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

Abstract

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 two temperature equations assuming 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 foam layer lengths (𝑆 = 0 − 1), pore densities (𝜔 = 10 − 40 𝑃𝑃𝐼), and Reynolds numbers (𝑅𝑒 = 4000 − 16,000) 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 𝑅𝑒 = 16,000. In contrast 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 𝑅𝑒 = 16,000.