Computational parametric investigation of solar air heater with dimple roughness in S-shaped pattern

A numerical investigation has been conducted to analyze the hydro-thermal characteristics of a solar air heaters when its absorber plate has S-shaped pattern dimple roughness. This analysis is conducted for appropriate levels of geometric constraints, such as relative roughness pitch and dimple diameter. Using commercial code ANSYS Fluent, various solar air heater configurations were simulated for Reynold number ranging from 4000 to 20,000. The present simulation model has been validated with Dittus–Boelter equation and are found to be in good agreement with it. It was found that S-shaped dimple roughness has yielded 2.45–3.55 times higher Nusselt number value and having 2.81–4.54 times larger friction factor compared to smooth solar air heater. It was observed that as dimple diameter increases, the Nusselt number increases but upto 2.8 mm and afterwards it decreases. Similar trend is also observed for relative pitch roughness, where it increases upto 10 and starts declining afterwards. Furthermore, the optimum solar air heater configuration has also been identified in terms of Nusselt number and friction factor. Among all configurations, maximum thermo hydraulic performance value of 2.15 was obtained for dimple diameter of 2.8 mm and relative pitch roughness of 10 at Reynold number of 20,000.