THERMAL PERFORMANCE INVESTIGATION OF ONE AND THREE SIDES CONCAVE DIMPLE ROUGHENED SOLAR AIR HEATERS

The present paper deals with the results of experimental investigation conducted upon one and three sides concave dimple roughened solar air heater ducts and examine the effects of roughness and flow parameters on thermal efficiency results. The present investigation is carried under the Reynolds number range of 2500-12500, relative roughness pitch of 8-15 and relative roughness height of 0.018-0.045. The augmentation in fluid (air) temperature flowing under three sides concave dimple roughened duct is found to be 34.87% more than one side roughened duct. The plate temperature excess range for three sides roughened duct is significantly lower (12.5- 28.5˚C) compared to one side roughened duct (17.5-35.5˚C). The maximum thermal efficiency is obtained at relative roughness pitch of 12 and relative roughness height of 0.036. . The augmentation in thermal efficiency of three sides over those of one side roughened duct is found to be 44-56 % for varying p/e and 39-51 % for varying e/Dh.