Horizontal Convective Condensation of Alternative Refrigerants Within a Micro-Fin Tube

This paper presents local convective-condensation measurements for four refrigerants: R134a, R410A (R32/R125, 50/50% mass), R125, and R32 in a micro-fin tube. Both heat transfer and pressure drop measurements are provided. The heat transfer degradation associated with R410A was shown to be relatively small and believed to be mostly due to nonlinear property effects. The measured convective-condensation Nusselt numbers for all of the test refrigerants were correlated to a single expression consisting of a product of dimensionless properties. The correlation was shown to predict some existing data from the literature within acceptable limits. The correlation poorly predicted the heat transfer performance of cross-grooved, micro-fin tubes. The pressure drop measurements for the micro-fin tube were predicted satisfactorily by an existing correlation for flow-boiling pressure drop in a smooth tube. Correlation of the pressure drop measurements suggested that the heat transfer enhancement was due to the fins behaving as a surface roughness.