Thermo-hydraulic performance of wavy channel configurations in flat plate solar air heaters

Solar air heaters provide a well-established means for harnessing solar thermal energy, but their efficiency is fundamentally limited by the low convective heat transfer coefficient of air. To address this limitation, various enhancement techniques, such as artificial surface roughness and jet impingement, have been extensively investigated. Wavy channels have also been explored as an alternative enhancement strategy. However, existing studies have predominantly focused on fully corrugated absorber plates. Configurations in which the flow path alone is wavy while the absorber plate remains flat have received considerably less attention. Moreover, most investigations have focused on sinusoidal waves, while other wave shapes have received considerably less attention. This study addresses these gaps by evaluating a solar air heater configuration comprising a flat absorber plate and a wavy bottom channel. Four periodic wavy profiles, including rectangular, triangular, trapezoidal, and sinusoidal, were systematically evaluated using computational fluid dynamics (CFD) simulations to determine which geometry offers the most favorable thermo-hydraulic performance. The study parametrically analyzed the influence of wave amplitude and frequency for each profile, revealing substantial performance differences among the geometries. The triangular wavy channel emerged as the most effective configuration for heat transfer, achieving Nusselt numbers 2.1 and 3.1 times greater than that of a straight channel at Reynolds numbers of 15,000 and 10,000, respectively. In contrast, sinusoidal channel exhibited the lowest friction factors across all tested conditions, thereby minimizing pumping power requirements. Most notably, both triangular and sinusoidal designs delivered superior overall thermo-hydraulic performance. At a Reynolds number of 15,000, the triangular channel achieved an optimal thermo-hydraulic performance parameter (THPP) of 1.15, while at a Reynolds number of 10,000, the sinusoidal channel attained a peak THPP of 1.73. A THPP greater than unity confirms that the net energy benefit from enhanced heat transfer outweighs the energy penalty of their increased flow resistance.