Optimizing of a metal foam-assisted solar air heater performance: a thermo-hydraulic analysis of porous insert placement

A numerical assessment of the heat transfer efficacy of a solar air heater (SAH) was carried out. The SAH is supplied with a porous metal foam layer to improve thermal mixing. Both the local thermal non-equilibrium (LTNE) and Darcy-extended Forchheimer (DEF) models were employed to forecast fluid and thermal transport within the partly filled SAH channel. The analysis was performed for various values of dimensionless foam layer lengths ( S = 0 - 1 ), pore densities ( ω = 10 - 40 PPI ), and Reynolds numbers ( R e = 4000 - 1 6 , 000 ) at a fixed value of layer thickness ( H f = 0.6 ). Based on the position of the porous layer, three distinct arrangements, marked as Case 1, Case 2, and Case 3, were explored. Regarding the parameters examined, the findings indicate a definite improvement in the average Nusselt number ( Nu ), but unfortunately, the friction factor also increases unfavorably. By reducing the length of the porous layer, a reasonable reduction in heat transfer rate and a significant decrease in pressure drop were noticed. The results showed about 26.64%, 48.73%, and 70.74% reductions in pressure drop by reducing the dimensionless foam length from 1 to 0.25, 0.5, and 0.75 respectively for ω = 10 at R e = 16 , 000 . On the other side, there are only about 11.05%, 23.11%, and 40.78% reductions in Nu . The exhaustive analysis of the thermal performance of SAH was conducted using the thermal performance factor (TPF), which considers the trade-off between the SAH channel’s potential for improved heat transmission and its cost for pressure loss. The TPF may reach a maximum of 2.82 compared to the empty channel when the metal foam layer is inserted with S = 1 , for ω = 10 , and R e = 16 , 000 .