REDUCING OF EFFICIENCY OF SMOKE REMOVAL SYSTEM WITH ARTIFICIAL IMPULSE DURING "PLUGHOLING"

Abstract

Efficiency of smoke removal systems may be reduced due to the phenomenon of "plugholing", which lies in the fact that the clean air out under ceiling smoke layer due to the action of lift forces passes through the smoke ejection hole. Amodified zone model for calculation of thermal and gas dynamics of fire under action of a smoke removal system with artificial impulse during "plugholing" is proposed. Reducing the flow rate of a mixture of gases and smoke leaving from under ceiling layer outside the room is taken into account by introducing the rate coefficient. A numerical study of thermal dynamics picture of fire in the model room with model combustible load by using the modified zone model and a three-dimensional field model is made. It is considered the room in the form of a parallelepiped with dimensions of 30x25x15 m. Combustible material is turbine oil. Volumetric flow rate of fan of smoke removal system are 30000, 60000 and 90000 m³/h. Dependencies between velocity of lowering the bottom border of the under ceiling layer and the time of fire, that obtained with the use of the modified zone model and a three-dimensional field model, are compared. It is shown that the smoke removal system efficiency is significantly reduced when "plugholing" is occurred. The flow rate of a mixture of gases and smoke leaving from under ceiling layer outside the room is 2 times less than in the case of the absence of "plugholing". It is found that to prevent "plugholing" in the case of smoke removal system with artificial impulse for each fan there is critical minimum square of the hole of smoke removal system, which essentially depends on the thickness of under ceiling layer at the time of the beginning of system work.