Flow boiling heat transfer investigation of new refrigerant blends in a minichannel.

Mixtures of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) are suitable as drop-in substitutes in refrigeration and air conditioning due to their low environmental impact and good thermodynamic properties. In this work, the flow boiling heat transfer of four HFOs/HFCs mixtures has been studied inside a 0.96 mm diameter channel. Three of those mixtures, R513A (R1234yf/R134a, 56/44% by mass, GWP100-y = 629), R516A (R1234yf/R152a/R134a 77.5/14/8.5% by mass, GWP100-y = 131) and R515B (R1234ze(E)/R227ea, 91/9% by mass, GWP100-y = 299), are azeotropic mixtures, while the fourth is a quasi-azeotropic mixture R450A (R1234ze(E)/R134a, 56/44% by mass, GWP100-y = 547, ΔTGL = 0.64 K at 30°C). Tests were performed at Tsat = 30°C and mass flux between 400 and 600 kg m-2 s-1. The data have been compared with the HTC of R134a, to assess the feasibility of its drop-in substitution. The comparison between experimental data and the prediction from some semi-empirical models is also assessed.