INFLUENCE WALL HEIGHT OF SMOKE EJECTION HOLE ON THE RISE “PLUGHOLING” DURING WORK OF THE SMOKE REMOVAL SYSTEM WITH A NATURAL IMPULSE

Efficiency of smoke removal systems with a natural impulse 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.The analysis of influence of smoke ejection hole height on the appearance of “plugholing” is made. Obtained analytically by using the one-dimensional Bernoulli equation formula for calculating critical volumetric average temperature of under-ceiling gas layer, when begins “plugholing”. The formula takes into consideration the height of the hole. A numerical study of thermal dynamics picture of fire in the model room is made with model combustible load by using a three-dimensional field model. We consider the room in the form of a parallelepiped with dimensions of 30
25
15 m. Combustible material is turbine oil. Combustion power is constant over time and is 1.26 and 11.34 MW. Size of smoke ejection hole in the ceiling is 1.2
1.2 m or 3
3 m. Dependencies between critical volumetric average temperature of under-ceiling gas layer and the height of the hole, that obtained with the use of the formula and three-dimensional field model, are compared with experimental data given in the literature. The dependence between the mass flow rates of the gas mixture, leaving the outside of the room, and the height of the hole is obtained. It is found that the height of the hole significantly affect the appearance of “plugholing” and the maximum mass flow of the combustion gases removed from the room through the hole.