Optimized Baffle Design for Augmented Thermal Transfer in Solar Air Collectors

Solar air collectors (SACs) in solar air heating systems used for crop drying, space heating, and ventilation experience mitigated heat transfer because of viscous sublayers, low air density and low air thermal capacity. Angled baffles with perforations on heat transfer surfaces improve SAC thermal performance. This paper experimentally analyzes the effect of staggered racetrack-shaped perforated V-baffles at attack angles ($\alpha$) of $45^{\circ}, 60^{\circ}, 120^{\circ}$, and 135°, and pitch ratios ($p / e$) of 2, 6, and 10, with turbulent Reynolds numbers ($R e$) ranging from 5400 to 14,400 in an air heater duct. Results show higher j (Colburn j-factor) and $\boldsymbol{f}$ (Fanning friction factor) for baffled surfaces compared to the plain surface, which decreases with increasing $R e$ and $p / e$. An $\alpha$ of 120° gives the maximum $f / f_{s}$ of 17.99 for $p / e$ of 2 at the highest $R e$, while $\alpha$ of 135° with the same $\mathrm{p} / \mathrm{e}$ yields the maximum j value of 0.00893 at $R e 10,351$. The maximum $j / j_{s}$ and $J F$ factor values are 2.51 and 1.057, respectively, at the highest $R e$. The correlations formulated for j and f align well with the test data.