THE JOURNAL OF CHEMICAL ENGINEERING EDUCATION
Volume 3, Number 1, November 1964
Editor: Robert Lemlich
Associate Editor: Daniel Hershey
The Common-Core Concept and Undergraduate Chemical Engineering
Education. A. X. Schmidt
Location and Selection of Process Control Instrumentation.
-- M. E. Findley
Some Extracurricular Facets of Chemical Engineering Education
at the University of Alabama. -- J. H. Black and A. H. Still
Extracurricular Interests: A Colloquium for Engineering
Seniors. H. B. Kendall and P. H. Black
Information for Contributors and Subscribers
Solution to Previous Problem
Translation of Titles
The Journal of Chemical Engineering Education is published at ir-
regular intervals at the University of Cincinnati, Cincinnati 21, Ohio,
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A number of journals are faced with a common problem. They
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fers from the opposite problem insufficient papers but adequate
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This journal is sorely in need of more manuscripts. Full-
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controversial views, special reports, suggestions for curricula,
lecture, or laboratory, and other types of contribution are all
needed. The main criterion for selection for publication is perti-
nence to chemical engineering-education.
Considering its nature, the journal has a goodly number of
subscribers. The shortage is in-writers not readers. It is this
insufficiency of suitable papers that so severely limits the number
of issues appearing each year.
So if you have something to say (and who does not) this is
your opportunity to say it. Just send it to the editor. If it
is at all pertinent, you will have an audience!
THE COMMON-CORE CONCEPT AND UNDERGRADUATE
CHEMICAL ENGINEERIG- EDUCATION
A. X. Schmidt
Chairman, Chemical Engineering Department
The City University of New York
New York 31, New York
To the extent that common-core treatment reduces educational costs
and brings students of different motivations into more frequent contact,
it merits active support. However when pushed too far, it reduces
courses and curricula to a lowest common denominator, both as to content
and student motivation.
Until such time as the chemical background of othor engineering
students is substantially increased, attempts to force the core concept
too far does particular violence to the BChE curriculum and training.
Serious thought should be given to the question before a General Engineer-
ing curriculum is sanctioned by the chemical engineering profession through
the mechanism of accreditation.
The trend toward common-core curriculum and the controversy ac-
companying it are inevitable results of two compelling pressures cur-
rontly acting on engineering education; first, the mounting cost of
this education, coupled with the temporary shortage of physical facili-
ties, and second, the rapid acceleration in scientific and technological
progress; that is, the ever increasing rate at which basic scientific
knowledge itself is increasing, together with the remarkable increase
in the rate at which it is being translated into the applied science
of engineering. Let us consider briefly how these factors operate.
A common-core course when it is introduced in place of separate
courses serving different sets of students from different disciplines,
tends to conserve classroom space, increase the interchangeability of
instructors, facilitate student programming and reduce the number of
class sections. In all these ways it is economically attractive and
helps to relieve the first of the two pressures cited above. It also
increases "interdisciplinary" contact among students with different
motivations and ultimate objectives.
The author is a member of the AIChE Education Projects Committee and
chairman of the Subcommittee on Undergraduate Curricula.
As little as twenty-five years ago, the pace of scientific and
technological progress was still slow enough for engineering know-how
assimilated by the engineering undergraduate to be applicable during a
large part of his professional lifetime. Engineering know-how was dis-
pensed in the engineering curriculum in sizeable doses, and properly so.
Know-how is only successfully taught to motivated individuals who have
the prospect of applying it directly, frequently and actively in their
professional work. Specialized know-how by its very nature, keeps the
several disciplines apart and to the extent that it is a legitimate part
of the undergraduate curriculum, to that same extent is common-core
treatment excluded. But in today's engineering world technological know-
how changes so fast that it represents a highly perishable commodity,
largely doomed to obsolescence in as little as five years. It becomes
a steadily less attractive ingredient of undergraduate training. Couple
this factor with an extended and rapidly expanding body of basic scienti-
fic knowledge and an obviously-growing need for greater mastery of mathe-
matics, physics and chemistry by all engineers, and the second pressure
toward common-core curriculum is accounted for. (It also accounts for
the somewhat naive concern that "engineering as a profession is in danger
of losing its identity"). The elimination of ephemeral know-how from the
curriculum leaves room for the addition of more know-why. Know-why rests
on basic science and engineering science, both of which lend themselves
naturally to common-core treatment, in sharp contrast to know-how which
must, of necessity, be specialized.
The writer assumes that the question confronting the engineering pro-
fession is no longer whether there shall or shall not be an increase in
the common-core curriculum of engineering, but rather the extent to which
the common-core concept shall be carried and the conditions under which it
is natural and desirable and those under which it is artificial and detri-
To understand and appreciate the sharply conflicting opinions and
often heated arguments that are taking place over the common-core ques-
tion, both in and out of meetings of our curriculum committees, it is
essential to try to evaluate the backgrounds in which opposing viewpoints
are generated. For this purpose, at some risk of oversimplification, let
us examine the undergraduate academic backgrounds of four classical
branches of engineering as they have existed up till now,
The undergraduate civil engineer's basic science training stands
mainly on two legs -- mathematics and physics. Chemical training is
casual, rarely going beyond two semesters of freshman chemistry. The
mathematics requirement is neither as intensive nor extensive as that of
the electrical engineer's. In the day-to-day thinking of the civil en-
gineering student, changes in physical state are infrequently dealt with
and chemical changes only rarely. Thermodynamics is not stressed. Much
of the thinking is in terms of statics and permanence rather than dynamics
and change. After all, a bridge is designed to remain in fixed position
and to stay the hand of time.
The undergraduate electrical engineer's training in basic science
also rests mainly on mathematics and physics but in both areas the train-
ing is characteristically intense and at a high level for undergraduates.
But, as with the undergraduate civil engineer, chemical training is sparse
and thermodynamics plays a minor role. Once again, phase changes and
chemical changes are infrequently dealt with. However, electrons flow
swiftly, and changes in electrical and magnetic effects and interconver-
sions of energy give this discipline a more dynamic quality.
The budding mechanical engineer has a technical background which
again rests .mainly on mathematics and physics; once again chemical train-
ing is confined to a sketchy freshman level. However, what little there
is of it is applied on occasion in order to cope with such matters as
combustion. Furthermore, phase changes, heat transfer, power generation
and energy conversions, moving parts and moving machines combine to create
an atmosphere of change and motion. Thermodynamics is essential.
The undergraduate chemical engineer's basic training includes mathe-
matics, physics and chemistry. Of necessity his training stands on three
legs, not two. Since the particles he deals with move frequently from
one physical phase to another and react frequently with one another to
form new kinds of matter, he must almost continually apply the fundamental
laws of chemistry and physics simultaneously in order to cope with a world
in which both physical and chemical changes of all sorts are the accepted
norm and lack of change is a most unusual condition. His thermodynamics
must deal generously with chemical as well as physical processes and he
must add chemical kinetics to his armament.
This brief delineation of typical undergraduate engineering atmo-
spheres reminds us that considerable differences in training have existed
to meet the past professional needs of various branches of the engineering
profession. There are important differences in the relative amounts of
static and dynamic thinking, as well as in the intensity and breadth of
training in the basic sciences. These differences color the attitudes
that are brought into deliberations on common-core curriculum, in cur-
riculum committees and elsewhere,
The proponents of the common-core approach invariably state that
the objective is to broaden tho education of all engineering students to
meet increasingly sterner requirements of the engineering profession as a
whole. If that were indeed the case, there would be no cause for chemical
engineers to be concerned over it. However, as we shall see, this is un-
fortunately not so. Let us assume that there are three legitimate reasons
for any curriculum change; improvements of the curriculum content, reduc-
tion of the cost of education without damage to the curriculum, or im-
provement of student motivation.
Speaking to the last factor first, student motivation is regarded
by many educators as an outstandingly important determinant of the re-
sults obtained in the classroom. It is believed that some students,
impressed by bridges and roads wish to become civil'engineers; that radio
hams or television buffs aim toward electrical engineering; that chemistry
enthusiasts lean toward chemical engineering, while the machine-minded
are attracted to mechanical engineering. While it is true that many
students appear to come into engineering for no clearlywdefined reason
at all, it is also true that even these usually wish to identify kith a
professional discipline after a year or two -- or so we are led to believe.
Training in The Basic Sciences:
Let us take a somewhat harder look at the disparities in the basic
science training of students in the four disciplines previously discussed.
After all, that is where common-core problems start.
For example, within currently prevailing practice, the mathematical
training of electrical engineers usually exceeds that of other engineering
students. This is both necessary and proper, not only because their in-
tended profession requires it, but, just as important, because they are
often mathematically motivated. A mathematical language barrier tends to
exist between them and their fellow students. It often appears at an
early stage and continues to widen with time.
Chemical engineering undergraduates have been devoting roughly half
an academic year more to basic science than other students. This has
been used mainly in acquiring chemical background, particularly in physi-
cal and organic chemistry. Again, this is both necessary and proper be-
cause of professional requirements and motivation. For these important
reasons a massive chemical language barrier currently exists between
chemical engineering students and most other engineering students.
Having acquired sound grounding in both basic sciences, chemical
engineers, in their study of material and energy balances, thermodynamics,
reaction kinetics, properties of materials, chemical plant design, etc.,
are continually required to think in broad terms about systems in which
both physical and chemical changes are taking place. It is this sustained
simultaneous preoccupation with both the physical and chemical worlds that
is the overriding distinction and the cardinal virtue of the chemical en-
gineer's training. In none of the other three undergraduate disciplines
discussed has this breadth of viewpoint been necessary, nor has it been
Common-Core Curriculum Under the Status Quo:
Having taken recognition of the existence of differences in profes-
sional thinking, student motivation, and the basic training of engineering
undergraduates that has existed up till now, let us explore the limits to
which the common-core approach can and should be applied; first, without
important changes in present student motivation or basic science training,
and later, with them.
No great error is introduced if it is assumed that two half-year
terms ( 8 credits) of chemistry, three (or four) terms of college level
mathematics, and three or four terms of physics currently represent the
statistical extent to which basic science training is common to the under-
graduates in the four disciplines under discussion. Coupled with the usual
amounts of cultural and non-technical courses this is enough for at least
two full years of common-core curriculum.
Where else can the common-core concept be applied legitimately? Any
courses requiring no knowledge of chemistry, just mathematics and physics,
are distinct possibilities.
A partial list would include such subjects as (1) the transfer of
momentum, heat and mass (2) measurement and control of process variables
(3) mechanics of solids (4) analog and digital computation, and (5)
graphics. However, certain important provisos should be attached. Proper
motivation must be preserved for all students entering the course and no
attempt must be made by any discipline to attenuate the course content to
a point seriously below the requirements of any other discipline! To be
legitimate, any curriculum change should result in an upgrading, not a
degrading of content.
In the above discussion, two sources of controversy are indicated.
Whenever a common-core course is designed for students with disparate
backgrounds and objectives, the tendency is to produce a course rendered
assimilable by the students having the weakest background and made pala-
table to those having the weakest motivation. To cite one instance,
electrical engineers might find a core course dealing with circuits,
fields and electronics unacceptable despite all efforts to make it other-
wise. If given at a level suitable for highly-motivated future electri-
cal engineers, it might be unassimilable by the other students. If pre-
sented at a level suitable for the latter group, it might prove boring
and time-wasting for the former.
For similar reasons, under present conditions, no course requiring
more than the most rudimentary knowledge of chemistry can be fitted into
a common-core curriculum without penalty to chemical engineering trainees.
Subject matter such as the following is patently not negotiable; material
and energy balances involving chemical change, engineering thermodynamics
and kinetics, unit operations theory, unit processes, polymer theory,
chemical plant design, etc.
Careful examination indicates that as long as engineering students
of other motivations and other disciplines remain comparatively untrained
in chemistry, roughly one third of the present undergraduate chemical en-
gineering curriculum cannot be fitted successfully into a common-core
pattern. Any attempt to force the common-core concept beyond that point
does violence to the chemical engineering undergraduate curriculum as
it now exists by diluting, weakening or narrowing it.
This situation has its ironic side. For the reasons cited, the
chemical engineer often finds himself in opposition to the establish-
ment of a core course and, as a consequence, charged with obstructionism.
His "reactionary" posture originates from the fact that the same core
course that represents a broadening of viewpoint to many of his colleagues
represents attenuation and retreat to himself. Versed in both basic sci-
ences, he is asked to make common cause with those versed in only one.
Common-Core Under a Changed Set of Conditions:
The no plus ultra of the common-core concept is a completely
standardized undergraduate training called General Engineering. Can such
a curriculum serve as a satisfactory substitute for the present BChE cur-
To explore the possibilities, let us set up a hypothetical situation
where all engineering undergraduates take basic scientific training equal
to what is now given only to the chemical engineers. This would include a
year each of general, organic, and physical chemistry and three or four
terms each of physics and mathematics. If one could now homogenize the
motivation of the students to the point where they were all willing to
regard themselves as "Engineers-in-training" or "Pre-professional-
engineering candidates" for four years, then, conceivably, the entire
student body could be put through a program in which, by the continuous
simultaneous application of the fundamental laws of physics and chemistry,
the highly desirable broad viewpoint which characterizes the current
chemical engineering curriculum could be maintained. However, this could
only be accomplished if the student body, regardless of ultimate objective,
continually studied subjects dealing with matters chemical as well as
physical throughout their curriculum. Material balances would have to
be performed on chemical as well as physical processes. Heat balances
would have to be performed where chemical heats of reaction as well as
sensible and latent heats were involved. Chemical kinetics would need
to be included. The thermodynamics courses would have to cover the
thermodynamics of chemical as well as physical processes. Materials
would have to be studied from the viewpoint of molecular and atomic
structure, rather than more superficially. If this were done, and only
if it wore done, would such a general engineering curriculum afford a
basic training equal in quality and depth to that of the current chemi-
cal engineering curriculum. So far as the chemical engineering profes-
sion is concerned, anything short of this full treatment would represent
a retreat from its current standards of undergraduate education.
It could be argued that no General Engineering curriculum will or
should carry the emphasis on matters chemical to the extent described
above. And for good reasons. It is doubtful whether that much chemical
knowledge or thinking is necessary for all future engineers, even taking
full recognition of the deeper penetrations that chemistry is making into
our daily lives. It might be difficult to sustain the interest and moti-
vation of future bridge builders and electronics specialists through that
much chemistry. One might also argue plausibly that costly chemical
training in such depth would be wasted on them. In other words, a Gen-
eral Engineering curriculum, designed to maintain the full educational
content of the current undergraduate chemical engineering curriculum
might be economically wasteful and pedagogically unsound.
Where does one go from here? Many educators now feel that the
frontiers of science and engineering have expanded to the point where
the engineering profession will no longer be able to meet the challenge
of the future unless engineers in all disciplines are better grounded in
the basic sciences and there is greater understanding and interchange of
ideas among them. If this is so, the chemical illiteracy that has marked
the education of many engineers up till now must be corrected. No longer
must their ability to think be confined almost solely to physical phe-
Great forward strides could be made by adding two or three additional
half-year courses in chemistry to the basic science requirement of non-
chemical engineers, thereby bringing the time devoted to the fundamentals
of physics and chemistry to about the same level. A strong case can be
made for a full year of intensive physical chemistry and a course in or-
ganic chemistry because such training would greatly enrich subsequent
studies of thermodynamics, electrochemistry, combustion, energy conver-
sions, material and energy balances, metallurgy, properties of materials,
corrosion, nuclear phenomena, water and sewage treatment, etc. In other
words, it would catalyze and greatly facilitate all future expansion and
improvement of the engineering science content of all engineering curricu-
One may get even more vociferous by stating that any attempt to ex-
pand the common-core concept or create a General Engineering curriculum
without substantially increasing the chemistry content above the two-
course ( 8 credit) level would represent a menace to engineering educa-
tion in general and to chemical engineering education in particular.
Designed for the chemically innocent, such a "General Engineering"
curriculum would produce a final graduate, already out of high school
for three or four years, with a rudimentary knowledge of chemical phe-
nomena. Had he been chemically motivated originally, what would have
happened to that motivation by now? If he still wished to enter the
field of chemical engineering, would he first have to "reach back" to
acquire basic training in chemistry, shed the restricted viewpoint of
his "General Engineering" education, and pick up much of the training
now contained in any good BChE curriculum; to wit, organic and physical
chemistry, material and energy balances, chemical kinetics, unit opera-
tions theory and laboratory, chemical plant design, etc? To the chemical
engineering profession this would represent an unacceptable curricular
architecture. The process would be highly inefficient and only a stu-
dent with unusual motivation would survive it.
The discussion may be summarized as follows.
1. Legitimate common-core treatment reduces educational costs by ef-
ficient use of classroom space, facilities, and instruction staff,
reduction in the number of class sections of small size, and more
efficient student programming. It also brings students of different
motivations into more frequent contact. To the extent that these
ends are served it merits the active support of all engineering
2. On the other hand, the common-core concept, when pushed too far,
tends to reduce courses to a lowest common denominator, both as
to content and student motivation.
3. Until such time as the chemical background of other engineering stu-
dents is substantially increased, one third of the current BChE
curriculum does not lend itself to common-core treatment. Attempts
to force the concept beyond this point does violence to the existing
4. The inclusion of two or three additional semesters of chemistry,
(particularly physical and organic chemistry), to the current basic
science requirement of nonchemical engineers would make possible
notable quantitative and qualitative advances in engineering science
training and common-core content.
5. No fully integrated General Engineering curriculum yet proposed
appears to be a satisfactory replacement for the present BChE cur-
riculum. Undergraduate chemical engineering motivation and curricu-
lum content suffer damage when common cause is made with any curricu-
lar plan in which the world of chemical change is dealt with less
intensively or less extensively.
The following recommendations are made to the chemical engineering
1. that extension of the common-core treatment in undergraduate educa-
tion be supported wherever it can be effected without attentuation
of curricular content or student motivation.
2. that strong support be given to the inclusion of additional chemistry,
particularly physical and organic chemistry, into the basic science
training of nonchemical engineers in order to catalyze notable
quantitative and qualitative advances in common-core content and en-
gineering science training.
3. that most serious thought be given to the question before a General
Engineering curriculum is sanctioned by the chemical engineering pro-
fession through the mechanism of accreditation.
LOCATION AND SELECTION OF PROCESS CONTROL
M. E. Findloy
Associate Research Professor
Department of Chemical Engineering
Summary: Consideration is given to the important factors in lo-
cating and selecting control instruments for use on chemical processes.
Some factors of importance in selecting variables to be controlled and
manipulated are limitations on the degrees of freedom, the desired pro-
cess performance, the possibilities of measuring and manipulating per-
formance, and the dynamics and stability of control. An 8-step pro-
cedure is suggested involving 1. sketching, 2. division into com-
ponent parts, 3. sketching signal flow between variables and component
parts, 4. selecting measurements of process performance, 5. select-
ing manipulations of process performance, 6. selecting controls to
insure assumptions in 4 and 5 and insure suitable operating conditions,
7. checking dynamics and stability, 8. checking all variables and
possible variations and providing for extreme conditions.
In spite of the emphasis on process dynamics, control theory, and
stability analysis, many chemical engineers participate in control work
primarily in selecting or improving instrumentation for process control.
In many of these control systems the main problems are in obtaining
suitable measurements of process performance and in selecting the best
place and method of manipulating the process. Another problem is whe-
ther a sufficient number of variables or possibly too many variables are
controlled on a given system. Often the engineer has little to rely
on other than his own common sense in arriving at such decisions. It
is the purpose of this paper to try to present some of the factors which
should be considered in locating and selecting control instruments and
to provide a tentative procedure which might prevent overlooking such
factors. Relatively simple systems will be considered, but these should
be sufficient to illustrate the important points.
Various methods of applying single control loops in certain appli-
cations have been given by Eckman (2,3) and Shilling (7). Solheim has
discussed continuous reactor control (8), and examples of distillation
control systems have been given by Shilling (7), Brown (1), Rosenbrock
(5), and Perry (4). The importance of various control characteristics
for processes and operations have been discussed by Rosenbrock (6),
and numerous examples of specific process instrumentation have been
presented in the literature. However, general methods of arriving at
control instrumentation have been lacking in the literature, even though
the most important considerations have been discussed thoroughly but
Basically the purpose of a control system is to maintain the vari-
ables in a specific process at values which will insure satisfactory
process performance. This involves the variables as a part of the
process and also the variables as part of a control system. As part
of the process it is usually the steady state effects of the variable
which are most important, and as part of a control system it is the dy-
namics which influence the stability and adequacy of control. Therefore,
it is desirable to use two methods of representation to aid in process
control selection. The functioning of the process can be best visualized
by a flow diagram or sketch of the process while the control loop re-
lationships can be better understood with a signal flow diagram, which
indicates the relationships between variables. An illustration of the
uses of diagram in control selection can be seen by considering the
evaporator in Figure 1.
F1 F2 T1 -V
Xl 2-- F1 -----
F ------ -----i G
Q -------------- [r4
Figure 1. Process sketch, A, and signal flow diagrams, B & C, of an evaporator.
Figure 1 A is a process sketch which illustrates the equipment and changes
taking place. This helps in visualizing the effects of the variables on
process performance, especially in material and energy balances, both
steady state and dynamic. Figure B is a signal flow diagram indicating
that V, F2, X2, and T2 (vapor flow, liquid outflow, composition, and
outlet temperature) are a dynamic function, G, of the independent vari-
ables T1, F1, X1, and Q (heat flow). Figure 1 C shows how a signal flow
diagram can be written if the process is linearized at operating condi-
tions and the effects of the variables are separated. V, F2, and X2
could be rearranged (with different G functions) depending on the vari-
able considered as the output variable. Only one output might be shown
if desired. Consideration of the outputs of signal flow diagram allows
the selection of variables which most indicate process performance, and
consideration of inputs allows selection of suitable variables to mani-
pulate to maintain process performance.
The controlled variable, usually c in control equations, should
usually be a variable representative of process performance, such as
product rate or quality, or some condition which is important to main-
tain for proper functioning, such as level, temperature, pressure, or
concentration. The manipulated variable, m in most control equations,
should be a variable which can be directly changed to give a definite
consistent effect on the controlled variable in its control loop.
Selection of the proper controlled variables and manipulated vari-
ables in a given process is often the most important step in the appli-
cation of control instrumentation. It is often difficult because of
the compromises which mast be made to obtain satisfactory measurement,
adequate dynamics for stability, suitable manipulating devices, and con-
sistent responses. Complex intorelationships among variables and loops
may also cause trouble.
In selecting variables to be controlled and manipulated by simple
control loops, there are certain limitations on the possible selections.
Some of these are as follows:
1. Among any group of variables the number of effective control
loops involving these variables cannot exceed the number of degrees of
freedom, which is the number of variables minus the number of fixed re-
lationships among these variables. This is probably of most importance
in considering material flows and component separations. For example,
assuming a separation system involving components A and B, as in Figure
2, the following equations apply:
Figure 2. Separation system.
First considering F, P, W, total mass flow rates, F = P + W and only
3 1 = 2 of these 3 variables may be controlled. Considering composi-
tions as well as flows there are 6 variables and
F = P + W
F XFA = P XA + W X WA
(component B is fixed by the above 2 equations)
so that 6 2 = 4 of the above 6 variables may be controlled. However,
as shown before only 2 of these can be from F, P, and W. Thus the do-
grees of freedom may determine which variables as well as how many vari-
ables can be controlled.
By considering the degrees of freedom additional conclusions are ob-
served, such as 2, 3, 4, and 5.
2. A manipulated variable in one control loop may not be manipu-
lated in another control loop. A manipulated variable in one loop may
be the controlled variable in a second loop if the manipulation acts
through the controlled variable in the first loop. This produces one
effective loop on the original variable. For example, in Figure 3,
c2 = ml = Flow
.... LC = Level Controller
.7 FC = Flow Controller
-- c = level
j LC -------
m2 = Flow
Figure 3. Liquid level and flow control systems.
to control c2, the tank outflow, m2, affects cl, the level, which in
turn causes m2 or c2 to change due to control loop number one. Note
that m2 and c2 could not be reversed.
3. The same variable may be used as c in two loops, but the same
measurement and set point should be used in both loops, or in other
words one variable can be controlled by two manipulations. Two close-
ly related variables should not be controlled independently unless one
of the manipulations affects the relationship between the two variables.
4. The desired values of the controlled variables must be possible
to attain, and should be well within the capability of the system under
extreme conditions if the control system is to be relied on. For
example in the separation system of Figure 2, if F, XFA, P, and XpA are
to be controlled or fixed variables, then P.times XpA must be less than
F times XFA under all conditions. The equipment must also be capable of
producing the set point values of P and XpA under the range of conditions
encountered. Otherwise the manipulation may go to an extreme position
and upset the system.
5. If a special control technique of combined feed forward and
feedback control or control of a multi-variable function is used, this
acts like a single control loop and eliminates only one degree of free-
dom, regardless of the number of variables.
It is important in selecting control instrumentation to keep in
mind the desirable characteristics of control loops. Among these are
Ao As simple as is possible with adequate control.
B. Controlled variables as closely related to desired performance
C. Manipulated variables with as definite effects on controlled
variables as possible.
D. Minimum dynamics or time delays between manipulated variables
and their effects on controlled variables. This is especially
true for transport lag or dead times.
E. Minimum dynamic interaction between control loops, and usually,
minimum steady state interaction.
F. Resonant or natural frequency of the control loop should
be higher than the expected frequency of process distubrances
In many cases it is possible to improve the control of a process
by improving the design of the process itself. Such improvements for
control purposes should be based on all the above limitations and de-
sirable characteristics, as well as desired process performance.
Since each process has its own characteristics and its own pur-
poses, the .selection of control instrumentation cannot be accomplished
simply by following a procedure, but usually depends on some quite
unique aspects of each process. The procedure suggested here is pri-
marily aimed at bringing attention to the factors which should be con-
sidered. The importance of a particular factor may vary widely from
case to case, and the effort applied in each step should vary accord-
The following steps in selecting control instrumentation are
1. Sketch the process and locate all variables of major importance,
particularly variables of production rate, quality, and important condi-
tions, and variables affecting rates, quality, and conditions*
2. Divide the complete process into various operations and pro-
cesses which can be effectively separated, as far as effects of vari-
ables are concerned.
3. Sketch a simplified signal flow diagram representing component
operations and processes as blocks showing input and output variables
4. Write down the major goals of the entire process in order,
considering product quality, product rates, and/or special character-
istics or conditions. For each of these goals select one or more vari-
able measurements which will reasonably accurately indicate performance,
and which are suitable for controlled variables. Consider measuring,
dynamic, and manipulating possibilities. If it is necessary to make
assumptions, they should be listed or kept in mind for step #6.
5. Letting the above measured variables be controlled variables,
attempt to find suitable manipulated variables for each loop. Consider-
ation should be given to the limitations, the desired control charac-
teristics, and the dynamics of the control loops. If there is difficulty
in selecting suitable manipulated variables, it may be advisable to in-
vestigate the possibilities of other variables or locations within the
process for use in measuring process performance. The possibility that
there might be several almost equally effective control schemes should
not be overlooked. If it is impossible to select an adequate simple
control loop for the major process goal, consideration should be given
to more complex control loops such as cascade control, and feed forward
control, or the use of special computing components or computers. List
assumptions for step #6.
6. Once the major performance control loops have been established,
consider each component process or operation and its major purpose. Se-
lect the necessary controlled and manipulated variables, and study their
effects on the major control loops, and their effects on the proper op-
eration of the overall process. Care should be taken to make sure there
is sufficient control to insure the assumptions involved in Steps 4 and
7. Each control loop should be considered from the standpoint of
dynamic stability and if necessary detailed dynamic analysis should be
made. Control functions can be selected according to control theory
8. Reconsider each variable, with the likely variations, and the
results of these variations with the selected control systems. This
should insure that no unexpected consequences will occur.
Occurrences such as power failures, interrupted flows, and the like
should be anticipated and the necessary alarms, fail-safe.pbsitions,
and interlocks should be selected p i:on '
As an example of this procedure, a distillation column can be used
to represent a single but somewhat complex operation.
Step 1 is a sketch of the process with the major variables
as in Figure 4,
Figure 4. Distillation column.
Step 2 is probably not necessary in this case although some insight
might be obtained by considering the reboiler and condenser and associ-
ated flows as separate units.
For Step 3 a signal flow diagram might be as in Figure 5 A or
Figure 5 B.
YF B -
Figure 5. Signal-flow diagrams of distillation system.
For Step 4 the characteristics of this still, and its purpose should
be known. In. this example let the purpose of the still be to separate
light fractions from a high boiling product with A and B being the low
boilers and C being the product. .The purpose may be satisfied by main-
taining a low concentration of A and B in the bottoms and a low concen-
tration of C in the distillate. Under steady state, product flow rates
would be fixed by the composition and flow of the input streams, pro-
viding output compositions are controlled. Measurement of composition
is quite complex and it is assumed that temperatures at constant pres-
sure in the column will be adequate measures of both overhead and bottoms
compositions (4). Temperatures will be taken a few plates from ends to
improve sensitivity of the measurement to changes in composition. Thus
temperatures in the column are to be used as measurements of composi-
tion and performance. The rate of production is to be set by the feed
rate and feed composition which are controlled outside the system con-
sidered here. Assumptions are constant pressures at temperature control
For Step 5, manipulated variables are selected. Several methods are
available for manipulating compositions (and thus temperatures) but most
involve changing the reflux ratio and, or, reboil rate, A convenient
method here would be to manipulate Q2 and thus reboil rate in order to
hold T2 constant. A control valve could manipulate reflux flow to hold
distillate composition and T1 constant.
In Step #6, level controls or overflows can manipulate product and
distillate flows, in order to maintain steady state conditions. Some
other variables which should be considered in Step 6 include insuring
the constant pressures assumed above, which could be done with a vent
control valve at the overhead condenser or the distillate tank. P2
could probably be assumed constant if P1 were controlled constant, or
vice versa. To maintain uniform operating conditions, Hf, the feed en-
thalpy, could be held constant by the use of a heat exchanger and tem-
perature control of a higher pressure feed line.
Step 8 would include reviewing all the variables and fixing many
of the control details, such as automatically shutting down the column
if the feed flow is stopped.
The final system might be as shown in Figure 6.
PC --- Vent
T "-----. 1 Excess Cooling Water
Fixed F ^VV- L Overflow D
V -- I Overflow B
Q TC TC 2
Figure 6. Example of distill.ati.oyn control.
It is important to note here that the above discussion should not
be considered as an adequate method of distillation control. It is
only intended to show how a control system can be decided upon in a
In a more complex processing system such as indicated in Figure 7,
the procedure would be basically the same as described above. Here we
are considering a reactor to produce C from A and B followed by a still
to separate unreactod A and B as distillate for recycle to the reactor.
A stripper serves to further purify the product.
Steps 2 and 3 are illustrated by the signal flow diagram in Figure
Step 4 would depend on the process goals which we will take as, 1,
a given constant flow rate of P and 2, negligibly small amounts of A
and B in P. Assuming P contains negligible A and B and unlisted com-
ponents are unimportant, the flow at P depends upon the flow and com-
position at B or at F. If the reactor is the source of most variations
due to factors such as impurities, catalyst activities, temperature and
pressure, it would be desirable from dynamics considerations to have a
measurement of P or a related variable immediately following the reactor.
Assuming the still makes a fairly consistent separation of A and B from
C, the flow and composition of F might be a good indication of the prod-
uct rate P, and the complete system performance. However, the flow F
would vary with distillate recycle flow possibly independent of varia-
tions in the product rate. The flows FA and FB would be directly re-
lated to flow B and thus P as long as steady state conditions are ap-
proximated, and the rate of conversion is maintained, and the two
separations are adequate. The conversion can be measured by the com-
position of F if specific gravity, viscosity, conductivity, spectro-
photometry, electrochemical, or other rapid response type of measure-
ment will indicate concentration. Automatic chromatography might also
be satisfactory if long delays can be avoided. In any case, sample
transport time should be as small as possible.
In Step 5, FA and FB could be controlled by manipulation of feed
control valves, or by positive feed constant speed pumps. The compo-
sition at F could be controlled by manipulating pressure, heat input
(temperature), or possibly other factors. In this case it might be
permissible to manipulate pressure with an outlet control valve to ob-
tain a constant composition of C in stream F.
In Step 6 the assumptions of adequate separation may be insured
by procedures similar to the distillation procedure already discussed,
which makes up a part of this reactor system. The steady state as-
sumption can also be taken care of in the same way. Constant temper-
ature in the reactor is obtained by manipulating heat input. A
relatively complete instrumentation system for this process is shown
Reactor Still T
QR XFB XBC 3 z
Figure 7. Reactor distillation stripper process.
D F_. D
F Reactor TR Still
A --- XBA
XA --- XBB
FB > Stripp
XB R ,
PR could be input, output, or intermediate variable for tho reactor.
Figure 8. Signal flow diagram of process in Figure 7.
in Figure 9. A flow recorder on toi product stream could be used by
operators to make sure production was'being maintained and.for informa-
tion on necessary adjustments to FA ahd FB. If more sophistication is
desired the flow P could be controlled by cascading and manipulating
set points of the flow controllers on FA and FB.
CC = Composition Control FR = Flow Recorder
PA = Pressure Alarm
Figure 9. Reactor distillation stripper process with controls.
Most systems would be more complex than those used as examples, and
more compromises would be necessary due to inadequate dynamics, measuring
devices, unknown factors, etc., but as a start on such complex systems
the procedure outlined might be useful.
Where considerable difficulty might occur would be in selecting
composition measuring instruments, in sampling techniques, and distil-
lation and similar dynamics. In multi-step processes where final product
rate is highly important and initial input must be the manipulated vari-
able, the dynamics might present an extreme problem. A solution to this
problem might be obtained by using several shorter loops comparable to
a series of tanks with outlet flow control on the last tank and with
level (c) to input (m) control on each tank.
While the above procedure is based primarily on common sense, it has
not been tested extensively in practice. It does appear to be one method
of arriving at many of the process control systems described in the liter-
ature using the accompanying descriptions and reasonable assumptions.
With proper use and improvemonts,it is possible a procedure such as this
could save considerable time in locating and selecting control instru-
1. Brown and Assoc., "Unit Operations", p. 362, Wiley (1950).
2. Eckman, D. P., "Principles of Industrial Process Control", p. 193
3. Eckman, D. P., "Automatic Process Control", Wiley (1958).
4. Perry, "Chemical Engineers Handbook", 4th Ed., pp. 22-94 to 22-107,
5. Rosenbrock, H. H., Trans. Instn. Chem. Engrs. 40:35-53 (1962).
6. Rosenbrock, H. H., Chem. Engr. Progr. 58: No. 9, 43 (1962).
7. Shilling, G. D., "Process Dynamics and
and Winston (1963).
Control", Holt, Rinehart
8. Solheim, 0. A., Control Engineering Z: No. 4, 107 (1960).
The new Indian Institute of Technology at Kanpur, which is as-
sisted by U. S. funds and nine U. S. universities, is seeking Ph.D.
Chemical Engineers of Indian nationality for staff positions. Further
information may be obtained from the Registrar, IIT Kanpur, P. O. Box
239, Kanpur, U. P., India.
SOME EXTRACURRICULAR FACETS OF
CHEMICAL ENGINEERING EDUCATION AT THE UNIVERSITY OF ALABAMA
J. H. Black, Head, and A. J. Still, Professor
Department of Chemical Engineering
University of Alabama
Abstract: There appear to be four noteworthy extra-curricular
bonuses in the chemical engineering course work at the University of
Alabama. These include training in leadership and oral expression,
which applies to the graduates' community lives, and training in
common stock and life insurance evaluation, which applies to their
--- -- -- -- -- -- a - - - - - - -a -a
Some years ago, a survey reported that, for several reasons,
chemical engineers make ideal husbands, and rumor has it that they are
also excellent cooks. These extracurricular advantages of a chemical
engineering education are apparently unintentional and common to all
chemical engineering curricula.
The Chemical Engineering Department at the University of Alabama,
however, has in its curriculum some additional and noteworthy extra-
curricular objectives of value to its students. These bonuses are by-
products of three "practical" courses which are included in the cur-
riculum along with the usual fundamental courses in chemical engineer-
ing and engineering science.
The first of these bonuses is leadership training. The Unit
Operations Laboratory class is divided into groups of four members
each with the position of group leader rotating with each experiment.
Each student thus has several opportunities to acquire experience in
leadership, in supervision, and in organizing the work of others. This
method is in contrast to those laboratory situations in which the stu-
dent with native organizational ability naturally takes over the leader-
ship of the group, thus contributing to his development but not at all
to the development of the retiring members of the class.
This training at Alabama is a little more impressive when the
nature of the laboratory course is considered. The group leader is in-
structed only that his group is to determine certain operating charac-
teristics of the equipment under study. Thus, with the exception of a
*Presented at the A.I.Ch.E. national meeting in Pittsburgh, May 1964.
Publication release was obtained by the author.
distilling column, a doubled effect evaporator, and an adiabatic drier,
.the equipment is checked out of the stockroom, piped properly to the
necessary pumps and tanks, and properly instrumented. This means that
the group leader has the responsibility of designing an experiment to
produce the desired information, to make work assignments to keep all
members of the group gainfully employed on the task at hand, to finish
the work in the allotted time, and to present a meaningful report on
the work accomplished.
While this training has some obvious curricular advantages, it
also has extracurricular bonuses in community activities of various
sorts, from leadership in United Fund drives to leadership in local
government. Leadership in community affairs by chemical engineers is
certainly to be encouraged and is a worthy extracurricular objective
of our colleges and universities.
A second extracurricular bonus is derived from the Process Design
course, which in reality is a development and process design project.
A hypothetical situation is created in which the students work as de-
velopment engineers for a fictitious company. Each student has a dif-
ferent and modest project on which the laboratory work has been com-
pleted, and he is to develop the laboratory information into a commercial
process design. During the year each student is required to present
several prepared and extemporaneous "seminars" to his fellow "engineers"
in the "company", to acquaint them with the progress of his project. The
student thus gains experience in oral reports. These experiences are in
addition to the usual course-work in public speaking required of all
engineers at Alabama, but more meaningful to him because the talks are
related to a situation which is very real to him.
This extracurricular advantage is closely related to the first one
cited in that it has applications to community affairs. The student can,
after graduation, preside at meetings and make oral reports on community
projects with more confidence,
The last two extracurricular objectives, the third and fourth,
involve the personal life of the student after graduation, and both
are a by-product of our Chemical Engineering Economics course. Both
these topics have evolved naturally as a result of discussions of the
organization of business enterprises which, together with the topics of
capital investment and profitability estimation, make up our economics
course. Discussions of business organization in this course have led to
studies of common stock ownership and evaluation and, through discussions
of the function of business insurance, to a study of life insurance,
The topic of common stock evaluation, the third extracurricular
bonus, has been of great interest to the students. The discussions
evolved from explanations of the ownership of American business. To
spark interest in the students, a fictitious sum of $1,000 is given to
each student at the beginning of the term for him to invest, on paper,
in common stocks. He must keep the instructor informed of all purchases
and sales, and make a report of his progress at the end of the term. His
results are compared to some index of the stock market such at the
Dow-Jones average. Student interest has been so high that about two
or three lectures are devoted to the topic of investment in common
stock. The difference between investing and "playing the market" or
gambling is carefully pointed out. Actually, as a result of this ex-
tracurricular bonus, more than one student has begun his investment
planning and investment activity in the holding of common stocks while
still in school.
It might be worthwhile here to discuss the criteria we teach the
student to use in choosing a stock. In addition to pointing out how
important good company management is to the success of the enterprise,
we discuss several yardsticks for measuring management success. The
first of those is the historical earnings per share and how this can be
extrapolated. The second is the historical price-to-earnings ratio and
how this can be used to estimate future potential. The third is earn-
ings as a per cent of investment and how this reflects upon the quality
of company management.
Figure 1 is a semi-log plot of the earnings of an actual company
against the year. This is a typical plot of a good, steady-growth com-
pany, but not at all typical of some companies with cyclical earnings.
By using the semi-log plot, the earnings can be projected into the fu-
ture and the per cent growth in earnings calculated. In a similar manner,
in the upper part Figure 1 the high and low stock prices are plotted for
each year, and the best line is drawn through the highs and the lows
parallel to the earnings line. In this manner the historical price-to-
earnings ratios are calculated and applied to the projected earnings.
The result is a plot of reasonable high and low values for the stock.
In this way, the student can estimate what a reasonable price is for
the stock and estimate its future potential.
Figure 2 is a plot of the earnings of the company as a per cent
of the assets of the company. Ideally, this value would increase with
time, but it does give an indication of how effective and wise the com-
pany management has been in investing in new plants and equipment, in
the acquisition of other companies, and in the use of depreciation funds.
This extracurricular objective of common stock evaluation helps
the future graduates at Alabama in their private lives by giving them
some criteria for investing their savings. It also contributes to
their understanding of how our free enterprise system works and gives
them an awareness of their stake in the success of our economy.
The topic of life insurance, the fourth extracurricular bonus,
has also been a subject of great interest to the students. The three
aspects of insurance, the risk function, the sinking-fund function,
and the banking function, are applied to life insurance. Although this
topic of insurance is first introduced in a discussion of business in-
surance, it has been extended to a discussion of life insurance as a
result of student interest.
--o I 1 I 1 I I
S56 58 60 62 64 66
Figure 1. Plot of price and earnings per share versus year.
I I I I i
Ca c 0
54 56 58 60 62 64 66
Figure 2. Plot of per cent earnings versus year.
The various types of life insurance, such as term, decreasing term,
annuity, ordinary lifo, and endowment are covered. The characteristics,
the advantages, and the disadvantages are pointed out. Thus, the stu-
dents got an understanding of what types of insurance are available and
have some knowledge upon which to base decisions affecting the welfare
of themselves and their families.
In summary, there are four noteworthy extracurricular objectives
of the Chemical Engineering curriculum at the University of Alabama
which are of benefit in the community and private lives of our gradu-
ates. These educational bonuses are training in leadership and oral
expression and studios of common stock and life insurance evaluation.
INFORMATION FOR CONTRIBUTORS
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Manuscript typing should be double spaced. Three copies should
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Authors of manuscripts accepted for publication receive 20 re-
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EXTRACURRICULAR INTERESTS: A COLLOQUIUM FOR ENGINEERING SENIORS
H. B. Kendall, Chairman, Department of Chemical Engineering, and
P. H. Black, Chairman, Department of Mechanical Engineering
Ohio University, Athens, Ohio
Abstract: At Ohio University, chemical and mechanical engineering
seniors attend a regular colloquium where they hear and.question speak-
ers on various "non-technical" topics. Subjects presented include
ethics, labor relations, patents, graduate study, modern art, personal
investments, philosophy, religion, hobbies, and others.
We engineers are reminded frequently that we, too, are members of
society This comment, or thought, is apt to rear its ugly head on
numerous occasions, in fact, almost anytime when we get into a discus-
sion with others or with one another about the place of engineers in
today's world. It probably is a pretty good thing that we are constant-
ly reminded of our responsibilities. We all are aware that the engineer
often finds himself in a responsible position in business, in government,
in education, or wherever his particular background and interests may
lead him. At any rate, the engineer frequently finds that the "non-
engineering" aspects of his work take on more importance, temporarily
or permanently, than the more technical aspects do. As a result of the
many non-technical features of engineer's work and life, most engineers
(with a strong push from their professional organizations) have recog-
nized that an engineer must be, to use the well worn cliche, "well
rounded". This admission by engineers of the importance of the non-
technical facets of their work has led to the increasing interest in edu-
cating the "whole" man which has become apparent in engineering curricula,
especially since World War II. One manifestation of this interest is the
current E.C.P.D. requirement that work in humanities and social studies
be included in all engineering curricula. The question that we engineers
and engineering teachers must ask is: To what extent is this requirement
actually doing a good job in preparing the student for his future responsi-
Humanities and Social Studies in Engineering Curricula:
Let us take a brief look at some aspects of the humanities and social
studies requirements in engineering curricula. Obviously, the value re-
alized from taking such courses will vary considerably from one student
to another, and very possibly, just as much from one school to another.
*Presented at the A.I.Ch.E. national meeting in Pittsburgh, May 1964.
Publication release was obtained by the author.
For example, in a technical school where all- students are enrolled in
engineering or science curricula and where block scheduling is possible,
it is also quite possible to lay out a meaningful 4, 6, or even 8 se-
mester sequence in humanities and social studies which will contain
courses that are well correlated with each other as well as slanted
toward the engineering student. However, in a large university, where
considerable choice as to what courses are to be taken is left to the
discretion of the student, it is quite possible that a poor selection
of courses will be made by the student. There may be several reasons
for this poor selection. For example, the student may not be sure of
his interests. Or, he may make his selections based primarily on cer-
tain professors that he wants -- or (too often) does not want! Or, he
may just be looking for the easiest way out of his requirements. At
Ohio University, as at most schools, faculty members make an effort to
advise engineering students as to what non-technical courses might prove
to be most beneficial to them. Usually, this advice is accepted. How-
ever, even with the best of advice, the student -- especially at the
Freshman and Sophomore level when many of these electives are taken -
often has no real objective in mind in taking the non-technical courses.
He can see no value in them and he has therefore no motivation toward
them. Too late, frequently, the student realizes what opportunities he
has missed in the early years of his college career, and he begins to
wish that it was possible for him to backtrack and learn a little bit
about some of these important non-tochnical topics.
The Engineering Colloquium:
About a dozen years ago, one of the present writers P. H. Black
decided that something should be done to meet and overcome the short-
comings of the "non-technical" education of the engineering seniors.
He reasoned that in their senior year most engineering students would
have matured enough to begin to appreciate the relevance of their
earlier humanities and social studies courses to their professional
lives after graduation from the University. He decided that it would
be profitable to give these students a chance to hear and think about
some aspects of "living" at a time when the students were beginning to
realize that these things were truly important, and when it was too late
to go back and pick up some of the courses they wish they had taken
earlier. Thus, the "Engineering Colloquium", now shared by Chemical
and Mechanical Engineering Engineering students at Ohio University
came into being.
The organization and operation of the colloquium is extremely
simple. It meets twice a week for the first half of the Spring semes-
ter each year. All seniors in Chemical and Mechanical Engineering are
required to attend the colloquium and they receive one hour's academic
credit for their participation. They are encouraged and invited to
bring guests to the lectures, and often the lecture hall is nearly
filled with wives and friends of the students. The "ground rules" for
the speakers are also simple. No engineers are allowed to speak to
the students, except on non-technical subjects such as labor relations,
or ethics, or similar topics. The students are required to write a
brief summary of each talk together with a constructive criticism of
the talk. At the end of the series they are asked to hand in the sum-
maries and criticisms, with a brief discussion oif favorite topics pre-
sented, value of the series to them, etc. : This final requirement has
proven of real help to us in planning the colloquia for following years.
It might be of some interest to present a general idea of the types
of speakers and types of subject matter that are presented. Of course
the list will vary from year to year but the following would be typical
for any given year:
An art teacher discussing the present condition of
art in the United States.
A philosophy professor presenting his viewpoints on
religion and its relationship to normal life.
A physical education professor discussing the impor-
tance of a serious personal physical fitness program
for the modern man.
An investment counselor talking about personal invest-
An engineering administrator discussing the manage-
ment role of engineers in our changing society.
A speech therapist speaking about the art of communi-
Every year one of the speakers has been the Graduate College Dean
of the University, talking about the opportunities for graduate study
in engineering. We know that this has influenced many young men to go
on to graduate school. One of the popular features of the colloquium
has been a series of five or six meetings devoted to discussion of the
U. S. patent system. We have been fortunate that we have had available
in our community a gentleman who was formerly in charge of the patent
work for a large industrial organization. He has been a popular speak-
er and has been able, even in this very short time, to instill in the
engineering students something of the value and operation of the Ameri-
can patent system. Each year, a speaker discusses professional ethics
with the students so that they obtain a better understanding of their
responsibilities as professional men in our society.
Value to the Student:
We feel that there are many values that are realized by the stu-
dents that participate in this colloquium just before they graduate
from the University. any of these values have been mentioned earlier,
either directly or indirectly. Certainly the speakers, if well se-
lected, open many new horizons to the students. That the students are
interested in most of these subjects becomes apparent when the question
and answer period arrives at the end of each formal talk. In this re-
gard, I should point out that each speaker is asked to spend only 20 or
30 minutes in a formal presentation so as to provide about equal time
for informal discussion of his subject matter. As a result of these
talks, we have found that the students begin thinking of such things
as their place in their chosen profession, their need for financial
independence, the importance in their lives of art, music, or litera-
ture, or why they might profit by continuing on to graduate school.
It seems to me this is the "real" value of the program. It pro-
vides an opportunity for students to hear of many things, some of which
are entirely new to them. It is amazing to note the skepticism and, al-
most, unhappiness that greets the announcement that the next speaker
will be talking about "modern art", and then to find how interested the
students really can become in this subject because of the stimulus pro-
vided by a good and enthusiastic lecturer. This is merely one example,
but it illustrates the point. In other words, the Colloquium presents
the seniors with an opportunity to hear about things that are important
to people, so that they are reassured that all of life is not merely a
computer, or a handbook, or a hard hat.
We in the Chemical and Mechanical Engineering Departments of Ohio
University are convinced of the value of this colloquium program. As
indicated earlier, we know that several have decided to enter graduate
school as a result of what they have heard here. We know that several
students have been impressed with the value placed on personal and pro-
fessional ethics by prominent men in and out of engineering. We are
delighted when we receive a comment such as one from the Colloquium
last Spring: "The only way to improve the Colloquium would be to have
more speakers over the full semester or even for the full year, It is
truly an asset to a young engineer". We commend the engineering Col-
loquium to all!
SOLUTION TO THE PREVIOUS PROBLEM
which appeared in 2: No. 2, 32 (1963).
Restatement of Problem:
A certain neighborhood grocer weighs his pennies 100 at a time,
rather than counting them. He claims that because his scale is quite
accurate he has "never made an error". If the average deviation in
the weight of single pennies in circulation is 1%, would the grocer's
claim of near infallibility seem plausible?
For a normal distribution, the standard deviation C is 1.25
times the average deviation. Therefore, 6 is about 0.0125 w, where
w is the average weight of a penny.
For the average weight-per-penny of 100 pennies, 6' is 0.0125w/J100
or 0.00125w. For the total weight of 100 pennies, &n is 0.00125 w x 100
or 0.125 w.
Now, an actual error of one penny must correspond to an error in
weight of at least half a penny or 0.5 w (because of roundoff). Di-
viding this interval by ( yields 0.5 w/0.125 w = 4 standard deviations.
From the usual four-place table of area under the normal curve of error,
this high a result corresponds to virtual certainty. Thus, even lack-
ing complete normality, the grocer's claim of having never made an er-
ror would seem quite plausible.
Now try this one on your students
Consider an infinitely long, counterflow, water to water, heat
exchanger. Making appropriate assumptions, prove that the temperature
pinch must occur at the inlet of the stream with the larger flow rate,
and nowhere else along the exchanger.
The solution will appear in the next issue.
In his communication on mathematical errors in engineering work,
Prof. Kowalczyk indirectly raises a secondary issue when referring to
penalties assessed on student examinations. This issue is the funda-
mental philosophy of examinations.
In engineering we can distinguish two basic types of testing
problems, realizing that all real problems lie somewhere between these
In one type we are asking the student to do something which he has
been shown how to do to see if he has mastered it. Here the primary
factors are memory and skill in manipulation, and no one can serious-
ly argue with severe penalties for inaccuracy in execution, particu-
larly on an "open book" type of examination.
In the second type, we are asking the.student to apply what he is
supposed to have learned in an entirely different situation from that
in which he learned it. I must add here that I think this is a far
better type of test of an engineer since it foreshadows what is so
often his situation in his profession, and examines the depth of his
understanding, Here, particularly in view of the severe time limit
so often in effect, manipulative errors should not be a cause for major
penalty, despite the obvious necessity of avoiding them in engineering
Thus, the attitude toward student errors should reflect the
purpose of the tasks set for them, and the limitations within which
they are expected to accomplish those tasks.
Since our major effort on examinations is testing understanding
rather than manipulative accuracy, this raises the question of how
one develops in the students an appreciation of the necessity of this
accuracy. The method that I have found satisfactory is to stress un-
derstanding on tests and manipulative accuracy on reports, where the
(in theory) lesser time pressure makes manipulative errors less justi-
In this way the student develops a feeling for the importance
of manipulative accuracy. Furthermore, since much of his work output
on the job will be in the form of reports, a habit of care here is
very valuable to him.
D. L. Vives
Auburn University, Alabama
Kowalczyk, Lc S., J. Chom. Engr. Educ. 2: No. 2, 28-30 (1963).
TRANSLATION OF TITLES
Spanish Montserrat Ventura and Patricia O'Connor
German M. Zimmer
Current Issue: Volume 3, Number 1, November 1964
The Common-Core Concept and Undergraduate Chemical
Engineering Education. 3
Quo se entionde per "Cursos Comunes" y studios de
pregraduados en Ingenieria Quimica.
Das allgomeine Pflichtfachkonzept und die Anfaongeraus-
bildung im chemischen Ingonieurwesen.
Location and Selection of Process Control Instrumentation. 11
Donde ponor y come sleoccionar los Instrumentos para
control do process.
Platz und Auswahl dor Instrumentation fuor
Some Extracurricular Facets of Chemical Engineering Educa-
tion at the University of Alabama. 23
Algunas facetas on Educacion Quimico-Ingeniora extra
al program do class on la Univorsidad do Alabama.
Einigo Wahlfachprogranmo in der Chemie-Ingoniour-
Ausbildung an der Universitaet von Alabama.
Extracurricular Interests: A colloquium for Engineering
Extra actividados do comun interest: coloquio
para ostudiantes do cuarto aio.
Intorosso an Wahlfaechern: Ein Kolloquium fuor
Studenton im 4. Ausbildungsjahr der Fachrichtung