Tunnel solar chimney optimisation: Ventilation & smoke exhaust analysis

• Analyzed the effect of cavity cross-section on temperature profile inside solar chimney • Investigated the airflow rate through the solar chimney under the varied cavity configurations. • Proposed an exponential model to represent the vertical temperature inside cavity. • Developed a theoretical model for airflow rate under normal and fire conditions. Solar chimneys offer energy-efficient building ventilation, but their application in tunnels, especially for smoke extraction, remains underexplored. This study experimentally and theoretically investigates solar chimney performance in a tunnel under normal ventilation and fire conditions. Experiments systematically varied chimney geometry, solar radiation (200–1200 W/m 2 ), and fire heat release rate. Results show vertical temperature inside the chimney follows a 1/4 power relationship with height, with thermal gradients improving in narrower cavities. Air inflow rate increased proportionally to the 1/3 power of solar radiation. Volumetric flow rate improved with chimney height and cross-section, with width having a greater impact than depth. Smoke exhaustion efficiency correlated strongly (R 2 > 0.99) with a novel dimensionless parameter incorporating chimney geometry and fire power. A theoretical model incorporating an exponential vertical temperature profile accurately predicts volumetric flow rate for both ventilation and smoke exhaustion scenarios. These findings provide validated tools for evaluating and optimising solar chimney design in tunnels.