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An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of the strength of secondary flow on the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6 to 1 to obtain the optimum baffle pitch for 6000 < Re < 14000. The maximum thermohydraulic performance parameter (THPP) is obtained as 2.28 for Rp = 0.75 at Re = 6000. With this optimum Rp, the impact of gaps at leading, at trailing, and at both leading and trailing apices is studied as three different configurations. Maximum heat transfer enhancement of 2.47 times is obtained for multiple inclined baffles with the gap at trailing apex for Re = 14000 with a corresponding increment of 3.07 times in friction factor (f). Maximum THPP is obtained as 2.69 for gap at the trailing apex for Re = 6000. With lower exergy losses, the present SAH design has higher exergetic efficiency, collector efficiency and is cost-effective compared to ribbed rectangular SAH.