50 --- Paper Sacks
Polyethlene Sacks
150-

r 100

S 20 40 60
Recycling Rate %

80 100

Figure 5. Atmospheric emissions for grocery sacks.
Basis: 60,970 polyethylene sacks, 30,395 paper sacks
Spring 1992

sive comparison difficult.
d) Petroleum requirements of polyethylene sacks:
Fuel:
S39.5 x 106 BTU ( 1 Ib petroleum 0.032 b petroleum
60,790 sacks 2 x104 BTU ) sack

Material

0.2632 oz 1b (1.2)0.020 lb petroleum
sack 16 oz sack
Total = 0.052 lb petroleum/sack

Petroleum requirements of paper sacks:
Fuel:

49.5x 106 BTU ( 1Ib petroleum 0 lIb petroleum
30,395sacks (0.1)2x104 BTU sack

Two polyethylene sacks require more than an order
of magnitude more petroleum than a paper sack.
Sample Answers for the Questions for Discussion
1) The term "100% recycle" implies that all of the
material in a grocery sack can be recovered, but
complete material recovery is generally impossible
to achieve. In the case of polyethylene and paper
sacks, manufacturers invariably print identification
labels or advertisements on the sack. The printing is
usually done with an ink or dye that is undesirable
in the remanufacturing process and is not easily
removed. In addition, a variety of consumer items,
such as foods and beverages, can contaminate the
sacks in a similar manner. In both cases, the con-
taminants could lower the quality ofremanufactured
sacks to a point where the sacks are unusable. There-
fore, in order to meet quality specifications, some of
the recycled material containing the contaminants
at concentrated levels is removed as a purge stream,
and additional raw material and energy are required.
2) Many nations have adopted the reusable grocery
sack concept with significant success, where success
is measured by the number of people actively prac-
ticing the concept. Shoppers may reuse their du-
rable sacks made out of nylon, jute, or thick cotton-
string netting hundreds of times. The effect of gro-
cery sack reuse as opposed to sack recycle is illus-
trated in Figure 1. Sack reuse is represented by the
product recycle loop; note that there is less energy,
atmospheric emissions, and waste associated with
the product recycle loop than with the materials
recycle loop. All material and manufacturing steps
are bypassed for the life of the sack. However, be-
cause the manufacture of typical durable grocery
sacks involves an order of magnitude more energy
85

n i i

use and emissions than the manufacture of a paper
or plastic sack, the consumer must use the sack at
least ten to twenty times before an environmental
benefit is achieved.
CONCLUSION
Assessing the total environmental impact of any
product is a difficult process, involving evaluations
of processing steps ranging from raw material acqui-
sition to post-consumer waste disposal. Comparing
the environmental impact of competing products is
even more complex. Making comparisons between
products usually involves making trade-offs between
very different environmental impacts.
The purpose of this problem is to illustrate the
difficulties involved in comparing the total environ-
mental impact of different products. Paper and plas-
tic grocery sacks were used as a case study. To com-
pare paper and plastic grocery sacks we found that
we must evaluate the trade-offs between energy use,
pollutant emissions, and the depletion of natural
resources. Plastic sacks appear to result in less at-
mospheric emissions and require less energy. On the
other hand, paper sacks rely on a renewable re-
source for material and energy. Thus there is no
clear, environmentally superior product. The con-
sumer is left with a difficult choice, and as illus-
trated in the problem this choice must be made with
incomplete information.
REFERENCES
1. Hocking, M.B., "Paper versus Polystyrene," Science, 251,
504 (1991)
Suggestions for Further Reading
Resource & Environmental Profile Analysis of Polyethylene
and Unbleached Paper Grocery Sacks, Franking Associates,
Ltd., Prairie View, KS (1990)
Federal Office of the Environment, "Comparison of the Ef-
fects on the Environment from Polyethylene and Paper
Carrier Bags," Bismarckplatz 1, 1000 Berlin 33, RFG, En-
glish version. August (1988)
Riggle, D., "Recycling Plastic Grocery Bags," Biocycle, p 40,
June(1990) '

Second Law of Thermodynamics
Continued from page 81.

The extra cost of erasing these digits exactly cancels
any energy gain elsewhere in the system.
The conundrum of Maxwell's demon has been re-
solved by applying the concepts of thermodynamics
of irreversible computation.
In our discussions, we assumed the behavior of
the demon to be completely deterministic, i.e., one
instruction is completed before it goes on to the next

instruction. What is not so clear is what would hap-
pen if the demon could wander a little, i.e., if the
demon knew its instructions but was not quite sure
of the order in which to carry them out. The demon
would then proceed from one step to another, going
forward or backward, in a somewhat random fash-
ion. In the long run, this might allow the demon to
extract some work.
There is no doubt what the outcome of the above
argument is going to be, but it is a loophole which
has yet to be closed.
REFERENCES
1. Maxwell, J.C., Theory of Heat, 4th ed., Longmans, Green &
Co., London, 328 (1875)
2. Bennet, C.H., Sci. Am., 255(11), 108 (1987)
3. Maddox, J., Nature, 345, 109 (1990)
4. Peterson, I., Sci. News, 137, 378 (1990)
5. Smoluchowski, M., Z. Phys. (1912)
6. Smoluchowski, M., Lecture Notes, Leipzig (1914)
7. Szilard, L., Z. Phys., 53, 840 (1929)
8. Bennett, C.H., IBM J. Res. Dev., 17, 525 (1973)
9. Landauer, R., IBM J. Res. Dev., 3, 183 (1961)
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11. Landauer, R., Nature, 335, 779 (1988)
12. Caves, C.M., Phy. Rev. Letters, 64, 2111 (1990) O

Liquid-Liquid Processes
Continued from page 71.

information is obtained by the Stirred Transfer Re-
actor, which is a modified Lewis cell. The interfacial
area between the contacted liquid phases needed for
the estimation of mass transfer and reaction rates is
calculated from information about the drop size dis-
tribution and the dispersed-phase volume fraction.
The former is obtained by the Microphotographic
Technique and/or the Laser Capillary Spectropho-
tometer Technique and the latter by the Ultrasonic
Technique.
Tracer concentration measurements by the La-
ser Photometric Technique yield information about
flow properties, i.e., axial mixing parameters in both
phases. Drop size-concentration bivariate distribu-
tions are obtained by the Laser Capillary Spectro-
photometry Technique. This information is extremely
valuable in model discrimination and parameter es-
timation of models describing droplet breakage and
coalescence. It also provides information on dispersed
phase mixing. Finally, the Ultrasonic Technique is
also employed for the control of the dispersed-phase
volume fraction in extraction columns to secure non-
flooding optimum operation.
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28. Kirou, V.I., L.L. Tavlarides, J.C. Bonnet, and C. Tsouris,
AIChE J., 34, 283 (1988)
29. Schmidt, H., C. Tsouris, E. Eggert, and L.L. Tavlarides,
AIChE J., 35, 507 (1989)
30. Schmidt, H., and E. Eggert, KfK-Bericht, Nr 3630, 227
(1984)
31. Verhoff, F.H., PhD Dissertation, University of Michigan,
Ann Arbor, MI (1969)
32. Verhoff, F.H., S.L. Ross, and R.L. Curl, I&EC Fund., 16, 371
(1977)
33. Bae, J.-H., and L.L. Tavlarides, AIChE J., 35, 1073 (1989)
34. Mukkavilli, S., C.K. Lee, I. Hahh, and L.L. Tavlarides, Sep.
Sci. and Tech., 22(N2&3), 395 (1987)
35. Zeitlin, M.A., and L.L. Tavlarides, AIChEJ., 18, 1268 (1972)
36. Sovova, H., and A. Havlicek, Chem. Eng. Sci., 41, 2579
(1986)
37. Bonnet, J.C., and L.L. Tavlarides, I&EC Res., 26, 811 (1987)
38. Tsouris, C., L.L. Tavlarides, and J.C. Bonnet, Chem. Eng.
Sci., 45, 3055 (1990)
39. Yi, J., and L.L. Tavlarides, I&EC Res., 29, 475 (1990)
Spring 1992

40. Tsouris, C., and L.L. Tavlarides, I&EC Res., 29, 2170 (1990)
41. Tsouris, C., and L.L. Tavlarides, Annual AIChE Meeting,
Chicago, IL, Nov. 11-16 (1990) 31

book review

COMPUTATIONAL METHODS

FOR PROCESS SIMULATION
by W. Fred Ramirez
Butterworths, 80 Montuale Ave., Stoneham, MA 02180;
$52.95 (1991)
Reviewed by
Sangtae Kim
University of Wisconsin
This book provides a thorough overview of the many
facets of computations in the chemical engineering cur-
riculum. The contents of the book are ordered along the
lines of a typical undergraduate curriculum. Chapters 1
through 3 present overall material and energy balances
and dynamics of lumped parameter systems. Students
who have mastered simple ODEs will have no problem
with this material. Chapter 2 also provides an introduc-
tion to the IMSL library. Indeed, the IMSL routines are
exploited throughout the book, and readers who have al-
ways wanted to learn these routines will find many excel-
lent applications in this book.
Chapters 4 and 5 deal with applications from unit op-
erations: the chemical reactor and reaction kinetics, and
separation (e.g., multicomponent distillation) operations.
Chapter 6 starts with a summary of the microscopic
equations of change, using the notation and sign conven-
tions of Transport Phenomena by Bird, Stewart, and
Lightfoot. Some details are omitted (e.g., the constitutive
equation for a Newtonian fluid) but with references to
Transport Phenomena. These set the stage of modeling of
distributed parameter systems and the BVP and PDE
examples of chapters 7 and 8.
By covering a wide array of chemical engineering appli-
cations (unit operations, biochemical/biomedical processes,
environmental modeling are some of the areas encoun-
tered), the author has woven into this book just about
every computational method of utility to the chemical
engineer, with coded (Fortran/IMSL) examples for those
interested in immediate application of concepts to fre-
quently encountered chemical engineering mathematical
models.
Because the book covers the entire spectrum from in-
troductory chemical engineering courses, e.g., material and
energy balances, to senior-level courses on process dynam-
ics and process design, a course based on this book would
have to come somewhere near the end of the curriculum,
perhaps as a senior-level elective. The book may also be of
value to those who have already mastered the typical
chemical engineering curriculum, e.g., the chemical engi-
neering practitioner, and are now involved in some aspect
of computational or mathematical modeling of chemical
engineering processes. 1
87

classroom

HELPING STUDENTS DEVELOP A

CRITICAL ATTITUDE TOWARDS

CHEMICAL PROCESS CALCULATIONS

NOEL DE NEVER, J. D. SEADER
University of Utah
Salt Lake City, UT 84112

Before we had digital computers and process de-
sign software, a chemical engineer's education
usually included the application of graphical corre-
lations of thermodynamic properties for pure compo-
nents and certain binary and ternary mixtures to
make combined material balance, energy balance,
and phase equilibrium calculations. Examples and
homework problems of this nature were widely used
in the most popular chemical engineering textbooks
and were believed to have great educational value
because the solution to a complex problem could be
readily followed and understood from a graphical
display, which also offered considerable visual
insight into the phenomena being studied. Since
the advent of digital computers, textbooks have
slowly migrated toward computer solutions of ex-
amples and homework problems, but in many cases
the nature of the examples and problems has been
retained so that they can be solved with or without
a computer. Even the rules for the annual AIChE
Student Contest Problem state that students are
free to use available computer programs, but their
use is not essential.
Some of the early lessons that students must learn
when using computer programs to do process calcu-
lations are:
SThe program is making assumptions of which the user
may not be aware. This is particularly true of the choice
of thermodynamic property correlations, for which the

Since the advent of digital computers,
textbooks have .., migrated toward computer
solutions ..., but in many cases the nature of the
examples and problems has been retained so that
they can be solved with or without a computer.

Copyright ChE Dwision, ASEE 1992

Noel de Nevers has been a faculty member at
the University of Utah since 1963. His principal
interests are fluid mechanics, thermodynamics,
and air pollution. He has also developed a course
and edited a book of readings on Technology
and Society. In addition to his technical work,
three of his laws were published in the 1982
Murphy's Laws compilation and he won the cov-
eted title of "Poet Laureate of Jell-O" at the
annual Jell-O Salad Festival in Salt Lake City.

J.D. Seader is Professor of Chemical Engineer-
ing at the University of Utah, where he has been
a faculty member for twenty-five years. He re-
ceived the University Distinguished Teaching
Award in 1975 and served as Chairman of the
department from 1975-1978. His current research
interests include process synthesis, energy-effi-
cient separation techniques, recovery of synthetic
crude oil from tar sands, and restrictive diffusion.

program's default values are most often used.
Different property correlations may give drastically dif-
ferent computational results; it is not always easy to
determine which result is the best.
The best computer-aided result may be inferior to the
result of a classical graphical method that utilizes a
more accurate representation of the thermodynamic prop-
erties.
These lessons are illustrated in the following ex-
ample, which we believe has great educational merit.
Do not assume that our showing the limitations of
computer programs means that we oppose student
use of computers. We strongly favor that use, but we
strive to teach our students that the proper com-
puter solution of a process-engineering problem has
the following steps:
hand solution of the problem or an approximation
thereof
computer solution of the problem
analysis to determine if the computer has truly solved
the problem we think it has solved
examination of the effect of different assumptions,
particularly thermodynamic property selections, on the
computer solution
extensive application of the computer solution to
explore ranges of problem parameters, seeking some
kind of optimum solution
Chemical Engineering Education

Vapor
Saturated
vapor at H20
A 250 pso
80 w %Condenser
80 lt % o
Ammonia Expansion J
10,000 Ib/hr valve

(a) Problem Statement u V d

3754 lb/hr NH3
2 lb/hr H20
Dew-Point Vapor 0 -5,800,000 Btu/hr 3756 lb/hr
290F

molD mol%
vapor vapor
or 4246 lb/hr NH3
1 Ib/hr H20

(b) Results from Graphical Solution, using VLE data in (5)

3578 Ib/hr NH3
60 lb/hrH2
0 -5,800,000 Btu/hr 3580 lb/hr
Dew-Point Vapor
250 sia 138TF 0 ^
c() R s ondensrer S
27 36
molG mo%
vapor vapor 4422 lb/hr NH3
1998 Ib/hr H20
64201b/hr
(c) Results from Chemshare Simulation. Case 4 described in text
Figure 1. Comparison of the graphical solution and the
best of the ChemShare solutions.

0.0 0.2 0.4 0.6 0.8 1.0
WL Fraction Ammonia
Figure 2. Graphical solution to the example problem. The
students locate the feed point by its overall composition
and enthalpy and then construct tie lines, using the equi-
librium constructions lines (not shown) until they locate
the tie line which passes through the feed point (in this
case the 80 F tie line, as closely as one can read the graph).
The vapor and liquid compositions at the end of that tie
line are those which simultaneously satisfy the material
and energy balances and the equilibrium relationship.
Spring 1992

EXAMPLE
The following is a problem which the textbook
intends to be solved by the classical graphical
method:

A mixture of ammonia and water in the vapor phase,
saturated at 250 psia and containing 80% by weight
ammonia, is passed through a condenser at a rate of
10,000 lb/hr. Heat is removed from the mixture at a
rate of 5,800,000 Btu/hr. . The mixture is then
expanded to a pressure of 100 psia and passes into a
separator. A flow sheet of the process is given as Fig.
P5.19 [reproduced in this paper as Figure la]. If the
heat loss from the equipment to the surroundings is
neglected, determine the composition of the liquid
leaving the separator. . (b) Using the enthalpy-
concentration diagram method.
HIMMELBLAUtl, PROBLEM 5.19(B), PAGES 514-515

Our sophomore students solve this problem first
by hand, using an enthalpy-concentration diagram,
locating the point corresponding to the enthalpy and
concentration of the inlet to the flash vessel, and
then by trial and error, constructing tie lines for
various assumed liquid concentrations until they find
the tie line that passes through the inlet concentra-
tion and enthalpy. This is a standard procedure,
illustrated in Figure 2 and long discussed in "Mate-
rial and Energy Balance" textbooks.
The result, as summarized in Figure 1(b), is that
the outlet vapor is 99+wt% ammonia, the outlet
liquid is about 68 wt% ammonia, the outlet temp-
erature is about 80F, and the outlet molar V/F
(Vapor/Feed ratio) is about 0.38. One can also
readily solve graphically for the feed inlet (dew
point) temperature of 2900F, and the temperature of
the vapor-liquid mixture leaving the heat exchanger
of 133'F. The enthalpy-concentration diagram in
Brown, et al.,[21 is the most easily readable and
usable of the ones we have found, because of its large
size and fine grid.
After the classical graphical solution to this prob-
lem has been discussed in class, we ask the students
to solve the same problem on a digital computer with
the ChemShare process simulation program, Design
11,[31 using each of the following four choices of thermo-
dynamic correlations for K-values (KI = yi/xi) and
enthalpies, respectively:

1. The default option (which requires no thermodynamic
property selections by the students). It uses STDK
(Chao-Seader-Grayson-Streed) and STDH (Redlich-
Kwong).
2. APISOUR (special K-value option recommended by the
American Petroleum Institute for mixtures containing
ammonia and water) and the STDH default for
enthalpies.

3. APISOUR and LAT (Redlich-Kwong enthalpies for the
vapor and pure-component latent heats to obtain
liquid enthalpies).
4. PENK (Peng-Robinson) and PENH (Peng-Robinson),
both with BIN PAR = PENG1 for binary interaction
parameters.

We ask the students to compare the results of the
computer-aided calculations to the graphical result
as shown in Table 1. This gets the students' atten-
tion! Most students have come to believe that a
computer print-out is divine revelation, so the obvi-
ously wrong answers from an industrial-grade flow-
sheet simulator come as a shock. The final set of
answers, Case 4, using the Peng-Robinson equation
of state with binary interaction parameters (which
is also shown in Figure Ic) is a good approximation
of the graphical solution, but the other results are
grossly wrong. As expected, the APISOUR choice for
K-values gives reasonable results for the material
balance, but the accompanying selections (STDH or
LAT) for enthalpies lead to very poor estimates of
the outlet temperature.
After the students get over their shock, we dis-
cuss why they found the bizarre answers in Table 1.
The Himmelblau problem is an excellent choice for a
graphical solution using an enthalpy-concentration
diagram because the ammonia-water system is one
of only a few well-known systems that exhibit a
negative deviation from Raoult's law, causing liquid-
phase activity coefficients, YiL, to have values less
than one, and because the system shows a large heat
of mixing (heat of solution). For the liquid, using the
enthalpy-concentration diagram, we estimate the in-
tegral heat of mixing to be minus 88 Btu/lb.
With this in mind, we discuss with the students
why the first three computer cases in Table 1 did so
poorly with this seemingly simple problem. The an-
swer is that the first three thermodynamic property
estimation procedures do not treat this nonideal sys-
tem well. For Case 1, the computer output specifi-
cally warns that, "Water is treated as an immiscible
component." Many students don't even notice this
statement. Obviously, that treatment is wrong and
is the cause of the wrong results for Case 1. By
treating water as immiscible, the inlet stream is
determined to be a gas-liquid mixture, with 97% of
the water in the liquid phase, even though the stream
is explicitly specified in the input-data commands as
a dew-point stream. The computer program has ac-
tually interpreted the dew point specification as that
referring to the first droplet of pure liquid ammonia
immiscible in water, which corresponds to the secon-
dary dew point which occurs at a lower temperature
after 97% of the water has condensed. This results
90

in lowering the enthalpy of the feed to the cooler
enough that the cooler outlet temperature is calcu-
lated as -91.60F. The simulator does not consider ice
formation, so that the water is shown as a liquid at
-91.60F.
The water-immiscibility problem can be eliminated
in Case 1 by adding to the input data the general
command NOIMM. If this is done, the computed
values for the three quantities in Table 1 are 74.90F,

TABLE 1
Comparison of Graphical and Design II Solutions

ChemShare Design II
Case 1 Case 2 Case 3 Case 4
Graphical Default K APISOUR APISOUR PENK and
Hand Default H Default H LAT PENH with
Solution PENG1
Outlet T,'F 80 -91.2 -0.7 10.6 83.4

Liquid mass
fraction 0.68 0.80 0.68 0.67 0.69
ammonia

Molar V/F 0.38 0 0.366 0.399 0.358

TABLE 2
Comparison of K-Values for the Graphical and
Design II Solutions

K-value at Graphical -- ChemShare Design U -
80F and Hand Default K ADISOUR PENK PENK with
100 psia Solution NOIMM PENG1
Water 0.0047'41 0.0081 0.0051 0.0048 0.0017
0.0014151

Ammonia 1.44 1.41 1.75 9.63 1.38

Here for the first case we show the K-values using the NOIMM option;
n the default mode which treats water as immiscible, the K-values are
aot reported by the simulation program. As discussed in the text, we show
wo estimates for the Kof water, based on data in (4) and (5); both of these
data sources lead to the same K for ammonia.
These are not the K-values for the cases described in Table 1, which
how a variety of temperatures. Rather, they are the K-values presented by
ChemShare Design II for an isothermal flash at 80"F and 100 psi, for all
the K-value options shown.

TABLE 3
Integral Heat of Mixing for
68 Weight Percent Ammonia in Water at 80F

ChemShare Design II

Case 1 Case 2
Graphical Default K APISOUR
Hand Default H Default H
Solution

Integral heat
of mixing, -88
Btu/lb mixture

Case 3 Case 4
APISOUR PENK and
LAT PENH with
PENG1

0 +56 0 -57

Chemical Engineering Education

0.76, and 0.179, which are closer to the correct val-
ues than those found for Cases 2 and 3, but not as
close as those found for Case 4.
Two factors contribute to the poor values com-
puted for the outlet temperature in Cases 2 and 3,
the K-values, and the enthalpies. This is illustrated
in Tables 2 and 3. Table 2 compares the K-values
computed from an isothermal flash on the feed mix-
ture at 800F and 100 psia (outlet conditions from the
graphical solution). The K-value listed in Table 2 for
water from the graphical solution could not be found
from the enthalpy-concentration diagram because
the vapor mol fraction of water, less than 0.0015, is
too close to the axis to be accurately read. Instead
the vapor mole fraction of water was estimated from
other published data.
Published values of the ammonia-water vapor-
liquid equilibrium are in good agreement on the
behavior of the ammonia, but in considerable dis-
agreement on the small concentration of the water
in the vapor phase. For the vapor-liquid mixture
leaving the flash at 80F and 100 psia, with 0.32
weight fraction water in the liquid phase, by inter-
polating from the vapor-pressure data for ammonia-
water mixtures given in Tables 3-21 to 3-24 in Perry's
Chemical Engineers'Handbook,141 one estimates the
liquid-phase activity coefficients to be ,water = 0.87
and Yammonia = 0.97 and the water content of the gas
stream in Figure lb to be 5 lb/hr. If one extrapolates
the more recent data of Gillespie, Wilding, and Wil-
son[51 from 313 to 300 K, one estimates the activity
coefficients to be Ywater = 0.27 and Yammonia = 0.93 and
estimates the water content of that gas stream to be
2 lb/hr. Both of these water amounts are negligible
for practical purposes. From these estimates, one
computes two K-values for water (both shown in
Table 2) of 0.0044 based on Perry's Chemical Engi-
neers' Handbook and 0.0014 based on Gillespie, Wild-
ing, and Wilson. We consider the latter the more
reliable. Both sources give the same K-value for
ammonia, 1.44.
It can be seen from Table 2 that the best agree-
ment with the hand graphical method for the K-
value of ammonia is given by the STDK and PENK
(with PENG1 option) methods. The APISOUR K-
value is high by 22%, while the PENK (without the
binary interaction parameter) is badly in error. The
K-values for ammonia play a major role in the solu-
tion to this problem. The K-values for water, which
are very small, play a minor role because the amount
of water in the vapor is so small. The STDK gives
a high value, APISOUR and PENK give values
which practically agree with Perry's Chemical Engi-
Spring 1992

neers' Handbook, and PENK and PENG1 give a
value which practically agrees with Gillespie, Wild-
ing, and Wilson.
STDK is incapable of estimating values for YiL of
less than one because STDK applies the regular
solution theory, which is only capable of estimating
YiL values of greater than one. APISOUR should be
capable of good estimates of K-values because it is
based on the regression of experimental data. Ini-
tially, the Peng-Robinson equation of state was most
commonly used to estimate K-values and enthalpies
for mixtures containing only nonpolar and slightly
polar compounds, such as hydrocarbons and light
gases. However, the incorporation of a temperature-
dependent binary interaction parameter into the bi-
nary mixing rules makes it possible, as shown by
Heidemann and Rizvi,161 to consider applications to
mixtures containing highly polar compounds. The
PENG1 data-file option in Design II includes binary
interaction parameters for the ammonia-water sys-
tem, which were obtained from regression of experi-
mental equilibrium data. These interaction parame-
ters are applied to the estimation of both K-values
and enthalpies.
Either the K-value correlation or the enthalpy
correlation can lead to wrong answers. Table 3
shows the computed heats of mixing at 80'F and the
saturation pressure for a liquid mixture containing
68 wt % ammonia from several correlations. For
those cases in Table 2 that had reasonably good
estimates of the K-values, the cases with poor esti-
mates of the heat of mixing led to the worst esti-
mates of the outlet temperatures shown in Table 1.
The results given in Table 3 show a very wide
range of values. The best agreement is obtained
from PENH using the PENG1 parameters. Thus,
the use of PENK and PENH with PENG1 gives the
best compromise between estimates of K-values and
enthalpies, and thus the best computer solution for
the Himmelblau problem, as summarized in Figure
Ic. This choice for thermodynamic properties is the
only one involving consistent estimates of enthalpies
and K-values because the same equation of state is
used for both estimates. However, the success of this
choice is largely due to the use of the PENG1 para-
meters, which were regressed from experimental data
for this particular binary system.
None of the physical property estimation pack-
ages we found in Design II gives a solution to this
problem that is within chart-reading accuracy of the
hand solution, which is probably the most reliable
solution because it is based directly on the experi-
mental data for this particular binary system. The
91

computer simulation packages all must sacrifice some
accuracy in treating particular non-ideal systems in
order to use general estimation procedures which
are likely to give satisfactory results for many sys-
tems, including those for which experimental data
are not available. A physical property model which
used the experimental binary data for this system
could be written, and would presumably be as accu-
rate as those data; indeed, the ChemShare system
does include a few special models for important com-
mercial mixtures, including the APISOUR model for
K-values of ammonia-water systems, but it is not
accompanied by a special enthalpy model.
The Design II computer-aided program of the
ChemShare Corporation is only one of a number of
such programs that can be used to study the effect of
selected thermodynamic property correlations on the
solution to the above Himmelblau problem. These
other programs include ASPEN PLUS of Aspen Tech-
nology, Inc., CHEMCAD of Chemstations, Inc.,
FLOWTRAN of CACHE/Monsanto, HYSIM of Hypro-
tech Ltd., and PRO/II of Simulation Sciences, Inc.
For example, the CHEMCAD program gives the re-
sults in Table 4, which are quite similar to the re-
sults of Table 1 for the Design II program.
While teaching our students to be skeptical of
computer output, we also teach them to be skeptical
of copies of charts in textbooks. Both of the authors
have written textbooks17,81 and know that the graphic
artists in publishing houses often copy figures poorly.
A most instructive example of that type is the same
ammonia-water enthalpy concentration diagram uti-
lized above, as redrawn on page 837 of the classic
textbook by Hougen, Watson, and Ragatzl91 where
the draftsman clearly drew the Equilibrium Con-
struction Lines incorrectly. Those construction lines
don't even intersect the corresponding saturated va-
por lines for pure ammonia vapor. In a graduate
thermodynamics class, we regularly hand out copies
of the incorrect diagram (without pointing out the
error) and assign the problem of calculating the liq-
uid-phase activity coefficients (modified Raoult's law
type, assuming ideal gas behavior) for ammonia and
water in a liquid that is 20 weight percent ammonia
at 100'F. Using that chart, one finds Yammonia = 0.20
and water = 2.2. Most graduate students will turn in
these numbers in their homework without the slight-
est thought about whether they are possible, which
they obviously are not. Both common sense and the
Gibbs-Duhem equation show that these values are
far from being possible. (It is possible and is occa-
sionally observed that a binary mixture may have
the activity coefficient of one component greater than

TABLE 4
Comparison of Graphical and CHEMCAD Solutions
CHEMCAD
Graphical PR K-Values Sour water K-Values
Hand Solution PR H-Values SRK H-Values
Outlet T F 80 80.0 20.7

Liquid Mass
Fraction 0.68 0.708 0.652
Ammonia

Molar V/F 0.38 0.32 0.43

one, and that of the other component less than one.
Gillespie, et al.,151 show this behavior for ammonia-
water. But this behavior only occurs near the pure
component end of the binary, where one of the activ-
ity coefficients is very close to unity.) Using the
ammonia-water enthalpy-concentration diagram in
Brown, et al.,121 one computes for this mixture activ-
ity coefficients of 0.21 for ammonia and 0.92 for
water, which are possible. From the vapor pressure
data for ammonia-water systems in Perry's Chemi-
cal Engineers' Handbook, one finds similar plausible
estimates of 0.20 for ammonia and 0.97 for water, or
from Gillespie, Wilding, and Wilsoni51 extrapolated
values of 0.25 and 0.91, respectively.
Another amazing example of the persistence of
misdrafted figures is the terminal velocity-diameter
plot for spherical particles shown in Perry's Chemi-
cal Engineers' Handbook.1101 This same figure has
appeared in the third, fourth, fifth, and sixth edi-
tions of this reference book without the editors notic-
ing that in copying it from its original source,1111 the
draftsman straightened the curves for small par-
ticles settling in air, which the original source cor-
rectly shows as gently curving because of the Stokes-
Cunningham correction factor. To add insult to in-
jury, the figure says that the Stokes-Cunningham
correction factor is included; this draftsman's error
has excluded it.

Whiting[12,131 discusses further the educational
uses of errors that can be found in textbooks, refer-
ence books, trade journals, and research journals.
Errors may be due to missing information, or mis-
prints, or they may be intentional. In some cases a
problem statement may be poorly written and/or
ambiguous, such that many interpretations are pos-
sible. Such was the case with the 1991 AIChE Stu-
dent Contest Problem. In our senior class of fifteen
students, the problem statement was interpreted in
fifteen different ways, none of which was in agree-
ment with the interpretation intended by the au-
Chemical Engineering Education

thors of the problem. The problem statement pre-
sumed a certain level of industrial experience. With-
out that experience the problem statement was sub-
ject to many interpretations.
We believe that chemical engineering students
should be exposed early in the educational process to
the fact that many realistic problems can be solved
by a variety of methods involving the use of graphs,
tables, equations, and black-box computer-aided com-
putational techniques, and that the computed an-
swers may depend strongly on which correlations for
thermodynamic properties are used. They need to
learn of the many sources of such correlations, along
with their limitations and recommended regions of
applicability. Also, they need to be aware of experi-
mental sources of data and how to make compari-
sons between experimental data and empirical cor-
relations. Finally, they need to appreciate possible
interactions among mass balance, energy balance,
and phase equilibrium computations, which are so
well illustrated by the relatively simple Himmelblau
problem previously discussed. By educating chemi-
cal engineering students in this manner, we hope to
make them critical in the same manner as one of our
senior chemical engineering students, Kory Judd,
who gave the student talk at the 1986 University of
Utah Commencement and said, "I came to the Uni-
versity believing most everything I heard. I will leave
questioning most everything I encounter."
Although some people argue that the use of com-
puter calculations in chemical engineering educa-
tion results in less critical chemical engineers, we
believe that when the computer is used in the five-
step sequence listed at the beginning of this article,
the student is likely to develop a critical attitude
towards chemical process calculations. The student
should develop confidence in such calculations (after
applying the five-step procedure) and should utilize
them to advantage often in his/her career. Use of
computer-aided programs permits a student to study
a problem from different viewpoints and perspec-
tives, often using more than one property correlation
and/or operation model so that comparisons can be
Spring 1992

made and sensitivities determined. Furthermore, as
illustrated before with the Himmelblau example,
many problems can be dissected to show cause and
effect in the simultaneous application of more than
one fundamental law or constitutive relationship.
Computer-aided calculations used after or in con-
junction with hand calculations can help develop
engineers who are critical of their own work and
that of others, and who will be likely to use state-of-
the-art computer process simulators effectively.

REFERENCES
1. Himmelblau, D.M., Basic Principles and Calculations in
Chemical Engineering, 4th Ed., Prentice Hall, Englewood
Cliffs, NJ (1982)
2. Brown, G.G., et al., Unit Operations, John Wiley & Sons,
New York, p. 592 (1950)
3. Design II User's Guide, ChemShare Corporation, Houston
(1988) (We thank the ChemShare Corporation for donating
the use of this simulator to our students.)
4. Liley, P.E., R.C. Reid, and Evan Buck, "Physical and Chemi-
cal Data," in Perry's Chemical Engineers' Handbook, 6th
Ed., D.W. Green and J.O,. Maloney, eds, McGraw-Hill, NY,
pp. 3-71 to 3-73 (1984)
5. Gillespie, P.C., W.V. Wilding, and G.M. Wilson, "Vapor-
Liquid Equilibrium Measurements on the Ammonia-
Water System from 313K to 589K, Research Report RR-90,
Gas Processors Association, Tulsa, OK (1985)
6. Heidemann, R.A., and S.S.H. Rizvi, "Correlation of
Ammonia-Water Equilibrium Data with Various Modified
Peng-Robinson Equations of State," Fluid Phase Equilibria,
29,439(1986)
7. de Nevers, N., Fluid Mechanics for Chemical Engineers,
2nd Ed., McGraw-Hill, NY (1991)
8. Henley, E.J., and J.D. Seader, Equilibrium-Stage Separa-
tion Operations in Chemical Engineering, John Wiley &
Sons, New York (1981)
9. Hougen, O.A., K.M. Watson, and R.A. Ragatz, Chemical
Process Principles: Part II. Thermodynamics, 2nd Ed., John
Wiley & Sons, New York, p. 837 (1950)
10. Sakiadis, B.C., "Fluid and Particle Mechanics," in Perry's
Chemical Engineers' Handbook, 6th Ed., D.W. Green and J.
Maloney, eds, McGraw-Hill, New York, Fig. 5-80 (1984)
11. Lapple, C.E., et al., Fluid and Particle Mechanics, Univer-
sity of Delaware, Newark, DE, p. 292 (1951)
12. Whiting, W.B., "Errors: A Rich Source of Problems and
Examples," Chem. Eng. Ed., 25, 140 (1991)
13. Whiting, W.B., "Textbook Errors: A Rich Source of Prob-
lems and Examples," 1987 ASEE Annual Conference Pro-
ceedings, Reno, NV, p. 1631, June (1987) O

REQUEST FOR FALL ISSUE PAPERS
Chemical Engineering Education publishes a special fall issue devoted to graduate education.
It consists of 1) articles on graduate courses and research, written by professors at various universities,
and 2) ads describing their graduate programs. Anyone interested in contributing to the editorial
content of the 1992 fall issue should write to CEE, indicating the subject of the
contribution and the tentative date it will be submitted.
Deadline is June 1, 1992.

laboratory _

MONITORING AND CONTROL OF A

FED-BATCH FERMENTATION

JosE A. TEIXEIRA, MARIA L. SOUSA,
SEBASTIAO FEYO DE AZEVEDO, MANUEL MOTA
University of Porto
Rua dos Bragas, 4099 Porto Codex Portugal

Fed-batch operation is growing in importance in
the fermentation industry. Major biotechnologi-
cal products such as penicillin and baker's yeast are
obtained in units operating under such a regime.
Fed-batch culture is an effective means of overcom-
ing inhibition from high initial substrate concentra-
tions. Many authors have reported the use of pro-
grammed nutrient feeding to increase the yield and
productivity of cells and metabolites. 1-41
The introduction of equipment for the on-line moni-
toring and computer control of batch fermentors al-
lows for a several-fold increase in productivity.151
Fed-batch operation is more complex than the classi-
cal batch operation. Exploiting for the former all the
flexibility and power of computer control strategies
together with innovative fermentation technologies
is becoming a necessary feature of operation for com-
petitive production/cost ratios.
As it stands, elucidative (yet simple) experiments
dealing with fed-batch operation should be included
in the traditional chemical engineering curriculum.
The experiments should be designed to help the

J''. L Jose A. Teixeira is a Lecturer in the chemical
engineering department, University of Oporto where
he earned his licenciate in chemical engineering in
1980. He earned his PhD from the University of
Oporto in 1988. His main interests are in fermenta-
tion and enzymatic technology.

Maria Luisa Sousa is a graduate of the chemical
engineering department, Oporto University (1990).
She is currently a research assistant working for
her PhD in flocculation bioreactors.

student develop an understanding of how com-
puters can be used to improve the operation of
fermentation processes.
The experiment described below consists of a very
simple laboratory-scale fed-batch operation of an al-
coholic fermentation. Baker's yeast is the micro-or-
ganism and glucose is the carbon source. It enables
the students to become familiar with fed-batch op-
eration, on-line monitoring and computer control (i.e.,
sensing, serial and parallel communications), and
model-based control decisions, all at the same time.
The experiment is inexpensive and can probably be
carried out in chemical engineering departments
around the world.

BACKGROUND
In alcoholic fermentation, using Saccharomyces
cerevisiae, the stoichiometry of glucose conversion to
ethanol and CO2 is given byll

C6H1206-
(glucose)

--2C2H50H + 2C02
(ethanol) (carbon dioxide)

From this equation it may be seen that 0.511 g of
ethanol and 0.489 g of CO2 are produced from each
gram of consumed glucose. As some of the glucose is
used for the production and synthesis of secondary
products and cell components, the real stoichiom-

Sebastiao Feyo de Azevedo is an associate pro-
fessor of chemical engineering at the University of
Oporto. He is a licenciate in chemical engineering
from the University of Oporto (1973) and eamed
his PhD in chemical engineering from the Univer-
sity of Wales (1982). His interests are in the areas
of modeling, optimization, and process control.

Copyright ChE Division, ASEE 1992

Manuel Mota is an associate professor in the de-
partment of chemical engineering, University of
Oporto, where he earned his licenciate degree in
1972. He received his PhD in biochemical engi-
neering from INSA (Toulouse) in 1985. His main
interests are industrial microbiology and fermenta-

Chemical Engineering Education

etry yield is known to be 90-95% of those values.
Accepting these approximate glucose conversion
yields, it is possible to follow the kinetics of a fer-
mentation by measuring the mass of CO2 released.
Another important aspect of alcoholic fermenta-
tion, employing glucose as substrate and yeast as
microorganism, is the inhibition of glucose consump-
tion at high glucose concentrations.161 To avoid this
inhibition phenomena, the fed-batch fermentation is
preferred. In this process, fermentation is started
batchwise with a small glucose concentration. When
all the initial substrate is consumed, a new addition
of fermentation medium is made in an amount such
that the glucose concentration level remains just
below the point of where it produces inhibitory ef-
fects. It may be said that, by operating in this way,
the fed-batch fermentation is a sequence of batch
fermentations of increasing volumes.

EXPERIMENTAL SET-UP AND PROCEDURE
The proposed experimental set-up is shown in
Figure 1. Fermentations are carried out in magneti-
cally stirred 1-liter Erlenmeyer flasks. The balance,
a Mettler PM4600 device (accuracy of 0.005 g), is
prepared for remote control with its internal com-
mands for bidirectional communication with a com-
puter via serial RS-232 protocol. An IBM-PC com-
patible microcomputer is employed.
The fed-batch fermentation medium is pumped
by a Braun FE411 peristaltic pump. On-off control
of the pump is implemented through one of the heavy-
duty relay channels of a CIL PCI6380 interface from
Microsystems LT. (United Kingdom) connected to
the computer via a parallel IEEE port. A Brain Boxes
Professional 488 is the internal IEEE interface card
inside the computer.
The microorganism employed is baker's yeast. A
typical composition of the fermentation medium pre-
pared is presented in Table 1, together with other
conditions for the experiment.
The medium is initially autoclaved at 121 oC for
twenty minutes, and pH is adjusted to four with
H3PO4. An initial amount of 50 ml of medium is put
into the Erlenmeyer flask, and 5 g of pressed baker's
yeast are then aseptically inoculated (for details of
aseptical inoculation see reference 7). A good sus-
pension of yeast cells in the medium is obtained by
providing some agitation. The flask is then placed on
the analytical balance and after a short period for
stabilization (approximately two minutes), data ac-
quisition is started. The loss of overall mass ob-
served is due to the CO2 released. At the end of
Spring 1992

The introduction of equipment for the
on-line monitoring and computer control
of batch fermentors allows for a several-fold
increase in productivity. Fed-batch operation is
more complex than the classical batch operation.

Figure 1. Experimental set-up.

operation (batch or fed-batch), residual glucose con-
centrations are determined by the DNS method.[sl
Fed-batch operation can be carried out under dif-
ferent strategies.191 The initial experiments given to
the students correspond to 'constant rate of increase
of nutrient feed rate' under the condition of total
consumption of glucose in each batch. With the
experimental set-up as described, alternative feed-
ing patterns (namely constant flow rate of nutrient
feeding and constant stepwise nutrient feed rate)
can be readily implemented. The students are
encouraged to implement and compare different
forms of operation.
The algorithm for the control of the whole opera-
tion is straightforward. By continually monitoring
the total mass, i.e., the amount of CO2 released, it is
possible to detect the instant corresponding to a
residual glucose concentration Gr in the medium.
The amount of fresh medium Mf to be pumped inorder
to raise the glucose concentration up to a limit G1 is

TABLE 1
Conditions for Fed-Batch Fermentation Experiment

Medium composition (per liter of medium):
KH2PO, 5 g
(NH4)2SO 2 g
Carbon source (glucose) 50 g
MgSO4.7H,0 0.4 g
Yeast extract 1 g

Initial Volume ------------------------------------- V = 0.05 1
Total volume of added medium ----------------- V,. = 0.5 1

Glucose concentration limit to stop addition
of fresh medium ----------------------------- G, = 5 g.1-1

calculated and the task is automatically implemented
by simple on-off action on the pump. The procedure
is stopped optionally where a time limit is observed
or when the total volume VT set for "added fresh
medium" is reached.

EQUATIONS FOR MONITORING AND CONTROL
All the equations for monitoring and for control
decisions are obtained by manipulation of the mass
balance equations. In the following,
GM = concentration of glucose in the fresh medium
p, = density of the medium
YCO2= theoretical stoichiometry mass yield of
glucose conversion to CO2 (0.489 g of CO/g of
glucose)
l = conversion yield factor (considered as 0.95)
assumed constant throughout the operation

Also, and assuming that the fed-batch is a se-
quence of batch operations, the following variables
are defined:
(i) G,"' is the concentration of glucose in batch i,
at instant t (referred to the beginning of that
batch). In particular, G'" represents the
concentration just after fresh medium has
been added.
(ii) Mt'" is the total mass of batch i at instant t
(referred to the beginning of the batch). Mo I
represents the initial mass, after fresh
medium has been added. Mt'i is the variable
monitored in the whole process.
(iii) M,'" represents the mass of fresh medium
added at the end of batch i, i.e., in prepara-
tion for batch i+1.

For batch i, employing the yield definition, the
amount of CO2 released is related to the glucose
consumption by the mass balance equation

M' M( =(M(G() MG / pM -M(i)G /p)Yo2 (2)

Rearranging Eq. (2), the concentration of glucose at
any instant Gti) can be related to the monitored
variable Mt(i) by the equation
K M')G(i (M Mi))
G('=- - (3)
SKM(i) (3)
t
where
K = Yco2 /PM (4)
The instant responding to total consumption of
glucose (i.e., Gtr = Gr = 0 ) corresponds to a total
amount of CO2 released Mi) in batch i, given by
96 2
96

M =(M Mk)= K M()G( (5)
co2 0 tr
where the subscript tr means time corresponding to
residual G,.
For the first batch (i = 1)
Mo = VoM (6a)
and
G') =GM (6b)

where Vo is the initial value.
For a fed-batch operation where each batch is to
be carried out up to the point of total consumption of
glucose, Eq. (5) gives the reference for addition of
fresh medium. The total amount M(i) to be added at
the end of the batch in order to start batch i+1 with a
glucose level given by G1 is obtained from a mass
balance to glucose

M G ') + M')2GM =(M') + MMt)Gi (7)
tr tr f f ir)GI (7)
which can be appropriately rearranged as

M = GI G(i)
M) = MI) G- Gtr (8)

For the particular case of Gri) = 0, then
M i) = M(i) 1 (9)
f tr GM G,

Mti) is the set-point for addition of fresh medium.
Due to the natural lag in the pump response time,
the mass of fresh medium effectively added tends to
be slightly higher than the value set by the com-
puter. This little problem is overcome by program-
ming the computer to use the values effectively added.
This means that for batch (i+1), the computer gives
a direct reading of Moi+,1 and the following values
should be calculated:
(i) Mass of fresh medium effectively added
(Mi) = M(i+l) -Mi) (10)
f 0 tr
(ii) Glucose concentration at the beginning of
batch i+1
M(i)G(i) + (Mi+l) _- Mi)) GM
G(i+l) tr tr tr
MO =M (11)
0 M(i+l)

Under this assumption, the reference value for
the amount of CO2 to be released in batch i+1 is
given by

M (i+l) K(M()) GM (12)
2 tr f e
Equations (5), (9), (10), and (12) are the ones to be
employed in the programming of the algorithm.
Chemical Engineering Education

ASPECTS OF IMPLEMENTATION AND SAMPLE
RESULTS
The experiment described is routinely carried out
in the authors' laboratory by students taking the
biotechnology option. In order to run the experiment
the students are given the main specifications. They
become conversant with the problems of data acqui-
sition and write and implement the software. Com-
piled QUICK BASIC (version 4.5) is currently a good
option since it is a structured programming lan-
guage. The conditions given in Table 1 are only
suggestions and obviously can be changed. The soft-
ware should allow for the required flexibility; ex-
amples of parameters to be supplied by the user in
each experiment are glucose concentration in the
initial medium and in the medium to be added, glu-
cose limits, and total value and/or time for end of
operation.
The experiment lasts for about twenty-four hours,
but since it is computer controlled the students spend
only two hours in the laboratory during the first day
(for preparation and start-up) and two hours during
the second day (to collect data and conclude the
work). This time aspect in itself demonstrates to the
students the advantage of computer-controlled op-
erations, especially for processes which are known to
take a long time, as is typically the case for fermen-
tation processes.
Figure 2 shows a print screen of the monitor dis-
play for a case study conducted with the conditions
presented in Table 1. The evolution of CO2 agrees
with that predicted by theoretical considerations;
the rate of CO2 production is nearly constant. The
students can also check and find that the mass
of added culture medium increases as fermenta-
tion proceeds, and that a fed-batch fermentation

16 1000

S900

2 800 .
B
"700
8 -
AA -600
S
-500 '
4 -
o 0
S400

0- 300
0 4 8 12 16 20
Time [hr]
Figure 2. Print screen of the monitor display
Spring 1992

is a sequence of several "increasing volume" batch
fermentations.
Besides fitting the theoretical model, validation of
these experiments can also be made by confirming
that the mass ofCO2 released compares well (within
5%) to the one estimated by assuming the stoichiom-
etric conversion yield of glucose to CO2.
Inclusion of this experiment in the laboratory prac-
tice has undoubtedly helped students to understand
a controlled operation of fed-batch processes.

ACKNOWLEDGEMENT
This work was partially financed by INIC (Insti-
tuto Nacional de Investigacao Cientffica) and by
JNICT (Junta Nacional de Investigacao Cientifica e
Tecnol6gica) under research contract No. PMCT/C/
BIO/154/90.

NOMENCLATURE
G, = Limit for glucose concentration in the fermen-
tation medium to stop addition of fresh
medium (g.1)
G, = Concentration of glucose in the fresh medium
(g.l' )
G, = Residual glucose concentration (g.1-')
G,'" = Concentration of glucose in batch i, at instant
t (referred to the beginning of that batch)(g.1')
K = Constant (Eq. 2)
M~' =Mass of fresh medium added at the end of
batch i (g)
M ='" =Total mass of batch i at instant t (referred to
the beginning of that batch)(g)
Mt" = Mass of fermentation medium in batch i,
corresponding to glucose concentration Gr (g)
MC2 )tr = Mass of CO2 released in batch i set-point to
start addition of fresh medium (g)
V = Initial volume (1)
YCo2 = Stoichiometric yield of glucose conversion to
CO2 (g g)
PM = Density of fresh medium (g.11)
1 = Conversion yield factor

REFERENCES
1. Pirt, S.J., Principles of Microbe and Cell Cultivation, Black-
well, Oxford (1975)
2. Yoshida, F., T. Yamane, and K. Nakamoto, "Fed-Batch Hy-
drocarbon Fermentation with Colloidal Emulsion Feed,"
Biotech. and Bioeng., 15, 257 (1973)
3. Stanbury, P.F., and A. Whitaker, Principles of Fermenta-
tion Technology, Pergamon Press, Oxford (1984)
4. Mota, M., J.M. Besle, P. Strehaiano, and G. Goma, "A Simple
Device for Fed-Batch Control in Alcoholic Fermentation,"
Biotech. and Bioeng., 29, 775f (1987)
5. Albrecht, Ch., P. Keil, and W. Chalupka, in Computer Ap-
plications in Fermentation Technology: Modeling and Con-
Continued on page 103.

raw laboratory

A SYSTEMATIC APPROACH FOR

LONG-RANGE

LABORATORY DEVELOPMENT

BAHMAN GHORASHI
Cleveland State University
Cleveland, OH 44115

T today, the rapidly changing state of technology
Sand the almost daily introduction of new compu-
tational, electronic, and diagnostic hardware and
software systems can make even the most modern
laboratory facilities obsolete in a relatively short
period of time. This phenomenon is further acceler-
ated by the constantly changing nature of research
and instructional focuses. Now, more than ever, it is
essential to establish a systematic approach for long-
range laboratory development that incorporates a
modernization plan for equipment, instruments, and
computational systems, but that will, at the same
time, have minimal impact on operational budgets,
personnel training, and space needs.
PLANNING FOR FUTURE NEEDS
It is not too difficult to identify and define what
the state-of-the-art is at any given time. A more
challenging task is to project the future direction of
a particular field of science or discipline. Gen-
erally, the intermediate future direction is defined
by those scientists and educators who are at the
leading edge of technological and pedological re-
search. There is also a repertory of literature avail-
able for most scientific disciplines, and there are
periodicals that address the issues, e.g., Chemical
Engineering Education. r 1

Bahman Ghorashi received his BS from Wayne
State University and his MS and PhD degrees
from the Ohio State University. He joined the
Chemical Engineering Department at Cleveland
State University in 1978, and he is presently a
Professor and Assistant Dean of Research there.
He is chairman of the Diagnostics, Imaging and
Visualization Focus Group of the Ohio Aero-
space Institute and has served as a faculty rep-
resentative on the Board of Trustees of Cleve-
land State University.
@ Copyright ChE DivTsion of ASEE 1992

Now, more than ever,
it is essential to establish a
systematic approach for long-range
laboratory development that incorporates a
modernization plan for equipment, instruments,
and computational systems.

Perhaps the most important factor during the
"defining stage" is the views of industrial colleagues
and their perception of future needs. This is analo-
gous to "consumer input" and prepares students for
what will be expected of them in an industrial set-
ting. The input could come from both an industrial
advisory committee and a group of alumni who have
had industrial experience. There are also other
sources, such as professional societies which have
committees that deal with the future needs of a
particular discipline.
Other considerations in the planning stage in-
clude the needs, the expertise, and the growth op-
portunities that may be available in a certain geo-
graphical location. For example, if a particular re-
gion is well suited for research in polymer science
due to a concentration of polymer industry, research
institutes, and available funding, then such a factor
should be considered when establishing long-term
developmental objectives.
It goes without saying that from the beginning
the available expertise and interest of the faculty
should be a determining factor in all of these consid-
erations. Furthermore, any laboratory development
plan should be in harmony with both the overall
teaching focus of the department and the long-term
plans of the college and university. Given the faculty
interests and teaching goals, a lack of anyparticular
expertise can be remedied through proper training
courses offered by institutions, universities, and
equipment manufacturers.
Chemical Engineering Education

The level of available funding should not be a key
factor at this stage. Once a solid plan is established,
attention can then be given to the writing of labora-
tory development proposals for funding support, and
priorities can be assigned to the various plan seg-
ments in order to address the funding limitations.

LONG-TERM GOALS AND OBJECTIVES
Setting specific goals and developing a periodic
review plan should be accomplished with the help of
an advisory committee. It should consist of senior
members from both industry and academe in addi-
tion to alumni and a representative from the admin-
istrative component of the university. The
committee's task should be to review objectives and
make recommendations on the relevance and appli-

ESTABLISH THE
LONG TERM OBJECTIVES

Figure 1. Defining intermediate andfuture needs.

SINDUSTRyTY APLICABIETY
AISCY B E ACADEMIA BASIC SCIENTIF C PEINCS P-3
~ BUO8D-NG-UNCJGN:NG--CAPIT1L CST
E STABLISH THE GOALS M-INTENNLE COSTS
THE REVEW PROCESS LUMNI-- RECOMMENDATIONS

PROJECTED

Figur2.. L m bec
NO OF 9 STUDENTS 9Ur
,G SUB TECT AIRAS
*ACADEIA

~~---__! ---SPACE
FACiLTITYREUIRMENTS ^-- ULITIUTtES
SAFETY

MECHANISM
REVIIEW PROCESS [ FREQUENCY
REPORTS

Figure 2.. Long-term objectives
Spring 1992

Setting specific goals and developing a periodic
review plan should be accomplished with
the help of an advisory committee.

ability of the overall program to industrial concerns
and basic scientific principles. The committee should
also review capital and maintenance costs and should
assist in identifying potential sources of funding.
Special attention should be given to the safety pro-
gram, and a safety group should be appointed for
routine laboratory inspections.
The developmental plan should include a reason-
able and realistic initial projection of what the needs
will be for the ultimate number of technicians, stu-
dents (users), experiments, laboratory inspection fre-
quency, and facility requirements such as space, utili-
ties, and safety features. The latter is particularly
important if a building renovation or additional space
is to be considered. The above issues should be care-
fully addressed and the final recommendations should
be implemented without much additional change
(except for changes recommended by the advisory
committee during the periodic reviews). Figures 1
and 2 are summary charts showing the initial plan-
ning process.

SELECTION OF EXPERIMENTS

Certain laboratory experiments which demon-
strate very basic scientific principles must be incor-
porated into the undergraduate laboratory program.
The scale and degree of sophistication of these ex-
periments should be determined by certain factors
that will be described later in this section. The plan
should also include an optional menu of experiments
from which students can choose. These experiments
can be designed and built on an in-house basis by
one group of students and then modified and im-
proved by subsequent groups of students. They should
be viewed as temporary experiments-once they are
developed and fully tested, they should be replaced
or substantially modified to provide new and more
challenging experiences for the students.
If economic factors permit, it is advantageous to
obtain commercial-scale equipment in order to pro-
vide "real-life" experiences for the students. I recall
how helpful such an experience was when, as a stu-
dent at The Ohio State University, I worked with a
commercial-size triple-effect evaporator. It took al-
most one-half of a day just to bring the unit to a
steady-state condition. Then, when things did not go
as planned, there was only so much that could be
done through calculations and applications of theory.

Beyond that, as the technician in charge of the
unit pointed out, one had to develop a "feel" for it-
something that cannot be learned in school. Stu-
dents should be exposed to at least one such experi-
ence in order to learn and appreciate the limitations
and the range of applicability of theoretical prin-
ciples. Figures 3 and 4 are summary charts of
factors that should be considered in selecting labora-
tory experiments.

EQUIPMENT RESIDENCE TIME
Every effort should be made to assign a lifetime
period to each experiment and its equipment. As the
allocated period comes to an end, the experiment
and its various pieces of equipment should be prop-
erly replaced or modified. This is the only way to
keep a laboratory facility from becoming an obsolete
collection of antiquated equipment.
Other considerations include such concerns as
the long-term applications of an experiment, the
number of individuals who can be involved in the
experiment at any given time, the relevance of ex-
periments to the department's instructional and re-
search goals, the required frequency of updating,
and the required supplies, initial costs, maintenance
expenses, safety, and specialized needs. One indi-
vidual should be designated as the person in charge
of the experiment, and he or she should report to the
advisory committee as needs arise regarding any of
the above factors.

UNIT OPERATIONS
VS. SPECIALIZED EXPERIMENTS
A recent article by Landau and Rosenbergl21 on
the history of chemical engineering alludes to Arthur
Little's concept of unit operations, i.e., breaking all
the chemical processes into a handful of building
blocks or units. They say
An engineer trained in unit operations could mix and
match them as necessary. Such an engineer would be
flexible and resourceful in his approach to problem
solving...
This is precisely the way laboratory experiments
should be selected. The experimental procedure
should not be just a compilation of steps that have to
be followed one-by-one, but rather should challenge
the students to exercise their creativity and resource-
fulness. Including several building-block experiments
allows students to test the validity of different scien-
tific concepts. As an example, the analogy among
heat, mass, and momentum transfer can be illus-
trated with a set of similar experiments wherein
students can creatively combine different transport
mechanisms and compare the results.
100

LABORATORY TRAINING PERIOD
A student training period should precede any labo-
ratory activity. It should encompass lectures and, if
possible, a series of video and film presentations on
topics such as safety, objectives of the experiment,
use and handling of delicate and sophisticated in-
struments, report writing, and oral presentations of
results, as well as other appropriate topics, all tai-
lored to a specific laboratory (see Figure 5).

INDUSTRIAL SPONSORSHIP OF EXPERIMENTS
It is important to attract industrial sponsors, not
only to fund and support an experiment but also to
provide field data for direct comparisons with labo-
ratory results. This gives students a sense of what

Figure 3. Types of Experiments

REQUIRED UNIT OPERATIONS
AUXILIARY EQUIPMENT VERSUS SPECIALIZED
e.g., measurement instruments EXPERIMENTS

LONG-TERM
APPLICATIONS

NUMBER OF INDIVIDUALS NUMBER OF INDIVIDUALS
WHO COULD USE EACH WHO COULD USE THE
EXPERIMENT EXPERIMENT OVER THE
AT ANY GIVEN TIME EQUIPMENT'S LIFETIME

REQUIRED
FREQUENCY OF SAFETY
UPDATING

RELEVANCE OF THE EXPERIMENT
TO THE RESEARCH GOALS

REQUIRED SPECIALIZED
SUPPLIES NEEDS

BO RELEVANCE TO
LABORATORY OTAB
OTHER LAB
BUDGET
EXPERIMENTS

( COMMITTEE'S IN CHARGE OF THE
EVALUATION / EXPERIMENT

Figure 4. Choice of experiments
Chemical Engineering Education

they can expect in the field so far as error tolerance
and analysis are concerned. An individual from in-
dustry can be designated to work with the instruc-
tors, to give one or two lectures on his or her own
experiences, and to suggest new ideas. In effect, the
industrial partner would "adopt" an experiment.
This type of relationship with industry can be
mutually beneficial since (more often than not) new
ideas can be tested more easily in a laboratory than
in the field. Also, the loss-time associated with the
testing of new ideas in the field, using commercial
units, can be a prohibitive factor. Several years ago
we experienced the benefit of this approach when we
invited an industrial colleague to work with us on a
design project that he had already supervised in the
field. His comments and tips were most helpful to
us. He indicated later that he had also learned from
the students and that the design they suggested had
certain advantages over the design his engineering
staff had provided.
Another consideration is that smaller industries
may not have access to a research center and might

Figure 5. Factors in selecting equipment

Figure 6. Choice of equipment
Spring 1992

welcome a partnership with a university depart-
ment. Figure 5 summarizes the above discussion.

CHOICE OF EQUIPMENT
Obviously, the laboratory budget determines the
type and quantity of equipment that can be pur-
chased, its degree of sophistication, and the choice of
supplies. Budget constraints also affect other fac-
tors, such as operational cost and maintenance of
the equipment. In some cases, the initial capital cost
may be affordable but the operational and mainte-
nance costs may be prohibitive. In the planning stages
it is of paramount importance to include a periodic
maintenance budget and schedule for proper replace-
ment of outdated or worn-out parts. Other factors
such as ease of use, user-friendliness, and space
requirements have to be evaluated very carefully
before a decision is made on any piece of equipment.
As discussed earlier, the concept of unit opera-
tions applies to the choice of equipment as well. This
means that the expandability of an equipment's func-
tions, i.e., the mix-and-match concept, and its up-
grading potential should certainly be considered.
Many sophisticated instruments require train-
ing before they can be used to their full potential. In
many cases, training courses are offered either by
the manufacturers, through symposia, or university
short-courses. Examples of such instruments are
Laser Doppler Velocimeter (LDV) systems, different
imaging systems, and Scanning Electron Microscope
(SEM) systems. As the level of sophistication of mea-
surement instruments increases, the issue of train-
ing becomes an even more important factor. It can
be addressed in a number of ways. For example, the
author has proposed the establishment of a research
and training center for diagnostics, imaging, and
visualization techniques'31 by forming a consortium
of several Ohio universities and industry. This would
enable students, technicians, faculty, and industry
researchers to use the available facilities through-
out the state and to obtain training in certain highly
specialized laboratories. Figure 6 is a summary chart
of this section and includes some additional factors
which may be important, depending upon the type of
equipment in question.
One consideration in acquiring a relatively ex-
pensive piece of equipment or instrumentation sys-
tem is whether or not the equipment should be pur-
chased or leased. Obviously, the critical factor in
such a decision is the availability of required capital
and whether or not it would be economically advan-
tageous to purchase the equipment. This evaluation
should consider the estimated number of years that

LIFETIME OF THE EQUIPMENT

LECTURES
VIDEO AND FILM PRESENTATIONS
SAFETY
TRAINING PERIOD
OBJECTIVES OF EXPERIMENTS
USE OF INSTRUMENTS
REPORT WRITING AND
PRESENTATIONS
FUNDING
LECTURES
)USTRIAL SPONSORSHIP OF EXPERIMENTS LECTURE
FIELD DATA
COMPARISON OF
RESULTS

the equipment can be used, based on the
manufacturer's data, as well as projected laboratory
growth and long-term goals. There are other factors
tailored to specific pieces of equipment that cannot
be generalized, such as the general maintenance
requirements versus a lease-plan maintenance agree-
ment, projected frequency of upgrading of the soft-
ware system, and the depreciated value of the equip-
ment after a certain period.

CONCLUDING REMARKS
Any long-term laboratory development project
should be based on a methodical and systematic
plan to ensure its proper development. Many factors
have been described in this paper, but not all
of them are applicable to all cases. Different labora-
tories may require vastly different approaches at the
planning stage. The intent of the paper has been to
provide some general guidelines for the planning
and management of instructional laboratories. Sev-
eral of the guidelines are applicable to almost all
cases. They are
Establishment of an advisory committee to review the
objectives and plans and to make recommendations re-
garding the future needs of the facility.
Establishment of a channel for direct input from indus-
trial colleagues and alumni.
Long-term projections of the laboratory needs with regard
to the number and types of experiments, equipment, tech-
nicians, and student users.
Establishment of a periodic review process to evaluate
the progress and development of the facility, to assess the
laboratory needs, and to ascertain the necessity of mak-
ing modifications in the original plan.
Development of plans for proper replacement or upgrad-
ing of both software and hardware after a designated
period of time.
Establishment of a maintenance plan for the upkeep of
equipment and instruments.
Development of a complete training and safety program
for all individuals who use the facility.
It is not often that a complete new laboratory is
built from the ground up. More often than not,
an existing laboratory has to be renovated and up-
dated. The criteria discussed in this paper are
applicable in either case. Additionally, there are
many textbooks[4-7] that provide a survey of experi-
mental methods, experiment planning, instrument
selection, accuracy and economy, analysis of data,
and report writing.

REFERENCES
1. Chemical Engineering Education, Chemical Engineering
Division, American Society for Engineering Education.
2. Landau, R., and N. Rosenberg, "America's High Tech Tri-
umph," Amer. Heritage of Invention and Tech., 6(2), p. 58,
fall (1990)

3. Ghorashi, B., Center for Diagnostics Imaging and Visual-
ization, Brochure, CDIV, 2001 Aerospace Parkway, Brook
Park, OH 44142
4. Holman, J.P., Experimental Methods for Engineers, Fifth
Edition, McGraw Hill, New York
5. Tuve, G.L., and L.C. Dumholdt, Engineering Experimenta-
tion, McGraw Hill, New York
6. Doebelin. E.O., Measurement System Application and De-
sign, Fourth Edition, McGraw Hill, New York
7. Ray, M.S., Engineering Experimentation, McGraw-Hill, New
York(1990) 7

book review

ELECTROCHEMICAL ENGINEERING
PRINCIPLES
by Geoffrey Prentice: Prentice Hall, Englewood Cliffs,
NJ 07632 (1991)

Reviewed by
Ralph E. White
Texas A & M University

This book is an introductory-level textbook on
electrochemical engineering that could be used in a
senior-level undergraduate course or in a first-year
graduate-level course. The book contains nine chap-
ters and seven appendices and is 296 pages long.
The nine chapters are entitled: Introduction, Ba-
sic Concepts, Thermodynamics, Phase Equilibrium,
Electrode Kinetics, Ionic Mass Transport, Modeling
and Simulation, Experimental Methods, and Appli-
cations. The seven appendices are entitled: Conver-
sion Factors, Standard Electrode Potentials, Equiva-
lent Conductances, Activity Coefficients of Electro-
lytes at 25C, Mass Transport Correlations, Com-
puter Program for a One-Dimensional Cell, and Com-
puter Program for a Two-Dimensional L-cell. A solu-
tions manual is available for the problems given in
the text, and the computer programs given in the
last two appendices can be obtained in electronic
form from the author.
The first chapter is short but points out the im-
portance of electrochemical engineering in terms of
the amount spent annually ($28 billion in 1986 dol-
lars) on products such as aluminum, which are pro-
duced by electrochemical methods, and in terms of
the annual cost of corrosion (approximately $200
billion in 1991 dollars).
The second chapter presents basic concepts that
are needed in the study of electrochemical systems.
The author reviews electrochemical cell conventions,
Faraday's laws, the concepts of current and voltage
efficiencies, ion conduction, and transference num-
bers. Unfortunately, the author does not cite the
Chemical Engineering Education

references he used to prepare the figures in this
chapter nor in subsequent chapters; however, he
does provide a bibliography at the end of each chap-
ter.
The third chapter is on the thermodynamics of
electrochemical cells and includes a section on
Pourbaix diagrams which is very useful for under-
standing phase equilibria and cathodic protection.
This chapter should be studied by all chemical engi-
neering students.
Chapter Four presents discussions of phase equi-
libria and the concepts of electrochemical potential
and mean activity coefficients solutions containing
ionic species. The author also includes in this chap-
ter a detailed discussion on the Debye-Huckel theory
for electrolytic solutions. The author finishes this
chapter with discussions on the two concepts of a
potential in an electrolytic solution and liquid junc-
tion potentials.
The fifth chapter is on electrode kinetics. The
author begins the chapter by presenting a useful
description of the electric double layer on an elec-
trode. The author continues this chapter by present-
ing a derivation of the Butler-Volmer equation, which
is the commonly used reaction rate expression for
electrochemical reactions. He then presents and dis-
cusses simplified forms of the Butler-Volmer equa-
tion: the so-called linear and Tafel forms of the But-
ler-Volmer equation. He continues by presenting a
practical description of reference electrodes and their
use in measuring potential distributions in electro-
lytic cells. He also presents in this chapter a descrip-
tion of a study of the reaction mechanism for the
anodic reaction of zinc in an alkaline electrolyte. He
presents a reaction rate expression for this reaction
which is similar to the Butler-Volmer equation but
includes a potential-dependent pre-exponential term.
Finally, the author presents a very useful discussion
of the kinetics of corrosion processes and Evans'
diagrams. Finally, he provides a lucid description of
simplified forms of the reaction rate expressions for
corrosion reactions and associated expressions for
the corrosion potential.
Chapter Six contains a very useful presentation
of the fundamental equations used to describe mass
transfer in electrolytic solutions. This chapter should
be required reading for all chemical engineers. The
author uses the rotating disk electrode to demon-
strate how electrochemical reactions can be used to
develop mass transfer correlations in the form of the
Sherwood number as a function of the Reynolds and
the Schmidt number, for example. The final section
in Chapter Six is a brief discussion of how to treat
Spring 1992

the time dependence of a simple electrochemical re-
action.
In Chapter Seven, the author presents a classifi-
cation scheme for the types of current distribution
problems that have been modeled in the past. He
also presents a discussion of the Wagner number
which can be used as a characterizing parameter for
current distributions in electrochemical cells. Next,
the author presents a summary of analytical and
numerical methods that can be used to predict cur-
rent distributions. The next topic in this chapter is
on gas-evolving electrodes, which are found in many
electrochemical cells used in industry (e.g., chlor-
alkali cells), and the author presents a mass trans-
fer correlation for vertical, gas-evolving electrodes
for such cells. The final section in this chapter con-
tains a presentation of the equations that are used
for mass and charge transfer in porous electrodes,
which are important in such areas as batteries and
fuel cells.
Chapter Eight is entitled "Experimental Meth-
ods" and presents material on several popular ex-
perimental systems used in electrochemical engi-
neering. These are the rotating disk electrode, the
rotating ring-disk electrode, rotating cylinder elec-
trode, and parallel plate electrode systems.
The last chapter in the book contains descriptions
of several applications of electrochemical engineer-
ing principles. These include energy storage and con-
version, electric vehicles, thermally regenerative elec-
trochemical systems, and the electrochemical pro-
duction of adiponitrile. The author also includes de-
scriptions of monopolar and bipolar electrochemical
cells, the chlor-alkali process, and thermal manage-
ment of electrochemical cells. The final section of
this last chapter is on future developments in which
the author speculates that "the premium on effi-
ciency will stimulate additional research on electro-
chemical energy conversion and storage." I hope he
is right. 7

Fed-Batch Fermentation
Continued from page 97.
trol of Biotechnological Processes, N.M. Fish, R.I. Fox, and
N.F. Thornhill (eds) p. 321, Elsevier Applied Science, Lon-
don (1989)
6. Holzer, H., in Aspects of Yeast Metabolism, A.K. Mills (ed),
Blackwell Sci. Pub., Oxford (1968)
7. Pelczar, Jr., M.F., and E.C.S. Chan, Laboratory Exercises in
Microbiology, McGraw-Hill, New Yoirk (1977)
8. Chaplin, M.F., in Carbohydrate Analysis: A Practical Ap-
proach, M.F. Chaplin and J.F. Kennedy (eds) IRL Press,
Oxford (1975)
9. Burrows, S., in Economic Microbiology: Microbial Biomass,
H.R. Rose (ed), Academic Press, London (1979) 1-

AuwardLecture ..

INTERFACIAL TRANSPORT PROCESSES

AND RHEOLOGY

Structure and Dynamics of Thin Liquid Films

DARSH T. WASAN
Illinois Institute of Technology
Chicago, IL 60616
Thanks, ASEE. I consider myself fortunate to
join the roster of twenty-eight distinguished
chemical engineers who are previous recipients of
the 3M Lectureship Award. It is noteworthy that
many of them have gone on to receive even greater
accolades in their professional careers after their
achievements were first recognized by the ASEE
Chemical Engineering Division by this award.
I also consider myself most fortunate to have re-
ceived my academic training at two of the most pres-
tigious chemical engineering departments in the
world: first as an undergraduate student at the Uni-
versity of Illinois at Urbana-Champaign where I
studied under Tom Hanratty, John Quinn, Jim
Westwater, Daniel Perlmutter, Harold Johnstone,
and Max Peters (chairman at the time), and second
as a doctoral student at the University of California
at Berkeley under Andy Acrivos, John Prausnitz,
C. Judson King, Charlie Tobias, Eugene Petersen,
Don Hanson, and Charlie Wilke (my supervisor). I
thank these outstanding educators for not only pre-
paring me for the subsequent academic career but
also for providing me with their friendship for the
past thirty years.
I also want to thank my professional colleagues,
Howard Brenner (MIT), Norman Li (Allied-Signal
Corporation), Bill Krantz (Colorado), Dinesh Shah
(Florida), and Bob Kintner, Ralph Peck, Dimitri
Gidaspow, and Richard Beissinger (IIT), with whom
I have worked and shared several graduate students
and postdoctoral fellows.
Interfacial transport processes represent a
growing field of... research with applications
ranging from separation processes to engineered
materials and development of energy, food, and
environmental technologies.

Interfacial Transport Processes represent a
rapidly growing field of scientific research with ap-
plications ranging from chemical engineering sepa-
ration processes to engineered materials and devel-
opment of energy, food, and environmental technolo-
gies. In particular, interfacial transport processes
are of specific importance in those multiphase fluid
systems possessing a large specific surface, i.e., whose
surface-to-volume ratio is large and which utilize
substances (e.g., surfactants) that are interfacially
active.11' Applications of interfacial transport pro-
cesses where such conditions are met include: sepa-
ration processes such as distillation, flotation, and
liquid membranes; processing/flow/stability of emul-
sions; processing/flow/stability of foams; processing/
flow/stability of particle dispersions; ink-jet print-
ing; coatings; wetting; etc. In most of these applica-
tions, thin liquid films are found to arise. The thick-
ness of these films is typically on the order of the
long-range intermolecular forces (< 0.1 pm).
One of my major areas of research over the last
two decades has been the structuring and dynamics
of thin liquid films, focusing particularly upon the
importance of interfacial transport processes and
rheology. A critical thrust of our research program
has been the development of instrumental techniques
for measuring theological or flow properties of fluid-
fluid interfaces containing surfactants and polymeric
macromolecules. Two of our instruments (the Inter-
facial Viscometer and the Expanding Drop Tensiom-
eter) have been commercialized and are now used as
the primary tools in emulsion and foam-stability
research work. We have pursued the development of
reliable measurement techniques for dynamic sur-
face properties through a series of studies, both ex-
perimental and theoretical, which are aimed at un-
derstanding the role of interfacial theological prop-
erties such as surface viscosities and elasticities or
tension-gradients in the stabilization of liquid sur-
Copyright ChE Dwision of ASEE 1992
Chemical Engineering Education

factant films and thereby in the stabilization of col-
loidal dispersions such as emulsions and foams. This
work has been summarized in a recent text book.121
A new era of research on thin liquid film phenom-
ena was opened when we discovered a new mecha-
nism for the film stability induced by the formation
of "ordered" surfactant micelle structures inside the
film over distances of the order of 100 nm or 1,000A.
Recently, we have shown that the phenomenon of
multilayered structuring or stratification (i.e.,
internal layering of micelles) in thinning films is
much more universal and can also be observed with
concentrated submicron particle suspensions with
narrow size distribution and prevailing repulsive
forces.[3-71 The study of thin films of self-organizing
microstructures has applications to such diverse ar-
eas as ceramics processing, coatings, magnetic tapes
and discs, and emulsion and foam systems.

-t/

2h

c)

2h

d)

2h

2R I-

e)

2H *

f)

' : : : .g)

2i
k2 ** ** *:

Figure 1. Main stages in the evolution of a thin film.

Spring 1992

THIN LIQUID FILM PHENOMENA
Thin films have been the focus of scientific inter-
est since Hooke's report in 1672 to the Royal Society
regarding "holes" within stable soap films (later un-
derstood by Newton and Gibbs to be film regions
sufficiently thin to prevent the interference of light
rays reflected from upper and lower film surfaces).
Thin film formation, structure, and stability are con-
trolled by the hydrodynamic and thermodynamic in-
teractions between the two film surfaces. The hydro-
dynamic interactions dominate at film thicknesses
more than 100 nm or 1,000A and are greatly influ-
enced by the deformation and mobility of the sur-
faces. These, in turn, are greatly influenced by the
presence of surface-active species or surfactants ad-
sorbed at the film surfaces. Once a film has thinned
to less than 100nm, thermodynamic interactions
caused by van der Waals', steric, electrostatic, and
structural forces begin to dominate.
The main stages in the formation and evolution of
the thin liquid film between two approaching drops
or bubbles, as shown in Figure 1, are:
a. Two drops approach each other, resulting in their
hydrodynamic interaction;
b. Deformation of the drops leading to a bell-shaped
formation which is called a "dimple";
c. The dimple gradually disappears and a plane-parallel
film of radius, R, is formed. The film drains under the
combined action of suction at Plateau borders and the
disjoining pressure; subsequent thinning of the film
depends on the surfactant concentration;
d. At low surfactant concentrations (i.e., below the
critical micelle concentration, CMC), when the
disjoining pressure gradient is negative, it favors the
growth of corrugations at the film surfaces and at a
critical thickness, h,,, either the film ruptures or a
jump transition in thickness occurs, leading to a
stable or metastable structure. This process of
transition to stable or metastable state is known as
"black spot formation" since at these thicknesses the
film appears to be grey or black;
e. The black spots increase in size and cover the whole
film;
f. The formation of an equilibrium film whose lifetime
can be virtually unlimited and is dependent upon the
magnitude of the capillary pressure;
g. At high surfactant concentrations (i.e., above CMC),
when the structural component of the disjoining
pressure is positive, a long-range colloid crystal-like
structure is formed due to the internal layering of
micelles inside the film;
h. The thinning film exhibits a number of metastable
states and its thickness changes in a stepwise fashion;
the stratification depends on the micellar concentra-
tion and film size;
i. The film attains an equilibrium state with no more
stepwise changes, and the resulting film is stable,
thick, and contains micelles.

The stability and structure of emulsions or foams
are determined primarily by the relative rates of two
major breakdown processes, i.e., coalescence and floc-
culation of the dispersed droplets or gas bubbles.
Coalescence is controlled by the thinning and rup-
ture of the thin liquid films formed between two
droplets or between a single droplet and its bulk
homogeneous phase as the droplet approaches the
surface. Hence, if the colliding droplets have axial
symmetry, the process of coalescence can be split
into (a) mutual approach of two droplets to form a
plane-parallel film, and (b) thinning of the film to
such a thickness so that rupture can occur, followed
by (c) rupture itself when a hole is formed. Stages
(a) and (c) occur immeasurably fast so that the life-
time of the intervening film is essentially given by
stage (b). Experimental observations suggest that
the stability of thin liquid films is determined pri-
marily by the rate of thinning rather than by the
rupture process. Thus, the lifetime of the interven-
ing film is an important characteristic of dispersed
systems such as foams and emulsions and is directly
related to their stability.
The forces of interaction that govern the lifetime
of thin liquid films are the capillary pressure (suc-
tion at the Plateau borders) and the disjoining pres-
sure. The thermodynamic properties of thin liquid
films are different from those of the bulk surfactant
solutions. These films possess an excess chemical
potential that is manifested as an excess pressure.
Derjaguin coined the term disjoiningg pressure" to
characterize this excess pressure. Generally, the
disjoining pressure consists of the electrostatic re-
pulsion forces between ions on the two surface lay-

The ASEE Chemical Engineering Division Lecturer for 1991
is Darsh Wasan of the Illinois Institute of Technology. The
purpose of this award, for which the 3M Company provides
financial support, is to recognize outstanding achievement in an
important field of ChE theory or practice.
Darsh Wasan, a native of Bombay, India, came to the U.S. in
1957. He obtained a BS in chemical engineering from the Uni-
versity of Illinois at Urbana (1960) and a PhD. in chemical
engineering from the University of California at Berkeley (1965).
At Berkeley, he worked with Charles R. Wilke in the field of
mass transfer in turbulent flow, and his doctoral thesis work
was the subject matter of the 3M Annual Lecture that Charles
Wilke delivered at the 1964 ASEE meeting. Darsh joined the
faculty at the Illinois Institute of Technology as an assistant
professor in 1964, was promoted to full professor in 1970, and
was appointed chairman of the department in 1971, where he
remained until 1987. After serving twice as interim dean of the
college of engineering, he was made Vice President for Research
and Technology at IIT and its Research Institute in 1988, and in
1991 was appointed Provost and Vice President.
Darsh's research activities span a number of separate but

ers, the attractive van der Waals' forces among all
the molecules of the film, and the steric forces due to
steric hindrance in closely packed monolayers.

FILM DRAINAGE MODEL
The approach of two drops or bubbles under the
capillary pressure acting normal to the surfaces
causes liquid to be squeezed out of the film into the
Plateau borders. This liquid flow results in the con-
vective flux of surfactant in the sublayer (see Figure
2). Therefore, the surfactant concentration at the
surface is increased in the direction of the flow. The
nonuniform surfactant distribution leads to surface
flow which, in turn, gives rise to surface stresses.
The difference in concentration along the surface
results in a difference of the local values of surface
tension which produces a force (equal per unit length
to the gradient of surface tension) opposite to liquid
flow (Marangoni-Gibbs effect). In addition, the sur-
factant monolayer may undergo dilating and shear-
ing deformations which also produce surface stresses.
The sum of the above stresses must counterbalance

Surface tension gradient
opposes film flow

Figure 2. Marangoni-Gibbs effect in the thin film drainage
process. Surfactant is swept to the Plateau borders by flow
in the film and droplet phases, thereby creating surface
concentration gradients which engender surface tension
gradients.

interrelated fields focusing particularly
upon the importance of interfacial trans-
port processes and rheology. This re-
search, which has resulted in over two
hundred publications, including seven re-
search monographs, twelve book chapters,
and three U.S. patents, has been summa-
rized in his recent textbook, Interfacial
Transport Processes and Rheology, writ-
ten with his doctoral student, David
Edwards, and Professor Howard Brenner at MIT. He has di-
rected forty-five PhD and fifty-five MS students.
The novel instrumentation developed by his group for thin
film research and interfacial theological measurements has
been adopted by industry. He is the first engineering scientist
to ever receive the NSF Special Creativity Award twice. An
AIChE Fellow, his other honors include the ASEE Western
Electric Fund Award, the AIChE Chicago Section Ernest W.
Thiele Award, Syracuse University's Donald Gage Stevens Dis-
tinguished Lectureship Award, and the Bulgarian Academy of
Sciences Asen Zlatarov National Award. He is also well known
for his service to the professional societies.

06 Chemical Engineering Education

the tangential bulk stress from the film liquid which
causes surface flow.
Reynolds was the first to study the rate of ap-
proach between surfaces separated by a draining
film. His analysis assumed that the two surfaces
were both flat and rigid. As pointed out by many
researchers, Reynolds' equation represents a most
conservative prediction; it underestimates the veloc-
ity of thinning and hence overestimates the film
drainage time. Both theoretical and experimental
research have shown that drainage between two
liquid film surfaces is generally much more rapid
due in part to a fluidic mobility within the boundary
surfaces of the film. In fact, much of the thin-film
drainage research in the past four decades has fo-
cused on quantifying the relevant parameters within
thin film which determine whether the film will

0 5 10 15
Dimensionless Film Thickness,7h xl04
Figure 3. Interfacial mobility, or dimensionless drainage
velocity, versus dimensionless film thickness, at three val-
ues of the dimensionless interfacial elasticity.121
300 r I

10.1 10 10 102 103 104 105
Boussinesq Number, Bo
Figure 4. Dimensionless drainage time for the film to drain
from a dimensionless thickness hi to the thickness hf, ver-
sus Boussinesq number, at various values of the dimen-
sionless interfacial elasticity. 21
Spring 1992

drain rapidly (promote instability of the emulsion or
foam) or slowly (promote stability), largely on the
basis of the mobility of the boundary surfaces. We
have recently developed a generalized model which
accounts for the effect of the mobility of the surfaces
on film thinning phenomena by considering the ki-
netics of adsorption-desorption of surfactants, sur-
face and bulk diffusion, surface theological proper-
ties, and flow in both film and bulk phases.ls8
In Figure 3, the effect of the surface tension gradi-
ent upon surface mobility is shown in terms of the
dimensionless elasticity number Es. The surface-ten-
sion gradient in the thinning film is created by the
efflux of liquid from the film and the sweeping of
surfactant along the film surfaces to the Plateau
borders, as depicted in Figure 2. This creates a sur-
face-tension gradient that opposes film drainage, cre-
ating immobile film surfaces.
The effect of surface tension gradient on the film
drainage time is depicted in Figure 4. At high values
of tension gradient, i.e., high Es, bulk and surface
diffusion cannot counterbalance the surface tension
gradient (the Marangoni-Gibbs effect) and hence,
the velocity of thinning (or the drainage time) is
essentially given by the Reynolds' equation. How-
ever, for small values of Es, even at a moderate
surface viscosity (i.e., moderate Boussinesq number,
Bo), the thinning or approach velocity is several
times greater than Reynolds' velocity. An increase in
surface viscosity results in decreased surface mobil-
ity and hence, higher drainage time. Thus, the thin
film drainage model predicts that at low surface
viscosity (i.e., Boussinesq number less than 10), the
Marangoni-Gibbs effect will impart the more signifi-
cant influence on film drainage and, thereby, on the
drop or bubble-coalescence rate. Therefore, these
theoretical findings clearly suggest that differences
between estimated drainage times for films with
mobile surfaces (i.e., no surfactant and therefore no
surface theological stress) and immobile surfaces
(i.e., very large surface theological stresses leading
to a solid-like surface behavior) may be several fold.
It has also been reported that surface theological
properties may also considerably stabilize a thin
film by imparting a rigidity to liquid film surfaces.
The differences between estimated rupture times for
films with mobile surfaces and immobile surfaces
may also be several fold.19-101
Several factors may influence both the drainage
time and stability of thin liquid films, including film
viscosity, film thickness, surface diffusion and sur-
factant adsorption, and surface shear and dilata-
tional viscosities and elasticities.121

The theoretical findings of a thin film drainage
model, as discussed above, clearly suggest the im-
portant role that surface viscosities and elasticities
play in foam and emulsion stability. Indeed, correla-
tions between the surface shear viscosity and sur-
face dilatational elasticity and emulsion or foam sta-
bility have been reported by many investigators.
Surface theological properties also possess a di-
rect significance to the bulk rheology of emulsions
and foams. This may be attributed both to the pres-
ence of surfactants adsorbed to the surfaces within
foams or emulsions and their large specific surface.
The relationship between the macroscopic foam, rheo-
logical behavior and surface dilatational viscosity
and surface-tension gradients, as well as thin foam
film parameters such as disjoining pressure, was
recently considered.[21 We showed that for monodis-
perse, spatially periodic foams possessing a finite
foam film contact angle and relatively low disperse
phase volume fraction, the dilatational viscosity of
the foam depends primarily upon interfacial stresses
owing to the large surface-to-volume ratio of the
foam and is localized within the Plateau border zones
of the local foam structure. Interfacial viscosities
were shown to be most important for "wet" foam (i.e.,
relatively low dispersed phase volume fraction). How-
ever, the Gibbs elasticity (i.e., the interfacial tension
gradient) was shown to be most important for the
"dry" foam (i.e., dispersed phase volume fraction ap-
proaching one). The foam dilatational viscosity for
both wet and dry systems was found to be inversely
proportional to film thickness.
It may be concluded that the surface theological
properties, such as surface elasticity or tension
gradients and surface viscosities, play most impor-
tant roles in thin film drainage and stability and
thereby in both emulsion and foam stability, and in
their bulk theological behavior at surfactant concen-
trations near or below the critical micelle concentra-
tion (CMC).

ORDERED MICROSTRUCTURES KEY TO
THIN LIQUID FILM BEHAVIOR
At high surfactant concentrations (i.e., much above
CMC), it has been observed that thin liquid films
become thinner in a stepwise fashion-that is to say
that thinning foam or emulsion films formed from
micellar surfactant solutions exhibit a number of
metastable states before attaining an equilibrium
film thickness.
Figure 5 depicts an interferogram of films formed
from surfactant micellar solutions. We used the
microinterferometric method to investigate thin film
108

behavior, as described in recent papers.13-61 Using a
film formed from a micellar surfactant solution, we
observed the following:
As soon as the film forms, it starts to decrease in
thickness.
After it is thinner than 104nm, i.e., 1040A (the last
interferential maximum corresponding to the
monochromatic 546nm light reflected from the film),
the film thickness changes in steps (i.e., stratifica-
tion-see Figure 5).

Thinning film shows ordered structure

-90-- -

I I t I
-2

]? ~ ~ ~ ~ ~ ~ 4 1-1-- -- -efrr-.n-
0 t

Time --
Figure 5. Interferogram of film formed from solution of
nonionic detergent (Enordet AE 1215-30, 0.052 mol/1). As
film thins, less light is reflected. Formation of metastable
states of uniform thickness is revealed by "steps." Height
of step corresponds to thickness of film. Vertical distance
between steps corresponds to micelle diameter, about 10nm.
Width of steps is proportional to lifetimes of respective
metastable states.
Chemical Engineering Education

The film rests for a few seconds in a metastable,
uniformly thick state.
Then, dark spots (with smaller thickness than the
remaining part of the film) appear and gradually
increase in size (see Figure 6A).
The spots cover the entire film and the film "rests"
for a time in a new metastable state.
Then, even darker spots appear and, after their

A B
Figure 6. Stratification of films:
A. 0.1 mol/l sodium dodecylsulfate surfactant solution.
B. 30 wt% latex suspension with a particle diameter of
91 nm.
0.20

0.15 ORDER

0 stratifying
S0.10 films
a DISORDER
S 0.05 non-stratifying
films

0.00
0.08 0.09 0.10 0.11
NaCI Concentration (mol/l)
Figure 7. Phase diagram of order/disorder transition. Vol-
ume fraction of micelles versus concentration of added
NaC1. The curve represents the threshold concentration
separating the regions with and without stratification in
thinning foam films.
Spring 1992

expansion, a subsequent metastable state ensues.
This process continues until the film finally reaches
a stable state with no more stepwise changes. The
metastable state of the film appears in the interfero-
gram as a step-wise width in proportion to the life-
time of the respective state. The calculated height of
the steps is also shown in Figure 5, and the magni-
tude is approximately constant for all steps (about
10.6nm), which corresponds to micelle diameter,
about 10nm. For ionic surfactants, the effective mi-
cellar diameter includes the Debye diameter of the
surrounding electric double layer.
Some other findings: Foam films formed from con-
centrated suspensions of polystyrene latexes (see
Figure 6B) and silica particles stratify in similar
fashion.171 But there is one difference: Because the
particles are much larger than surfactant micelles,
with diameters exceeding the thickness of the last
interferential maximum, there can be constructive
as well as obstructive interference, and the thinner
spots sometimes appear brighter rather than darker
than the remaining thicker film. When the repulsive
force is electrostatic (as in latexes and micellar solu-
tions of ionic surfactants), adding salt to the mixture
suppresses stratification; above a threshold salt con-
centration, no stepwise transitions occur (see Figure
7). When the repulsion is the result of steric forces
(the case with nonionic surfactants) stratification is
temperature-sensitive.16l
All the experimental data for stratifying films
and theoretical analysis of these datal51 show that
stratification is a universal phenomenon and is due
to the formation of a long-range crystal-like struc-
ture within the liquid film and a layer-by-layer thin-
ning of such an ordered structure.
The driving force for the step-wise thinning of the
film is the gradient of the chemical potential of the
micelles at the film's periphery, as discussed in our
recent paper.1111 This ordering occurs because sur-
factant micelles or colloidal particles with narrow
size distribution interact via repulsive forces and
are forced into the restricted volume of the film.
Another way to demonstrate the presence of or-
dered structure inside a stratifying film is to form a
large film (2.5cm diameter) in a vertical frame in-
side a glass cylinder (see Figure 8). With foam films
formed from polystyrene suspensions, one observes
a series of stripes of different, uniform colors at the
upper, thinner part of the film. The different colors
are due to interference of the common (polychro-
matic) light reflected by the surface of the different,
uniform thickness stripes. The boundaries between
the stripes are very sharp, a consequence of the step-
109

wise profile of the film in this region, and the liquid
meniscus below the film appears as a region with
gradually changing colors where the order/disorder
transition region is observed. The different thick-
nesses of the stripes as determined by the difference
in reflectivity are marked on this figure. According
to the colloid crystal-like model, the different color
stripes contain different numbers of particle layers.
Figure 8 also shows the almost circular spots in the
order/disorder region. The colored spots of lesser
thickness than the surrounding film move upward
in the lower stripes and, eventually, fuse with the
corresponding upper stripe. By measuring the ve-
locities and size (radii) of these spots, one can esti-
mate the effective dynamic viscosity of the ordered
structure inside the film.
We observed similar sharply defined stripes with

40 nm, (1) layer-

70 nm, (2) layers-
100 nm, (3) layers-
133 nm, (4) layers-
167 nm, (5) layers-
200 nm, (6) layers-.
230 nm, (7) layers-

disorder/order transition--

Figure 8. Interference stripes in a vertical stratifying film
formed from 20 V% silica suspensions with particle diam-
eters of 19nm. Each color stripe represents a different
number of particle layers inside the thinning film.

FILM THICKNESS, h(nm)
Figure 9 Calculated disjoining isotherms II,(h) for thin
films with n micellar layers inside (h, = 0,1,2,3)./15

foam films formed from micellar solutions of nonionic
surfactant (e.g., ethoxylated alcohol, with 30 ethoxy
groups and 12-15 carbon chains) with a micellar
diameter of about 10nm. However, all stripes were
very grey in color, though with different intensities,
because the diameter of the micelles is small.
As discussed in a recent paper,15] we have devel-
oped the theoretical model to explain the stratifica-
tion in foam films of micellar solutions of ionic
surfactants. The micelles interact via screened elec-
trostatic repulsion forming an ordered structure due
to the restricted volume of the film. The model
permits, for the first time, calculation of the struc-
tural contribution to the disjoining pressure of the

7 cs 0 03 mol/1 n4
n;3
6 n=2
E
z
Z
E 5 n0

3 4
0
(3
LU

2 20 30 40 50 60 70 80 90 100
U,
w
x
0-

0 10 20 30 40 50 60 70 o80 90 100
FILM THICKNESS, h(nm)
Figure 10. Calculated isotherms of the excess energy for
unit area of the film, won(h), at the surfactant concentration
of 0.03 mol/liter and at different micellar layers inside the
film.[5/

Figure 11. Aqueous foam stabilized due to the stratifica-
tion in the foam bubble lamellae (20% silica particles with
diameter of 19nm).
Chemical Engineering Education

film that arises from the presence of micellar struc-
ture within the films.
Figure 9 shows the disjoining pressure isotherm
calculated from our theoretical modell51 for 0.03
mol/l concentration of sodium dodecyl sulfate. By
integration of disjoining pressure with respect to the
film thickness, we derived the expression for the
interaction free energy. The curves for the excess
free energy (see Figure 10) exhibit the structural
stability of films due to the inner multi-layering of
micelles. The curves exhibit minima, which corre-
spond to the metastable state (n = 1,2,3,...) and to
the final stable state (n = 0) of the film. A stepwise
film thickness transition can be interpreted as a
transition from a given metastable state to the next
one. The experimental values of the film thickness
are in good agreement with the ones calculated from
the theoretical model. The shape of these energy
curves also properly reflect the phenomenon of strati-
fication; the energy of the metastable state decreases
with the decrease in film thickness, and consequently,
the film stability increases. Work is in progress in
our laboratory to delineate effects of several factors
such as surfactant micellar concentration, electro-
lyte, temperature, and film curvature on the film
stratification phenomenon using our newly devel-

TABLE 1
Technological Impact of Thin Film Research

Coalescence of drops and bubbles as in Emulsions and
Foams
Tertiary Oil Recovery and other processes concerned with
multiphase flow in porous media
Spreading of liquids on solid surfaces as in Coating
processes
Magnetic Tapes and Discs involving deposition of thin
films of colloidal magnetic particles which must be well-
bound to the support surface
Tribology, the science of lubrication and wear, reveals the
importance of thin film lubricating layers whose properties
can be significantly different from those of the parent bulk
material
Space Technology has created a demand for thin film
coatings to make processing container wall selectively
wetting to certain fluids
Biotechnology which can provide economic pathways to
chemical feedstocks and novel products which require a
basic understanding of the lipid thin film layers which
constitute the cell walls
Ceramics processing, the intervening thin liquid films
between powder particles determine the stability of
colloidal dispersions and thereby influence the properties
of the engineered materials
Formation of new materials such as Biochips with pre-
scribed microstructures
Microelectronics industry employs a variety of deformable
films to selectively etch, form, and protect chips,
microsensors, and other types of microcircuitry

Spring 1992

oped surface force balance apparatus for films with
fluid surfaces.

CONCLUDING REMARKS
The formation of long-range ordered structures
inside thin films has many implications of both fun-
damental and practical significance. For example,
the dynamic process of stratification or multilayer
microstructuring in sub-micron thin liquid films can
serve as an important tool for probing the long-
range structural or interaction forces in concentrated
particle suspensions and colloidal dispersions. The
rheology of such dispersions containing stratifying
films will be quite different. We have recently at-
tempted to determine the dynamic viscosity of the
stratifying foam film as depicted in Figure 8. Such
measurements are detailed elsewhere.[121 The dy-
namic viscosity of the stratifying foam film was found
to be much higher than that of the pure solvent.
From a practical point of view, we have identified
a new mechanism for the stabilization of foam and
emulsion films via the presence of such ordered mi-
crostructures inside the films. The lifetimes of foams
or emulsions with stratifying films are observed to
be much longer.
Figure 11 clearly shows, for the first time, a pho-
tograph of an aqueous foam system stabilized due to
the stratification in the foam bubble lamellae.1131
Finally, at a recent NSF Workshop on "Inter-
facial Phenomena in the New and Emerging Tech-
nologies," thin film science has been identified as
one of the pivotal areas of basic research which is
needed to strengthen the competitiveness of U.S.
science and technology.ll41 Thin liquid films are gain-
ing large scientific and industrial applications, as
outlined in Table 1.

ACKNOWLEDGEMENT
This study was supported by the National Science
Foundation. The author gratefully acknowledges the
help provided by Dr. Alex Nikolov and Dr. David
Edwards in the preparation of this lecture material.

REFERENCES
1. Wasan, D.T., M.E. Ginn, and D.O. Shah, eds, Surfactants in
Chemical/Process Engineering, Surfactant Science Series,
28, Marcel Dekker, Inc. (1988)
2. Edwards, D.A., H. Brenner, and D.T. Wasan, Interfacial
Transport Processes and Rheology, Butterworth-Heinemann
(1991)
3. Nikolov, A.D., D.T. Wasan, P.A. Kralchevsky, and I.B.
Ivanov, in Ordering and Organization in Ionic Solutions, N.
Ike and I. Sogami, eds., World Scientific Publications, Co.,
Ltd., Singapore (1988)
4. Nikolov, A.D., P.A. Kralchevsky, I.B. Ivanov, and D.T.
Wasan, J. Colloid Interface Sci., 133, 1 (1989)
5. Nikolov, A.D., P.A. Kralchevsky, I.B. Ivanov, and D.T.
111

Wasan, J. Colloid Interface Sci., 133, 13 (1989)
6. Nikolov, A.D., D.T. Wasan, N.D. Denkov, P.A. Kralchevsky,
and I.B. Ivanov, Progress in Coll. and Poly. Sci., 82, 1 (1990)
7. Wasan, D.T., Donald Gage Stevens Distinguished Award
Lecture on "Structure and Dynamics of Thin Liquid Films,"
Syracuse University, November (1991)
8. Malhotra, A.K., and D.T. Wasan, Chem. Eng. Commun., 55,
95 (1987)
9. Gumerman, R., and G. Homsy, Chem. Eng. Commun., 2, 27
(1975)
10. Jain, R.K., and E. Ruckenstein, J. Colloid Interface Sci., 54,
1(1976)
11. Kralchevsky, P.A., A.D. Nikolov, D.T. Wasan, and I.B.
Ivanov, Langmuir, 6, 1180 (1990)
12. Basheva, E.S., A.D. Nikolov, P.A. Kralchevsky, I.B. Ivanov,
and D.T. Wasan, paper presented at the 8th International
Symposium of Surfactants in Solutions, Gainesville, FL: to
appear in Symposium Volume, K. Mittal, Ed. (1992)
13. Wasan, D.T., A.D. Nikolov, L. Lobo, K. Koczo, and D.A.
Edwards, in Progress in Surface Science, 39, 2 (1992)
14. Krantz, W.B., and D.T. Wasan, Proceedings of the NSF
Workshop on "Interfacial Phenomena in the New and Emerg-
ing Technologies," University of Colorado, May (1986) O

lU book review

PROCESS SYSTEMS ANALYSIS AND
CONTROL, 2nd edition
by D. Coughanowr
McGraw-Hill, 1221 Avenue of the Americas, New
York, NY 10020; $52.95 (1991)

Reviewed by
P.B. Deshpande
University of Louisville

I learned process concepts from the first edition of
this book when I was a student at the University of
Arkansas. The clarity of its presentation and the
effectiveness of the instructor (Carl Griffis) have
been the main reasons for my sustained interest in
process control for the last twenty years.
Much of the material from the first edition has
been retained in the second edition, but there are
additional new chapters on advanced control strate-
gies, process identification, sampled-data control,
state-space representation, multivariable control, and
computers in process control applications.
In advanced control, Professor Coughanowr
covers cascade and feedforward control, ratio con-
trol, dead-time compensation, and internal model
control. In the chapters on sampled-data systems
the author discusses sampling operations, Z-
transforms, design of sampled data controllers,
and stability. The chapter on state space method
is a good introduction to the subject, as is the
chapter on multivariable control.
In the chapter on computer simulation, the au-

thor discusses the use of TUTSIM and its potential
applications to process control problems. TUTSIM
uses an analog computing type of logic and is easy to
learn and use. In the last chapter the student is
introduced to distributed control concepts. The new
material is well written and clear. However, in many
instances the level of detail is so small that it is not
of much practical use. (But, in a first course in pro-
cess control, how many topics can be covered?) Also,
there does not appear to be enough examples and
problems in some of the chapters.
Having made a phenomenal impact on improv-
ing quality (and therefore competitiveness) in dis-
crete manufacturing industries, Statistical Quality
Control (SQC) concepts have arrived on the scene in
continuous industries as well. Statisticians are rou-
tinely consulted on issues of quality, but the control
engineer is on the sidelines, often unable to make an
impact on process operations. Control technologies
which can be shown to have a direct impact on qual-
ity are needed. This text, as well as others on the
market (including ours), does not appear to provide
these perspectives to the student.
In closing, the second edition is a good addition to
the collection of textbooks on undergraduate process
control, subject to the comments in this review. Stu-
dents and instructors alike will enjoy learning and
teaching from this book. D

REVIEW: CHEM PROCESS SAFETY
Continued from page 75.
how it might have been avoided, and how it can be pre-
vented in the future.
There are sample problems throughout the text, and
each chapter has problems and questions at the end. Most
of the sample problems are clear and easily followed. A
manual containing solutions for most of the problems is
available. A few of the solutions are incorrect, but the
errors are mostly minor and easily found. There are some
errors in printing, again mostly minor, and mostly identi-
fied in an errata list available from the authors. The
errors distract little from the presentation of the material.
I find the text to be a welcome addition; it presents
more than enough material for an undergraduate course
in chemical process safety. It contains sufficient refer-
ences that considerable additional material can be found,
either for incorporation by the instructor or for additional
study by the student. The book can also serve the practic-
ing engineer by providing a basic background for under-
standing other information that is available. The most
important accomplishment of the text may be that it pro-
vides the basis for including the study of chemical process
safety in the curriculum for chemical engineers. That is
something we need to have emphasized more strongly if
we are to be professionally competent. O
Chemical Engineering Education

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DEPARTMENTAL SPONSORS

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	The University of Toledo
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