Heat and Mass Transfer in Fires: Scaling Laws, Ignition of Solid Fuels and Application to Forest Fires

Abstract

Abstract:Fire is a phenomenon that covers a multiplicity of scales depending on the different processes involved. Length scales range from the nanometres when addressing material flammability to the kilometres when dealing with forest fires, while time scales cover a broad spectrum too. Heating of structural elements can be measured in hours while characteristic chemical times for reactions do not exceed the millisecond. Despite these wide ranges, a series of simple scaling laws seem to describe well a multiplicity of processes associated with fire. In this paper, flaming ignition of a solid fuel will be presented within the context of general scaling laws and forest fires. Therefore, the case of highly porous vegetable fuels will be investigated to extend the theory to the forest fires application.

A dimensional analysis of forest fuel layer ignition model: Application to the ignition of pine needle litters

“…Nevertheless, it seems, according to the same study [12], that the needle thermal behaviour is thermally thick in most ignition cases. This result is in accordance with experimental measurements [6,7], which show that the inverse of the square root of the time to ignition still seems to depend linearly on the imposed radiant heat flux. Hence, the model equations will not consider an equivalent medium for the fuel layer as often proposed for ignition modelling [7,13] or for forest fire propagation study [14,15,16].…”

An improved non-equilibrium model for the ignition of living fuel

“…The solid film is heated by radiation and cooled by convection on the front side, whereas on the rear side exchange is a convective flux with the liquid under it. The problem is then reduced to a one-dimensional finite-depth heat diffusion problem, as suggested in the classical ignition theory presented in Torero (2008), applied to vegetation in Torero and Simeoni (2010) and adapted to finite depth solids (Lamorlette and Candelier 2015), in order to evaluate the amount of heat actually reaching the liquid phase during the heating process leading to ignition. The present study provides insight on the flux distribution between phases.…”

Autoignition of Dead Shrub Twigs: Influence of Diameter on Ignition

“…Simplified physical models [6][7][8] use only a few equations to model comappropriate conditions. The autoignition [11,12,[26][27][28][29] and piloted ignition [11,19,20,[30][31][32][33][34] of cellulosic material exposed to a radiant heat source have been studied by many authors. The influences of external factors such as the heat flux and internal parameters such as the thermal properties and moisture content on both types of ignition were investigated.…”

“…The measurement of the specific heat of the twigs was performed using a differential scanning calorimeter: c p;tw ¼ 1834 J/(kg.K). The total heat transfer coefficient above the fuel (h T,u ) was determined using the following relationship [19,44]:…”