Study of in-tube condensation heat transfer of zeotropic R32/R1234ze(E) mixture refrigerants

•Condensation HTCs of low-GWP zeotropic mixtures of R32/R1234ze(E) are experimentally investigated.•HTCs of R32/R1234ze(E) yield significantly lower than those of pure R32 and R1234ze(E) but comparable to that of R410A.•Effects of mass flux, saturation temperature, and initial concentrations are studied.•HTCs are predicted by well-established pure fluid models as well as mixture models.•A new correlation of HTC for zeotropic mixture of R32/R1234ze(E) is proposed.•The newly proposed HTC model predicts current experimental data within a mean deviation of 8.5%. Despite of its widespread use in household HVAC&R systems, R410A is considered to be phased down because of its high global warming potential (GWP) (100-year GWP = 2088). Research efforts are going on in search of an alternative of R410A, which will have a much lower GWP with a comparable heat transfer characteristic. This work presents the analysis of heat transfer characteristics along with a prediction method during condensation of potentially low-GWP zeotropic mixtures of R32/R1234ze (E) as a replacement of R410A. At three different initial mass concentrations (0.25/0.75, 0.45/0.55, and 0.75/0.25) of R32/R1234ze(E), the heat transfer data were taken at saturation temperatures (30, 40, and 45°C) under a wide range of mass fluxes (100-500 kg m−2s−1) and vapor quality (0.9-0.1) inside a smooth horizontal tube. The effects of mass flux, saturation temperature, and initial mixture compositions on heat transfer coefficient (HTC) were clearly stated. Results show that mixtures of R32/R1234ze (E) exhibit lower HTCs than those of their pure forms due to the presence of a mass transfer resistance during condensation of the mixtures. The current investigation found that the mass transfer during the vapor-liquid phase change of the zeotropic mixture is largely governed by two of its key features: temperature glide and initial mass composition. Considering that, a generalized correlation of condensation HTC has been developed introducing a new dimensionless parameter which includes all the aspects to count the mass transfer resistance. The new correlation shows a better prediction than the previous models with a mean deviation of 8.5%.