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• CFD and exergy analysis of a solar air heater with semi-cylindrical sidewalls is proposed. • Semi-cylindrical sidewalls enhance the strength of secondary flow in a ribbed SAH. • A significant enhancement in the effectiveness parameter of 2.27 is obtained. • Lower exergy destruction leads to an enhancement of 95% in exergetic efficiency. • The proposed design outperforms ribbed rectangular SAHs for a wide range of Reynolds number. Solar air heater (SAH) with semi-cylindrical sidewalls and W-baffles is analyzed for energy and exergy efficiency in the turbulent flow regime. Computational fluid dynamics (CFD) analysis is carried out for a fixed baffle inclination (β) and varying the relative baffle height (R h = e/D) and relative baffle pitch (R p = P/D) in the range 0.046–0.115 and 0.46–1.15, respectively. For Reynolds number (5000 < Re < 17,500), the numerical methodology is substantiated using experimental and theoretical correlations obtained from the literature. Smaller vortices near the sharp corners are removed by rounding the sharp edges, allowing the flow of fluid from inside and horizontal walls of the duct towards the semi-cylindrical sidewalls. This increases the overall turbulent kinetic energy. A peak augmentation of 3.24 and 4.03 times is obtained for Nusselt number (Nu) and friction factor (f), respectively, in contrast to conventional SAH. With a maximum enhancement of 127% in the effectiveness parameter relative to smooth SAH, this novel SAH design is evidently energy efficient. Based on CFD results, new correlations are developed in terms of R h and R p , which predicts the values with an absolute deviation of 4% and 7.4%, respectively. With lower exergy destruction, maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, for the proposed SAH relative to conventional SAH. Upon comparison with ribbed rectangular duct SAH configurations, the present design with semi-cylindrical side walls outperforms at all flow Re. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) and exergy analysis are conducted to investigate the impact of secondary flow produced by V-ribs on the overall performance of a triangular solar air heater (SAH) duct. For a fixed relative rib pitch (R p = 10) and relative rib height (R h = 0.05), the effect of rib inclination (α) is studied using CFD technique for varying Reynolds number (5000 ≤ Re ≤ 20000). Based on the CFD simulation results, empirical correlations capable of predicting Nu and f with an absolute variance of 8.7%, and 4.7%, respectively, are developed. Employing these correlations, exergetic performance analysis is carried out. Maximum effectiveness parameter (ε) of 2.01 is obtained for α = 45° at Re = 7500. The exergy analysis reveals that the entropy generated is lower for the ribbed triangular duct compared to the smooth duct with maximum enhancement in exergetic efficiency (η ex) as 23% for α = 45°. The study is extended for the rectangular duct to compare the performance with the ribbed triangular duct SAH (α = 45°). Results show that ribbed triangular duct SAH (α = 45°) is superior over various configurations of the ribbed rectangular duct SAH at higher mass flow rates. • CFD and exergy analysis of a triangular duct solar air heater with V-rib is proposed. • Secondary flow in triangular duct significantly enhances the Nusselt number. • A significant enhancement in the effectiveness parameter of 2.01 is obtained. • Empirical correlations are developed for Nusselt number and friction factor. • The proposed design exhibits superior performance at high mass flow rates. [ABSTRACT FROM AUTHOR]