Abstract
Microfin tubes having an outside diameter (O.D.) of 7.0 mm are widely used in residential air conditioning systems and heat pumps. It is known that the mass fluxes for air conditioners and heat pumps under partial load conditions are several tens of kg/ms. However, literature surveys reveal that previous investigations were limited to mass flux over 100 kg/ms. In this study, we conduct R-410A evaporation heat-transfer tests at low mass fluxes (50– 250 kg/ms) using a 7.0 mm O.D. microfin tube. During the test, the saturation temperature was maintained at 8C, and the heat flux was maintained at 4.0 kW/m. For comparison purposes, we also test a smooth tube with a 7.0 mm O.D. The results showed that the heat-transfer enhancement factor of the microfin tube increased as the mass flux decreased up to 150 kg/ms, which decreased as the mass flux further decreased. The reason for this was attributed to the change of the flow pattern from an annular flow to a stratified flow. Within the test range, the frictional pressure drops of the microfin tube were approximately the same as those of the smooth tube. We then compare experimental data obtained with the predictions obtained for the existing correlations. † Corresponding Author, knh0001@incheon.ac.kr C 2015 The Korean Society of Mechanical Engineers
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