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Fire Protection Foam Behavior in a Radiative Environment. September 1995-September 1996.


pdf icon Fire Protection Foam Behavior in a Radiative Environment. September 1995-September 1996. (6763 K)
Boyd, C. F.; diMarzo, M.

NIST GCR 96-702; 182 p. October 1996.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB97-116131

Keywords:

foam extinguishing systems; foam expansion; computer models; fire protection; fire research; heat flux; heat radiation; insulation; temperature profiles; equations; thermal conductivity; thermal diffusion

Abstract:

A model is developed which predicts the behavior of a fire-protection foam subjected to heat radiation. Foam expansion ratio and radiative heat flux are input to the model. A mass and energy balance yield the foam destruction rate and the temperature distribution within the foam. The model separates the foam into its liquid, vapor, and air components. Continuity is satisfied for each. Ideal gas relations, a realistic density function, and foam expansion measurements are used in conjunction with continuity to compute the volume fraction and velocity of each component as a function of temperature. The energy equation is solved in a coordinate system moving with the foam front. Separate air, vapor, and liquid convection terms are computed. Radiation absorption is accounted for with a volumetric generation term. The absorption model is based upon experimental measurements. A volumetric evaporative term accounts for the latent heat of liquid vaporized within the foam. Liquid vaporization rates are determined from the liquid continuity equation. Saturated conditions and thermodynamic equilibrium are assumed throughout. Thermal diffusion is computed using an experimentally determined thermal conductivity. A steady state solution is computed with a second order Crank-Nicolson technique. Fixed values for the temperature at the evaporative front and in the far field are used as boundary conditions. Dimensionless results indicate the major terms in the energy balance are proportional to applied heat flux. The dimensionless temperature gradient in the near linear range of the profiles collapses to a single value.