Saturated flow boiling of HFC134a and its low GWP substitute HFO1234ze(E) inside a 4 mm horizontal smooth tube

•This paper investigates HFO1234ze(E) and HFC134a vaporisation inside a smooth tube.•HFO1234ze(E) and HFC134a exhibit similar heat transfer coefficients.•HFO1234ze(E) exhibits frictional pressure drop higher than those of HFC134a.•HFO1234ze(E) is a viable lower GWP substitute for HFC134a.

This paper presents the comparative analysis of HFO1234ze(E) and HFC134a during vaporisation inside a 4 mm smooth tube. The experimental tests were carried out at three different saturation temperatures (10, 15, and 20 °C) at increasing vapour quality up to incipient dryout to evaluate the specific contribution of heat flux, refrigerant mass flux, mean vapour quality, and saturation temperature (pressure). The heat transfer coefficients have a positive slope versus vapour quality and the slope increases with refrigerant mass flux and decreases with heat flux. Saturation temperature (pressure), refrigerant mass flux and mean vapour quality have a remarkable impact on the frictional pressure drop of both HFO1234ze(E) and HFC134a whereas the effect of heat flux appears marginal or negligible. Convective boiling seems to be the prevailing heat transfer regime in the present experimental tests. HFO1234ze(E) exhibits heat transfer coefficients similar to HFC134a and slightly higher frictional pressure drops.