Temperature stratification of heated air flow in a fire tunnel

Abstract

The temperature stratification of the heated air flow in a fire tunnel is investigated using the two- and three-dimensional experiments along with numerical models described in previous papers. It is found that the heated air flow can appear to be either a stratified or a mixed flow pattern in accordance with different ventilation velocities, heat release rates, and downstream positions. To deal with tunnel fire circumstances, the mixed convection is evaluated using a nondimensional variable Gr*/ReH 5/2. A quantitative relationship between Gr*/ReH 5/2 and a parameter which quantifies the varying degrees of the stratification at each tunnel cross section was established. By comparing the results from two- and three-dimensional analyses, the effects of secondary flow on the temperature stratification are discussed. The conclusions obtained are directly related to the safety considerations in tunnel fires.