A two-dimensional rectangular domain is considered with a discrete arrangement at equal distances from copper metal foam in a solar air heater (SAH). The local thermal non-equilibrium model is used for the analysis of heat transfer in a single-pass rectangular channel of SAH for different mass flow rates ranging from 0.03 to 0.05 kg/s at 850 W/m2 heat flux. Three different pores per inch (PPI) and porosities of copper metal foam with three different discrete thicknesses at equal distances are studied numerically. This paper evaluates the performance of SAH with 10 PPI 0.8769 porosity, 20 PPI 0.8567 porosity, and 30 PPI 0.92 porosity at 22 mm, 44 mm, and 88 mm thicknesses. The Nusselt number for 22 mm, 44 mm, and 88 mm thicknesses is 157.64%, 183.31%, and 218.60%, respectively, higher than the empty channel. The performance factor for 22 mm thick metal foam is 5.02% and 16.61% higher than for 44 mm and 88 mm thick metal foam, respectively. Hence, it is found that metal foam can be an excellent option for heat transfer enhancement in SAH, if it is designed properly.

In this work, aluminium wire mesh (WM) samples with 3, 9, and 18 pores per inch (PPI) and porosities of 0.894, 0.812, and 0.917, respectively, were combined together to form graded structures including 3-9-18, 9-18-3, and 18-3-9 PPIs. A 5 mm thickness for each WM was considered for a length of 2 m and inserted into a single-pass solar air heater (SAH) in which the height of the SAH was 120 mm. For the numerical analysis, a 3D numerical model was considered in ANSYS fluent software, and the Rosseland radiation model renormalization group (RNG) k-ε enhanced wall function was incorporated to account for solar radiation. The local thermal equilibrium (LTE) model was considered to obtain the heat-transfer characteristics of the WM. The numerical results of the thermohydraulic performance parameter (THPP) of the 9-18-3 PPI WM were 13.04% and 11.92% higher than the 3-9-18 and 18-3-9 PPI samples, respectively. Later, 25% of the 9-18-3 graded wire mesh (GWM) was considered at four different locations, i.e., 0, 0.5, 1, and 1.5 m away from the inlet, and analysed to obtain the best location for efficient heat transfer. The computational results show that 1.5 m away from the inlet is the best location among the different locations considered. The experimental results of the GWM at 1.5 m away from the inlet demonstrated a 20.91% and 23.32% increase in thermal efficiency compared to the empty channel for the 0.027 kg/s and 0.058 kg/s mass flow rates, respectively. From numerical-cum-experimental analysis, it was found that inserting 25% length of GWM of the entire length of the test section at a distance of 1.5 m from the inlet in single pass SAH improves the overall performance of the empty channel of single-pass SAH.