Abstract

Three-sides artificially roughened solar air heaters perform better than one-side roughened ones under identical operating conditions. The present paper is an outcome of the experimental investigations conducted upon three- and one-side concave dimple roughened ducts. The present investigation is carried out under the mass flow rate range (0.0060-0.0250) kg/s, relative roughness pitch (p/e) 8-16 and relative roughness height (e/D_h) 0.018-0.045. Thermal performance characteristics of three-sides and one-side roughened duct has been analyzed, compared and validated. The variation in plate temperature along the test length of the roughened duct has an appreciable impact on the heat transfer from the plate to the underside flowing air. The collector’s surface temperature is found to be 21% lower in the three-sides than the one-side roughened duct. Plate temperature excess for both three-sides and one-side roughened duct has been analyzed and compared. 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 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 augmentation in thermal performance due to the provision of roughness geometry in the form of concave dimple shape on the three-sides over one-side roughened duct is found to be 39-56% for varying p/e and 44-51% for varying e/D_h depending upon the operational mass flow rate of air and roughness geometry. The maximum thermal efficiency is obtained at relative roughness pitch of 12 and relative roughness height of 0.036. The results for efficiency ratio along with parametric variation influence on performance of the roughened ducts have also been discussed in detail.