an empirical study on flow boiling heat transfer characteristics of r-134a in a tube with novel inclined grooves

In the present study, the effects of different geometrical parameters on heat transfer coefficient in a novel grooved-tube during flow boiling of r-134a were investigated experimentally# the vapor quality varies within a range of 0#06 to 0#99, the mass flux varies from 16#5 to 105 kg/m2#s and heat flux varies between 3#5 and 25 kw/m2# the test section was made of copper with internal diameter of 20 mm and thickness of 1 mm# a new type of inclined grooves was created on internal wall surface of the tube# the effects of the angle of grooves with centerline of the tube, pitch to width (p/w) ratio of grooves and number of circumferential grooves in cross section of the tube were investigated in boiling flow, experimentally# the angles of grooves were set to three different values of 15, 30 and 45 degrees, the numbers of grooves were determined 4, 6 and 8, and (p/w) ratios of grooves were considered as 3, 5 and 7# the width of grooves was 2 mm and the groove-pitch length was set to 6, 10 or 14 mm in different cases# the experimental results of the present work reveal that heat transfer coefficient in boiling flow of r-134a increases with groove angles and numbers or by decreasing the groove-pitch length#