Estimation of the radiation extinction coefficient of natural fuel beds
Gilberto C. Vaz A , Jorge C. S. André B C and Domingos X. Viegas BA Department of Mechanical Engineering, ISEC–Polytechnic Institute of Coimbra, Rua Pedro Nunes–Quinta da Nora, 3030-199 Coimbra, Portugal.
B Department of Mechanical Engineering, Faculty of Sciences and Technology, University of Coimbra, Pólo II, Pinhal de Marrocos, 3030-201 Coimbra, Portugal.
C Corresponding author. Telephone: +351 239 790 728/732; fax: +351 239 790 771; email: jorge.andre@dem.uc.pt
International Journal of Wildland Fire 13(1) 65-71 https://doi.org/10.1071/WF03009
Submitted: 13 February 2003 Accepted: 23 September 2003 Published: 8 April 2004
Abstract
. The standard formula used to estimate the radiation extinction coefficient, kb (m–1), of solid porous natural fuel beds is examined and tested against laboratory experiments with isotropic beds of pine needles in the range of packing ratio, β, of 0.01–0.02. To measure kb in the tests, a setup using a parallel beam of white light radiation was constructed. The error of the standard formula is observed to be smaller than 10%. Similar tests were performed for a non-isotropic bed of pine needles with β ≈ 0.02, in which the maximum angle of inclination of the needles was limited to 30°, for two directions of incidence of radiation: horizontal and vertical. For each one of these two cases, original estimation formulae for kb are proposed alternative to the standard one. In these cases it is concluded that, while the standard formula may be in error by up to 20%, the new formulae have errors around 5% or smaller.
Additional keywords: isotropic/non-isotropic fuel beds; laboratory experiments.
Acknowledgements
The authors gratefully acknowledge the funding of the European Union through the research projects INFLAME (Contr. N. ENV4-CT98–0700, Progr. Env. & Clim. II) and SPREAD (Contr. N. EVG1–2001–00027, Progr. Ener., Env. & Sust. Dev.). The first author acknowledges the support got through a grant of PRODEP (Europ. Social Fund).
Albini FA (1985) A model for fire spread in wildland fuels by radiation. Combustion Science and Technology 42, 229–258.
Albini FA (1986) Wildland fire spread by radiation—a model including fuel cooling by natural convection. Combustion Science and Technology 45, 101–113.
André JCS (1996). A theory on the propagation of surface forest fire fronts. PhD thesis, Mechanical Engineering Department (University of Coimbra: Portugal) [In Portuguese]
Butler BW (1993) Experimental measurements of radiant heat fluxes from simulated wildfire flames. Proceedings of the 12th Conference on Fire and Forest Meteorology (Society of American Foresters: Bethesda, MD)
De Mestre N, Catchpole E, Anderson D , Rothermel R (1989) Uniform propagation of a planar fire front without wind. Combustion Science and Technology 65, 231–244.
Committee on Fire Research (1961) Publ. 949, U.S. Nat. Acad. Sci. Res. Counc
Fang JB (1969). An investigation of the effect of controlled wind on the rate of fire spread. Ph.D. Thesis (Chemical Engineering Department, University of New Brunswick: Canada)
Hottel HC, Sarofim AF (1967) Radiative transfer (McGraw-Hill: New York)
Vaz GC, André JCS , Viegas DX (2003) Fire spread model for a linear front in a horizontal solid porous fuel bed in still air. In
