Performance improvement of a solar air heater by covering the absorber plate with a thin porous material

The effect of covering the absorber plate of a solar air heater with a thin porous media is investigated in the present study. Simulations are carried out for turbulent flow and heat transfer in the solar heater and within the porous layer. The effects of different parameters such as Reynolds number, Darcy number and solid to fluid thermal conductivity ratio on the thermal and thermo-hydraulic performances of a solar air heater are studied. It is observed that the implementation of a thin porous layer over the absorber plate significantly increases the thermal and thermo-hydraulic performances of the solar air heater. The maximum increase in the thermal and thermo-hydraulic performances is more than 5 times of those obtained in a solar heater without porous medium. Meanwhile, the maximum increase in the frictions factor of the porous solar heater is 2 times of that in a solar heater without porous media at the maximum Reynolds number studied. The proposed configuration also reduces the risk of hot spots since no entrapped eddies are formed over the absorber plate. It is shown that the turbulence produced at the porous-fluid interface penetrates into the thin porous layer and enhances the heat transfer from the absorber plate. The results also reveal that the conduction heat transfer within the porous layer highly affects the thermal and thermo-hydraulic performances of the solar heater. © 2019 Elsevier Ltd