Modeling on burning of large-scale vertical parallel surfaces with fire-induced flow

An efficient numerical technique is developed to predict the burning rate in a large-scale vertical parallel PMMA walls fire with a buoyancy-induced flow. The strong coupling of the pyrolysis rate and wall fire-induced flow, in parallel configuration, is modeled by including the effects of the streamwise pressure gradient for the first time. Transport equations for mass, momentum, gas-phase mixture fraction and enthalpy are solved using a finite volume method. A two-dimensional adaptation of the Discrete Ordinates Method is used for estimating the flame radiation energy to the burning wall. Soot model is also included in order to permit application to radiative heat transfer within a flame. The results indicate that with increase of the wall spacing/height (L/H) ratio, convection flux increases slightly, and however, contribution by radiation decreases considerably from 90 to 70% of the total heat feedback to the pyrolyzing surface. It appears clearly that when the wall spacing/height ratio becomes so large (L/H > 0.3) that the interaction of the two diffusion flames between the opposing burning walls is unimportant, the predicted burning rate decreases dramatically and follows closely to the experimental data from a single 3.56 m high PMMA slab. Moreover, the analysis claims a maximum local burning rate for a wall spacing/height ratio (L/H approximate to 0.1). (C) 1999 Elsevier Science Ltd. All rights reserved.