Investigation of Refrigerant R134a Two Phase Flow Heat Transfer in Vertical Heat Exchanger Channel

Two phase flow boiling heat transfer and pressure drop in the vertical evaporator tube section of refrigeration system have been experimentally investigated using refrigerant R134a as a working fluid. The objective of the present work is to investigate experimentally the effect of heat flux, mass flux, vapor quality and saturation temperature on refrigerant flow boiling heat transfer characteristics in the evaporator of refrigeration system. These investigated parameters have significant impacts to enhance the thermal performance of the evaporator. The experimental investigations were conducted in smooth copper tube with inner diameter 5.8 mm and 600 mm length under different test conditions. The test conditions considered in this study were, for heat flux of 7.718-32.78 kW/m 2 , mass flux of 97.3-148.7 kg/m 2 .s , saturation temperature of 20.58 to -15.68 ̊C and vapor quality of 0.3-1. It can be concluded from the results that, the average heat transfer coefficient at relatively greater mass flux 148.7 kg/m 2 .s was higher in range of 21% compared to other mass fluxes at constant test conditions. The relatively higher value of heat transfer coefficient was observed at heat flux 32.78 kW/m 2 with average increase of 19% compared to the relatively lower value 23.38 kW/m 2 . The enhancement in local heat transfer coefficient at saturation temperature University of Thi-Qar Journal Vol.14 No.3 SEP 2019 Web Site: https://jutq.utq.edu.iq/index.php/main Email: utj@utq.edu.iq 2 15.68 ̊C was higher by about 12% than that for the relatively lower temperature -20.58 ̊C. The effect of increase in mass flux and heat flux on pressure drop in the evaporator tube was about 9% and 7.5% respectively.