Comparison of flow boiling pressure drop and heat transfer of R134a with low GWP alternative R1234ze(E) in a dimpled flat duct

Abstract

Abstract The low GWP (Global Warming Potential) refrigerant R1234ze(E) is a potential alternative of R134a. This study puts the emphasis on the comparison of the flow boiling pressure drop and heat transfer of R134a and R1234ze(E) in a dimpled flat duct. For the air-conditioning applications, the experiments are conducted at mass flux from 100 to 200 kg m−2 s−1, saturation temperature from 5 to 15 °C, heat flux from 2.5 to 10 kW m−2, and vapor quality from 0.1 to 0.95. The results show that the frictional pressure gradient of R1234ze(E) is 1.10 to 1.27 times that of R134a. The characteristics of the flow boiling heat transfer coefficient of R1234ze(E) are similar to R134a. The increasing flow boiling heat transfer coefficient with vapor quality in the tested range implies the convective evaporation dominates the heat transfer. It is also observed that the flow boiling heat transfer coefficient visibly increases with a rise in mass flux and decreases with the saturation temperature increment due to the increase in vapor to liquid density ratio. The enhancement effect of heat flux on the flow boiling heat transfer shows up at the highest value of 10 kW m−2 only. The heat transfer coefficient ratio of R1234ze(E) to R134a increases from 0.89 to 1.20 with an increase in vapor quality. The comparison of frictional pressure gradient and heat transfer characteristics between R1234ze(E) and R134a has been discussed from the viewpoint of fluid properties.