An Investigation of Steady Wall-Ceiling and Partial Enclosure Fires

A numerical model has been developed to: (a) study the buoyancy-driven combusting flows of partial enclosure fires and (b) to help assess the fire hazards of different burning materials. The calculations provide the flow patterns and distributions of velocity, temperature, species concentration, and flame location in the flow. The model assumes steady laminar flow and makes use of the flame sheet approximation to describe the gas-phase chemical reaction. In corresponding experiments, photographic determinations of flame location were made. Two different cases were studied: (i) a fire occurring in a wall-ceiling configuration with variable pyrolyzing length (of PMMA material); and (ii) a partial enclosure fire with variable soffit and pyrolyzing lengths (the latter of PMMA or POM materials). Good agreement was obtained between measurements and calculations of the flame location for the first case. However, a significant discrepancy was found for the second case and is attributed to the neglect of turbulence and radiation transport in the model. Notwithstanding these limitations, it is found that a simple laminar flow model provides a correct qualitative description of the evolution of partial enclosure fires. For example, stratified (layered) motions, recirculation zones and the so-called “firewind” are correctly predicted as a function of pyrolysis and soffit lengths. The present approach, of incorporating physico-chemical parameters and boundary conditions of practical systems into a numerical model for assessing fire hazards, is very attractive due to its relative ease of execution. The accuracy of the numerical prediction approach can be improved by including radiation and turbulent transport.