An experimental study of condensation heat transfer characteristics outside the horizontal metal foam tubes

The condensation heat transfer performances of R134a of 6 metal-foam tubes were investigated experimentally with different saturation temperatures (35°C and 40°C). The influence of metal-foam structure factors, the pore density and the thickness, were analyzed. The experimental results show that the tube with 130 ppi pore density has the best condensation heat transfer characteristics and its condensation heat transfer coefficient can reach to 3.06 times as that of the smooth tube. The thicker the metal-foam layer is, the worse the condensation heat transfer performance becomes. For 80 ppi and 130 ppi tubes, the capillary action is the dominant factor, while the low-finned-like effect is more important for 40 ppi tube.