Engineering Schemes

Heat Transfer With Change Of Phase 521

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FIG. 5-9 Chart for determining film coefficient hm for film-type condensation of pure vapor, based on Eqs. 5-88 and 5-93. For vertical tubes multiply hm by 1.2. If 4r/pf exceeds 2100, use is in U.S. customary units; to convert feet to

meters, multiply by 0.3048; to convert inches to centimeters, multiply by 2.54; and to convert British thermal units per hour-square foot-degrees Fahrenheit to watts per square meter-kelvins, multiply by 5.6780.

FIG. 5-9 Chart for determining film coefficient hm for film-type condensation of pure vapor, based on Eqs. 5-88 and 5-93. For vertical tubes multiply hm by 1.2. If 4r/pf exceeds 2100, use is in U.S. customary units; to convert feet to meters, multiply by 0.3048; to convert inches to centimeters, multiply by 2.54; and to convert British thermal units per hour-square foot-degrees Fahrenheit to watts per square meter-kelvins, multiply by 5.6780.

than 0.4 (at Reynolds number above 1000), the predicted values for film coefficient are lower than those predicted by the Nusselt theory.

The Dukler theory is applicable for condensate films on horizontal tubes and also for falling films, in general, i.e., those not associated with condensation or vaporization processes.

Vapor Shear Controlling For vertical in-tube condensation with vapor and liquid flowing cocurrently downward, if gravity controls, Figs. 5-9 and 5-10 may be used. If vapor shear controls, the Carpenter-Colburn correlation (General Discussion on Heat Transfer, London, 1951, ASME, New York, p. 20) is applicable:

FIG. 5-10 Dukler plot showing average condensing-film coefficient as a function of physical properties of the condensate film and the terminal Reynolds number. (Dotted line indicates Nusselt theory for Reynolds number < 2100.)

[Reproduced by permission from Chem. Eng. Prog., 55, 64 (1959).]

FIG. 5-10 Dukler plot showing average condensing-film coefficient as a function of physical properties of the condensate film and the terminal Reynolds number. (Dotted line indicates Nusselt theory for Reynolds number < 2100.)

[Reproduced by permission from Chem. Eng. Prog., 55, 64 (1959).]

where k,pr2=0.065(Npr!re

0 0