VISUAL APPARATUS IN THE CHEMICAL ENGINEERING LABORATORY R. I. HUNTINGTON University of Oklahoma, Norman, Oklahoma
M a n s discoveries have been made in various chemical engineering operations over the past 20 years as the result of the use of visual equipment. Although the metals have many advantages over transparent materials such as glass and clear plastics, the former materials of construction have hidden from view the nature of many reactions which otherwise would have been difficult to explain. The development of better grades of pyrex glass and the discovery of new plastics have also contributed much to the use of these materials for the construction of visual experimental equipment. It might be of interest to the laboratory instructor to have some of the experiments described in which visual equipment can be used to a good advantage.
HEAT TRAKwER
STUDIES
The phenomena of nuclear and film b d i n g of liquids as well as dropwise and film condensation were unknown until experiments were performed in glass equipment (4, 6, 7, 8, 10). Until then the low boiling rates occuring with high At's were unexplainable. These two types of boiling can easily be demonstrated in the laboratory as shown in Figure 1. With a steam pressure of 57 lbs. per sq.in. gage and 304"F., nuclear boiling produces 120 ml. of condensate in a fixed time while with saturated steam a t 212 lb. per sq. in. gage or 392OF. the film boiling produces only 40 ml. of condensate. The condensation of atmosoheric steam on the ontside surface of a water-cooled tube can be carried out quite easily in a pyrex-jacketed apparatus. The nature of the condensation (such as film or dropwise) of steam on the outside surface of the tube can be readily observed through the glass jacket. In Figure 2 the vertical tube is equipped with thermocouples which are buried into the metal tube wall on the side opposite the entrance of the wires into the glass-jacketed space so as to eliminate eddy currents or other disturbances a t the point of temperature measurement. Hebbard & Badger (5) were among the first investigators to employ this unique technique of obtaining tube wall temperatures. Patterson (8) et al., improvised a means of collecting the condensate separately from a vertical tube, thereby making the apparatus substantially adiabatic except for small heat losses through the ends of the tube. The steam condensate which is collected a t the base of the metal tube is often as much as 10' to 60°F. below the steam temperature. Quigg (lo), et al., measured the thickness of the steam condensate by clamping a micrometer onto the pyrex glass jacket apd observing t,he contact of the screw with the film. Although this method is relatively crude the measurements of the film thickness appeared to be consistent, with increasing thickness of the condensate layer toward the lower end of the tube. In Figure 3 is shown a similar pyrex-jacketed condenser which can be readily placed in any position from the horizontal to the vertical, since one end is hinged and the other is equipped with flexible metal hoses for the steam and water streams. The two condensers in Figures 2 and 3 have proved to 6e invaluable a s unit operation equipment in providing the student with firsthand knowledge of certain heat transfer mecha~
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Upper: nuclear boiling 01 water a t 304'F.. A T 94°F. L ~ elrn~boiling ~ of ~water: 392°F.. bT Note that rate of boiling is about m m t h i r d ao faat as in the wperfigure.
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463
For a number of years our staff had wanted to pur- columns but visual observation through slits cannot chase a two-effect evaporator for the unit operations compare to the unrestricted view provided by the laboratory but had found the prefabricated apparatus latter. In one experimental study the low efficiency to be too expensive for its budget. Necessity proved of a perforated plate could not be explained until a itself aeain to be the mother of invention as shown by Figure 4. The two vertical effects consist of 4-in. X 30-in. pyrex tubes in each of which is coiled 8 to 10 feet of 6/la-in. copper tubing for the respective condensing surfaces. Five-gallon glass bottles serve as liquid accumulators for the overhead condensate, the heat exchanger condensate and the concentrated solution comprising all three streams from No. 2 effect. The inert gases from these bottles are evacuated by means of a small water aspirator. The apparatus has performed very smoothly; furthermore it has the advantages of being visual Figurs 3. Hoat Transfer Units. Prosision for Variation i n All Positions from Hori=ontal to Vertical throughout and of reaching (1) To Left: unsteady Bow of heat from oondensins stream t o B oylinder filled with sand. (2) To right: steady state conditions visual condensation of steam on a copper tubs. u
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glass cdumn \rar used. It took only a fca. ~ninutest o tind out t11:lt the (::lust! of r l ~ i dlow effivienqy was due to the fact t h n t thc liquid wa.: falling through thr pvrforations before it had; chance to flow across the By using smaller perforations this difficulty was corrected and the plate gave higher efficiencies than the bubble plate. A 12411. X 20-in. filling-station glass cylinder which was used in this st.udy made it possible to observe the bubbling action on the tray, as well as the nature of the entrainment which took place in the vapor space. PRESSURE-VOLUME ISOTHERMS
In preparing the chemical engineering student for a course in fractionation and absorption, the elements of vapor-liquid equilibria should first be studied. P-V, P-T,and V-Tgraphs present the concept of phase behavior quite clearly to some students who are milling to accept natural laws in this manner. However, the
Figun, 5.
Visual P-V-T Apparatus
(Figure 5) which can be used effectively in a classroom or unit operations laboratory 'for bringing home t o the student these physical phenomena far more effectively than can be done by graphs. In operating the P-Vapparatus the gas or vapor first displaces water or mercury from the Lucite cylinder. Then a small hand pump is used to force in a liduid in which the vapor is insoluble, thereby increasing the pressure through the one or more phase regions.* From the P-V graph which is obtained from the isothermal compression through the dew point and bubble point pressures,, the composition of the vapor can be determined if it consists of one or two components only. ABSORPTION
A 4-in. X 4-ft. pyrex tube filled with Berl Saddles (Figure 6) makes an ideal packed tower in which absorption experiments can be made. The glass walls make it possible for one to observe the nature of the flow of the absorbent over the surface of the packing as well as the tendencies toward flooding. BATCH VAPORIZATION OF HYDROCARBON MIXTURFS
I.~.YI~
4.
smallT W O - E B ~ C ~ ~ ~ ~ ~ o . . , t~ourb e sfor settling ~ s t e s OE solids
Evaporation losses from atmospheric storage tanks vary with the ratio of diameter to depth of the vessels * The Refinery Supply Co.. Tulsa, Oklahoma, is prepared to
assemble this spparatus.
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465
in which the cmde oil or gasoline may be confined. This experiment can be carried out before a class over a period of several weeks or months by subjecting the same hydrocarbon mixture to the atmosphere in graduated cylinders having different diameters but the same height (Figure 7). The change in A.P.I. gravity can be taken along with the shrinkage of the liquid. By material balances the A.P.I. gravity of the more volatile components which are lost by evaporation can be calculated by difference. The average Mid-Continent crude oil loses about 2.5 per cent by volume for every degree loss of A.P.I. gravity. The apparatus shown in Figure 8 would be preferred over t,hat in Figure 5 .
Figure 7.
Cornp.rison of Evaporation Rater for water i n Vessels of Different Depth to Diameter Ratios
the height of the column. Movies of these flow experiments have been taken for various air-water ratios a t the several visual sections. Anyone who cares to see this film may obtain it free for a short time loan by writing the School of Chemical Engineering a t the University of Oklahoma.
Figure 6.
Pyrex Abso~borP-skod with Borl Saddlns
FLUID FLOW
Coates (8) has described several pieces of apparatus which have been used a t Louisiana State University for demonstrating the nature of the flow of liquids under viscous and turbulent conditions by injecting a dye into the main stream of fluid. By means of glass staudpipes he has shown the pressure gradient for the flow o f liquid through an orifice. Cromer and Huntington (3) carried out a number of air-water lift experiments in a 90-foot tower a t the University of Oklahoma. Visual pyrex glass located a t regularly spaced intervals provided a means of observing the nature of the flowconditions throughout
rigvre 9.
~ l ~ ~ ~ ~ i aase ~ . ~TUL.~S i l ~for. settling d ~~t~~ oc s d i d s
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466
SETTLING RATES
The effect of particle size, shape, and density on settling rates can be demonstrated quite clearly by causing various objects to fall freely through vertical elass tubes which may be filled with anv viscous fluid such as glycerin and ciear lubricating oil." The apparatus shown in Figure 9 provides an effective means of carrying out instruction in this operation.
F i g " . .
8.
Evaporstion of C ~ d Oil e in Vessels Having Various D ~ p t h
to Diamet.. Ratios
ACKNOWLEDGMENT
The author wishes to express his appreciation to the
chemical engineering staff members; L. S. Reid, F. C. Fowler, J. M. Campbell, Jim Huitt, and laboratory technicians John Fox and E. J. Hopkins, who designed and built the major portion of the unit operations equipment for our laboratories.
(1) ASHRAF,F. A., T. L. CUBBAGE, AND R. L. HUNTINGTON, Ind. Eng. Chem., 26, 1068 (1934). (2) COATES,J., Chemical Engineering Meeting, Madison, Wisconsin, September, 1948. (3) CROMER, S., AND R. L. HUNTINGTON, Trans. Am. Inat. MininoMet. Enom.. 136.79 11940). DREW,T: B., AND^ C. GUEL;,ER,~ r a n sAm. . Inst. Chem. Engrs., 33,449 (1937). HEBBARD, G . M., ~ L N DW. L. BADGER, ibid., 26,420 (1934). NAGLE,W. M., ET AL.,ibid., 31, 593 (1935). NAGLE,W. M., AND T. B. DREW,ibid., 30,217 (1933-34). PATTERSON, W. C., ET AL.,ibid., 33,216 (1937). P Y O ~W. , T., C. A. JACKSON, AND R. L. HUNTINGITON, Ind. Eng. Chem., 27,821 (1935). QmGG, H. T.,W. C. MOYER,AND R. L. HUNTINGTON, ibid., 30. 1047 (19.18). S , JR.,'H. G. CORNEIL, ET AL., Trans. Am. Inst (11) S O ~ ~ E RM. Chem. Engrs., 34,71 (1938)
