Numerical and experimental analysis of the effectiveness of solar air heaters combined with a continuous V-shaped ribbed roughness parameter

Abstract

The low thermal efficiency of conventional solar air heaters due to weak convective heat transfer remains a critical limitation for solar thermal applications. This study presents a combined experimental and numerical investigation of a single-pass solar air heater enhanced through the integration of continuous V-shaped rib roughness and externally mounted flat-plate reflectors to simultaneously intensify internal turbulence and augment incident solar irradiance. Four configurations of smooth and roughened absorber plates, each with and without reflectors, were designed, fabricated, and tested under real ambient conditions over a mass flow rate range of 0.02–0.05 kg/s. The reflectors increased the incident solar radiation on the absorber surface by up to 40%, leading to consistently higher absorber and outlet air temperatures. At a mass flow rate of 0.05 kg/s, the thermal efficiency improved by 2.9% for the smooth configuration and 3.87% for the roughened configuration with reflectors. The roughened collector with reflectors achieved a maximum air temperature rise of 37.81 °C at 0.02 kg/s. A three-dimensional computational fluid dynamics model employing the RNG k–ε turbulence model was developed to capture the coupled thermo-hydraulic behavior. The numerical predictions resulted in good agreement with experimental results, with a maximum deviation of 12%. Furthermore, the inclusion of artificial roughness introduces a frictional penalty. As a result, the combined enhancement yields an overall thermo-hydraulic performance improvement of up to 1.45 net gain in system performance. The results show that the rib-induced turbulence along with reflector-assisted solar augmentation enhances heat transfer as well as the overall efficiency of solar air heaters. This integrated way helps to improve the performance of drying and space heating applications in a cost-effective manner.