Diffusion-thermal stability of gas filtration combustion waves in an inert porous medium

A mathematical model for the filtration gas combustion taking into account thermal conductivity, diffusion, and intense interfacial heat transfer is presented. The temperature dependence of the chemical reaction rate is approximated by a δ-function and the thermal-expansion coefficient of gases behind the combustion front is taken into account. Unsteady combustion regimes are analyzed using the method of small perturbations. The boundaries of the longitudinal and spatial stability for steady regimes of the filtration combustion wave are obtained. The dependence of the Lewis number on the thermal-expansion coefficient of the gas mixture along the boundary of stability is derived, along with other relations.     

Thermal explosion in an inert porous medium

We have investigated thermal explosion (autoignition) of a reaction mixture situated in an inert porous medium. We consider a two-temperature model in the adiabatic formulation. We isolate the following regimes for the process: explosive, explosive with delay, slow regime with a discontinuity between the temperature of the reaction mixture and the temperature of the inert medium, slow and fast regimes without such a discontinuity. We determine the limits of the regions of existence of these regimes.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 3–10, July–August, 1992.     

Stabilized gas combustion wave in an inert porous medium

A stabilized gas combustion wave in an inert porous medium with intense internal interphase heat exchange (at low velocities) is considered to elucidate the mechanism underlying the increase in the burning velocity of the homogeneous gas mixture due to the porous medium. It is shown that the major factor of the increase in the burning velocity is conductive heat recuperation from the postflame zone to the region of the fresh mixture through the solid skeleton of the porous medium. Analytical dependences of the degree of increase in the burning velocity of the mixture in the stabilized wave on the determining parameters are obtained. The possibilities and restrictions of the use of the results to analyze the operation of porous burners are discussed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 8–15, September–October, 2008.     

Combustion-wave propagation through an inert obstacle in real condensed systems

Displacement of combustion products behind the chemical-reaction front in a condensed system is shown to affect combustion-wave propagation through an inert obstacle. In the experiments, pressed specimens of a Ti+C+20%TiC mixture containing an obstacle in the form of a tantalum band 10 μm to 0.6 mm thick were used. Dependences of the delay of the combustion wave during penetration through the obstacle on the obstacle thickness were obtained for the cases of small (<1 mm) and large (≈4.5 mm) displacements of the material behind the chemical-reaction front. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 43–47, November–December 1998.     

Influence of the initial gas pressure on the detonation limits and parameters of low-density secondary explosives in an inert porous medium

This paper reports the results of an experimental study of the detonation of low-density (3–40 mg/cm³) secondary high explosives (HEs) in evacuated and gas-filled inert porous media. A convective-jet mechanism of detonation propagation was found to occur under all conditions studied. The effects of the type of HE and initial gas pressure on the critical density of the HE and detonation parameters were elucidated. It is shown that, in the presence of air, detonation can occur at a lower volume-averaged density of the HE than in the case of the evacuated media and there are two limits (minimal and maximal) for the initial gas pressure. As the volume-averaged density HE decreases, the limits approach each other and, for a certain critical density of the HE, detonation exists only at one value of the initial pressure. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 106–117, May–June, 2009.     

Drying characteristics of starch in an inert medium fluidized bed

The effects of gas velocity (0.32 to 0.67 m/s), inlet gas temperature (25 to 100 °C) and the mass ratio of starch to inert particles (0.1 to 0.4) on the drying rate of starch in a 0.083 m-ID × 0.80 m-high inert medium fluidized bed were investigated. The drying mechanism in an inert medium fluidized bed can be classified into adhesion-dispersion, evaporation and disintegration steps. The drying rate increases with the increasing inlet gas temperature and velocity; the rates being about 10 times those reported for an agitated pan dryer. However, the drying rate decreases slightly as the mass ratio of starch to inert particles increases. Also, the drying rate exhibits a maximum at an optimum bed porosity. The drying rate data obtained in an inert medium fluidized bed have been correlated with the relevant dimensionless groups, i.e. Stefan and particle Reynolds numbers based on the theory of isotropic turbulence.     

Influence of liquid hydrocarbons on the ignition of metal powders in shock waves

Ignition of mixtures of metal powders with liquid hydrocarbon fuels in an atmosphere of pure oxygen and air behind reflected shock waves is studied experimentally. It is shown that the ignition delays for the mixtures are determined by the liquid phase, and the times of combustion are primarily determined by the particle size of the solid phase. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 108–113, March–April, 1998.     

Effect of an inert high-modulus ceramic wall on detonation propagation in solid explosive charges

The effect of an intert high-modulus ceramic wall on detonation propagation in charges of a solid heterogeneous explosive was investigated experimentally and numerically. Subdetonation pressures occurred at the boundary between the wall and the explosive for the conditions investigated. Here the detonation velocity increased, and the mass velocity and the pressure at the detonation front decreased, which is explained by the indirect effect of an overtaking wave into the unreacted explosive and the chemical reaction zone. Transverse waves, which affect the detonation parameters, propagate perpendicular to the detonation front with a velocity of ∼6 km/sec. The initial decomposition rate of the explosive directly after the compression shock determines the degree of the transverse-wave effect. Novosibirsk State Technical University. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 5, pp. 107–114, September–October, 1994.     

On the problem of laminar flame propagation in a gas with an inert dust

This paper presents a mathematical model and the results of calculation of the velocity of propagation of the flame front in a fuel gas with suspended inert particles taking into account the thermal expansion of the gas and the dynamic relaxation of particles. Dependences of the steady-state flame velocity on the particle size and mass concentration are obtained.     

Parameters of air shock waves when combustion is transformed into detonation

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 5, pp. 111–115, September–October, 1989.     

Interaction of weak shock waves with a layer of a powdered medium

Results of analytical and numerical studies of the interaction of linear and weakly nonlinear air shock waves with an infinite layer of a powdered medium and with a finite-thickness layer are presented. Approximate analytical expressions for phase-pressure distributions in the powdered medium are obtained. It is found that the gas pressure at the “gas-powder” interface is continuous for linear waves and experiences a sudden change for nonlinear waves. The dependences of phase pressures on a shielded solid wall obtained by solving a general nonlinear system of equations of motion of a powdered medium and an approximate analytical solution of linear equations are compared. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 131–140, March–April, 2000.     

Effect of velocity nonequilibrium on the laminar flame propagation characteristics in an air-dispersed medium

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 5, pp. 38–44, September–October, 1992.