Boiling of the new low-GWP refrigerants R1234ze(Z) and R1233zd(E) inside a small commercial brazed plate heat exchanger

•This paper investigates R1234ze(Z) and R1233zd(E) vaporisation inside a BPHE.•R1234ze(Z) exhibits boiling heat transfer coefficients 17–22% higher than R1233zd(E).•R1234ze(Z) exhibits frictional pressure drops 7–32% lower than R1233zd(E).•R1234ze(Z) and R1233zd(E) are very promising as low GWP fluids for HTHP and ORC. This paper presents the heat transfer coefficients and the frictional pressure drops of R1234ze(Z) and R1233zd(E) boiling inside a commercial Brazed Plate Heat Exchanger (BPHE): the effects of heat flux / mass flux, saturation temperature / pressure, outlet conditions and fluid properties are investigated. The boiling heat transfer coefficients are controlled mainly by heat flux / mass flux and evaporator outlet conditions. The degrees of superheating at the outlet of the evaporator produces a degradation of the average boiling heat transfer coefficient in the whole evaporator, particularly for R1234ze(Z). The frictional pressure drops exhibit a quadratic dependence on refrigerant mass flux. Saturation temperature / pressure has a remarkable influence only on the frictional pressure drops. R1234ze(Z) exhibits boiling heat transfer coefficients higher and frictional pressure drops lower than those of R1233zd(E). There is a reasonable agreement between the saturated boiling heat transfer coefficients and the calculated values by two recent models for boiling inside BPHE.