Propagation of plane supercompressed detonation waves in gases

An approximate mathematical model has been constructed for the propagation of plane supercompressed detonation waves in gases. An exact analytical solution of the Riemann wave type has been obtained and so have approximate analytical solutions that describe the excitation and attenuation of supercompressed waves when detonation is initiated in the galloping mode. M. A. Lavrent'ev Institute of Hydrodynamics, Novosibirsk, 630090. Translated from Fizika Goreniya i Vzyrva, Vol. 31, No. 5, pp. 101–113, September–October, 1995.     

Numerical study of heat waves in the oxidation of a magnesium wire

A mathematical model of ignition of magnesium samples is proposed based on the concept of the existence of thermal deceleration of a chemical reaction responsible for ignition. The model gives realistic values of temperatures after sample ignition and is in satisfactory agreement with experimental data on the dependence of the radius of a small particle on the limiting temperature of the ambient medium. It is shown that heat waves can be excited by heterogeneous oxidation of Mg wire located in the external flow. The range of parameters in which self-excited wave regimes are observed fits experimental data on oxidation of metal wires qualitatively and in order of magnitude. The problem of initiation of an ignition wave by the initial distributions of the sample temperature is solved numerically, and the stability of heat waves to small and finite perturbations is shown. Tranlated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 29–38, November–December 1998.     

Hybrid autowaves in filtration combustion of gases in a catalytic fixed bed

A mathematical model of autowave processes in a heterogeneous medium with chemical reactions in the gas phase and on the catalyst is constructed. The coefficients of heat and mass transfer between the phases and the thermal conductivity of the solid phase are determined from the current values of system parameters. The model describes three types of autowaves: waves due to filtration combustion of gases in the low-velocity regime, waves due to a catalytic reaction, and hybrid waves. The behavior of phase trajectories of the dynamic system is studied by methods of qualitative and numerical analysis, and an effective technique is developed for searching for a physically grounded autowave solution of the problem. The laws of propagation of autowaves due to filtration combustion of gases and hybrid autowaves are numerically examined, and the effect of system parameters on the basic technological characteristics of autowave processes is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 3–13, March–April, 2008.     

Model of Vapor—Air Gasification of a Solid Fuel in a Filtration Mode

A two-temperature mathematical model of steady filtration combustion of a solid fuel in open systems is proposed. Air or a mixture of air with water vapors is considered as a gaseous oxidizer. The model takes into account that the heat capacities of the phases depend on temperature and composition and that the reactor length is finite and allows obtaining the composition of gaseous combustion products. Calculated results on gasification of a mixture of carbon with an inert component are presented. It is demonstrated that thermodynamic calculations are important for obtaining the upper estimate of gasification efficiency. Even a sufficiently long reactor becomes “short” in the regime of transient combustion waves, which results in more intense entrainment of heat by combustion products and, as a consequence, in lower efficiency of the process. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 65–72, January–February, 2006.     

Shear rate dependence of thermal conductivity and its effect on heat transfer in a Non-Newtonian flow system

The purpose of this research was to investigate the extent to which the thermal conductivity of non-Newtonian fluids is affected by fluid motion, and then the effect of this shear-rate-dependent thermal conductivity, measured in Lee [1995], on the heat transfer for a typical convective system. Such information would have important implications in the design and analysis of non-Newtonian thermal systems such as are found in food processing operations, polymer processing, paint manufacturing, biological systems and many others. A simple parallel plate flow model with temperature-independent properties gave increases in heat transfer on the order of 30–80 % compared to the heat transfer with shear-rate-independent thermal conductivity in Newtonian fluid flow over the entire temperature range (20–50 °C) of CMC solutions depending on the inlet average velocity due to the effect of the shear-rate-dependent thermal conductivity.     

Characteristics of stationary spherical waves of gas combustion in inert porous media

Stationary spherical waves of gas combustion in porous media were studied theoretically and experimentally. It is shown that in spherically convergent and divergent gas flows, the waves differ in the type of stability: they are stable in a divergent flow and unstable in a convergent flow. A mathematical model for standing spherical waves is proposed that establishes the dependences of the coordinate of a standing wave on the gas-flow rate, mixture composition, and parameters of the porous medium and the gas and describes the experiment adequately. It is shown that allowance for heat losses leads to the appearance of limits of existence for standing spherical waves. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 9–19, March–April, 1998.     

Regimes of gas combustion in a porous body of a cylindrical heat generator

A stationary model of filtration combustion of a gas with allowance for conditions at the entrance to the porous body and conditions of heat exchange with the gas phase surrounding the burner and with the heat exchanger is proposed and numerically analyzed. Ranges of parameters where the regime of gas combustion with a narrow reaction zone near the outer surface of the porous body are determined. Mechanical stresses arising in the porous body owing to high temperature gradients and gas pressure in the pores are estimated. The rate of gas combustion and the radiative heat flux from the burner surface are plotted as functions of process-dependent parameters. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 18–29, January–February, 2009.     

Steady states of the surface of a nonadiabatic flame near the limits

Within the framework of a weakly linear model, which describes a nonadiabatic flame near the limit of its propagation caused by heat losses, steady states of the combustion-wave from are studied. Three-dimensional structures of the wave front are formed because of diffusion-thermal instability of the planar flame. The limits of propagation of a curved flame front are shown to expand if the diffusion-thermal instability is taken into account: a cellular flame can exist at heat losses higher than the critical value for the two-dimensional flame. The stability of steady solutions, which describe the cellular flame near the limits of its propagation, is studied. For sufficiently high heat losses, steady solutions for a nonadiabatic flame with front discontinities are obtained. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 3–11, July–August 1999.     

Bubble detonation in polydisperse media

Detonation waves in polydisperse bubble media have been studied experimentally. Data on the critical initiation conditions and on the structure and properties of detonation waves were obtained. The characteristics of detonation waves in poly- and monodisperse media were compared. The behavior of gas bubbles with various diameters in the detonation wave have been investigated. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 3, pp. 114–119, May–June, 1997.     

Multi-spot modes of unsteady gasless combustion of a thick-walled cylinder under adiabatic conditions

Propagation of multi-spot spinning waves in a cylindrical specimen with a coaxial inner channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics (longitudinal and tangential velocities, “pitch,” and maximum temperature and period) are demonstrated by an example of two-spot spinning waves for specimens of different sizes with a fixed channel radius, for specimens of a particular size with different channel radii, and for specimens with a constant wall thickness and varied inner and outer radii. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 3–14, January–February, 2007.     

Ignition of a system of hot spots in the presence of heat transfer through the side surface

An asymptotic analysis is used to study the ignition of a reactive cylindrical body in which, initially, there is a periodic system of hot spots. The effects of the heat transfer through the side surface of the cylinder and the adjacency of hot spots on the ignition regimes are studied. The solution shows that the critical ignition conditions depend considerably on the heat-transfer regime. The adjacency of the hot spots leads to finite changes in the parameters only if they are sufficiently close to each other. The results obtained for a heat-insulated side surface are compared with known solutions. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 17–21, March–April, 2000.     

Model for the propagation of a stationary reaction front in a viscoelastic medium

A coupled thermomechanical model for the propagation of a stationary chemical-reaction wave in a condensed medium is developed. Stresses and strains that arise during the reaction as a result of thermal and “concentration” expansion of the material are related by Maxwell’s equations for a viscoelastic medium. The expression for the heat flux is written as a generalized Fourier law with finite relaxation time for the heat flux. It is shown that deformation of the material in the reaction zone can lead to an apparent change in the activation energy, heat effect, and other characteristics of the system. This model allows for the existence of two different — subsonic and supersonic — regimes of propagation of the front, as well as the model in which the stress- and strain-tensor components are related by a generalized Hooke’s law. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4. pp. 41–51, July–August, 2000.     

Combustion limits of liquid monofuels

A mathematical model for steady-state nonadiabatic waves of filtration combustion of liquid monofuels in narrow tubes is proposed. Using this model, it is shown that combustion in this system can proceed in two regimes with different dominant mechanisms of heat transfer from combustion products to the preflame zone. The nature and parametric dependences of the limits of both regimes are analyzed. Calculations using the model are in good agreement with experimental data on the combustion of liquid hydrazine in narrow tubes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 29–39, March–April, 2008.     

Flame propagation in mixtures of monogermane and oxygen. II. Peculiarities of flame propagation and the structure of combustion waves

Different flame propagation regimes, including a two-wave regime, are studied in a closed pipe with single ignition of GeH₄−O₂ mixtures. It is shown that, depending on the initial conditions and, in particular, on the composition of the initial mixtures, spatially separated chemical reaction waves for oxidation and decomposition of monogermane are observed in certain parts of the reaction vessel which lead to the formation of a two-layer deposit of GeO/Ge. The temporal sequence of the separated combustion wave and wave from which layers of solid products are deposited, as well as the location of the deposition zones in the reaction vessel, are determined by two interacting chain processes—the oxidation and decomposition of monogermane. The thermal relaxation kinetics of the reactive mixture after passage of the combustion waves is determined by the rate of conductive heat transfer from heated solid particles (reaction products) to the gaseous phase. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 77–84, January–February 1999.     

Reflection of a shock wave from a rigid wall in a mixture of a liquid metal and solid particles

The problem of reflection of shock waves and expansion waves from a rigid wall in a mixture of liquid iron and small molybdenum crystals is considered. The study is performed within the framework of equilibrium and nonequilibrium approximations of mechanics of heterogeneous media with different pressures of the components. The mathematical model is verified by fitting the dependence of the equilibrium-frozen velocity of sound on the initial pressure in the mixture with available experimental data. In the equilibrium approach, the dependence of the type of the reflected wave on the type of the incident wave is determined. Direct numerical calculations within the framework of the nonequilibrium model of mechanics of heterogeneous media confirmed the validity of the reflection chart obtained. The possibility of significant compacting of molybdenum particles in reflected waves is revealed. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 97–107, July–August, 2000. This work was performed within the framework of the Integration Project No. 97-24 of the Siberian Division of the Russian Academy of Sciences.     

Improvement of Shaft Furnace Construction for Roasting Limestone

Specialists of the Ural State Technical University together with OAO Lipetskstal’proekt have carried out reconstruction of shaft furnaces for roasting limestone in OAO Nikolaevsk Alumina Plant. As a result of changing heat exchange conditions in the furnace a special construction is developed for a gas distribution core installed in the furnace firing zone, and other engineering solutions introduced make it possible to stabilize limestone roasting in shaft furnaces. Translated from Novye Ogneupory, No. 5, pp. 25–27, May 2008.     

Modeling of ignition of a solid-propellant plate by a low-temperature plasma jet

A problem of ignition of a semi-infinite solid-propellant plate by a low-temperature plasma jet formed in an igniter under a high-power electric discharge is considered. Particular attention is paid to formation and evolution of zones of forced gasification of the fuel under the action of a heat flux from the plasma to the propellant. The locations of these zones are determined by satisfying two conditions: the propellant surface reaches the gasification temperature and the heat flux exceeds a certain “threshold” value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 23–28, January–February, 2007.     

On the limits of flame propagation in a dusty gas

The limits of flame propagation in a gas with suspended inert particles in the presence of external heat removal have been studied. The mathematical model used is based on an unsteady heat-diffusion two-temperature model of gas combustion in the presence of inert particles. The problem is solved by a numerical method. A parametric analysis was performed, and critical values of the parameter that characterizes external heat removal are obtained. Dispersed-phase parameters are determined for which the two-temperature nature of the medium is insignificant. For this case, an analytic estimate for the critical parameters of flame quenching was obtained. At the moment of flame quenching, the normal flame-propagation velocity in a dusty, gas decreases by a factor of compared with the flame velocity in the dusty gas under adiabatic conditions. Tomsk State University, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 14–20, July–August, 1997.     

A convective detonation wave in a porous structure

A porous system in which a fuel on the surface of pores reacts with a gaseous oxidizer is considered. A simplified model for wave processes in such a medium is developed. It is shown that because of strong friction, detonation waves propagate in a regime that is different from the Chapman-Jouguet regime. The conclusions are supported by model simulations and physical estimates. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 98–106, January–February, 1997.