Influence of a misalignment of the cone or the sample holder on the view factor with a Monte Carlo approach

Abstract

The cone calorimeter is a fire test internationally standardized as ISO 5660-1 [1], developed at The National Institute of Standards and Technology in the 1980’s [2]. It allows to study different flammability and combustibility parameters, as the ignition time, mass loss, mass loss rate, gaseous emissions and the rate of heat released by materials exposed to radiant heat flux. However, the results obtained with this set-up are clearly dependent of several critical points, especially the aeraulic conditions around the material and the radiation thermal stress imposed to the material. It appears important to properly characterize this last one to ensure that the parameters obtained experimentally are correlated to the true experimental conditions.Among the critical points, the incident flux received by the sample holder through the radiant spirals of the cone calorimeter is identified as being the most significant. This incident flux depends on the temperature and the radiative properties of the spirals, and on the view factor between the spirals and the sample. This work focuses on the latter, and most specifically on the sensitivity evaluation of the geometrical parameters on the incident radiative flux. In order to determine the view factor, two distinct strategies may be applied. The first one is the algebraic derivations of geometric view factor that may be fastidious when the geometrical configuration increase in complexity. The second one consists in a rigorous experimental study by measuring the incident flux at different locations of the sample holder using flux meter. However, this approach is time-consuming and concedes a lot of measurement uncertainties. This article presents an intermediate method, easy, precise and allowing a parametrical study (axiality, horizontality, radiation coefficient, dimensions etc.) by means of a numerical Monte Carlo method.