Electrovortex Flow Research Articles

Transient behaviour of electrovortex flow in a cylindrical container

The mechanical behaviour of the oxide film that develops at the metal-air interface of molten A356 aluminum alloy is investigated in relation to the oxidation level. Based on two previous papers - the first one focusing on the chemical aspects of the oxidation process at the liquid surface of molten aluminum, the second one focusing on its mechanical characterization, the present paper aims at reconciling these two approaches usually considered separately in the literature and proposes a stand-alone mechano-chemical model. The oxidation process is first characterized from thermogravimetric analyses together with scanning electron microscopy imaging. Then the mechanical properties of the oxide layer are determined at a given oxidation level, making use of a new annular MHD surface viscometer placed inside a chemical reactor. The kinetic study delivers a better understanding of the oxidation process involved at the surface of the A356 alloy and leads to the development of a revised version of the Deal−Grove model. In addition, the mechanical study reveals the highly viscous and shear-thinning behaviours of the oxide layer. Figs 3, Refs 14.

Transient behaviour of electrovortex flow in a cylindrical container

This study is a continuation of the combined experimental and numerical investigation [1] of the flow of the eutectic GaInSn alloy inside a cylindrical vessel exposed to a constant electrical current. The emerging electrovortex flow driven by the interaction of the current, which is applied through a tapered electrode, with its own magnetic field might have both detrimental and advantageous effects in liquid metal batteries. While the former work [1] was mainly concerned with time-averaged results, this paper focuses on the transient behaviour of the electrovortex flow which becomes most relevant under the influence of an external axial field. The additional Lorentz force generated by the interaction of the imposed current with the vertical component of the geomagnetic field bz drives the ordinary electrovortex jet flow into a swirling motion. Velocity distributions and motion characteristics, such as spiral streamlines and shortened and irregularly swinging jet regions, are investigated. The mechanism is analysed in detail for bz = 25.5 {\mu}T. The maximum angular velocity of the rotating jet is basically linearly dependent on bz, at least for the values studied here. A good agreement between the transient simulation and the experimental result is shown.

The influence of a cylindrical cathode on the electro-vortex flow of liquid metal: Numerical simulations and laboratory experiments

The electro-vortex flow of a liquid metal in a cylindrical cell, placed into an external vertical magnetic field, in the case of an axial electric current application is studied numerically and experimentally. The results are compared to those previously obtained in the case of a localized electric current application. In the absence of the external magnetic field, the comparison shows no qualitative change in the flow structure. In the presence of the external magnetic field, a poloidal motion is suppressed. A critical magnetic field of poloidal suppression is shown to be approximately higher in the case of axial electric current application.

Experimental Study of the Velocity of the Electrovortex Flow of In-Ga-Sn in Hemispherical Geometry

The paper describes the application of the thermocorrelation method for measuring the velocity in a current-carrying liquid. An electrovortex flow occurs when the current passing through a conducting medium interacts with its own magnetic field. Measurements of the velocity of the turbulent electrovortex flow of the liquid metal (eutectic alloy In-Ga-Sn) were carried out in a hemispherical container in the range of currents of 100–450 amperes in the presence and absence of compensation of the Earth’s magnetic field. The efficiency of the thermocorrelation method in a current-carrying liquid has been demonstrated. The dependences of the axial velocity on the current and the velocity profiles along the axis were obtained. It was found that the presence of the Earth’s magnetic field leads to a significant decrease in the average value of the axial velocity in the entire range of currents.

The role of boundary conditions on the free surface of a liquid metal in an electrovortex flow

An electro-vortex flow between two hemispherical electrodes is considered. The influence of the type of boundary condition on the surface of a conducting liquid medium on the velocity field in the volume is studied numerically. The dependences of the velocity on the axis of the vessel on the radius of the small electrode and the parameter of the electric vortex flow are obtained for various types of boundary conditions on the surface.

Influence of pulsed modes of a magnetic field on an electric vortex flow

Using a fiber-optic velocity transducer, the effect of external pulsed magnetic fields on the structure of electrovortex flows is experimentally investigated. It is shown that an external pulsed magnetic field can lead to the appearance of oscillations of significant amplitude in a liquid metal.

Application of the video correlation method to measure the velocity on the surface of a liquid metal

In this work, the applicability of the video correlation method proposed by the authors for measuring the velocity on the surface of a liquid metal in an electrovortex flow in a hemisphere is investigated. The method is based on calculating the cross-correlation of the brightness signals of two closely spaced points in the video. It is shown that the method allows quite simply determining the velocity of the liquid metal.

A Numerical Study on the Influence of an Axial Magnetic Field (AMF) on Vacuum Arc Remelting (VAR) Process

A comprehensive numerical model is proposed to study the influence of an axial magnetic field (AMF) on the solidification behavior of a Titanium-based (Ti–6Al–4V) vacuum arc remelting (VAR) ingot. Both static and time-varying AMF are examined. The proposed 2D axisymmetric swirl model includes calculating electromagnetic and thermal fields in the entire system composed of the electrode, vacuum plasma, ingot, and mold. A combination of vector potential formulation and induction equation is proposed to model the electromagnetic field accurately. Calculations of the flow in the melt pool and solidification of the ingot are also carried out. All governing equations are presented in cylindrical coordinate. The presence of a weak AMF, such as the earth magnetic field, can dramatically influence the flow pattern in the melt pool. The “Electro-vortex flow” is predicted ignoring AMF or in the presence of a time-varying AMF. However, the flow pattern is “Ekman pumping” in the presence of a static AMF. The amount of side-arcing has no influence on the pool depth in the presence of an AMF. Modeling results are validated against experiments.

Modelling Rayleigh-Bénard convection coupled with electro-vortex flow in liquid metal batteries

Liquid Metal Batteries (LMBs) are a promising grid-scale energy storage technology that offers low costs per kilowatt-hour, high energy and current densities, as well as low fade rates. The all-liquid composition of the batteries, as well as the presence of temperature gradients and electric and magnetic fields, result in the occurrence of multiple fluid phenomena. These can affect the hydrodynamic stability of the battery, thereby making their interactions critical to understand. In this work, the interaction of Rayleigh-Bénard convection and Electro-vortex flow is investigated as these types of flow will be present in Liquid Metal Batteries from laboratory to grid-scale. A single-layer electrode is simulated, and the computed results compared with experimental data from the literature. It was found that Rayleigh-Bénard convection is unsteady in the liquid metal electrode. The introduction of a 2 A current stabilises the convection cells, whilst the introduction of a 40 A current leads to the dominance of Electro-vortex flow at the central region of the electrode. The results in this work match experimental data closer than previously published models offering insight into the interaction between Rayleigh-Bénard convection and Electro-vortex flow in the anodes of discharging Liquid Metal Batteries.

Efficient mixing by swirling electrovortex flows in liquid metal batteries

Abstract

Stirring of liquid metal in electrovortex flow in a hemispherical volume under the influence of external magnetic field

The results of calculations of the stirring rate of liquid metal in a system simulating a DC arc furnace are presented. The equations of motion and transfer of impurity were solved for the electric vortex flow of a liquid metal between two hemispherical electrodes under the influence of an external axial magnetic field. The quality of mixing was characterized by the deviation of the impurity concentration from the mean and was calculated at each time step. It is shown that the effect of an external magnetic field can both accelerate and slow down mixing. These results can be used in electrometallurgy to assess the effectiveness of electromagnetic stirring.

Evolution of a strong electrovortex flow in a cylindrical cell

The mechanism of poloidal flow suppression in an electrovortex flow is verified in a liquid metal experiment and supported by numerical simulations. The results are shown to be valid for both converging and diverging poloidal flows, as well as for solid and free upper boundaries. It is shown that the threshold value of the external magnetic field, above which the poloidal suppression occurs, is comparable with the magnetic field of Earth that is weak.

Asymptotic expansion of the solution of the equation of a slow axisymmetric electrovortex flow between two planes

Asymptotic expansion of the solution of the equation of a slow axisymmetric electrovortex flow between two planes

Simulation of the electrovortex flow in a linear approximation under the action of the external magnetic field

Electrovortex flows appear in a liquid metal when a non-uniform current interacts with its own magnetic field. They are very important in different electrometallurgical processes connected with melting of metals. We describe the electrovortex flow in a hemispherical container which is connected with experiment which is carried in Joint Institute of High Temperature. Our main aim is to study the influence of the extermal magnetic field, because the experiment shows that even weak Earth magnetic field can change the characteristics of the flow.To solve this problem we formulate a system of equations using Stokes approximation. They are solved with Thoms’ boundary conditions using the time marching method. Our numerical scheme gives us the opportunity to parallelize the computing process. For the calculations we use the CUDA technology. It allows us accelerate the calculation process, even if we use low-power user graphics cards. We hope that our experience can be used to solved another similar problems.

Analytical study of the velocity and pressure of the electrovortex flow in hemispherical bowl in a Stokes approximation

The problem of an electrovortex flow in a hemispherical bowl with an internal electrode is considered. In the framework of the Stokes approximation, analytical expressions for the velocity and pressure fields are obtained. Two types of boundary conditions were used: non-leakage on the entire boundary (with no-slip condition on the free surface and partly slip on the electrodes) and an approximate adhesion condition on the electrodes. The non-leakage condition corresponds to the homogeneous Dirichlet boundary condition for the vector potential and the vorticity on the entire boundary. An approximate adhesion condition is posed using the Thom difference approximation. The analytical expressions for the velocity and pressure fields are written uniformly for both types of boundary conditions.

Investigations of electrovortex flows with multi electrode power supply

Investigations of electrovortex flows with multi electrode power supply

Asymptotic Expansion of the Solution of the Equation of a Slow Axisymmetric Electrovortex Flow Between Two Planes

Electrovortex flows are of great interest both from the viewpoints of theoretical magnetohydrodynamics and applications. They arise when the electric current of variable density passes through a conducting medium (such as a liquid metal). The interaction between the current and self magnetic field of the current induces a nonpotential electromagnetic force that causes a vortex flow of the liquid. As a model problem, we consider a stationary flow between two parallel planes. The flow is described by the stream function for which we obtain a nonlinear fourth-order partial differential equation. For moderate values of the electrovortex flow parameter, we investigate the problem by the asymptotic series expansion in the powers of this parameter. We describe the process of successive approximations of various degrees and present the flow pattern that is given by two first terms. This asymptotic solution is shown to be rather close to the numerical solution of the problem.

An electrovortex flow around two fully submerged electrodes

Electrovortex flow (EVF) of liquid metal in container with submerged electrodes and bifilar current supply relates to problem of melt stirring in electrometallurgical aggregates like welding, electroslag remelting, direct current (DC) electrical arc furnaces (EAF) and others. Maximum values of electromagnetic (EM) force and flow velocity are developing in the region between electrodes. Sophisticated 3D flow patterns are forming around them. In presenting paper, the examples of measured electrical potential and 3D self-magnetic field of supplied DC in comparing with numerical calculation results as well as with quasi-2D model of EM fields are discussed. Several numerically computed 3D EVF patterns are presented for two regimes: i) laminar and ii) turbulent, which is obtained with LES (Large Eddy Simulation) approach. There is good qualitative and quantitative correspondence between experimentally obtained data and numerical computations results as well as with previously published results.

The influence of electric current application configuration on the electro-vortex flow structure of conductive medium in cylindrical cell

A numerical study of the liquid metal electro-vortex flows (EVF) in a closed cylindrical cell, the radius of which is equal to its height, is performed. A direct current of 1000 A is applied through the electrodes at the bottom cylinder face, and is collected at the entire surface of the cylinder top end face. Various configurations of electrode location are considered. Namely, from one to five electrodes are placed on the cylinder bottom end face. The three-dimensional fields of the conducting medium flow velocity in the cell are obtained as a result of numerical simulations. The EVF is non-stationary in all considered regimes. In the one-electrode case, the flow is poloidal and is represented by one large-scale vortex. In the multielectrode case, the flow consists of multiple small-scale vortices, the size and quantity of which depend on the configuration of the electric current application. At the same electric current value of 1000 A, the mean flow velocity and characteristic frequency of the process are higher for the localized current application — 6.4 and 2.5 times respectively.

Electro-vortex flow of liquid metal in a cylindrical cell with localized current supply and variable aspect ratio

Electro-vortex flow of liquid metal in a cylindrical cell with localized current supply and variable aspect ratio