THE DISPERSION OF FIRE SUPPRESSION AGENTS DISCHARGED FROM HIGH PRESSURE VESSELS : ESTABLISHING INITIAL/BOUNDARY CONDITIONS FOR THE FLOW OUTSIDE THE VESSEL

Abstract : This work reports on part of an effort to study the dispersion and extinguishment effectiveness of Halon and Halon alternative fire extinguishment agents discharged from N2-pressurized vessels. In the systems under consideration, as the agent exits from the vessel, thermodynamic and fluid dynamic instabilities lead to flashing and breakup of the agent into a two phase droplet/gaseous jet mixture. This occurs in a transition region relatively close to the vessel exit orifice/nozzle. Downstream of this region the two phase agent jet then mixes with the ambient air environment and is dispersed in the protected space. A mathematical model has been developed previously to simulate the time dependent discharge of the agent from the pressure vessel. Using the output of this model and thermodynamic and fluid dynamic considerations of the phenomena in the transition section, the present work develops a method for determining a set of initial/boundary conditions at an initial section of the jet, downstream of the transition region. These initial/boundary conditions are in a form that can be used to formulate and solve the problem of the development and dispersal of the ensuing mixed air/two- phase-agent jet. Example applications of the developed methodology are presented. These are for agent discharge from a half liter cylindrical discharge vessel with a circular discharge nozzle/orifice of diameter 0.019m. Simulations involve discharge of the vessel when it is half filled with either Freon 22 or Halon 1301 and then pressurized with N2 to 41.37x10(exp 5) Pa (600 psi).