INVESTIGATION OF THE EFFECT OF THERMAL STRATIFICATION ON THE PERFORMANCE OF A SOLAR AIR HEATER

Abstract

Flat plate solar air heaters have been extensively employed to deliver heated air at low to moderate temperatures for space heating, crop drying and industrial applications. However, solar energy is an intermittent energy source and there is always time or rate mismatch between supply and demand of energy. Solar energy storage system stores energy when the collected amount is in excess of the requirement of application and discharges energy when the collected amount is inadequate. Solar air heating systems, which utilize rock-beds for energy storage, are quite common. The overall performance of such systems is influenced significantly by the temperature distribution in the rock-bed energy storage unit. In the present experimental work, observations of the variations of temperature distribution with time "along" the height of the rock-bed have been made. The thermal stratification present in the pebble-bed affects the inlet air temperature of solar air heater, which further affects the useful heat gain by the collector. The effect of varying inlet temperature on the efficiency of solar air heater has been investigated. The efficiency is found to be decreasing with increase in inlet air temperature. Results are also presented in terms of stratification coefficient and heat exchanger effectiveness for the collector. iii