Home – Home – Jornals – Thermophysics and Aeromechanics 2002 number 1

The paper is resumptive. The results of different authors in the field of water-steam plasma technological application are presented. Particular attention is given to the water-steam plasma obtained with the aid of an electric arc. The experience suggests that the future lies with this very technique of plasma generation since electric-arc generators of plasma have high efficiency and practically no limitations both in capacity and in the flow rate of a plasma-forming gas, which is especially important for a large-capacity industry.

The results of experimental investigations of electron concentration distribution in a cathode cavity and charge column, of plasma potential on a column axis, of electron temperature in the column are presented, as well as the topograms of equipotential surfaces and the lines of equal temperatures of electrons. The analysis of the obtained characteristics allowed to determine the reasons of localization of the most heated region of the cathode inside the cavity and the dependencies of temperature maximum position on electric current and plasma-forming gas flow rate, and the mechanism of self-maintaining of the region of maximum potential decline inside the cathode hollow where the main power is supplied into the discharge plasma; this analysis also permits to clarify the role of the plasma-forming gas and its flow rate in generating the processes progressing in a high-current arc discharge with the hollow cathode, and the reasons of high spatial stability of a plasma column in the inter-electrode space and plasma column orientation on the cathode axis.

Specific power inputs and other characteristics of plasma thermochemical preparation (TCP) of coal for incineration were calculated using the "Plasma

Basing on the equilibrium magnetogasdynamic model of plasma the computation of the gas (argon) flow and heating in the initial interval of a cylindrical channel provided with a diaphragm depending on the variation of the current strength, geometric parameters of the diaphragm, gas flow rate and torque has been carried out. The peculiarities of the behavior of the arc flow characteristics in the channels have been studied, which are related to a sudden variation of the cross section with and without regard for gas swirl. It is shown that for the localization of the plasma arc flow in the region near the axis it is necessary to mount a diaphragm also in the outlet cross section of the channel along with the gas swirl. The computed results agree qualitatively with experimental data.

The generation of crossflow instability waves in a swept-wing boundary layer by wing-surface vibrations is experimentally studied. For various disturbance frequencies, the excitation of wave trains of vibration-induced disturbances and their further development in the boundary layer are quantitatively examined. Following a Fourier decomposition of the wave trains into normal three-dimensional modes, the spectral amplitudes of various instability modes were compared with the amplitudes of respective spectral surface-vibration components. As a result of the study, complex-valued receptivity coefficients were obtained for various disturbance frequencies as functions of spanwise wavenumber, which turned out to be independent of the particular shape of surface vibrations.

To study flow characteristics before and behind the obstacle, an attachment region position of a separated flow and flow structures near an underlying surface, a shear subsonic turbulent flow around two-dimensional obstacles of a square cross section was experimentally investigated. The aspect ratio of the obstacle height to the turbulent boundary layer thickness in a mounted point of the model h/  was varied from 3.2 up to 0.2. It is shown that at a larger part along a wingspan (transverse coordinate) the upper obstacle surface flow has a quasi-two-dimensional character, excluding the regions bearing against side ends. At the same time a flow structure near the underlying surface is three-dimensional practically in all cases. For certain, attachment of the shear layer separated from the obstacle has an unstable character. It was set a dependence of the attached region position of the separated flow on the obstacle immersion level in the turbulent boundary layer. The influence of a slip angle on a separated flow transformation and on a width of the quasi-two-dimensional flow region is shown.

By using the flows past planar and conical shocks near the axisymmetric cones at zero incidence the characteristics of the waveriders are investigated, whose lower surface is described by a power-law function. A parametric analysis of the effect of the cross section shape on the lift-to-drag ratio has been carried out for the on-design flow regimes, and also the data have been obtained on the integral heat fluxes for a given surface temperature T _w = const. The results of comparison are presented for different constraints for the geometric parameters of waverider configurations, which are optimal in the lift-to drag ratio sense for the considered types of the basic flow.

The effect of a texture transition and selective reflection in cholesteric liquid crystals was applied for a study of structure of near-wall flow in a channel. For the range of Re_Dh from 1.8^. 10³ to 18^. 10³, the method of liquid-crystal thermography was applied for research of heat transfer and flow structure on a model of heat exchanger at different angles between the main stream and the rib direction. The empirical relationships for integral number Nu with number Re and heat exchanger geometry are presented.

Stability of the structure of emulsion formed by oil drops suspended in an alcohol-water solution of an identical density under the action of a local heat pulse is experimentally studied. Stability of the emulsion structure characterized by the distribution of the numerical concentration of drops over the medium volume is considered within a time period where the interaction (mutual attraction) of drops with a given initial volume concentration may be neglected. As a result, a condition was determined according to which the emulsion structure is stable if the product of the amount of heat brought to the medium by the local heat pulse and the heat-pulse duration does not exceed some value, which is constant for a given liquid.

The method for more accurate definition of the form equations of state was proposed on the basis of thermodynamic analysis. This statement was checked on the example of several equations of state: van der Waals and Redlich

It is shown for ideal gas considered within the framework of a continual mathematical model that the quantities accepted as the heat flux density often do not correspond to the conditions necessary for such a status. In this connection, the procedure for choosing a quantity accepted as the heat flux density is refined and corrected. The commonly accepted assumptions on the driving forces of the diffusion of medium components are corrected respectively. It is shown that neither the gradients of chemical potentials of the gas molecular components nor of their ratios to temperature are the driving forces for the diffusion transport of component masses relative to medium motion with mean mass velocity but the quantities - Grad[(R/_i)lnp_i], where pi is the partial pressure of the i-th molecular component of gas, _i is its mole mass. The assumption is stated on the existence of such a type of the diffusion fluxes densities of components, to which the Onsager coefficients equal to zero of the mutual influence between the heat flux and diffusion fluxes correspond. The relations are obtained between the coefficients of multicomponent mutual diffusion and thermal diffusion ratios, which correspond to two variants of assumption realization.

A multi-channeled high-voltage pulse generator is designed intended for spark-discharge visualization and measurement of gas flow velocity in wind tunnel facilities. The conditions for spark-discharge ignition both in a uniform and sharply non-uniform velocity field are established. A two-pulsed spark-discharge ignition regime is realized, which allows to enlarge the controlled gas-flow zone by a factor of 2   3. The minimum amplitude of a voltage pulse for obtaining a second spark discharge and the maximum time interval appropriate for tracing the initial spark are determined. A description of practical implementation of the spark-tracing method in a supersonic gas jet is given. Results of direct flow-velocity measurements in a short-duration wind tunnel facility are reported.

The electric and luminous characteristics of low-frequency inductive discharge of transformer type (IDTT) in mercury vapor were studied experimentally for different parameters of the discharge: mercury vapor pressure in the discharge chamber and the input power of the discharge. The energy distribution over the spectral range of 250 - 600 nm and volt-ampere characteristics were measured for the following discharge parameters: power 2 - 100 kW (specific power 10 - 500 W/cm), mercury vapor pressure 2 - 40 kPa. The IDTT characteristics were analysed using a U-like channel model for axisymmetric thermal arcs; the results were compared with characteristics for regular arc discharge in mercury vapor. The dependency of key electric and luminous characteristics of IDTT on the discharge parameters is very close to those for mercury arc discharge.