Evaporation Heat Transfer of R134a on outside of Smooth and Enhanced Tubes

Increasing attention has been paid to the flow and heat transfer in annular channels since their intensive applications in engineering. In this study, evaporation of the outer surface of two enhanced heat transfer tubes (2EHT) was compared to the performance of a smooth surface copper tube through experimental research. The refrigerant flowed in an annular space between the outer tube and the test tube. The outside and inside diameters of tubes used in this study were 19.05 and 17.10 mm, respectively. Tests were performed using refrigerant R134a as the working fluid, over the saturation temperature of 6 degrees C for evaporation, the quality range of 0.1-0.8 and the mass fluxes is from 30 to 58 kg/m(2)s. It is observed that through different surface structures, the heat transfer area increased, while both the nucleate boiling and convective boiling were improved, leading to the heat transfer coefficient of 2EHT being significantly enhanced. According to the evaluation, the evaporation enhanced tube had better enhancement effect. Finally, correlation analysis was conducted based on experimental data. The results from correlation analysis can be implemented to predict the experimental heat transfer coefficients within a deviation of +/- 10%.