JANUARY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
mold and bacteria from air circulated for process work, such as in bakeries, breweries, and other fermentation industries, offers interesting possibilities entirely independent of the health aspect. It is hoped that this work will stimulate interest among manufacturers of air-washing equipment toward the development of still more efficient apparatus for effecting bacterial control. Probably a higher degree of bacterial reduction than that reported here could be obtained by providing more intimate contact between the washing water and the circulating air, so as to prevent any short-circuiting of the air through the bactericidal sprays.
Literature Cited (1) Am. Pub. Health Assoo., Standard Methods of Water Analysis,
8th ed., 1936. (2) Andrew, British Patent 295,070 (May 12, 1927). (3) BaskervilIe, Charles, J. IND. ENG.CHIM., 6, 238 (1914). (4) Cambier, M.R., Bull. acad. mdd., [3]102, 13 (1929). (5) Clark and Gage, Mass. Dept. Health, Ann. Rept., 1912. (6) Douglass, Hill, and Smith, J.Ind. Hyg., 10,219 (1928). (7) Drinker, Phillip, and Wells, W. F., Heating, Piping, Air Coonditioning, 6, 408 (1934). (8) Ficker, Arch. Hug., 69, 48 (1909).
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(9) Hill, L., Bull. Inst. Mining Met., No. 205-6, 1 (1921). (10) J . Am. Med. Assoc., Feb. 7, 1914, p. 423. (11) Larson, G.L., J . Am. SOC.Heating Ventilating Engrs., 22, 11 (Oot., 1915). (12) Leech and Sherman, British Patent 294,586 (Jan. 27, 1927). (13) MoConnell, W.J., Refrigerating Eng., 31, 79 (Feb., 1936). (14) Mass. Dept. Health, Ann. Report, 1934,p. 166. (15) Rowe, A. H., Med. J . Record, 138,345 (1933). (16) Ruehle, G. L. A., Am. J . Pub. Health, 5, 603 (1915). (17) Wells, W. F.,Am. S.Hug., 20, 611 (1934). (18) Wells, W. F., Am. J . Pub. Heallh, 23, 58 (1933). (19) Wells, W. F . , J . Ind. Hug., 17, 253 (Nov., 1935). (20) Wells, W. F., and Fair, G. M., Science, 82, 280 (Sept. 20, 1935). (21) Wells, W. F., and Stone, W. R., Am. J . Hug., 20, 619 (1934). (22) Whipple, G. C., and Whipple, M. C., Am. J . Pub. Health, 3, 1138 (1913). (23) Winslow, C. E. A., Eng. News, 59, 629 (1908). (24) Winslow, C. E. A,, Proc. Am. SOC.Civil Engrs., 51, 794 (1925). (25) Winslow, C. E. A., Science, 28, 28 (1908). (26) Winslow, C. E.A,, and Robinson, E. A., S. Infectious Diseases. 7, 17 (1911). (27) Yaglou, C. P., Drinker, Phillip, and Blackfan, K. D., Trans. Am. SOC. Heating Ventilating Engrs., 36 (No.867), 383 (1930). REC~IVBID September 21, 1936. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 to 11, 1936.
HEAT TRANSFER WITH
Nonflammable Organic Compounds FOSTER DEE SNELL Foster D. Snell, Inc., Brooklyn, N. Y.
T
HE problems of heat transfer include applications in a multitude of industries. Convenience dictates their use in many simple installations in place of lowpressure steam. In some cases, temperatures above those of low-pressure steam are desired, without the complications of high-pressure systems. A related application is for still higher temperatures and greater heat transfer with a lower pressure than could be obtained with steam. I n others, heat must be removed under conditions where an intermediate circulating medium is desirable instead of direct application of refrigeration. Media Used The materials used for the purpose are so numerous and the purposes so varied that only a partial survey would be justified here. By far the least expensive and most widely used heat transfer medium is water, in the liquid or gaseous phase. It has obvious disadvantages. At temperatures between 0" and 100" C. it is corrosive to many metals unless corrosion inhibitors are added (7). At temperatures above loo", pressure is necessary; a t temperatures below 0" salts must be added and the resulting medium is increasingly corrosive. Over 200°, pressures become high for saturated steam and efficiency poor for superheated steam. The use of fixed gases other than superheated steam is unimportant commercially.
The use of fused salts for the purpose is very old. Complex chloride mixtures with zinc chloride predominating (12,13) and sodium dithionate solutions (31) are illustrative. Lowmelting metallic alloys have been similarly used. Both are limited in their application by relatively high melting points and frequent corrosive attack. This field was broadened some years ago by the use of metallic mercury (10). It is applicable, over the range of -39" to 357" C . , but the supply
Mixtures of tetrachlorobenzene, trichlorobenzene, dichlorobenzene, achloronaphthalene, diphenyl, etc. , show satisfactory characteristics as heat transfer media in laboratory and small-scale operative comparisons. Suitably selected mixtures are liquid from -50" to 200" C. The change of viscosity is moderate over this range as compared with competitive fluids. There is no appreciable corrosive effect on metals, even at high temperatures, in the presence of moisture. Evaporation at room temperature is slight. The mixtures are nonflammable over the range extending above their boiling points. They do not polymerize or sludge at high temperatures. Connections can be made with either metal hose or rubber substitutes. Toxicity presents no serious problem.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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is strictly limited and the price high. Oxidizing conditions must be avoided, the vapors are highly toxic, and it amalgamates with nearly all metals except steel. Oil as a heat transfer medium is mainly a substitute for water because of its higher boiling point. The supply is practically unlimited, the price not unreasonable. Disadvantages included sluggish flow a t low temperatures, decomposition to give carbon residues (14) and sludges, and low thermal capacity. Oxidation must be avoided. Its use in cooling internal combustion engines has been recommended (25).
VOL. 29, NO. 1
for commercial use, although it is not yet in large-scale use to the writer's knowledge. The data presented refer to a mixture of equal weights of commercial trichlorobenzene and a-chloronaphthalene. Other data indicate similar results for several other mixtures.
Viscosity Change A typical set of viscosity data is that shown in Figure 1. The mixture used freezes a t -37" C. The temperatureviscosity curve shows relatively small increase a t temperatures down to below 0". For comparison, a similar curve for a special grade of lubricating oil is superimposed as representing better-than-normal commercial results with oil. The curves are self-explanatory so far as comparison of the media is concerned.
Corrosion The corrosive effect of water is often serious; that of salt solutions when used for low temperatures is much more so. The effect of such a nonflammable compound was therefore
20 30
50
iC0 200 300 5M IWO 2000 3m) 5wO VISCOSITY 5AYBOiT i N SECONDS
FIQURE 1. CHANQE IN VISCOSITY WITH TEMPERATURE
Diphenyl oxide with a melting point of 26" C. and a boiling point of 258", or diphenyl melting a t 69" and boiling a t 256" are in use as a eutectic mixture melting a t 12" (11, 15, SO). This melting point is sufficiently low to limit the possibilities of freezing in case of shutdown. Various mixtures have been used. Diphenyl oxide and carbon tetrachloride (6) ; diphenyl oxide and naphthalene, pyrene, or p-hydroxydiphenyl (5); diphenyl, diphenyl oxide, and naphthalene (20); and more complex mixtures (18). Addition of materials such as diphenylamine lowers the freezing point of the oxide, and mixtures have been produced with freezing points as low as -38" C. (21, 22, 23, 32). The cost of such diphenyl or diphenyl oxide mixtures is not prohibitive, but their flammability and decomposition at elevated temperatures limit their use. The conditions for explosion of one of these mixtures containing diphenyl oxide and diphenyl have been studied (16). Related materials are secondary alkyl esters of polycarboxylic acids such as diisopropyl phthalate (19, lY), mixed dihydric alcohols (2, 3 ) , diethylene glycol with or without additions (9, 28), mixed glycerol and ethylene glycol (Zd), vegetable oil containing oleic acid (8),and alkylated aromatic compounds (17, 26). Halogenated compounds form another class. Those used included compounds of sulfur, oxygen, and fluorine such as SOzFzor SOF,(4), compounds of carbon chlorine and fluorine such as dichlorodifluoromethane, products of chlorination of diphenyl ketone ( I ) , and complex condensation products such as those of chlorobenzene and chlorobenzyl chloride by the action of aluminum chloride (1). Availability of chlorinated cyclic compounds suitable for the purpose still further expands the field. Trichlorobenzene is well suited for this purpose. It possesses the advantage of nonflammability. The commercial product is necessarily a mixture melting a t about 11" and boiling a t about 213" C. I n proper admixture with a-chloronaphthalene, tetrachlorobenzene, dichlorobenzene, diphenyl, or several other materials, the freezing point can be lowered to -50" (29). The applicability over a wider range is offset by its inability to reach the higher temperatures without creating a pressure system. Laboratory data indicate the desirability of such a mixture
determined by adding 1 per cent of water and refluxing with sheets of different metals individually for 10 hours. There was no weighable loss in the case of aluminum, cast and wrought iron, and galvanized iron. Losses of 2.3 mg. from 18 grams of copper and 2.1 mg. from 22 grams of brass were considered negligible. In no case did the specimens show visible evidence of corrosion. Although laboratory data on corrosive effects are frequently misleading, they can probably be accepted for the present as indicative of noncorrosive properties, in view of confirmatory plant experience with tri-chlorobenzene.
Effect of Temperature About 2 ounces of the mixture were heated in an open iron crucible a t 160" C. for 46 hours. During that time about 90 per cent evaporation occurred. The remainder had not changed in physical properties, other than color by concentration of minor impurities, and no gummy residue or sludge had deposited on the sides or bottom of the crucible. Since such a compound will necessarily be exposed to the air at times, in charging and otherwise handling it, the rate of evaporation was determined a t room temperature of approximately 24". The data are shown in Figure 2. The compound evaporates when heated, without objectionable residue. This is confirmed by commercial practice of distillation of the chlorinated hydrocarbons from iron or
steel a t atmospheric pressure without noticeable decomposition. Laboratory data are not available, however, on its decomposition in transition from the liquid to the vapor phase a t pressures above atmospheric, in which sludging difficulties are encountered with many such media. From the structure and known stability of the material, it is improbable that decomposition will occur a t those temperatures.
