A case study on thermal performance of solar air heater with down apex position of open trapezoidal ribs with gaps

This study aims to experimentally explore the impact of multiple open trapezoidal ribs with gaps (MOTRG) on the thermal efficiency of a rectangular duct in a solar air heater (SAH). The designed parameters of ribs i.e. relative limb length (L/w), relative pitch ratio (p/e), relative gap ratio (g/e) and relative rib height (e/Dh) are varied as 0.2–1.0, 6–12, 1–5 and 0.023–0.056, respectively. The experiments have been conducted for Reynolds number (Re) span of 2000–16000. Since then, open trapezoidal rib designs have made significant improvements to SAH performance. A highest value of 78.86% of thermal efficiency has been observed corresponding to α = 60°, g/e = 1, L/w = 0.8, p/e = 10, W/w = 6, and e/Dh = 0.043. The global best values of enhancement factors of 3.032, 2.726 and 2.496 have been found for insolation values of 1000 W/m2, 800 W/m2 and 600 W/m2. The findings demonstrate that, when compared to other roughened SAH ducts, the MOTRG roughened duct provides superior thermal performance.