Method for Computing Heat Transfer Between Connected Compartments in a Zone Fire Model.
Method for Computing Heat Transfer Between Connected
Compartments in a Zone Fire Model.
Forney, G. P.; Moss, W. F.
NISTIR 6190; 32 p. July 1998.
Order number: PB98-148216
heat transfer; compartments; zone models; fire models;
radiation modeling; radiative heat transfer
This note describes a method for calculating conductive
heat transfer between connected compartments in a zone
fire model. The conduction problem is solved by
dividing a compartment into six partitions corresponding
to the floor and ceiling and the front, right, back and
left walls. The wall partitions are further divided
into several equally sized horizontal slabs or strips in
order to approximate the vertical wall temperature
profile. Radiative and convective flux boundary
conditions are computed for the front and back surface
of each partition/strip. Some of the difficulties
encountered when computing radiation exchange for large
numbers of wall surfaces are alleviated by taking
advantage of symmetry and the numerical characteristics
of the linear system of equations that are solved. All
strips have the same height. Strips on opposite walls
have the same width. Strips do not change size with
time. Using this information, the number of necessary
configuration factor and transmissivity factors are
reduced substantially as is the computing time for these
factors. For wall surfaces that are nearly black, i.e.
emissivities close to one, the system of equations to be
solved (the net radiation equations) are strongly
diagonally dominant. Therefore iterative algorithms
(analogous to ray tracing) rather than direct methods
such as Gaussian elimination can be used for determining
the net radiative fluxes.