Based on a refrigeration cycle using R134a as a working fluid

the falling film evaporation on horizontal tubes was used in the evaporator.The heat transfer characteristics of the falling film evaporation were investigated experimentally under different conditions.The heat fluxes varied from 8 to 40 kW·m-2 and the mass flow rate of the sprayed liquid ranged from 0.005 to 0.04 kg·m-1·s-1.The performance of a smooth tube and two enhanced tubes(a TJX tube and an EX tube)were tested in the experiment.The two enhanced tubes were designed for the falling film evaporation specifically.The experimental data were processed by using the modified Wilson method.The test results show that the heat transfer characteristics of the falling film evaporation are mainly associated with heat flux and mass flow rate.For all tubes

the heat transfer coefficient increases before the occurrence of the critical heat flux.The performance of enhanced tubes are better than that of smooth tube

especially the EX tube with grill channels on the surface.With the oil in the refrigeration system

the presence of oil in the experimental loop deteriorates the heat transfer coefficient significantly.Finally

a new heat transfer correlation is used to predict the heat transfer coefficient of the smooth tube

and correction factors for the heat transfer prediction of enhanced tubes are proposed.