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Over the past decades the hydrochlorofluorocarbon (HCFC) refrigerant R-22 has been used as the working fluid in many air-conditioning systems. But it will bi phased out in a short period of time (before 2020) because of its high ozone depletion potential (ODP) and comparatively high global warming potential (GWP). As a result, the search for a replacement for R-22 has been intensified in recent years. Owing to the fact that there are no single-component HFCs which have thermodynamic properties close to those of R-22, binary or ternary refrigerant mixtures have been introduced. The alternative refrigerants evaluation program (AREP) technical committee has established an updated list of the potential alternatives to R-22. Some of the alternatives on the AREP’s list are R-401A, R-401B, R-401C and R-507. Among the various alternatives to R-22, three refrigerants are gaining most favorable support depending on application and system design [6]: a look-alike zeotropic mixture such as 407C, higher pressure, nearly azeotropic mixtures like R-410A or R-410B, and the lower pressure refrigerant R-134a. Some studies were carried out and reported in the literature dealing with the subcooled flow boiling, saturation flow boiling, evaporation and condensation heat transfer of R-134a in ducts of various test section geometries, including smooth and micro-fin tubes, plate heat exchanger and the other enhanced heat transfer tubes for refrigerant R-134a [4,5,7-10]. However, the two-phase heat transfer characteristics for R-407C and R-410A [11-15] and R-410A[16-21] flow in ducts are less examined.
In the following the relevant literature on the boiling heat transfer for R-410A is briefly reviewed. It should be mentioned here that the refrigerant R-410A is a mixture of 50 wt% R-32 and 50 wt% R-125 which exhibits azeotropic behavior. Sami and Porirer [16] compared the evaporation and condensation heat transfer data for several refrigerant blends proposed as substitutes for R-22, including R-410A, R-410B, R-507 and the quaternary mixture R-32/125/143a/134a inside enhanced-surface tubing. They showed that the two-phase heat transfer coefficients and pressure drops increased with the refrigerant mass flux for all alternative refrigerants and R22. In a continuing study [17], they presented the data for R-410A and R507 in a double fluted tube indicating that for the refrigerant Reynolds number higher than 4.2 × 106 , R-410A had a greater heat transfer rate than that of R-507. Wang et al. tested nucleate boiling on several commercially available enhanced-surface tubes to assess the pool boiling heat transfer performance for R-22, R-123, R-134a, R-407C, and R-410A. The heat transfer coefficient of R410-A was found to be higher than that of R-22 for most enhanced tubes. This outcome was attributed to the higher latent heat, thermal conductivity and specific heat for R-410A and the corresponding liquid viscosity was lower. Ebisu and Torikoshi [19] measured the evaporation heat transfer coefficient and proposed empirical correlations for R-410A, R-407C and R-22 flowing inside a horizontal smooth tube. Their results showed that the evaporation heat transfer coefficient of R-410A was 20% higher than that of R-22 up to the quality of 0.4, while the heat transfer coefficients for both R-410A and R-22 became almost the same at the quality of 0.6. Furthermore, the pressure drop for R-410A was about 30% lower than that of R-22 during evaporation. The quantitative differences in the pressure drops between R-410A and R-22 were mainly attributed to the differences in vapor density of two refrigerants. The greater the vapor density, the smaller the pressure drop of a refrigerant. A similar study was carried out by Wijaya and Spatz [20] for refrigerants R-22 and R-410A in a horizontal smooth copper tube. Their data showed that evaporation heat transfer coefficients for R-410A were much higher (about 23-63%) than those for R-22, while the R-410A pressure drops were 23-38 % lower than those for R-22. The advantageous heat transfer characteristics and pressure drops for R-410A were ascribed to the better transport properties for R-410A. Shen et al. [21] provided the data for the pool boiling heat transfer coefficient of the binary mixture R-32/R-125 with different mole fractions of R-32. The results indicated that the pressure and the heat flux dependence of the heat transfer coefficient for the R-32/R-125 mixtures did not significantly differ from of pure components.