Interactions of bubbles in acoustic Lichtenberg figure

The evolution of acoustic Lichtenberg figure (ALF) in ultrasound fields is studied using high-speed photography. It is observed that bubbles travel along the branch to the aggregation region of an ALF, promoting the possibility of large bubble or small cluster formation. Large bubbles move away from the aggregation region while surrounding bubbles are attracted into this structure, and a bubble transportation cycle arises in the cavitation field. A simplified model consisting of a spherical cluster and a chain of bubbles is developed to explain this phenomenon. The interaction of the two units is analyzed using a modified expression for the secondary Bjerknes force in this system. The model reveals that clusters can attract bubbles on the chain within a distance of 2 mm, leading to a bubble transportation process from the chain to the bubble cluster. Many factors can affect this process, including the acoustic pressure, frequency, bubble density, and separation distance. The larger the bubble in the cluster, the broader the attraction region. Therefore, the presence of large bubbles might enhance the process in this system. Local disturbances in bubble density could destroy the ALF structure. The predictions of the model are in good agreement with the experimental phenomena.     

Determining the rate of electric discharge creeping over a water surface

We examine various methods based on specific experimental results for finding the rate of propagation of a pulsed discharge over a water surface.     

Study of the leader of a spark discharge over a water surface

This paper discusses an experimental study of the leaders of incomplete spark discharges with a capacitance of 0.1 and 1 μF over a water surface when the initial voltage is 3–6 kV in discharge gaps 8 and 22 cm long, having side branches and without branches. The distributions of the field, the current, the current density, the conductivity, and the electron concentration along the leader have been determined, as well as the changes in the velocity and length of the leader as it evolves. It has been established that the evolution of the leader has a self-maintained character, and that the product of the storage capacitance and the initial potential difference between the head of the leader and the water surface is an invariant of its spatial evolution. Zh. Tekh. Fiz. 68, 44–50 (July 1998)     

Characteristics of a glow discharge in atmospheric pressure air over the water surface

The current-voltage characteristics, the amount of cathode fall, and the spectra of plasma radiation from different spatial domains are presented versus the molecular band intensity of products arising in an atmospheric-pressure air glow discharge over the distilled water surface. The plasma electron temperature is also reported. The distance to a liquid cathode or anode is varied from 1 to 10 mm at a discharge mean current of 10–36 mA.     

Determination of plasma characteristics in the plasma of a pulsed discharge propagating over a water surface using spectral methods

The results of spectral investigations of the electron density and excitation temperature in the plasma of a pulsed discharge propagating over a liquid surface are presented.     

The velocity of streamer tips in impulse point-to-plane corona in air,using Lichtenberg figure techniques

Positive and negative streamer lengths were measured in point-to-plane impulse corona in air at atmospheric pressure using Lichtenberg figure technique. Applying short time pulses from 9 to 40 nsec duration time-distance plots were obtained, which allowed one to determine the streamer tip velocity. For a 4 cm gap, a 1 mm diameter point, and a 30 kV pulse an average tip velocity of 1.8×10⁸ cm/sec was found. Comparing these data withHudson's photomultiplier measurement, we may identify the Lichtenberg figure with the “primary” streamer ofHudson. The negative streamer tip velocity in the cathode part of the gap was approximately an order of magnitude smaller than the positive streamer velocity.     

Stages of an electric discharge gliding on a water surface

Three stages of a pulse electric discharge were revealed. The discharge occurred in the atmosphere along a free water surface between a tip placed at some distance from the water surface and a distant electrode immersed in the water. Original Russian Text ? A.F. Aleksandrov, D.N. Vaulin, A.P. Ershov, V.A. Chernikov, 2009, published in Vestnik Moskovskogo Universiteta. Fizika, 2009, No. 1, pp. 95–97.     

Underwater current distribution induced by spark discharge on a water surface

Discharge current distributions generated underwater by spark discharges from the atmosphere to free water surfaces with conductivities in the range 0.07–10.0 S/m were investigated using a laboratory-scale electrode system consists of a discharge electrode and nine underwater grounding electrodes. Discharge emission on the water surface, which shows significant change with slight increase in conductivity, affects the current distribution in the water. The electric potential of the water surface also changes significantly with slight increase in conductivity. Results of numerical calculations of the underwater discharge current based on the water surface potential agree with the experimental results.     

Distribution of electron flows over the cathode surface in a discharge with oscillating electrons

The mechanisms governing the distribution of the longitudinal electron flows over the cathode surface in a discharge with oscillating electrons are studied experimentally. The influence of the discharge gap length on the magnitude and distribution of the electron flows is investigated. It is shown that intense longitudinal electron flows in a tube of diameter d _a =31 mm can form only with short anodes of length l _a =2.5–3.5 cm. The distributions of the electron current over the cathode surface at various discharge conditions are determined.     

Ignition of hydrocarbon films by a pulsed discharge propagating above a water surface

We present the results of experimental investigations into the ignition and combustion of hydrocarbon films deposited on a water surface by a pulsed discharge propagating above the liquid in motionless air under atmospheric pressure.     

Creepage discharge along the surface of solid dielectrics in water

Experimental data is given for the discharge voltage for creepage discharge in tap water as a function of the thickness, flange length, (creepage path over dielectric surface), permittivity of the solid dielectric, field configuration, polarity of the applied voltage pulse, and a number of other parameters. The experimental data discussed are the delay time with dielectric flange sparkover by creepage discharge, the average discharge propagation rate for both polarities, and the creepage discharge current and leakage resistance.     

Some properties of the gas discharge in a magnetron geometry

The discharge in a magnetron geometry was experimentally investigated. At pressures less than 10^–2torr a high-voltage discharge (similar to corona discharge) burns, which discontinuously turns into glow discharge when the pressure is rising. Magnetic field changes the glow discharge in a similar way as the rising of pressure does (the cathode regions are getting shorter, etc.). The pressures and magnetic fields were found in which the positive column occupies 3/4 of the discharge space (gap distance 4 cm) and where an electric field 100 V/cm can be measured.The authors wish to thank Dr. P.unka and Dr. V.Kopecký for a valuable discussion and J.Dvoák and A.Kapar for technical assistance throughout the measurement.     

Back discharge in multipoint-plane geometry in flue gases

The paper presents investigations of back discharge occurring in air and flue gases produced by the process of burning of liquefied petroleum gas or charcoal. The discharge was generated between a multineedle electrode and plate covered with fly ash layer. The aim of this work was to determine the effects of back discharge in multineedle-to-plate electrode configuration on the fly ash layer covering the plate electrode. Level of NO_x and CO emission was also measured. It was found that the chemical composition of flue gas can be changed in the domains where the back discharge occurs, for example, additional amounts of nitrogen oxides (NO and NO₂) are produced and also carbon oxide (CO) was produced at higher discharge current.     

Dynamics of a radiating surface discharge

We have elaborated a code for numerical treatment of two-dimensional problems of the dynamics of a surface discharge with inclusion of radiative energy transfer. The gas dynamic, electric, and radiative properties of a surface discharge in atmospheric air have been studied experimentally for a total energy input of 100 J/cm in the input power range 3–6 MW/cm. A new technique involving a discharge sliding along a conducting surface is applied to initiate an extended surface discharge. The calculations agree satisfactorily with the experiments. The method elaborated here makes it possible to calculate a broad class of linear discharges with an eye to produce a radiation source with problem-oriented spectral power characteristics.     

Electrical characteristics of a corona discharge reactor of multipoint-to-plane geometry

The current-voltage characteristics of the discharge in multipoint to plane geometry have been studied experimentally. In this electrode configuration the space charge produced by each point influences the discharge processes from adjacent points. The total current and the current from one of the discharge points isolated from the rest of the electrode have been measured. The current-voltage characteristics have been examined for both positive and negative polarities as a function of interpoint distances and interelectrode spacing. The power per unit volume of the discharge has been determined for the different geometrical parameters of the reactor. The experiments were carried out in air at normal pressure and ambient humidity.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This paper is based on research sponsored by the Polish Committee for Scientific Research (KBN grant No. P40103304).     

MHD squeezed flow of water functionalized metallic nanoparticles over a sensor surface

Present study is devoted to analyze the magnetohydrodynamics (MHD) squeezed flow of nanofluid over a sensor surface. Modeling of the problem is based on the geometry and the interaction of three different kinds of metallic nanoparticles namely: copper (Cu), alumina (Al₂O₃) and titanium dioxide (TiO₂) with the homogeneous mixture of base fluid (water). The self-similar numerical solutions are presented for the reduced form of the system of coupled ordinary differential equations. The effects of nanoparticles volume friction, permeable velocity and squeezing parameter for the flow and heat transfer within the boundary layer are presented through graphs. Comparison among the solvent are constructed for both skin friction and Nusselt number. Flow behavior of the working nanofluid according to the present geometry has analyzed through Stream lines. Conclusion is drawn on the basis of entire investigation and it is found that in squeezing flow phenomena Cu–water gives the better heat transfer performance as compare with the rest of mixtures.     

Microwave discharge on a dielectric surface in vacuum

The paper describes the results of investigation of a discharge arising in vacuum on the surface of solid dielectric materials when irradiated by intense (up to 25 MW/cm²) electromagnetic centimeter wave radiation. When the density of the microwave energy flux exceeds some threshold value depending on the target material, a discharge emerges in the vicinity of the surface. Its emergence is associated with the evaporation of the target material and the breakdown of evaporated matter. The thus forming plasma initially has the form of a thin (on the wavelength scale) layer with the electron density of the order of 10¹⁶ cm^?3. It is demonstrated experimentally that effective generation of multiply charged ions occurs in the plasma. The measured energy distribution of ions in expanding plasma agrees with the predicted distribution obtained in solving the problem on quasineutral expansion into vacuum of a localized bunch of collisionless plasma with cold ions.     

Electrode surface erosion in a high-frequency discharge plasma

The surface erosion of electrodes made of different materials in the plasma of a high-frequency discharge, which is used for pumping ion lasers at a frequency of 10 MHz, is investigated. It is found that the erosion is due to blistering. The effect of the electrode temperature and material, as well as of the gas type, on the erosion evolution under typical operating conditions of a gas discharge tube is studied. The concentration of blistering products (dust particles) in the discharge is estimated in the framework of geometrical optics. Ways to prevent blistering in the discharge under such conditions are suggested.