Computing Radiative Heat Transfer Occurring in a Zone Fire Model

摘要

Radiation, convection and conduction are the three mechanisms which a zone firemodel 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 submodels in a zone fire model. The 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 the 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.