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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mech. Eng. | doi: 10.3389/fmech.2019.00053

Air permeability of the litter layer in broadleaf forests

  • 1School of Mechanical Engineering, Faculty of Engineering, Computer and Mathematical Sciences, University of Adelaide, Australia
  • 2School of Chemical Engineering, Faculty of Engineering, Computer and Mathematical Sciences, University of Adelaide, Australia
  • 3School of Life and Environmental Sciences, University of Sydney, Australia
  • 4Research Centre for Fire Engineering, Department of Building Services Engineering, Faculty of Construction and Environment, Hong Kong Polytechnic University, Hong Kong

Fuel on the ground, such as leaves, twigs and decomposing matter, accumulate over time and account for a large percentage of the total fuel load in forests. In fire events, material on the ground is often referred to as a fuel bed. The air permeability of a fuel bed is a critical factor that influences fire behaviour because it controls the amount of air or oxygen available for combustion within the fuel bed. The aim of this study is to provide a better understanding of the air permeability of the fuel beds in forests. The air permeability for different fuel beds were determined using experimental and theoretical methods. The pressure drop across the fuel bed samples were experimentally measured using a verified permeability testing rig. The air permeability was then calculated using Darcy's Law or the Forchheimer equation from the pressure drop measurements, depending on the Reynolds number. The particles in the fuel beds were characterised in terms of particle size and shape. Based on the particle characterisation, the air permeability of the fuel beds was also calculated using the Kozeny-Carman equation. The results show that the experimental method is preferred when determining the air permeability for natural forest fuel beds due to the variability in the size and shape of the particles. The effect of Reynolds number on effective permeability was aslo investigated, and it was found that the transition from Darcian to non- Darcian flow occur at different Reynolds numbers for different fuel particles. For example, the transition occurs at 5 and 15 for gum bark and decomposing matter, respectively. The significance of this study is that it increases the ability to predict the air permeability of fuel beds in forests, which is essential for modelling wildland fire behaviours involving in porous fuel beds. All the samples were dried at 105 OC to remove moisture in the samples.

Keywords: wildfire (bushfire), wildland fire, Air permeability, natural forest fuel bed, litter layer

Received: 25 Apr 2019; Accepted: 16 Aug 2019.

Copyright: © 2019 Wang, van Eyk, Medwell, Birzer, Tian, Possell and Huang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Houzhi Wang, School of Mechanical Engineering, Faculty of Engineering, Computer and Mathematical Sciences, University of Adelaide, Adelaide, SA 5005 AUSTRALIA, Australia, houzhi.wang@adelaide.edu.au