Thermal–hydraulic analysis of a solar air heater fitted with a wire-roughened absorber plate

Abstract

This study is to evaluate heat transmission and friction in a rectangular solar air heater with a V-shaped wire rib roughness on the absorber plate that operates in fully formed turbulent flow. Additionally, studies are performed to generate prediction equations for the average friction factor, Stanton number, and efficiency index. The Reynolds number $(Re=5000$ – $30,000)$ , angle of attack $(\alpha =$ 20 ${}^{\circ }$ –90 ${}^{\circ }$ ), relative roughness pitch $(p/e=20$ – $40)$ , relative roughness height $(e/D_h=0.01$ – $0.04)$ , and the aspect ratio $(W/B=1$ – $10)$ was varied. The efficiency index $(\eta )$ is commonly employed as a thermo-hydraulic performance metric. It is computed as $\eta =\left(\frac{N{u}_{av}}{N{u}_s}\right)/\left(\frac{f_{av}}{f_s}\right)$ . The wire roughness and airflow parameters $(Re,\alpha ,p/e,e/D_h)$ are optimized to maximize heat transfer while retaining minimal friction losses. On the basis of resemblance criteria, average Stanton numbers, average Nusselt numbers, and even average friction factors are derived. The results are compared to those obtained with a smooth absorber duct under similar airflow circumstances in order to assess the increase in heat transfer coefficient and friction factor. The $Re,e/D_h,p/e$ , and $\alpha$ have a significant influence on thermo–hydraulic performance, according to these studies. With $\alpha ={50}^{\circ }$ , $p/e=40$ , $e/D_h=0.01$ , and $W/B=5$ , the optimal configuration geometry for wire roughness and solar air heater duct is identified.