Simulating Smoke Transport in Large Scale Enclosure Fires Using a Multi-Particle-Size Model

Abstract

In computational fluid dynamics (CFD) based fire simulation, the particle-laden smoke is usually assumed to be in a gaseous state. This is due to the assumption that most of the smoke particles have diameters less than about 2.0 µm and so their settling velocities can be ignored compared with the intensive turbulent fire gas flow. This simplification can lead to severely under-predicted smoke levels in the lower layer at remote locations from the fire source. This problem is addressed in this paper through the development of a multiparticle-size model which takes into consideration the uneven mass size distributions of smoke particles. The model divides the smoke particles into three groups with various diameter ranges. The transport of smoke particles in each group is represented by a governing equation, in which the gravitational force is addressed by adding a correction into the convection term. The efficiency of the model to reproduce smoke transport is demonstrated by simulating a large scale PVC cable fire experiment conducted in a long corridor. Compared with a conventional smoke transport model, the new model is shown to be better able of reproducing the measured experimental smoke data and the recorded visibilities.KEYWORDS: smoke transport, smoke particle, CFD, drift flux model, large-scale enclosure fire. NOMENCLATURE LISTING

Soot Deposition and Gravitational Settling Modeling and the Impact of Particle Size and Agglomeration

“…For each aerosol species in the gas phase, a gravitational settling velocity is calculated and imposed on the convective term (in the z-direction) in the FDS species transport equation. This approach is similar to the drift flux model for smoke transport described in Hu et al [8]. The gravitational settling velocity is also included in the total deposition velocity to deposit aerosols onto upward-facing flat surfaces, as described below.…”