Measurements of convective and radiative heating in wildland fires
David Frankman A , Brent W. Webb A , Bret W. Butler B E , Daniel Jimenez B , Jason M. Forthofer B , Paul Sopko B , Kyle S. Shannon B , J. Kevin Hiers C and Roger D. Ottmar DA Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602, USA.
B US Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, 5775 Highway 10 W, Missoula, MT 59808, USA.
C Eglin Air Force Base, Jackson Guard, 107 Highway 85 N, Niceville, FL 32578, USA.
D US Forest Service, Pacific Northwest Research Station, 400 N 34th Street, Suite 201, Seattle, WA 98103, USA.
E Corresponding author. Email: bwbutler@fs.fed.us
International Journal of Wildland Fire 22(2) 157-167 https://doi.org/10.1071/WF11097
Submitted: 12 July 2011 Accepted: 27 June 2012 Published: 11 September 2012
Abstract
Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was much less variable in time, increasing nearly monotonically with the approach of the flame front and largely declining with its passage. Irradiance beneath two crown fires peaked at 200 and 300 kW m–2, peak irradiance associated with fires in surface fuels reached 100 kW m–2 and the peak for three instances of burning in shrub fuels was 132 kW m–2. The fire radiative energy accounted for 79% of the variance in fuel consumption. Convective heating at the sensor surface varied from 15% to values exceeding the radiative flux. Detailed measurements of convective and radiative heating rates in wildland fires are presented. Results indicate that the relative contribution of each to total energy release is dependent on fuel and environment.
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