Experimental study on nucleate pool boiling heat transfer characteristics of R32 + R1234yf binary mixtures

Abstract

• Boiling heat transfer deteriorated most at x R32 = 0.4277 for different heat fluxes. • Mass transfer resistance weakened the bubble coalescences at high heat flux. • Phase equilibria and physical property together affected heat transfer of mixtures. • The accuracies of two existing correlations were improved to within 5.6%. Although R1234yf is a new environmentally-friendly refrigerant with low GWP, its thermal performance is inferior to that of conventional refrigerants. Mixing R1234yf with R32 can overcome the respective shortcomings of each component. Therefore, understanding the pool boiling heat transfer characteristics of R32 + R1234yf mixtures is of great importance to the design of heat exchangers and the optimization of thermal systems. This study carried out the pool boiling experiments of R32, R1234yf, and their binary mixtures. The boiling curves, heat transfer coefficients, and bubble images of pure and mixed refrigerants were obtained. The results showed that the addition of R32 effectively improved the heat transfer performance of R1234yf. Meanwhile, the mixing effect weakened the bubble coalescence and enhanced the heat transfer performance under high heat flux. It was found that the heat transfer deterioration of mixtures was not only influenced by the vapor–liquid phase equilibrium but also related to the nonlinearly varying physical properties. Based on the experimental data, eleven widely used correlations for boiling heat transfer coefficient of binary mixtures were analyzed with two selected and further modified. The prediction performances of the modified correlations improved significantly, with the mean absolute relative deviation (MARD) reducing to 5.16% and 5.53%, respectively.