Numerical Study of heat transfer characteristics of Rectangular channel with combined roughness

Abstract

The study numerically investigates convective heat transfer enhancement in a solar air heater (SAH) duct using semi-circular roughness elements on the absorber plate. A three-dimensional, turbulent airflow model is analyzed with fixed heat flux and validated against the Dittus–Boelter correlation for smooth ducts. The flow in the rectangular channel is steady, incompressible, and turbulent, with constant properties throughout. Air properties such as density and viscosity remain uniform, and the solar radiation over the absorber plate is also uniform, facilitating calculations. The no-slip condition applies as a boundary condition in CFD simulations; minor heat losses to the environment can be neglected. It examined the influence of geometric configuration, particularly the p/e = 7, 8, 9, 10 and 11 relative pitch ratio between roughness elements, on the duct's thermal performance. These variables are investigated in turbulent flow conditions with Reynolds numbers (Re) between 3000 and 24,000. Results indicate that these roughness elements increase heat transfer rates by up to 262% compared to smooth ducts at a Reynolds number of 24,000, with optimal configurations yielding a Nusselt number approximately 2.3 times higher and a maximum thermal–hydraulic performance parameter of 1.61 at specific geometric conditions as under specific conditions at Re = 24,000, P = 22 mm, and P/e = 10.