Numerical investigation on the performance of solar air heater having staggered semi-frustum roughness on the absorber plate

Solar air heater is widely employed in applications such as space heating and agricultural drying, due to their simplicity and cost-effectiveness. In this study, a three-dimensional numerical investigation is conducted to evaluate the thermal and hydraulic performance of a solar air heater featuring an absorber plate modified with semi-frustum-shaped roughness elements. The simulations are performed using ANSYS FLUENT, incorporating the RNG k-ε turbulence model to capture the complex flow characteristics. The SIMPLE algorithm is applied for pressure–velocity coupling, and the finite volume method is used to discretize the governing equations. Two key geometric parameters, the relative exit radius and the relative roughness pitch, are varied within the ranges of 0.156–0.781 and 0.0078–0.0156, respectively. The analysis is conducted over a Reynolds number range of 4,000 to 24,000. Results indicate a considerable improvement in maximum heat transfer enhancement of 2.47 times compared to a smooth duct. The maximum value of the thermo-hydraulic performance parameter is found to be 1.70 at a relative exit radius of 0.0156 and a relative roughness pitch of 0.312.