Study on the confinement velocity in centralized smoke exhaust mode with top double vents

Abstract

The confinement velocity in centralized smoke exhaust mode with top double vents is investigated through reduced-scale experiments and numerical simulations. An equation for calculating the dimensionless confinement velocity and smoke back-layering length in this mode is derived from theoretical analysis, model experiments, and numerical simulations. The findings indicate distinct confinement velocity transition points for both normal-type and slit-type smoke vents, and that both sensitive and insensitive areas increase with the increase of fire source heat release rate. For the normal-type smoke vent, the confinement velocity to total confinement velocity ratio is approximately 0.6, with the smoke back-layering length to tunnel hydraulic diameter ratio around 3. For the slit-type smoke vent, these ratios are approximately 0.85 and 2, respectively. The ratio can be calculated to get the corresponding confinement velocities and smoke back-layering lengths. The confinement velocity and total confinement velocity for the slit-type smoke vent are lower than those for the normal-type, demonstrating a more significant smoke control effect and superior exhaust performance.