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INDUSTRIAL AND ENGINEERING CHEMISTRY
mated to be 42.4" C., whereas the Tymstra value is about 32.3" C. It is apparent from a comparison of the space between the gas and water curves on Figures 2 and 3 that the Haug and Mason mean would be much greater than the true mean. Although the value predicted by Tymstra's method is close to the true mean, it is again emphasized that without knowing what mean value of the widelv varvinn coefficient to use &th such a mean temperature kfferckcej the latter
Vol. 26, NO. 11
as compared with 695 square feet in the design used in the example above. Because of the low rates of flow, a condenser nearly nine times as large is required. This emphasizes the faulty design used in some standard equipment and the desirability of providing for high velocities of both water and gas streams.
ACENOWLEDGMENT The authors acknowledge with thanks the assistance of T. H. Chilton, R. P. Genereaux, and S. J. Hill in the calculation of the above example.
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FIGURE4. OVER-ALLCOEFFICIENT OF HEAT TxmsmR, u (P. c. U./(HOUR)(SQUARE FOOT) (" C.), AND HEATTRANSFERRED, q (MILLIONSOF P. c. u. PER HOUR)vs. LENGTH OF EXCHANGER, L (FEET) value is of little use. The true mean can be calculated only when the surface area required has already been determined and hence is of academic interest only. I n the present problem 695 square feet of condenser surface is required to condense 9000 pounds of water vapor per hour from 100 pound moles of inert gas. I n order to condense 9000 pounds of water vapor per hour in the absence of inert gas and otherwise under similar conditions of temperature, water velocity, and design, 340 square feet of surface would be required. The presence of the inert gas requires for this case a condenser twice as large to condense the same amount of water vapor. If only the inert gas were to pass through the same heat interchanger, 152 square feet of surface area would be sufficient to cool the gas from 95" to 40" C. A common design of condenser used in the gas industry for removing water vapor and tar from coal gas consists of large vertical tubes, 3.5 inches 0.d., spaced on 7-inch centers. Water flows inside the tubes and the gas mixture flows downward outside the tubes, countercurrent to the water stream. With the terminal conditions of both gas and water streams as in the problem cited, both streams will be moving a t a slow rate and the water below its critical velocity. To condense 9000 pounds of water vapor from 100 pound moles of inert gas entering saturated a t 95" C. and leaving a t 40" C., a condenser surface of 6120 square feet would be required
NOMENCLATURE A = area, sq. ft. c = sp. heat at constant pressure, P. e. u./(lb.)(" C.) D = diam. of tube, ft. dA = element of surface area dq = increment of total heat transferred per unit time G = mass velocity through min. cross section, lb./(hr.) (sq. ft.) h = film coefficient of heat transfer, P. c. u./(hr.) (sq. ft.)(" C.); h, refers to the condensate, hd to the dirt film, ho t o the combined conductances other than the gas film, h, to the sensible heat transfer coefficient, hr to dq/(t, - tJdA, h, to the water film j = heat transfer or mass transfer factor (1, 3) k = thermal conductivity, P. c. u,/(hr.) (sq. ft.) (" C./ft.). Izd = diffusion coefficient, sq. ft./hr. K = molar mass transfer coefficient, lb. moles/(hr.)(sq. ft.)(atm.) L = length, ft. M = mol. weight; M , refers to the av. gas compn., M , to the condensable vapor, M,x to the molar latent heat. m = weight flow, lb./hr. P = partial pressure, atm.; p , refers t o the vapor pressure at to p , to noncondensable gas partial pressure in the main body, p,' to that adjacent to the condensate surface, pgf to the log mean of p , and pg', pv to vapor pressure ' q = heat transferred, P. c. u./hr. Re = Reynol? number, D G / p t = temp., C.; t, refers t o gas temp., t , to temp. of condensate surface, t, t o water temp.; At = over-all temp. difference, At, = log. mean of terminal temp. differences u = over-all coefficient of heat transfer, P. c. u./(hr.)(sq. ft.)(" C.) x = latent heat, P. c. u./lb. viscosity, lb./(hr.) (ft.) P = P = density, lb./cu. ft.
LITERATURE CITED (1) Chilton, T. H., and Colburn, A. P., IND.ENQ.CXEM.,26, 1183 (1934). (2) Chilton, T. H., and Genereaux, R. P., Trans. Am. Inst. Chem. Engrs., 29, 161-73 (1933). (3) Colburn, A. P., Ibid., 29, 174-209 (1933). (4) Colburn, A. P., and Hougen, 0. A., Bull. Univ. Wis., Eng. Expt. Sta. Ser. No. 70,81 (1930). (5) Huff, W. J., Chairman, Am. Gas Assoc. Proc., 7, 1147-56 (1925). (6) MoAdams, W. H., "Heat Transmission," p. 185, Figure 72, McGraw-Hill Book Co., New York, 1933. (7) Ibid., p. 263. (8) Tymstra, S. R.,Bull. Univ. Wash. Eng. Expt. Ser. No. 72 (1933).
RIWSIVED September 15, 1934. Presented as part of the Symposium on Diffusional Processes before the Division of Industrial and Engineering Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14. 1934. This paper is Contribution 145 from the Experimental Station of E. I. du Pont de Nemours & Company; it is a revision of a paper presented by 0. A. Hougen under the title "Condensation of Vapors from Nonoondensing Gases in Surface Condensers" at the Ithaca meeting of the Society for the Promotion of Engineering Education, June 20. 1934.
CORRECTKON. In the article by Ashraf, Cubbage, and Hunt- note refers to the 7-foot commercial column mentioned in Table ington on "Entrainment in Oil Absorbers" which appeared in the I1 instead of to the 12l/2-inch column. On page 1071, Table 111, CHEMISTRY,section D, the tray spacing should read 16 instead of 15 inches. October number of I N D u s T R u L AND ENGINEERING R. L. HUNTINGTON two minor errors have been found: On page 1069, Table I, foot-
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