The formulation of a multiple absorption coefficient zonal method (MACZM) is presented. The concept of generic exchange factors (GEF) is introduced. Utilizing the GEF concept, the MACZM is shown to be effective in simulating accurately the physics of radiative exchange in multidimensional, inhomogeneous, nongray media. The method can be applied directly to a fine-grid finite-difference or finite-element computation. It is thus suitable for direction implementation in an existing computational fluid dynamics (CFD) code for analysis of radiative heat transfer in practical engineering systems. The feasibility of the method is demonstrated by calculating the radiative exchange between a high-temperature (similar to 3,000K) molten nuclear fuel (UO2) and water (with a large variation in absorption coefficient from the visible to the infrared) in a highly three-dimensional and inhomogeneous environment simulating the premixing phase of a steam explosion.

Importance of thermal radiation for transition to flashover in a compartment fire will be demonstrated. A one zone model is developed with the objective of capturing the key mechanisms responsible for the initiation of flashover, i.e. physics of flashover. Thermal radiation is shown to be a key point and the inclusion of a three-dimensional radiation model is essential in the development of an accurate understanding of flashover. The heat transfer from the bounding wall of the compartment, the particulate concentration in the hot layer and the ventilation opening are shown to be key parameters which can lead to thermal instability and the resulting initiation of flashover. (C) 2004 Elsevier Ltd. All rights reserved.