Researches on Air Shutter for Fire Protection (3)

Abstract

In this Report, first of all it is mentioned how side flows which have ununiform velocity distributions as in fire influence on the flow characteristics of air shutters, and next how to design them.
Then, assuming push flow, pull one and side one to be two dimensional potential flow, three flows are combined theoretically.
The results are as follows:
(1) The mode of push-pull flow of the shutter varies according to the velocity distribution pattern of side flow, even if each volume flow rate is constant.
(2) In such cases, the nearer the position of the point where the velocity of side flow shows maximum situates at the suction side of the shutter, the stabler the flow becomes. In other words, the position of center of gravity of side flow influences at a great extent on the stability of push-pull flow.
(3) Furthermore, the smaller the maximum velocity of side flow is, the stabler the push-pull flow becomes, under the condition that the mean velocity and distance of center of gravity of side flow from the pull side of air shutter are constant.
Next, in order to confirm the conclusions described above, the experiment on the practical flow has performed by employing a model and the results coincide well with the conclusions (1)-(3) abovementioned.
Consequently, relating to the design of air shutter for fire protertion the concrete standards are obtained as follows.
(1) As the side flow of smoke which runs near the ceiling in fire is faster than the one which runs near the floor, the shutter ought to be designed so as the flow is inhaled in ceiling side, and this way is affirmed also from different regard that a smoke has a buoyancy because of its temperature.
(2)The volume rate of suction flow Q₃ can be culculated from next equation by “Flow Ratio Method”
Q₃ = Q₁(1+m · K_Buni )
where, Q₁ : Volume rate of push flow,       m³/min
m : Break safety factor determined accordingly velocity distribution pattern of side flow
K_Buni : Break limit flow ratio culculated by employing the mean velocity of side flow