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Computational Modeling and Validation of Aerosol Deposition in Ventilation Ducts

Published

Author(s)

Kristopher J. Overholt, Jason Floyd, Ofodike A. Ezekoye

Abstract

In fire models, the accurate prediction of aerosol/soot concentrations in the gas phase and aerosol/soot deposition thicknesses in the condensed phase is important for a wide range of applications, including human egress calculations, heat transfer in compartment fires, and forensic reconstructions of fires. During a fire, in addition to soot transport by advection and diffusion, a significant amount of soot can be deposited on surfaces due to various mechanisms. As a first approach of quantifying aerosol deposition predictions under non-reacting flow conditions, this study identifies important parameters related to aerosol deposition under various flow conditions and compares predicted aerosol deposition quantities to experimentally measured data. The computational tool used in this study was the computational fluid dynamics (CFD) fire model, Fire Dynamics Simulator (FDS). At the onset of this study, turbulent and thermophoretic aerosol deposition mechanisms were available in FDS version 5.5.3. In this study, an additional mechanism for gravitational settling was implemented in FDS version 6.0.0. To compare the predicted results to experimentally measured data, 16 tests conducted by Sippola (2002) were used in which ceiling, wall, and floor aerosol deposition velocities for various sizes of monodisperse fluorescent particles and various air velocities in a ventilation duct were measured. The duct had smooth walls and was square with cross-sectional dimensions of 15 cm x 15 cm. The particle diameters were 1, 3, 5, 9, and 16 μm, which is within the range of soot particle sizes that would be expected in a fire scenario. The air velocities in the duct were 2.2 m/s, 5.3 m/s, 9.0 m/s. The experiments were simulated in FDS, and the measured and predicted aerosol deposition velocities were compared and found to be in reasonably good agreement. Additional predicted quantities are presented, including detailed velocity profiles and aerosol concentrations in the duct.
Citation
Fire Technology

Keywords

aerosol deposition, CFD modeling, gravitational settling, computational modeling

Citation

Overholt, K. , Floyd, J. and Ezekoye, O. (2014), Computational Modeling and Validation of Aerosol Deposition in Ventilation Ducts, Fire Technology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914996 (Accessed April 21, 2024)
Created June 20, 2014, Updated February 19, 2017