An Experimental Investigation on R134a Evaporation inside an Internally Discrete Inclined Grooved Tube

Abstract

In this experimental study, heat transfer and pressure drop characteristics of R134a evaporating flow are investigated inside a horizontal internally grooved tube with discrete inclined grooves. The test evaporators are made of smooth and grooved copper tubes of 20 mm inner diameter. The length, width, and depth of grooves are 6, 2, and 0.5 mm, respectively, and the angle of the grooves with the tube centerline is 30°. The test conditions include mass flux in the range of 16.5 to 105 kg/m2s, vapor quality of 0.06 to 0.98, and heat flux of 3.5 to 25 kW/m2. The experiment results show that the boiling heat transfer coefficient of R134a in the grooved tube is 1.25 to 1.65 times higher than that of the smooth one. The frictional pressure drop of R134a inside the grooved tube is 10% to 60% higher than the smooth tube. Moreover, by increasing mass flux, the heat transfer coefficient, and frictional pressure drop of R134a refrigerant inside horizontal smooth and grooved tubes increase as well. In conclusion, the energy performance of R134a evaporating flow inside the grooved tube is more efficient than that in the smooth tube regarding energy saving in most experiments.