Experimental and analytical study of the influence of the incident heat flux in cables heat release

Abstract

Cone calorimeter is widely used to study fire behaviour of materials employing small size samples. This equipment allows obtaining parameters such as time to ignition (TTI), heat of combustion, mass loss rate (MLR), or heat release rate (HRR) under different heat fluxes. Some studies have considered a linear fitting between MLR and HRR peaks and the incident heat flux. In accordance with this hypothesis, the computer model Fire Dynamics Simulator (FDS) has included a simple model to extrapolate burning rate data collected from a cone calorimeter test to the heat feedback occurring during a simulation. Nevertheless, deviation in the prediction of the HRR peaks at 75 kW m−2 of approximately 39.3% and of 37.1% for the first and second peak, respectively, were found. Therefore, this work presents a correlation between the incident heat flux and the global HRR per unit area curve, testing up to five different cables and several heat fluxes. To do so, some modifications of the FDS correlation are performed to consider the effect of the flame heat flux in the decomposition of the cables. Once experimental data are acquired, a computational analysis is carried out using FDS to achieve the flame heat flux in the samples. Additionally, this flame heat flux has also been obtained from the literature. As a conclusion, the addition of the flame heat flux to the cone calorimeter incident heat flux provides better predictions than the linear fitting methodology defined in the FDS Guide. Furthermore, this correction is checked with: (1) the example included in FDS guide, decreasing the HRR peaks errors from around 38% to around 25%; and (2) to seven different cables from the literature, decreasing the HRR peaks relative errors, as average, from 14.2 to 9.5% approximately.