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A multiscale model of wood pyrolysis in fire to study the roles of chemistry and heat transfer at the mesoscale

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Title: A multiscale model of wood pyrolysis in fire to study the roles of chemistry and heat transfer at the mesoscale
Authors: Richter, F
Rein, G
Item Type: Journal Article
Abstract: Pyrolysis is a key process in all stages of wood burning from ignition to extinction. Understanding each stage is crucial to tackle wildfires and assess the fire safety of timber buildings. A model of appropriate complexity of wood pyrolysis and oxidation is missing, which limits the understanding of fires fuelled by wood. Progress towards this aim has been slow in recent years, as the role of chemical kinetics is still debated. Three predominant theories hypothesis that chemistry is either infinitely fast (de Ris), a function of char depth (Atreya), or a function of heat flux (Suuberg). This paper proposes a novel multi-scale model of wood pyrolysis and oxidation for predicting the charring of timber. The chemical kinetics sub-model was previously validated at the microscale (mg-samples). We favourably compare the complete model against a large range of mesoscale experiments (g-samples) found in the literature of different moisture contents (0–30%), heat fluxes (0–60 kW/m2), oxygen concentrations (0–21%), grain directions (parallel/perpendicular), and combinations thereof. The model was then used to calculate the transient Damköhler number of wood at different depths and heat fluxes. This analysis showed that chemistry and heat transfer are both important at all heat fluxes and stages of burning relevant to fire, which unifies the three theories by Suuberg, Atreya, and de Ris. We argue that the model is of currently appropriate complexity to predict the charring of timber. These findings improve our understanding of wood pyrolysis and the modelling of timber burning across scales.
Issue Date: 1-Jun-2020
Date of Acceptance: 26-Feb-2020
URI: http://hdl.handle.net/10044/1/81736
DOI: 10.1016/j.combustflame.2020.02.029
ISSN: 0010-2180
Publisher: Elsevier
Start Page: 316
End Page: 325
Journal / Book Title: Combustion and Flame
Volume: 216
Copyright Statement: ©2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Sponsor/Funder: EPSRC
Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/M506345/1
EPSRC Doctoral prize 2019/20
Keywords: Science & Technology
Physical Sciences
Technology
Thermodynamics
Energy & Fuels
Engineering, Multidisciplinary
Engineering, Chemical
Engineering, Mechanical
Engineering
Pyrolysis
Wood
Multiscale
Modelling
Smouldering
Timber
SMOLDERING COMBUSTION
MASS-TRANSFER
BIOMASS
IGNITION
GASIFICATION
KINETICS
OXYGEN
SCALES
Science & Technology
Physical Sciences
Technology
Thermodynamics
Energy & Fuels
Engineering, Multidisciplinary
Engineering, Chemical
Engineering, Mechanical
Engineering
Pyrolysis
Wood
Multiscale
Modelling
Smouldering
Timber
SMOLDERING COMBUSTION
MASS-TRANSFER
BIOMASS
IGNITION
GASIFICATION
KINETICS
OXYGEN
SCALES
Energy
0902 Automotive Engineering
0904 Chemical Engineering
0913 Mechanical Engineering
Publication Status: Published
Open Access location: https://doi.org/10.1016/j.combustflame.2020.02.029
Online Publication Date: 2020-04-08
Appears in Collections:Mechanical Engineering
Grantham Institute for Climate Change



This item is licensed under a Creative Commons License Creative Commons