Experimental study of entropy generation during condensation in inclined enhanced tubes

Abstract In the current study, the influence of inclination angle, temperature difference, mass velocity, and vapour quality is investigated on the entropy generation rate in an inclined enhanced tube during the flow condensation of R134a. The enhanced tube is a microfinned tube with a helix angle of 14o. The experiments are carried out at a saturation temperature of 40 °C, heat fluxes of 230–270 W, mass velocities between 200 and 400 kgm−2s−1, qualities of 10–90%, and inclination angles between -90o and +90o. Results show that the frictional contribution becomes significant when compared with the heat transfer component of the total entropy generation rate at the mass velocities ≥300 kgm−2s−1. The overall minimum total entropy generation corresponds to the mass velocity of 300 kgm−2s−1, quality of 25%, and inclination angle of +5o, while the maximum total entropy generation is obtained for the mass velocity of 400 kgm−2s−1, inclination angle of -60o, and quality of 90%. For optimal design, the inclination angle of − 10 o ≤ β ≤ + 10 o is proposed for minimal total entropy generation for vapour qualities less than 75%, and + 90 o for qualities greater.