CONDENSATION HEAT TRANSFER AND PRESSURE DROP OF R134A IN HORIZONTAL MICRO-SCALE ENHANCED TUBE

This study was performed to investigate the heat transfer and pressure drop of R134A during condensation inside a stainless steel micro-scale enhanced surface tube (EHT tube) and smooth tube. The tests were conducted at a saturation temperature of 45 degrees C, over the mass fluxes range of 100 to 200 kg/m(2)s, the heat fluxes of 14-25 kW/m(2), an inlet vapor quality of 0.8 and outlet vapor quality of 0.2. The heat length and inner diameter of the tested tube were 2 m and 11.5 mm. The micro-scale enhanced surface tube has complex surface structures composed of dimples and petal arrays background patterns. It can be observed the condensation heat transfer coefficients of the EHT tube is about 1.6-1.7 times higher than that of a stainless steel smooth tube. Enhancement of the EHT tube was achieved due to disruption of the boundary layer, secondary fluid generation, increasing fluid turbulence and heat transfer area. In addition, considering the friction pressure drop, the EHT tube produces the larger friction pressure drop, which is 1.05-1.20 times as compared to the smooth tube. Finally, the performance factors were performed to evaluate the enhancement effect of the EHT tube based on heat transfer coefficient-pressure drop evaluation criteria value (eta(1)) and heat transfer coefficient-area evaluation criteria value (eta(2)).