A solar air heater is a simple device designed to collect solar radiation for air heating purpose and the heated air can further be used for space heating, drying, etc. The conventional air heater (solar assisted) has poor performance and with this work an attempt has been made to improve its performance by providing surface roughness over the heated surface. The roughness employed over the surface has elliptical cavity and its dimensions and placement over the heated surface is defined with the 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). A CFD code has been development and validated with the experimental results to do the parametric analysis for understand the effect of proposed surface roughness on the performance of air-heater. It is concluded that the proposed surface roughness promotes the local turbulence, flow separation, and strong vortices in the flow-field with resulted comparatively higher thermal performance in the proposed air-heater. But, this higher thermal performance achieved at the expense of higher pressure loss in the passage. 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. However, the overall performance is 1.75 times higher in the proposed air-heater in comparison to the conventional designs.

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.