Influence of thermal contact on heat transfer from glowing firebrands

Abstract

The influence of thermal contact between a glowing firebrand and the target fuel bed on the resultant heat transfer into the fuel bed was investigated in this study. A zero dimensional (0-D) model for the firebrand coupled to a transient two dimensional (2-D) explicit finite difference model for the fuel bed were used simulate transient heat transfer from a firebrand deposited on a fuel bed. Two firebrand shapes, a disk shaped firebrand in contact with the fuel bed and a cylinder shaped firebrand with a protruding node in contact with fuel bed, were considered. A model was proposed to estimate the thermal contact resistance between the firebrand and the target fuel bed. Heat transfer from a cylinder shaped firebrand with two contact points was also investigated. The model developed in this study provided detailed information on the temperature distribution and thermal penetration depth in the target fuel bed. Predictions made by the model were in qualitative agreement with experimental data reported in the literature. The firebrand thermal contact resistance model presented in this study can be a useful tool to account for variations in firebrand shape and surface irregularities in both the firebrand and the target fuel bed. Keywords: Wildland-urban interface (WUI) fires, Firebrands, Heat transfer, Thermal contact resistance