Abstract
Solar chimneys have emerged as an effective passive ventilation strategy that harnesses buoyancy-driven airflow to reduce the mechanical cooling loads. While recent research has explored various enhancements using integrated systems, such as phase change materials and earth-to-air heat exchangers, geometric surface optimization remains an untapped passive method for improving chimney performance. This study investigated the use of transverse rib roughness on the absorber wall of a solar chimney to enhance natural convection and airflow. Three rib geometries, triangular, trapezoidal, and quarter-circular, were evaluated through detailed computational fluid dynamics (CFD) simulations. Key geometric parameters, including the relative roughness height (e/D) and relative pitch (p/e), were systematically varied, along with the chimney inclination angle (θ), across a range of modified Rayleigh numbers. Among the tested configurations, triangular ribs at e/D equal to 0.2, p/e equal to 3.0, and θ = 90° delivered the highest improvement in performance, achieving an 8% increase in mass flow rate owing to stronger flow recirculation and enhanced thermal mixing, thereby representing a meaningful improvement in passive ventilation performance without increasing the system complexity. A new correlation was established to forecast the increase in mass flow rate compared to a smooth wall, achieving a high coefficient of determination (R 2 = 0.9878). The findings reveal a critical trade-off between thermal enhancement and flow resistance, highlighting the importance of optimal rib spacing and height.
Abstract by the authors, reproduced under the CC BY-NC 4.0 licence. Original publication via the link below.