THERMOHYDRAULIC PERFORMANCE OF PACKED-BED SOLAR AIR HEATERS

This work is aimed at experimentally investigating the thermohydraulic performance characteristics of packed-bed solar air heaters. The ther mohydraulic performance parameter called ''effective efficiency'' has been employed to express the net useful thermal energy gain, taking in to account the equivalent thermal energy required to produce the work energy necessary to overcome the additional friction or hydraulic loss es as a result of packing the solar air heater duct with absorber matr ices. It is observed that the thermohydraulic efficiency decreases wit h the increase in the values of bed depth to element size ratio and be d porosity, but it increases with an increase in mass how rate of air, attains a maximum and subsequently decreases with further increase in mass flow rate. The use of a packed-bed will be beneficial if it is o perated in the higher temperature rise parameter range, i.e. when rela tively higher grade thermal energy output is required or when relative ly lower insolation values are available.