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Mechanics
The study of development of heat process in the condensed substance caused by heat inclusion is carried out numerically. The considered processes may occur in some technological processes when the radiation flux falling on substance is absorbed by its heterogeneous inclusion and may result in formation of a hot spot around this inclusion. For similar processes one of the main parameters is necessary minimum of heat reserve in hot spot which may lead to ignition of the substance. In the case of ignition the main factor is the determination of ignition time which may fluctuate from milliseconds to twenty four hours depending on the parameters of the system. In this work the ignition process is analyzed when there has been a hot region of the inclusion in the reactive substance. The purpose of this work consists in determination of igniting conditions independence of the temperature and heat reserve in the hot spot and also determination of influence of ignition on inflammatory process. The unlimited reactive substance (RS) is considered when there is an inert hot body of spherical form at the initial time. An ideal heat contact takes place on the boundary of the RS with the hot body. The heat transfers in to RS from heat body and spreads in it according to the law of heat conductivity. Exothermic chemical process in RS is submitted to the Arrhenius law and a simple kinetic law of m order. The temperature of the heat body at small dimension and great heat conductivity is determined by average temperature according to the balance of heat flux on the boundary, "RS - inert body". At the result the mathematical description of the process is represented by the equation of heat conductivity and diusion for the inflammable component taking into consideration the heat arrival and expense of the inflammable component during the chemical process. The moment of sharp temperature rise after which the wave of ignition spreads in RS was taken as the ignition time. The analysis of the calculation result showed strong dependence of the critical reserve in the hot inert body and corresponding ignition time at the initial temperature of the hot body. When initial temperature of the hot body is risen the critical heat reserve and corresponding ignition time decrease by ignition moment, the heat lay in RS decreasing. The regimes of unstable ignition are observed on account of the burning out. The account of the burning out results in the rise of critical heat reserve, ignition time sharply increasing and the ignition point displacing from the surface of inert heat body into the depth of the substance. The account of the burning out also influences on time of exit to constant regime of the burning.
The 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 N 016-02).
Note. Abstracts are published in author's edition
Last update: 06-Jul-2012 (11:52:45)