October, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
Since the rate of condensation of the turpentine and water was found to be substantially constant during a run, the rate of heat flow in B. t. u. per hour was found by multiplying the net weights of the components obtained during the run by their respective latent heats and dividing the sum by the length of the run in hours. Since the tube-wall temperature varied around the perimeter of the tube, an average value was obtained by plotting the thermocouple readings in millivolts against the angular position of the thermocouple, and integrating the resulting curve with a polar planimeter. This procedure gave a true average of the temperature around the tube, since the calibration curve is a straight line over small intervals of temperature. The average temperatures of the various points were then plotted against the position of the thermocouple along the length of the tube. This curve was integrated (by means of a polar planimeter) over the length of the condensing section to give a mean of the tube-wall temperature. From this value and the vapor temperature, the temperature drop ( A T ) through the film of condensate was obtained. No correction was made for the slight temperature drop through the thickness of copper between the thermocouple junctions and the condensate film, since the greatest possible error was of the order of 0.2 to 0.3 per cent of the corrected temperature drop through the h.
Results The turpentine used in these experiments was freshly distilled from gum obtained from the slash pine (P. curibaea) and had a specific gravity of 0.8675 (6Oo/6O0 Fa). Typical curves of temperature variation around the tube at two points along its length are shown in Figures 2 and 3. Figure 2 shows a typical curve of temperature variation around the tube at a point along the tube and is plotted on rectangular coordinate paper. Figure 3 is a curve which was obtained in another experiment and is plotted on polar coordinate paper. I n both cases the angular position on the tube (0" being the top) is plotted against the tube-wall temperature a t that point. The protractor used in measuring the angle was set in a horizontal position by eye, and the zero point was off about 15" in several of the experiments. However, this would not affect the integrated value of temperature. The curves are similar to those obtained by Baker and Mueller (1).
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When pure turpentine was condensed, film-type condensation was obtained. The coefficient of heat transfer through a condensate film oan be expressed by the equation: h = q/AAT
where h
film heat transfer coefficient, B. t. u./(hr.)/(sq. ft.)/(" F.) A = he&&nsfer area, sq. ft. q = heat transferred, B. t. u./hr. AT = temperature drop through condensate film, F. =
All terms except h are determined from the data, and h is calculated. The value for latent heat of steam was taken from Keenan (3)and that for the latent heat of turpentine from Perry (6). Figure 4 shows effect of temperature drop through the film on the film coefficients. The data were obtained using equilibrium vapors of turpentine and water with the exception of the one point, well above the general curve, which represents a nonequilibrium mixture, in that excessive water vapor was present. These data are given in Table I. The latter condition is generally present in a turpentine-water condenser, and since this point is higher than the curve, Figure 4 will furnish conservative values of h for the design of condensers for turpentine stills. Further work is contemplated using the vapor mixtures encountered in actual practice, but until this is done, the values determined from the curve of Figure 4 are recommended for predicting the film coefficient on the vapor side of a condenser handling the vapor of a turpentine still.
TABLB I. RESULTS OBTAINEDBY CONDENSING MIXBD VAPORS OF TURPENTINE AND WATERON A SINGLE HORIZONTAL TUBE" h, B. T. Turpentine Steam Av. TubeU./HrJ/ Run Condensed, Condensed, Wall Temp., Mean Vapor (Sq. Ft.)/ Lb./Hr. No. Lb./Hr. F. Temp., F. (" F.)
1) 2 3 4 5 6 a
b
44.7 31.7 27.6 18.8 19.2 23.8
38.4 25.0 22.1 15.0 15.8 19.4
119.8 139.8 152.2 179.7 177.6 169.4
204.1 203.G 204.0 203.9 203.6 203.7
374 326 354 514 502 488
Area of test section, 1.378 square feet. Nonequilibrium.
Literature Cited 600,
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(1) Baker, E. M., and Mueller, A. C., IND.ENG.CHEIM., 29, 1067-72 500
. f ?*
400
. d
300
=
r
!
X
2001
20
I
30
I
40
NON EQUILIBRIUM
50
60
70
80 90
(1937). (2) Baker, E. M., and Tsao, U., Trans. A m . Inst. Chem. Engrs., 36, 617-39, 783 (1940). (3) Keenan, J. H.,"Steam Tables and Mollier Diagram", New York, Am. SOC.Mech. Engrs., 1930. (4) Langen, Forsch. Gebiete Ingenieurw., 2, 359 (1931). (5) Patton, E. L., and Feagan, R. A., Jr., IND.ENG.CHEM.,ANAL. ED., t o be published. (6) Perry, J. H., et al., Chemical Engineers' Handbook, New York, MoGraw-Hill Book Co., 1934.
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FIGURE4. FILMCOEFFICIENTS FOR CONDENSING MIXEDEQUILIBRICM VAPORS OF TURPENTINE AND WATERON A SINGLE HORIZONTAL TUBE
The condensation obtained while condensing mixed vapors of turpentine and water was the film-dropwise type described by Baker and Mueller (1). The turpentine apparently condensed as a film, and the steam condensed dropwise in and on this film.
Permeability and Absorption Properties of Bituminous Coatings-Correction On page 992 of the August, 1941, issue the sentence six lines from the bottom of the first column should read: "The data ( I ) have shown that the asphaltene portion of asphalt is much less permeable to water vapor than the oily viscous medium." A. P. ANDERSON AND K. A. WRIGHT
