Estimating Thermal Radiation Fields from 3D Flame Reconstruction

The dominant mechanism for the spread of a fire in a building is radiative heat transfer from flames. Therefore, in order to understand how a fire might develop it is necessary to determine the thermal radiation field surrounding a fire. The heat flux at any target location depends upon the flame’s emissive power and the shape factor between the flame’s surface and the target. To determine the shape factor, it is necessary to define the geometry of the flame surface, and develop a method for obtaining the shape factor for that geometry. In this article we describe a method for determining the flame geometry using image-processing techniques. Images of the fire are recorded using two cameras and the flame is reconstructed in three dimensions. Once the surface of the flame has been defined it is possible to calculate the shape factor at a given target. Using the shape factor and an estimate of the emissive power of the flame, the heat flux at the target can be determined. Repeating this process for multiple targets builds a thermal radiation field. Results from applying the method to a controlled flame produced by a diffusion burner show a high correlation between estimated and measured heat flux values.