CRITICAL DIAMETERS OF POROUS MEDIUM PARTICLES IN NON-ADIABETIC FILTRATION COMBUSTION OF METHANE-AIR MIXTURE

<p> The nonadiabatic case of propagation of a stationary wave of  combustion of a methane-air mixture in an inert porous medium is considered. A large number of temperature profiles of porous medium and gas obtained by numerical solution of the problem are analysed. The realisation of phase temperature profiles satisfying the boundary conditions is taken as a basis for the existence of a low-speed stationary mode of wave propagation.  For dangerous velocities of methane-air mixture blowing into a porous block, the boundaries of existence of a stationary mode of wave propagation on the plane of the porous medium particle diameter and heat transfer coefficient to the external medium are determined. The lower boundaries correspond to the minimum diameters of porous medium particles, and the upper boundaries<br>correspond to the maximum diameters. At relatively high value of the heat transfer coefficient, the upper and lower boundaries intersect, and further,<br>there is no stationary regime. With the decrease of the blowing rate of the mixture, the intersection points shift towards the decrease of the heat transfer coefficient, i.e. the area of existence of the stationary mode narrows and at the minimum blowing rate disappears. The effective pore diameters, wave velocity, wave propagation time and maximum temperature of the porous medium were determined at the lower and upper regime boundaries. The wave structure transforms as the particle diameter increases from minimum to maximum for any fixed heat transfer coefficient. At the minimum critical particle diameters, due to a significant increase in the intensity of interphase heat exchange, the temperature profiles of the phases merge and there is no sharply detached temperature peak of the gas mixture. The maximum of the heating zone thickness and minimum of the cooling zone thickness are observed at 2/3 of the particle diameter interval for any fixed heat transfer coefficient. As the upper limit (maximum diameter) is approached, the thickness of the heating zone decreases and the cooling zone increases.</p>