STUDY OF THE CONDITION FOR SMOKE REVERSE LAYER TO FORM IN TUNNEL FIRE

摘要

The smoke reverse layer found in tunnel fire is generally regarded as the result of smoke buoyancy plume rising from the fire source. While the plume impinging the tunnel ceiling, the pressure of the stagnation point is higher than that of the ambient, and it is the higher pressure that drives the smoke flowing in the direction opposite to the ventilation flow. Applying a model of buoyant plume in cross flow, it is concluded that the formation of smoke reverse layer is mainly influenced by five factors (the buoyancy flux of plume source, the ventilation velocity, the height of tunnel, the size of fire source, and the gravity acceleration). These five factors can be combined into three dimensionless numbers that will be useful in conducting the experimental modeling of smoke reverse layer. Finally, an inequality, which prescribes the condition for smoke reverse layer starting to form, is given.