Mathematical model for intumescent coatings growth: application to fire retardant systems evaluation

Abstract

Intumescent coatings are designed to react when they are heated, by building up a swollen multi-layered insulating structure. The substrate onto which they are applied is then actively protected. In a military framework, it is crucial to provide efficient protection to a wide range of devices and vehicles, which must be able to sustain intense thermal conditions such as fires or explosions. For this purpose, the behaviour of intumescent paints under exposure to high thermal fluxes is investigated. In order to develop and validate a model describing heat transfers in materials protected by intumescent coatings, experimental simulations of different types of radiative aggressions were carried out. A 45 kW solar furnace was used as a heat source, which allowed simulating fires and explosions. Temperature ranges and kinetics calculated by the model are similar to those observed and measured during the experiments. The mathematical model, initially developed for fire simulations, also proves efficient in the case of thermal fluxes induced by brief, violent explosions. However, the results show that a better identification of each layer's thermal properties is needed to improve the accuracy of the model. For this purpose, an experimental identification campaign using the solar furnace has to be developed.

Assess the Fire Resistance of Intumescent Coatings by Equivalent Constant Thermal Resistance

“…InFigures 8, 9and 13, the steel temperatures calculated by Equation15 are also presented, which match well with the test data in the range of steel temperatures from 400°C to 600°C. In those calculations, constant thermal resistance determined byEquation 16 …”

“…As shown in Figure 1, when exposed to flame or radiation, broadly, a intumescent coating undergoes the following reaction steps [3,14,15], -At early heating stage, a large amount of thermal energy is absorbed by the coating, whose temperature increases quickly; -When the temperature of the coating reaches a critical temperature, the polymer matrix melts and degrades to form a viscous fluid. The inorganic acid source in the coating will undergo thermal decomposition normally at temperature of 100°C to 250°C [3].…”

“…Till now, several models have been developed to study the heat transfer of intumescent coatings under heating [2,7,[13][14][15]. These models are primarily onedimensional, and concentrated on the effects of swelling on the thermal properties of coatings.…”

“…These models are primarily onedimensional, and concentrated on the effects of swelling on the thermal properties of coatings. The structure of chars is always simply assumed to be constituted of vapor and solid materials, or to be a porous media, and the thermal conductivity of chars, k c , is determined by k sol , k vap and f v [2,13,15]. (In Refs.…”

“…Here, k c , k sol and k vap are thermal conductivities of char, solid and vapor, respectively; and f v is the void fraction of the char. In intumescing or swelling process, the structure of coatings is divided into two layers, virgin coating and char [7,13,15]. (In Refs.…”