Computing Radiative Heat Transfer Occurring in a Zone Fire Model.
Computing Radiative Heat Transfer Occurring in a Zone
Forney, G. P.
NISTIR 4709; 49 p. November 1991.
Fire Science and Technology, Vol. 14, No. 1/2, 31-74,
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
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radiative heat transfer; zone models; numerical analysis
Radiation, convection and conduction are the three
mechanisms which a zone fire model must consider when
calculating the heat transfer between fires, wall
surfaces and room gases. Radiation dominates the other
two modes of heat transfer in rooms where there are
fires or hot smoke layers. The computational
requirements of a radiation model can also easily
dominate the work required to calculate other physical
sub-models in a zone fire model. This report presents
algorithms for efficiently computing the radiative heat
exchange between four-wall surfaces, several fires and
two interior gases. A two-wall and a ten-wall radiation
model are also discussed. The structure of this
radiation model is exploited to show that only a few
configuration factors need to be calculated directly
(two rather than 16 for the four-wall model and eight
rather than 100 for the ten-wall model) and matrices
needed to solve for the net radiative flux striking each
surface are shown, after the appropriate transformation
is taken, to be diagonally dominant. Iterative methods
may then be used to solve the linear equations more
efficiently than direct methods such as Gaussian
elimination. The radiation exchange algorithms are
implemented as FORTRAN subroutines named RAD2, RAD4 and
RAD10. These subroutines along with a test driver are
available from the author.