Abstract
The implementation of the climate change agreement intensified the actions of government agencies and industries to phase out refrigerants with high global warming potential (GWP). This study investigated refrigerant blends as possible low GWP alternatives for R410A in a refrigerating application. The cycle efficiency and flammability of binary and ternary blends among 19 pure refrigerants were evaluated based on an ideal vapor compression refrigeration cycle model with application conditions of water chillers. The mixtures R32/R290 and R32/R1270 were selected based on the acceptable efficiency and availability. Further investigation of the pool boiling performance of the two mixtures with various mass fractions was conducted. The results showed that the heat transfer coefficient deteriorated as the temperature glide and the vapor–liquid fraction difference became larger, and increased with the increasing of the vapor pressure and thermal conductivity. Meanwhile, the heat transfer coefficient of the two mixtures did not deteriorate at the mass fraction of R32 near 70 wt%, where the near-azeotropic mixtures were formed. The results show that the pool boiling heat transfer performances of R32/R290 (70/30 wt%) and R32/R1270 (70/30 wt%) were 2.23% lower and 8.67% higher than that of R410A, respectively, and R32/R1270 (70/30 wt%) has 9.3% higher performance than pure R32 at low heat flux. Six correlations were compared against the present data. None of the correlations can accurately predict both the R32/R290 and R32/R1270 mixtures. A modified correlation based on three of the six previous correlations was developed taking account the vapor–liquid fraction difference, temperature glide, heat flux, and system pressure. The prediction performances of the modified correlation were improved for both mixtures with the mean absolute deviation of 5.95 % and 6.58 % for R32/R290 and R32/R1270, respectively, and most of the data points within the deviation band of 15 %.
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