Thermal Performance Evaluation of Ribbed Solar Air Heater Through Computational Fluid Dynamics

Abstract

Solar air heaters (SAHs) are widely used for space heating, crop drying, and industrial preheating applications; however, their performance is often limited by low convective heat transfer between the absorber plate and flowing air. The present study investigates the thermal performance of a V-shaped ribbed solar air heater using Computational Fluid Dynamics (CFD). A three-dimensional model of a rectangular duct equipped with discrete V-shaped ribs on the absorber plate was developed and analyzed over a Reynolds number range of 3000–18000. The steady-state Reynolds-Averaged Navier–Stokes equations were solved using the SST k–ω turbulence model to accurately capture near-wall effects and flow separation around ribs. The results reveal that the introduction of ribs significantly alters the internal flow structure by generating recirculation zones and enhancing turbulence intensity near the heated surface. Quantitatively, the average Nusselt number of the ribbed configuration was found to increase by approximately 80% to 140% compared to a smooth duct, depending on the Reynolds number. However, the friction factor also increased by about 1.5 to 2.2 times due to additional flow resistance induced by the ribs. Despite this pressure penalty, the thermo-hydraulic performance parameter (THPP) remained greater than unity across all operating conditions, reaching a maximum value of approximately 1.35–1.45 at moderate Reynolds numbers. The temperature contours demonstrated improved heat extraction from the absorber plate and a more uniform thermal distribution in the ribbed duct. Overall, the study confirms that V-shaped rib roughness is an effective passive technique for enhancing the thermal efficiency of solar air heaters. The CFD analysis provides detailed insight into the flow and thermal mechanisms responsible for performance improvement and can serve as a reliable design tool for optimizing rib geometry in high-efficiency solar air heating systems.