Experimental study on models of velocity and heat transfer of n-butanol spill fire

Spill fire refers to a fire scenario in which the leakage liquid fuel is ignited during its spreading process. Although the spill fire exhibits a lower burning rate than pool fire, it significantly increases the fire risk due to the continuously expanding combustion area. The heat and mass transfer mechanism and physical model of spill fire velocity have not yet been established. This investigation is performed within a trench that has dimensions of 100 cm in length and 20 cm in width. The heat transfer characteristics and model of spill fire velocity are explored at six discharge rates (V̇ = 80, 120, 160, 210, 290, 380 mL/min) and seven slope angles (θ = 0°, 1°, 2°, 3°, 4°, 5°, 7°). It is observed that the steady-state burning area of spill fire diminishes and finally disappears as the slope increases, while the velocity of spill fire exhibits a trend of increasing - decreasing - increasing. A predictive model for the velocity of spill fire is developed based on the mechanical equilibrium. At lower discharge rates (V̇ = 80, 120, 160 mL/min), the values of velocity of subsurface flow (u_s) and spill fire velocity (u_f) are close, with u_s slightly larger than u_f. At higher discharge rates (V̇ = 210, 290, 380 mL/min), the values of u_s and u_f remain close in the slope range of 0° to 3°. However, once the slope exceeds 3°, the relative difference between the two velocities ranges from 25 % to 167 %. Therefore, the predictive model is not suitable for the spill fire in gravity-dominated stage. Additionally, a heat transfer model for subsurface flow area is established, revealing that when the spill fire cannot spread over whole trench, the forced convection heat loss contributes between 84.14 % and 96.34 % of total heat flux.