Temperature evolution from stratified- to well-mixed condition inside a fire compartment with an opening subjected to external wind

Author: Ren, F., Hu, L. H., Zhang, X. L., Sun, X. P., Fang, X.

Journal: Proceedings of the Combustion Institute

DOI: 10.1016/j.proci.2020.06.232

Keywords: Temperature non-uniformness, Compartment fire, External wind, Stratified, Well-mixed, spill plume, pool fires, behavior, flashover, mechanism, profile

Abstract: 

It is well recognized that with increase in heat release rate (HRR), the compartment fire evolves from stratified- (hot gas in upper part and cool air in lower part) to well-mixed (uniform temperature) condition. However, such evolution for a fire compartment with an opening subjected to external wind, with a complex flow buoyancy-wind interaction, has not been quantified in the literature despite of its practical significance. The present study investigated experimentally the evolution of temperature spatial non-uniformness, namely the temperature difference between the upper- and lower part, inside a fire compartment with flow developing from stratified- to well-mixed condition with one opening subjected to external wind for various opening dimensions, HRRs and wind speeds with total 310 conditions. It was found that this temperature difference first increased then decreased with increase in HRR; and the HRR for the turning point (with maximum temperature difference) was found to be 0.6 times of the critical HRR for flame ejection under no wind condition. Such temperature difference, as well as its maximum value that can be reached, decreased with increasing of wind speed. A non-dimensional model was proposed based on physically the competition of the wind vent-mixing effect with the buoyancy effect inside the compartment and such competition at the opening, as well as the heat release/loss balance inside the compartment. The temperature difference between the upper- and lower-part of the compartment was found to be well represented as a function of wind Froude number at the opening and that inside the compartment, heat release to heat loss ratio and HRR. These new findings and the proposed non-dimensional model provide the basis for understanding fire growth and temperature evolution inside a compartment under complex buoyancy-wind interaction. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.