Impact of roughness parameters on heat transfer and fluid flow behaviour of solar thermal air collector: CFD-based analysis

In this investigation, the Nusselt number and friction factor characteristics of a solar thermal air collector that incorporates S-shaped ribs roughness on the absorber plate are examined. To find out the impact of crucial geometric parameters on the thermohydraulic performance parameter, computational fluid dynamics simulations were utilized. These parameters included relative roughness pitch, relative roughness height, arc angle, relative roughness width, and a Reynolds number varied from 2400 to 20000. A 3D model, analyzed with the RNG k-ε turbulence model in ANSYS Fluent, exhibits significant gains in Nusselt number and friction factor relative to smooth surfaces, achieving improvements of up to 5.33 and 2.84 times, respectively. The S-shaped ribs geometry of the unique design optimized the thermohydraulic performance parameter to a value of 3.80, exceeding earlier artificial roughness configurations. The innovation of the present research lies in establishing, for the first time, a detailed computational fluid dynamics-based optimization of S-shaped ribs having multiple geometric parameters. This study demonstrates that S-shaped ribs is a more efficient roughness geometry compared to the previously utilized artificial roughness, resulting in improved thermohydraulic performance parameter in solar thermal air collectors.