Evaporation heat transfer and pressure drop characteristics of R1234ze(E)/R32 as a function of composition ratio in a brazed plate heat exchanger

This study investigates the evaporation heat transfer coefficient and two-phase frictional pressure drop of refrigerant mixture R1234ze(E)/R32 at various R1234ze(E) composition ratios in a brazed plate heat exchanger. The heat transfer coefficient of R1234ze(E)/R32 shows a concave curve as a function of composition ratio owing to the temperature glide of the mixture, whereas the two-phase frictional pressure drop increases exponentially with respect to the composition ratio. In addition, the averaged evaporation heat transfer characteristics of R32, R1234ze(E)/R32 (85%/15%), and R1234ze(E) are compared by considering the European Union (EU) regulations for global warming potential (GWP). For regulation phase A (GWP > 750), R32 exhibits the best heat transfer performance, whereas for regulation phase B (GWP > 150), R1234ze(E) shows a favorable averaged heat transfer coefficient compared to R410A and R134a. Finally, based on the measured data, correlations for the Nusselt number and two-phase friction factor for R1234ze(E)/R32 are derived as a function of composition ratio using a nonlinear interpolation method with the pre-developed correlations for pure R1234ze(E) and R32. (C) 2019 Elsevier Ltd. All rights reserved.