Abstract
Enhancement of evaporation heat transfer is required for saving energy and making compact evaporators of air conditioners. Although internal grooves are widely used as means to improve the heat transfer performance of tubes, their optimum shape and spiral angle have not been clarified. In our long-term research program, a rectangular channel is used instead of circular tube because this geometry will allow for a better control of the groove shape in future studiesu. In this paper as a first report, characteristics of the evaporation heat transfer and pressure drop inside a rectangular channel with smooth surface have been studied by using HCFC22 as a working fluid. The experimental results are compared with experimental results for a smooth tube and with already existing equations. The rectangular channel, 10mm in width, 5mm in height, and 300mm in 1ength, was set horizontally, and the upper and lower surfaces were heated electrically with Nichrome heaters. Evaporating pressure was 0.49MPa, vapor quality was varied from 0.1 to 0.9 mass velocity was varied from 86 to 345kg/(m2s), and heat flux was varied from 2.33 to 9.30kW/m2. Average heat transfer coefficient of the upper and lower surfaces compared well with the predicted values except for low mass velocity region where the heat transfer coefficient of the upper surface was much lower than that of the lower surface. Pressure drop of the rectangular channel was found to be close to that of the smooth tube for a given mass velocity.
