The effect of microscopic and global radiative heat exchange on the field predictions of compartment fires

This paper reports on some further results of the CFD simulations of large-scale compartment fires previously reported in Wen et al. (Proceedings of the Combustion Institute , vol. 27, 1998) and Wen and Huang (Fire Safety J 2000;34(1)). It focuses on the use of the laminar flamelet approach and highlights the effect of microscopic radiation on the field predictions of temperature and species concentrations in compartment fires. The flamelet calculations with and without microscopic radiation are performed using RUN-1DL (Rogg. RUN-1DL Manual, 1099) . Radiative properties in the flamelet are calculated by a modified exponential wide band model. Global radiation is coupled with the field calculation through the discrete transfer radiation method (Shah. Ph.D. thesis, Imperial College of Science and Technology, 1979) and Hubbard and Tien's (ASME J Heat Transfer 1978;100:235–9) mean emission and absorption coefficient concept. The soot model of Leung et al. (Combust Flame 1991;87;289–305) is used for soot predictions. Improved agreement with experimental data on temperature distributions has been achieved by including the microscopic radiation in the flamelet calculation. Microscopic radiation is also found to have significant effect on the predictions of soot and OH radical but its effect on the predictions of CO2, CO and H2O are found to be marginal. The present study recommends that radiative heat exchange at microscopic level (within the laminar flamelet) should be included when using the laminar flamelet approach to compute turbulent reacting flows.