Discharge of Fire Suppression Agents From a Pressurized Vessel: A Mathematical Model and Its Application to Experimental Design.
Discharge of Fire Suppression Agents From a Pressurized
Vessel: A Mathematical Model and Its Application to
Experimental Design.
(3015 K)
Cooper, L. Y.
NISTIR 5181; 59 p. May 1993.
Halon Alternatives Technical Working Conference 1993.
Proceedings. HOTWC 1993. (Halon Options Technical
Working Conference.) University of New Mexico; New
Mexico Engineering Research Institute; Center for Global
Environmental Technologies; National Association of Fire
Equipment Distributors, Inc.; Halon Alternative Research
Corp.; Fire Suppression Systems Assoc.; and Hughes
Associates, Inc. May 11-13, 1993, Albuquerque, NM,
529-549 pp, 1993.
Sponsor:
Air Force, Wright Patterson AFB
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Order number: PB93-198927
Keywords:
fire extinguishment; fire suppression; aircraft safety;
fire safety; discharge pressure; halons; pressure
vessels; experimental design
Abstract:
A mathematical model and associated computer program is
developed to simulate the discharge of fire
extinguishment agents from N2-pressurized vessels. The
model is expected to have three applications. First, to
establish an experimental design and procedure which
closely simulates discharge of a field-deployed vessel;
second, to evaluate the discharge characteristics of a
wide range of alternative-agent/pressure-vessel
configurations, thereby extending the slow and
relatively costly experimental method of making such
evaluations; and finally, to predict vessel exit flow
conditions to be used to solve the problem of agent
dispersal outside of the discharge vessel. The model is
used in example calculations which address the first of
these applications. The field-deployed system, which
forms the basis of the example calculations, involves a
half-liter cylindrical discharge vessel with a circular
discharge nozzle/orifice of diameter 0.019m. The vessel
is half-filled with liquid Freon 22 and is pressurized
with N2 to 41.37x105Pa (600psi). Vessel discharge is
initiated by actuation of an explosive cap over the
nozzle/orifice. The simulating experimental
configuration involves a modified field-deployed system.
A diaphragm with nominal 41.37x105Pa (600psi) rupture
pressure [actual values between 37.92x105Pa (550psi) and
44.82x105Pa (650psi)] replaces the explosive cap. The
system is equipped with a high-pressure N2 holding tank
connected to the discharge vessel via an orifice. An
experimental run begins with the onset of
through-orifice N2 flow from the holding tank. The
vessel is pressurized to the point of diaphragm rupture
and this is immediately followed by vessel discharge.
The model is used to simulate discharge of the
field-deployed system and pressurization/discharge of
the experimental system. Simulations of the experimental
system involve holding tank volumes of 2.5x10-3m3 or
2.5x10-5m3; orifice diameters of 0.005m, 0.001m, or
0.0005m; and initial vessel pressures of 9.38x105Pa
(136psi) (the saturation pressure of Freon 22 at 294K)
and 34.47x105Pa (500psi). From the calculations it was
determined that the 2.5x10-3m3 holding tank with the
0.0005m orifice could be used to simulate accurately the
discharge of the field-deployed system and that it is
reasonable to expect that this experimental design would
give good simulations even when extended to a range of
parameters and agent materials well beyond the scope of
the present calculations. Calculations also indicated
that use of the 2.5x10-5m3 holding tank and/or the
0.005m orifice would not be consistent with an
acceptable experimental design.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899