Fire Protection Foam Behavior in a Radiative Environment. September 1995-September 1996.
Fire Protection Foam Behavior in a Radiative
Environment. September 1995-September 1996.
Boyd, C. F.; diMarzo, M.
NIST GCR 96-702; 182 p. October 1996.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
Order number: PB97-116131
foam extinguishing systems; foam expansion; computer
models; fire protection; fire research; heat flux; heat
radiation; insulation; temperature profiles; equations;
thermal conductivity; thermal diffusion
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.