Abstract:

Temperature distribution inside the smoke layer was not uniformly distributed in tunnel fires. Taking smoke stratification into consideration, the present study theoretically and numerically investigated longitudinal decay of cross-sectional averaged smoke temperature and propagation velocity. This study assumed that temperature inside smoke layer in a cross section linearly decreased with height. According to theoretical analysis, heat loss through lateral walls is 50% lower than that obtained from traditional calculations. Decay rates of smoke temperature and propagation velocity mainly depend on smoke mass flux and heat transfer coefficient between smoke and tunnel walls. Impingement of smoke plume is generally followed by a density jump, during which plenty of ambient air is entrained into the smoke layer. As a result of the density jump, the increment of smoke mass flux is approximately 10% of smoke plume entrainment, which makes quantification of flow rate more accurate. Prediction models regarding cross-sectional averaged smoke temperature and propagation velocity are proposed. Models are consistent with FDS results, indicating that results might be useful in fire safety engineering.

Key words: tunnel fire, smoke temperature, propagation velocity, decay, density jump