Numerical analysis of flow boiling heat transfer characteristics of alternative refrigerants in minichannels

This study examines the flow boiling heat transfer characteristics of alternative refrigerants. A detailed literature review reveals inconsistencies in prior research regarding the effects of heat flux, mass flux, vapor quality, saturation temperature, and channel geometry on heat transfer coefficients. To address these gaps, numerical simulations were performed for R1234ze(E), R290, R600a, and R1270 in a small-diameter horizontal smooth tube with an internal diameter of 1.88 mm. Operating conditions included mass fluxes from 375 to 870 kg/m² s, vapor qualities from 0.1 to 0.9, heat fluxes of 55 and 65 kW/m², and saturation temperatures of 30 and 40 °C. The numerical model was validated against experimental data for R1234ze(E). Results demonstrate that hydrocarbons exhibit superior heat transfer coefficients compared to R1234ze(E) due to their favorable thermophysical properties. This work provides a comparative evaluation of alternative refrigerants, resolves inconsistencies in the literature, and offers insights into the development of sustainable and efficient heat transfer systems for horizontal tube configurations. To achieve this, the study adopts a unified simulation framework, rigorously validated against experimental data, enabling clear performance benchmarking of several low-GWP refrigerants under identical thermal and geometric conditions.