Flow Boiling Heat Transfer of Refrigerant 32 Outside a Three-Dimensional Enhanced Tube With Rhombic Stripes and Spherical Patterns

Abstract Flow-boiling heat transfer characteristics of Refrigerant 32 on the outside surface of a three-dimensional diamond-shaped enhanced copper tube have been experimentally investigated. One enhanced tube has been studied along with a smooth tube (ST tube) of the same diameter for comparison purposes. The enhanced tube has diamond stripes and spherical patterns on its surface and is referred to here as the LEHT tube. Experimental conditions included saturation temperatures of 279, 283, and 288 K; average vapor qualities ranging from 0.2 to 0.8; and mass fluxes ranging from 70 to 230 kg/(m2 s). Both the heat transfer coefficient and the frictional pressure drop in the LEHT tube were found to increase with an increase in the mass flux. For the smooth tube, the effect of the average vapor quality on the heat transfer coefficient was found to be less significant compared to that of the LEHT tube. The heat transfer coefficient of the LEHT tube was also found to first increase and then decrease as the vapor quality increased. Finally, the frictional pressure drop in both tubes has been found to be inversely proportional to the saturation temperature, with the saturation temperature having little impact on the heat transfer coefficient. Gungor and Winterton's correlation was modified and fitted to the experimental data for the heat transfer coefficient to produce a new correlation for the LEHT tube.