The literature survey reveals that condensation or evaporation studies on R-404A alternative refrigerants are very limited. Especially for the multiport tube, no prior investigation exists. In this study, four R-404A alternative refrigerants (GWP100≤2500: R-448A, R-449A and GWP100≤150: R-455A, R-454C) - including R-404A (GWP100 = 3922) were tested in a multiport tube having 0.80 mm hydraulic diameter. The tests were conducted changing the mass flux from 380 to 760 kg/m2s, vapor quality from 0.2 to 0.8. During the tests, the saturation temperature and the heat flux were maintained at 45 °C and at 6 kW/m2. The results showed that the heat transfer coefficients of the alternative refrigerants were higher than those of R-404A. The reason was attributed to the better thermo-physical properties of the alternative refrigerants. Especially, at a high mass flux of this study, the gas core and the liquid film became turbulent, which mitigated the malign effect of temperature glide by strong mixing. Hence, the alternative refrigerants yielded higher heat transfer coefficients than R-404A. Some correlations with mixture correction predicted the heat transfer coefficient reasonably well with RMSE of approximately 0.20. An interesting finding is that even better predictions (RMSE of 0.13) were obtained when the correlation was not mixture corrected. The pressure drops were generally in the reverse order to the value of vapor density. Pressure drops of alternative refrigerants were larger than those of R-404A. The pressure drop correlations generally underpredicted the data.
|ジャーナル||International Journal of Heat and Mass Transfer|
|出版ステータス||Published - 2021 11月|
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