Performance Analysis of Solar Air Heaters with Dimpled Roughness in Equilateral Triangular Ducts

Solar air heaters (SAHs) offer a practical and environmentally friendly method of harnessing solar energy. Enhancing the thermal performance of SAHs is critical, and various techniques, including surface modifications, have been explored. This experimental study investigates the influence of dimpled rib roughness on the thermal and hydraulic performance of a SAH with an equilateral triangular duct. The experiments were conducted over a range of operating conditions: relative roughness height (e/D) from 0.023 to 0.058, relative roughness pitch (L/e) from 3 to 9, relative roughness width (S/e) from 6 to 18, and Reynolds numbers from 6000 to 18000. The results indicate that the dimpled rib configuration significantly enhances heat transfer compared to smooth SAH. The maximum enhancement in the Nusselt number (Nu) and friction factor (f) is 5.78 and 2.26 times higher, respectively, than the smooth SAH. The highest performance enhancement criteria (PEC) value of 4.64 is achieved at e/D=0.058, L/e=3, and S/e=6. Additionally, empirical correlations for Nu and f were derived based on experimental data, providing valuable tools for SAH design optimization. This study demonstrates the potential of dimpled ribs to significantly improve SAH performance, making it a viable option for efficient solar energy utilization.