Spontaneous ignition of a dust deposit. The effects of time-periodically varying ambient temperature.:The Effects of Time-Periodically Varying Ambient Temperature
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概要
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Thermal stability of a cylindrical dust deposit subject to the time periodic variation of ambient temperature is investigated, where the cylinder is symmetrically heated by an exothermic zero-order chemical reaction. (i) The dimensionless heat balance equation is solved numerically. At a larger value of frequency, the same criterion can be used as that proposed for a constant ambient temperature. However, at the smaller range of frequency, both the ignition tempertaure and the induction time are decreased with decreasing frequency and increasing amplitude. (ii) By applying an approximation to the term of heat generation, the heat balance equation is solved analytically. The critical values of the dimensionless groups obtained from the above simulation corresponding to the infinite induction time are substituted into the analytical solution, leading to an empirical criterion used to predict the ignition temperature. A graphical method is also illustrated. By comparing of the calculations with published experimental data, this criterion is found to be widely applicable for ambient temperature variations in stepwise as well as periodical ways.
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