Abstract
In this study, the thermal and effective efficiencies (ηthe and ηeff, respectively) of a dimple-roughened jet impingement solar air heater (DRJISAH) are analytically examined. The analysis is performed based on the following conditions: Reynolds number (Re) = 3000–24000; solar irradiance (Isr) = 700–1000 W/m2; dimple height ratio (ed/Dhd) = 0.016–0.031; dimple pitch ratio (pd/Dhd) = 0.269–0.810; arc angle (αd) = 30°–75°. An enhancement in ηthe by 18%–29% is achieved, which is corresponding to the ηthe of a jet impingement solar air heater. The ηeff of a DRJISAH is greater than that of a flat-plate solar air heater (FPSAH). However, at high values of Re, the useful thermal energy gain is dominated by frictional losses in the duct; thus, the FPSAH has a higher ηeff value than the DRJISAH. The optimum ηthe and ηeff for the DRJISAH are 74% and 70%, respectively, at ed/Dhd = 0.031, pd/Dhd = 0.269, αd = 60°, and Isr = 1000 W/m2. In addition, each dimple parameter is plotted against Re to obtain the best ηeff for the specified Re.
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