The effect of particle coagulation and fractal structure on the optical properties and detection of smoke

Numerical simulation and analysis of the effect of coagulation on the optical properties of smoke and its detectability are given for a burner fire in a multi-room environment. The specific extinction coefficients are calculated for smoke composed of polydisperse spherical particles and soot fractal-like aggregates. Qualitatively different dependencies of specific extinction on mean-volume diameter and, due to coagulation, smoke residence time are illustrated for these kinds of smoke by 2-D and 3-D simulations of fire-driven smoke flow. The light-scattering and ionisation detector response and time needed to trigger an alarm are compared in terms of the coagulation effect. Calculations without consideration of coagulation underestimate the response of the light-scattering detector and overestimate the response of the ionisation detector. The inclusion of coagulation and the fractal-aggregate description reduces the sensitivity of modelling results to uncertainty in input data concerning the size of the smoke aerosol particles inside the flame zone. (C) 2001 Elsevier Science Ltd. All rights reserved.