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Discharge of Fire Suppression Agents From a Pressurized Vessel: A Mathematical Model and Its Application to Experimental Design.


pdf icon 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

Available from:

: National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush Service (Telephone Orders Only) 800-553-6847;
Website: http://www.ntis.gov
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.