Condensation heat transfer coefficients of enhanced tubes

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

In solar power generating plants, dry cooling towers are used when there is scarcity of water. Normally, condensation of the steam occurs in dry cooling towers in tubes at inclined angles. Almost all the previous work on condensation was in horizontal and vertical tubes until recently when work was done on condensation in inclined tubes but limited to smooth tubes and one type of enhanced tube. The purpose of this paper is to continue on previous work and present heat transfer coefficients and pressure drops during the condensation of R134a in an enhanced tube of inner diameter of 8.67mm with 60 fins with height of 0.22mm spiraled at an angle of 37o. The experiments were conducted at condensing temperatures of 30oC and 40oC at mass fluxes between 300 kg/m2s and 400 kg/m2s and various vapour qualities. It was found that the heat transfer coefficients and pressure drops increased with mean quality. Overall, the heat transfer enhancement factors were between 2.1 and 2.9 and the pressure drop penalty factors were between 1.2 and 1.8 with the enhancement more pronounced at lower mass fluxes. Finally, the heat transfer and pressure drops increased with decrease in condensing temperature.