Temperature evolution and transition inside fire compartment with an opening subject to external sideward wind

Abstract

The temperature evolution inside a fire compartment with an opening under external sideward wind (parallel to opening) is investigated in this paper. Phenomena associated with this scenario are not known and have not been previously studied. An experimental model consisting of a fire compartment (0.4 m cubed) with an opening of various dimensions and a vertical facade wall was employed under external sideward wind ranging from 0 to 2 m/s. A propane porous burner of various heat release rates (HRR) was set inside the compartment, and a CCD camera recorded the flame. Vertical thermocouple arrays measured temperatures at the windward and leeward sides of the fire source. Results showed that when there was no wind, the temperatures at the two sides of fire source were nearly identical because of the symmetry. At a relatively low HRR, the temperature at the windward side was higher than that at the leeward side. At a relatively high HRR, interestingly, the temperature at the windward side turned to be lower than that at the leeward side, suggesting the existence of a critical HRR for this transition. The critical HRR was shown to decrease as the sideward wind speed increased, while increase with the opening size. This transition was interpreted based on the relative strength of buoyancy to the inertial force of external sideward wind. A non-dimensional correlation was then proposed to characterize the critical HRR as a function of a newly derived wind Froude number (Fr=Uw2/gℓ˜), where ℓ˜=W3/4H1/4 was a characteristic length, accounting for the competition between the buoyancy and the wind inertial force at the opening. The present study reports new phenomena with quantitative data and proposes a physics-based non-dimensional correlation, providing basic understanding of the fire dynamics inside a compartment with an opening under external sideward wind.