Two-Phase Flow and Heat Transfer of a Non-Azeotropic Mixture inside a Single Microchannel

In the recent years much attention has been paid to the use of fluorinated propene isomers for the substitution of high-GWP refrigerants in refrigeration and air conditioning applications. However, the HFOs (hydrofluoroolefins) cannot cover all the applications due to their thermodynamic properties. For the purpose to obtain a fluid that brings together the good heat transfer characteristics of HFCs, such as R410A, and the environmental friendly behavior of HFOs, in the latest literature it was attempted to blend R1234ze(E) with another refrigerant, R32. R32 has relatively low GWP and excellent thermodynamic characteristics. Therefore, a zeotropic mixture of R1234ze(E) and R32 can be used in the field of air-conditioning due to its mild impact on the environment. In this paper, a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) is investigated. In particular the frictional pressure gradient and the local heat transfer coefficients during flow boiling and condensation of this mixture in a single microchannel with 0.96 mm diameter are measured. Tests are carried out in the experimental apparatus available at the Two Phase Heat Transfer Lab of the University of Padova. The heat transfer coefficients are compared against predicting models available in the literature. The new experimental data are also compared to heat transfer data of pure R1234ze(E) and R32. This allows to analyze the heat transfer penalization due to the mass transfer resistance of this zeotropic mixture. Pressure drop data are also used to assess predicting pressure gradient correlations.