An efficient design of triangular solar air heater having three-dimensional cavities as roughness elements for improving heat transfer augmentation: A CFD analysis

A solar air heater is a simple device designed to collect solar radiation for heating applications. Usually, the overall performance of a solar air heater is poor because of the low thermal conductivity of the air. An attempt has been made to improve the performance of the existing solar air heater by producing the local turbulence in the flowfield with the help of a circular cavity that is positioned on the absorber plate. The dimensions and placement of these circular cavities are defined using the three dimensionless parameters: relative cavity depth (Dd); relative crosswise distance (Dc); and relative flow-wise distance (Df) which varied from 0.016 to 0.038, 6–14, and 6 to 14, respectively. The effect of these circular cavities has been analyzed on the hydraulic and thermal performance using numerical simulations which were performed by developing a CFD code on Fluent software. The circular cavities promote the local turbulence in the flowfield which support the vortex generation and results in better heat transfer to the air from the absorber plate. The augmentation of heat increases substantially by 2.57 times at the expanse of 2.3 times increase in pressure at relative cavity depth (Dd); relative crosswise distance (Ds); and relative flow-wise distance (Dl) of 0.038, 10, and 10, respectively. Moreover, the overall performance of the proposed found to be 1.75 times the conventional solar air heater under similar conditions.