Effect of geometrical parameters on entropy generation during R134a boiling flow inside unique internally grooved tubes: Experimental approach

Abstract

Generally, using heat transfer enhancement techniques in heat exchangers always accompanies frictional pressure drop amplification; entropy generation analysis is a suitable technique to investigate the heat transfer and pressure drop together. In this study, the effects of tube's geometrical parameters and flow conditions on entropy generation during two-phase boiling flow of R134a refrigerant in horizontal internally grooved tubes are experimentally investigated. The experimental tests are conducted in a wide range of operating conditions, including mass flux of 16.5–105 kg/m2s, vapor quality of 0.06–0.98, and heat flux of 3.5–25 kW/m2. Test evaporator tubes are made up of copper of 20 mm inner diameter with nine types of discrete inclined grooves on the tubes' internal wall surface. The results represent that using the grooved tubes is desirable for the majority of test conditions except for mass fluxes between 20 and 80 kg/m2s at vapor qualities higher than about 0.4–0.5. The ratio of groove pitch length to groove width within the geometrical parameters has the most notable effect on the total entropy generation. Besides, a new correlation is developed for entropy generation of R134a evaporating flow inside internally grooved tubes with discrete inclined grooves.