Spatial distribution of CO2 dimers in axisymmetric gas jets expanding in a vacuum

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 56–62, January–February, 1989.     

Stability of one-dimensional gas flows in expanding regions

The stability of gas flows produced by the motion of a flat piston or the decay of an arbitrary discontinuity is considered. The boundaries of the region (or regions) in which the development of perturbations is considered are planes (shock wave, contact discontinuity, piston, etc.) which move away from each other.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 112–119, March–April, 1981.     

Formation of inversion in jet of CO2-H2O-N2 gas mixture expanding through a slot

A calculation is made of the kinetics of vibrational relaxation of CO₂ molecules in a CO₂ -H₂O-N₂ mixture escaping into a vacuum from a slot. The examination of vibrational relaxation led to a solution of the kinetic equations corresponding to the most important channels of energy exchange in vibration-vibration and vibration-translation processes. It proved possible to consider the dynamics of a nonequilibrium gas in an approximation of the adiabatic motion of a medium with an effective adiabatic index corresponding to a certain degree of freezing in of the vibrational component of the heat capacity of the gas. The calculated values of the gain index agree well with experimental data. The gain index was calculated with allowance for Doppler and Lorentz mechanisms of line broadening. The results of the calculation were analyzed.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 25–31, November–December, 1973.The authors thank A. S. Biryukov and N. N. Sobolev for advice and comments and É. A. Ashratov and G. K. Bunin for conducting the gasdynamical calculation on an electronic computer.     

Modelling of the movement of gas streams with coarse particles

M. A. Lavrent'ev Institute of Hydrodynamics, Siberian Division of the Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 112–118, March–April, 1995.     

Kinetics of electron recombination in a molecular gas expanding into a cavity

The kinetics of recombination in a diatomic or polyatomic gas dispersing into a cavity is investigated in a model gas with one ionization potential and one electron affinity. In addition to the recombination reaction in triple collisions, which play the most important role in the case of a monatomic gas [1], dissociative recombination, ion-atom charge transfer, and reactions involving negative ions are considered. The qualitative differences in the kinetics of recombination of a molecular gas (in comparison with a monatomic gas) are due to the smallness of the relative electron concentrations at the instant of disturbance of ionization equilibrium and to the important contribution of dissociative recombination reactions and the kinetics of formation and recombination of negative ions.In addition, owing to the greater specific heat of a polyatomic gas and the corresponding lower rate of cooling on dispersion, recombination due to collision of three charged particles is not, as distinct from the case of a monatomic gas, decisive for the asymptotic values of the adiabatic exponent and residual ionization. For this reason the values of the adiabatic exponent can be assigned irrespective of a in the solution of the equations of the kinetics of recombination of diatomic and polyatomic gases. Expressions for the instant of failure of the equilibrium relationship between electrons and, respectively, positive and negative ions are obtained.The relationship between the charged-particle concentration in a gas in ionization nonequilibrium and the time for known values of the reaction rate constants is expressed by quadratures. The values of the rate constants of some ionization processes are known only in order of magnitude. However, available data on rate constants indicate that for practically any initial data for dispersion of the products of explosion or combustion of chemical compounds ionization equilibrium is upset at a time when there is still an equilibrium ratio of concentrations of electrons and negative ions.     

Effect of temperature level on parallel mixing of two gas streams

In the present paper, attention is focused to clarify how temperature level may affect parallel mixing of two gas streams initially separated by a splitter plate. This is achieved by computing distinct cases with different inlet temperatures and comparing the corresponding results. A recently proposed kinetic model is utilized for the simulation of the flow field. The model provides a separate equation set for one component species of the system and an equation set for average quantities of the mixture. Thereby, it can automatically describe diffusion processes without the use of any coefficients for ordinary, pressure, and thermal diffusion which are generally required during Navier-Stokes computations of gas mixtures.     

Thermal effect of a freely expanding gas jet on a flat plate

An experimental investigation was made into the thermal effect of a single gas jet on a plate at Mach numbers of the nozzles in the range 2–6.1, specific heat ratio = 1.4, total pressure difference up to 6·10⁷, gas temperature 450–520 °K in the forechamber, and pressure in the forechamber (10–20)· 10⁵ Pa. The proposed dimensionless numbers made it possible to obtain generalized dependences of the distribution of the heat flux to the plate on the conditions of the problem. A method of approximate calculation of the heat fluxes is proposed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 119–126, July–August, 1981.     

Possibility of the occurrence of dissociation reactions of multiatomic molecules during rapid cooling in an expanding supersonic stream

We investigate the possibility of the occurrence of the reaction involving the dissociation of N₂O and the exchange reaction N₂O+CON₂+CO₂ during rapid cooling of a gas mixture due to supersonic expansion in a nozzle. A numerical solution of the equations for the balance of vibrational energy and the kinetics of the chemical reactions under nonequilibrium conditions is given. We find the values of the parameters that are necessary for the experimental observation of the phenomena considered.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 48–53, March–April, 1973.     

Visualization of the pressure fields of gas streams by the method of holographic interferometry

The pressure field is determined from the deformation of an assembly of membranes uniformly distributed over the walls confining the stream. The deformations are recorded by the method of two-exposure holographic interferometry. The possibilities of the method are illustrated on the examples of flow over a Zhukovskii profile and flow in a nozzle. Direct visualization of the isobars in the field of flow is accomplished.     

Spectroscopic diagnostics of a plasma expanding into a background gas and a magnetic field

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 3, pp. 13–19, May–June, 1992.     

Filtration characteristics of granular bed with layered drawers for removing dust from gas streams

Filtration tests were conducted on a granular bed filter with layered drawers filled with corundum particles with sizes between either 1 mm and 1.5 mm or 2 mm and 3 mm or with quartz sand particles with sizes between 0.125 mm and 1.5 mm.Filtration velocity,filter particle thickness,and filter particle size were all found to influence the filtration efficiency and the pressure drop of both the fixed granular bed and the layered-drawer granular bed.Granular strata with different thickness ratios also strongly influenced the filtration efficiency and pressure drop.For a granular bed with two sizes of filter particles,the coarse granules in the upper layer capture dust with large particle sizes,while the fine granules in the lower layer capture dust with smaller particle sizes that passes through the filter cake and upper layer.Optimal operating conditions were determined at which the filtration efficiency was found to be 99.42%with a bed pressure drop of 320 Pa.     

Possibility of forming an inverted distribution over the rotational levels of nitrogen in an expanding gas stream

A number of theoretical papers have been devoted to an investigation of the relaxation kinetics of the population of a system of rotational levels of molecules in a stream of gas freely expanding from a sonic nozzle [1–3]. The complexity of the task of constructing models of relaxation and of collisions consistent in accuracy, however, as well as the difficulties in solving the resulting system of kinetic and gas-dynamic equations, lead to the necessity of using substantial approximations. Some disagreement between the experimental data and calculated results [1, 2] requires an evaluation of the accuracy of the various approximations used and further refinement of the theoretical models. In contrast to [1], in order to bring out the possible mutual influence of nonequilibrium energy exchange between the degrees of freedom of nitrogen molecules and the variation of the gas-dynamic parameters, the calculation presented below is based on a numerical solution of a self-consistent system of kinetic and gas-dynamic equations for the populations of rotational states and the temperature, density, and velocity of gas in the stream. Collisional probabilities of rotational transitions, calculated with allowance for the long-range part of the potential of the interaction between molecules [4], are used for this.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 9–16, May–June, 1986.     

Effect of surrounding gas on velocity distribution function of molecules in molecular beam

Molecular-beam methods have become widely used in recent times for the study of flows of rarefied gases [1]. However, the very first experiments with molecular beams for agasdynamic source [2] showed that the measured intensities fell below theoretical predictions. Most devices for the creation of a molecular beam by means of a gasdynamic source have pumping equipment of comparatively low capacity and beam formation in them occurs with residual gas present. It was shown [3] that the residual gas penetrates into the jet and significantly reduces the intensity of the molecular beam. This and subsequent work [4, 5] were confined to measurements of intensity (density) and there are no data in the literature on the effect of residual gas on other parameters of the distribution function. The present work was devoted to a study of the effect of residual gas on the distribution function in a molecular beam defined from a jet in the scattering mode [6]. The work was performed on the small molecular-beam generator [7] and on the VS-4 low-density gasdynamic tube [8] at the Institute of Thermal Physics, Siberian Branch, Academy of Sciences of the USSR. Measurements of the distribution function by the time-of-flight method [9] were performed on the small molecular-beam generator and measurements of gas density on the VS-4.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fizito, No. 4, pp. 11–19, July–August, 1976.The authors are grateful to A. K. Rebrov for valuable discussions.