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Simulation of Fires With Radiative Heat Transfer.


pdf icon Simulation of Fires With Radiative Heat Transfer. (723 K)
Mell, W. E.; Baum, H. R.; McGrattan, K. B.

International Conference on Fire Research and Engineering (ICFRE2), Second (2nd). Proceedings. National Institute of Standards and Technology (NIST) and Society of Fire Protection Engineers (SFPE). August 3-8, 1997, Gaithersburg, MD, Society of Fire Protection Engineers, Boston, MA, 26-36 pp, 1998.

Keywords:

fire research; fire protection engineering; radiative heat transfer; simulation; thermal radiation; transport equation

Abstract:

Thermal radiation is the dominant mode of heat transfer in very large fires. Even in small pool fires (diameter of 0.1-0.3 m) radiative feedback to the fuel surface is significant. The purpose of this paper is to describe a model of radiative transport in gases that is suitable for use with a large eddy simularion (LES) approach for fire dynamics developed at NIST. This LES model of convective transport and combustion heat released was developed by distinguishing between physical processes that can be explicitly computed and those that operate at length and time scales too small to be resolved (i.e., subgrid). The same strategy will be attempted here for the thermal radiation generated by the fire. The starting point is the radiative transport equation for gases. For the present purposes it is sufficient to understand that the fluid mechanics is calculated on an Eulerian finite difference grid in rectangular coordinates. The velocity and temperature fields so calculated are assumed to be large scale phenomena resolvable on the grid. The combustion phenomena that drive the flow are assumed to be of subgrid scale, whose consequences can be represented by Lagrangian "thermal elements". These elements release sensible energy into the gas as they are convected with the large scale fluid motion.