Thermal and Hydrodynamic Enhancement of a Ribbed Trombe Wall for Passive Solar Heating

Enhancing the thermal performance of the Trombe Wall is crucial for improving the energy efficiency of passive solar heating systems. This study presents a three-dimensional numerical analysis to investigate the combined effects of internal rib density and geometrical configuration on the thermo-hydrodynamic behavior of a Trombe wall. Using a finite-volume method with laminar flow assumptions based on the Reynolds number, the research is conducted in two sections. First, four rib densities (Nr = 3, 5, 7, and 9) are evaluated using a rectangular rib geometry to identify the best rib number. Subsequently, four innovative designs are compared: rectangular (Model A), semi-circular (Model B), crossed semi-circular (Model C), and spaced semi-circular (Model D) ribs. The findings indicate that while increasing rib count enhances heat transfer through secondary-flow intensification, improvements become marginal beyond Nr = 5 due to excessive flow resistance. At Re = 1600, the Nr = 5 configuration achieves a 68% increase in the average Nusselt number over a smooth channel while maintaining acceptable friction levels. The thermal enhancement factor of case Nr = 5 is the highest in all evaluated Re numbers. Regarding geometry, the model with crossed semi-circular ribs (Model C) provides the maximum thermal enhancement at Re = 1600, with nearly a twofold increase in heat transfer (compared to the smooth channel), albeit at the cost of higher pressure losses. Conversely, the spaced semi-circular ribs case (Model D) achieves the best thermal enhancement factor of 1.51, a 12.7% increase in heat flux, and a lower Poiseuille number. Overall, this study demonstrates that enhanced ribbed configurations can significantly improve Trombe Wall efficiency, with the spaced semi-circular design and five ribs.