A generalized analytic method for predicting refrigerant charge amount in a variable refrigerant flow (VRF) system.

The search for alternatives to high GWP refrigerants primarily focuses on the use of natural fluids (hydrocarbons, ammonia, carbon dioxide) and new synthetic refrigerants having low GWP. Unfortunately, single-component low-GWP refrigerants so far cannot cover all the applications unless some drawbacks, such as flammability, are accepted. A solution may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. In this paper, the boiling heat transfer performance of a non-azeotropic mixture of R1234ze(E) and R32 (0.26/0.74 by mass) is investigated. This blend exploits the good characteristics of R32 reducing at the same time its GWP value. Local flow boiling heat transfer coefficients have been measured in 1 mm internal diameter microchannel. The heat transfer coefficients of the present mixture are compared against predicting models available in the literature. The new experimental data are also compared to the boiling heat transfer of the pure components R1234ze(E) and R32, to analyze the heat transfer penalization due to the mass transfer resistance.