Analytical and experimental investigations of packed bed solar air heaters under the collective effect of recycle ratio and fractional mass flow rate

This research work presents the thermal performance of a packed bed solar air heater under the combined effect of recyclic flow and fractional total mass flow rate. The investigated solar air heater consists of three air flow ducts and the fraction of total mass flow rate serves as an input to first and second ducts of the solar air heater. Based on the inputs, the first duct consists of single air pass whereas the second and third ducts are operated under recyclic air flow. In order to produce the recyclic effect, air exiting from the outlet of the second duct is recycled back through the third duct to the inlet of the second duct and gets mixed with inlet fraction of the total mass flow rate of the air. In order to predict the effect of fractional total mass flow rate two cases are considered i.e. when two streams of i) equal fraction ii) unequal fraction of mass flow rate flowing through the first and second duct of solar air heater by dividing the total mass flow rate. Moreover, results of this solar air heater are compared with another recyclic type solar air heater under similar geometric and operational flow parameters. The results indicate that the thermo-hydraulic efficiency of the proposed solar air heater is significantly higher at lower recycle ratio and the equal fraction of total mass flow rate.