Conditions of exothermal conversion in a porous bed with diffusional supply of gaseous reagent

Kolovertnykh, N. E.; Ulybin, V. B.; Khudyaev, S. I.; Shteĭnberg, A. S.

doi:10.1007/bf00783933

Combust Explos Shock Waves

1982

DOI: 10.1007/bf00783933

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Conditions of exothermal conversion in a porous bed with diffusional supply of gaseous reagent

N. E. Kolovertnykh¹,

V. B. Ulybin²,

S. I. Khudyaev³

et al.

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“…The effect of the diffusion of the reactants of the chemical process on the ignition regimes of the porous layer has been studied [8][9][10][11][12][13][14][15][16]. As one might expected, the main features distinguishing the thermal ignition of porous systems from that of homogeneous layers have been observed in the case of hindered diffusion.…”

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“…As a result, the regions of the stable (single) steady state, quasisteady regimes, Frank-Kamenetskii regimes, ignition and extinction conditions of the system, and selfoscillation regions were determined. Kolovertnykh et al [9] performed a physical analysis of the characteristic exothermic reaction regimes obtained in [8] for a porous layer. Takeno and Sato [10] studied the steadystate problem for a porous layer taking into account the temperature and reactant concentration distributions with boundary conditions of the first kind.…”

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Critical conditions of thermal explosion of a porous layer

Burkina

Prokof’ev

2008

Combust Explos Shock Waves

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The conditions and regimes of thermal ignition of a reactive porous layer are investigated under asymmetric conditions on its lateral surfaces and with an oxidizer supply to the layer by diffusion or filtration through the cold boundary. For a zero-order reaction, an analytical dependence of the critical value of the Frank-Kamenetskii parameter on the Zel'dovich parameter is obtained, which separates the regions of steady-state and unsteady regimes. A numerical analysis is made of the critical value of the Frank-Kamenetskii parameter on the Zel'dovich parameter, the Todes parameter, which determines the oxidizer consumption, and the parameter determining the oxidizer supply to the layer: the Lewis numbers or the filtration analog of the Peclet parameter.Key words: porous medium, natural filtration, critical conditions, thermal explosion, analytical and numerical solutions.The conditions of thermal self-ignition of reactive materials are one of the key issues of fire and explosion safety, and their investigation has therefore proceeded in parallel with the development of ignition and combustion theory, starting from the work of van't Hoff [1]. The critical conditions of thermal self-ignition of homogeneous reactive media with simple kinetics were determined and studied in the classical theories of Semenov [2] and Frank-Kamenetskii [3]. Subsequent investigation has shown that a chemical process or a thermal situation are capable, by virtue of complexity, of significantly changing the self-ignition limit [4]. The special features of chemical processes in porous materials, as was noted even by Zel'dovich [5], are related to the delivery of some reactants to the zone of localization of the chemical process and to the complex heat-transfer mechanism. The indicated specificity results in ignition regimes of porous systems qualitatively different from the ignition regimes of homogeneous media. The ignition limits and times of porous systems and the location of the ignition spot depend greatly on the conditions of the process and are determined by heat and mass transfer.Investigation of the initiation of chemical processes 1 Tomsk State University, Tomsk 634050; roza@ftf.tsu.ru.in porous media has been carried out in three directions: 1) self-ignition; 2) ignition of porous media by a hot body and radiative and convective heat flows; 3) hotspot ignition of porous media. The present paper is concerned with the processes related to the first direction. The effect of heat convection due to gas blowing through a reactive layer on the critical conditions of thermal explosion under symmetric conditions on the layer walls was studied by Eremin and Kolesnikov [6]. Steady-state temperature profiles and the dependence of the critical value of the Frank-Kamenetskii number Fk * on the Peclet parameter Pe were obtained numerically using a one-temperature model for a zero-order chemical process. The dependence for Pe < 4 was approximated by a polynomial with an accuracy of 4%. It was established that, for large values of the Peclet par...

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Critical conditions of thermal explosion of a porous layer

Burkina

Prokof’ev

2008

Combust Explos Shock Waves

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Critical conditions for self-ignition of magnesium and zirconium powders

Karpova¹,

Goncharov²,

Kochetov³

1986

Combust Explos Shock Waves

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Conditions of exothermal conversion in a porous bed with diffusional supply of gaseous reagent

Cited by 2 publications

References 2 publications

Critical conditions of thermal explosion of a porous layer

Critical conditions of thermal explosion of a porous layer

Critical conditions for self-ignition of magnesium and zirconium powders

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