Experimental and CFD-based thermal performance prediction of solar air heater provided with chamfered square rib as artificial roughness

An experimental and two-dimensional computational fluid dynamics (CFD) analysis of a solar air heater has been carried out using chamfered square rib as artificial roughness on the absorber plate. The relative roughness pitch (P/e = 7.14–17.86), chamfer angle (α = 0°–40°), Reynolds number (Re = 3800–18,000) and relative roughness height (e/D = 0.042) are chosen as design variables for analysis. A uniform heat flux of 1000 W/m2 is maintained on the surface of absorber plate. CFD code, ANSYS FLUENT 14.5 with renormalization group k-ε model was chosen. An enhancement in Nusselt number and friction factor with decrease in relative roughness pitch (P/e) is presented and discussed with reference to experimental and CFD analysis. The effect of chamfer angle and Reynolds number on enhancement of Nusselt number and friction factor is also presented. Optimum configuration of roughness element for artificially roughened solar air heater has been determined in terms of thermo-hydraulic performance parameter. The chamfer angle of 20° on square rib and relative roughness pitch of 7.14 provide best thermo-hydraulic performance of 2.047 considering the maximum heat transfer and minimum pressure drop.

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