Performance based investigation of inclined spherical ball roughened solar air heater

Abstract

Heat transfer augmentation for inclined spherical ball roughened solar air heaters has been investigated and reported in this work. The roughness geometry investigated has advantages of both protruded shape and inclined pattern. This investigation covers the determination of all performance parameters viz., thermal, thermohydraulic and exergetic efficiency and its variations as these parameters are essential to justify the practical utility of the roughened system. The impact of roughness on performance is determined and compared to smooth plate air heater at identical flow conditions. Experimental study on spherical ball roughness aligned inclined to flow direction has not been performed to the best of author’s knowledge. The key outcomes were inline with literature as the maximum thermal efficiency for roughened ducts obtained was 81 % compared to 38 % for smooth duct at flow rate of 0.0319 kg/s. With varying roughness configuration, maximum effective efficiency was found 0.67, 0.748, 0.725 and 0.739 respectively at flow rate 0.0372, 0.0391, 0.04 and 0.0418 kg/s. The determination of exergetic efficiency along with thermal and effective efficiency is something that makes present work different from other works since most of the work performed on roughened solar duct system only deals with thermal and effective efficiency determination. The variation in exergetic efficiency with Reynolds number and temperature rise parameter at different roughness geometrical orientations revealed that as Reynolds number changed, both smooth and rough absorber showed maximum exergetic efficiency at same Reynolds number but rough absorber showed maximum exergetic efficiency at temperature rise parameter of 0.0295, 0.0274, 0.031 and 0.045 with maximum exergetic efficiency being 0.0246, 0.037, 0.0262 and 0.0349 respectively.