INVESTIGATION OF THE EFFECT OF SYSTEM AND OPERATING PARAMETERS ON THE PERFORMANCE OF PACKED BED SOLAR AIR HEATING SYSTEM

Abstract

Solar air heaters are generally used for low to moderate temperature applications. These systems are cheap and easy to maintain, but suffer from the disadvantage of low thermal efficiency because of lower coefficient of heat transfer of air. Several methods have been proposed for the enhancement of the efficiency of such collectors. Packing the bed with porous medium is one of the promising method to achieve the enhancement. Packed bed offers the advantage of high heat transfer area to volume ratio, usually accompanied by high heat transfer coefficient. A bed packed with wire screen matrices have been analyzed in this work. Using energy balance for packed bed solar air heater, the equations governing the heat transfer process have been obtained for steady state conditions. A computer program has been developed in C++ to solve these equations and to predict the thermal and effective efficiencies at the given system and operating parameters. Thermal and thermohydraulic efficiencies were found to be a strong function of system parameters (porosity of bed, pitch & diameter of wire mesh, number of layers) and operating parameters (air mass flow rate, solar radiation). Based on different combinations of system & operating parameters different beds were analyzed, and results from the analysis were used to optimize the performance of the collector for effective efficiency. Design plots have been prepared to represent the optimum values of bed parameters as a function of operating parameters. These plots can be used for the selection of bed parameters to yield a maximum effective efficiency under the given set of system and operating parameters.