E. E. Son

Vapor-air discharges between Jet electrolytic cathode and metal anode at low pressure

447 Discharges in a vapor gas medium with electrolytic electrodes attract significant interest at present [1–9]. One of the new methods of generating nonequilibrium low temperature plasma is that of using the vapor air discharge arising between the jet and solid electrodes. The nonequilibrium low temperature plasma of vapor air discharge is characterized by a plurality of effects useful for process applications. Vapor air dis charges between a jet electrolytic cathode and a solid anode may be of further interest from the standpoint of studies of physical phenomena. Nevertheless, such discharges have hardly been studied. It is the objective of the present study to investigate the special features of the development of discharge between a jet electro Vapor Air Discharges between Jet Electrolytic Cathode and Metal Anode at Low Pressure

Electrical breakdown voltage of transformer oil with gas bubbles

Electrical breakdown strength of liquid-gas micro bubble mixtures of transformer oil with sulfur hexafluoride and air for the case of quasi homogeneous gas inclusions distribution and 10% volumetric gas content was experimentally investigated. DC voltage up to 140 kV was applied to a 8 mm gap between hemispherical electrodes. It is shown that transformer oil bubbled with air leads to threshold breakdown voltage decrease by 34% and 19% when bubbled with sulfur hexafluoride. The stabilization effect of sulfur hexafluoride micro bubbles on the value of threshold breakdown voltage is observed.

Numerical simulation of the dynamics of noncongruent melting of binary materials

Numerical simulation of the dynamics of incongruent phase transitions in binary materials under the action of a laser radiation pulse was carried out. A mathematical model proposed earlier was used, which allowed for the possibility of formation of two-phase zones within the condensed phase. Specific calculations were carried out for hyperstoichiometric uranium oxide. The major characteristics of the process were compared with those calculated earlier within the framework of the simpler Stefanov’s model, which assumes the existence of solely solid and/or liquid phases delimited by interfacial areas. In particular, it was demonstrated that the use of different mass transfer models in the condensed phase has virtually no effect on the appearance of the calculated thermogram of the surface, which is one of the major characteristics of the process that is experimentally registered. The model with the two-phased zone, as opposed to Stefanov’s, predicts the formation of an extended region of partial alloying in the material. The character of solidification of this region should be considerably different from solidification of the region of complete alloying.

Kinetic and electrical phenomena in gas–liquid systems

Disperse systems consisting of a liquid and gas bubbles located in it are considered. Two possible versions of evolution of bubbles under the conditions studied are assessed. In simple liquids, contact between two bubbles causes them to merge, as the separating film breaks. In the case of complex organic liquids, amphiphilic film is formed on the surface of bubbles, and the lifetime of bubbles in contact increases with their size. Under an external electric field, chains of bubbles are formed, lined up along the electric field potential lines. The presence of bubbles in liquid greatly lowers the breakdown threshold, as the critical parameters of the breakdown field in liquids are two to three orders of magnitude higher than those in gases at atmospheric pressure. Various breakdown mechanisms in liquids are discussed from the viewpoint of formation of the gas phase during the passage of an electric current through a liquid medium. The character of propagating a streamer in separate bubbles is studied with their random distribution in liquid and in the case of formation of some structures of bubbles; the critical parameters of disperse systems, that can lead to their electrical breakdown, are presented. Along with the general concepts of electrical breakdown in dispersed systems, experimental studies of these processes are considered, and the nature of electrical breakdown in liquid dielectrics, including transformer oil, is discussed.

Electrical breakdown of soil under nonlinear pulsed current spreading

Laboratory investigations on pulsed current spreading from spherical electrodes and evolution of electrical breakdown of silica sand with different water contents under a 15–20 kV voltage pulse were carried out. A sharp nonlinear decrease in the pulsed resistance of soil was observed when the current density exceeded a certain threshold value. Then ionization-overheating instability develops and leads to current contraction and plasma channel formation in the soil. The method for determination of the threshold electric field for ionization is proposed. Electrical discharge in wet sand was found to develop with a significant delay time for long discharge gaps similar to thermal breakdown.

Plasma aerodynamics in a supersonic gas flow

We perform an experimental study and numerical simulation of the process of periodic initiation of spark extended discharge in air flow with a Mach number M = 2. Critical parameters of the discharge are measured in a high velocity air flow, and visualization of the gas flow in the presence of the discharge is performed. The influence of the discharge on the flow near the body surface streamlined by the supersonic flow is studied.

Pulsed electrical discharge in conductive solution

Electrical discharge in a conductive solution of isopropyl alcohol in tap water (330 S cm−1) has been studied experimentally applying high voltage millisecond pulses (rise time ~0.4 , amplitude up to 15 kV, positive polarity) to a pin anode electrode. Dynamic current–voltage characteristics synchronized with high-speed images of the discharge were studied. The discharge was found to develop from high electric field region in the anode vicinity where initial conductive current with density ~100 A cm−2 results in fast heating and massive nucleation of vapor bubbles. Discharges in nucleated bubbles then produce a highly conductive plasma region and facilitate overheating instability development with subsequent formation of a thermally ionized plasma channel. The measured plasma channel propagation speed was 3–15 m s−1. A proposed thermal model of plasma channel development explains the low observed plasma channel propagation speed.

Fluid flow with abrupt viscosity-temperature dependence

The paper is focused on studies of channel viscous flow stability with the high dependence viscosity on temperature (thermoviscosity effect). It is shown the essential influence of this effect on the entrance length or transition from any initial profile to the stationary profile of the plane channel flow. The obtained solution has an inflection point in the velocity profile for the certain range of flow parameters. This evidence with respect to Rayleigh’s inflection theorem involves thermoviscous media deserving consideration objects for stability problems.

Shock wave-boundary layer interaction on the non-adiabatic ramp surface

The boundary layer separation of the supersonic air flow over the heated compression ramp has been investigated. Particle Image Velocimetry and Shlieren non-invasive visualization methods were used to study the influence of surface heating on the structure of separation zone. The linear dependence of separation length on the temperature ratio was found. The influence of surface heating on separation region instability was studied. It was found experimentally that increase of wall temperature causes intensification of separation region fluctuations.

Rayleigh?Taylor instability in a visco-plastic fluid

The Rayleigh–Taylor and Richtmyer–Meshkov instabilities of a visco-plastic fluid are discussed. The Bingham model is used as an effective rheological model which takes into account plastic effects. For the purposes of numerical simulation a one-mode disturbance of the contact surface between two fluids is considered. The main goal of this work is to construct numerical 2D and 3D models and to obtain the relationship between yield stress and the development of instability.