smPtmb=# 1941
INDUSTRIAL A N D ENGINEERING CHEMISTRY
are d y the result of inaccurate machinii or of an ediort to build too much flow capacity in a given body siae. It is well to he auspicious of control v d m of very hi& capacitg. ratinga. The next larger body sine may be well worth the additional &. Figure 8represents~tivelyaimple applications. Afaotor that w88 neglected is the p i b l e &ect upon the oil flow of the means used for atamiastion. Another important factor is viscoSity. Ifthe oil is very viscous, it is important to provide a anitable heating s m which will as~urefluidity. Adjustsble resistsnoesto flow, such aa valvea V in Figure 8, must be maintained within a limited range; otherwise the eiTective chsraateristio will be seilously altered. Preferably atop. should be provided to limit the range of motion. If shut05 valves are required, they should preferably be =parste. Consider a complicated but fairly common caee for which the & d T e &tadan&’ ‘c is not readily caloulsted. The teonperature of vapor from a fractionsting column is controlled by adjusting the flowrate of ratlux supplied by a dire& &ing reciprocating pump with the control valve on the steam side of the pump. The flow of d u x is dependent upon the inherent valve charactmktio, the steam supply pressure, the pressure drop a01088 the valve, tbe &&nay of the pump, and the p m a w against which it is working. When such a chain is involved, a ked e d i d v e characterintic can he maintsined only when each contsollable element is held constant. A frequent causeof troublein this particnlar cam is an oversise or badly worn pump which &wen to function in accordance withanydetmtma ‘ blelaw. If, instead of a raciprocating pump, a centrifugal pump is
1109
used with a control valve in the diaohsrga,and parti&ly if the pump is driven at esaeatially constat sped aa by an induotion motor, the b b l e variable faotom are greatly raduced. The a h a r a ~ t i cof the centrifugal pump e n h into the efiective charactmktic. Testing
Tmuble shooting on the more di5cult control applications may be greatIy facilitated by pmviding for pressure taps on either side of the control valve and by installing an orificefor flow megsurements. The ediective valve characteristic can then be readiiy determined at any t i e . In the caee of the d e r diaphrtxgn-motor operated valves, it is convenient to use a dial gage such 88 the Ames No. 88, with a range of one inch, to measure the position of the valve stem. Rehnnces (1) Barman. D.J., Rsfrna N&md &dim Mfr.. 18.60-61 (nu., 18as). (2) BrLtol. E.8.. and P h .J. 0..Trmu. Am. Sa. M r d . E w & . Bo. 81160 (1988). (3) Cdender. A, and Btsvemm, A. B.. Soc. Cham. I d . . &a. CAm.Sw.GTOUP, 18.108-16 (Oat. 16.1936). (4)F.imhild. C.0.. Indrumenfa,13,8344 (Nov., 1940). (6) orsbe. J. J.. Bound& R. E ..and Ckmek, R. W..‘Plotu. Am. rtul. CF-. E W ~ . . a l i a (1033). (6) Hnider. E.D .. Ram. Am. SOO. M r d . Enpn., Bo. 683-40 (1988). (7)I-&. A,.J . l n d . FU* 7,117-38 (Feb.. 1984). (8) Muon, C. E., and PhilMok. 0. A,. Tmtu. Am. Soc. M d . E m & , 6!4 M (1940). (0) Bmith, E. 8..Zbid., 53.291-308 (18a6). (io) &pitrd~. A. F.,m..BZ. 6i-m ( 1 ~ ) .
as.
EDUCATION, EXPERIENCE, AND ENGINEERS w.d.a+ Don Cbemid Company, Ann A r h r , Mioh.
of THOSE . of us. who. have been active in the profwion rememcheuucal engmeenng for a considerable time c ~ n
her the days when it WBB largely applied laboratory chemistry. The training and point of view of most of the older men who were in charge of departments of chemical enginsering were to a great extent those of the laboratory chemist. It required a c o d e r a b l e stretch of the imagination to call the coulsee then given “engineering c omes”. However, thanks primarily to the activities of the group at Massachusetts Institute of Technology (and, we believe, also to a certain extent to OUT group at the University of Michigan), a gradusl undmtanding of the eignifiosnce of unit operations became, if not actually widespread, at least accepted in a part of the schools and the profwion. The crying need of chemical engineering at that time was for a fuller understanding of the theory of these unit operations. Consequently the firat thing that moat of us fought for WBB an adequate reBearch program to advance our understanding in this field. This movement haa now progressed to the point where practically every school with chemical engineering courses worthy of the name has a unit operations laboratory and at legst one man on the stsg who is trying to do some theoretical research in unit operations. One of the indices of the growth
in this field is the satisfactory symposia which have heen held during Christmasweak for a number of yearn. At the Sympsium on Separation operations held in Ann Arbor, December, 1939,I was asked to open the program, and some of my statements at that time called forth considerable critickm. This WBB largely due to the fact that, because I was trying to be brief, I did not amplify or explain my m marks; the present tslk is primarily an amplification of those statements and a plea for a new point of view for the teaching of chemical engineering. what I mid ttpt called forth 80 much criticism waa a p proximately this: “The papers p m t e d st this symposium are not chemical engineering. The type of work they represent may be neeeasary to the advance of chemical engineering, but it is not dl of chemical engineering or even the most important part of it.” What I am trying to get a c r m is the idea that, when a piece of purely theoretical research is finished or when the differential equations have been integrated, the problem is not solved, contrary to the opinion of many of the bright boys who are teaching chemical engineering. At that point the problem has just begun. Any definition of engineering that , can possihly be worded w i l l refer to it aa an art. An art it is, and an art it must remain for a much longer period than will he
1104
INDUSTRIAL AND ENGINEERING CHEMISTRY
compassed by the experience of emn the youngest man here.
Them are too many things that we do not h o w and toomany things that are too complicated to expm mathemstidy at
present, for us to solve enginwing problems by pure calculation at the desk. The engineer is the man who must build equipment, sesemhle it into a process, and make it run, whether or not he bas all the theoretical data necessary for its calculation. He must think of equipment in t e r n not of nicely 80lved diBerential equations but of actual chunks of east iron and steel that somebody shall be able to fabricate, assemble, and operate in terms of a working, practical, emnomical prooeas.
ONE of the incidents that hss remained in my memory for many years happened when a certain design of c r y d l k r wan being worked on. A young and very able man who had made some of the calculations was then presented with the problem of translating these problems in terms of actual equipment. Hi% reply was, “I’m not interested in that; that’s nothing hut theart.” It is unfortunate that the situation in many schools is such that the most brilliant young men who have natural ability for theoretical work are encouraged to go on for doctora’ degrw and then to seek teaching positions. Many schoola must of newssity hire such men; because a man good enough to amount to anything 88 a teacher, who has had any appreciable experience in industry, is usually good enough so that the school cannot match the salary that industry will pay. The natural d t , however, is that more and more teaching positions are 6Ued with men who have an exaggerated idea of the importance of theory without the practical experience to balance it. Them men believe that, if they are turning out students who can carry out intricate calculations, they am trainingengineera. My own opinion in that they are not. The worstpartof theaituation, however,isthatowingtothemethods now employed for selectingyonnger men to teach chemical engineering,tbia point of view is becoming e&-perpetuating. Because of this ljmited point of view ofmany of the younger men in chemical engineering, what I have tried to say in the past baa been misunderstood. Immediately after my r e marks at the ayrnposium in Ann Arbor a young man who WBB teaching in the petroleum field and speeialising in therm* dynamics said to me that the petroleum industry bad ~peoifid y stated they wished the schools to give men a basic training and not to teach them petroleum technology. This in comet, and I fuUy approve. I believe that the details of technology are not suitable subject matter for instruction in c o u m in chemical engineering, and that technology is of value only aa it provides a background and a perspective for the more fundamental aspects of chemical engineering. The very fact that this man made such a remark shows that he did not understand what I w88 trying to get a c m . Other teacbers have complained to me that practice cannot be taught in school; that during the four to six years a man in in the university be must concentrate on the theoretical 88pectsofhisprofession,andthatitshouldbe.tbejohofindustry to tesob him practical details. With thia point of view also I am in complete accord. For many yeara when I waa teaching unit operationslabom tory, I vigorously oppased all those types of experiments in which a man is given a mimeographed outline tellinghim that, to determine the heat transfer coe5cient of a certain piece of apparatus, he is to open valves A, C, and F and close d v e s B, D, and Q, read thermometers 1 and 2, etc., and that Snauy the heat t r a d e r coe5cient M item 67 minus item 32, divided by 124. I have no use for such experimentsor any other experiments which try to teach a man how to operate a particular type of equipment inatead of trying to teach him what goes on in the equipment.
VaL 33, No. 9
IF, THEN, I am not talking about teaching more technology, and if I am not talking about factual information on the operation of speci6c equipment, what am I talking about? What I have in mind is a point of view, something extrrnnely inhqible but nevertheleas supramely importsnt. For inst9noe,I know of a young engineerwho had to design a couple of beams to go acm a W 20 feet in diameter to support a stirrerand a 6horsepower motor. He dove into his notes and form& and came out with the statement that it needed two plate girdera, each with a m b 6 feet deep, to mp port the stirrer. Now, n good many rsilmad bridgea with a %foot span carry main-line freight trains without girdera 6 feet deep. When he was faced with thia statement, he said he couldn’t help it, that waa the answer given by the formula. Lster he found he had made a mistake of two or three place in hin decimal point. The important point in this mtuation is not that he made the mistake and not that he didn’t have the expmience to recognise that the solution waa ridicnlous; it is that when the error w88 pointed out to him, he did not conaider it eeriou~or important. He thought the mere fact that he had used the correct formula waa the only thing worth conaidaing, and that themfore he should have been c r d i k d with the correct S O ~ U ~ ~ofO the U problem. Any one ofmany conma on machine design will teach the to hold a student how to design the number of bolts nepair of 5ngea together under a certain pressure. I had such a problem once. It involved holding a cover onto a reaction vessel carrying 160 pounds pmure. It was eaay enough to figure the total streas on the cover and the total crom ~ection of the bolts necessary to hold it down. So far as the formula waa concerned, and nnfortnnatdy so far as many of the men teaching this work are concerned, the answer might be 136 ‘/Finch bolts spaced at 7/8 inch, or 36 ‘/,inch bolts spaced on %inch centers, or eight 1-inch bolts spaced on IZinch centers. To anyone who has handled such matehd, and eepeciaUy to anyone who hss had to d e such a piece of apparatus tight with his own hands, there is not much choice of answera. AE far BB I am concerned, I would use about 30 6/&nch bolts. Then a dudent cornea to you and says, “How do you know which one of tho= ~nswerais correct?” The question of whether or not you can tell him which one is correct is exadly what is involved in this point of view I am talking about. Another illustration coma to mind. Laat year I had an experience in starting some rotary continnous filteru. For a long time we were troubled hy the fact that the feed box design was not correct so that the cake had holeain it, and the screen blinded so that we could not get any air throngh. What good rn all the nim Werentid equations in the world on rates of filtrationwhen the SCis blocked or the cake hsa hole8 in it? I am not advocating that the man who is tesohing filtration teach his students how to design filter feed boxes or teach them d the stunts that could be needto keep a screen open. What I am aeking in that the man who teaches filtration h o w something about them di5cnlties and that he mabe the fact that this kind of d i 5 i d t y may make d hia theoreticalinvestigations worthleas. With the proper point of view, a proper balance between theory and practice, and a props underuhding of how far d r a y a man may be led by undue dependence on thaory and ignorance of practice, the liat of couma and Bubject matter need not be dilTerent from what it is now in any school that M a eerious offender in the aapecta I have been diecueaing. A PSYCEOLOOICALfactor, too,in the later development of the & u b t hasscmre bearing. When a mangoes out on his job freah from school and enthusiastic about theory, he 5d9
SOPtemk 1941
INDUSTRIAL A N D ENQINEERING CHEMISTRY
that the old-timers are contemptuous of theory. Thst this is t a w is no psrt of my thesis; the young student may be snfIieiently imbued with this idea of theory to overlcak this antipathy on the part of the old-timsrs. If he d w not have the p r o p bdsnca, however, when he beginsto appls his theonea there will be en many holes he eannot plug and KI many caw where his theory feuSdownthst he too r e d l y swings over to the old-timers’ way of thhking. In d too many cwea this wmpletdystopshisfurtherprof&dgrowth. I am using a good many wordn to say what might be explpesed more aimply; hut I muember the old pedagogical maxim, “Lsaming eomea by repetition“, en sll I can do is re peat o ~ e a . n d a ~ ethat r 1~ ~ y ~ -Who u n g mteschingchemical enginem would have a better appreciationof the practical point of view. It may well be that the tspe of man who produces our beat theoretical work in not intemted in and oan never be fully appreciative of the pintoof view I am trying to define. It may be tbat the men who do the heat theoretical inveatigation must remain pure theoriata, and that we must have enme kind of a middleman on ow tascbing M B -man ~ who is 80quainted with the theoretical aspects of the problems, who has a proper reape& for theory and is not afraid to nea it, but who at the same time undwntande the practical side and knows how in his pHsepltstion and his attitude t o d the students to temper thetheoretical with the practical. SOME of the younger m p may sak how they can ever get this practical point of view. Induetry is not willing to take them on for short peri&,they cannot sflordto work in indw trywithout companeation,dififleavetheunivemiityand go into industry with any w c c w at d,the university never pets therm back. wbat can be done? It is my perer~nalesperience, extending over a long periodof y-, that one can sccnmnlate~tbis point of view for himsell by studiona attantionto the fast that he must understand the practical side. It is most imtmctive to have to design a p p rat-. The next beat thing, however, ia, when walking thmngh a plant, to look at everg piece of apparatus in teamsof detsils. Too many univeraiity mem go through a plant looking at the proaess only, and the apparstus is merely an extarnal symbol of what goes on inside. Try going through a plant without paying particular attention to proem and looking at the apparatusaa apparatus How is it put together? How is it held up? How thick are the tlangea and how big ara the bolta? How are connectionsmade betwean pipe linea and the equivalent? How mstuftingboxes designed? It is not newwry to limit oneself to chemical equipment. Any piece of machinery you sea can be made a mine of experience. For instgnce,you have
d mall freight ClVB thousands of times. How many of you know exactly how the weight of the car is traderred to the journals on the d e ? Yet when you are
standing waiting for a train witb a freight car on the siding o p posite, leaa than one minute of resl looking at that freight car willtellyouhowitisbuilt. Of course you aren’t going to deeign freight cara-that is not the Point; but if you ever resoh the staga when3 you immediat..?.?y SnIaIyae evmythkg you sea In teams of how it in made, how it in put together,and how it worlrs, you will be Burpriaed at the amount of practical eaperieace
1108
you can accumulate, even though your job megns sitting at I ) desk or standing behind a lecture platform.
ALL of this may sound 811 if I were minimizingthe value of the theoretical investigations and attempts to analyae mathe m a t i d y the varioua thingn we hew to deal with in chemical engineering. This b not true. I do not in the least minimise this work, and I believe that the profession m o t h o p to advance except in the exact measure in which this new t h e retical work advances. I am pleading, however, that in the teaching of our young men there be a judicious admixture of ordinary horn ~ e n s e and theory and a recognition of the fact that all the theory we can soquire in the next hundred yearn is still going to leave an infinite number of engineering problem to be d v e d by born senae, intuition, or a knowledge of practice. The enginem, after d,is the man who has to make thineg run. Wbile he can usually d e them run much better in so far as he u n h stands the theory hack of them, there ia a multitude of thineg he must do that he uever can analyze from a theoretical viewpoint. Part of what I am oomplaining about ia unavoidable, t e caw the t e m m e n t of the true theorist and the able re search worker may not be c o m m m t e witb the acquiring of practical .howledge. I am afraid, however, that an apprec i a b part of the di5cult.y I am discuaeing is due to indolence. It in much easier to sit at a desk and write papers than to take oy’8 vacation, one’s weds end, and one’s spare time to go out into plants to 6nd out what makes the wheels go round. I m not often moved to he parlicularly eariow in m y talks, but I am reminded of a couplet from one of Kipling‘8 pornns. It has to do with a man named Tomlinson whose soul could not be judged either way because he had led such a negative life:
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Ye have ye haw heard. ye have though+ Good lack% tbetde isget to run; By the worth of the body that once ye had Give answer1 What have ye done?
