OPTIMIZATION OF THICKNESS OF PACKED BED SOLAR AIR HEATER USING STONE PEBBLES AS MATRICES

Abstract

The principal applications in which solar air heaters are being used are drying for agricultural and industrial purposes. Solar air heater have been used for many application requiring low to medium grade thermal energy. Like space heating and cooling, agriculture drying, timber seasoning chemical processes and powder generation. It is mainly due to their low manufacturing cost, simple design, operation and maintenance. Their usefulness as quantitative energy collection has been limited because of lower thermal efficiency primarily as result of lower convective heat transfer coefficient between the absorber plate and air, leading to higher plate temperature, due to which greater thermal losses. Several methods for the enhancement of heat transfer coefficient and hence the improvement of thermal performance of solar air heater have been proposed and investigated by a number by a number of investigator. One of the method of improving the thermal performance of the solar air heater is to enhance the heat transfer rate to the air by packing the duct of solar air heater by stone pebbles, such a system absorbs solar air radiation in depth and has a ratio of heat transfer area to volume and hence high transfer capability, resulting in an increase in thermal efficiency of the collector. Packed beds are generally used for storage of thermal energy from solar air heaters. In this paper experimental study has been conducted on a porous packed bed solar air heater using stone pebbles as packing material. The effect of air massflow rates and bed porosity on the thermal performance of packed bed solar air heaters are investigated. It is seen that heat transfer coefficient and friction factor are strong functions of geometrical parameters of the porous packed bed. The results of a packed bed solar air heater shows a substantial enhancement in the thermal performance as compared to the conventional collector also a decrease in porosity increases the volumetric heat transfer coefficient.