The evaluation of energetic and exergetic performances of solar air heater using transverse wire rib roughness with various gaps - an experimental study

Abstract This paper presents an experimental investigation into the performance of solar air heaters using transverse wire ribs with various gap configurations (Ng = 1, 2, 3, 4, and smooth). The study was conducted under diverse outdoor meteorological conditions in Jagdalpur, India. The key parameters utilized were mass flow rates ( ṁ = 0.01891–0.03937 kg/s), relative roughness height (e/D = 0.043), and relative roughness pitch (p/e = 10). The results demonstrate that energetic efficiency (η I ) increases with mass flow rate, reaching the maximum of 83.5% for Ng = 2 at ṁ = 0.03937 kg/s. The exergetic efficiency (η II ) was obtained to improve with higher solar irradiance, elevated temperatures, and lower relative humidity, reaching a maximum of 3.67% for Ng = 2 and ṁ = 0.02889 kg/s. Moreover, the highest instantaneous thermal efficiency improvement factor (TEIF) for Ng = 2 was 13.42 at ṁ = 0.01891 kg/s, with corresponding values of 12.91, 11.30, 12.01, and 9.78 at higher flow rates. The TEIF percentage range for Ng = 1, 2, 3, and 4 was 1.93–1.44%, 2.16–1.52%, 1.81–1.23%, and 1.76–1.14%, respectively, indicating the superior performance of Ng = 2. Based on these findings, the present design of solar air heaters can be effectively utilized for air drying processes, offering a sustainable and energy-efficient solution for various industrial and agricultural applications.