Dispersion of Fire Suppression Agents Discharged from High Pressure Vessels: Establishing Initial/Boundary Conditions for the Flow Outside the Vessel

摘要

The 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 exists from the vessel, thermodynamic and fluid-dynamic instabilities lead to flashing and break-up 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 (600psi).