Evaporation, Heat transfer, Pressure drop, Helical-grooved tube, Small-diameter, R32
Experiments were conducted examining pressure drop and heat transfer for flow boiling inside horizontal smooth and two internally helical-grooved small-diameter tubes with outer diameter of 4.0 mm. The geometric parameters of internally helical-grooved tubes are the groove number of 25 and 40, helix angle of 16 and 17 Â°, fin height of 0.1 and 0.2 mm. The heat transfer and pressure drop are measured in a range of mass velocities from 50 to 400 kg/(m2s) and a range of heat fluxes from 5 to 20 kW/m2 at saturation temperature 15 Â°C. The pressure drop of microfin tubes were 1.1 - 2.0 times than the smooth tube. The heat transfer coefficient of microfin tubes were 1.3 - 6.5 times than the smooth tube. The pressure drop and heat transfer characteristics of the internally helical-grooved tubes for evaporation flow were examined and compared with those of the smooth tube.