Heat transfer from superheated vapors to a horizontal tube

Abstract

Experimental data are reported for condensing Freon-114 (tetrafluorodichloroethane) and steam at several pressures. The condition of the vapors ranged from saturation to 180°F. of superheat. The condensing tube containing embedded thermocouples was 3/4 in. in diameter and 3 ft. long. Visual observation showed that steam condensed by dropwise condensation in part. Increase of superheat in the vapor at constant pressure caused a lowering of the tube-wall temperature, which was indicative of a lowering of the surface temperature of the condensate. The lowering of the condensate-surface temperature below the saturation temperature was computed from the experimental tube-wall temperatures, the heat flux, and Nusselt's equation for the condensate-film resistance. The lowering of the condensate-surface temperature is correlated with degree of superheat. An interfacial coefficient of heat transfer between the superheated vapor and the condensate surface is reported based on the computed surface temperatures. Schrage's analysis and equations for relating mass and heat transfer with conditions at an interface were simplified and used to correlated the experimental condensing load with the degree of superheat.