Experimental Study of the Influence of Rectangular Trapezoidal Ribs on Pressure Drop in a Flat-Plate Air Collector

This study experimentally investigates the influence of rectangular–trapezoidal rib configurations on the thermohydraulic performance of a flat-plate solar air collector. Tests were conducted across a Reynolds number range of 1000–12,000, considering variations in rib inclination (30°, 60°, 120°, and 150°), length, spacing, and arrangement (inline vs. staggered). The results show that staggered ribs with reduced spacing significantly improved heat transfer, achieving a maximum thermal efficiency of 39.2%, but at the cost of increased pressure losses reaching 55 Pa. Using Vaschy–Buckingham dimensional analysis, empirical correlations were developed to predict pressure drop and Nusselt number as functions of rib geometry and flow conditions. These correlations demonstrated excellent agreement with experimental data, with coefficients of determination exceeding 0.99. The findings provide valuable tools for designing and optimizing ribbed absorber surfaces in solar thermal systems, enabling a clear trade-off analysis between thermal enhancement and aerodynamic penalty. These results are especially relevant for applications, such as solar air heaters, crop dryers, and ventilation systems, where space and fan power are limited, and performance depends critically on managing both heat transfer and flow resistance.