Condensation and evaporation of R134a, R1234ze(E) and R1234ze(Z) flow in horizontal microfin tubes at higher temperatures.

Abstract

The hydrofluoro-olefins R1234ze(E) and R1234ze(Z) are anticipated to be environmentally friendly working fluids for industrial high-temperature heat pumps. This study presents the experimental data obtained for the heat transfer coefficient and pressure gradient of these refrigerants in a horizontal microfin tube measured at temperatures of 65°C for condensation and 30°C for evaporation. For condensation, the heat transfer coefficient and pressure gradient of R1234ze(Z) are higher than those of R1234ze(E), mainly because of the higher vapor velocity due to the lower vapor density, higher liquid thermal conductivity and latent heat compared with those of R134a and R1234ze(E). For evaporation, the heat transfer coefficient of R1234ze(Z) was somewhat higher than those of R134a and R1234ze(E), but only for higher vapor qualities. However, the pressure gradient of R1234ze(Z) was notably higher than that of R134a and R1234ze(E). A comparison between experimental and predicted values validated that the heat transfer coefficient (HTC) and pressure gradient of R1234ze(E) and R123ze(E) can be accurately predicted using existing correlations and currently available predictions for thermophysical properties.