Comparative experimental studies of flow boiling heat transfer phenomena in smooth and enhanced tubes using R407C

This study investigates flow boiling heat transfer and pressure drop characteristics of R407C (zeotropic mixture) in newly shaped copper-made horizontal enhanced and smooth evaporator tubes of 1000 mm employing a vapour compression refrigeration cycle at ambient pressure and saturation temperatures of 15 - 45 degrees C. The enhanced tube has 60 trapezoidal microfins with a helix angle of 20 degrees and a height of 0.22 mm leading to a 1.83 times increase in surface area. The effects of mass fluxes of 50-250 kg/m(2)s, and heat fluxes of 10-80 kW/m(2) on the heat transfer coefficient (HTC) and pressure drop, were examined. 1.55, and 1.35 times higher mean HTCs, and pressure drops are recorded for the enhanced tubes with +/- 9% and +/- 14.5% mean absolute errors respectively with the established correlations including smooth tube findings. The results emphasize the importance of using accurate and validated correlations in refrigeration systems. Local Nusselt number variation with Jakob subcooling number and locations over the evaporator and parametric variation studies are also incorporated to analyse and capture the experimental trends comprehensively.