The Study of the Confinement Velocity in the Longitudinal Ventilation Tunnel Fire

Abstract

For the situation that the smoke exhaust vents are located on both sides of the fire source, critical ventilation velocity is not appropriate to evaluate the smoke control effect. “Confinement velocity” is proposed as the characteristic parameter to study the longitudinal ventilation by O.Vauquelin in this situation. However, there have been few studies on confinement velocity. An experimental study was carried out on two reduced scale tunnel models. The main objective is to analysis the relationship between confinement velocity and fire heat release in this situation. Helium and air in different ratio was used as the smoke, and the "cold smoke" produced by smoke generator was put into the mixed gas in order to measure the length of smoke layer. The experimental models were based on the half tunnel as flow field at two sides of fire is symmetrical. The CFD model was created on the basis of the experiment, and the results were basically accord with the experimental results. It was shown from the experimental results that the critical point of the confinement velocity is between L / H = 2 to L / H = 4 in section 1, between L / H = 1 to L / H = 2 in section 2, rather than a fixed value; Two tunnel models had similar dimensionless confinement velocity, but the dimensionless total confinement velocity was different.