Thermohydraulic performance of packed-bed solar air heaters

Abstract

This work is aimed at experimentally investigating the thermohydraulic performance characteristics of packed-bed solar air heaters. The thermohydraulic performance parameter called “effective efficiency” has been employed to express the net useful thermal energy gain, taking into account the equivalent thermal energy required to produce the work energy necessary to overcome the additional friction or hydraulic losses as a result of packing the solar air heater duct with absorber matrices. It is observed that the thermohydraulic efficiency decreases with the increase in the values of bed depth to element size ratio and bed porosity, but it increases with an increase in mass flow 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 operated in the higher temperature rise parameter range, i.e. when relatively higher grade thermal energy output is required or when relatively lower insolation values are available.