Nucleate pool boiling and filmwise condensation heat transfer of R134a on the same horizontal tubes

Pool boiling and condensing heat transfer of R134a on one plain and three enhanced surfaces are experimentally investigated. The saturation temperature in pool boiling is 6 °C and condensing is 40 °C. The heat flux ranges from 8 to 86 kW/m². The enhanced tubes include integral-fin, pyramid and re-entrant cavity surface. The outside diameter of test tubes is 19 mm and the length of test section for boiling is 1100 mm and condensing is 1800 mm. Integral-fin tube has lower heat transfer coefficient in boiling and condensing. The deviations of experiment result and Owen or Webb models are within ±10% for integral-fin tube in condensing. Pyramid surface provides quite close heat transfer coefficient with re-entrant cavity surface in pool boiling and condensing at heat flux greater than 70 kW/m². The heat transfer performances of re-entrant cavity surface tube is the highest among the three enhanced tubes in either pool boiling or condensing at not high heat flux. The heat transfer coefficients can be 1.9-4.8 and 14.8-19.3 times those of a plain tube in pool boiling and condensing respectively. The decreasing rate of heat transfer coefficient for re-entrant cavity surface is also higher than pyramid surface in condensing. Literature survey on nucleate pool boiling and filmwise condensation is also conducted.