Chemical engineering education

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

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

Subjects

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

Notes

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

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
oclc - 01151209
lccn - 70013732
issn - 0009-2479
Classification:
lcc - TP165 .C18
ddc - 660/.2/071
System ID:
AA00000383:00083

Full Text








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EDITORIAL AND BUSINESS ADDRESS

Department of Chemical Engineering
University of Florida
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Chemical Engineering Education
VOLUME XVIII NUMBER 3 SUMMER 1984


DEPARTMENTS

The Educator
98 Esin and Erdogan Gulari of Wayne State and
Michigan, H. S. Fogler, R. H. Kummler
Department of Chemical Engineering
102 ChE at Syracuse University, Allen J. Barduhn,
Lawrence L. Tavlarides
Views and Opinions
106 Teaching Professional Ethics, Donald R. Woods
Class and Home Problems
110 Thermal Conductivity of a Hotdog, Michael J.
Matteson, Jude T. Sommerfeld
Classroom
112 Dimensionless Education, Graham F. Andrews
116 The Thermodynamics of Exergy, Pablo G.
Debenedetti
122 Process Design in Process Control Education,
M. Nazmul Karim
128 The Two Lost-Work Statements and the Combined
First- and Second-Law Statement, Noel
de Nevers, J. D. Seader
140 Kinetics and Catalysis Demonstrations, John L.
Falconer, Jerald A. Britten

Lecture
124 How We Make Mass Transfer Seem Difficult,
E. L. Cussler

Laboratory
132 Tray Drying of Solids, Artin Afacan,
Jacob Masliyah
136 A Microcomputer Based Laboratory for
Teaching Computer Process Control,
Babu Joseph, David Elliott
109 Letters to the Editor

109, 139, 144 Book Reviews



CHEMICAL ENGINEERING EDUCATION is published quarterly by Chemical
Engineering Division, American Society for Engineering Education. The publication
is edited at the Chemical Engineering Department, University of Florida. Second-class
postage is paid at Gainesville, Florida, and at DeLeon Springs, Florida. Correspondence
regarding editorial matter, circulation and changes of address should be addressed
to the Editor at Gainesville, Florida 32611. Advertising rates and information are
available from the advertising representatives. Plates and other advertising material
may be sent directly to the printer: E. O. Painter Printing Co., P. O. Box 877,
DeLeon Springs, Florida 32028. Subscription rate U.S., Canada, and Mexico is $20 per
year, $15 per year mailed to members of AIChE and of the ChE Division of ASEE.
Bulk subscription rates to ChE faculty on request. Write for prices on individual
back copies. Copyright 1984 Chemical Engineering Division of 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 of the ASEE
which body assumes no responsibility for them. Defective copies replaced if notified
within 120 days.
The International Organization for Standardization has assigned the code US ISSN
0009-2479 for the identification of this periodical. USPS 101900


SUMMER 1984










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"Keeping all the balls in the air"


H. S. FOGLER
University of Michigan
Ann Arbor, MI 48109
R. H. KUMMLER
Wayne State University
Detroit, MI 48202

Dual-career families are becoming common-
place, but the effort required to succeed on all
fronts is enormous. Careers as researchers and
tenured professors of chemical engineering mean
complicated logistics for Esin and Erdogan Gulari
in the planning of their daily routine.
For Esin, it means getting up at 6 a.m. to drive
the 45 miles from Ann Arbor to Detroit to teach
her morning undergraduate class at Wayne State
University, returning after teaching her evening
graduate class.
For Erdogan, it means preparing their son
Bora's breakfast and getting him off to school
before going to The University of Michigan to
teach his morning class and meet with graduate
students.
For both of them it means making sacrifices
and juggling schedules and setting priorities. But
the Gularis want it all and are willing to work at it.


[Esin's] interest in transport and
physical properties of fluids make her one
of WSU's leading instructors in transport phenomena,
unit operations, and thermodynamics.

Copyright ChE Division, ASEE. 1984


Two outstanding careers in chemical engineering
are at least partial evidence that their hard work
has paid off.
They received their B.S. degrees in chemical
engineering in 1969 from Robert College in Istan-
bul, Turkey, and were married the following
summer. In the fall they began graduate school at
Caltech, both choosing Professor Neil Pings as
thesis adviser. After receiving their Ph.D. degrees
in 1973, Erdogan accepted a postdoctoral fellow-
ship with Professor Ben Chu at the State Uni-
versity of New York at Stony Brook while Esin
combined teaching of physical chemistry with re-
search under Professor Chu's direction.
In 1974 the Gularis returned to Turkey, where
they accepted positions as Laboratory Manager
and Technical Manager of a large vegetable-oil
extraction plant along the Aegean coast. They were
responsible for the design and construction of a
coal- and oil-fired power plant, and were also in
charge of the technical operation, which included
extraction and refining plants, product control and
improvement. Of the experience, Erdogan says, "It
taught me how to deal with and manage people.
It was an interesting change from being a postdoc
to holding a position of responsibility for many
people."
But the small town was isolating intellectually,


CHEMICAL ENGINEERING EDUCATION









and when plant construction was finished and
start-up problems solved, management of the
routine operation did not provide sufficient chal-
lenge. So they gave up secure jobs in Turkey in
search of positions involving teaching and re-
search in the U.S.
Esin and Erdogan returned to the academic
environment at SUNY-Stony Brook and resumed
postdoctoral work with Professor Chu in the area
of laser lightscattering. In 1978 Erdogan accepted
an offer to join the faculty at The University of
Michigan. During their first year in Ann Arbor,
Esin taught chemistry at nearby Eastern Michigan
University. In the spring of 1979 she joined the
chemical engineering department at Wayne State
University.

ESIN GOES TO WSU
The legend of Esin Gulari at WSU began with
an incident that has become an infamous story.
During her second interview, just as the faculty
had determined that Esin was indeed the scholar
and teacher they wanted and were busy convincing
her that WSU was the place for her, her car was
towed away by the Parking Authority. Was this
a warning about the Big City Campus or a sign
that WSU would not let her go?
In an incredibly short time Esin has created a
laser lightscattering laboratory and built a student
research group of a half dozen students actively
pursuing research projects. Her students are also
welcome in Erdogan's Ann Arbor laboratory when-
ever additional equipment is necessary.
At Stony Brook, Esin, jointly with Erdogan,
developed an inversion technique to evaluate
particle size distributions of colloids and polymers
from dynamic light scattering data. Her research
at WSU now centers on using lasers, "a nonin-
trusive and precise probe," to study fluctuations in
fluids.
A major focus of her research concerns the
diffusion of compressed gases in liquids and
medium molecular weight hydrocarbons in dense
gases with urgent interest because of the use of
CO, as a miscible solvent in tertiary-oil recovery
and supercritical extraction processes. Esin has
been able to use photon correlation spectroscopy to
measure the binary diffusion coefficient at elevated
temperatures and pressures in these systems. Her
group introduced the use of a "probe particle" of
known radius for measuring liquid viscosities.
Most recently, she has been concerned with the
physical properties of polymeric emulsions. The


average molecular weight and the molecular
weight distributions determine the principal physi-
cal properties, and hence it is crucial to be able
to predict and control the polydispersity of a
polymer. Understanding the mechanism of initi-
ation is an important goal of Esin's research. She
has demonstrated the existence of at least two
competing mechanisms in the polymerization of
styrene in microemulsions.
Future research efforts for Esin's group will
involve the use of a unique detection scheme of
diffraction patterns to characterize diesel sprays.
Esin brings simultaneous dedication to teach-
ing and research. Moreover, she brings en-
thusiasm and personal qualities which motivate
those around her. Members of the WSU faculty
who appreciate her sense of humor are in awe of
the tough taskmaster image she maintains with
her students. She teaches with equal ease at the


Esin and students discuss their latest problem.

undergraduate and graduate levels and has intro-
duced a special graduate course in optical spectro-
scopy in chemical engineering research. Her inter-
est in transport and physical properties of fluids
make her one of WSU's leading instructors in
transport phenomena, unit operations, and thermo-
dynamics.
It is obvious that both Esin and her students
enjoy their work. Much of her time is dedicated to
one-on-one instruction. Even the casual observer
cannot help but notice the many hours that gradu-
ate students spend in her office and laboratory and
their total involvement in her research projects.
Industry recognizes the excellent results Esin
achieves. Her students are in demand, and she has
a steady stream of visitors examining her labora-
tory so that they can emulate the equipment. She
consults for industry in the Detroit area and also


SUMMER 1984








has visited laboratories in Ludwigshafen, Ger-
many, in collaborative efforts.
There is another facet of Esin's career: service
to AIChE. She has served as director, secretary,
and was recently elected as vice chairman of the
Detroit Section. During her tenure, the Detroit
Section has enjoyed some of its most successful
years, culminating with the outstanding local
Diamond Jubilee Program last year.

ERDOGAN SETTLES IN AT MICHIGAN
For Erdogan, research is not only a scholarly
challenge, it's fun. As his graduate students say,
coming to the lab "is like coming to play. A new
project or a new piece of equipment is like a new
toy to him." His enthusiasm is contagious, and
his students enjoy their work. Actually, they say,
he is as excited about their successes as he is about
his own, and he often spends extra hours in the
lab sharing their highs (or lows).
Erdogan is happiest tackling new problems
rather than doing what somebody else has already
done or is currently doing. "Don't reinvent the
wheel," and "an hour in the library is worth ten
in the lab," he tells his students. His interest in
new frontiers led him to research in periodic and
unsteady state operation of catalytic reactors.
Erdogan's two most significant research ac-
complishments have been: the establishment of

[Erdogan] is working on unsteady state
operation of catalytic reactors and has developed a
reactor system that allows investigation of transient
phenomena in the millisecond time range.

dynamic lightscattering as a reliable means of
measuring the mutual diffusion coefficient and
thermal diffusivity; and with Esin, the develop-
ment of an indirect inversion technique to evalu-
ate the Fredholm integral of the first kind in order
to obtain particle size distributions from dynamic
lightscattering data.
He is currently working on unsteady state
operation of catalytic reactors and has developed
a reactor system that allows investigation of
transient phenomena in the millisecond time
range.
Erdogan's work in adsorption of sulfonate
based surfactants on germanium oxide was the
first molecular investigation of surfactant adsorp-
tion which clearly demonstrated which functional
group was responsible for adsorption, and it
showed that the hemimicelle theory of adsorption


Not a conventional teacher, Erdogan enjoys the chal-
lenge of the classroom.
was not in agreement with the molecular picture
of adsorption.
In order to carry out his research Erdogan first
had to build his laboratory-almost from scratch.
He has built a spectroscopy lab matched by few
across the country, and other investigators now
send both their students and their samples for test-
ing to his lab.
Part of the challenge of research is in teaching
research. He expects and encourages his students
to do their own thinking and experimentation.
According to his graduate students, "If you come
up with a good idea, you are encouraged to try it
out. He is very open-minded and almost never im-
poses his own way of doing things. He would
rather have you try and fail than not try at all."
He believes in students' independence in the
laboratory and in the classroom. For that reason
Erdogan would not be described as a "con-
ventional" teacher. He often leaves holes for
students to fill in on their own, inviting thought
and investigation rather than providing every de-
tail for them. But he is very willing to spend time
with individuals when they request additional in-
formation or guidance.
"One of the rules I try to follow in teaching
is to make sure that the students understand


CHEMICAL ENGINEERING EDUCATION










On local waters... Professors Gulari are known as Bora's mom and dad. When he was six
years old, weighing only 43 pounds, Bora was the youngest windsurfer in the world. He won the
championship in the Ann Arbor "B" fleet competition over nine other contenders when he was only seven years old.


that I am there to help and encourage them in their
learning process, both on a one-to-one basis and
also in the classroom, and that I care about them."
In order to better interact with the students, he
divides his large classes into small discussion
groups where problems can be discussed informal-
ly. "My emphasis in these discussion sessions is
not just to solve problems or answer questions,
but also to get the students to think and arrive
at the answer, starting with the most fundamental
definitions or equations."
"To me, teaching is more than a requirement
of the job. I do not agree with the claim that good
researchers make poor teachers." Erdogan is de-
termined to get the material across, even to the
largest classes, and he will try new approaches
when old ones fail.

FAMILY ACTIVITIES WATER-ORIENTED
Busy teaching and research schedules for
husband and wife leave little spare time for the
Gulari family. As much time as possible, though,
is spent on one of the nearby lakes or rivers. The
Gularis are avid sailors. They started sailing as a
means of relaxation while writing their theses at
Caltech, and Bora tasted the salty spray of the
Mediterranean when he was only three months old.
A tribute to Erdogan's sailing abilities came in
the fall of 1983 when he was sponsored by the sail-
boat manufacturer Banshee in the national
championships in Alemeda, California. He finished
second in 1982 and fifth in 1983 in this single-
handed mono-hull class.
Recently the Gularis' interests have turned to
windsurfing. "I love the freedom and independence
windsurfing offers," says Esin. "After work, on a
day when the westerly blows, it is very refreshing
to feel the board take off and literally fly for an
hour." "I especially like to sail in stormy weather,"
says Erdogan. "While physically demanding, it
provides total mental relaxation."
On local waters around Ann Arbor, Professors
Gulari are known as Bora's mom and dad. When
he was six years old, weighing only 43 pounds,
Bora was the youngest windsurfer in the world.
He now beats many adults, even on windy days. He
won the championship in the Ann Arbor "B" fleet
competition over nine other contenders when he


was only seven years old. He has appeared on tele-
vision news shows, and many regional newspapers
have carried articles and photographs. At the age
of 8, Bora Gulari has developed into a "big-shot"
windsurfer.
Collaboration, yet independence, seems to be
a key to the mutual success of the Gularis. They
shared the expertise of common dissertation and
postdoctoral advisers and have co-authored a


Bora, a champion windsurfer, displays his skill.

number of papers. Sharing the same initials,
though, has led to occasional mixups, with Erdogan
getting credit for Esin's papers. To minimize the
problem and to clearly show their independence
in research, they have made special efforts not to
work on closely related problems and have not co-
authored any papers for the last six years.
Both The University of Michigan and Wayne
State University are proud of the professional re-
lationship the two Professors Gulari have fostered
between the schools. Chemical engineering in the
State of Michigan certainly benefits from this
unique sharing of knowledge and ideas. L

Note: The authors would like to acknowledge
Valerie Franklin for her invaluable assistance in
preparing this article.


SUMMER 1984



























General view of Quadrangle 2 of Syracuse University with domed stadium for 50,000 people on the left.


departmentt


SYRACUSE UNIVERSITY


ALLEN J. BARDUHN AND
LAWRENCE L. TAVLARIDES
Syracuse University
Syracuse, NY 13210

O UR CHEMICAL ENGINEERING department is an
important part of the L. C. Smith College of
Engineering, which is named after the famous
Smith of typewriter fame who was born and raised
in the area of Syracuse. The college is one of eleven
at Syracuse University which has 11,000 under-
graduate and 4,000 graduate students from all
fifty states and ninety-four foreign countries. A
mosque, a synagogue, and several churches (ortho-
dox, catholic and protestant) are all within a short
walking distance of the S.U. campus.
The university began its first academic year in
1871 and was established as a residential uni-


The department and Syracuse University
as a whole are currently engaged in a new
enterprise: the Center for Advanced Technology in
Computer Applications and Software
Engineering (CASE Center).

Copyright ChE Division. ASEE, 1984


versity by the Methodist Church, but it has since
become nonsectarian. There are enough residential
facilities (dormitories, fraternities, sororities, and
individual apartments) on or near campus to house
the entire student body (and their families, in the
case of graduate students).
We take pride in our university as well as our
department. In 1966 the university was elected to
the prestigious American Association of Uni-
versities (AAU), to which belong only fifty-two of
the better known universities in the nation, includ-
ing all the Ivy League institutions.
The department and Syracuse University as a
whole are currently engaged in a new enterprise:
the Center for Advanced Technology in Computer
Applications and Software Engineering (CASE
Center). Formally designated by the governor in
February, 1984, the CASE Center is one of seven
New York State Centers for Advanced Technology.
It is a particularly promising example of the
current national trend toward increased inter-
action between universities and industry. Building
upon Syracuse University's longstanding ties with
industry, the Center is helping to improve the
University's research facilities, to strengthen
academic programs, and to support economic
growth in New York. Current projects conducted


CHEMICAL ENGINEERING EDUCATION








through the Center by chemical engineering
faculty members include investigation of electro-
migration in thin film microconductors, develop-
ment of knowledge-base on properties of materials,
and work on computer software for finite-element
analysis in chemical separation theory.
Our campus of two hundred acres is well
maintained and has the only domed stadium in
the state of New York. A recent visitor to our
department (a seminar speaker) said, "This
campus looks just like a university campus ought
to look!" The campus is adjacent to the State Uni-
versity of New York (SUNY) College of Environ-
mental Science and Forestry, which has a first-
class chemistry department. All S.U. students may
take courses there.
Syracuse University has always emphasized
the sports of football and basketball, and some of
us professors used to view this practice with dis-
dain. But right after 1959, when S.U. won the
national championship in football, we got the
largest and best crop of chemical engineers we
had ever seen. Since then we don't disdain our
superiority (some years) in sports.
The city of Syracuse was named after the
Greek city-state of the same name, now in Sicily.
It was in the old Syracuse that Archimedes shouted
in his bathtub, "Eureka!" when he discovered the
principle of buoyancy 2200 years ago. We always
mention this in Transport I (fluid mechanics). The
mayors of Syracuse, New York, and Syracuse,
Sicily, frequently visit each other in current times.
Syracuse is in the center of New York state
and has excellent air transportation since it is
served by four major airlines and six feeder lines.
The city is near the beautiful and largest state
park in the nation, Adirondack State Park. It is
an industrial city that is host to many diversified
industries which include Allied Corporation
(Chemical Sector), important divisions of Gen-
eral Electric, General Motors and Bristol-Myers;
Millers and Matts Breweries, and a host of other
companies making ball bearings, electroplated
items, specialty steels, etc. Syracuse is also the
headquarters of the Carrier Corp., the first and
original air-conditioning company in the world,
and of Crouse-Hinds the manufacturer of elec-
trical components and of the first commercial red
and green traffic signals in about 1920.

THE DEPARTMENT
Our department was originally a part of the
Chemistry Department and we awarded our first


BS in chemical engineering in 1917, our first MS
in 1922, and our first PhD in 1949. We separated
from chemistry and became part of the Engineer-
ing College as the Department of Chemical Engi-
neering and Metallurgy in 1914, but our title was
changed in 1973 to Chemical Engineering and
Materials Science.
Our department chairman before 1954 was
Charles D. Luke, who left to take a job with the
government. The next chairman was James A.
Luker, and when he became Dean of Engineering
we began looking for another chairman. Then
some wag suggested we look for a chairman named


Hinds Hall, home of chemical engineering and civil
engineering.

Lukest so that we would have the procession of
Luke, Luker, Lukest!
Some notable BS graduates have been Andreas
Acrivos (1950), now teaching at Stanford, the late
Leon Lapidus (1945), formerly a professor and de-
partment head at Princeton, and Donald G.
Stevens, former Vice President of SOHIO.
The department presently consists of fourteen
full time faculty, including three professors of
materials science and eleven professors of chemi-
cal engineering. A fifteenth has full time ad-
ministrative duties as Vice President for Re-
search and Graduate Affairs of S.U. There are
104 undergraduate students, 43 graduate students,
9 post doctoral research associates, and 3 visiting
scholars. The department presently occupies
27,000 square feet of space in Hinds Hall and Link
Hall, exclusive of classrooms.

THE UNDERGRADUATE PROGRAM
One of the outstanding features of our under-
graduate program is the individual attention we
give our students. The present (1984) student-to-


SUMMER 1984








faculty ratio is less than fifteen. This structure
gives us the opportunity to interact closely with
the students so that we can instill a sense of pride
in their engineering and scientific accomplish-
ments and a high level of confidence in their back-
ground. All of the eleven faculty members in
chemical engineering are involved in undergradu-
ate teaching.
Another characteristic of our program is the
participation of undergraduate students in re-
search projects. This year over twenty percent of
the seniors and some juniors are performing re-
search under the guidance of the faculty. Some
seniors have had articles accepted for publication
in technical journals prior to graduation and have
given presentations at national AIChE meetings.
The undergraduate curriculum is a typical
blend of mathematics, physical sciences, and engi-
neering courses. Most of our students follow the
General Chemical Engineering Option which
covers the traditional program terminating in the
senior courses in process design and control. By
replacing certain upper level courses in the general
option, students can tailor their program of study
to the options in environmental systems or
materials science. For the former option, courses
in biology, air pollution, and waste treatment are
added, while courses in the structure and proper-
ties of materials, polymer science and processing,
and metallurgy can be added in the latter option.
A few years ago, a freshman chemical engi-
neering computing course was instituted, and this
year it is being taught in our new microcomputer
laboratory. All of the courses (especially those in
design and control) are being updated to reflect
the growing importance of computers in the engi-
neering profession. It is also useful to get the
freshman students into chemical engineering
courses before their sophomore year. We are
pleased to report that renovation of the under-
graduate laboratory will begin this summer. In
addition to moving to a new location with more
space, modern instrumentation (including micro-
computers for data acquisition and analysis) and
new experiments in materials properties and pro-
cessing are being installed, with funds provided
by the IBM Foundation.

GRADUATE EDUCATION AND RESEARCH
The Department of Chemical Engineering and
Materials Science offers a MS and a PhD in chemi-
cal engineering. Masters candidates may pursue
the thesis or non-thesis option, although all


students on research or teaching assistantships
must complete a master's thesis. The thesis is 6
semester hours of the 30 semester hour total. The
PhD requires 90 semester hours beyond the BS of
which up to 39 hours may be doctoral dissertation.
Presently there are 43 full-time Chemical Engi-
neering and Materials Science graduate students
in the department, 40 percent of whom are PhD
candidates.
Considering the size of the department, re-
search covers a broad spectrum that includes bio-
medical, catalysis, surface science, materials
science, polymers, electrochemistry, process simu-
lation and control, separation and transport pro-
cesses.
For the twenty-three years prior to 1980,
Allen J. Barduhn did a lot of research on desalting
sea water by freezing and by gas hydrate forma-
tion and became an expert on the growth rates of
ice crystals and the thermodynamics of many gas
hydrate systems. In 1964 Barduhn invented the
eutectic freezing process for treating waste
waters.
John C. Heydweiller is investigating the op-
timal design of entire processes by using the
Rayleigh-Ritz approach to incorporate distributed
models. This project involves the investigation of
various approximating functions and search pro-
cedures to find an efficient and robust combination.
Another topic of interest to Heydweiller is the
numerical solution of partial differential equations,
particularly those involving steep fronts.
Vasilios A. Karagounis is interested in the
photolithographic fabrication of dissolved oxygen
and pH sensors on silicon chips. Theory is de-
veloped for unsteady state measurements of
oxygen concentration using cyclic voltommetry at
high scan rates. He is also investigating the ad-
hesion of metals on polymer substrates. This study
concentrates on the development of plasma treat-
ments of substrates which will increase the
number of covalent chemical bonds at the metal-
polymer interface. The scanning electron micro-
scope (SEM), electron spectroscopy for chemical
analysis (ESCA), and Auger spectroscopy are
used to examine the interface.
Mathematical models for insulin and glucose
metabolism in humans are also being developed
by Karagounis. Simulation studies, using the Ad-
vanced Continuous Simulation Language (ACSL),
explore the effectiveness of different control
schemes (feedback, feedforward, adaptive and in-
ferential) in controlling glucose in diabetic
patients with an artificial pancreas.


CHEMICAL ENGINEERING EDUCATION









Hao-wen Liu, in materials science, is studying
cyclic loading at elevated temperatures which
reduces service lives of engineering structures and
engineering components. Oxidation, particularly
grain boundary oxidation, is being investigated as
the damaging mechanism for the reduced service
lives. Also, the slip systems associated with crack
growth and the applied stresses on these slip
systems are being studied. The characteristics of
crack tip deformation in large scale yielding and
in general yielding are being analyzed and the
results of the crack tip field analyses are being
used to study elastic-plastic fracture mechanics
and crack growth in strain controlled fatigue.
Using a cyclic mechanical load, cyclic slip will
take place in crystalline materials. Fatigue damage
is closely related to the changes in dislocation
structure caused by cyclic slip and the resulting
crystal distortion, which is measured with x-ray
diffraction. The results of this study enable us to
monitor fatigue damage in materials and engineer-
ing structures.
The relationship between the molecular struc-
ture of the polymer chain and the physical be-
havior and performance of the material is being
investigated by George C. Martin. His primary
interest is in the physical properties and applica-
tions of polymers. He is investigating the use of
polymer elastomers as integral components in
micro-electronic and micro-optical devices. He is
interested in the rheology and characterization of
polymer composites, especially with respect to the
nature of the curing process, the glass transition
temperature, and the mechanical performance and
processing of the materials.
P. A. Rice recently completed an investigation
of the stripping of emulsified refrigerant from
water in a vacuum spray chamber. This work
shows that the major mechanism for the removal
of emulsified refrigerant is the flashing of the
droplets as they are exposed to the chamber at-
mosphere when the surface of the disintegrating
liquid sheet expands. Rice is also pursuing an inter-
esting joint project with Upstate Medical Center
on the effect of ethanol on the rate of amino acid
transport in the human placenta.
Ashok S. Sangani is studying the fluid me-
chanics and stability of magnetic fluids or sus-
pensions of magnetized solids. Such phenomena
are important in leakproof seals and magnetic ink
jet printers. The development of theoretical models
for prediction of the effective transport properties
of two phase media is another research interest
of Sangani.


Klaus Schrider is presently interested in
magnetic properties of fine particles and thin films.
He is studying the effect of ultrasonic stress waves
on magnetization changes. The materials used in
these investigations are BiMn alloys with small


Faculty of Chemical Engineering and Materials Science.
Front Row left to right: Liu, Sangani, Tavlarides,
Heydweiller, Barduhn, Stern. Second Row left to right:
Martin, Tien, Karagounis, Schroder, Schwarz, Rice, Vook.
Missing are C-S Wang (on leave) and V. Weiss, who is a
Vice President of S.U.

ferromagnetic BiMn precipitates, and MgO with
magnesioferrite precipitates. Schrdder is also
measuring the effect of a non-magnetic overlayer
on the magnetization of thin iron and nickel films.
James A. Schwarz is our specialist in catalysis
and is investigating adsorption-desorption kinetics
of reactive gases important in the production of
synthetic fuels and is developing novel methods of
analyzing surface reactions using cyclic operations.
He has recently extended his interests in surface
chemistry to the area of micro-electronic device-
fabrication and reliability.
S. Alexander Stern is studying the separation
of gaseous and liquid mixtures by selective
permeation through polymer membranes. In the
area of gas separation, the studies are concerned
with the mathematical modelling of new concepts
of membrane process design, such as recycle and
multimembrane permeators. The results of these
studies are being tested experimentally. The sepa-
ration of azeotropic mixtures by pervaporation,
osmotic distillation, and osmotic phase separation
is also being studied theoretically and experi-
mentally. The main research effort is being de-
Continued on page 152.


SUMMER 1984









views and opinions


TEACHING PROFESSIONAL ETHICS*


DONALD R. WOODS
McMaster University
Hamilton, Ontario, Canada L8S 4L7

We expect all of our graduates to "behave as
professionals." One characteristic is that profes-
sionals are ethical. This simple statement has four
interesting components
Personal ethics: individuals have their own internal
ideas of right and wrong that they may or may not
be aware of.
Professional ethics: our engineering profession (as
national organizations and as state or provincial as-
sociations) have published codes of ethics which they
expect all professionals to use as their value system.
Microethics: some value decisions involve us as in-
dividuals being ethical in our professional context.
Macroethics: some value decisions involve ensuring
that our company or institution behaves ethically.
What types of learning experiences can be used
in the classroom to sensitize our students to this
important professional attitude, and what re-
sources are available?

BACKGROUND EXPERIENCES
If students have difficulty identifying their own
ethics, then some techniques on values classifica-
tion could be used. Some resources include Barrs
et al [1] and Larson et al [2]. In these experiences,
students learn to express their personal values. So
far in our program, we have not used this as an
introduction.

CODES OF ETHICS AND RESOURCES
A unified code [3], the AIChE code [4], and
various state or provincial codes [5] are available.
Some are more explicit than others and help guide

*Paper presented at the AIChE Annual Meeting in Los
Angeles, CA, in November, 1982.


For homework, each student is
to pose an ethical problem and submit it before
class to one of four classmates who have
been identified as facilitators.


the student into the practical application of the
principles. Since our provincial licensing agency
requires that young professionals pass a written
examination in ethics, we use the Ontario Code.
The codes are compared by Unger [6]. Fortunately,
Larry Sentance of APEO headquarters helped me
by providing worked examples of ethical situations
and elaborations as to which sections of the code
are pertinent [5]. Other sources of examples and
interpretation are given by Alger et al [7]. My
favorite examples are the Garrison Wyoming
Rocky Mountain Fertilizer case [8] and Geza
Kardo's case study of the Heron Road Bridge [9].

IN-CLASS USE
Our in-class exploration of ethics is a two-hour
experience within a four-credit, 26-week long
course on process analysis, professionalism, cost
estimation, and process synthesis. Components of
this course have been described elsewhere [10, 11,
12]. One of the required texts contains a nine-page
description of micro- and macroethics, the code of
ethics, and examples of interpretation [5].
For the ethics portion of the course, the code
of ethics is described, and the meaning is il-
lustrated by selected examples which are presented
by the instructor. For homework, each student is
to pose an ethical problem and submit it before
class to one of four classmates who have been
identified as facilitators. In the next class, each
facilitator in turn presents to the class his/her
choice of a challenging case situation. Examples
are given in the Appendix to this paper. Each case
is discussed in small groups of about five students,
and then each group verbally reports
What sections of the code apply
What the code says
What the group considered to be alternative actions
What actions they would take
Thus, each group discussed four cases. As instruc-
tor, I have merely played the role of facilitator.
If asked to judge the responses however, I would
share my own views.
Often, problems on the final exam relate to

Copyright ChE Division, ASEE 1984


CHEMICAL ENGINEERING EDUCATION
























Don Woods is a graduate of Queen's University and the University
of Wisconsin. His teaching and research interests are in surface phe-
nomena, plant design, cost estimation, and developing problem
solving skills.

ethics. A typical exam problem is
You are a professional engineer working for Company
A. You submit a design for a new process. The plant
manager, also an engineer, is quite old and has been
in a management position for the last thirty-five years.
Many of your colleagues feel his technical ability has
virtually disappeared. The plant manager receives your
proposal, but before implementing it he decides to
make some small changes to increase its profitability.
You realize that these changes, although profitable,
could introduce a safety problem. But because of the
nature of the case, you decide to keep quiet. Later,
some of this process equipment blows up and a couple
of workers are severely injured. Did you act unethically
in this case? Discuss the case fully and make recom-
mendations if possible.

STUDENT RESPONSE

Student response has been overwhelmingly
favorable. They suggest that they learned a lot and
enjoyed the approach taken. They do not, however,
recommend that more time be spent on it.

OTHER IDEAS AND DISCUSSIONS

Many examples have been presented about re-
sponses to ethical situations. See, for example, the
interesting series in Chemical Engineering [13, 14].
These have tended to report consensus viewpoints.
What I enjoy about our approach has been the
specific link between an established code of ethics
and the situation. That is, the requirement to
interpret one's actions in the context of the code.
Whistleblowing is a fascinating topic but one
that should not be discussed idealistically out of
context of the real possibility of being fined or
blacklisted. Steps are being taken within various
engineering professions [15] to help identify work-
able, whistleblowing procedures. Once these are in
place, I can see the importance of professional


engineers from the Practice and Ethics Committee
describing cases of action taken in order to il-
lustrate how best to proceed.

SUMMARY

A two-hour experience on professional ethics
is part of a senior level course on process analysis
and professional practice. The provincial code of
ethics is explained by using examples. The students
then pose ethical problems and discuss/report their
solution to those problems in the context of the
code.

ACKNOWLEDGEMENT

I am pleased to acknowledge the assistance of
L. C. Sentence of the Association of Professional
Engineers of Ontario for his generous help in the
initial presentation of this program and to Dr.
J. W. Hodgins, whose insight helped me to develop
the program. The pleasure comes from the
students, and I am pleased to acknowledge their
contributions, through examples and discussion, to
this program. E

REFERENCES
1. Barrs, S., A. L. McMurray, W. J. Stevenson, and R. L.
Widernau, "Values Education," Ontario Secondary
School Teacher's Federation, 60 Mobile Drive,
Toronto, Ontario, 1975.
2. Larson, R. S. and D. E. Larson, Values and Faith,
Winston Press, 430 Oak Green Grove, Minneapolis,
MN, 1976.
3. Slowter, E. E. and A. G. Oldenquist, CEP, Jan., 1982,
p. 24 [Table 4 is the proposed unified code].
4. West, A. S., CEP Feb., 1981 p. 22 [Exhibit 4 is the
adopted AIChE code].
5. Woods, D. R., Financial Decision Making in the Pro-
cess Industry, Prentice-Hall, 1975 [Table 1.2, p. 10 is
the current Association of Professional Engineers of
Ontario Code of Ethics].
6. Unger, S. H., Controlling Technology: Ethics and
the Responsible Engineer, Holt, Rinhart, and Winston,
1982.
7. Alger, P. L., N. A. Christensen, and S. P. Olmsted,
"Ethical Problems in Engineering." Am. Soc. Engi-
neering Education, Washington, DC.
8. Merson, B., "The Town that Refused to Die," Good
Housekeeping, Jan 1969, p. 160.
U. S. Department of Health, Education and Welfare,
"Summary of Conference on Intrastate Air Pollution
in the Powell County, Montana Area," Washington,
DC.
U. S. Department of Health, Education and Welfare,
"Powell County, Montana, Air Pollution Abatement
Activity," National Air Pollution Control Administra-
tion, Division of Abatement and Control, Durham,
NC 27701, July 1967.


SUMMER 1984








9. Kardos, G., "Heron Road Bridge." Case ECL 133A
in Engineering Case Library, Stanford Engineering
Case Program, Stanford University, Stanford, CA,
1969.
10. Woods, D. R., "A Complement to Design: Trouble
Shooting Problems," Chem. Eng. Education, 1, p. 19,
1966.
11. Woods, D. R., "Innovations in a Process Design and
Development Course," Chem. Eng. Education, 2, pp.
162-170, 1968.
12. Woods, D. R., Editor, "Using Trouble Shooting
Problems," Chem. Eng. Education, 15, pp. 89-92, 96,
1980.
13. Popper, H. and R. V. Hughson, "How Would You
Apply Engineering Ethics to Environmental Prob-
lems?" Chem. Eng., 77, No. 24, p. 88, 1970.
Hughson, R. V. and H. Popper, "Engineering Ethics
and the Environment: The Vote is In," Chem. Eng.,
78, No. 5, p. 106, 1971.
14. Hughson, R. V. and H. Popper, "Ethics," Chem. Eng.,
May 5, 1980.
Hughson, R. V. and P. M. Kohn, "Ethics," Chem. Eng.,
Sept. 22, p. 132, 1980.
15. Currie, J. "Chapter Committee Looks at Disclosure
Process for Whistleblowers," APEO Dimensions, Sept.
Oct., pp. 48 and 49, 1982.

APPENDIX: EXAMPLE PROBLEMS
Case 1
There is a major energy crisis in the country.
All of the company's efforts are directed toward
the design and development of new energy sources
for such things as a steam generation plant.
Out of the old files, you dig up what is believed
to be a brilliant design of a solar heater for the
steam generation plant. The idea was proposed
over fifty years ago and since, at that time, there
was no energy crisis and fossil fuels were cheap,
the design was economically unfeasible and there-
fore canned. However, in the light of the present
situation it would be most economical and would
save the company a lot of money, as well as con-
serving other depleted energy resources.
Only a handful of engineers had seen the
original plan and in the ensuing fifty years they
had all passed away. Nobody in the company
today has ever seen the design.
Because of poor economic conditions, you have
recently taken a cut in salary. You see yourself as a
very hard worker and have contributed much to
the company in the way of process optimization,
but you have received very little credit or recog-
nition for all your work. This design would give
you that recognition along with a generous sug-
gestion bonus. The savings to the company would
far exceed what you would get as a bonus. So you


make some minor adjustments to the design and
submit it as an original idea. The bonus would
have to be forfeited if it were known that the
design was created over fifty years ago. This way,
both the company and you come out ahead and no
one is the loser. After all, you did the research,
found the old plans, and modified them for present
use. It would be unfair if you got nothing for your
efforts.
Would this be ethical? (E. R.)
Case 2
In a waste treatment process, some of the acti-
vated sludge must be removed in order to keep the
recycled sludge at a specified concentration. This
spent sludge is used as landfill. Recently, you have
found that this sludge has been concentrating a
chemical which is known to be cancer producing.
By allowing this sludge to be used as landfill, this
chemical is returned to the watershed through
leaching. You have notified the company of the
problem, but they refuse to do anything about it.
Is this ethical? (R. A. B.)
Case 3
Within the last year, the parasite spruce bud-
worm has infected approximately 25% of the
forests in Nova Scotia. Most of the infestation is
confined to northeastern Nova Scotia and Cape
Breton Island, where the economy is heavily de-
pendent on forest products. Failure to control
the pest could result in the loss of this industry.
When the infestation first became apparent,
the Nova Scotian government decided against
spraying because the emulsifier in the spray was
linked to an outbreak of a rare children's disease
in New Brunswick, where spraying is carried out
every summer. As an engineer with the ministry
responsible for the environment, you estimate that
about half the people in the province live in rural
areas and that they obtain their water supplies
from small, inland lakes and private wells. It is
likely that the emulsifier will make its way into
drinking water if spraying is carried out. Should
you go along with the considerable pressure placed
on you and the government by the forestry in-
dustry in the hope of saving the industry and the
thousands of jobs involved? (V.)
Case 4
You are an engineer working at a steel mill.
You come in on a night shift and discover that the
smelter gas from the smelter is being shunted past
the electrostatic precipitators in order to make the


CHEMICAL ENGINEERING EDUCATION








tonnage of steel that is required on the shift. There
is a butterfly valve that can be turned so that all of
the dirty gas just goes right out of the stack.
Since it is at night, there are no complaints from
people in the surrounding area or from the en-
vironment board. You are the engineer working
on the control of the precipitators, not in the pro-
duction department.
What should you do? (K. H.)

Case 5
I am a fourth year engineer seeking employ-
ment. In January, I am offered a job by company X
and am given ten days to accept their offer. I ac-
cept their offer.
Two weeks later I receive a better offer, in pay
and position. I take the second offer and tell the
first company that I am unable to work for them.
1. Is this ethical?
2. Would the situation change if I was offered
another job in May just before I was to report for
company X?
3. Does a company expect this to happen?



P letters

SAFETY PROBLEM CHALLENGED
Dear Sir:
I read with interest Professor Jan Mewis'
article, "How Much Safety Do We Need in ChE
Education."
Unfortunately, the equation used by Professor
Mewis to solve the tank overflow problem is not
rigorous, and can give outrageously bad results. A
rigorous derivation and the correct solution to the
protective system problem can be found on p. 459
of Reliability Engineering and Risk Assessment,
by E. J. Henley and H. Kumamoto, Prentice-Hall
Inc., Englewood Cliffs, NJ, 1981.
I agree with Professor Mewis that all engi-
neers should receive some training in reliability
and safety analysis. Short courses, such as given
by the AIChE are, in my opinion, adequate. In
many European countries risk studies such as
those mandated in the nuclear industry are re-
quired of all industry. I think this is very unfortu-
nate. You really can't legislate safety; it is an in-
dividual and corporate responsibility.
Ernest J. Henley
University of Houston


Substantial ChemistryTexts
from Prentice-Hall
CHEMICAL PROCESS CONTROL: An Introduction to
Theory and Practice
George Stephanopoulos, The National Technical University of Athens
1984 704 pp. (est.) Cloth $34.95
CHEMICAL AND PROCESS THERMODYNAMICS
B.G. Kyle, Kansas State University
1984 512 pp. (est.) Cloth $32.95
MASS TRANSFER: Fundamentals and Applications
Anthony L. Hines and Robert N. Maddox, both of Oklahoma State University
1984 500 pp. (est.) Cloth $30.95
BASIC PRINCIPLES AND CALCULATIONS IN CHEMICAL
ENGINEERING, Fourth Edition
David M. Himmelblau, The University of Texas at Austin
1982 656 pp. Cloth $33.95
PROCESS FLUID MECHANICS
Morton M. Denn, University of Delaware
1980 383 pp. Cloth $33.95
DIFFRACTION FOR MATERIALS SCIENTISTS
Jerold M. Schultz, University of Delaware
1982 287 pp. Cloth $35.95
NUMERICAL SOLUTION OF NONLINEAR BOUNDARY VALUE
PROBLEMS WITH APPLICATIONS
Milan Kubicek, Prague Institute of Chemical Technology;
Vladimir Hlavacek, SUNY at Buffalo
1983 336 pp. Cloth $34.95
For further information, or to order or reserve examination copies, please write: Ben E. Colt,
College Operations, Prentice-Hall, Inc., Englewood Cliffs, NJ 07632.
For "SUPER-QUICK" Service, dial TOLL FREE (800) 526-0485*
between 8:15 a.m.-4:45 p.m., EST, Mon.-Fri.
.not applicable in New Jersey, P nti Hall
Alaska, Hawaiior Puerto Rico. Pentice-Hall


n book reviews

FUNDAMENTALS OF FLUIDIZED-BED
CHEMICAL PROCESSES
by J. G. Yates
Butterworth Publishers, 10 Tower Office Park,
Woburn, MA 01801,1983; $49.95

Reviewed by L. T. Fan
Kansas State University

This lucidly written book contains five chapters.
The first, which is the longest, deals with some
fundamental aspects of fluidization. The modeling
of fluidized-bed reactors is discussed in the second
chapter; the majority of available models are
compiled. The last three chapters cover the applica-
tion of fluidization technology. More specifically,
chapter three focuses on the well-known Fluidized
Catalytic Cracking Process and chapter four on the
combustion and gasification of coal. The last
chapter outlines a number of miscellaneous pro-
cesses, including production of several chemicals,
sulphide ore roasting, and reduction of iron ores.
Continued on page 144.


SUMMER 1984









iFY---- -- ^-------------------------------'-~-' ---------
n class and home problems




THERMAL CONDUCTIVITY OF A HOTDOG


MICHAEL J. MATTESON AND
JUDE T. SOMMERFELD
Georgia Institute of Technology
Atlanta, GA 30332


PROBLEM STATEMENT
In a proposed new chemical engineering labora-
tory experiment, students are to determine the
thermal conductivity of a hotdog. The procedure
consists of inserting a thermistor into the center
axis of the hotdog, about midway between its ends,
and then totally immersing the hotdog in an agi-
tated tub of boiling water. The thermistor is then
used to measure the temperature increase of the
hotdog with time. A sketch of this experiment is
shown in Fig. 1.
The results of one such experiment are shown
in Fig. 2. In this experiment the initial hotdog
temperature was 700F, and the boiling water
temperature was 212F. The density of the hot-
dog (diameter = 1 inch) may be taken as 50
lbs/ft3, and its heat capacity as 1.0 BTU/lb-F.
From these data and those of Fig. 2, determine
the thermal conductivity of this hotdog. It may be
assumed that the surface temperature of the hot-
dog is the same as the boiling water temperature
(that is, the convective heat transfer coefficient at
this surface is very large).


!00-
s80
60
40
40 -
20 -
00- 0
80
600 1 2 3 4 5 6 7 8 9 1011 121314
TIME (e) ,MIN.


FIGURE 2. Center-line
time (0).


temperature (t) as a function of


SOLUTION
The partial differential equation for unsteady-
state heating (or cooling) by conduction in one
direction (radial) with cylindrical geometry is
well known [1]

k ( t \ at t (1)
pc, L ar + r ar 0-
If one makes the following conventional definitions

T tw -t(2)
w to

ro
k
a k (4)
PCp
aO
z = (5)
ro2
Eq. (1) becomes
DT a'T 1 T
az ax2 x ax
The boundary conditions for this problem, in terms
of the new variables, are
(i) T(1,z) = 0forz > 0 (7)


FIGURE 1. Sketch of experimental apparatus.
Copyright ChE Division, ASEE. 1984


(ii)

(iii)


T (0,z) = 0 for z > 0
ax
T(x,O) = 1 for O x < 1


CHEMICAL ENGINEERING EDUCATION
























Michael J. Matteson is Director of the Fine Particle Technology
Laboratory and professor of ChE at Georgia Tech. He received his BS
and MS degrees from the University of Washington in 1960 and his
D.Eng. degree from the Technical University Clausthal (Germany) in
1967. He came to Georgia Tech in 1969 after a post-doctorate at the
University of Rochester. Dr. Matteson was a Fulbright Lecturer at the
University of Vienna, 1974-75. (L)
Jude T. Sommerfeld has been a professor of ChE at Georgia Tech
since 1970. He teaches courses on process control, distillation, reactor
design and process design, and his research interests include energy
conservation. He has also served as a consultant to numerous in-
dustrial organizations. Dr. Sommerfeld received his B.Che degree from
the University of Detroit, and his MSE and PhD degrees in chemical
engineering from the University of Michigan. (R)

Note that end effects were neglected in the deriva-
tion of Eq. (1).
Eq. (6) with its associated boundary conditions
is a standard Sturm-Louiville system [2] and its
solution is given by
Go 2 exp (-n2z)
T(x,z) = I J n) Jo(Xn) (10)
n=l XnJ, (X,)
where hA is the nth root resulting from solution of
the following equation
Jo () = 0 (11)
From Eq. (10), the expression for the center-line
temperature (at x = 0) is

T(0,z) = 2exp(-X.2z) (12)
n.= X .J (X.)
In many practical calculations, it is necessary to
consider only the first term in the infinite series
summation of Eq. (12).
Choosing a value of 0 = 5 min (= 1/12 hr), we
read from Fig. 2 a value for the center-line
temperature of 166F. Hence

T(0,z) 212-166 0.324
212-70
As a first approximation, we consider only the
first term on the right-hand side of Eq. (12). The


~t ~;
~1~


SUMMER 1984


first root of Eq. (11) is X, = 2.405 and J1(X1) =
0.5191 [3]. Equating this first term to T(0,z) and
solving for z, we find that z = 0.276. Hence
ro2 (1/24)2 (0.276)6
a 0 (1/12) 0.00576 ft2/hr
a (1/12)
and k = apc, = (0.00576) (50) (1.0)
= 0.288 BTU/hr-ft-F
Let us evaluate the second term in the summation
of Eq. (12) to -determine its significance. Here,
h, = 5.520 and J1(X2) = -0.3403 [3]. Using the
value of z determined above, we find the value of
this second term to be equal to -0.000234, which
is less than 0.1% of the first term.
Graphical solutions to Eq. (10) or (12) also
exist in the form of the Gurney-Lurie charts. Here,
m = k/roh = 0 because h is infinite, in accordance
with the earlier assumption regarding the surface
temperature. Again using the same center-line
data point at 0 = 5 min, we find from the Gurney-
Lurie chart for long cylinders [4] that z = 0.28.
Hence, a = 0.058 ft2/hr and k = 0.29 BTU/
hr-ft-F. o
REFERENCES
1. Carslaw, H. S. and J. C. Jaeger, Conduction of Heat
in Solids, 2nd Edition, Clarendon Press, Oxford,
England (1959).
2. Churchill, R. V., Fourier Series and Boundary Value
Problems, McGraw-Hill Book Company, New York
(1941).
3. Jahnke, E. and F. Emde, Tables of Functions, Dover
Publications, New York (1945).
4. McAdams, W. H., Heat Transmission, 3rd Edition,
McGraw-Hill Book Company, New York (1954).
NOMENCLATURE
cP heat capacity of cylinder, BTU/lb'F
h surface heat transfer coefficient,
BTU/hr.ft2.0F
Jo Bessel function of the first kind and of order
zero
J1 Bessel function of the first kind and of order
one
k thermal conductivity of cylinder,
BTU/hr-ft-F
m k/roh
r variable radius, ft
ro radius of cylinder, ft
T dimensionless temperature = (tw t) /
(tw -to)
t variable temperature of cylinder, F
to initial temperature of cylinder, F
tw water temperature, F
x dimensionless radius = r/ro
z dimensionless time = aO/r.2
a thermal diffusivity of cylinder, ft2/hr
= k/pc,
Xn n-th root of the equation Jo (X) = 0
p density of cylinder, lbs/ft3
0 time, hrs










Classroom


DIMENSIONLESS EDUCATION


GRAHAM F. ANDREWS
State University of New York
Amherst, NY 14260

CONSIDER FOR A MOMENT the confusion imposed
on engineering undergraduates. At some point
in a junior-level fluid mechanics class the subject
is dropped for a class or two while the students are
presented with a series of strange propositions.
(a) Mass, length, and time are "fundamental
dimensions." Although this probably seemed self-
evident to Osborne Reynolds, it sounds very
strange to the post-Einstein generation. Mass,
length, and time, far from being "fundamental",
all depend on how fast you are going. If pressed,
the professor may point out that, in fact, any set of
three dimensions (velocity, energy, and area, for
instance) could serve as the basis on which the
others could be defined. Mankind has simply chosen
mass, length, and time as a convenient group and
set up standards for them at various places around
the world. Even this explanation leaves some
students uneasy; if mankind selected these three
dimensions at random and then labelled them
fundamental, it is surely guilty of, at best, abuse
of the English language.
(b) Buckingham's ir Theorem. This is the
centerpiece of the subject, and it is totally unlike
any theorem the student has ever seen before or
(with the possible exception of the Phase Rule)
will ever see again. No proof is offered. In fact, a
survey of the standard works (Becker [1] gives a
comprehensive list) leaves doubt about what would
constitute an adequate proof.
(c) Dimensionless groups. The student has in-
vested considerable effort in grasping concepts like
pressure and viscosity, but suddenly these hard-
won ideas disappear, subsumed into groups named
after dead foreigners he has never heard of. This
is not reassuring.
(d) The purpose of dimensional analysis is, in
effect, to reduce the number of variables in a
problem. This idea may be introduced in the con-
text of fluid flow in smooth pipes where five vari-

Copyright ChE Division. ASEE 1984


Graham F. Andrews is an assistant professor of chemical engineer-
ing at the State University of New York, Buffalo, where he has been
since 1979. He received his BSc in mechanical engineering at Imperial
College (London), and his MS (1975) and PhD (1969) in chemical
engineering from Syracuse University. His research interests are in
biochemical engineering, specifically fluidized-bed bioreactors, bacterial
coal desulfurization, and oxygen transfer from bubbles.

ables (pressure gradient, pipe diameter, fluid
velocity, viscosity, and density) are reduced to two
(the Reynolds number and friction factor). This
is obviously extremely useful. It allows us to draw
one graph good for all fluids in all smooth pipes,
and vastly reduces the number of experiments we
must do to develop the form of the general pressure
drop-flow rate relation. But, explained in this
fashion, this ability to "reduce the number of vari-
ables" is disconcerting to the student.
Consider, for example, the pendulum problem.
There will be general agreement in a class that the
period, t, of a simple pendulum will depend on its
mass m, its length 1, and its gravitational accelera-
tion g. Applying dimensional analysis to these
quantities gives the solution
t Vg/l = constant (1)
The mass cannot appear in the solution because no
other quantity involved contains the mass dimen-
sion, so we cannot create a dimensionless group
involving m. So, having said very little about
pendulums and absolutely nothing about the laws
of dynamics, we have proven that the period is
independent of the pendulum mass and proportion-


CHEMICAL ENGINEERING EDUCATION








al to the square root of its length. At first glance
this appears close to witchcraft.
In summary, the traditional approach to teach-
ing dimensional analysis is confusing. The purely
formal procedures for deriving the form of dimen-
sionless groups are often stressed while basic
questions go unanswered. These include "Why does
it work?" and "If equations written as dimension-
less groups are so simple and descriptive, why
aren't all equations written this way?" (Bernoulli's
equation is a case in point.) Furthermore, it leaves
the unfortunate impression that dimensional
analysis is a branch of transport phenomena, an
impression that is reinforced when the dimension-
less numbers that arise in other subjects are not
identified as such, being named not after dead
foreigners but after living Americans (Thiele
modulus) or even no one at all compressibilityy,
etc.). Consequently, students may not add dimen-
sional analysis to their armory of techniques for
confronting new problems. As an example, try the
following problem on a senior or graduate class:
"A zero-order reaction occurs at rate r gm/cm3 s
in an isothermal, semi-infinite slab of porous
catalyst in which the reactant diffusivity is D
cm2/s. What happens to the reactant uptake rate
per unit area of the slab when its concentration
at the slab surface is doubled?" This problem, and
others like it, can be solved by a simple application
of Buckingham's theorem, but few will attempt it
simply because they do not associate this theorem
with kinetics.

A BETTER APPROACH
To determine how dimensional analysis should
be taught, we start from its role in engineering.
Engineers are often asked to solve real-world
problems where no exact mathematical solution
is possible. It is here that dimensional analysis is
a powerful tool, combined with either physical
models (a procedure known variously as the em-
pirical approach, similarity solutions, or the scale-
up method) or with the unsolvable differential
equations describing the problem (see for example
Bird, Stewart and Lightfoot's [2] treatment of free
convection on a vertical wall). It is valid and useful
in all engineering disciplines and in all branches
of chemical engineering, appearing most often
in transport phenomena only because turbulence is
our most intransigent real-world phenomenon.
It follows that the topic should be included in
the "introduction to engineering" course that
freshmen are usually required to take. The author


Engineers are often asked to solve
real-world problems where no exact mathematical
solution is possible. It is here that dimensional
analysis is a powerful tool ...

has been doing this successfully for a number of
years at SUNY at Buffalo using the method de-
scribed below.
The main difficulty is textbooks. Although
dimensional analysis is well covered in the
standard transport texts (notably Bennett and
Myers [3]), they are of little help in freshman
courses where the examples must be kept simple
and the context general. Of the many texts avail-
able for "introduction to engineering" courses,
only one [4] known to the author includes the
subject. However, they all introduce the idea of
fundamental and derived dimensions as the basis
of unit systems, and many introduce the idea that
all terms in an equation must be dimensionally
homogeneous. This is taken as the starting point
for giving some insight into what dimensional
analysis is, and why it works.

Principle
You can't add x oranges to y apples and get z
bananas.

Or
All terms to be added, subtracted or equated
in an equation must have the same dimensions.
This intuitively obvious principle can be
demonstrated with known equations such as Ein-
stein's E = mc2, Bernoulli's equation, and the
equation for sonic velocity in a gas. It is important
to point out at this stage that dimensional con-
sistency is a condition for the existence of an
equation. Consistency of the units is an additional
requirement if the equation is to give the right
answer.

Corollary
Any relation between physical quantities can
be written as a relation between dimensionless
groups.
Again, this is easy to demonstrate using the
equations introduced above.

Observation
There are fewer dimensionless groups than
dimensional variables. This is immediately ap-


SUMMER 1984








parent from the previous exercise. Einstein's
equation goes from three variables (E, m, c) to
one group (E/mc2), Bernoulli's equation from five
variables to two groups (an Euler number and a
Froude number), and the equation for hoop
stresses in a thin-walled pressure vessel goes from
four variables to two groups. Buckinghams
theorem is now introduced as the answer to the
natural question of how many groups there will
be in a given situation.
With this background, exercises like the pendu-
lum problem seem far less like witchcraft. We
hypothesize a relationship between the quantities,
m, 1, g, t, but we are not free to arrange these vari-
ables in any fashion we choose. Their possible ar-
rangements are constrained by the requirement
that they be dimensionally consistent. One way to
ensure this consistency is to arrange the variables
in dimensionless groups. Buckingham's theorem
tells us how many groups are required. No com-
bination of the variables which includes m can be
dimensionless, so m must not be relevant to the
problem.
Given this introduction, the students can ac-
cept the work of counting the independent funda-
mental dimensions and determining the form of
the dimensionless groups. These are now seen for
what they are-merely useful, formal techniques
for deriving logical results. Several excellent
problems involving just one group are available
for practice. They include the frequency produced
by a guitar string, the drag force on an automobile,
the height of the bow wave on a ship, the power
required to stir a liquid, the pressure generated
by a pitot tube, the speed of descent of a parachute,
and centrifugal force.

REYNOLDS' SIMILARITY PRINCIPLE
If a physical situation can be completely de-
fined by n variables, or (n-m) dimensionless
groups, it follows logically that in order for two
situations to be identical, the simplest condition
we need invoke is that the dimensionless groups
must have the same values in the two situations.
This important principle is the basis of both physi-
cal modelling and its inverse process, scale-up.
While it is easy to state, it is difficult for students
to grasp. The idea that, for example, lead shot
falling through water is somehow "identical" to a
tennis ball falling through air is very strange at
first; the size, velocity and fluid properties are,
after all, different in the two cases.
This is a situation where "one in the eye is


worth three in the ear." Films showing model
parachutes opening underwater, or Reynolds ex-
periment done with various fluids and pipe
diameters, are more convincing than hours of ex-
planation. Old war movies are also good teaching
aids. The physical situation (the bow wave, wave-
induced oscillations, etc.) of the model ships that
are "torpedoed" in these movies is always observ-
ably different from that of a real ship, in spite of
the best efforts of the special effects men of that
era. (In fact, given the number of variables, it is
impossible to make all the relevant dimensionless
groups the same on the two scales.) In The Dam
Busters, the story of the destruction of the Ruhr
dams by bombs that bounced along the surface of
the impounded lakes, Barnes-Wallace, the engi-
neer-hero (a fine role model for any engineering
student), is seen testing his ideas by bouncing
ping-pong balls across a swimming pool.
WHY DOES IT WORK?
Experience shows that, even with the best
teaching techniques, dimensional analysis makes
students uneasy. The difficult question inevitably
arises: "How can we learn so much about pendu-
lums while saying so little about the laws of dy-
namics?" The answer is outside engineering in
metaphysics. Dimensions are human inventions
that we impose on nature in order to understand it
scientifically. Einstein's description of scientific
theories as "free creations of the human mind"
applies equally well to the dimensions that under-
lie the theories. Mass, length, and time are funda-
mental only in the sense that they were defined
very early in human history in response to very
fundamental questions: "How much grain should
I store for the winter?" How far from my house
does my neighbor's land start?" "How long will
it take to reach the next waterhole?"
To those who doubt this view, it can be pointed
out that other beings (with other senses, on other
planets) may have invented a completely different
set of dimensions. A race of scientific dogs, for
example, may well believe "smell intensity" to be
extremely fundamental. Intelligent deep sea fish,
in their naturally-buoyant, constant-temperature
environment, would never have defined the con-
cepts of weight and temperature in the same way
that early man did. Or consider a planet with no
moon and no tilt to its axis, that revolved on its
axis once for every rotation of the planet around
its star. The inhabitants would still grow old and
die, but their lifetimes could not be divided into
days, months and years because these units, which


CHEMICAL ENGINEERING EDUCATION







imposed the concept of time on our ancestors,
would not exist. Time may well appear to them not
as a fundamental dimension, but as a esoteric
consequence of the second law of thermodynamics.
Uneasiness about dimensional analysis arises
because subconsciously we hold a different view of
dimensions. Mass, length, and time were defined
so long ago and appear so early in our education
that we think of them as self-evident "things" and
not as human inventions. Deep down we cling to
Newton's view of "absolute space" and "absolute,
true mathematical time of itself and by its own
nature flowing uniformly without regard to any-
thing external." We forget that Newton's basis for
these views was not scientific but theological. To
him they were perfect ideas in the mind of God.
Even the theory of relativity, which destroyed the
idea of mass, length, and time as "absolute,"
could not change their status as "fundamental."
Dimensional analysis is nature's way of re-
minding us that it is universal and can hardly be
affected by the particular set of dimensions our
species happens to choose and label "fundamental."
It follows that if we wish to describe nature we
must use variables from which all our concepts
have been cancelled, i.e. dimensionless groups. If
the dimensionless groups describing two physical
situations are the same, then the "nature" of the
situations must be identical, irrespective of
whether we are dealing with lead shot or tennis
balls. Imposing our own concepts onto our de-
scriptions of nature only increases their com-
plexity (by increasing the number of variables)
and reduces their universality. If we wished to
communicate our knowledge of fluid mechanics
to engineers on the timeless planet mentioned
above, we could send diagrams of Reynolds' ex-
periment with the laminar/turbulent transition
marked with the binary equivalent of 2300. This
would be understood. The markings v = 1 cS, d =
1 cm, V = 2.3 cm/s would be incomprehensible,
even in binary.
Is it worthwhile trying to explain this to a
group of freshmen? Perhaps it is. Mankind's
search for wisdom has always been slowed by our
arrogance, our illusion that we occupy a uniquely
privileged position in the universe. Assigning a
special position to our planet hindered acceptance
of Copernican astronomy. Assigning a special
position to our species hindered acceptance of the
theory of evolution. Similarly, assigning a special
position to our concepts of mass, length, time, etc.
hinders acceptance of the similarity principle
(and, incidentally, relativity). If the next genera-


tion of engineers understands this, they will be a
little wiser for it.

CONCLUSIONS
Dimensional considerations are central to
chemical engineering. They are the basis of scale-
up, they allow us to use just one chart for j-factors
etc. for all fluids and scales of operation, and some-
times they enable us to derive quite detailed results
just from the form of differential equations. Given
this importance, the conventional way of teaching
dimensional analysis is unsatisfactory. Routine
procedures for deriving dimensionless groups are
often stressed over questions of why and how it
works, and the student gets the distinct impression
that the entire subject is a branch of transport
phenomena.
Since dimensional analysis is applicable to all
branches of engineering, it should be introduced
in freshman or sophomore general engineering
courses. Junior transport phenomena students can
then appreciate that they are seeing a particular
example of a general truth. The subject is best
taught by writing known equations as relations
between dimensionless groups. A comparison of
the dimensional and dimensionless forms then
shows Buckingham's theorem as a direct conse-
quence of the dimensional homogeneity of equa-
tions.
Mankind invented mass, length, time, etc., and
then recombined them into more complex concepts
(velocity, energy, etc.). Science got underway by
describing nature as the relationship between
those concepts. But since nature cannot be bound
by human inventions, all these relationships (even
the most profound) are necessarily of such a form
that our concepts, the dimensions, cancel out. They
are most simply written as relations between
dimensionless groups, and it is only in this form
that we could communicate our knowledge to other
species whose science may have developed from a
completely different set of dimensions. Nature
itself is dimensionless. O

LITERATURE
1. H. A. Becker, Dimensionless Parameters: Theory and
Methodology, Applied, Science Publishers, London
1976.
2. R. Bird, W. Stewart, E. Lightfoot, Transport Phe-
nomena, Wiley, p. 330, 1960.
3. C. 0. Bennett, J. E. Myers, Momentum, Heat and
Mass Transfer, Chap. 13, McGraw Hill, 1982.
4. R. Mayne, S. Margolis, Introduction to Engineering,
McGraw Hill, New York 1982.


SUMMER 1984









Classroom


THE THERMODYNAMIC FUNDAMENTALS

OF EXERGY

PABLO G. DEBENEDETTI
Massachusetts Institute of Technology
Cambridge, MA 02139


AVAILABILITY IS A thermodynamic function
whose difference between any two states of a
system gives the limiting (reversible) value of
work associated with a given change and environ-
ment conditions. Changes in availability, there-
fore, can be used to evaluate the thermodynamic
performance of a process.
Exergy is shown to be an extension of the
concept of availability when it becomes necessary
to quantify a flowing stream's capacity to produce
useful work, given stream and environment con-
ditions. Exergy can therefore be thought of as
a property of the stream (for a given environ-
ment), and can be used as a basis for assigning an
economic value to it, based on its work producing
capacity.
A stream's exergy is a function of the refer-
ence environment. Since this choice is completely
arbitrary, except for the requirement that the
environment be in equilibrium, computed values of
exergy and exergetic efficiency can only be used
for comparison (for a given reference state), not
in an absolute sense. The equilibrium constraint,
on the other hand, eliminates from consideration
many realistic, non-equilibrium environments.
S"'

,/ P1


System I / i
7 I I W/
IW
a, Wl I


T &Te
a b c
FIGURE 1. a) Closed system. b) Closed system showing
boundaries needed for availability analysis. c) Open
system showing boundaries needed for availability
analysis.


Pablo G. Debenedetti was born in Buenos Aires, Argentina. He
obtained his chemical engineering degree from Buenos Aires University
in 1978. He worked at Oronzio de Nora, Milan, Italy, as a process
engineer from 1978 to 1980. He holds an MS degree in chemical engi-
neering from M.I.T., where he is currently a PhD candidate, working
in the field of mass transfer with supercritical fluids.

Once these limitations are understood, how-
ever, exergy can be fruitfully used in process
analysis and design, in cases where it is necessary
to quantify the efficiency with which useful work
is obtained from the process streams [1-9]. The
thermodynamic fundamentals of exergy are de-
veloped below, emphasizing similarities and differ-
ences between exergy and availability.

AVAILABILITY
Availability is a thermodynamic function whose
difference between any two given equilibr-
ium states of a system is a measure of the maxi-
mum work obtainable from (or the minimum work
required to effect) the given change. Since, as
will be shown below, the concept of exergy follows
quite naturally from the closely related thermo-
dynamic function known as availability, the latter
will be considered first.
Consider (Fig. 1.a) a closed, simple system
i.e., a system whose boundaries are impermeable
to mass flow, contains no internal adiabatic, im-
permeable, or rigid boundaries, and is not acted
upon by force fields or inertial forces [10]. For
the present analysis, the environment with which
the system interacts can be imagined as consisting

Copyright ChE Division, ASEE 1984


CHEMICAL ENGINEERING EDUCATION








of a heat reservoir [11] at a temperature To, and an
isobaric work reservoir at a pressure Po. For any
differential process, we can write (Fig. 1.a)

dU = 6Q 6W (1)
where 8Q, and 8W, represent inexact differentials.
Now consider Fig. 1.b, where any Carnot engine
needed to transfer heat reversibly between the
system and the environment has been added. The
following relations apply


dS = -A
-r T

dS = + 6S*
"s T
dU = 6Q 6W
6S > 0


where 8S* is the entropy created as a result of
the (irreversible) processes occurring within the
boundaries shown in Fig. l.a. Therefore
6W + TO 6S = T dS dU (6)
For finite changes
W + TOS = TOAS AU (7)
Since we are interested in useful work, we
must subtract from W the portion that constitutes
expansion work against the surrounding pressure.
For reversible operation, therefore, the maxi-
mum useful work that can be obtained from a
closed system in going from a specified initial to
a specified final state, while interacting with sur-
roundings at P, and To, is

Wmaxnet= T(Sf Si (f i) f Vi) (8)
Eq. (8), as written, is not restricted to cases
where Vf > Vi. If a partially evacuated container
fitted with a frictionless piston and filled with an
ideal gas is compressed reversibly and isothermal-
ly by the surroundings up to Pa, the work ob-
tained is now Po (Vi Vf) minus the compression
work done by the environment on the container,
T,(Si S,).
The right hand side of Eq. (8) is only a
function of the end states, To and Pa; the following
state function is normally called availability
B = TOe 9 Pe (9)
so that finally

Wmax,net -AB (10)
If we now consider an open system, under steady


Exergy is shown to be an extension of the
concept of availability when it becomes necessary to
quantify a flowing stream's capacity to produce useful
work, given stream and environment conditions.

state conditions, the First Law now yields, (Fig.
1.c)


0 = Q- + I He e- E
e


(11)


where summations are over all entering and leav-
(2)
ing streams, respectively, and ne may differ from

(3) ni if chemical reactions occur. The corresponding
entropy balance, with To denoting the heat reser-
(4) voir's temperature, reads


0= + + See -
6 e
substituting for Q
:= E (H TB S)f (Ht TeSZ) 6 -

For reversible operation

(max = I (He TSe); I (H Te
e


(12)


(13)


(14)


As before (see Eq. 8), the maximum (reversible)
work obtainable is a function only of the end states
and the environment's conditions. Accordingly, we
can define an availability for flow systems [3]


B' = H ToS

Wmax = J Bn Bj nBn
e


Given an environment which is the sole net
heat source (or sink) with which the system
under consideration interacts, and which is
characterized by To and Po (closed systems) or
T, (open systems), differences in availability,
therefore, represent limiting values for the maxi-
mum (minimum) work that can be obtained from
(that is required to achieve) any given change.

EXERGY
If we define efficiency as W/Wmax, it follows
from the preceding discussion that, for open
systems under steady state conditions and with
given end states, the thermodynamic performance
(efficiency) of a process can be analyzed by means
of the function known as availability.
Even though availability is a property of the


SUMMER 1984








stream (given T,), only changes in availability are
of interest, since B' is only defined up to an arbi-
trary constant. Exergy is a function introduced to
overcome this limitation; this is done by selecting
an equilibrium environment as the reference state.
Then, the availability change arising from the
complete equilibration of any given stream with
the environment is defined as the stream's exergy.
Specifically, for a flowing process stream of
components 1,.. ,j,..., n at arbitrary conditions
T, P, yj, exergy is defined as the maximum work
(per mole of stream) that can be obtained upon
its equilibration with the environment, the latter
A
being characterized by T,, Po and pj., when heat
interactions take place with a single source-sink
A
at T,. Here, ujs denotes the chemical potential of
component j in the environment.

Exergy = = H(Te,Peyje) TeSe(T ,P ,je)

Je y je(Tee'PojYje) (17)
j=1


max = TeS 1 Y j ^j (18)

Eq. (18) can be obtained either by direct calcu-
lation of the various heat and work interactions
resulting from the reversible equilibration process,
or by setting outlet conditions equal to environ-
ment conditions in Eq. (16).
In analyzing any particular process, therefore,
availability balances can be made around the
various process blocks (unit operations) to deter-
mine thermodynamic efficiencies. Exergy, on the
other hand, is useful if, in addition to the thermo-
dynamic efficiency of a given unit operation, we
are interested in analyzing how the overall pro-
cess utilizes the capacity to produce useful work
of all its streams.
An availability balance around a turbine, for
example, will yield a value for its isoentropic
efficiency. The exhaust stream exergy, however,
is not taken into account in such an analysis. If
the exhaust stream is neither recycled nor used
downstream, for example, it should have as low an
exergy as possible. For energy recovery schemes,
on the other hand, a compromise must be reached
between exhaust exergy and power output.
It should be emphasized, however, that since
the choice of the reference environment is arbi-
trary, except for the requirement that it must be
in chemical equilibrium, comparisons are only


meaningful for a particular ground state.
EXERGY BALANCES
In defining exergy, the requirement that the
environment be in chemical equilibrium has been
introduced at the outset, since exergy has been
defined as a maximum work. It should be clear that
only in the limit where equilibration with the en-
vironment occurs reversibly is the resulting work
maximum and path-independent. If irreversibili-
ties are allowed in the hypothetical equilibration
process, then the work becomes path-dependent
and exergy loses its meaning; it is no longer mean-
ingful to quantify a stream's capacity for pro-
ducing work, since we no longer have a "measuring
rod" (the maximum work). In this section, the
above considerations will be translated into
thermodynamic relationships and the concept of
an exergy balance will be developed.
Consider (Fig. 2) a steady process. Whenever
heat interactions result in a finite change in pro-
cess temperature, an infinite series of differential
Carnot engines, rather than a single engine, must
be used. Since there may be any number of such
infinite series, with Q1 referring to the system (see
Eq. (1) for sign convention)

Wcarnot = I n 1 (19)

where the summation has as many terms as pro-
cess temperature changes, and 7 is the Carnot
efficiency, 1 TO/T. Therefore

S= I 1 I fn 1 (20)

where the first summation contains as many
terms as there are adiabatic work interactions
Availability
Boundary

Exargy
Boundary

PaP
Pa System
Yje nj
.j.


7777//,//// Te
FIGURE 2. Open system. Availability and exergy
boundaries are shown.


CHEMICAL ENGINEERING EDUCATION








across the exergy boundary (Fig. 2).
Eq. (13) can now be rewritten in terms of heat
and work interactions taking place across the
exergy boundary (the actual system's boundary)

W1 I n 6q = 1 (He TeSe)nf

(H TeS)l TeS* (21)


To obtain
quantity
n
x = 1 k
Rearranging
n
X1 =je"je


an exergy balance, consider the



Yje j"ee 1 jl je (22)


n n
- nj j = (nje it j
n---'


For non-reacting components, nje = n j; for
reacting components, on the other hand, stoi-
chiometric constraints apply, so that
n n
,l (nje.- njt)e je = (nke ktk) j ,l Vji jg (24)
(n1 -k je (24)

where (nke -nkl) is the reaction rate (molar basis)
of any arbitrary reacting component, and vj is the
jth component's stoichiometric coefficient.
The summation on the right hand side of Eq.
(24) represents the sum of Gibbs energy changes
resulting from all reactions actually taking place
in the process under consideration, if they were
to occur in the environment. However, as discussed
above, the latter must be in equilibrium, hence
these chemical potentials must necessarily satisfy
n
1 vj = 0 (25)

Eq. (25) is a direct consequence of the equi-
librium constraint without which, as discussed
above, exergy cannot be defined. Its significance
can best be shown by means of an example: sup-
pose we consider a process where the reaction

CO + 02 + CO2

takes place. Then, for an environment containing
specified mole fractions of CO2 and 02, and no
measurable amount of CO, the equilibrium con-
straint imposes a non-zero, trace mole fraction of
CO. As will be shown in the next section, in calcu-
lating the exergy of a flowing stream, this quantity


is explicitly or implicitly calculated.
Because of Eq. (25), we can now rewrite Eq.
(21) as an exergy balance


I In i = (He TSg I Y )le
e .' e j=1


n
(H TeS jl YJ{gJe)n Teo-

Taking into account the definition of exergy,

I Q rI 6 = I I Tgt


(26)


(27)


From Eq. (20), it follows that the left hand
side of Eqs. (13) and (27) are identical. Conse-
quently, so are the respective right hand sides.
Thus, from a strictly thermodynamic viewpoint,
no new information has been gained from the in-
troduction of exergy. Moreover, in deriving Eq.
(27), the condition of chemical equilibrium has
been imposed upon the environment.
It is the above mentioned possibility of using
exergy as a basis for the quantification of the work
producing capacity of a stream that justifies its
use, at the expense of introducing arbitrary re-
strictions on the environment's characteristics.
Exergetic efficiency is defined as
rate of generalized exergy transport
n = from control volume
ex rate of generalized exergy transport (28)
into control volume
In computing exergy flows,
exergy associated with any stream is given
by
n
(H ToS yjAj)
j=1
heat interactions are converted into exergy
flows by introducing a Carnot efficiency (thus, for
example, if the process were isothermal and
Te = T1 = To, there would be no heat flux con-
tribution to exergy even under non-adiabatic con-
ditions).
all work interactions are equal to correspond-
ing exergy fluxes. Therefore,
n
e (Ht-TeSt- I1 Yj + I 1 -Q I n Ql1
nex = *= --- i- --- ^---f-
n
(He T6Se e Yje"je)ne
e j=1


= 1 -


TeS
n
Z (He T0Se I YjiiJe)nf
e j=1l


SUMMER 1984








If thermodynamic efficiency is evaluated using
availability rather than exergy, then, from Eq.
(13) we obtain


S+ (H TeSz)Z

I (He TeSe)ne
e


TS
= 1- (30)
S(He ToSe)ne
e


which has a different numerical value than Aex. As
stated before, availability balances provide a com-
plete description of the efficiency of the process
under study. Exergy is introduced when, in ad-
dition, streams are ranked according to their po-
tential for work production.
In Eq. (29) it must be noted that, if some
work interaction terms are negative, or any heat
interaction terms are positive, they should be in-
cluded in the denominator with a positive sign ac-
cording to the definition in Eq. (28). Eq. (29), as
written, is only valid for positive work and nega-
tive heat interactions. (See Eq. (1) for sign con-
vention.)

CALCULATION OF THE EXERGY OF
A FLOWING STREAM
Eq. (17) can be rewritten as follows,

S= H(T,P,y) TeS(T,P,y)
H(Te,Pe,y) + ToS(Te,Pe,y)
n j
4 yJHj (TgPY) ToSj(Te'PeY) je] (31)
j=1
This can be expressed as
T T1 P Z(Te)
= C(P)1 TdT + R/PL l,+f dP
C P (


P

ae ^ e- d


n
J+ y (TO.PO'yj)
=1 -


If we consider the case of an ideal gas stream,
T Tn
f Cp[l dT+ RT0 n E0+ Yj ( -je)
p T Pe j=1 (33)

In the exergy literature, the three terms on the
right hand side are called,
"thermal availability"


Exergy introduces no new thermodynamic
information, but is useful in ranking process streams
according to their potential for producing useful
work ... it is used to treat problems that require
both economic and thermodynamic analysis.

"pressure availability"
"chemical availability"
P-V-T data are needed in order to evaluate the
pressure availability for streams which cannot
be treated as ideal gases.
The last contribution to Eq. (33) is the work
that can be obtained when a stream component
already at To and P, is reversibly equilibrated
with the environment.
As an example, suppose a stream contains CO,
while the reference environment contains quanti-
ties of 02 and CO2. Then, for an equilibrium en-
vironment containing COz and 02

+ i =0 (34)
eco +2 02 co = (34)
Assuming ideal gas behavior, and for P. = 1 bar

pOi = pi1(Te) + RTe in yei (35)
which, when substituted into Eq. (34), yields
1
RT0 An YBCO = AGI(Tg) RTe[9n yeCO 2 An y602]
2 2
(36)
so that, finally,
CO(T',Pe'yCo) eCO(TPo',Y c) = RTe An Y-C (37)

with RT, In y,co calculated from Eq. (36).
Since the right hand side of Eq. (36) does not
contain yco, it might be thought that the same re-
sult can be attained without the equilibrium con-
straint, just by specifying yeco, and yo,, and
setting the environmental content of CO to 0.
However, in this alternate approach, Eq. (36) is
arrived at by considering a series of reversible
steps, one of which inevitably involves chemical
reaction which, for maximum work, can only take
place in an equilibrium environment (van't Hoff
box). Thus, it is the inclusion of the equilibrium
reaction vessel rather than the neglect of the
equilibrium constraint that characterizes this ap-
proach. In the present paper, on the other hand,
the van't Hoff box is indistinguishable from (and
belongs to) the environment. It is important to
understand, however, that equilibrium must
always be assumed when calculating maximum
work.


CHEMICAL ENGINEERING EDUCATION


- je(Te'PoYje )








CONCLUSIONS
Availability contains all the thermodynamic in-
formation necessary for a Second Law analysis of
efficiency. Exergy introduces no new thermody-
namic information, but is useful in ranking pro-
cess streams according to their potential for pro-
ducing useful work. Hence, it is used to treat
problems that require both economic and thermo-
dynamic analysis [1, 2, 6, 7].
The following limitations, however, should be
borne in mind:
1) An environment which is in stable thermo-
dynamic equilibrium eliminates from considera-
tion many realistic choices of environments whose
components are not in equilibrium, but are pre-
vented to react by kinetic barriers.
2) Although thermodynamic consistency is
required in the selection of an equilibrium en-
vironment, such a choice, once consistency is satis-
fied, is completely arbitrary, and, moreover, the
results are sensitive to the stable components se-
lected.
3) The present analysis is limited to cases
where the system under consideration exchanges
heat with a single reservoir. El

REFERENCES
1. Evans, R. B. and M. Tribus, "Thermo-Economics of
Saline Water Conversion," Ind. & Eng. Chem. (Proc.
Des. & Dev.) 4 (2), 195-206, 1965.
2. Gaggioli, R. A. and P. J. Petit, "Use the Second
Law, First," Chemtech, 7, 496-506, 1977.
3. Sussman, M. V., "Steady-Flow Availability and the
Standard Chemical Availability," Energy, 5, 793-
802, 1980.
4. DeNevers, N. and J. D. Seader, "Lost Work: A
Measure of Thermodynamic Efficiency," Energy, 5,
757-769, 1980.
5. Szargut, J., "International Progress in Second Law
Analysis," Energy, 5, 709-718, 1980.
6. El-Sayed, Y. M. and M. Tribus, "The Strategic Use of
Thermoeconomic Analysis for Process Improvement,"
AIChE National Meeting; Detroit, MI, August 16-19,
1981.
7. Tsatsaronis, G., P. Schuster, and H. Rdrtgen, "Exergy
Analysis of the Nuclear Coal Hydrogasification Pro-
cess," AIChE National Meeting; Detroit, MI, August
16-19, 1981.
8. Evans, R. B., Ph.D. Thesis, Dartmouth College, Han-
over, NH, 1969.
9. Moran, M., Availability Analysis: A Guide to Efficient
Energy Use; Prentice-Hall, Englewood Cliffs, N.J.,
1982.
10. Modell, M. and R. C. Reid, Thermodynamics and its
Applications, 1st Ed., Chapter 2, Prentice-Hall, 1974.
11. Denbigh, K., The Principles of Chemical Equilib-
rium, 4th Ed., Chapter 1, Cambridge University Press,
1981.


NOMENCLATURE


B availability (J)
B' open system flow availability
(J/mole)
Cp molar heat capacity (J/mole-K)
H stream molar enthalpy (J/mole)
n molar flow rate (mole/s)
p partial pressure (N/m2)
P pressure (N/m2)
Q heat interaction (J)
Q rate of heat interaction (W)
R gas constant (8.3144 J/mole*K)
S stream molar entropy (J/mole*K)
S entropy (J/K)
S* created entropy (J/K)

S* rate of entropy creation (W/K)
T temperature (K)
U energy (J)
V volume (m3)
W work interaction (J)
W rate of work interaction (W)
X defined in text

y mole fraction
Z compressibility factor
i7 Carnot efficiency
l7ex exergetic efficiency
v stoichiometric coefficient
q/ exergy (J/mole)
to molar free energy of formation at To and P.
(J/mole)
A
11 component chemical potential in mixture
(J/mole)

Subscripts

1 refers to boundary shown in Fig. l.a or
exergy boundary
entering stream
f final state
i initial state
j jth component
I leaving stream
r heat reservoir
a system
6 environment conditions (To, Pe,
yjo)
extensive property


Superscripts

partial molar property
o standard conditions


SUMMER 1984









Classroom


PROCESS DESIGN

IN PROCESS CONTROL EDUCATION*


M. NAZMUL KARIM
Colorado State University
Fort Collins, CO 80523

IN THE SPRING OF 1981, the author started teach-
ing a process control course at Colorado State
University. It was realized at that time that most
universities taught the course following certain
text books and that the course contents usually did
not give an overall idea on how to integrate the
concepts of process control into the overall process
design. Dr. Morari (Wisconsin) and Dr. Stephano-
poulos (Minnesota) [1] have advocated the need
for integrating process control into the overall
plant design. However, their ideas are too detailed
and are beyond the scope of an undergraduate
curriculum. Recently, Prassinos, McAvoy, and
Bristol [2] presented some ideas about understand-
ing complex control structures. However, none of
these schemes have been classroom tested in any
undergraduate program. The course at CSU was
thus designed to expose students to the complexi-
ties of designing an instrumentation and control
system for the overall plant. It was recognized that
this would be a tremendous undertaking by

Presented at the poster session of the 1982 ASEE
Summer School for Chemical Engineering Faculty at Santa
Barbara, CA.
TABLE 1. Semester Design Project
INSTRUMENTATION/CONTROL OF OLEFINS PLANT
The accompanying brochure describes the C-E Lummus
process for manufacturing olefins. Flowsheets and material
and energy balance information are provided in the bro-
chure. The following are the purposes of the project:
1. Identify the control variables, manipulative variables,
and the disturbances for individual equipment. Pair the
possible control and manipulative variables.
2. Get approximate models for each system. Obtain the
parameters of the models wherever possible.
3. Design control strategies for all the operations. Add
safety features and information-oriented data col-
lection systems when necessary.
4. Get rough estimates of the cost of the overall instru-
mentation of the plant.


The experience of the author is that
students should be taught process control from
the overall plant design concept. They should be
exposed to the complexities and interconnections
of different process units.

students who were seemingly unaware of the diffi-
culties that could be encountered in such a project.
PROJECT FORMAT
The students were divided into groups of two
or three and were given the whole semester to
complete the project. Table 1 shows the type of in-
formation (besides the flowsheet [Fig. 1]) that
was given to the students.
In 1981, students designed an overall control
system for the sodium dodecylbenzene sulfonate
plant [3]. In 1982, the students designed an instru-
mentation and control system for an olefins plant.
This was a C-E Lummus plant [4]. Typically,
students were given flowsheets and some mass and
energy balance information. They were taught
how to select manipulative and control variables
(using relative gain array). They were asked to
make simplifying assumptions, where needed, to
arrive at a steady state model of the individual
unit operations. Where possible, they obtained
dynamic models. They had to select the appropriate
control schemes for individual unit operations,
with particular emphasis on the possibility of re-
ducing interactions between the loops decouplingg
control). They had to design feed-forward control-
lers if appropriate dynamic or steady state models
were available, to guard against disturbances.
Then students had to identify the safety features
of the plant and design proper instrumentations
(like override control, safety alarm) to alleviate
the safety problems. They had to draw a P&ID
diagram for the overall system. The students were
given instrument catalogs from which to select
their instrument hardware (including computer
systems). After selecting the appropriate hard-
ware, they contacted the instrument vendors to
get the unit prices. They finally calculated the cost
Copyright ChE Division, ASEE. 1984


CHEMICAL ENGINEERING EDUCATION









of total instrumentation and control which was
compared with that obtained using plant design
texts [3].
DISCUSSION
Accomplishments
* Students were able to apply the concepts learned in the
"structured lectures" to a "real" plant.
* Students realized that in real life the instrumentation
and control problems were not as simple as given in
most of the texts.
* Students learned the practical aspects of looking up in-
formation in the vendor's catalog and of becoming
familiar with the present state of the art as far as the
availability of different instruments is concerned.
* Students learned to make simplifying assumptions to
arrive at different models.
* Students learned about the possibility of application of
advanced control techniques in the overall design of the
plant.
* The experience gave the students a broader outlook on
the design aspects of a plant.
Shortcomings
* Since the department of chemical engineering at CSU is
new, it does not have "canned" computer programs to
generate steady state and dynamic models of the unit
processes.
* It was difficult to get the necessary information from
the companies about the processes (C-E Lummus was
Dodecene


Heavy Spent
alkylated acid
hydrocarbons
FIGURE 1. Flow diagram for the manufacture of so-
dium dodecylbenzene sulfonate.* Students designed
the overall instrumentation and control system for this
plant.
*Reprinted with permission of McGraw-Hill Book Company
from Plant Design and Economics for Chemical Engineers,
3rd Edition, 1980, by M. Peters and K, D, Timmerhaus;
page 22.


M. Nazmul Karim is an assistant professor in the Department of
Agricultural and Chemical Engineering, Colorado State University. He
received his PhD from the University of Manchester, England, in
1977. His research interests include process control for multi-variable
systems, adaptive control of chemical and biochemical systems, and
computer aided design. Dr. Karim has been involved in teaching
undergraduate and graduate level courses in process control for more
than five years. He has been a consultant to petrochemical companies
and also to UNIDO.

reluctant to provide any more information about their
plant than was already available in the literature).
* Students found it difficult to talk to some vendors, main-
ly because they were not actual customers. Students
often did not have enough process information to all
the questions the vendors asked them.
CONCLUSION
The experience of the author is that students
should be taught process control from the overall
plant design concept. They should be exposed to
the complexities and interconnections of different
process units. As far as the author is aware, no
textbook currently deals with this aspect. The in-
dustry should provide information about some
"typical" plants so that students can arrive at
simplified models. Students should have access to
computer programs to obtain simplified models of
the different unit processes and should be exposed
to catalogs published by instrument vendors. The
experience at CSU in trying to teach the concept
discussed above has been reasonably successful. O
REFERENCES
1. Morari, M., Y. Arkun, and G. Stephanopoulos, AIChE
Journal, Vol. 26, No. 2, pp. 220-232 (1980).
2. Prassinos, A., J. J. McAvoy, and E. Bristol, "A
Method for the Analysis of Complex Chemical
Schemes." Proceedings of ACC 1982 Conference,
Arlington, Virginia, June 14-16, 1982. pp. 1127-1132.
3. Peters, M. and K. D. Timmerhaus, Plant Design and
Economics for Chemical Engineers, McGraw-Hill, 3rd
Edition, 1980.
4. ARCO/Chemical Company, Lyondell Olefins Plant,
C-E Lummus Combustion Engineering Inc. Publica-
tion.


SUMMER 1984









0 P"U lecture


HOW WE MAKE MASS TRANSFER SEEM DIFFICULT


E. L. CUSSLER
University of Minnesota
Minneapolis, MN 55455


M ASS TRANSFER IS ONE of the few subjects taught
only in chemical engineering. It is taught be-
cause it is important in the chemical process in-
dustries, basic to such operations as gas treating,
liquid-liquid extraction, catalyst effectiveness, and
cooling tower design. Fluid mechanics is, of course,
taught in chemical engineering, but it is also care-
fully covered in civil engineering and in applied
physics. Heat transfer is also taught in mechanical
engineering, and thermodynamics is a core course
in chemistry, just as it is in chemical engineering.
However, mass transfer is taught in detail only in
chemical engineering, and as such, is a unique
focus of our profession.
I have no trouble explaining mass transfer at
neighborhood parties. Over the years, I have
learned to dread the social question, "What do you
do, Ed?" If I answer, "I teach chemical engineer-
ing," the conversation switches to cars or sports.
If I say, "I teach mass transfer," I get the re-
sponse, "What on earth is mass transfer?" After
I reassure my listener that mass transfer has
nothing to do with the Teamsters, I can generally
give a good brief answer.
However, most students think mass transfer is
difficult, much harder than fluid mechanics or
chemical thermodynamics. This is not true: mass
transfer is easier. To prove this to yourself, try
explaining a mass flux, a momentum flux, and a
chemical potential at that same neighborhood
party. Explaining the mass flux is easy: it is the
mass transferred per area per time. Explaining
the momentum flux is harder: no non-engineer will
easily accept "the flux of y-momentum engendered

I have found that the best way to
overcome the carelessness in defining a system
is a lot of drill on simple problems. I don't devote
a single lecture exclusively to this, but try to sprinkle
simple examples throughout the course.

Copyright ChE Division, ASEE. 1984


Ed Cussler has been Professor of Chemical Engineering at the
University of Minnesota since 1980. Before that, he taught at Carnegie-
Mellon University. He is the author of over 80 papers, including the
book Diffusion: Mass Transfer and Fluid Systems, published this year by
Cambridge University Press.

by z-motion." Explaining the chemical potential is
almost impossible: if it were not, there would not
be such a glut of thermodynamics books.
But if mass transfer is easy, why do students
think that it's hard? I believe it's because you and
I teach it badly. We take a relatively simple subject
and make it a nearly incomprehensible tangle of
subscripts, superscripts, unit conversions, dimen-
sionless correlations, correction factors, archaic
graphs, and turgidly-written textbooks. We make
a mess of it, so students think it's hard.
I think we should stop this tangled teaching,
stop making students hate this cornerstone of our
profession. In this paper, I have suggested three
changes by which we may begin. First, we need to
spend more time on simple problems which use a
single, simple definition of mass transfer co-
efficients. Second, we need to use a different ap-
proach for describing analogies between mass,
heat, and momentum transfer. Finally, we need a
more coordinated approach for problems of diffu-
sion and chemical reaction. Each of these changes
is discussed in more detail below.

SIMPLE PROBLEMS (for Undergraduate Courses)
Undergraduates have the same problems with
simple mass transfer problems as they do in


CHEMICAL ENGINEERING EDUCATION









thermodynamics: they define the system carelessly
and they get the units fouled up. We all do this.
When I presented this material at the ASEE
summer school, the professors present made the
same mistakes. I do, too.
I have found that the best way to overcome
the carelessness in defining a system is a lot of drill
on simple problems. I don't devote a single lecture
exclusively to this, but try to sprinkle simple
examples throughout the course. In this, I always
choose problems in dilute solution, for these are
basic. Extensions to concentrated solution can
wait until these basics are mastered.
Three problems which I find useful in intro-
ducing the idea of a mass transfer coefficient are
given in the Appendix. Try to solve at least one
without looking at the solutions. They are easy,
but you can't depend on having taught them be-
fore. Problems like these humble me, making me
more sympathetic with my students' difficulties.
The three problems in the Appendix use a
common definition of the mass transfer coefficient
k, given by

Ni = kAci = 1 Ac) (1)

where N1 is the flux, Ac, is the concentration differ-
ence, D is a diffusion coefficient, and 1 is a charac-
teristic distance, sometimes called a "film thick-
ness." I know that this distance is hypothetical and
that it depends on the diffusion coefficient. Still, I
find its use a tremendous advantage for two
reasons. First, it establishes a clear connection
between mass transfer and diffusion, one which


I think we should stop this
tangled teaching, stop making students hate
this cornerstone of our profession. In this paper I
have suggested three changes...


the students easily remember. Second, it avoids
the curse of units, which is a chief reason that
mass transfer seems hard.
To illustrate this curse of units, compare the
definition of the mass transfer coefficient in Eq.
(1) with the other common definitions summarized
in Table 1. Obviously, the units for k vary widely
because the units used for concentration vary
widely. This variation confuses students, clouding
the physical meaning of the problem. Moreover,
it is unnecessary. It is as if we wrote the ideal gas
law as

pV = nT (2)
Then we would describe the temperature T not
only as K and R but as (l-atm/gmol), as
(kJ/kgmol), as (psia-ft3/lbmol), as (m3'Pa/
kgmol). Such a description would compromise any
physical intuition which students had about the
meaning of temperature. In the same way, if we
use the plethora of mass transfer coefficients in
Table 1, we obscure the student's intuition about
mass transfer.

ANALOGIES (for Undergraduate Courses)

Most undergraduate courses on transport pro-
cesses discuss fluid mechanics first, then describe


TABLE 1
Common Definitions of Mass Transfer Coefficients*


Basic Equation
N, = kAc,


N, = k'AP,


N, = k"Ax,


N1 = k'" Ac, + cjv


Typical Units of k**
cm/sec

mol/cm2 sec atm


mol/cm2 see


cm/sec


Remarks
Common in the older literature; best because of its simple
physical significance (Welty et al. 1969; Fahien, 1983).
Common for gas absorption; equivalent forms occur in
biological problems (Sherwood et al., 1979; McCabe and
Smith, 1975; Treybal, 1980).
Preferred for some theoretical calculations, especially in
gases (Bennett & Myers, 1974; Geankoplis, 1978; Edwards
et al., 1979).
Used in an effort to include diffusion-induced convection in
concentrated solutions (Bird, et al., 1960).


*In this table, the interfacial flux N, is defined as mol/L2t and the concentration c, as mol/L3. Parallel definitions where
N1 is in terms of M/L3 are easily developed. Definitions mixing moles and mass are infrequently used.

**For a gas of constant molar concentration c, k = RTk' = k"/c. For a dilute liquid solution k = (M2H/p)k' = (M2/
p)k", where M2 is the molecular weight of the solvent, H is Henry's law constant of the solute and p is the solution density.

SUMMER 1984 19.1








heat transfer, and conclude with mass transfer.
These courses sensibly outline analogies between
these processes, and conclude with a gaggle of
dimensionless groups codifying the analogies.
This often confuses all but the most mathematical-
ly adroit students.
The usual way in which the analogies are
taught may be summarized as follows. First,
diffusion in one dimension is described by Fick's
law
de
D d (3)
dz
where D is the diffusion coefficient. If this diffu-
sion takes place into a semi-infinite slab, the con-
centration profile is
c- C = erf z/V4Dt (4)
C1i clo
where co and c1. are the concentrations at the
slab's surface and far within the slab, respective-

... we professors draw the analogy between
mass, heat, and momentum transfer. If each process is
subject to mathematically equivalent boundary
conditions, then each leads to results
of the same mathematical form.

ly. Similarly, thermal conduction is described by
Fourier's law
dT
-q = k d (5)
dz
where k is the thermal conductivity. If conduction
takes place into a similar semi-infinite slab, the
temperature profile is
T To
S erfz/V4at (6)
T. To
where a (= k/pC,) is the thermal diffusivity and
To and T. are the temperatures of the surface of
the slab and far within the slab, respectively.
Finally, momentum transport follows Newton's
law
dv
dz
where T is the momentum flux or the shear stress
and p is the viscosity. If a flat plate is suddenly
moved in an initially stagnant fluid, the velocity
v of the fluid is
v-V
0-V erf z/V4vt (8)
where the plate's velocity is V, the fluid's velocity


far from the plate is zero, and the fluid's kine-
matic viscosity is v( = ( /p).
At this point, we professors draw the analogy
between mass, heat, and momentum transfer. If
each process is subject to mathematically equival-
ent boundary conditions, then each leads to results
of the same mathematical form. Many say this is
a more intimidating way: each process depends on
combining a linear constitutive equation and a con-
servation relation to yield mathematically con-
gruent results. The phenomenological coefficients
of diffusion (D), of thermal conductivity (k),
and of viscosity (,p) are thus analogous.
Many students find this conventional analogy
confusing. Sure, Eqs. (3), (5), and (7) all say a
flux varies with a first derivative. Sure, Eqs. (4),
(6), and (8) all have an error function in them.
But D, k, and u do not have the same physical
dimensions. Moreover, D appears in both Eqs. (3)
and (4), but k in Eq. (5) must be replaced by a
in Eq. (6). The viscosity in Eq. (7) is replaced
by the kinematic viscosity v in Eq. (8). These
changes frustrate many students, and undercut
any value which the analogies have.
The source of confusion stems from the ways in
which the basic laws are written. In Fick's law
(Eq. 3), the molar flux varies with the gradient
in moles per volume. To be analogous, the energy
flux q should be proportional to the gradient of
the energy per volume (pCpT). In other words,
Eq. (5) should be rewritten as
k d d
-q pp dz (pCpT) = a (pCT) (9)

Now mass and heat transfer are truly analogous.
Just as Eq. (4) follows from Eq. (3), so Eq. (6)
follows from Eq. (9). Similarly, Newton's law for
momentum transport can also be rewritten so
that the momentum flux is proportional to the
gradient of the momentum per volume (pv)


d d
- dz (pv) = v (pv)
p dz dz


(10)


This new form leads directly to Eq. (8).
Just as the fundamental laws for mass, heat,
and momentum transfer can be made more
parallel, so can expressions for mass transfer co-
efficients and heat transfer coefficients. The inter-
facial mass flux already varies with the difference
in moles per volume.


N, = kAc,


(11)


The interfacial heat flux must be modified so that
the energy flux varies with the energy difference


CHEMICAL ENGINEERING EDUCATION








TABLE 2
Analogies Between Processes Are Clearer With Flux Equations In An Uncommon,
But Dimensionally Analogous Form.


MASS TRANSFER


HEAT TRANSFER


MOMENTUM TRANSFER


Common Form Analogous Form Common Form Analogous Form Common Form Analogous Form


concentration c1 moles/volume temperature T energy/volume
C, pCpT
diffusion coef. D diffusion coef. D thermal conduct, thermal dif. a
(Eq. 3) (Eq. 3) k (Eq. 4) (Eq. 9)


mass transfer
coefficient k
(Eq. 11)


mass transfer
coefficient k
(Eq. 11)


heat transfer
coefficient h
(Eq. 12)


(h/pCp)
(Eq. 12)


velocity v

viscosity /L
(Eq. 7)
friction
factor f
(Eq. 13)


momentum/
volume pv
cinematic visc. v
(Eq. 10)
(fv/2)
(Eq. 13)


Dimensionless
Groups


Schmidt number Schmidt number Prandlt number Prandlt number
p/pD v/D ACP/k v/a


Sherwood
number kd/D
Lewis number
k/(pCpD)


Stanton Nusselt number Stanton number
number k/v hd/k (h/pC) /v
Lewis number
a/D


per volume

h
q = hAT p= A(pCpT) (12)

Thus the mass transfer coefficient k corresponds
less directly to the heat transfer coefficient h than
to the quantity h/pC,. The appropriate parallel
for momentum transfer is the dimensionless
friction factor f, defined as
1 fv
7 = f( pv2) = ( ) (pv-O) (13)

Thus (fv/2) is like k and (h/pCp).
When these equations are written in these
parallel forms, they automatically suggest the
most common dimensionless groups. For example,
the ratio of coefficients in Eqs. (3) and (10) is
v/D, the Schmidt number. The ratio of coefficients
in Eqs. (11) and (13) is (k/v)(2/f). Because
(2/f) is itself dimensionless, this is equivalent to
k/v, the Stanton number.
These analogies, summarized in Table 2, have
made my teaching of mass transfer more effective.
I can see the light dawn on dozens of student faces:
that quite pause, and then a slow "Oh, I see .. ."
Try this yourself the next time you lecture on a
problem like the wet bulb thermometer.

CHEMICAL REACTIONS (for Graduate Courses)
A third area in which we can improve our
teaching concerns the coupling of mass transfer
and chemical reaction. I have had trouble teaching


this material (even to graduate students) for two
reasons. The first is that, in most curricula, courses
in transport phenomena are very separate from
those in chemical kinetics and reactor design. I
could do a better job if the mass transfer and re-
action courses were more completely integrated.
We haven't solved this problem.
The second reason that mass transfer and re-
action are poorly taught, which I struggle to avoid,
hinges on the distinction between heterogeneous
and homogeneous chemical reactions. I make this
distinction either in chemical terms or in mathe-
matical ones, and I often forget to tell the students
which terms I am using.
I can best illustrate this by an example.
Imagine we are discussing that old warhorse of
reaction kinetics, ethane dehydrogenation on
platinum. The overall reaction is simple.


CH6 ; CH4 + H2


(14)


My modeling of the reaction can be more subtle.
If the platinum is a simple crystal, I treat this re-
action as heterogeneous, occurring on the surface
of the crystal. This is the route taken in chemistry
courses or at the start of reaction engineering
courses where mechanisms matter. However, if
the catalyst is dispersed in a porous support, I
discuss catalyst effectiveness factors as if the re-
action were homogeneous. The chemistry is the
same, but my mathematical treatment changes.
To look at this in more detail, consider the key
Continued on page 149.


SUMMER 1984


Variable

Physical
Property
Transfer
Coefficient









MT classroom


THE TWO LOST-WORK STATEMENTS AND THE

COMBINED FIRST- AND SECOND-LAW STATEMENT


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

A LL OF THE FUNDAMENTAL thermodynamic de-
velopment for computing the reversible work
of processes was apparently known and published
by 1903. Therefore, this paper and similar papers
discuss only the question of which of the many
possible approaches for applying thermodynamic
analysis to various kinds of processes is easiest to
teach, easiest to understand, and most likely to be
applied correctly by the average engineer.

WHY USE LOST WORK?
This paper is largely about the "lost work" ap-
proach, which has some advantages over other ap-
proaches. The first advantage of lost work is that
it has a very high intuitive content. This was the
reason it was first introduced. In many important
cases, it is exactly equal to the work converted to
friction heating.
The second advantage is that the sum of the
lost work and the work actually performed is
equal to the reversible work

dWre = dW + dLW (1)
This reversible work has a character quite differ-
ent from either the actual work or the lost work,
which are both path functions whose value de-
pends upon the path followed going from the
initial to the final state. However, the reversible
work, their sum, is a state function; its value de-
pends only on the initial and final states of the
system and the heat and matter flows across the
system boundaries; it is independent of the path
actually followed.
The third advantage of the lost work is that it
can be used to make direct computations of the re-
versible work, the lost work, and the thermo-
dynamic efficiency of any process.

Copyright ChE Division, ASEE, 1984


This paper is largely about the
"lost work" approach, which has some advantages
over other approaches. The first advantage ... is that
it has a very high intuitive content .... In many
important cases, it is exactly equal to the
work converted to friction heating.

WHAT IS THE ALTERNATIVE?
If one does not wish to use the lost-work ap-
proach to the second-law analysis of chemical pro-
cesses, the alternative is the availability-exergy-
essergy approach. Another paper [5] attempts to
show that, although the other approach has many
advocates and is widely used, it is generally not
as suitable for the analysis of chemical engineering
processes as is the lost-work approach.

WHY ISN'T LOST WORK USED?
A principal purpose of this paper is to show
that lost work has not been widely used because
there exist in the literature two very different
quantities that both go by the same name, "lost
work." For reasons that will be clear later, we call
these two definitions LWm (for mechanical lost
work) and LWt (for thermodynamic lost work).
The existence of these two different quantities has
led to confusion and misapplication of the lost
work with the result that the lost work has not
been utilized as widely as it should have been.
Although the concept of "wasted work," "dis-
sipated work," "useless work," or other such terms
was present in the literature for many years and
the correct theoretical basis for the application
of the concept was shown by Gibbs in 1876 [7], as
far as we know, the first to use the term "lost
work" in the chemical engineering literature and
in chemical engineering textbooks and handbooks
was G. G. Brown [3]. As far as we can tell, he
formulated it independently of others who may
have had similar ideas before him. He then worked
with Sliepcevich [2] and Martin [10] who extended
and developed the idea. Several authors adopted


CHEMICAL ENGINEERING EDUCATION
























Noel deNevers has been a faculty member at the University of
Utah since 1963. His principal technical 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 this
article he returns to one of his early loves, thermodynamics. He asserts
that there is no "Energy Crisis," but there may be an "Entropy Crisis,"
although that may be hard for the public and the politicians to grasp.
In addition to his technical work, he recently had three of his laws
published in the 1982 Murphy's Laws compilation and won the coveted
title "Poet Laureate of Jello" at the annual Jello Salad Festival in Salt
Lake City. (L)
J. D. Seader has been a faculty member at the University of Utah
since 1966. Prior to that, he was employed by Chevron Research and
Rocketdyne. His principal technical interests are equilibrium-stage
operations, process synthesis, process simulation, and synthetic fuels.
He is a Director of the AIChE and was the Annual Institute Lecturer in
1983 for AIChE. He has prepared the section on distillation for the
forthcoming sixth-edition of the Chemical Engineers' Handbook and is
currently the Executive Officer of CACHE. (R)

lost work and used Brown's formulation in text-
books [1, 16, 17].
Meanwhile, Van Ness developed a different
version of the lost work [14, 15]. His version ap-
pears in his thermodynamics textbook with Smith
and in the 5th Edition of Perry's Handbook. On
the other hand, Brown and Sliepcevich's version
appears in the 3rd and 4th editions of Perry's
Handbook. To our knowledge, no one has pre-
viously shown that between the 4th and 5th
editions of Perry's Handbook, the fundamental
thermodynamic orientation toward lost work
changed. We believe that this change is significant
and should be known and understood by chemical
engineers.
Turning now from the history of the two
concepts, let us contrast them by means of dis-
cussion and Table 1.

THE TWO LOST-WORK CONCEPTS


We begin by defining two auxiliary quantities,
Work converted to heat (or to internal
energy) = WCTH (2)
Work to restore system = WTRS (3)


The first of these (WCTH) is the amount of
shaft work, falling weight work, or its equivalent
(j PdV work, electrical work, decrease in kinetic
or potential energy, and decrease in magnetic or
chemical or diffusional potential to do work) that
is converted to heat or to internal energy. This is
equivalent to mechanical, frictional rubbing as in
a brake.
The second of these (WTRS) is the amount of
work that must be supplied to restore a system
to its original conditions after some process of
change has occurred in the system. The restoration
process exchanges heat only with the infinite sur-
roundings at To.
The quantities WCTH and WTRS are not in
general the same; they are the same if and only if
the system considered is uniformly isothermal at
the temperature, To, of the infinite surroundings.
The earliest published reference to the lost
work that we have found is in Brown et al [3]
In any process the increase in internal energy due
2
to heat effects TdS is equal to the sum of the heat
1
absorbed from the surroundings and all other energy
dissipated into heat effects within the system due to
irreversibilities such as overcoming friction occurring in
the process,


TdS = q + (Iw)


where lw = "lost work," energy that could have done

TABLE 1
Comparison of the Two Lost-Work Definitions


Definition
Definition in terms of
dSirr
Unambiguously defined
for non-isothermal
systems?
Computable for an iso-
thermal system without
reference to surround-
ings temperature?
Leads to a reversible
work statement that is
an unambiguous state
function for all cases
including non-


isothermal cases?


LWm
Mechanical
Lost Work
LWm = WCTH


LW,
Thermodynamic
Lost Work
LW= WTRS-W


dLWm = TdSirr dLW,=TodSirr


YES


YES


SUMMER 1984









... as far as we know,
the first to use the term "lost work" in
the chemical engineering literature and in chemical
engineering textbooks ... was G. G. Brown.

work but was dissipated in irreversibilities within the
flowing material.
Although Brown directed it at irreversibilities in
flowing streams, the concept of lost work given
above can, in principle, be applied to any type of
process.
This idea was expanded and placed in more
general form by Brown and Sliepcevich [2]

Lost Work. Because, as commonly used, TdS does
not differentiate between heat and loss of potential
energy, another expression (Iw) is used to designate all
potential work dissipated in overcoming resistances or
in irreversibilities or "lost work." It represents the
energy that might have been evident as work if it had
not been so dissipated. Accordingly

f TdS = q + (w) (1)

The lost work defined in these two equations is
equivalent to
LW = WCTH (4)
We may also utilize the formulation of the
second law shown by Denbigh [6] (attributed by
him to de Donder), in which a term is introduced
for the irreversible entropy production. In it, for a
closed system, we would have
dS = dQ/T + dSirr (5)
Comparing Eq. (5) with the definition of 1w given
in the two preceding quotes, we find that Brown's
definition of lost work is equivalent to
d(LW) = TdSirr (6)
In Table 1, we have called this definition of the lost
work LWm; i.e., mechanical lost work. Eqs. (4)
and (6) are shown as the first two entries of Table
1 under LWm.
The other definition of lost work (which we
call LWt, thermodynamic lost work, and shown
as a column with that heading in Table 1) was
also apparently first defined by Brown and
Sliepcevich [2]. In that article, they followed their
basic definition of the lost work quoted above with
two subcases. In an isothermal subcase, they write
their entropy balance with a quantity (1w),. In
the other subcase, for systems that exchange heat


only with the surroundings at To, they write their
entropy balance with a quantity (1w)o. They do
not in any way remark in that article (or any other
subsequent publication we have found) that (lw)o
is not the same quantity as (lw)T. However, if we
follow their examples, we find that (lw) is the lost
work in their basic defining equation while, sub-
stituting their (lw)o into Eq. (5), we see that
d(lw)o = TodS,,r (7)
or

(lw) o= (lw)T (8)
T
(In the terms used in this paper, LWt = (To/
T) LWm.) (8a)

The second definition of lost work ((lw)o =
LWt) was arrived at independently by Van Ness.
He informs us that his development was totally
independent of that of Brown, Sliepcevich, and
Martin. In 1956, Van Ness published his first paper
on the topic, in which he defined the lost work as
minus the value in Eq. (7). (The choice of whether
to make the lost work positive or negative is
arbitrary; Brown makes it positive, Van Ness
originally made it negative, then switched and
made it positive [12]. We use the positive value
here.)
In his 1956 article [14], Van Ness arrived at
his definition by considering the reversible work
necessary to restore a system to its original con-
dition after some change has occurred in the
system, allowing heat exchange with the sur-
roundings only at To and subtracting the work
done by the system during that change. The proofs
are shown there that
LWt = WTRS W (9)

Thus, we show in Table 1 this property of LWt.
At this point, the application of the two defini-
tions to a simple example may make their differ-
ence clear. Consider a system consisting of an
isobaric, adiabatic container filled with a vapor-
liquid mixture of helium at its normal boiling
point of 4K. Work added to the system by means
of a friction brake, as shown in Fig. 1, is converted
to internal energy of the helium. The irreversible
entropy increase of the system is equal to the work
input (WCTH) divided by the system tempera-
ture, Tsys, where the conversion takes place. But is
the work input the same as the lost work? Accord-
ing to the definition proposed by Brown (Eq. 4),
it is the same; work input converted to friction
heat equals lost work.


CHEMICAL ENGINEERING EDUCATION








Suppose we decide that the lost work is not
simply the work input converted to internal
energy but also the amount of reversible work that
would be required to restore the system to its
original state, as apparently first suggested by
Van Ness [14]. To restore the system, suppose we
use a refrigerator of some ideal type to extract
heat from the system in an amount equal to the in-
crease in internal energy and reject heat to the
surroundings (assumed to be infinite) at tempera-
ture To. By straightforward application of the
theory of Carnot refrigerators, we have


WTRS = LW( To T ys
I Toys )


(10)


Unlimited amounts of heat may be rejected to or
absorbed from the infinite surroundings at To.
Normally, the surroundings temperature can be
taken as that of the nearest body of water (for
example, a river, lake, or ocean) or the water
temperature that can be easily reached in atmos-
pheric cooling towers or atmospheric air. Assum-
ing that To is 25C (298K), from Eq. (10), the
reversible work to restore the helium system is
(298 4) /4 or 73.5 times the work input converted
to internal energy.
For the system in Fig. 1, Brown defined the


lost work as the work input to the system, which
is equal to LWm. From a practical engineering
viewpoint, we believe that this definition is in-
correct. If the work input is converted to internal
energy of helium, thus causing some of it to vapor-
ize isobarically at its normal boiling point, then
somewhere else in the world some helium liquefier
is doing the work to remove that same amount of
heat to supply us with liquid helium. That helium
liquefier may be part of our plant or that of our

To our knowledge, no one has
previously shown that between the
4th and 5th editions of Perry's Handbook, the
fundamental thermodynamic orientation
toward lost work changed.

liquid helium supplier; but, either way, we must
pay for the work it does. Thus, in practical terms,
the real loss is not only the work converted to in-
ternal energy but also the reversible work required
to offset this irreversible conversion. Therefore,
we assert that the practical definition of the lost
work is that definition apparently first used by
Brown and Sliepcevich [2], which they called (lw)o
but which they apparently never subsequently used
and which was later independently introduced by
Van Ness [14] and which we term the "thermo-
dynamic lost work" (LWt), where, in general


LWt = WTRS W


(11)


In the particular case of the friction brake in
helium,


LWt = WTRS + LWm


(12)


FRICTION BRAKE THAT
CONVERTS WORK INPUT
TO INTERNAL ENERGY
FIGURE 1. Friction brake to convert work to internal
energy.


because LW, is simply the negative of the thermo-
dynamic work produced by the system. Combining
Eqs. (10) and (12) to eliminate the WTRS, we
obtain


To
LWt = LWmTo
T,,ys


(13)


Why is LWt not equal to WTRS? If there is no
exchange of work between the system and its sur-
roundings during the irreversible process, then the
W in Eq. (11) is zero, and LWt = WTRS. But for
cases in which the external work during the ir-
reversible process is not zero, the W term is sig-
nificant. We may see this by considering a general,
irreversible process in a closed system that pro-
ceeds from State 1 to State 2. The work to restore
the system to State 1, exchanging heat only with
the surroundings at To, is independent of the ir-
Continued on page 146.


SUMMER 1984










M 1 laboratory


TRAY DRYING OF SOLIDS


ARTIN AFACAN AND JACOB MASLIYAH
University of Alberta
Edmonton, Alberta, Canada T6G 2G6


T HE EXPERIMENT described in this paper is de-
signed to expose the students to two topics:
the principles of drying and simultaneous heat
and mass transfer. Drying of solids is considered
to occur in two stages, a constant rate period
followed by a falling rate period. In the constant
rate period, the rate of drying corresponds to the
removal of water from the surface of the solid.
The falling rate period corresponds to the re-
moval of the water from the interior of the solid.
The rate in either case is dependent on a number
of factors. Some of these are the air wet and dry
bulb temperatures, flow rate of air, the solids
characteristics and the tray material.









*-





Artin Afacan is a chemical technologist in the department of
chemical engineering at the University of Alberta. He received his
BSc (1975) in chemical engineering from Istanbul Technical University.
He has had industrial experience with TEROCHEM and for the last four
years he has been involved with the design of pilot scale experi-
ments in unit operations, process control, and reaction engineering.
He is currently involved in an oil sands research project. (L)
Jacob H. Masliyah is a professor of chemical engineering at the
University of Alberta. He received his BSc (1964) in chemical engineer-
ing from the University College, London, his MSc (1966) from the
University of New Brunswick, and his PhD (1971) from the University
of British Columbia. He has had industrial experience with CIL and
is presently involved with the heavy oil sands industry. His research
interests are in the areas of mathematical modelling of process
equipment, transport phenomena, and numerical analysis. He has
over fifty publications in scientific journals. (R)


1. Blower (3200 RPM, 115 V, 1/8 horsepower)
2. Electric Heater (3000 W at 208 V)
3. Orifice Plate (Orifice diam: 6.5 cm)
4. Manometer
5. Water Reservoir (Flask) for Wet-Bulb Thermometer
6. Dry-Bulb Thermometer (Mercury Thermometer)
7. Digital Balance (SARTORIUS MAX, 4000 g)
8. Wet-Bulb Thermometer (Mercury Thermometer)
9. Sample Tray
10. Water Reservoir (Flask) for Wet-Bulb Thermometer
11. Gate to control Air Flow
12. Screen
TC = Temperature Controller (Thermo El 600, 208 V)
T = Thermocouple (Type J)
FIGURE 1. Schematic of experimental equipment.



THEORY

Drying can be described in terms of gas mass-
transfer and heat transfer coefficients. The rate
of drying is given by

N, =k(Y Y) = q (1)
Xs
where q is the total heat supplied by the gas
stream to the solid and it is given by

q = he(T,-Ts) + h, (T,-Ts) + Uk (Tg-Ts)
(2)

where he, hr, Uk are the heat transfer coefficients
for convection, radiation, and conduction, re-
spectively. They are given by Treybal [1] as

he = 14.3 G08 (3)
hr = Er(Tr4-T,4)/(T,-T,) (4)

Uk = [(1/he) (A/A.) + (Zm/km) (A/A,)
+ (Z,k/k,) (A/Am) ]-
(5)

C Copyright ChE Division, ASEE, 1984


CHEMICAL ENGINEERING EDUCATION








Making use of Eqs. (1) and (2), the relation-
ship between T, and Y, becomes

(Y, Y) A U,
(Y8-Y)X. (1 + u- ) (Tg -Ts)
(hc/ky) h

+ hr (Tr-Ts) (6)

where (he/ky) ratio is related to Lewis number,
Le, and is given by Henry and Epstein [2] as


kC, = 0.567
kjC. \Pr


Cs is the specific heat of saturated gas at Ts.
For an air-water system the Lewis number
is approximately equal to unity. Eqs. (3) and (7)
are used to evaluate he and ky, respectively. Simul-
taneous iterative solution of Eq. (6) with the
saturation humidity curve provides the solid sur-
face temperature T, and the corresponding value
of the humidity, Y,. Once Y, is known, Eq. (1) can
be used to calculate the theoretical drying rate, Ne.
The absolute air humidity Y is measured experi-
mentally from the dry and wet bulb temperatures.

EQUIPMENT
A schematic diagram of the experimental set-
up is shown in Fig. 1. It is a wind-tunnel type
tray dryer designed to give a good control of air
temperature and air flow rate. It consists of an
air blower, a heater and an orifice plate in the air
duct, and a tray sample mounted on a digital bal-
ance. The air flow rate is controlled by a gate in

"o

0.24 ---- I
Dry-Bulb (C) Wet-Bulb ("C)
-0
---- 58 25
o 0.20 74 30.5
S---- 82 31.5
S--- 100 36
0.16

o 0.12
o Air Flow Rate = 1.38 kg/m2 s

Z 0.12 -

X 0.08

C 0.04-
O

0
0 0 720 1440 2160 2880 3600 4320 5040
o Time 8, s

FIGURE 2. Variation of moisture content with time
for different air temperatures.


= Leo-567


SUMMER 1984


The reasonably good agreement
in the calculated rate of drying and that
observed experimentally makes students feel confident
in applying engineering design correlations.


the blower inlet line, and its flow rate is measured
by a pre-calibrated orifice-meter. The temperature
is controlled by a closed-loop on-off controller. Wet
and dry bulb thermometers are placed at the inlet
and outlet of the drying chamber. The wet-bulb
temperature is measured by a mercury ther-
mometer, with its bulb covered by a wick kept
in a water reservoir. The water reservoir is at-
tached to the bottom of the duct as shown in Fig.
1. This method of measuring the wet-bulb
temperature was simple and inexpensive. How-
ever, this method was later replaced by humidity
sensors to obtain more accurate and direct
measurements.
The cross-section of the air duct is 0.12 m X
0.12 m and that of the drying chamber section con-
taining sample tray is 0.185 m X 0.28 m. The
sample tray is made of aluminum sheel metal
having a thickness of 0.001 m and dimensions of
0.125 m X 0.16 m X 0.007 m.

EXPERIMENTAL PROCEDURE
Two sets of experiments are performed: one
set is at a constant air temperature and different
air flow rates, and the other is at a constant air
flow rate and different air temperatures. The dry-
ing material used is Ottawa-sand (35-48 Mesh).
The tray sample is loaded with about 250 g of
sand and placed over the balance in the drying
chamber. The weight of the tray and the sand is
recorded. When the desired conditions of tempera-
ture and air velocity are reached (about 10 min),
the sample tray is removed and the sand is wetted
to give a desired initial moisture content. A stop
watch is started and the balance reading is taken.
Subsequent balance readings are taken at about
three minute intervals. Drying is assumed to be
complete when at least three consecutive readings
are unchanged. The wet/dry bulb temperatures
at the inlet and outlet of the drying chamber and
air flow rate are recorded at least three times
during the course of a run to give average operat-
ing conditions.
The same procedure is repeated for other runs
at different operating conditions. The range of the
variables studied are: air flow rate, 1-1.5 kg/m2s;









(xo104)


to
E 10
ca
.f8


-I 6-0 3
SAir Flow Rate = 1.380 kg/m2
c. Dry-Bulb Wet-Bulb
4 (C) (C)
58 25
S74 30.5
2 A 82 31.5
---- 100 36

0 0.025 0.050 0.075 0.100 0.125 0.150 0.175
Moisture Content X, (kg of water/kg of dry solid)
FIGURE 3. Variation of drying rate with moisture
content for different air temperatures.


air temperature, 50-100C; sand initial moisture,
15-20%.

RESULTS AND DISCUSSION
From the measurement of the weight of the
sand sample, the moisture content (X) of the
sample at different times is calculated. A typical
plot of the variation of moisture content with
time is shown in Fig. 2.


(x10-4)


"0 0.025 0.050 0.075 0.100 0.125 0150 0.175
Moisture Content, X (kg of water/kg of dry solid)
FIGURE 4. Variation of drying rate with moisture
content for different air flow rates.


The drying rate is calculated from the relation-
ship

dX 1
N = -Sdo A

where the rate of change of the moisture content,
dX/do, is obtained from the slope of the curve
X vs 0 of Fig. 2. The drying rate is then plotted
against the moisture content. Figs. 3 and 4 show
typical plots of the variation of the drying rate
with moisture content at constant air flow rate
and constant air temperature, respectively.
Fig. 5 gives a comparison of the constant dry-
ing rate, Ne, calculated using Eq. (1) with that
experimentally measured. The agreement is with-
in 20%, with the calculated values being con-
sistently lower.
Since the variation of the latent heat of vap-
orization and that of the radiation heat transfer


(x10-4)
16.0



S / /
Co /






S41.0
C 7.


Air Flow Rate = 1.38 kg/m2s
x
1.0 I I 6 I I .0 I 4
1.0 4.0 7.0 10.0 13.0 16.0 19.0 (xO-4)
Theoretical NC, kg/m2s

FIGURE 5. Comparison between experimental and
theoretical drying rates at different air temperatures.



is fairly small for the range of temperature cov-
ered in this experiment, the overall drying rate
Ne becomes directly proportional to the overall
driving force Tg T). Fig. 6 shows such a de-
pendence.
The effect of air flow rate on drying rate
during constant drying period is shown in Fig. 7.
It shows that the constant drying rate, N,, is pro-
potional to G-8. The linear dependence of N, on
G-8 is not surprising as the convective heat trans-
fer is the major mode of transfer and the convec-
tive heat transfer coefficient, he, is proportional to
Go. as given by Eq. (3).


CHEMICAL ENGINEERING EDUCATION









CONCLUSION
The drying experiment proposed here is useful
in presenting the concept of simultaneous heat
and mass transfer. The reasonably good agree-
ment in the calculated rate of drying and that ob-

(x10-)
14 -
Constant Air Flow Rate 1.38 kg/m2s
c 12 Theoretical
E n Experimental

10-
O
z

8

C 6-


E 4
SRange of Air Temperature
c Dry-Bulb 58 100C
O 2 Wet-Bulb 25 36C
CO
^I I I I I


"0 10 20 30 40 50
Driving Force, (Tg Ts)


60 70


FIGURE 6. Effect of temperature driving force on dry-
ing rate at constant air flow rate.


served experimentally makes students feel con-
fident in applying engineering design correla-
tions. Ol

REFERENCES
1. Treybal, Robert E., Mass-Transfer Operations, Mc-
Graw Hill Inc., 1980, Chapters 7 and 12.
2. Henry, H. C., and N. Epstein: Can. J. Chem. Eng., 48,
595, 602, 609 (1970).

NOMENCLATURE

A Drying surface area [m2]
A, Nondrying surface area of drying solid
[m2]
Am Average solid surface area [m2]
C, Saturated specific heat of the gas
[J for mixture/kg (air) "C]
C, Specific heat [J/kg'C]
DAB Diffusivity [m2/s]
G Mass velocity of gas [kg/m2.s]
h, Heat transfer coefficient for convection
[w/m2-K]
h, Heat transfer coefficient for radiation
[w/m2.K]
k Thermal Conductivity of gas [w/m2.K]


(x10
( 3
CM
E 2
zo

Z 10
ca
ru
05
C:
0 5
0'


t-
CO
o
0
U,


-4)










Experimental
Theoretical
Air Temperature
Dry-Bulb Wet-Bulb
72C 28C


1.75


1.25 1.50
Air Mass Velocity, G kg/m2 s


FIGURE 7. Effect of air velocity on drying rate at
constant air temperature.

ks Thermal Conductivity of solid (sand)
[w/im2K]
km Thermal conductivity of tray [w/m2.K]
k, Gas phase mass transfer coefficient
[kg dry air/m2s]
Le Lewis number [Le = Sc/Pr]
N Drying rate [kg/m".s]
N, Constant drying rate [kg/m2.s]
Pr Prandtl number [Pr = Cp //k]
q Total flux of heat received at the drying
surface [w/m2]
qc Heat flux due to convection [w/m2]
qk Heat flux due to conduction [w/m2]
q, Heat flux due to radiation [w/m2]
S Mass of dry solid (sand) [kg]
Sc Schmidt number [Sc = j/p DAB]
T, Absolute temperature of gas (dry-bulb) [K]
Tr Absolute temperature of radiating surface
[K]
T, Absolute temperature of solid surface [K]
Uk Overall heat transfer coefficient [w/mM.K]
X Moisture content of a solid [kg of water/kg
of dry solid]
Y Absolute humidity [kg water vapor/kg dry
air]
Y, Saturated humidity at surface of solid
temperature [kg water vapor/kg dry air]
Zm Metal thickness [m]
Z, Sand thickness [m]
Greek Symbols
E Emissivity of drying surface
dimensionlesss]
0 Time [s]
Xs Latent heat of vaporization at T. [J/kg]
< Stefan-Boltzman Constant 5.729x10-8
[w/m2.K4]
A Viscosity [kg/m-s]
p Density [kg/m3]


SUMMER 1984










laboratory


A MICROCOMPUTER BASED LABORATORY FOR


TEACHING COMPUTER PROCESS CONTROL


BABU JOSEPH AND DAVID ELLIOTT
Washington University
St. Louis, MO 63130

M OST SCHOOLS NOW REQUIRE undergraduate
students in chemical engineering to take at
least one course in process dynamics and control.
The advent of the microcomputer has had a major
impact in the instrumentation and control field,
and this must be reflected in the curricula through
added coverage of digital control systems and ex-
posure to computer based data acquisition and
control systems. In order to meet this demand,
Washington University undertook the development
















Babu Joseph received his PhD in chemical engineering from Case
Western Reserve University and teaches courses in process design and
process control, both at the undergraduate and graduate levels, at
Washington University. His research interests are in the areas of process
dynamics, control, simulation, and optimization, with special emphasis
on the study of coal conversion process systems. His outside interests
include reading, hiking, and canoeing. (L)
David L. Elliott received his PhD in system science from UCLA in
1969 and has taught mathematical systems at Washington University
since 1971. Besides microcomputer applications, he is interested in the
geometric approach to nonlinear systems, stemming from his work in
the 1960s on the attitude control of underwater vehicles (U.S. Naval
Ocean Systems Center) and the identification of enzyme-kinetics
models for blood coagulation. He has published papers on bilinear
systems, nonlinear observers, and linearization of systems by co-
ordinate and feedback transformations. He is an editor of Mathematical
System Theory and a former editor of the IEEE Control Society News-
letter. (R)


FIGURE 1. Computer system configuration.


of a new laboratory course specifically designed
to teach the principles of process data acquisition
and control using digital computers. The structure
of the laboratory and the course are discussed in
this article.

COMPUTER SYSTEM CONFIGURATION
A decision was made early in the development
of the laboratory to provide as much exposure as
possible to the computing hardware used without
getting engrossed in computer system architecture.
We finally decided on using a set of dedicated
Apple microcomputers, primarily because of their
low cost, availability of plug-in compatible modules
for data acquisition, and their popularity as a
general purpose personal computer. The students
like having their "own machine" to work with. It
is also fun to work with after a few basic
commands have been mastered. Particularly at-
tractive is the graphics capability which allows
data or results to be represented graphically using
a very small set of commands. It does not hurt to
have a few video games which the students can
play during off hours.
Although the Apple has a wide variety of
languages that could be used, we selected Apple-
soft, which is a floating point version of BASIC.
Students who take the course have already been
exposed to computers and we generally found that
the students can be brought up to speed (including
Copyright ChE Division, ASEE. 1984


CHEMICAL ENGINEERING EDUCATION


W


ChE_-K-









the use of graphics) in about two laboratory
sessions. These sessions generally involve stepping
through the tutorial manuals rather quickly. Un-
like the manuals written for large computer
systems, these manuals are very well written and
quite easy for the students to follow. An important
advantage of an interpretive language like BASIC
is the ease with which small programs are written,
edited, and debugged. The students can write and
use mostly their own programs and yet run the
experiment within the time allocated.
In addition to the computer, a disk drive allows
students to store their programs and data. Each
student is issued a diskette for his exclusive use.
For converting the Apple to a data acquisition
device, two 'cards' which plug into the mother
board of the Apple were added. One is a real-time
clock which enables timing of the data acquisition.
The other is an A-D/D-A manufactured by
Mountain Computer which allows sixteen channels
each of analog-to-digital and digital-to-analog con-

TABLE 1
List of Experiments


EQUIPMENT
FIG. USED


EXPERIMENTS*


2 Stirred Pot Calibration of a Temperature
Sensor
Modeling the Dynamics of the
Heated Tank
Feedback Control of Tempera-
ture
3 Pressurized Calibration of Pressure
Tank Sensor
Dynamics of Tank Pressure
On-off Control of Pressure
4 Hot and Cold Calibration of Level Sensor
Water Mixing Dynamics of Tank Level
Tank Feedback Control of Tank
Level
Multivariable Control of Level
and Temperature
5 Heated Bar Data-logging Using a
Multiplexer
Steady state Modeling
Feedback Control of Tempera-
ture
Cascade Control


6 pH Control *

*


Titration Curve Measurement
Feedback Control of pH
Nonlinear feedback Control of
pH


*A detailed manual describing the hardware used and de-
tailing the experiments is available from the authors.


... Washington University undertook the
development of a new laboratory course specifically
designed to teach the principles of process data
acquisition and control using digital computers.
The structure of the laboratory and the
course are discussed in this article.


I To Drain
FIGURE 2. Temperature control experiment.

version. These are limited to 8-bits of accuracy.
For the experiments described here, this was
sufficient. It is estimated that a basic system con-
sisting of the Apple computer, one disk drive, a
monitor, a clock and a AD/D-A board can be pur-
chased for less than $3000 at current market
prices. This, in fact, is the major cost of setting
up the laboratory. The experiments themselves
are homebuilt. Fig. 1 shows the sketch of a typical
computer system configuration.

EXPERIMENTAL SETUPS

The laboratory consists of five experimental
setups, all built by undergraduate students as part
of independent study projects. Figs. 2-6 show the
schematic of each experimental setup and Table 1
lists the experiments performed with these setups.
The stirred-pot experiment shown in Fig. 2 is
perhaps the easiest one to build and work with. The
experiment centers around measurement and
control of the temperature of water in a stirred
coffee pot. The power input in the heating element
can be manipulated by the computer. The students
get a chance to develop some simple dynamic
models and verify the theory by comparison with
experimental data. Also this setup allows the study
of different types of feedback control laws such as
proportional only, PI, and PID.
The pressurized tank setup, shown in Fig. 3,
offers an opportunity to study the behavior of
surge vessels. The dynamics are easy to model and
verify experimentally. The solenoid valves allow


SUMMER 1984









on-off control of tank pressure. The needle valves
allow the time constants to be adjusted. This ex-
perimental setup is adapted from a similar ex-
periment at the University of California, Santa
Barbara.
Fig. 4 shows the schematic of an experiment to
study multivariable control. This setup is dis-
cussed extensively in the recent book by W. H. Ray
on advanced process control. The setup is used
initially to study control of level alone and then
to study the simultaneous control of level and
temperature.
Fig. 5 shows the schematic of the heated-bar
setup, another experiment that was adapted from
the University of California at Santa Barbara.
This setup introduces the concepts of multiplexing
(using one channel to collect multiple data) ; it
also enables the study of cascade control systems
where the temperature at one end of the bar is
controlled by adjusting the set point of an inner
temperature control loop.
The pH control setup shown in Fig. 6 was built
to demonstrate the effect of nonlinearities in feed-
back control. A simple nonlinear feedback
controller can be designed to achieve good pH
control in this case.
Additional equipment in the laboratory include
a small analog computer which allows one to do
hybrid computing. For example a simple third
order process can be simulated on the analog con-
troller and then hooked up with the digital com-
puter for feedback control study.

COURSE OUTLINE

This course is taken mainly by seniors in
chemical engineering and SSM (systems science
and mathematics). It is assumed that the students
have been exposed to a course in control so that
they are familiar with basic concepts of feedback
control, block diagrams representation, and trans-
fer functions. The course, which consists of one
hour lecture and three hours of laboratory, covers
the topics shown in Table 2. Note that we give the
students some exposure to advanced control such as
feedforward, cascade, and multivariable control.
During the last few weeks of the course, lecture
time is devoted to cover topics of special interest
to the students. Students are required to complete
a project which may involve the design of new ex-
periments with the existing equipment or by build-
ing new setups. This gives them an opportunity to
explore any one aspect of the subject area in a little
more depth. O


ATMOSPHERE

FLOWMETER


AIR SUPPLY


FIGURE 3. Pressure control.

TABLE 2
Course Outline


WEEK LECTURE
1 Programming in Basic,
Programming the Apple
Computer
2 Introduction to Real-Time
Programming
3 Basics of Signal Pro-
cessing A/D-D/A
Conversion Funda-
mentals
4 Modeling of Dynamic
Systems
5 Feedback Control
of Processes


6 Analysis of Feedback
Control Systems
7 Feedforward Control
8 Cascade Control
9 Multivariable Control
10 Current Methodology of
Computer Control

11-14 Advanced Topics of
Special Interest such as
Fast Fourier Transform,
Digital Filtering,
Identification, Multi-
tasking, Computer
Architecture, etc.


CHEMICAL ENGINEERING EDUCATION


LABORATORY


Experiments using the
Real-time Clock
Calibration of Tempera-
ture Sensor


Dynamics of the
Temperature Sensor
Modeling and Control
Experiments based
on each of the Setups
in the Lab.


" /


Implementation and
Testing of Advanced
Control Methods
Project










ACKNOWLEDGEMENTS
The authors would like to express their sincere
appreciation to the National Science Foundation,
the Apple Foundation and the School of Engineer-

Hot Water
/ Solenoid
TP T ^Cold Water /
T I


I I I

0 PTo Drain
II L
L -J
IL -Z Computer

FIGURE 4. Temperature and level control.


INSULATION


HEATING TAPE

FIGURE 5. Heated bar experiment.


FIGURE 6. pH control experiment.


ing at Washington University for providing
financial support for the laboratory through equip-
ment grants. Special thanks to our student, Dale
Millard, who worked diligently on the hardware
for the experiments and invented the power-
controller circuit.

REFERENCES

The following books are used as reference
material for the course.
1. Real Time Computing, D. A. Mellichamp, Editor, Van
Nostrand Reinhold Co., New York (1983).
2. Computer Process Control, by P. Deshpande and R. H.
Ash, ISA Publications (1981).
3. Digital Computer Process Control by C. L. Smith,
Intext Publication (1972).
4. Minicomputers in Industrial Control, T. J. Harrison,
Ed., ISA Publications, Instrument Society of America
(1978).
5. Microcompressors for Measurement and Control, by
D. M. Auslander and P. Sagues, Osborne, McGraw-
Hill (1981).
6. Process Modeling, Simulation and Control for Chemi-
cal Engineers by W. L. Luyben, McGraw-Hill (1973).


S ,[book reviews

CHEMICAL AND PROCESS
THERMODYNAMICS
by B. G. Kyle
Prentice-Hall, Inc., 1984, xvi + 512 pgs. $37.95

Reviewed by Truman S. Storvick
University of Missouri-Columbia

It appears that all chemical engineering
thermodynamics textbooks are created equal. Each
author intends to provide the student with an
introduction to the subject and to show how spe-
cific applications in process design calculations
can only be done by careful applications of the
principles of equilibrium thermodynamics. Be-
cause this subject is the foundation of all chemical
engineering, there have been many books written
on the subject.
Professor Kyle has done what all authors have
done with this subject the past two decades. He
has taken the basic ingredient list assembled by
Dodge [1] and by Hougen and Watson [2] and
brought it up to date with new experimental data
and worked examples. The ordering of the topics
is not the same as one finds in the textbooks
written by Smith and Van Ness [3] or by Sandler
Continued on page 145.


SUMMER 1984










NE classroom


KINETICS AND CATALYSIS DEMONSTRATIONS


JOHN L. FALCONER AND
JERALD A. BRITTEN
University of Colorado
Boulder, CO 80309

C CLASSROOM DEMONSTRATIONS ARE valuable ad-
ditions to a lecture course in kinetics and
catalysis. Over the last few years we have used
a number of short demonstrations in class to show
that catalysts can dramatically increase the rates
of chemical reactions. These demonstrations are
also used to show the different types of catalysts
and their properties and the effects of temperature,
concentration, and heat transfer on reaction rates.
We have found, however, that videotapes of these
demonstrations have many advantages over live
demonstrations:

Noise, odor and safety are all controlled for a video-
taped demonstration
Chemicals and solutions, which can degrade in a
year, do not have to be reordered or remade each
year
Time is not spent setting up gas cylinders, beakers,
hot plates, liquid nitrogen dewars, safety shields and
so forth in a classroom. Setup of a VCR machine
and a TV screen takes very little time
Smaller and safer quantities of chemicals can be
used. A 50 ml beaker will fill the entire TV screen
when a zoom lens is used, and a white background
makes color changes easily visible. Thus, a better
demonstration results by videotaping a reaction in
a 50 ml beaker than for a live demonstration with
a 500 ml beaker
An elevated 21-inch TV screen can be easily seen
by all students in the class
Videotaped demonstrations are guaranteed to work
on the first try

Short descriptions of each of the demon-
strations that we have videotaped and shown


A more dramatic demonstration
of hydrogen oxidation results when the
oxygen concentration is increased by using pure
oxygen instead of air.... The mixture reacts
explosively, and very loudly.

Copyright ChE Division, ASEE 1984


during the semester are presented. Because we
cover a range of topics in the lectures, demonstra-
tions are shown for acid and zeolite catalysis,
solution catalysis, and supported and unsupported
metal catalysis. In general, these are not new
demonstrations; they have been described pre-
viously and are compiled here for easy use. The
resulting videotapes are not professional quality,
but they demonstrate the important points very
effectively. Note that many of these reactions are
dangerous and must be done carefully in a hood
and with safety glasses.

1. CLOCK REACTION
This is the standard kinetics demonstration
that can be used to show the effects of temperature,
concentration and a catalyst on the rate of re-
action [1, 2]. Fifty ml of solution A and 50 ml of
solution B are combined in a 250 ml beaker. Then,
50 ml of solution C are added, and the mixture is
stirred until reaction is complete, as indicated by
a color change from cloudly to blue. For the
solution concentrations listed below, at room
temperature the blue starch complex forms after
25 s.
Since the reactions are not first order, reaction
time is increased significantly by addition of
distilled water to the mixture. Similarly, reaction
time is decreased by heating above room tempera-
ture. By adding a small amount of FeSO, solid,
which acts as a catalyst [2], reaction time is de-
creased to 10 s.

Solutions
A: 5.5 g (NHj) 2S20 dissolved in distilled
water to yield one liter of solution;
B: 0.13 g NaS2Os,5H20 dissolved in distilled
water to yield one liter of solution;
C: 50 ml KI dissolved in 600 ml of 10% po-
tato starch solution, which is then diluted
with distilled water to one liter.

2. OSCILLATING REACTION
This demonstration, which has been called the
color blind traffic light [3, 4], shows the unusual


CHEMICAL ENGINEERING EDUCATION






















John L. Falconer is Associate Professor of chemical engineering at
the University of Colorado, where he has been since 1975. He has a
BS from Johns Hopkins University and a MS and PhD from Stanford
University. His research interests are in heterogeneous catalysis on
metals and the applications of surface analysis techniques to the
study of catalytic reactions. (L)
Jerald A. Britten is a PhD student in the Department of Chemical
Engineering at the University of Colorado. He completed his BS at
Michigan State in 1979 and his MS at Colorado in 1981. His PhD
thesis work involves modeling of instabilities in combustion in porous
media. (R)

behavior that can occur in a complex reaction
system. It is easy to prepare and is described in
detail by Lefelholz [3] and Boulanger [4]. It can
also be used to show the effects of temperature and
concentration on reaction rates.
The following solution is prepared in 3 N
H2SO :
0.005 M ceric ammonium sulfate
(Ce (NH4) (SO4) 42H20);
0.1 M malonic acid (CsH404) ;
0.05 M potassium bromate (KBrOs).
This solution is heated with agitation to 40C and
about 40 drops of the redox indicator ferroin
(1,10-phenathrolein ferrous sulfate complex) are
added dropwise. The solution immediately begins
to change color from violet to blue and back to
violet, with a period of about 50 s, as the concentra-
tions of Ce 3 and Ce4+ oscillate periodically. The
ferroin changes color as the oxidation state of Ce
ion changes. The color change is clearly recorded
by the camera against a white background. The
period of oscillation depends on the degree of
agitation provided by a magnetic stirrer, and is
lengthened to 72 s upon addition of about 2 ml of
indicator added at once. The solution concentra-
tions are not critical but a single portion of ferroin
added at once can create a long induction period
[4].
3. HYDROGEN OXIDATION IN AIR
Oxidation of hydrogen in air over supported
metal catalysts is used to show activity differences


of metals and the increase in rates that occurs
with increased surface area. This demonstration
also shows how heat removal can be limiting for
exothermic reactions on supported catalysts.
A half-inch diameter, vertical brass tube is
used to support a wire mesh screen on which a
piece of tissue paper is placed. A catalyst sample
is placed on top of the tissue, and hydrogen from
a gas cylinder is flowed into the bottom of the tube
through a tygon tube. For 0.3 g of a 5% nickel/
silica catalyst, nothing is observed. Similarly for
0.3 g of pure platinum wire, no visible indications
of reaction are seen. However, when a 0.3 g sample
of a 5% platinum/silica catalyst is placed on the
tissue, significant reaction occurs. The heat re-
leased by the reaction heats the catalyst until it
glows red, and after less than a minute the tissue
paper ignites. Small quantities of catalyst and thus
low flow rates of hydrogen can be used, since the
camera zoom lens is used to fill the screen with the
catalyst and make this demonstration visible.
4. HYDROGEN-OXYGEN EXPLOSION
A more dramatic demonstration of hydrogen
oxidation results when the oxygen concentration
is increased by using pure oxygen instead of air
[5]. A 6-oz taped bottle is filled with approxi-
mately a 2:1 mixture of H2 and 02 and then sealed
with a rubber stopper. The exact ratio is not
critical. The stopper is then removed and approxi-
mately 0.1 g of powdered, supported platinum
catalyst is dropped into the bottle from a spatula.
The mixture reacts explosively, and very loudly.
When a piece of white paper is taped to the back
of the bottle and low background light is used, a
flame is seen shooting out the top of the bottle.
This demonstration shows that catalysts can dra-
matically increase reaction rates; the reaction is
extremely slow at room temperature in the ab-
sence of a catalyst. It can also be used to show the
effect of surface area since a platinum wire
dropped in the bottle does not cause an explosive
reaction.
Larger bottles (10 oz and 15 oz) have been used
for this demonstration, but they are not safe for a
classroom demonstration because the noise is al-
most deafening. This demonstration should be done
with great care; the platinum catalyst must be
completely cleaned out of the bottle before a repeat
experiment is attempted.
5. ACID-BASE PROPERTIES OF SOLIDS
The fact that many solid oxides which are used
as catalysts or catalyst supports have acidic sites


SUMMER 1984








and basic sites is easily shown using indicators for
powders suspended in solution. No quantitative
measure of acid strength is made, but the presence
of acidic and basic sites and the differences be-
tween oxides are easily shown.
A series of 250 ml beakers are each filled with
50 ml of distilled water which contains a small
amount of dissolved bromothymol blue indicator.
This indicator changes from yellow to blue over a
pH range from 6.0 to 7.6. In our case it was yellow
in distilled water. Ten to fifteen grams of a
powdered oxide (y-zeolite, SiO,'Al1Os, TiO2, A1203,
MgO and SiO,) are added to each beaker. Malonic
acid and sodium hydroxide are also added to two
beakers to show the similarity between liquid acids
and bases and solid acids and bases.
The malonic acid produces no color change. The
zeolite powder produces a dirty-yellow, cloudy ap-
pearance in the solution, which turns light green
over a period of minutes. The silica-alumina
powder does not change the color of the solution
significantly. The titanium dioxide powder forms
a milky suspension with the water, with a slight
blue-green tinge. Alumina powder changes the
solution to a deep blue-green color. Magnesia
powder produces a deep blue when added. The
NaOH solution turns the indicator solution a very
dark blue. Two samples of powdered SiO, were
used. One caused no appreciable color change of
the solution, indicating acidity, while the other
sample turned the solution a dirty blue-green of
intensity less than that of the A1203 mixture.
Differing treatment histories of these silica
samples are probably the cause of this discrepancy.
The acid-base properties of most of these solids
are strongly dependent on such factors as tempera-
ture, duration of heat treatment, and the amount
of adsorbed water. The order of acid strength
given for these solids will be different if a non-
polar solvent is used instead of water [6]. Water
interacts significantly with solid surfaces and can
alter the acidic character. Impurities in the solids
can also affect acidity. For example, aluminas are
usually weakly acidic, but this can be enhanced sig-
nificantly by impurities such as a chloride. Some
commercial aluminas are basic, in that a sus-
pension in water exhibits a pH above 7, which is
caused by the presence of sodium.

6. HIGH-TEMPERATURE ZEOLITE REACTIVITY
A rare-earth exchanged x-zeolite can be used
to show the properties of solid acids for hydro-
carbon cracking [7]. Three and one-half grams of


paraffin wax are placed in each of two 50 ml
beakers and heated with a hot plate to 260C. At
this temperature, the wax is a liquid. Into one
beaker is dropped one gram of the zeolite powder,
and into the other beaker SiO2 or SiO,'AlO
powder is added. A slight bubbling is seen for
silica or SiO2AlOs,, but vigorous reaction occurs
almost immediately for the paraffin in contact with
the zeolite. When both beakers are cooled after a
few minutes of reaction, the paraffin in the zeolite-
containing beaker has turned dark, while the para-
ffin in the other beaker has not. This demonstration
is particularly convenient on videotape since it is
not necessary to wait in class for the cooling to
occur. Also, a rather unpleasant odor is given off
by the hot wax, and 50 ml beakers minimize this.
These small beakers would be difficult to see in a
live demonstration, however.

7. LOW-TEMPERATURE ZEOLITE REACTIVITY
The ability of catalysts to accelerate reactions
even at very low temperatures is shown by iso-
prene cracking below -1460C [7].
Approximately 5 ml of isoprene (2-methyl-1,3-
butadiene, m.p. -146C) in a test tube are frozen
by immersion in liquid N2 for about one minute.
The test tube is mounted on a stand in front of a
white background for good contrast, and a gram
of baked zeolite powder is poured into the tube
on top of the solid isoprene. As the isoprene melts
and contacts the zeolite, it immediately cracks and
turns a light brown color. When a powdered silica-
alumina catalyst is used, the isoprene remains
colorless. The color change of the zeolite-contacted
isoprene is pronounced enough to be easily re-
corded by the camera, providing that ice, which
deposits on the side of the tube after removal from
the LN2 bath, is periodically wiped off. A more
pronounced color change, with the formation of a
black solid, occurs when two grams of baked zeolite
are added to 5 ml of isoprene. Also, some spatter-
ing of the zeolite occurs. With more zeolite, a
violent reaction occurs and the entire mass turns
black [7].

8. COPPER CATALYSIS OF NH3 OXIDATION AND
SODIUM PEROXIDE DECOMPOSITION
This demonstration, described by Koch [8],
shows both gas-phase and liquid-phase catalysis.
Copper metal is used to catalyze the oxidation of
ammonia, and cupric ion catalyzes the decomposi-
tion of sodium peroxide. Ammonia is obtained
from 60 ml of concentrated ammonium hydroxide


CHEMICAL ENGINEERING EDUCATION








in a 250 ml flask. Four grams of sodium peroxide
are slowly added and some decomposition takes
place. A cone of copper (made from a circle of
copper foil) of approximately one inch diameter
is heated to a red glow and suspended in the flask
about two inches above the liquid surface. The
cone is suspended from a wire through a hole in
the top of the cone. The hot copper catalyzes the
oxidation of gas-phase ammonia to NO and HO
[8]:
4NH, + 50, 4NO + 6H20
2NO + 02 -> 2NO, and so forth.
The cone continues to glow as heat is generated by
the oxidation reaction.
The generation of oxygen can also be catalyzed
by the addition of 1 M copper sulfate, since cupric
ion catalyzes the decomposition of sodium perox-
ide:
2Na,0, 2NaO + 02.
A drop of the copper sulfate solution will increase
the rate of oxygen production significantly. An
almost detonating mixture can be formed [8].

9. AMMONIA OXIDATION AND REACTOR STABILITY
An experiment that is similar to the previous
one can be used to demonstrate both catalytic ac-
tivity and reactor stability. Hudgins [9] described
this experiment in detail, and it will be only briefly
summarized here. Concentrated ammonium hy-
droxide solution is placed in the bottom of a 200
ml erlenmeyer flask, and a copper wire is heated
to incandescence and suspended above the solution.
Copper wires of different diameters (No. 12, 18,
24), were used; the smallest wire melts, and the
glow of the largest wire very slowly diminishes.
The No. 18 wire, however, continues to glow for
some time. Hudgins [9] indicated these results for
different size wires demonstrate control of a
catalytic reaction by heat transfer across a film.
However, it appears that the heat and mass
transfer coefficients increase as the wire diameter
decreases for a horizantal wire [10]. Thus, this re-
action may be controlled by mass transfer.
To demonstrate reactor stability, the wire is
withdrawn from the flask and then quickly re-
placed when the glow fades; the wire starts glow-
ing again. A larger perturbation in temperature
extinguishes the glow. This demonstration can also
be used to show that transient temperatures are
easily produced in catalyst particles with exo-
thermic reactions [9]. The glowing wire shows up
extremely well on videotape.


10. OXIDATION OF TARTARIC ACID
This is an excellent example of solution cataly-
sis, the role of a complex as an intermediate, and
the effect of temperature on reaction rate [11].
Color changes, which indicate the presence of an
intermediate, are marked and show up well on the
videotape when filmed against a white background.
A 0.3 M aqueous solution of potassium sodium
tartrate (KNaC4H6O6-4HO) is prepared, and 300
ml are mixed with 100 ml of 6% HO22 in a 700 ml
beaker on a stirred hot plate. The tartrate solution
is heated to 50'C with magnetic stirring, and 25
ml of a 0.3 M aqueous CoCl2 solution is added. Im-
mediately after addition of the cobalt, the solution
is light pink. After a few-second induction period
the solution changes to a dark green as a cobalt-
tartrate complex is formed as an intermediate.
The oxidation of tartrate is evidenced by the vigor-
ous evolution of CO, gas. This frothing necessi-
tates use of the large beaker. As the reaction goes
to completion and gas production stops, the solu-
tion returns to its original light pink hue as the
original cobalt is reformed. The total time of the
reaction, as measured by this color change, is
133 s. At 60C the induction time is markedly
shorter, the reaction more vigorous, and the re-
action time measured by the color change is 63 s.
No reaction is observed before addition of the co-
balt solution at either temperature.

11. CATALYST PREPARATION
The various steps in preparation of a sup-
ported nickel catalyst by impregnation were video-
taped over several days, so that the preparation
steps can be condensed into a few minutes of tape.
This videotape shows how promoters and nickel
salts are added from solution by incipient wetness,
and it shows the rapid uptake of water by a porous
solid. Samples of the support after various stages
in the preparation are also shown in class.

12. ADDITIONAL DEMONSTRATIONS
Other demonstrations that may be useful in-
clude Raney nickel oxidation, to demonstrate the
high reactivity of a high surface area metal, and
silica gel preparation from solution.
We usually include a laboratory tour to show
the equipment used for catalysis research in
chemical engineering. We plan to videotape the
operation of this equipment so that the class will
have a better idea of its purpose and use. At
present, this lab tour includes an Auger spectro-


SUMMER 1984









meter, an XPS spectrometer, a static chemisorp-
tion apparatus, differential reactors with gas
chromatography, a mercury porosimeter, and a
temperature-programmed desorption system.
Since we also discuss bulk and surface struc-
tures and Miller indices notation, cork ball models
have been used for these structures. Close-up video-
tapes of the various structures and of zeolite struc-
tures will allow students to study them at their
leisure. The bulk structures that demonstrate
Miller indice notation were prepared using tem-
plates for the different symmetries [12].


SUMMARY

Eleven kinetics and catalysis demonstrations
have been briefly described. By videotaping these
demonstrations, we are able to easily use them each
year in a catalysis and kinetics course. Videotaping
improves the demonstrations, makes them more
visible and safer, and results in better use of class
time. O]


ACKNOWLEDGMENTS

We would like to thank John Ma for his help
on some of these demonstrations and Professor
David E. Clough for obtaining the videotaping
system and encouraging us to use it.


REFERENCES

1. Steinbach, 0., F. King and V. Cecil, Experiments in
Physical Chemistry, American Book Co., 256 (1950).
2. Alyea, H. N., Tested Demonstrations in Chemistry,
5th ed., 179 (1955).
3. Lefelholz, J. F., J. Chem. Ed. 49, 313 (1972).
4. Boulanger, M. M., J. Chem. Ed. 55, 584 (1978).
5. This demonstration is similar to one used by R. J.
Madix at Stanford.
6. Tanabe, K., Solid Acids and Bases, Academic Press,
New York (1970).
7. Weisz, P. H., Chemtech, p. 498 (August 1973).
8. Koch, B., University of Northern Colorado, un-
published report, 1982.
9. Hudgins, R. D., Chem. Eng. Ed. 9, #3, 138 (1975).
10. Welty, J. R., C. E. Wicks, and R. E. Wilson, Funda-
mentals of Momentum, Heat and Mass Transfer, pp.
357-358 (1976).
11. Ruda, P. T., J. Chem. Ed. 55, 652 (1978).
12. Chalmers, B., J. G. Holland, K. A. Jackson and R. B.
Williamson, Crystallography: A Programmed Course
in Nine Modules, Educational Modules for Materials
Science and Engineering, Pennsylvania State Uni-
versity, 1978.


REVIEW: Fluidized-Bed Processes
Continued from page 109.
The book is intended mainly for use by final-
year undergraduate students or graduate students
in chemical engineering. In view of its contents,
however, the book should be regarded more as a
reference monograph than as a classroom text.
The book will also be a useful reference for re-
searchers, development engineers, and designers
in the field of fluidization technology. In fact, the
book can be recommended to anyone who wishes
to be initiated into the science and art of fluidized-
bed chemical processes.
The book is indeed concise, containing only 222
pages. Obviously it is extremely difficult, if not
impossible, to cover all aspects of fluidized-bed
chemical processes in detail in a book of this size.
Unfortunately, some topics of current importance
are omitted. Examples are the stochastic be-
havior of fluidized-bed chemical processes and the
performance of relatively shallow and wide
fluidized bed (or the so-called horizontal fluidized
bed). According to Bukur, Carem and Amundson
(Chapter 11 of Chemical Reactor Theory: A Re-
view, Edited by Lapidus and Amundson, Prentice-
Hall, Inc., Inglewood Cliffs, NJ, 1977), "It is our
view that probably no deterministic model will
ever describe such reactors with any precision."
The horizontal flow fluidized beds have been used
extensively to process solid materials because
these fluidized beds tend to yield better quality
and higher conversion of solid products than con-
ventional vertical fluidized beds. O

PROBABILISTIC ENGINEERING DESIGN:
PRINCIPLES AND APPLICATIONS
by James N. Siddall
Marcel Dekker, Inc., 1983; 544 pages, $65.00
Reviewed by Ernest J. Henley
University of Houston
Probabilistic design and risk analysis have
been my 'bread and butter' research activities for
the past fourteen years. It's been a lonely road:
most chemical engineering academicians appear to
have convinced themselves, and each other, that
the path to the podium lies in double-precision, de-
terministic models (based, frequently, on experi-
mental evidence as reliable as the Las Vegas
gaming tables). At our shop, the required BS
course in statistics has gone the way of under-


CHEMICAL ENGINEERING EDUCATION









graduate literacy and the PhD language require-
ment. Indeed, I have become so inured to this bias
that I was genuinely delighted to receive Professor
Siddall's book, "Probabilistic Engineering De-
sign," for review from the editors of this esteemed
journal. At long last; somebody cares!
Before editorializing further, let me describe
what is in this book and its strong and weak points.
Chapters 2-5, in the author's words, "provide a re-
view of the necessary material and background for
the text." These 145 pages describe the concepts
and theorems of probability, probability distribu-
tions, moments of a distribution and generation
of probability density functions. The level of
scholarship is high, the presentation is excellent
and the examples are interesting, current, and
pertinent. Although I find myself occasionally
disagreeing with Professor Siddall, I admire his
courage in telling it like he sees it. For example,
only in the Appendix do we find a (brief) discus-
sion of confidence limits for distributions because,
the author tells us, engineering intuition is a better
basic tool in risk decision making.
The rest of the chapters cover: (6) Probabilis-
tic Analysis (Primarily Monte Carlo and moment
relationships) ; (7) Sequential Events (Markov
chains, Monte Carlo, Random Time Functions);
(8) Order Statistics and Extreme Values; (9, 11,
12) Reliability and Failure Modes; (10) Design
Options (only 14 pages) ; (13) Optimization
(four pages only).
From page 145 on, the treatment and topics
become somewhat uneven. Professor Siddall, at
times, looses patience with his readers. Advanced
Monte Carlo methods are developed in detail;
basics are almost ignored. The author assumes
that the reader is sufficiently familiar with
Lagrangian multipliers and Newton-Raphson
techniques that he uses them without explanation
(or listing them in the index). Markov chains are
accorded one paragraph: we are told that problems
that can be solved by Markov methods are better
solved by Monte Carlo. One of Professor Siddall's
research interests, E. T. Jaynes' maximum en-
tropy principle, is accorded quite a bit of space in
this text. Personally, I feel the same way about
the maximum entropy principle as the author feels
about Markov methods, but why should we agree
on everything?
A very nice feature of this book is the copious
computer programs which appear throughout.
Also, a well documented, 105-page software pack-
age for probabilistic design forms one of the Ap-


pendices.
This is an excellent, well-written, interesting
book. I enjoyed it, and I am unabashedly pleased
to have been cited four times in the Author Index.
The crying shame of it all is:
a) The publisher printed it on cheap paper
from typed, hard-to-read copy. The equa-
tions occupy too much space, and the price
($65.00) is outrageous.
b) Every chemical engineering curriculum
should have a required course based on the
material in this book: none do. Of course,
there is no room for this, and many other
things, in our aborted four-year curricu-
lum. If we went to a five- or six-year cur-
riculum there would be; and, if we did this,
then maybe the Copley Square Hotel in
Boston would not have the Chutzpah to
give its head janitor the title of "Engineer-
ing Consultant." E

REVIEW: Process Thermodynamics
Continued from page 139.
[4], for example. Ordering the presentation may
be more a matter of style than pedagogical
necessity.
The first eight chapters, or about one third
of the book, cover the first law, second law, pvT
behavior, thermal effects and the calculation of
the thermodynamic properties of matter. The
classical Carnot engine-Clausius inequality de-
velopment of the entropy function is used in this
treatment. Phase equilibrium and chemical equi-
librium each occupy about 100 pages of material.
The last 100 pages are given to thermodynamic
analysis of processes, physico-mechanical pro-
cesses and compressible fluid flow. The text is care-
fully crafted and free of troublesome production
errors. There are numerous worked examples and
the list of exercises for students seems adequate.
"One may reasonably ask, 'Why another book
on thermodynamics; are there not more than
enough on this subject now?'" is the opening
sentence in the preface to B. E. Dodge's book.
Forty years and many textbooks later Professor
Kyle has written another traditional chemical
engineering thermodynamics textbook. We all
agree on the major topics and tradition may have
bound us to small variations in development and
presentation. If you are using one of the widely
adopted textbooks in your course this book could
serve you. The best textbook for me and for you
is the one our students can read and that matches


SUMMER 1984









our teaching style. Professor Kyle has given us yet
another option in that tradition. O

References
1. B. F. Dodge, Chemical Engineering Thermodynamics,
McGraw-Hill, New York, 1944.
2. Hougen, O. A. and K. M. Watson, Chemical Process
Principles, Parts I and II, John Wiley, New York,
1947.
3. Smith, J. M. and H. C. Van Ness, Introduction to
chemical Engineering Thermodynamics, Third Edi-
tion McGraw Hill, New York, 1975.
4. S. I. Sandler, Chemical and Engineering Thermo-
dynamics, John Wiley, New York, 1977. O

LOST-WORK STATEMENTS
Continued from page 131.
reversible path that brought the system from State
1 to State 2. But if that path produced useful work,
we could have stored it and used it to partly offset
the work of restoration; if it produced no useful
work, then all of the work of restoration must be
supplied externally. Hence the thermodynamic
lost work, as apparently first stated by Van Ness
[14] is the work to restore the system minus the
external work produced.
We can now proceed to complete Table 1, which
shows the differences in properties of the two
definitions of lost work. The first question is
whether they are unambiguously defined for non-
isothermal systems. From the definitions in terms
of dSirr, it is easy to see that LWt is unambiguously
defined for a non-isothermal system because the
system temperature does not appear in its defini-
tion (only the infinite surroundings temperature
does). The system temperature is implicitly
present in the dSirr term, but that is unambiguous.
On the other hand, LWm has a T in its definition
in terms of dSirr. If that T is constant, both in
space and in time, then the definition is unam-
biguous. But if it is not, then there is no un-
ambiguous definition of LWm. For example, we
could consider the irreversible flow of heat through
a solid conductor from a reservoir at Th to one at


T,. Here


1
dSirr = dS = dQ (
T,


1
Th )


To TO
dLWt = TodSir, = dQ ( To To)
T, Th


dLWm = TdSi,. = dQ (
Tc


T
T )


(14)


(15)



(16)


LWt is perfectly unambiguous, but LWm is only de-
fined if we can define a proper value for T. We
could set it equal to Te, in which case LWm is equal
to the work that would have been produced by a
Carnot engine withdrawing dQ of heat from the
high-temperature reservoir and operating between
Th and T,. Or we could set it equal to Th, in which
case LWm would be equal to the amount of work
that a Carnot engine would produce by withdraw-
ing (Th/Te) dQ of heat from the high-temperature
reservoir and rejecting dQ of heat to the low-
temperature reservoir. One could persuasively
argue for either of these values or perhaps for
some intermediate one. The point is that there is
no obvious or unambiguous definition of LWm for
this case. Van Wylen and Sliepcevich have tried to
deal with this problem. Van Wylen [16] says
In summary, the lost-work concept assumes that
there is a reservoir available at the temperature T re-
quired for the given situation. The concept of irreversi-
bility assumes heat transfer with the surroundings only
at temperature To.
Here he is clearly referring only to LWm and does
not mention the existence of the other definition
(LWt). Van Wylen uses another quantity which he
calls irreversibilityy" which is identical to what we
call LW,.
Sliepcevich [11] says

It is apparent that the evaluation of the terms
8(Qj/T1) and (alw/T) in Eq. (4-155) [a general entropy
balance] will pose certain difficulties either if the
temperature of the system is not uniform throughout
or if the temperature, even though uniform throughout,
changes during the process.

and also
Note that the latter [Eq. 4-193, a steady flow entropy
balance using LWm] cannot be solved explicitly for
(dQi) or (dLW)i unless the temperature of the system
T is constant and uniform throughout, in which case,
Ti = T = Ti = To. For this very special case, Eq. 4-193
yields....

These three statements must surely have con-
vinced any practitioner that the lost work
definition to which they apply, (LWm), is of very
little, if any, practical utility.
The next line on Table 1 asks whether the two
values of LW are computable without reference to
the surroundings temperature. LWm obviously is
because in its definition, nothing related to To ap-
pears. One unit of mechanical work converted to
internal energy has the same value of LWm
whether it is at the temperature of the sun or that
of liquid helium. On the other hand, LWt cannot be


CHEMICAL ENGINEERING EDUCATION








computed independently of the surroundings
temperature. If the surroundings temperature is,
for example, 20C, then the conversion to frictional
heat of one unit of mechanical work has a value of
LWt less than one unit for system temperatures
greater than 20C and more than one unit for
system temperatures lower than 200C.
To close this section, consider a non-thermo-
dynamic analogy that may clarify the distinction
between the two kinds of lost work. If one drops
a bottle of wine on his kitchen floor and the bottle
breaks, then he has certainly lost the wine. The
LWm is analogous to the assertion that what is lost
is the wine. The LWt is analogous to the assertion
that not only is the wine lost, but also someone
must clean the kitchen floor.

REVERSIBLE WORK OR
COMBINED-LAW STATEMENTS
To consider the next line in Table 1, we must
introduce the idea of the reversible work, or the
combined first- and second-law statement. We be-
lieve that the simplest way to show such a state-
ment is to begin with open-system, unsteady-state
energy and entropy balances,
d(mu),,, = hjdmj + dQi dW (17)

dQi dLWt (18)
d (ms),,, = sjdmj + + (18)
j Ti To
Then we multiply Eq. (18) by To and subtract it
from Eq. (17), finding (after rearrangement)

dW + dLWt = I (h Tos)jdm + (1 To ) dQi
i Ti
-d [m(u Tos) ],, (19)
or, in terms of the availability function (b = h
- Tos),

dW + dLWt = Y bjdmj + 1 (1 To) dQ,
j i Ti
-d [m(b Pv) ],, (20)
The sum of the two terms on the left of the
equal sign is the reversible work
dW, e = dW + dLWt (21)
for a process occurring in the system and having
the same initial and final states of the system, the
same flows of matter in and out, and the same ex-
changes of heat at all temperatures except To.
This equation has the remarkable property of
showing that the sum of two path functions (dW
and dLWt) form a state function.
Here we use the term "state function" in a


somewhat broader sense than it appears in many
thermodynamics texts. There it refers to a
property of a fixed mass of matter, like entropy,
showing that the changes of this property depend
only on the initial and final states of the system,
and do not depend on the path taken to get from
the initial to the final state. Here we expand that
idea to include the possibility that there is heat
exchange with the system at temperatures other
than To and that there may be flows of matter
across the system boundaries.
The value of dWrev can be computed unam-
biguously for any system using only the terms on
the righthand side of Eq. (19) or (20) ; i.e., the
data on the initial and final states of the system
and the flows of heat and matter across its
boundaries. (It is not necessary to know the value
of dQ at To or of dW.) If we also have data on dW
or on dQ at To, it allows an equally unambiguous
computation of dLWt.
Is the same type of formulation possible for
LWm? Apparently not. If we substitute from Eq.
(13), we find

dW + dLWm = bjdmj + 1 (1- T ) dQi
T,,ys i dTi


-d[m(b Pv)],y,


(22)


but unless the system is isothermal, both over time
and space, there seems no way to evaluate or at-
tach meaning to the lefthand side of Eq. (22).
Thus, in Table 1 we indicate that LWt leads to an
unambiguous combined statement but that LWm
does not.
It is also interesting to ask who introduced Eq.
(20) or its equivalents into engineering. The
fundamental ideas go back as far as Gibbs [7]. The
idea of maximum reversible work, exchanging
heat only with the surroundings at To goes back at
least as far as Gouy [8] and Stodola [13]. Kestin
[9] refers to the basic result as the "Gouy-Stodola
Theorem."
Brown and Sliepcevich [2] show an equation
similar in form to Eq. (20) (using what they
called (lw)o), including terms for kinetic and po-
tential energy but without the terms for a change
in the system nor for heat flows at temperatures
other than To. Martin [10] devotes a considerable
fraction of his thermodynamics slides to develop-
ing equations of the same form and content as Eq.
(20). Denbigh [6] thoroughly works out a batch
equivalent of Eq. (20) and indicates how one
would find the open-system equivalent. Smith and
Van Ness [12] also show forms that are equivalent


SUMMER 1984









to Eq. (20). Certainly others could be cited.

THE UTILITY OF LOST WORK AND
THE COMBINED STATEMENT

As shown elsewhere [4, 5], the lost-work ap-
proach to second-law analysis of processes is
generally simpler than the competing approaches.
Its assumptions and limitations are clearly stated
and can be removed when needed (e.g., one easily
can include terms for kinetic energy, etc.). The
combined statement is one of extreme power and
generality, which should occupy a central place in
any treatment of thermodynamic efficiency.

CONCLUSIONS
The adoption and use of the lost-work concept
has been strongly hindered by the existence, in the
chemical engineering literature, of two very differ-
ent quantities that both bear the name "lost work."
The thermodynamicc lost work" is much more
useful and practical than the "mechanical lost
work." Using the thermodynamic lost work, one
can formulate a combined statement of the first
and second laws, which shows that, although the
actual work and the lost work are path functions,
their sum, the reversible work, is a state function.
This allows the direct computation of the re-
versible work of irreversible processes. D

LITERATURE CITED
1. Balzhiser, R. E., M. R. Samuels, and J. D. Eliassen,
Chemical Engineering Thermodynamics, Prentice-Hall
(1972), p. 139.
2. Brown, G. G., and C. M. Sliepcevich, "Practical
Thermodymics," Chem. Eng. Progress, 48, 493 (1952).
See also Chem. Eng. Progress, 49, 77, for correction
of typographical errors in this paper.
3. Brown, G. G., et al., Unit Operations, John Wiley
(1950), p.137.
4. de Nevers, Noel, "The Two Fundamental Approaches
to Second-Law Analysis of Processes," Proc. Eng.
Fnd. Conf. on Foundations of Computer-Aided Pro-
cess Design, R. S. H. Mah and W. D. Seider, eds., En-
gineering Foundation, N.Y. 1981.
5. de Nevers, Noel, "The Second Way to use The Second
Law," Chemtech, 12, 307-317 (1982).
6. Denbigh, K. G., "The Second-law Efficiency of Chemi-
cal Processes," Chem. Eng. Science, 6, 1 (1956).
7. Gibbs, J. W., "On the Equilibrium of Heterogeneous
Substances," Proc. Conn. Acad., 3, October, 1875, May,
1876. Reprinted in The Collected Works of J. Willard
Gibbs, Vol. 1, Longmans Green, NY, 1928, Equation
54, p. 77.
8. Gouy, M., "Sur les transformations et l'equilibre en
Thermodynamique," (concerning transformations and
equilibrium in thermodynamics), Comptes Rendus,
108, 507 (1889).
9. Kestin, J., "Availability: The Concept and Associated


Terminology." Energy, 5, 679-692 (1980).
10. Martin, J. J., Thermodynamics. Slides and descriptive
text prepared for the American Institute of Chemical
Engineers (1965).
11. Sliepcevich, C. M. et al., "Thermodynamics," in Chemi-
cal Engineers' Handbook, J. H. Perry, Ed., 4th
Edition, McGraw-Hill (1963), p. 4-33.
12. Smith, J. M., and H. C. Van Ness, Introduction to
Chemical Engineering Thermodynamics, Second
Edition, McGraw-Hill (1959).
13. Stodola, A., Die Dampfturbinen, Springer Verlag,
Berlin, 1903, p. 209. (see also later editions and
English translation).
14. Van Ness, H. C., "Thermodynamics for Process Evalu-
ation" Petroleum Refiner, 35, 165-168 (1956).
15. Van Ness, H. C., "Thermodynamics," in Chemical
Engineers' Handbook, R. H. Perry and C. H. Chilton,
Editors, 5th Edition, McGraw-Hill (1973), p. 4-74.
16. Van Wylen, G. J., Thermodynamics, John Wiley, New
York (1959), p. 156 (The same material is continued
in later versions of this text by Van Wylen and
Sonntag).
17. Van Wylen, G. J., and R. E. Sonntag, Fundamentals
of Classical Thermodynamics, Second Edition, John
Wiley and Sons (1976).

NOTATION

b availability function per unit mass
(h Tos), J/kg
h enthalpy per unit mass, J/kg
lw lost work (used in Brown and Sliepcevich
papers), J
(lw)T lost work of an isothermal process (used
in Brown and Sliepcevich papers), J
(Iw) o lost work of a process that exchanges heat
only with the surroundings at To (used in
Brown and Sliepcevich papers), J
LW lost work, J
LWm mechanical lost work, J
LWt thermodynamic lost work, J
m mass, kg
P pressure, pa
Q heat, J
q heat (used in Brown and Sliepcevich
papers), J
S entropy, J/K
s entropy per unit mass, J/kgK
Sirr irreversible entropy production, J/K
T temperature, K
To temperature of the infinite surroundings,
oK
Tsys system temperature, K
Te, Th temperatures of hot and cold reservoirs,
oK
v volume per unit mass, m3/kg
V volume, m3
W work, J
Wrev reversible work, J
WCTH work irreversibly converted to heat or
internal energy, J
WTRS work required to restore a system, ex-
changing heat only with the infinite sur-
roundings at To, J


CHEMICAL ENGINEERING EDUCATION








MASS TRANSFER
Continued from page 127.
results which I give for each case. I make the
major approximation that the reaction is first
order and irreversible, so that things stay simple.
For the single crystal, I might begin with a mass
balance on the ethane near the crystal
d2ce
0 = D d- (15)
dz2
The left hand side is zero because the reaction is
assumed to be in steady state, and no reaction
term appears because the reaction takes place
only at the crystal's surface. After many machina-
tions, I present the result

N1 = C10(16)
N (l/k.) +(1/K) (1)
where N, is reaction rate in moles per crystal area
per time and co is the bulk concentration. The
quantity ki describes ethane mass transfer from
the bulk to the surface: it is a mass transfer co-
efficient. The quantity K2 describes the reaction
rate on the catalyst surface. Thus this process in-
volves two steps in series, and is a chemical analog
to the resistances in series found throughout trans-
port phenomena.
In contrast, if I describe the same reaction in
a porous catalyst, I begin with a mass balance on
the ethane in the catalyst:

0 = D d -K2c (17)
Again, the value of zero on the left hand side indi-
cates steady state, and the diffusion term accounts
for ethane moving into the catalyst pores. Now,
however, a reaction term is present, describing the
same reaction, now being modeled as if it were
homogeneous. The two rate constants are related,
but in a non-trivial way
a
K2 (1/k + (a/K2 (18)
where a is the surface area per volume of the
catalyst, and k, now refers to mass transfer from
the pores' core to the walls. The solution to Eq.
(17) is

N, = (DK') coth K2,d2)o (19)

where d is a length characteristic of the pellets'
size. This is very different than the result reported
in Eq. (16), even though the chemical reaction is
identical. No wonder students get confused.
In my teaching, I try to reduce this confusion
by first lecturing on heterogeneous reactions and
then turning to homogeneous reactions. This split


is artificial, but seems pedagogically effective. In
my discussion of heterogeneous reactions, I use
examples from non-petrochemical areas like
electrochemistry, fermentation, and detergency,
since these nontraditional subjects will be more
important to our present students than they have
been in the past. In the lectures on homogeneous
reactions, I cover the more familiar ground of
catalyst effectiveness and gas treating with re-
active solvents. My presentation is imperfect, but
it seems better now than a few years ago.
Splitting the material on heterogeneous and
homogeneous reactions does clarify the concept of
"diffusion-control." This important area is often
carelessly treated in research, even though it is
incessantly quoted. It means three separate things.
First, for a heterogeneous reaction, "diffusion-
control" means that the reaction rate is not in-
fluenced by chemical kinetics, although it may be
altered by chemical equilibria. The rate for a first
order irreversible reaction is found by letting K2
become large in Eq. (16).
Second, for a homogeneous reaction, "diffusion-
control" means that the reaction rate depends on
both diffusion and kinetics. For the simple case
above, the rate constant as Ks' becomes large can
be found from Eq. (19) to be (DK,') ". Third, in
chemistry, "diffusion-control" refers to a reaction
governed by the Brownian motion in a well-mixed
solution. Entering graduate students in engineer-
ing remember this third definition best.

CONCLUSIONS
I believe that we can improve our teaching of
mass transfer by making three simple changes.
First, we need to use a single, simple definition of
mass transfer coefficients. Such a definition lets
students reinforce their intuition and reduces
problem solution by number plugging. Second, we
need to alter our use of analogies, which is most
easily effected by writing flux equations in more
parallel terms. Third, we need to repeatedly stress
the differences between the mathematical models
used for chemical reactions and the actual chemis-
try of these reactions.
These three changes have improved my teach-
ing. Still, I use them with a convert's pious zeal,
which is infecting. They may not work for you,
but I hope that they will galvanize you into con-
tinuing efforts to make mass transfer seem easier.
After all, the unique parts of our profession de-
serve our finest efforts. [


SUMMER 1984









REFERENCES
1. R. B. Bird, W. E. Stewart, and E. N. Lightfoot,
Transport Phenomena, Wiley, New York, 1960.
2. W. L. McCabe and J. C. Smith, Unit Operations of
Chemical Engineering, McGraw-Hill, New York, 1975.
3. R. E. Treybal, Mass Transfer Operations, McGraw-
Hill, New York, 1983.
4. R. W. Fahien, Fundamentals of Transport Phenomena,
McGraw-Hill, New York, 1983.
5. J. R. Welty, C. E. Wicks, and R. E. Wilson, Funda-
mentals of Momentum Heat and Mass Transfer, Wiley,
New York, 1976.
6. D. K. Edwards, V. E. Denny, and A. F. Mills, Transfer
Processes, McGraw-Hill, New York, 1979.
7. C. J. Geankoplis, Transport Processes and Unit
Operations, Allyn and Bacon, Boston, 1978.
8. C. 0. Bennett and J. E. Myers, Momentum, Heat, and
Mass Transfer, McGraw-Hill, New York, 1974.

NOTATION
a surface area per volume (Eq. 18)
c, concentration of species "1"
Cp specific heat capacity
D diffusion coefficient
f friction factor (Eq. 13)
h heat transfer coefficient (Eq. 12)
ji diffusion flux of species "1"
k mass transfer coefficient
k', k", k"' alternative mass transfer coefficients
(Table 1)
k thermal conductivity
I characteristic "film" thickness (Eq. 1)
n number of moles
N1 interfacial flux of species "1"
p pressure
pi partial pressure of species "1"
q heat flux
t time
v velocity
V velocity of boundary (Eq. 8)
V volume (Eq. 2)
X, mole fraction of species "1"
z position
a thermal diffusivity (Eq. 9)
K2, K2' reaction rate constants (Eqs. 16-17)
L viscosity
v cinematic viscosity
p density
T shear stress

APPENDIX: THREE SIMPLE EXAMPLES
Example 1: Humidification
Water is evaporating into initially dry air in
the closed vessel shown schematically in Fig. 1 (a).
The vessel is isothermal at 25C, so the water's
vapor pressure is 23.8 mmHg. This vessel has 0.8 1
of water with 150 cm2 of surface area in a total
volume of 19.2 1. After three minutes, the air is
5% saturated. What is the mass transfer co-
efficient? How long would it take to reach 90%
saturation?


(a) Humidification
air

cl(t)

water


(b) Packed bed


(c) A gas bubble


Cl(z)


FIGURE 1. Three easy examples. Each situation leads to
a simple problem. In (a) we assume that the air is at
constant humidity except near the air-water interface.
In (b) we assume that water flowing through the packed
bed is well mixed except close to the solid sphere. In
(c) we assume that the liquid is at constant composition
except near the bubble surface.
Solution
The flux at three minutes can be found directly
from the values given
N: = (vapor concentration) (air volume)
(liquid area) (time)
(. 23.8 1 mol 273\,
760 22.4 298 1 O1
150 cm2 (180 sec)


mol
= 4.4-10-8 mol
cm2*sec


(A-l)


The concentration difference is that at the liquid's
surface minus that in the bulk solution. That at the
liquid's surface is the value at saturation; that in
the bulk at short times is essentially zero. Thus
from Eq. (1) we have
4.4.10 mol = k 23.8 1 mol 273 0
cm2sec \760 22.4-10 cm3 298 0


k = 3.4-10-2 cm
sec


(A-2)


This value is lower than that commonly found for
transfer in gases.
The time required for 90% saturation can be
found from a mass balance: (accumulation in
gas phase) = (evaporation rate)

dt Vc = AN, = Ak [c, (sat) cl] (A-3)


CHEMICAL ENGINEERING EDUCATION








The air is initially dry, so
t =0 c1 =0 (A-4)
We use this condition to integrate the mass balance


ce =1-exp[-(kA/V) t]
c, (sat)


(A-5)


Rearranging the equation and inserting the values
given, we find

t v- n 1 C
kA c, (sat)


18.4-103 cm3
cm
3.4-10-2 m- 150 cm2
sec
= 8.3-103 sec = 2.3 hrs


In (1-0.9)


(A-6)


It takes over two hours to reach 90% saturation.
Example 2: Mass Transfer in a Packed Bed
Spheres of benzoic acid 0.2 cm in diameter are
packed into a bed like that shown schematically in
Fig. l(b). The spheres have 23 cm2 surface per
cm3 bed. Pure water flowing at a superficial
velocity of 5 cm/sec into the bed is 62% saturated
with benzoic acid after it has passed through 100
cm of bed. What is the mass transfer coefficient?
Solution
The answer to this problem depends on the
concentration difference used in the definition of
the mass transfer coefficient. In every definition,
we choose this difference as the value at the
sphere's surface minus that in the solution. How-
ever, we can define different mass transfer co-
efficients by choosing the concentration difference
at various positions in the bed. For example, we
can choose the concentration difference at the bed's
entrance and so obtain

0.62 c, (sat) (vo
N1 -062 Cl(sat) (v) k (c, (sat) 0)
a (lA)
0.62 c, (sat) 5 (cm/sec) A
23 (cm2/cm3) (100 cm)A (
where A is the bed's cross section. Thus

k = 1.310-3 cm(A-8)
sec
This definition for the mass transfer coefficient is
infrequently used.
Alternatively, we can choose as our concentra-
tion difference that at a position z in the bed, and
write a mass balance on a differential volume
AAz at this position: accumulation = (flow in
minus out) + (amount of dissolution)


0 = A civo -Cvo
z z+A


I + (AAz)aN, (A-9)
z


Substituting for N1 from Eq. (1), dividing by AAz,
and taking the limit as Az goes to zero, we find


dc, ka
d = [c,(sat) c,]
dzThis is subject to the initial condition
This is subject to the initial condition


z= 0


c, = 0


(A-10)


(A-11)


Integrating, we obtain an exponential of the same
form as in the first example


c = 1 -exp[-(ka/vO) z]
c, (sat)


(A-12)


Rearranging the equation and inserting the values
given, we find


c, (sat)


5 cm/sec In (1- 0.62)
(23 cm2/cm3) (100 cm)


= 2.110-3cm
sec


(A-13)


This value is typical of those found in liquids.
This type of mass transfer coefficient definition is
the same as a log-mean value.
Example 3: Mass Transfer from an Oxygen Bubble
A bubble of oxygen originally 0.1 cm in di-
ameter is injected into excess stirred water as
shown schematically in Fig. l(c). After 7 min,
the bubble is 0.054 cm in diameter. What is the
mass transfer coefficient?
Solution
This time, we write a mass balance not on the
surrounding solution but on the bubble itself
d 4
d (c, 4rr3) = AN1 = -4rrr2k(c (sat) -0)
dt 3
(A-14)
where r is the radius of the bubble at any time, t.
This equation is tricky: c refers to the oxygen
concentration in the bubble, (1 mol/22.41) at
standard conditions; but c (sat) refers to the
oxygen concentration at saturation in water, about
1.5-10-3 mol/1 under similar conditions. Thus
dr c, (sat)
r -=-k c sat -0.034 k (A-15)
dt tt
This is subject to the condition


t = 0 r = 0.05 cm


(A-16)


SUMMER 1984


k = -( n( 1 -
Saz \








so integration gives
r = 0.05 cm 0.034 kt (A-17)
Inserting the numerical values given, we find
0.027 cm = 0.05 cm 0.034 k (420 sec)
= 1.6-10-3 cm/sec (A-18)
Remember that this coefficient is defined in terms
of the concentration in the liquid, and would be
numerically different if it were defined in terms
of the gas phase concentration. E


DEPARTMENT: Syracuse University
Continued from page 105.
voted to an investigation of transport mechanisms
of small molecules in rubbery and glassy polymers,
and to some important applications of these
mechanisms. The applications include the develop-
ment of high-selectivity, high-flux membranes for
fluid separation processes, the design of controlled
drug delivery systems, and the improvement of
adhesion of integrated circuits.
Lawrence L. Tavlarides is conducting research
on chemically reactive turbulent liquid dispersion
and chemical reaction kinetics. The objective of
the research in liquid dispersions is to provide a
fundamental basis for the design and scale up of
extractors and reactors. The microscopic droplet
rate processes of coalescence and breakup are
analyzed with population balance equations and
Monte Carlo simulation techniques. Hydrodynamic
turbulent flow models are also developed to predict
the local turbulent kinetic energy and energy dis-
sipation in mechanically agitated turbulent dis-
persions. Hydrometallurgical solvent extraction in
Tavlarides' group is focused on multiple metal
chelation reactions and chemical equilibria. In-
trinsic chemical kinetic models are developed for
reactions occurring at or near the liquid-liquid
interface using the novel liquid jet recycle reactor.
Thermodynamic based heterogeneous equilibrium
models are also developed. The above simulation
models are employed with the kinetic and equi-
librium models to predict conversion and se-
lectivity. Other studies by this group include
catalyst deactivation by surface carbon to deter-
mine kinetic rate models for synthesis reactions.
Chi Tien's major research activities are in
three areas: fluid-particle technology, liquid phase
adsorption, and biochemical engineering. The
fluid-particle technology research covers a broad
spectrum of topics including deep bed filtration of
liquid suspensions, aerosol filtration in granular


and fibrous media, and in fluidized beds with or
without magnetic stabilization, and stratification
and segregation of particles in sedimentation and
liquid fluidized beds. In filtration research a theo-
retical framework which incorporates all the im-
portant aspects of filtration process has been de-
veloped to quantitatively describe the dynamic be-
havior of the process.
In liquid phase adsorption studies, efficient
algorithms are developed for exact and detailed ad-
sorption calculations in various process configura-
tions involving systems with arbitrarily large
number of adsorbates, formulation of the species-
grouping procedure for simplifying multicom-
ponent adsorption calculations and establishment
of a characterization procedure which describes
gas solution with unknown adsorbates as solution
with a fixed number of pseudo-species of ad-
sorbates.
In biochemical engineering research, Tien's
group is studying the interaction between ad-
sorption and bacterial growth when granular ac-
tivated carbon is used to treat liquid waste contain-
ing both adsorbable and biodegradable organic
substrates. The work is applied to fluidized bed
biofilm reactor design.
Professor Vook is studying various properties
of current carrying and sliding electrical contacts.
The work is carried out in an ultra high vacuum
system where electrical contact resistance, friction
coefficient, and the chemical composition of the slip
ring surface (by Auger electron spectroscopy) are
measured in situ as a function of contact force,
current through the contact, and gaseous lubricat-
ing environment. The goal of this work is to under-
stand the physical and chemical forces that limit
the current-carrying capacity of the moving
(rotating) electrical contact. Vook is also develop-
ing thin film coatings and surface pretreatments
for preventing the out-of-core radioactive build-
up that occurs on austenitic stainless steels used
in boiling water nuclear reactors.
Chiu-Sen Wang is on leave for a few years and
working at CalTech in the area of particle
deposition in branched airways (e.g. the lungs),
and in aerosols.
These projects illustrate the breadth and depth
of the research interests of the faculty at Syra-
cuse. There is breadth in the number and variety
of research interests and depth in that several
faculty members work in the key areas of
separation and transport processes, chemical re-
action engineering, fluid-particle technology, and
materials science. E


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