Evaporation heat transfer and pressure drop of low GWP R-404A alternative refrigerants in a multiport tube

Considering the phase out of the hydrofluorocarbons (HFCs), the search for an alternative refrigerants is of an urgent issue. In this study, four R-404A alternative refrigerants (R-448A, R-449A, R-455A, R-454C) were tested in a multiport tube having 1.61 mm hydraulic diameter. The tests were conducted changing the mass flux from 200 to 400 kg/m²s, heat flux from 2.8 to 6.5 kW/m² at the saturation temperature of 15 °C. The results showed that the heat transfer coefficients of R-404A were higher than those of the alternative refrigerants. However, the pressure drops of R-404A were smaller than those of those of the alternative ones. Possible explanations are provided based on the thermophysical properties and the temperature glides amongst refrigerants. At a low heat flux, the heat transfer coefficient increased as the mass flux or vapour quality increased. At a high heat flux, however, the heat transfer coefficient was relatively independent of the mass flux or vapour quality. This suggested that both the nucleate boiling and the convective heat transfer contributed to the heat transfer in the present multiport tube. Comparison with the existing correlations revealed that the mixture correlation of Shah [53] reasonably predicted the heat transfer coefficients with the RMSE of 0.16, although the trends between the data and the predictions were somewhat different. The pressure drop data were reasonbly predicted by several mini-channel correlations with the RMSE of 0.16.