OPTIMIZATION OF PACKED BED SOLAR AIR HEATERS

Abstract

It has been pointed out that the value of heat transfer coefficient between the absorber plate and the air is low in the case of solar air heaters resulting in lower values of thermal efficiency of such collectors. Several methods have been proposed to enhance this heat transfer coefficient and consequently improve the thermal performance of air heaters. Packing the duct of a solar air heater with a porous material has been shown to be an efficient method of enhancement which apart form increasing heat transfer coefficient, results in some energy storage too. However, the use of packed bed results in higher friction factor requiring more pumping power. As a result, there is need to optimize the system to obtain maximum benefit from the packed bed while still keeping the pumping power at minimum possible level. In this work, the heat transfer and friction characteristics of the solar air heaters provided with packed bed duct have been studied. Based on thermo-hydraulic consideration; relationships between system and operating parameters to result in optimum performance, have been developed. ° These relationships can be utilized for the efficient design of a thermo hydraulically optimized system. The plots for thermal efficiency and the pressure drop per unit length for a system operating under optimum conditions have been