Advanced knowledge of the mechanisms and kinetic parameters controlling the thermal decomposition of peat is of importance for understanding smouldering peat fires and quantify fire risk. Smouldering fires not have the visual impact of the flaming front but constitute an important wildfire phenomenon because of the associated large carbon emissions and damage to a valuable ecosystem. Moreover, in case of extreme dry conditions or strong winds, smouldering fires develop easily into scrub or forest flaming fire. In this context, a thermal study on three different types of peat has been conducted: two high-moor peat types collected in Edinburgh (Scotland) and in Tomsk (Siberia), and one transition peat from Tomsk. The botanical composition, degree of decomposition and ultimate analysis were determined for the different samples and compared. These parameters were correlated to thermal behavior obtained by Thermogravimetry experiments. Significnalty different degradation behavior is observed for the different peat types. A kinetic method to predict the temperature of the sample at high heating rates is applied. Comparison shows a good correlation between experimental and numerical results.
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 ...
The regularities of formation of temperature fields in a plane three-layer system with a not-through cross connection (connector) are considered with boundary conditions of the second kind on one exterior surface of the system. The character of distribution of the temperature fields in the zone of influence of the steel connector is investigated experimentally. The results of the experiment are compared to the numerical solution of the problem with boundary conditions of the second and third kind on the interior surface of the wall. Their satisfactory agreement is shown.The regularities of heat transfer in a plane three-layer system with a not-through heat-conducting connection (connector) have been investigated theoretically in [1]. To extend this investigation it became necessary to solve the problem of heat conduction in a plane three-layer system with a not-through cross connection in the case of boundary conditions of the second kind on one exterior surface of the system for optimum designing of energy-saving enclosing structures of buildings and development of systems of their external thermal protection (warmth-keeping).The present work seeks to develop an efficient numerical method of solution of the problem, which is rapidly adaptable to different configurations of multilayer external enclosures with cross connections, to compare results of numerical solution of the problem of heat transfer in a three-layer exterior wall with a connector in the case of boundary conditions of the second and third kind on its interior surface, to experimentally investigate the character of distribution of temperature fields in the zone of influence of a steel connector, and to compare the results of numerical solution to experimental data.Physicomathematical Formulation and Method of Solution of the Problem. Heat transfer through a plane multilayer system with a cross connection will be considered using a brick three-layer exterior wall with a cylindrical connector as an example (Fig. 1). The internal and external layers of the enclosure represent the brickwork and the central layer is a warmth-keeping jacket. The ends of the connector are embedded in the internal and external layers of the enclosure. The geometric dimensions of the layers of the enclosure and the connector are prescribed. The thermophysical characteristics of the wall material (λ i , ρ i , and c i , i = 1, 4 ___ ), which are generally dependent on temperature, are known. The temperature of the medium t g,e and the heat-transfer coefficient α w are prescribed on the exterior surface of the enclosure, and the heat-flux density q 0 is prescribed on the interior surface. The temperature profile over the enclosure thickness t 0 , t 12 , t 23 , and t w outside the zone of influence of the connector is determined from the known value of q 0 from the analytical solution of a one-dimensional stationary heat-conduction problem [2].We will solve the problem formulated in a cylindrical coordinate system (Fig. 1). The origin of coordinates will be located on the inte...
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