Thermal–hydraulic evaluation of solar air heaters with symmetrical gap arc rib roughness
摘要
This study introduces a novel approach to enhance the thermal and hydraulic performance of SAH by employing symmetrical gap arc rib roughness combined with staggered segments as a turbulence promoter. The proposed roughness geometry is achieved by segmenting the arc into equal parts along the absorber plate width, with the objective of inhibiting boundary layer reformation along the arc length and providing staggered rib elements in front of each gap with the objective of maximizing fluid mixing. Boundary layer disruption and fluid mixing combinedly enhance the rate of heat transfer from the absorber surface to the flowing fluid. Experimental investigations were conducted to evaluate the impact of the relative position (P′/P) and size (r/e) of staggered rib segments on the performance of the SAH duct. Several design parameters, including Ng, W/H, e/Dh, P/e, g/e, and α, set at 3, 12, 0.0433, 10, 3, and 30°, respectively, were considered constant in the fabrication of the roughness geometry. In this experimental study, P′/P and r/e were varied between 0.2–0.8 and 2–5, while the Reynolds number (Re) ranged from 3000 to 14,000. The experimental results indicate a 2.31 times increment in the Nu compared to a smooth duct for P′/P value of 0.4 and r/e values of 3. Similarly, the friction factor (f) showed an enhancement of 3.46 and 3.24 times relative to a smooth duct for P′/P of 0.4 and g/e of 5, respectively. The maximum thermo-hydraulic performance (THP) was observed to be 1.60 for r/e of 3 and P′/P of 0.4.