Modeling and identification of heat- and mass-transfer processes in intumescent heat-insulating materials

Abstract

The development and use of intumescent heat-insulating materials is important for ensuring fire safety and refractoriness of various structures exposed to powerful sources of heat energy [1][2][3][4][5]. Under heat loading such materials can increase in thickness by a factor of greater than several tens [3][4][5], forming a heat-insulating layer with a low thermal conductivity and thereby protecting the wall of the structure against damage. The number of such materials and the cost of thermal tests for their certification and prediction of heatinsulating properties constantly increase [5]. In this connection, it seems reasonable to use an approach that includes a study of the physical and chemical processes occurring in heated layers of intumescent coatings and their identification and mathematical description. This makes it possible to construct physically plausible mathematical models that can give well-founded predictions in the development of new, more effective coatings.Attempts to realize this approach have been undertaken by Buckmaster et al. [1][2][3][4]. Thus, for example, some heat-and mass-transfer mechanisms in a fire-insulation coating based on chlorosulfonated polyethylene (CSPE) and thermally expansible graphite (TEG) have been studied [3, 4]. Intumescence and thermal" destruction of the binder were found to proceed in the same temperature interval. This feature and also the high porosity of the heat-insulating layer significantly complicate identification of the observed physicochemical processes; therefore, it is necessary to split them into simpler processes, study them sequentially, and identify each of them separately. This experimental procedure is described in detail in [6], where a diagram of preliminary and basic experiments is given. In the first stage, the thermophysical characteristics of intumescent material were determined [8] over a wide temperature range by solution of the inverse problem of heat conduction for each individual stabilization temperature using the method of stabilized states [7]. The macrokinetic constants for the first step of thermal dest uction of the polymer binder were found using the results of dynamic exp,.riments [4]. This process is exothermic and can be described by a first-order solid-state reaction with a temperature dependence in the form of Arrhenius' law. The adiabatic regime of the first step of this reaction was found to be similar to the ignition process of condensed substances [9, 10].In this paper, a most complete model of intumescent material is proposed and the thermal destruction of the polymer binder and intumescence of the filler are identified over the studied temperature range using experimental data on the temperature fields and the dynamics of growth of the heat-insulation layer under heat loading.1. Experimental Procedure and Physical Concepts of the Processes. In accordance with the procedure of [6], we split spatially the processes in the physicochemical experiment and consider the diagram of the experiment shown in Fig. 1. The studied ...

Modeling of the Thermal Protection of a Multilayer Material Under Fire Conditions

“…On the basis of the experimental [7,8] and evaluated theoretical results [9,11], a corrected formulation of the problem on stoichiometric destruction of a multilayer heat shield material has been obtained. To obtain reliable theoretical results, it is necessary to take into account the specifi city of the internal structure of the BRFC under heating: the heat release by thermal decomposition and the heat fl ow across the tablet.…”

“…In [9,11], it was shown that such a process of BFRC destruction corresponds with good accuracy to the real process. However, in the present paper, as opposed to [9,11], the heat propagation by conduction along the transverse coordinate r is taken into account [8]. Such account is also taken in modeling the heat and mass transfer in the wood [12] and the substrate.…”

“…It was assumed that by virtue of the low temperatures the concentration of methane Computational Procedure, Tests, and Input Data. The experimental dependences of the mass loss, the expansion ratio and density of the BFRC depending on the temperature were taken from [8,9] and are given in Table 2. The thermophysical characteristics of the BFRC (SGK-1) determined in [7,8] are given in Table 3.…”

“…The experimental dependences of the mass loss, the expansion ratio and density of the BFRC depending on the temperature were taken from [8,9] and are given in Table 2. The thermophysical characteristics of the BFRC (SGK-1) determined in [7,8] are given in Table 3. The formulas for the heat conductivity coeffi cients 3, λ and 3,⊥ λ (4) were taken from [18], expressions (17) were taken from [13], and equalities (9) and (10) were taken from [12].…”

“…The thermophysical constants of the asbestos cement are given in [20]. The thermokinetic constants for the SGK-1 obtained in [7] are given and were evaluated in [8]. The specifi c heat conductivity coeffi cients of air at a constant pressure c pg and c p5 from (4) and (10) were found by the interpolation formula taken from [21].…”