A variable property heat transfer model for predicting soil temperature profiles during simulated wildland fire conditions
Ebenezer K. Enninful A and David A. Torvi B CA Division of Environmental Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK, S7N 5A9 Canada.
B Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK, S7N 5A9 Canada.
C Corresponding author. Email: david.torvi@usask.ca
International Journal of Wildland Fire 17(2) 205-213 https://doi.org/10.1071/WF07002
Submitted: 22 December 2007 Accepted: 19 November 2007 Published: 17 April 2008
Abstract
A numerical model of heat transfer in dry soil was developed to predict temperatures and depth of lethal heat penetration during cone calorimeter tests used to simulate wildland fire exposures. The model was used to compare predictions made using constant and temperature-dependent thermal properties with experimental results for samples of dry sand exposed to heat fluxes of 25, 50 and 75 kW m–2. Depths of lethal heat penetration predicted using temperature-dependent properties were within 2 to 10% of the values determined using measured temperatures, while predictions made using constant properties were within 10 to 21% of the experimental values. In both cases, predictions made by the model were within the 1-cm accuracy with which the depth of seeds and plant shoots in the soil can be determined in practice. The model generally over-predicted the depth of lethal heat penetration in dry or moist soil when temperature-dependent properties were used, and over-predicted the depth of lethal heat penetration in soils with a moisture content of greater than 10% if constant thermal properties were used.
Additional keywords: computer model, cone calorimeter, depth of lethal heat penetration, heat transfer, numerical methods, thermal properties.
Acknowledgements
The authors thank Profs J. D. Bugg, O. W. Archibold and Y.-H. Lin of the University of Saskatchewan, Mr K. Johnson of the Northwest Territories Forest Management Division, Dr M. Alexander of the Canadian Forest Service and Mr M. Ackerman of the University of Alberta for technical advice on various aspects of this study. They also thank Mr C. James and Mr D. Deutscher of the University of Saskatchewan’s Department of Mechanical Engineering for technical assistance with the experiments reported in this paper. Financial assistance from the College of Graduate Studies and Research and the Division of Environmental Engineering at the University of Saskatchewan, and the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.
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