Condensing heat transfer of pure refrigerants and refrigerant mixtures flowing within horizontal microfin tubes: A new model

A new model is developed to predict the heat transfer coefficients (HTCs) of pure refrigerants and refrigerant mixtures condensing within horizontal microfin tubes. A 1312–point experimental database from 22 sources was compiled for this purpose. The data comprise CO2, R1234yf, R1234ze(E), R134a, R22, R407C, R404A, and R410A, 2.64–8.98 mm diameter tubes, −25 °C to 50 °C saturation temperatures, vapor qualities from 0.02 to 0.98, reduced pressures from 0.16 to 0.81, and heat and mass fluxes ranging from 1.79 to 98.1 kW/m2 and 49.0 to 872.5 kg/m2 s, respectively. To develop the model, one hundred twenty unique dimensionless parameters pertinent to condensing flows in microfin tubes were first selected. Multi-variable regression analysis was then applied to identify the most significant of these variables influencing the condensation Nusselt number. On an overall basis, the new model performs significantly better than any of six extant correlations. The new model was then assessed for different refrigerants, and many ranges of diameter, heat and mass flux, vapor quality, and reduced pressure. Generally, the new model is reasonably accurate, with mean absolute deviations generally smaller than 20–25%. The model also predicts annular flow HTCs fairly accurately. Parameter ranges in which Cavallini et al. (2009), the best of the extant correlations, gives better predictions than the new model and those in which more data would be useful for further analysis are also identified. In general, the new model can be recommended for a large variety of refrigerants under practically significant operating conditions.