Thermal and effective efficiency based analysis of discrete V-down rib-roughened solar air heaters

Abstract

A parametric investigation of discrete V-down rib-roughness geometry in the absorber plate of solar air heater has been carried out and results obtained are compared with those of conventional flat plate solar air heater. The thermal and thermohydraulic performance evaluation has been carried out for various values of Reynolds number and roughness parameters of discrete V-down rib-roughness geometry in the absorber plate of solar air heater duct. The performance curves are plotted in terms of Reynolds number and temperature rise parameter. The discrete V-down rib-roughened solar air heater performs better as per thermal efficiency or heat energy gain criteria for the investigated range of Reynolds number and rib-roughness parameters. The thermal efficiency is high for discrete V-down rib-roughened solar air heater due to higher turbulence; however, the pumping power required for air flow also increases. The thermohydraulic performance on the basis of effective efficiency is a more suitable criterion as it takes into account both the heat collected and the pump work required. For Reynolds number range (or temperature rise parameter) generally employed in solar air heaters, the discrete V-down rib-roughened solar air heater gives higher effective efficiency. It was found that there exist optimum roughness parameters of discrete V-down rib for a given Reynolds number (or temperature rise parameter) at which the effective efficiency is the highest. Curves of optimum roughness parameters based on effective efficiency criterion are also plotted.