Yu. Dolinsky

Melting dynamics in current‐carrying conductors and its effect on electrodynamic characteristics

This work studies the dynamics of melting in current‐carrying conductors. Formulae are derived which describe the dependence of temperature at the front of phase transition upon the distance from the axis of the conductor. The thermodynamic stability of a phase transition front is investigated. It is shown that due to strong variations of conductivity during melting the rate of change of conductivity is of the same order as an active resistance of a conductor. Clearly the magnitude of this effect depends upon the ratio of electric conductivities in liquid and solid phases. The effect is stronger when this ratio is lower.

Peculiarities of coexistence of phases with different electric conductivities under the influence of electric current

Abstract In this study using Volmer–Zeldovich model and Ginzburg–Landau models we showed that in the domain of coexistence of phases under the influence of the electric current the phase equilibrium curve splits into two different curves for the direct and inverse phase transitions. It is demonstrated that there exist thermodynamic regions where both phases are metastable simultaneously. The latter effect occurs due to the splitting of the phase equilibrium curves into two curves, i.e. the equilibrium curves for the direct and for the inverse phase transitions. We investigated the dynamics of surface phase transition in current-carrying conductors. It is showed that inductance change has a strong effect on the dynamics of phase transitions. At the initial stage of phase transition ponderomotive forces caused by the inductance change prevent surface crystallization and promote surface melting.

Addressing water vaporization in the vicinity of an exploding wire

The phase state of thin (∼1μm) layer of water adjacent to the surface of rapidly heated thin wire 100±50μm in radius is analyzed by computer hydrodynamic calculation. It is shown that when heating of a wire to a temperature of 420°C is achieved in less than ∼500ns, the trajectory of the phase state is contained in the liquid part of the phase diagram. This suggests additional proof of and an explanation for the absence of shunting plasma discharge in fast underwater electrical wire explosions.

Critical currents in normal conductors

It is shown that in a normal conductor the value of a current that generates a magnetic pressure equal to the critical pressure may be considerably lower than it is generally considered. The lower value of the critical current occurs due to the shift of the whole curve of phase equilibrium in the presence of strong electric current. This shift arises due to the additional work performed against ponderomotive forces which prevents from the formation of the nucleus of a phase with a lower value of electric conductivity. In case of the Van der Waals model of the critical state the value of the critical current calculated taking into account the shift of the phase equilibrium curve is by factor 2–3 less than the critical current determined when this effect is neglected.

Thermophoretic interaction of heat releasing particles

This study investigates thermophoretic force acting at heat releasing (absorbing) particles near the interface between two media with different thermal conductivities. This force is caused by the induced temperature gradient which is proportional to the rate of heat release (absorption) by the particle. Therefore the magnitude of the thermophoretic force is proportional to the rate of heat release (absorption) by the particle, and its direction depends upon the sign of the parameter κ1–κ2, where κ1 is thermal conductivity of a host medium and κ2 is thermal conductivity of the adjacent medium. The obtained results imply that a heat releasing (absorbing) particle is attracted (repelled) to the interface when thermal conductivity of a host medium is less than thermal conductivity of the adjacent medium. Thus, e.g., growing in air by condensation particle is attracted to a metal surface while an evaporating in air particle is repelled from a metal surface. The change of temperature distribution caused by heat...

THERMAL AND ELECTRODYNAMIC EFFECTS IN MELTING CURRENT-CARRYING CONDUCTORS

This work studies dynamics of melting in current‐carrying conductors. It is shown that during equilibrium melting, when the dynamics of a phase‐transition front are determined by a heat balance, there exists a single‐valued correlation between the rate of inductance change and a temperature at the phase‐transition front. It is demonstrated that, although surface melting begins at temperatures less than the melting temperature of the current‐free conductor, corrugation of a phase‐transition front occurs at this temperature. It is shown that the nucleation rate of nuclei flattened in the direction normal to a conductor’s axis is negligibly small. Current dynamics at the stage of melting are analyzed for the case of a fixed external voltage. It is demonstrated that there exists an instability stage at which an excitation of the electric current occurs. Conditions for the experimental observation of the predicted phenomena are discussed.

Dynamics of electromagnetic field in imploding conducting shell

In this study we derived explicit analytical solutions of two problems. First is a problem of accumulating of magnetic fields in imploding shells with different geometries. The second problem is determining the eigenmodes of a resonator with moving walls. Using the obtained exact solutions we found the regions of validity of an adiabatic approximation when the frequency of the resonator follows the instantaneous values of geometrical parameters, and the amplitude is determined by a conservation of a magnetic flux. The obtained solutions are of interest in design of devices for generation of ultrastrong magnetic fields and powerful electromagnetic radiation.

Ponderomotive forces in liquid conductors with macroscopic solid inclusions

This work studies the ponderomotive forces occurring in liquid conductors with macroscopic inclusions. It is shown that if the electric conductivity of inclusions is higher than the electric conductivity of the host medium then the inclusions are attracted to the axis of a conductor. In the opposite case the ponderomotive forces repel the inclusions towards the surface of a conductor. It is shown that if a certain relation between an amplitude and a frequency of an electric current is satisfied, the parametric resonance in the oscillations of the inclusions with electric conductivity higher than that in the bulk of the conductor can occur. The moments of the ponderomotive forces exerted on a particle of a nonspherical shape are determined. It is shown that the direction of the moment of a ponderomotive force alternates depending upon the sign of the difference between the electric conductivity of an inclusion and of the host medium.

Local heating of heterogeneous current-carrying conductors

We study the heating of current-carrying conductors with inclusions when the kinetic coefficients of inclusions are different from those of the conductor. It is shown that if the surface temperature of the conductor is maintained constant and the thermal conductivity of the inclusion is higher than the thermal conductivity of the conductor, the temperature distribution in the vicinity of the inclusion is strongly different from the temperature distribution in a homogeneous conductor. Depending on the parameters of the system the temperature at the location of an inclusion can be two times higher than the temperature at the same location without an inclusion. We investigate the behavior of the temperature difference as a function of the distance between the center of the spherical inclusion and the conductor’s surface. We analyze different components of Joule heating, which are associated with the change of the configuration of the electric current caused by the inclusion and with the change of temperature...

Levitation and oscillations of neutral particles in a constant electric field

We investigate oscillations of polarized particles embedded in a host liquid and subjected to a constant electric field. In the considered range of parameters there exist repulsion forces between particles which can cause particle levitation and oscillations in the system. We study the eigenfrequencies of oscillations of the levitated particle and demonstrate that oscillations frequency decreases when the amplitude of the electric field grows. Consequently, the lower frequency cut-off of the excited oscillations is determined by the maximum strength of the external electric field whereby the particle motion is not overdamped. The upper bound of the oscillations frequency is determined by the minimum strength of the electric field which is required for particle levitation. We analyze two simple geometrical configurations when a spherical particle is levitated by another immobilized spherical particle and the particle is levitated above the plane interface between two half-spaces with different permittivity...