HORIZONTAL CONVECTIVE BOILING OF R134A, R1234YF/R134A, AND R1234ZE(E) WITHIN A MICRO-FIN TUBE

This paper presents local convective boiling measurements in a micro-fin tube for R134a and two low global warming potential (GWP) refrigerants: R1234yf/R134a (56/44% mass) and R1234ze(E). The heat-transfer coefficients of the three test fluids were compared at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux using an existing correlation from the literature. The resulting comparison showed that refrigerant R134a exhibited the highest heat-transfer performance in large part due to its higher thermal conductivity compared to the tested low-GWP refrigerants. For the example case presented here, the heat-transfer coefficient for R1234yf/R134a (56/44) remained within 5% of the heat-transfer coefficient for R134a, having essentially identical performance for qualities less than 30%. The heat-transfer coefficient for R1234ze(E) is roughly 700 kW/K-1 . m(-2) (approximately 14%) less than that of R134a for qualities greater than 30%. The smaller heat-transfer coefficient of R1234ze(E) compared to that of R134a is primarily due to the 11% smaller thermal conductivity and the 21% smaller reduced pressure compared to R134a at this test temperature.