An Experimental Study of R134a Condensation Heat Transfer in Horizontal Smooth and Enhanced Tubes

In this paper, the condensation heat transfer characteristics of R134a inside enhanced tubes using two types of surface structures with different materials were investigated, which were then compared with plain tubes under the same test conditions. The enhanced tubes were: 1EHTa tube with dimpled and petal arrays structure and 1EHTb tube with protrusion and similar petal arrays structure. The experiment was conducted for a mass flux ranging from 100 to 200kg m(-2) s(-1) with saturation temperature of 318.15K. The inlet and outlet vapor qualities were fixed at 0.8 and 0.2, respectively. The test tubes had the same outer diameter of 12.7mm. Results showed that the dimpled and protruded surface tubes enhanced the convection condensation heat transfer and the heat transfer coefficient was 1.4-1.6 times higher than that of the smooth tube. Heat transfer enhancement of the 1EHTa and 1EHTb tube was mainly due to the complex roughness surface structures that created swirling and increased the interface turbulence. The condensation heat transfer coefficient increased slightly with increasing mass flux. The pressure drop penalty was found to increase as mass flux increased. Compared with the smooth tube, the pressure drop of Cu-1EHTa tube, SS-1EHTa tube, and Cu-1EHTb tube were 1.15, 1.21, and 1.14 of smooth tube, respectively. Enhanced tubes exhibited higher performance factors (PFs) compared to the smooth tube. The average PF was 1.3-1.5. A new correlation of heat transfer coefficient has been developed within +/- 15% error band.