Double Duct Packed Bed Solar Air Heater Under Combined Single and Recyclic Double Air Pass

Abstract

The present work intended to investigate thermal and thermohydraulic efficiencies of two different models of recyclic double pass packed bed solar air heaters experimentally. ModelI consists of single air pass through two glass covers as well as double air pass caused due to recycle of the air exiting from the packed bed duct formed between the absorber plate and the glass cover through another duct integrated between the absorber and back plates to inlet of the packed bed duct. On the other hand, modelII consists of only double air pass originated due to recycle operation constituted between the similar solar air heater elements as that of modelI. Twelve numbers of wire mesh screens to form 95% bed porosity were used. Both solar air heater models were tested under the range of packed bed Reynolds number from 300 to 1500 for air mass flow rate and recycle ratio of 0.01 kg/s to 0.025 kg/s and 0.3 to 1.8, respectively. Results revealed that thermal performance of modelI is found to be 15% higher than that of modelII. The optimum value of the recycle ratio for modelI and modelII are obtained as 0.9 and 1.2, respectively, at a mass flow rate of 0.025 kg/s that yields the best thermohydraulic efficiency of 77% and 67%, respectively. Moreover, optimum solution for recycle ratio and air mass flow rate during off sun shine hours are also obtained and presented in the current work.