Numerical investigation of heat transfer enhancement in a rectangular solar collector using TiO2-Cu/water hybrid nanofluid and perforated baffle

초록

This study numerically investigates the thermo-fluidic characteristics of a rectangular-sectioned solar absorber channel, a key component of parabolic trough solar collectors (PTSCs), utilizing staggered perforated baffle-type vortex generators and a TiO2-Cu/water hybrid nanofluid. While these modifications significantly improve heat transfer, they also increase flow resistance and pressure drop. To mitigate this negative effect, perforated holes are introduced into the baffles, aiming to modify flow structure and reduce pressure losses. A detailed parametric study is conducted to investigate the effects of Reynolds number (10,000-50,000), baffle blocking ratio (h/H = 0.2-0.7), and perforation diameter (d = 2.5-10 mm) on heat transfer and pressure drop. Special attention is given to the relationship between vortex core formation and heat transfer enhancement, highlighting the critical role of vortex dynamics. Results show that increasing the baffle blockage ratio significantly enhances secondary flow intensity and promotes the formation of strong longitudinal vortices, leading to improved Nusselt numbers and performance evaluation criteria (PEC). Notably, the PEC at a perforation diameter of 2.5 mm is nearly twice that at 10 mm, while larger perforations diminish transverse vortex motion and reduces heat transfer. The optimal configuration for maximizing heat transfer while minimizing pressure losses is achieved with small perforation holes and high baffle blockage ratios. Specifically, the most effective performance is achieved when the vortex cores are displaced from the perforation centerline by a distance approximately equal to the hole diameter (delta/d approximate to 1.0). This configuration yields superior heat transfer and hydraulic efficiency compared to conventional absorber designs.

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