Flow boiling heat transfer of a zeotropic binary mixture of new refrigerants inside a single microchannel

This study presents an experimental investigation of flow boiling of a zeotropic mixture in a microchannel. In the recent years much attention has been paid to the possible use of fluorinated propene isomers for the substitution of HFC fluids, being in most cases high-GWP refrigerants. However, the available HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump and refrigeration systems when used as pure fluids because their thermodynamic properties are not suitable for all operating conditions and therefore some solutions may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. In the present paper a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) has been studied. The local heat transfer coefficient during flow boiling of this mixture in a single microchannel with 0.96 mm diameter is measured at a pressure of 14 bar, which corresponds to a bubble temperature of 26.2 C. The flow boiling heat transfer coefficients measured in the present test section are discussed, with particular regard to the mass transfer mechanism in the microchannel. The new experimental data are also compared to flow boiling data of pure R1234ze(E) and pure R32 to analyze the heat transfer penalization due to the mass transfer resistance of the mixture.