Estimating net heat flux from surrogate firebrand accumulations using an inverse heat transfer approach

Abstract

An experimental study is presented that investigates the heat flux from firebrand accumulations to a substrate. Surrogate firebrands produced from wood pellets were deposited on an inert solid substrate. An inverse heat transfer model is used with temperature measurements in the substrate to calculate the net heat flux into the substrate. The thermal boundary condition (heat flux) can then be used to assess the hazard from firebrand accumulations and better understand the ignition potential of combustible structural material by firebrands. Peak net heat fluxes were found to be between 4 and 9 kW m-2 and to depend primarily on the initial particle temperature. The exposure duration increases with increasing firebrand accumulation mass and decreasing deposition area. For sustained smouldering accumulations, the substrate is exposed to prolonged heating with a net heat flux between 1 and 3 kW m-2. Peak gauge heat fluxes were found between 30 and 80 kW m-2. This depends on the initial particle temperature and deposition area. The method shown herein is a robust tool to assess hazardous conditions in the wildland-urban interface, related to firebrand accumulations.