Experimental investigation for thermal performance of inclined spherical ball roughened solar air duct

This work deals with determination of thermal efficiency of spherical ball roughened collector aligned inclined to flow direction. Roughened collector produces more heat transfer compared to smooth ones but heat transfer augmentation comes at the cost of increased frictional losses. Lesser thermal efficiency of solar air heater has necessitated researchers to focus on its improvement by providing artificial flow modification techniques in the flow field. Laminar sublayer beneath the absorber plate will get disturbed and this helps to increase turbulence level of air. Present work discusses the influence of inclined spherical ball shaped roughness element and improving its thermal performance. Design considerations, geometries used viz. relative roughness pitch 9–18, relative roughness height 0.024–0.040, height-diameter ratio 0.5–2, angle of attack 35°-75°, flow conditions and their influence on turbulence viz. Reynolds no 2500–18500, heat transfer rate, absorber temperature and thermal performance enhancement factor have been thoroughly discussed. Finally concluding remarks and future scope for additional enhancement in performance of solar air heater is proposed. Maximum thermal efficiency for roughened ducts was found as 81% compared to 38% for smooth duct at parameters viz. ‘relative roughness pitch = 12, ‘relative roughness height’ = 0.036, ‘height-diameter ratio’ = 1 and ‘angle of attack’ = 55֠ at mass flow rate = 0.0319 kg/s.