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Mechanics
In many respects the regime of ignition of a reactive substance subjected to a powerful thermal flow of radiation is determined by the absorbability of its near-surface layer. With the purpose of improving ignition conditions or achieving an inverse effect the warmed up layer of the substance can be specially modified in an initial condition or "can be programmed" on respective alterations of the absorbability in the process of the temperature increasing. The aim of this work is investigation of influence of the absorbability of the reactive substance on its ignition process depending on temperature.
The ignition of the half-limited translucent substance by a flow of radiation is considered. The falling radiant flow of heat passes through a surface of the substance and is absorbed inside it with the coefficient of absorption inversely proportional to temperature $kappa = k/T^m$. For simplification of the process model the following assumptions are accepted: the pressure of the flow of radiation is not taken into account; it is supposed that the radiation is isotropic and for radiation transfer diffusion approximation with the average coefficient of absorption on all frequencies is applied; simple kinetics of the chemical process is examined; the heat transfer through the reactive substance is provided by the thermal conductivity mechanism. The mathematical description of such a process is submitted by the equation of distribution of heat in a body, equation of diffusion for combustible components and equation of radiation transfer.
The problem was solved numerically by difference scheme by a running method with iterations. Accuracy of calculations on time of ignition $sim 1%$, on temperature $sim 4%$.
The character of the ignition process of the substance was studied under changes of a degree of dependence of the coefficient of absorption on temperature m. For comparison the changes in the characteristics of the process were investigated, when at various m the coefficients of absorption were equal between themselves at high temperature Т$_*$ or at initial temperature Т$_0$. The analysis of the results enables us to come to the following conclusions. At equality of the absorption coefficients at high temperature Т$_*$ the warming-up zone of the reactive substance is essentially narrowed with increase of a degree of dependence of the absorption coefficient on temperature m. The change of the coefficient of absorption influences the time of ignition. At equality of the coefficients of absorption at high temperature the time of ignition decreases with growth of a degree of dependence of the coefficient of absorption on temperature, and at equality of the coefficients of absorption at the initial temperature the time of ignition on the contrary grows at increase of a degree of dependence of the coefficient of absorption on temperature. Taking into account of thermal radiation of the substance does not practically influence the time of ignition.
Work is supported by the grant RFBR (project № 03-03-33075) and Ministry of Education of Russian Federation and CRDF within the framework of the program BRHE (project № 016-02).
Note. Abstracts are published in author's edition
Last update: 06-Jul-2012 (11:52:45)