A New Heat Transfer Coefficient Correlation for Condensing Flows of Pure Refrigerants and Refrigerant Mixtures within Horizontal Microfin Tubes

摘要

A new correlation is presented to predict the heat transfer coefficients (HTCs) of pure refrigerants and refrigerant mixtures condensing within horizontal microfin tubes. This is accomplished by first putting together a 1084 point experimental database from 21 sources. The data includes CO_2, R1234yf, R1234ze(E), R134a, R22, R407C, R404A, and R410A, 2.64–14.61 mm fin root 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/m~2 and 49 to 872 kg/m~2.s respectively. The correlation was developed in two steps. One hundred fifteen 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 variables influencing the flow condensation Nusselt number. First, the new correlation was evaluated and compared with six extant correlations on an overall basis. Comparisons were also conducted with the best among the extant correlations, Cavallini et al. (2009), for data sorted by refrigerant and fin root diameter. Overall evaluation for the entire database shows that the new correlation is significantly better than any of the extant correlations. In general, the new correlation shows reasonably good predictions, which are better than those of Cavallini et al. (2009), are for most parameter bins, with MAD values generally smaller than 20-25%. Based on the bin analysis, parameter ranges in which Cavallini et al. (2009) gives better predictions than the new correlation are also identified. Similarly, bins in which more data would be useful for further analysis are also identified. With these few exceptions in mind, the new correlation can be confidently used as a reasonably reliable predictive tool for a large variety of refrigerants under different operating conditions of practical interest.