CONDENSATION HEAT TRANSFER IN SMOOTH AND THREE-DIMENSIONAL DIMPLED TUBES OF VARIOUS MATERIALS

Abstract

The heat transfer and pressure drop of R410A and R32 within a smooth and an enhanced dimpled tube were measured for mass fluxes from 100 to 400 kg m^-2 s^-1, average vapor qualities between 0.2 and 0.8, and saturation temperatures between 35°C and 45°C. The test section was 2 meters in length, and the outer and inner diameters of the tube were 9.52 and 8.32 mm, respectively. The inner surface of the enhanced tube was dimpled. Three dimpled tubes and three smooth tubes, differing by material (copper, aluminum, and stainless steel) were tested to examine the material effect. The measured condensation heat transfer coefficient (HTC) for the copper smooth tube was 1.10 to 1.16 times higher than that of the aluminum, and likewise, between 1.19 and 1.31 times higher than that of the stainless-steel tube. Similarly, the condensation HTC for the copper dimpled tube was 1.06 to 1.15 times higher than that of the aluminum dimpled tube, and 1.26 to 1.38 times higher than that of stainless-steel dimpled tube. In general, and the condensation HTC for R32 was greater than that for R410A, mainly due to the greater liquid thermal conductivity of R32. Flow patterns were observed for different vapor qualities and used to establish corresponding heat transfer mechanisms. Finally, a new correlation for dimpled tubes was proposed based a modified smooth tube correlation, which predicted the measurements within an error band of 20&#37.