CONDENSATION HEAT TRANSFER AND PRESSURE DROP CHARACTERISTICS OF R-134A IN HORIZONTAL SMOOTH TUBES AND ENHANCED TUBES FABRICATED BY SELECTIVE LASER MELTING
This study investigates the condensation heat transfer and pressure drop of R134a inside two enhanced tubes and one smooth tube fabricated by Selective Laser Melting (SLM). The results were compared to a plain commercial aluminum tube. The enhanced tubes consist of a tube with a metal foam structure and a tube with eight short circumferential pin fins. The experiments were conducted at mass fluxes from 50 to 150 kg/m2·s. Throughout the experiments, the inlet and outlet vapor qualities were maintained at 0.9 and 0.3, respectively and two saturation pressures of 13.4 bar and 11.6 bar were investigated. The effects of fin height, fin inclination angle and mass flux on the heat transfer coefficient and pressure drop were studied. Our results show that for the wavy flow pattern, the saturation pressure, mass flux, and fin structure have significant effects on the condensation heat transfer coefficient and pressure drop. At saturation pressure of 13.4 bar, the 'frontal impact' on the fins with eight-fin tube has a higher heat transfer coefficient than the ‘back impact’. With an increase in the refrigerant mass flux or a decrease in the refrigerant saturation pressure, the difference in heat transfer coefficients between the frontal and back impact for the same tube structure reduces. The heat transfer coefficients of the metal foam tubes are higher than that of the smooth SLM tube with a large penalty of pressure drop in test section. The eight-fin tube demonstrated the highest heat transfer coefficient (h) of up to 2 times as compared to the h values of commercial aluminum tube.