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. ,tJ l7{EFACE

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TO. TIm. THIR.D,,.E DITI01\I
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The field of thermal ,system design and analysis continues to develop. The
number of workers is gro\\"ing, technical papers appear in greater numbers,
and new textbooks are _being written.
. .
The major objective of this third ,edition is tQ organize so.me of the
new approaches that are now ,avaHabJe and to provide more flexibibty to
- instructors who use Design of Thermal Systems as a texL The changes to the
twelve chapters of the second edition are modest and mainly constitute the
inclusion of some additional end-of-chapter problems. Chapters 13 tPJ"Dugh \
19, ho\v~yer, are all new_ One possible use of th~ text is to cover the

first twelve chapters in an advanced-level undergraduate course and the
remaining seven chapters as a graduate COjJfse. In some engineering schools
students already have some J.01d of optimiiatlOn course prior to ' taking the'
thermal design course. For those classes certai)1 chapters of the fIrst hvelve
(usually the ones on search methods, dynamic prograrrul:ring, and linear
proirarruning) can be omi.tted and material can be supplemented from the,
new seven chapters.
Several of the new chapters are exten~ions of the introductions offered
in the lust twelve chapters, especially mathematical moqeling, steady~state
system simulation', and search methods. Chapter 14 addresses $.Orne of the
challenges that arise when simulating Jarge, thennal systems. New material
appears in Chapter 15 on dynamic be'h~yior, in Chapter 18 which introduces
calculus of variations as a companion to dynamic programming, and in
Chapter 19 on probabilistic approaches to design, which is exploratory.
'.,
The author thanks colleagues both at the University of nlinois at
Urbana-Champaign and at other engineering schools for continued input and
suggestions during [he past several years on how to keep the ,book fresh.
~qraw2Hjl1 would rus,9. like to thank the foHowing ' reviewers for
their
useful comments: John R. Biddle, California State Polytechnic.

many

I t>


PREFACE TO TI-IE THIRD EDmON

X


University, Po'mona; Theodore F. ' Smith,.:1be University 0 '- 0 a; Edward
Q~ Stoffel" CalifonUa State Polyt~chnic .Uriivers~ty; San Luis Obispo; John
A. Tichy, ,Rensselaer Polytechnic Institute;, Daniel T. Va1~I! . e, ~larkson
,College;
?lld 'William' J. 'Wepfet" qe'. . . .
' ,

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The title, Design of Thermal Systems, refie,cts the three concepts embodied
in this book: design, thennal~ and "systems. '


DESIGN
A frequ~nt product of the erig?neer's efforts is a drawing, a set' of calcu~a­
t!ons, or a report that is an abstraction an? .descriptio~ of hardware.' Within '
. ,epgineering education, thl? cookbook approach to design, often practiced
during the 1940s, discredited tpe ' design effort so that many engineering
schools dropped design courses 'from their curricula in the 1950s. But now
design has returned. This reemergence is Dot a re~apse to the earlier procedures; design is reappearing as a cre"ative and highly technica1 , ~ctivity.

THERMAL
Within many mechanical engineering curricula the tenn design J,s limited to
machine design. In order to compensate for this frequent lack of recognition
of thermal design some special emphasis on this subject for the next
few years is warranted. The designation thermal implies calculations and
activities 'based on principles of thermodynamics, heat transfer, and fluid
mechanics.
,
,The, hard,ware associated '1'ith therm~. systems iqcludes fans) pumps,
compressors, engines, expanders, ,'turbines, heat and mass exchangers, and
reactors .. all interconnected with some form of conduits. ' generally, the
.,working substances are fluids. These types 9f systems appear in such industries as power generatio'n, electric'and gas utilities, refrigeration, air conditioning and heating. and in the food, chemical, and process industries .
I

.
'

xiii


xiv


PREFACE TO nIE FIRST EDITION

SYSTEMS
Engineering e¢lucation is predominantly pro,cess )orielZted, while engineering
practice is predornioantly system 'orien(eil. .
cO,urses of study in e;ngi- " "
_' neering .proyide the student wi~
effec~ve exposure to such processes
as the flow of a compressible fluid through' a nozzle and the .bel;l3rytor of
" ,~hydrodynamic and theI"ID:al bou,ndary l~y~rs ,at solid,$q.rfaGes,._lhe ptacti~ing
" . en'g ineer, ,however) is lik~Iy
be confronted with, a task ~ucp' as. desigmng ,
: ~an: _~eG,o,n.~c:-:.sy.st~,Itl __!p~t ,}"~ceiv~~ p,~t~~ g~ _from a. pipeline- aijc;l .,stores ,
it underground '.fo~ )~fef~'~sag~'~ ·- 'Th~r~,~~~~:' a~- big~/iap.:l>.e~,een:Jmoyw~~~qg.~:,;:,~(,.j -,::,:;;" .~'S' ~':
, inqi~id~hl proces~es 4tld rl1e ,~,~tegraticm- ~f these prQc~s.s~s in ~n.·;engiriee~g. , -: '~:~. : " ,. ~~',
enterprise.
Clos~g the gap should ~ot b~ accomplished by diminishing the empha- .
si~ ' on pro~esses. A faulty .~no\vledge,' of fi?1dainentals may result in subs~:'
quent failure of the ~ystem. But -within a university enviroJ!illent, it is beneficial for future engineers to begin thinking in te~s of. systems, Another
re~sonfor more emphasis on systems in the llnjversity envirQnment, in additio,q to, influencing the (hought patterns of students, is that there are sqme
technjques-such as simulation and optinrizatjo~-which only re~ently have
been applied to thennal systems '. 'These are usefui t601s and the graduate
should have s6me facility with them. '
,
While the availability of procedures of simulation and optimization
js not a new situation, the practical application of these procedures has
only recently become widespread because . of ,the- availability of. the: djgital
computer. Heretofore, the lirriltation of time, did not permit hand calcula'tiqns: for example, of an pptirnization of a function that was dependent upon
dO,zens or hundreds of independent variables. This meant that in designing

systems consisting of dozens or hundreds of compof designing an optinll1J71 system was usually abandoned. The possibility of
oprin1iz~tion represents one of the few facets of design,

an

-'.

Most

to

I

OD,T LINE OF THIS BOOK'
The goal of this book ' is the design of optimum thennal systems. Chapters
6 through 11 cover topics and specific procedures in optimization. After
Chap. 6 explains the typical statement of the optinlization problem and
illustrates how this staten1enl derives from the physical situation, the chap-

ters chat follow explore optimization procedure,s such as calculus m~thods,
search methods, geometric programming, dynamic programming, and linear
programming. All these merhods have applicabiH ty' 10 nlany other types' of
problems besides thennal ones and, ·in this sense, are general. On 'the other
hand, the applications are chosen fr~m the therma1 field to emphasize the
opportunity for optimization in this cJass of problems .

..



PREFACE TO THE F1RST EDITION

If the .engineer inLmediately sets out to try to optimize a rnoderately ,
c.omplex thermal system he 'is soon struckl lDy the need for predicting the
performance of that sy~tem. gi veil CeI1aiIl inpu t conditions 3J."1d performance
charac'telistics of' components . This is the process of systein sirn.ulatiolL
System simulation' fl9t. only rp.ay be a, step
the optirmzation'
-but,
·may hav'e a usefuJne~s iI! its' O'1}JI;1 'right.' ,A-,sysren1 may.J~l~, ..gesigrted on. the '
. --,' ··bq.sis of some ..IDaXlrllUm;:-1oad",conditiori\'-but'-maybper~t~' g5·'·: perd~rit'dttl1e··~f~
tiille ' 9-t 1es.s'::t)i~in-maxjmiiiQ. load. System' simulitt-ioll.periuirs an exar.nination
of the. ope~a"tini' condi'ti~'n's that m~y pinpoint pos_s5hle operatiI;tg and c~ntrol
problems at non-design c.onditions.
'
.
.
Since. system simulation and pptimjzation on .any but· the simplest
problems .4?Ie complex. operations, the executio~~ of the ptob~en1 must be
performed on ·a computer. When using .~. computer, the equation forin. of
representation. of the performance of corpp~nents and expression of .prop- .
erties of ,su-bstances is much more' convenie.nt
tabular or graphical
representations. Chapter 4 on mathe~atical mo~eling: presents sOTI?-e techniques for equation development for the case where there is and also where
'. the;re is not some insight into the relationships based in thennallaws.
Chapter J~ .on econom.ics~ is appropriate because engineering design ,
and economics are inseparable. and because ,a frequent cnterion for optimization is [he economic one. Chapter 2, on workable systems, attempts
to convey one simple but imponant dis(inc~ion =-the difference be~een the
. design process that resui ts. in a workable system in contrast to an optimum.
system. The first chapter on engineering design emphasizes ·the importance

. of design in an engineering under1aking.
The appendix includes
problem statements of sevemJ. comprehensive projects which may run as part-time assignments during an entire
tenn. These tenn projects are industrially oriented b~[ require application
of some of the topics explained in the text.
. .
Th~ ~udience for which this book \vas written includes senior or fiisryear graduate ·students in mechanical or chemical engineering, or practicing
engineers in the thermal field. The background assumed is a knowledge of
thermodynamics heat transfer, fluid mechanics. and an awareness of the
performance charactens[ics of such thermal 'equipment as heat exchangers,
pumps, and compressors. The now generally accepted facility of engineers'
to do basic digi tal computer programming is also a requiremen..t.
9

in

process

than -

-

,

XV

some

I


ACKNOWLEDGI\1ENTS (,
Thennal system design is gradually emerging as an identifiable discipljne.
·.. Special recognition should' be given to the program coordinated by the
University of Michigan on Computers in Engineering Design Education,
which in 1966 .clearly delineated topics and defined directions that have
.since..P'oYed
to be productive. Acknowledgment should be given to activities
..
~.


"A.-vi"

PREFACE TO THE FIRST EDITION
-

,.

,

within the chemical engineering field for developments .that are clos.ely related, and -in some cases identical, to those in thy theIDlal stem of ll1echanical
.
I
..engmeenng.
_ .
.
M~y faculty members during the past five years have arrived, often '
.ind~pendently, at the same 'conclusion as the author: the rime .is -oppprtune' .
'. for .dever~pments in th~rmal-. q.~.s.ign. :Mjap.y ,of th.ese. fa<:;]Jlty memb~rs have .
.-:).,. .

-. ':share<;i some of.th~ir ~xperiences in the theilllal design·section' ... ..~ ...~ ~ · ::~··~~·~~:--~:· ·Ellgineering~,:N~Ws.__ and ..h.ave, thus, pirectly and -indirectly c'oritributed

,

,

iaeas 'e*p~ss'~d':jn' ,thisjJd6k;~:,=~~'."':: '-,;~,~,.~~ '~," .~,~,~ ,,\"

I

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This ,.manus'cn p~ ,is'- the'" '::. third~: id{tio~·~· (jt.~· t~:it~ ~in~ftte~a)·:: :~t:~ed~~;:iD:rtht:·:. ~'.~~ :.'~'.',. ': :

' .Design of Thermal Systems c611rse " at,th~ ,University 'ofTIlinois"at 'Urbana--- '-' .-Champaigll7.-I thank the students-Vl·ho have .worked with
in this :course
for their suggestions. for improvement of the
manuscript. The. second
edition
·
,
.
.
I
was an at!:factively printed ~ook1et prepared by my D~partment Publication
Office, George Morris, Pirector; June J(empka and Dianne Merridith, typists; and Don Anderson, Bruce Br~ckenfeld, 'and Paul Stoecker, draftsmen.
Special thanks are due to the Engine~Png Department of Alpoca Chemicals
.Corporation, Chicago, for their intert:st jn ,engineering·,.education and for
. their concrete evidence of this interest shown by printing the second edition.
Competent colleagues are invaluable as sounding boards for ideas and
a~ contributors ~f ideas of their own. Professor L. E. Doyle offered suggestions on the econoDljcs chapter and Prof C. O. Pedersen, a coworker
in ·the development of the ·thermal systems prqgrarn "at the Unive'rsity of
illiriois at ·Urbana-Champaign, prov]d.ed .a dvice at many stages . Mr. Donald
-R. \'\tin and a class of architectural engineering students at Pennsylvania
State University class-tested '~he manuscript and pf9vided valuable sugges. tions from the point of view of a user of the book. Beneficial comment~
and criticisms aJso came from the Newark College of Engineering, where
Prof. 'Eugene Stamper and a group of students tested the manuscript in one
of their classes. Professor Jack P. Holman of Southern Methodist University, -consulting editor of ~cGraw-Hil1 Book Company, supplied perceptive
.con1ments both in. terms of pedagogy as well as in the technical feattlfeS of
thennal systems.
The "illustrations in this book 'Were prepared by George Morris of
.Champaign~ IlJinojs.
By being the people that they are\ my wife Pat and children Paul,
Janet. and Anita have made the work on this book, as well as anyt..hing else

1 dO'1 seem worthwhile.

me

W. F. Stoecker

•.


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"ENGIl\TEERJ]\TG
DESIGN

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1.1 lNTRODUCTION

\

Typical ,professional activities of engineers include sales, construction,
. research, development, and design. Design will be our special concern in

this book ..The immedia,te 1>roduct of the design process ·is a report, a set of
calculations, andJor a drawing that are abstractions 'of hardware. -T he subject of the design may be a process,' an elem,e nt or component of a larger
assembly, or an entire system.
OUf emphasis will be
system design, .w here a system is defined
as a collection of components with interrelated performance. Even this
definition often needs interpretation, becau-se a large system sometimes
includes s·ubsystems. Furthe nn ore , we shall progressively focus on thermal systems, where fluids and energy in the form of heat anel work are
conveyed and converted. Before adjusting this focus, howe'ver, this chapter
will examine the larger picture fn~o which the technical engineering activ-

on

ity blends. We shaH call this larger operation an engineering-undertaking,

··implying that engineering plays a aecisive role but also dovetails with other
considerations. Engineering undertakings include a wide variety of commercial and industrial enterprises as well as municipally state-. and federally
sponsored projects.
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'atteritioIi has been devoted to the

e~gj~~erhi:g ~.dertakings. Studies on these .;~';"/' ;'~DJ.a.,'~IJ)t!o--'.Qi:;':,l.l~~'~:I~~k~i~Rr,t~1~~,~.,~.~,(,~,;~ "steps :'iih~: :procedUres used .reaching decisions.
":'2:::t~f!::'·~,(',';n':;; :; jr;", :":r:.~'n~ .....'V"UL~.L~~~.~~.4 'Qttii~~e 'studies' has been to stimllIate .enginee.rs. to-reflect'
" . ,, « ,.>,:<,.:': ~~p,# ·:'the ,,, .' proces~,es of theillselvfs and oth~rs ·o~ the proj ect','teani.
" ,:',-,,:,:: ,.':;',:~ ::';'~:'i~:~:~;,::,·':' CenaiPIYJh.~~pI:gGes,~, . ~q.I.~f?q~.ep'~e, 9f.',s!.~p'?,,~~llowed in each undertaking is
',:' -~~.~':~:.' ' '': ' ',;:. <:" diffeient~ ' an:d':no ,:oDel's~queDce~' incli.Idii:tgJ~·e·,on,~~· d,~$c;riped,~t.N.s. chapter,
,
is univers,aUy applicabl~. Since the ~starting ,.Ppjrit, the-:goar~~'::aiitf;:¢8:':sidg :,\r~<'~ ,.: 'r;:'
" c;:onditioris differ from ~ne' ~;ndertaking ' to the next, the" pIoc~dllre,s,'·':Pillst ' "',
.8 ..-.... ,r lIr . '. , "

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The advantage of analyzing the de<;:ision process, especjal~y in com~
plex undertakings, is that it ,l eads ,to a more logi~a1 coordinati0D of the ~aJ;ly
individual efforts consti~ting the entire venture. The flow diagram in Fig.
1-1 shows ·typical steps followed in the conception, evaluation, .and execu- ,
tion of ,the plan. The rectangular boxes, which indicate actions, may'represent consid,erable effort and e,xpenditures on large projects. The diamond
boxe~ represent decisions, e.g., whether to c;oIitinue the project or to mop
,
J
it.
" The technical engineerlng occurs mostly in activities 5 and 7, product
or system design and research an~ development. Ljttle will be said in this
chapter about product or system design because it will be 'studied in the
chapters to follow. The'tlow diagra!ll shows only how this design procedure
fits into the larger pattern of the '·undertaking. The individual nondesign
acri virie.s will be discussed next.

1.3 NEED OR OPPORTUNITY (STEP 1)

Step 1 in the flow diagram of Fig. 1-1 is to define the n~ed or, .opportunity.
It may seem easy to state the need or opportunity, but it is Dot always a
simple task. For example, the officials of a city.may suppose that their need
is to enlarge the reservoir so that it' can store a larger quantity of water for
municipal purposes. The officials may not have specified the actual need but
instead may have leaped to one possible solution. Perhaps the need would
better have been stated as a low water reserve d'uring certain times of the
year. Enlargem'ent of the reservoir might be one possible solution, but other
sol utions might b~ to restrict the consumption of water and to se6-k other
soutCes such as wells. Sometime's· possible-solutions are precluded by not
stating the need properly at the begmning.
,The word "opportunity" has po"sitjve connotations, whereas uneed"
suggests a defensi ve action. Sometimos the two cannot be distinguished. For
-example, an industrial firm may recognize a new product as an opportunity,
but if the company does not then expand its line of prpducts, business is
likely to decline. Thus the introct'uction of a new product is also a need.


ENGINEERING DESIGN
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Dere~ine

probability,
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development

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design and
cost estimares

Refine and revise

NOt feasible-drop

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commercial enterprises t typical needs or oppo~~J.t~rgiie in the renovation or expansion of facilities to manufactur~?,f;f -distribute a current
product. Opportunity also arises when the sale of a-.product not manufactured
by the-fh.ul is rising and the ro.arket potential stems favorable. Still a third
form in which nn opportunity arj'ses is through research and developmen[

In

~:I

.



4

DESIGN OF THERMAL SYSTEMS
~

,

within the organization. A new product may be developed intentionally Qf .
,a ccjperitally. Sometimes. a new use .of all eXlsting proQ.uct· can be found
by making a slight modification of it. An orgahization .maY know how to"
manufacture ,a g~JJ?my, sticky sup.stance and a.,ssign ' to the research ,and
developmefl;t department the task of fiIid,ing som~. use Jar it. . . ''':'~J
.' Of interest to us· a~ the ni~IPent is ~e nee~ or ()PP9rWni..ty th.a~ r~q~~es :.. " '
engineering design at a subsequent stage:" ' . , . .
' .

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1.4 CRlTERJA' 'O F

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mterion of sllcc,ess is' 'showillg a ,profit~"
providing a certairi" rate of telurtr .on the -investment. In public ' projects
. the criterion of success is the d~gree tq which Q-le need' is satisfied in relatipn .
to tile cos~~ monetary or otherwise:
'
.
. In a ,profit-and-loss ecopbmy, 0e expected earning power of a ' proposed conimercial project is a .dqmjn~tiDg influence on the ·decision
pro- .
ceed with the project. Strict monetary concerns are always tempered, bow~
ever: by. hunlan~ social, and political considerations to a .greater or ~esser
degree. In other words, a price tag is placed, on the' nonmonetary factors .
..A. factoD' may be located' at- a more remote site at a penalty in !be form of ,
transportation costs so that'its atmospheric. pollution or noise affects fewer
people. As an alternative, the plant may spend a lot on superior pollut~on .
c0!ltIo] in order to be a good neighbor to the surroundIng community .
. ' So:metlmes' a finn will desjgn and ' manufacture a product· that offers
·Jj'a le opportunity for profit sin1ply to round out a line of products. The
a\'aiI~biliry of this product, product A, peMits the sales force to say to a
prospective customer, "Yes, we can sell you product A, but'we recommend
product 'B 7~' which is a more profitable item in the company's line an~ may
acrually be superior to product A. ," .
Often a decjsion, particularly in an emergency, appears outside the
realm of economics. If a boiler providing steam for beating a rental office
building fails, the decjsion \vhether to repair or replace the boiler inay seem,
to be outside the realm of econQmics. The question can still be considered
an economic one. however, the penalty for nor executing the project being
nn overpov';'ering loss.
In· c'ommercial ente'r prises the' usual

i.e.~

to

1.5' PROBABILITY QF , SUCC~~S (STEP 3)
Plans and designs are a]ways dirdcted roward the future, for which only
probabiI ity not cenajnty, is applicable: There is no absolute assurance
Chl;H the pJanr will n)eet the success. criteria discussed in Sec .. 1.4, 'Only a
- li.k;]lihood or probability thai it wilJ po so.
The mention of probability suggests [he nonna} distribution cUrY"e (Fig.
1·2), an excel~en[ starting point for expressing uncertainty in the decisionmaking l?J:Oces
. s The significance of rhe distribution curve lies particolarly
I

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ENGINEERfNG DESIGN
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Probability distribution carve ..

in the evaluation of the area be~eath the cprve. The area under the curve
between xl arid-X2, for example~ represents the probability P of the event's

occurring between valli~s x 1 and X2', Thus,

Since the. probability .of the event's occurring somewhere in the range of x
is unity, the integration. over .the entire range of x is equal to 1.0:

I~o>Ydx = 1
The equation for the probability distribution curve is
.y

=.

h _h2(.:r -a)2
--e
'

. (1.1)

fo

The maxiffium value of the ordinate is hlF, which occurs when x == a.
This fact suggests that increasing the value of h alters the sh 4pe of the
distribution curve, as shown in Fig. 1-3. If hI is greater than h2 , tbe peak
of the h I curve rjses higher than lhat of the h2 curve:
.
To extend the probability "idea to decision making in an engineering
undertaking, suppose that a new product or facility is proposed and that
the criterion for success is a 10 percent rate of return on the investment
for a 5-year life of. the plant. After. a preliminary design, the probab~ity
distribution curve i's shown as indicated in Fig . 1-4. Since rough figures
were u~tIoaghout the evaluation, the distribution curve is ,flat, indicating

no great confidence in an expected percent of return of investment of. say
t

5


- .;:- J ,

-j '

, ... ..." -

x=a

" '0' -"

,\i..

x

F:IGliRE 1-3
Several different shapes of the probability distripution curve,

18 perc~nt, The expected rate of return is ,attractive enough, ho~ever~
to proceed to _a complete design, including cost estimates. If the most
probable return on investn1en{ after till s complete design were 16 percent, for
example, the confidence in this figure would be greater than-the confidence
in the 18 percen t figure after the preliminary design because costs have now
After 5 years


After 1 yeaI
After

pf operari on

construcrion

\
,o

8

16
I

Retum on investment. %

FIGURE 1-4
Disr.tibutieilllAi ~eS at -various stages of.decision making.

24


ENGINEERING DESIGN

'"/

been analyzed more carefuUy C).nd mar.keting studies have been conducted_
more thoroughly.
_ .

I L
The. probab il ity distribution curves at Hvo other stages~ after construction and after 1 year.of operation, show progressively greater q~grees of .
confidence. in·.the rate of retuill;after a 5-ye~r life. A.fier:.5 . ye~rs; th~ rate of
return- is kllQWn exactlY1 and th.e . :prob)abi1ifY;,distiibut~dn·"c~rve - degeD.e~tes- .>-,"-' into' 'a: c urve-.. that:- is' infinites tmally' ··ttli·riw·and'::illfini-tely. .:;hi gh~,~:;' -;,',;\ .:~:o ;'>:->.:~ ,-.. :~.,:-:~:.~;;. :'\.~.':.
-~h¢ re¢9ghition th.~~· pr:edj.¢.ti9~ :pf:fjJ.Jilte ?-eli.~vi6r is "rioi :deterrmriisii.c!t·"
so that only one ~Set of events or cOD:ditions \vill prevail, has spawned a ne\v
probabilistic approach ' to design (see the addirional readings p-~ the e~d of
the chapter and Chapter 19). One of the activities of this new study is .that" of quantifying the curves sho\vn in Fig_ 1-4. It is valuable for the .decision
maker to know not .only the most likely v3Jue of the rerum on investrTIent .
but also whether there i$' a high- or low.probability of achieving this mO${
_ likely value~ "

1.6. I\tIARKET .ANALYSIS (STEP 4)
If the undertaking is one in which a product or service' must eventually be
sold or leased to customers, there mus! be some indication of favorable
reaction by the potential consumer. An ideal fonn of the information provided by a' market ana-lysis would- be a set of cu[\(es like tl:ose in Fig.
l~? With an increase in .price, the potential volume of sales decreases until
- such a high price is reached that no sales can be made. The sales-volume _
to price relationship affects the· size of the plant or process because the unit
-price is often lo\ver in a large plant. For this reason, (h.e marketing and.plant
capabilities must be evaluated in conjunction with each other.

/

High sales and advertising effort

~ ~------------------------------~------~----~~

Prier:
f1GURE;M~_


End resulTof-a market analysis.


8

DESIGN OF THERMAL SYSTEMS

Because the sales and advertising effort influences the!"Volume of sales "
for a given price, a family of curves -is'expected. Since a cost is associated' :'~,:,
with the sales and advertising effort,sib~e a continuous increase of ,',
this effort resuits ~n dirninishffig improvement in sales there eXls'ts an " "
optimum level of sales and' adv~rtising effort. A marketing plan, should ,:' '
emerge 'simultaneously \vith the ,tec~cal plans Jor the undertaking~' ,

and

I

_

o,!

"r

' I,

_

"


. - -,.....

. ~" :.,

,'~':, 1 '.7: ,~~FEASIBlLITY,..(STEP

'.

~,

'

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'

'"

. ; •• •

~

•

•

-

fI


' ,:-

6} , -

~ .:

,"

•

'. : '

.'

,

:.!. ,~~·~:'I&A.,"·-:; 'I. -",,:2:,I:~:-~·;,;,"· ... .;-:-' ""
~.
~'.
i '"; .
i.
The' feasibility ,sWdy'," ,step "6, .;n-d,: 'the" :sllbs~qu~nt'feasi@rty, :a~ci#O:ii~
:,:,~:," ~:,~~,:"­
t~, w~ether the' project
'everi',possibie~' It "proJecl:may ' be -feasible," ,ar
possible, ,but not economi,cal. Infeasibility may result from unavailability
of inves~ent capital, land, labor; or favorable zoning regulations. Safety
codes or other regulatory Jaws may proJ:ribit.the enterprise. If an undertaking
is shown, to be infeasible, either altertlatives must be found or the project

must be dropped.

:--:'"

~

. . '. \' ..... . .", .... >... . . . :-~

.-.~:::'~~~~.-

-&

'is

..

-•

•

"

.

..

-

'


.

, ;

.

....

_

a,' •

refer

1.8 RESEARCH AND DEVELOPl\1ENT
(STEP'. 7)
If the product or process is one new to the organization, the results from
research and qevelopment (R&D) may be an important input' to the decision
'process. Research efforts may provIde the origin or improvement of the
" basic idea, and development ,work may supply . \vorking mo_dels or ,a pilot
pJant, dep~nding upon the natl.l!e of the undertaking.
Placing R&D in a late stage of decision' ~aking, as was done in Fig.
1-1, suggests that an idea originates somewhere else in the organization or in
the field and eventually is placed at the doorstep of R&D for transfonnation
into a workable idea. The possibility of the idea's originating in the research
group should also be exploited .and is indicated by the dashed line in Fig.
1-},. Rese:arch people often learn of new ideas in other'fields which might
be applied to their--Q\vn activity.

1.9 ITERATIONS

The loop in Fig. 1-1 emphasizes that the decision-making process involves
many iterations. Each pass through the loop improves the amount and
tbe quality of infQtmation and data., Eventual]y la point lS reac~ed" ,where
final decisions are made regardi~g the de~ignt prod\lction, and marketing
of the product. The substance that circulates through ~s flow diagram

is infonnatio,n which ' may be in. the form of reports and ~onyersatjons
a'nd f!1ay be both verbal and pictorial. The iterations are ' accompl ished by
c6mmunicatron between people, an'd this communication is interspersed by
t

go-~r-no-go

decisions.

..

•

'

_

-•

.


ENGINEERL"IG DESIGN


1.10 OPTI1VIIZA.TIOI\T

O~F

9

OPERA.,.TJOlr1
: .

)

The 1low diagr:ln1 of Fig. 1-1 termipates with1the constnJction or begin~ ing
of lnanufacture of a product.
service. Actually lli.~other stage takes over
. at thi:s point, which seeks to optimize rh~ ope~ation of- a given facil.ity. The
facility was designed on the ba~is , of.qc~ain,9-~sig.r:t p~ram~Fer5. which almost
jnevit~bly cha.11ge by the tirne the facility )s iri-'optration~"rr(e ,ilext ,challeng'e, :

or

. ,~thell ~ is": to··'op~.rate ihe-1~cility'· iri':'rJ1e-'bes't-~p'6s,s'i5ret'fri'a.n.:ne';:' ip-- 'tii:e~ Jigl11:~6..r"
'such facto(s a$-acnt~al costs arid ' pric~s. A' painful' activity occurs when ,th~"
project is not profitable and the ob.jective becomes ,that of minimizing the

loss.

1011 ' TECHNICAL DESIGN (STEP 5)
I

5 in Fig. 1-1, the product or system design, ,has no~,. been discussed~

'The reason for this omission is that the system design is 'the subject of this
book from this point on. This step 'js where the largest portion of eng'i neering
, time, is spent. System design as an activity lies some\vhere between the study
and analysis of individual processes or cOillponents and the larger decisions,
\vhich are heavily economic. Usually one person coordi~ates the planning of
the undertaking. This manager normally ~merges with a background gained
from experience in one of the subactivities. The manager's experience might
be in finane'e , engineering, or marketing, for example. Whatever the original
- discipline the manag~r must become conversant with -all the fields that play
role in the .decision-making process.
..
The word "desjgn~' encompasses a wide range of activities,. Design
may be applied to (he act of selecting a single member or part, e.g., the
size of a tube in a heat exchanger; to a ]arger co'mponent, e.g., the entire
shell-and-tube heat exchanger; or to the design of the system in which the
heat'ex:chang'er is only one component. Design activities can · be, directed
toward mechanical devices which incorporate linkages, gears'~ and orher
moving solid members, electrical or electronic systems, thermal systems,
and a multitude of others. -OUf concenrration win be on thennal systems
such as those in power generation, heating and refrigeration plants, the
food-processing jndustry, and in [he chemjcal and process industries.
.

S,t~p

a

1~12

7


SUMMARY

The flow diagram and description chapter are highly simplified and are nor sacred. Since mmost every undert~ing is different. there are almost infinite variations in startit:lg points,
goals, and intervening circumstanc~. The purpose of the study is to emphasize the advantage of sys.tematic planning. Certain functions are common in
the evaluation and pJanning of undertakings, particularly the iterations and
the dec~[ occur at various stages.

.""
'


10

DES1GN OF THERMAL SYSTEMS

ADDITIONAL READINGS
Introductory 'bQoks on engineering design

I
)

",

Alger, 1. R. M .. and C. V. Hays: Creative Synthesis in Design, Prentice-Hall. Englewo,od
Cliffs, N. J.~ 1964.
Asimow, M.: Introduction
to Design, 'Prentice-Hall, Englewood Cliffs, N. J.,c .1962.,_.
"

,_)
Beakley, Q. ~., and H. W. Leach: El1gi~1eering, ,f-n Introduction to a Creative Profession,
,
, Macm,!l1an, New York, 1967.
"
, '
"B'i ml; .H .', ,R.:. c..r.e~riv,e. ~ngi.neering Design, Iowa State Un,iversity Press, 'Ames, 1960-.·- .'
,~ '. " DJxori.-J:;R::·.bes"gn-'Erfifrreeri1'):g:~il:tVe!llil~eness, Analysis~' ,a nd Decision Ma~ng, :M:c(h:ay.;- '
,
,
Ifill, 'New' Y~~k,_ ~966. , "-, ~'~c/:'~' :~~::~.'i:,:,,::'..~:~,-::.,~'~i;-i,_,/.,:,<,~ , , ~ ~/ .~::,; _ « ,(,,: ~,"' ' :~'< ~ :~
';'~_: " ',;-,;,~:.~ ':'J ~1:';:,!.,_:v ~ ,
, Harrisberger, L.: Engin{!ersmD;lzshipJ .. APhilosopny· 'oj Des;in~ Brb6kS1C6re~· Berriiont~ '·Caiif.'~ '-., ., -, ', '

' : , , ',-r' "

' : .',

, :::,;

,. .

'
'
,
KriGk. E. V.,: 'An Introduction to Engineen·ng and Engineering Design, Wjley, New York,_
I

1966.

1965.
Middendorf, W. H.: Engineering Design, Al~yn
·1'4.isc;hke~

and Bacon, Boston, 1968.

c. R.: ~ lnrroduciion [0 Computer-Aid,ed,Des(gn

I!entice-Hall, Englewood Cliffs,
N. l., 1968.
,
11orris, G. E.: Engineenng. 'A pecision-Making Process, Houghton -Mifflin Company,
Boston~ 1977.
Woodson, T. T.:-Introduction to Engineering Des,ign, McGra~-Hill, New York, l ,~§6 .
7

. Probabilistic approaches to design
Ang, A. H-S., and \V, H. Tang: Probal;iliT), Concepts in Engineering ,Planning and Design.
Wiley, New York. 1975.
Haugen, E. B.: Probabilistic Approaches to Design, Wiley. New Yqrk, 1968.
Rudd, D. F., and C. C. \Vatson: Strategy of Process Engilleen'ng, Wiley, New York, .1968.

I

.
'

-

..... ' -

-.


I I

.

, ., : .. ,

. ', ..

,

...

"

•• 1

.'

. ."

.

r~)
[/
.

•

, '.

r

'

" "t~:':::,:::). ~.,:-;~,

!
'.J ~

: '.

•

..

'"

DESIGNING
.A WORKABJ-.JE
SYSTEIVl·
I

'r:

2.1 WORKABLE' AND OPT1l\1UM SYSTEMS
The simple but important point of this chapter' is the distinction ·betwee:p.'

designing a workable system and an optimum syst~m. This chapter also
continues the progression from the broad concerns of an undertaking~ as
d~scribed in Chapter 1, to a concentration on engineering systems and, even
,more specificull y, on thermal systems.
It is so often said that ~4there are many possible ans'wers to a design
prpblem'" tba.t the idea is sometimes conveyed that all solutions are equally
desira151e~ Actu~lly only·one solution is the optimum, where the optimum is
base~ Or:l some defined criterion, e.g., cost, size, or weight. The distinction
then win be made between a workable and an optimum system. It should not
be suggested that a workable system is' being sc·omed. Obviously, a workable syster:IJ is infinitely preferable to a nonworkable system. Fu rthenn ore ,
extensive effort in progressing from a workable toward an optimum system
may not be justified because of limitations in calendar time, cost of engineering time, or even ' the r~liability ,of the fundamental data on which the
design is· based. One point to be explored in this chapter is how superior
solutions may be ruled out in the design process by prematurely eliminating
so~e system concepts. Superior soiutions may also be precluded by fixing

interconnecting parameters betweerl components and selecting the components based on these parameters instead of letting the parameters float unti1
the optimum total system emerges.
~

.-

11


12

DESIGN OF TIfERMAL SYS1EMS

2~2

A WORKTCAJ3LE SYSTEM

.

A .workable system is one that .

''' '''. :~!•.

! •. • . .

,

1

,

.

',:'

I'

of

. 1 . .Meets the requi:rem:ents of the. pllrpose~;, the system, e.g., pr~viding the . .,
req~ired
of power, heating., cooling, or fluid flow., or sllITouild.ing
it spac~'vith a specified environm~nt so ·that peopI~ will ,be .. coIPf6rtable '. ,... ~
. :~~ . ~,~Qri_a~., ch~lnJca4 P.tq_c~s.~_ "Yi1Lp!oceed or not proceed

.
2~'~ ~iiil·'Na~e··:~ati~f~-~'t6~;/lif~~:~~·~fu.:~i~ten~ce·£_6s¢:/~:'!.~};,;~~c~::·.:.~'<'.:.:J :.,: .::' ~~<:: .:: :/~ : ~ -- ':'~':"'__
3. Abid~s by. ali constraints, · sllch as 'size, ' .we~ght~ .i~~p~r~trires~ ·'jpr~ss~i'e';< .' ~ '. ' "
materia) properti~s, noise, pollution,' etc. .
. .
.

amount

,1. .

..
'

- In summary,' a workable system ·.perfortlls .the

. .-

. imposed

'as~igned

·task within the

con~traints.

2.3 STEPS IN ARRIVING AT
A WORKABLE
.
.

... . . :SYSTEM
.
:~

The

t\VO

rriaj~r' steps in .achieving a workable system are (1) to select the

concept to be 'used an~ (2) 't 6 fix whatever parameters ar~ necessary to select

the components of the system. These parameters must be chosen so that 'the
design requirements .and constraints are satisfied.

2.4
. CREATIVITY' IN CONCEPT' SELECTION
'Engineering~ especially engineering design. is a potentially creative activity.

In practice creativity may not 'be exercised because of lack of ~ime for
adequate exploration, discouragen1ent by supervision or environment, or
the laziness and timjdity of the engineer. It is particularly in selecting the
concept that creativity · can be exercised. Too often only' one concept is
ever considered, the concept that was used on the last similar job. As a
standard practice, engineers should discipline themselves to review all the
alternative concepts in some manner appropriate to.· the scope of the project. .
Old ideas that were once discarded as impractical or uneconomical should be
constant1y reviewed. Costs change; new devices or materials on the market
D1ay make an app'roach successful today that was not .attractive 1a. years

. ago.

2.5 WOEKABLE VS. OPTIMUM 'SYSTEM
.

<

The distinction between the approaches used in aniving at a workable system
and an optimum system· can be inustrated by a simple example. Suppose
that the pump and piping are to be selected to convey 3 kgls from one
location to another 250 m away from the original position and 8 m higher... If
the design is approached with the limited objective of achieving a workable
system, the foJlowing procedure might be followe'd:


13

DESIGNlNG A WORKABLE SYSTEM

2 The ·.;::;lcvauoIl of 8
<•

•

.

ill

imposes a prc$sure
difference of

.
I
3)?

(8 m)(lOOO kg/ill )(90807 mls-'-)

=

7805 kPa

Arbitrarily choose. an additional 100 kPa to COlnpensate for, fg~tion in
the 250 ill of pipe.
, ' . I
... .'.~' :'. ,~."..
'.
'
. '
, '~2o' itccording to' the foregoi]J,g decision select a pur.o.p ,;vh:kI~l'. delivers 3 legIs
,
'. '. -,--Y:.agalnst a -pres~llre-~-d.i[ference...of~\L1,8 . 5); k:f)~.<~jnqllY-'~;iselect~,a~~:g~H~,}si?;~:~~:) r:,:f.~'Y\'"
frqni- a h,!IldqQok such "thaf the pressure' drop:in 250 m··'of.Jength is-)UO··::···· ., . "
kPa or less. A pipe size of - 5~ rlli-n' (2 'hi) satisfies the requirement . ~ .
1

. 'A~poaching the' same problem with the 9bjective of achieving an optimum system presupposes agreement on a c~terion to optimize .. A frequeptly
chosen criterion .is cOS.t (sometimes fn-st .~ost only in speculative projects,
.and sometimes the lifetime cost, GOI?-sisting of first plus lifetime pumping
and maintenance costs).
~ designing th~ optimum pump
piping system for minimum 'lifetime cost~ ,the pressure rise to be developed by the -pump is not fixed immediately but left free to float. If [he three major contributors to cost are

(1) the rust cost of the .pump, (2) the fIrst cost' of the pipe, and (3) the .lifetime pumping costs, these costs will vary as a function. of pump pressure,
as shown in Fig. 2-1. As the pump-pressure rise jnc.reases, the cost of the
Pl!mp probably Increases for the required flow rate of 3 kg/s because of the
- need for higher speed ~dJor larger impeller piameter. W~th the increase in
pressure rise) the power required. by' the' pump increases and is reflected in

and

,

Ui

o

First cost

U

" 0

of pipe

50

100

150

Pressure developed by pump. kPa

FIGURE 2 ... J
ContribUtions to costs by pump and piping systems.

250

' .'

~

.


14

DESIGN OF THE.KMAL SYSffi.\1S

a higb~~ lifetime 'pumping cost.' The first cost of the pipe, the third contrib- .
uto.r to, i:p.e t~t~ co.st,. "i;>ec~m~s 'e nornollsly hi~h as th~ presSUre available -to'
overcome fricTIon ill the pIpe .r educes to ~ero. The avaIlable press~e for. the'
.pipe is the pump-pr~ssuIe rise minus 78.5 .kPa. need~d for the difference in ,
'.elevation. An appropriate' optimization technique ~ ~~ used to deten;n1ne
the optim~ pump-pressure rise,.which in Fig. 2-1 is approximately-ISO kPa~ '-, _'
,

-. :

. " ,.-,

., . ! "

" Fip~lly the pump can '~e selec~~d . to develop l.?O-J~~" p'ressur~ -r ise':," ~~,

: .:

.... .~~::.::-; .', " ';;~-<., . .' :.~ ... pipe
:··J~P~.'

,-"
I'

!
:

--- , . -.

.

si.ze ~an be chosen such that the pressure drop

or"Ie~'s ':.

~J

!",:" . : ,;\'- , '

-, : • •

-

.-,

'" --.' ."

• . "

'.

... .Th~t~ne'er'ili~'~pr~edi~~-diseri~~i6rr'

' : ,:' ,;

due to friction
"

..

:_- ~ ,

.. - ' ... .

'~"

;

,a , ~;,

is 71.5
.,'.' ..

'.

:.'

mal6ires\t~ti()1~~ pref-~ten~~:"

-towax:d designing optinium systems.-· To·, temper thi.s bias, several additional
c~nsiderations should ,be_mentiqried. ,I f the job is a small one" the' cost 'of,
the increased engineering tim~ required Jor optimization ~a'y devour the
, -savings, if any. Not only the engineer's time but pressure of c!iIendar time,
-nlay not permit. the desigil to proceed beY0!1d a workable design.
t

2 .. 6 ' DESIGN OF A FOOD-FREEZING
_PLANT'
Large-s'cale engineering projects are extremely complex, ~'d decisions are
often intricately interrelated; not onJy do they influence each other in· the
purely technical area but als9 c~oss over into the technoeconomic ) social,
and human fields. To illustrate a few of the decisions.involved in a.;-ealistic
, ~ commerclal undertaking and- to provide a further example "B(the contrast
between a workable ~ystem and an optimum system~ consider the following
project.

.(\. [ooq company can buy sv/eet com and peas from farmers during the '
season and'sell the vegetables as frozen food throughout the year in a city
300 Ian away. What are the decisions and procedures involved in designing
the plant to process and freeze the crops?
.
The ,statement of the task · actually starts at an advanced stage jn
the decision process, because it is already assumed that a plant will be
constructed. This decision cannot realistically be made until some cost data

are available to evaluate the attractjveness of the project. Let us aSSUDle,
therefore, that
'arbitrarily selected soJuriq,p has been priced out and found
to be potentially piofita ble. We are likely then, to
ve at a sol utian that
is an improvement over the arbitrary selection.
Son1e major decisions tqat _ rpy..~,~ , .pe , ,m'lc;le . are (1) thew location,
(2) size, ~nd (3) type of freezinp pl~t. The plant could be located near
(he producing area, in the market. city, or somewhere between. The size
\vilI be strongly influenced by the market expectati'on. The third decision,
the type of freezing plant, embraces ,the engineering desjgn ~ These three
major ·decisions are interrelated. For example, 'the location an d' size of plant
might reasonably influence the type of system selected. The seJec£ion of the
type of freezing plant includes choosing the concept on wh'cb the freezing-

an

I

am

--

.:-


DESfGNING A WORKABLE SYSTE:v{

15

).

plant des ign \vv. li be based. A.fter the cO.ncept has been decided:. the inter:nal
design of the plant can proceed.
I )
.
An outline of the sequence of tasks and decisions by vvhich a wQrkable
, design could be arrived at ' i~ as follows:
, ...:.- :

' . ...' _- . --l. · I?~Gjde-.t.o locate the .plant i~ the ·.tharket ~ity adjacenf::t~ a
, ." ... :--'·:"~::' w~reflouse~~perated"by :.the -co_inpany.· . "~'" ' .0.·,,,,. -. ,; . . - . ' " :
2~ Select the , freezing · capac'i ty of the plaiil

-availability of
fini!l~.iQg.

~etpgernted
" . '. '

".- ......

on

.the· : basis o.f the :. curre.nt .'~.
the crop, the pqtential sale in the city, ~nd il vaiIahIe
'
.
.

-'34 Decid~ upon' the co~cept to be used in the freezing plant, e.g. the one
7

. ..

shown in Fig.' 2-2. In this system the food 'particles are frozen in a fluidized' bed4 in' \vhich low-temperature air blows up through a conveyor
chain, suspending the product being ·frozen. This air returns from the '
fluidized-bed conveyor to a. heat exchanger that 'is the evaporator of a
: re~rigerating unit. The refrigerating unit uses a reciprocating cOlnpressor
and water-cooled condenser. A cooling to\ver. in tum, cools the condenser water. rejecting heat to the atmosphere.
4. The design can be quantified by establishing certain valueS. Since the
throughput of the plant has already been detelmined, [he freezing capac~
ity in kilograms per second can be .c omputed by d.eciding upon the nUffi.' ber of shIfts to ·be operated. Assume that one shift is s.elected, so that
DQ":' the .r efrigeration load can be' calculated at, say, 220 kW. To proceed
with the design, the parameters shown in Table 2.1. can be pinned down.

Air

Water

Pump

f:m
FlG~

Schemaric flow di:lgram of freezinE

Condtnser

~.

pl~nr.