Thermal and thermohydraulic performance analysis of three sides artificially roughened solar collectors

摘要

Thermal and thermohydraulic performance characteristics for 3-sides concave dimple roughened collector has been investigated and presented here. The geometrical parameter of roughness element covers relative dimple pitch, height and depth 8-15, 0.018-0.045 and 1-2 respectively along with flow Reynolds number 2500-13,500. Thermal performance of artificially roughened SAH doesn't include a frictional loss that is generated while the air is propelled through the roughened ducts. Three sides roughened ducts have high thermal efficiency compared to 1-side roughened duct but that hike should not come at the cost of tremendous rise in frictional losses. The present investigation is aimed at determining the optimum roughness parameters at which maximum possible efficiency is obtained at minimum frictional losses. The optimum roughness parameter yielding the maximum thermal efficiency is 'p/e' = 12, 'e/D-h' = 0.036 & 'e/d' = 1.5 for both ducts. 3-sides concave dimple roughened SAH were having 44-67% more thermal efficiency than 1-side roughened duct under similar flow condition. Maximum effective (thermohydraulic) efficiency at varying 'e/D-h' obtained was 0.78 and 0.49 and that at varying 'p/e' obtained was 0.74 and 0.47 in the case of 3-sides and 1-side roughened ducts respectively.