Thermal and thermohydraulic performance of counter and parallel flow packed bed solar air heaters

In this paper, the counter and parallel flow packed bed solar air heaters are investigated theoretically and experimentally. Analytical model for these air heaters is presented. Numerical calculations have been performed under Hamirpur (latitude, 31° 40′ 47" N) prevailing weather conditions. The effect of air mass flow rates and bed porosity on the thermal and thermohydraulic efficiencies of the counter and parallel flow packed bed solar air heaters are investigated. The theoretical predictions indicated that the agreement with the measured performance is fairly good. The results showed that the thermal efficiency of the counter flow packed bed solar air heater is 11–17% more compared to the parallel flow packed bed solar air heater whereas, parallel flow system achieved a 10% higher thermohydraulic efficiency when air steadily flowed at differential mass rates in its upper and lower ducts compared to the counter flow system. Range of bed porosities and air flow rates over which the parallel flow system yields higher thermohydraulic efficiency than the counter flow have been identified and presented. It is also indicated that the peak values of the thermohydraulic efficiencies of counter and parallel flow packed bed solar air heater are obtained when the mass flow rate of air of flowing in each duct is 0.03 kg/s.