Heat Transfer and Entropy Generation Analysis of an Artificially Roughened Solar Air Heater with a Rib-Fin Profile Absorber

Recent studies show that solar air heaters (SAHs) with artificial roughness significantly outperform conventional designs with only minor modifications. In this study, the absorber plate of SAH is modified with a rib-fin roughness profile due to its high potential to induce turbulence in the airflow. This 2-dimensional numerical analysis investigates fluid flow, heat transfer characteristics, and entropy generation per unit volume. The Reynolds number (Re) is varied from 4000 to 18000, while the relative roughness pitch (P/e) is considered at three values: 8, 10, and 12. The governing equations are solved using the finite volume method and the Re-Normalisation Group (RNG) k-epsilon model. The thermo-hydraulic performance parameter (THPP) is calculated using the average Nusselt number (Nu) and friction factor (f), while total entropy generation per unit volume is determined using entropy generation due to friction and entropy generation due to heat transfer, helping to achieve an optimal solar air heater design. For the current rib-fin solar air heater, the maximum THPP is found to be 1.67, and the minimum entropy generation is 0.01605W/m3K. Correlations for the Nu and f are developed as functions of the Re and relative roughness pitch (P/e).