Heat transfer performance evaluation of a solar air heater duct with multiple tapered V-baffles

This report aims to study the heat transfer enhancement, pressure loss characteristics, and thermal performance of a channel equipped with multiple tapered V-shaped baffles (MTVBs). The effects of up-facing and down-facing orientations, converging (C) and diverging(D) configurations, variations in the taper ratio (eCR and eDR = 0.0 and 0.5), and Reynolds number (6000 ≤ Re ≤ 24,000) are examined. The performance of UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs is analyzed and compared with that of the conventional transverse baffles (TBs) and MVBs (eDR = 1.0). The experimental setup maintained a constant attack angle (α) of 45°, pitch ratio (p/H) of 1.5, width-shaped ratio (Wb/W) of 0.25, and blockage ratio (e/H) of 0.3. Tests were conducted at a fixed Prandtl number of 0.71, and a thermochromic liquid crystal sheet was utilized to assess the local Nusselt number distribution on the wall installed with UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs. The results reveal that the channel with MVBs (eDR = 1.0) achieves the greatest heat transfer rate, with a Nu/Nus ratio of up to 4.37 while a f/fs ratio reaching 48.12. In contrast, D-MTVBs at eDR = 0.0, despite having a lower Nu/Nus ratio (maximum 3.87), attain the maximum thermal performance of 1.39 at Re = 6000, owing to their optimized design that effectively enhances heat transfer while minimizing pressure drop.