Effect of geometrical and thermophysical characteristics of bed materials on the enhancement of thermal performance of packed bed solar air heaters

In this experimental investigation, a packed bed solar air heater has been designed, fabricated and tested under the local weather conditions of Roorkee, India. Data were obtained from May to June 1992. Tests were conducted to cover a wide range of influencing parameters,including the geometrical and thermophysical characteristics of absorber matrices, mass flow rates and input solar energy fluxes under actual outdoor conditions. The effects of these parameters on the thermal performance have been investigated, and the results have been compared with those of flat plate (plane) collectors. Based on thermal performance, the woven screen of different geometry (having the lowest values of bed thickness to element size ratio, bed porosity and extinction coefficient) and the copper woven screen (having highest value of thermal conductivity) have been found to be the best absorber matrices for packed bed solar air heaters. It is observed that the performance of the collector improves appreciably as a result of packing its duct with blackened absorber matrices, and this improvement is a strong function of the bed and operating parameters.