Abstract
Internal grooves are widely used as means to improve the heat transfer performance of tubes, but their optimum shape has not been clarified. In this paper, a rectangular channel with the test surfaces is used instead of circular tube. Two kinds of grooved surface with 0.34mm of the groove pitch are tested, the grooved surface 1 has 18 degree of lead angle and the grooved surface 2 has 0 degree of lead angle. The rectangular channel, 10mm in width, 5mm in height, and 500mm in length, was set horizontally, and the upper and lower surfaces were heated electrically with Nichrome heaters. HCFC22 was used as a working fluid. Evaporating pressure was 0.49MPa, heat flux was 4.65kW/m2, vapor quality was varied from 0.1 to 0.9, and mass velocity was varied from 86 to 345kgj(m2s). Heat transfer coefficient for the grooved surface 1 compared well with that for grooved tube with 18 degree of lead angle except for low mass velocity region where the heat transfer coefficient of the upper surface was much lower than that of the lower surface. Heat transfer coefficient for the grooved surface 2 was lower than that for the grooved surface 1.
