Modelling of intumescent coatings kinetics and dynamics of swelling
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abstract
Intumescent coatings are reactive fire protection materials used to protect structural elements, increasing the fire resistance time and the structural integrity of the building for a standard period of time. During the fire exposure the intumescent paint start to decompose, beginning to melt, bubble and to swell, forming a multi-cellular charred layer which decreases the heat transfer from the fire to the substrate. The process is highly non-linear and geometrically characterized by a free boundary, in contact with the fire gases, and a moving boundary, that divides the char and the virgin layers, which may be considered a generalized Stefan problem.
The intumescent coating behaviour is based on the energy and mass conservation equations for the gas and solid fractions, and the transport of gas through the porous char by empirical Darcy’s law. The numerical method is based on an approximation by finite differences with local and adaptive space refinement (r-h), with a decoupled time evolution of the energy and mass equations by the method of lines (MOL).
The methodology is applied to the one-dimensional two-phase Stefan problem and the viscid Burger equation. The results presented shows the mesh adaptation to the solution, increasing or decreasing the number of nodes with the “error” estimation. Also a comparison of expansion and temperature between the numeric and experimental results is made for intumescent coatings exposed to the standard fire curve (ISO834) on a fire resistance furnace.
