Optimizing the heating performance of Trombe walls with ribbed surfaces using three-dimensional CFD analysis

Abstract

Improving the thermal efficiency of Trombe walls is crucial for optimizing passive solar heating systems. Despite extensive research, the effect of ribbed surfaces on the thermo-hydrodynamic behavior has not been fully explored. This study aims to address this gap by performing a three-dimensional CFD analysis to investigate the combined effects of rib density (Nr = 3, 5, 7, 9) and rib geometry (rectangular, pentagonal, hexagonal, octagonal, triangular, and semi-circular) on heat transfer and fluid dynamics within Trombe walls. The simulations were conducted using ANSYS Fluent (2020 R1) under laminar flow conditions (Re = 600–1600), with boundary conditions including a constant solar flux of 748 W/m2, an ambient temperature of 293.75 K, and an external wind speed of 1 m/s. The model was validated against experimental data correlations for the Nusselt number (Nu) and friction factor (f), with deviations of less than 6%. The results show that ribbing significantly enhances heat transfer by disturbing the boundary layer and promoting vortex formation. The optimal configuration (Nr = 5) increases the Nusselt number by 68.3% at Re = 1600 (from 12.41 to 20.88). Triangular ribs provide the highest thermal enhancement, nearly doubling Nu (a 99.4% increase, from 12.41 to 24.75), but incur significant friction penalties, with f rising by 169.4% (from 0.0489 to 0.1317). In contrast, semi-circular ribs strike a balance, yielding a thermal enhancement factor (TEF) of 1.51 (+ 50.6%) and increasing heat flux by 12.7%. These findings demonstrate that Nr = 5 with the appropriate rib geometry can optimize Trombe wall efficiency, making it suitable for nearly zero-energy buildings (nZEBs).