A comparative analysis of thermo-hydraulic performance of a roughened solar air heater using various rib shapes

Abstract

ABSTRACT The thermal efficiency of the solar air heater (S.A.H.) is enhanced by introducing various artificial roughness geometries on the absorber surface. Artificial roughnesses in the form of a chamfered rib, right angle triangular and reverse L-shaped ribs, invented from square rib are presented. A comparative thermohydraulic analysis of these ribs is carried out using experimental, Computational Fluid Dynamics (C.F.D.) and analytical investigation. The experiments are carried out using rib height (e = 0.7,1 and 1.4), relative roughness pitch (P/e = 7.14 to 35.71), relative roughness height (e/D = 0.021, 0.03 and 0.042), Reynolds number (Re = 3800 to 18000) and duct aspect ratio (W/H= 5).The effect of rib shape, rib height (e), pitch (P), relative roughness pitch (P/e), relative roughness height (e/D), chamfer angle (α) and Reynolds number (Re) on heat transfer and friction flow is evaluated. Experimental results are validated using C.F.D. code ANSYS FLUENT 14.5, by simulating two-dimensional computational domain of roughened S.A.H. Based on the experimental results correlations for the Nusselt number and friction factor are derived. A mathematical model has been developed to investigate the effect of geometrical and operating parameters on the thermal and effective efficiency of a roughened S.A.H.