Investigation of enclosure fire dynamics with inclined ceilings

Abstract

Inclined ceilings are common in heritage and modern buildings, but little is known about their influence on compartment fire dynamics, and the relationships between inclined angle and fire dynamics parameters have not yet been clarified. A total of 24 bench-scale experiments were conducted in compartments with eight different kinds of ceilings, namely, flat ceiling (0°), single-slope ceilings of 15°, 30°, and 45° and double-slope ceilings of 15°, 30°, 45°, and 60°. The time to flashover, mass loss rate, heat release rate, gas temperature, and radiation heat flux to the floor were measured and analysed. It was found that for both single and double slopes, the time to flashover increased with increasing angle and is proportional to the reciprocal of the opening factor; the heat release rate and radiation heat flux at the floor decreased as the inclined angle increased, while the gas temperature at the same height during the fully-developed stage first increased and then decreased with increasing slope angle; and the influence of the inclined angle on these parameter changes was greater on single-slope than on double-slope. In addition, selecting the hot gas layer as the control volume, the theoretical differential calculation equations for thickness and temperature of the hot gas layer were established based on the mass balance and energy balance of hot gas, respectively. Furthermore, the dimensionless fitting equations were further proposed to facilitate the estimation of the thickness and temperature of the hot gas layer. Moreover, a theoretical model of the radiation heat flux ${\dot{\text{q}}}_{\text{f}}^{\text{"}}$ was developed based on the theoretical thickness and temperature of hot gas, which could well predict the radiation heat flux at the floor in compartments with different inclined ceiling angles. Finally, CFD (Computational Fluid Dynamics) simulations were performed to explore the temperature and velocity distributions in compartments with different inclined angles of the ceiling. The experimental and simulation results obtained, and the theoretical models proposed provided an essential basis to quantify the variation of the fire parameters with inclined angle and visualize the flow field of inclined ceiling compartments.