EXPERIMENTAL-STUDY OF THE HEAT-TRANSFER ENHANCEMENT OF AN OUTER TUBE WITH AN INNER-TUBE INSERTION

This experimental study aims to investigate the heat transfer phenomen a of an outer tube with an inner-tube insertion. The naphthalene subli mation method is adopted which measures the sublimation depth of napht halene necessary to reduce the local heat transfer through the analogu e relation between heat and mass transfer. The working fluid is air an d the data runs are performed for Reynolds numbers of 1058, 1360 and 1 965. The comparison between experimental and numerical results shows g ood agreement. It is also found that, with an inner-tube insertion, th e heat transfer rate of the outer tube increases as the Reynolds numbe r of the tube flow and the size of inner tube increase, as long as the inner tube is not Larger than a given size.