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

Abstract

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.