Magnetic levitation of large liquid volume

It is well known from experiments and industrial applications of cold crucible melting that an intense AC magnetic field can be used to levitate large volumes of liquid metal in the terrestrial conditions. The levitation confinement mechanism for large volumes of fluid is considerably different from the case of a small droplet, where surface tension plays a key role in constraining the liquid outflow at the critical bottom point. The dynamic interaction between the oscillatory motion of the free surface and the effects of turbulent flow is analysed using a unified numerical model, which describes the time dependent behaviour of the liquid metal and the magnetic field. The MHD modified k-? turbulence model is used to describe the mixing and damping properties at smaller scales not resolved by the macro model. The numerical multiphysics simulations suggest that it is possible to levitate a few kilograms of liquid metal in a cold crucible without requiring mechanical support from the container walls. Possible applications to the processing of reactive metals are discussed

MHD Stability in Aluminium Electrolysis Cells – From Complex to Simple Analysis

Numerical modelling has become a primary tool for design and optimization of commercial high amperage aluminium electrolysis cells. The design of industrial cells requires to account for a variety of their individual features: bus-bar network, cell bottom profile and side ledge, cathode bar design, ferromagnetic parts effect, operational adjustments due to the anode changes, etc. Analytical solutions in special cases provide benchmark tests and aid understanding of the basic physics. The commercial Trimet cell is analyzed using a simple theoretical, full numerical and advanced analytical problem solutions, which are compared with experimental measurements using wireless sensors to detect MHD instability onset

Large scale liquid metal batteries

Liquid metal batteries are possible candidates for large scale energy storage offering a possible breakthrough of intermittent wind and solar energy exploitations. The major concern over their practical implementation is the operation at elevated temperatures and sensitivity to liquid motion. The concept of liquid metal battery bears a close similarity to aluminium electrolytic production cells. The two liquid layer MHD effects can be projected to the three liquid layer self-segregated structure of the batteries. This paper presents numerical models for the three density-stratified electrically conductive liquid layers using 3D and shallow layer approximation accounting for specific MHD effects during periods of battery activity. It is demonstrated that a stable operation of these batteries can be achieved if reusing an infrastructure of existing aluminium electrolysis pot lines. The basic principles of the MHD processes in the cells are illustrated by the numerical example cases

Use of a Static Magnetic Field in Measuring the Thermal Conductivity of a Levitated Molten Droplet

Numerical models are used to analyze the complex behaviour of magnetically levitated droplets in the context of determining their thermophysical properties. We focus on a novel method reported in Tsukada et al. [4] which uses periodic laser heating to determine the thermal conductivity of an electromagnetically levitated droplet in the presence of a static DC field to suppress convection. The results obtained from the spectral-collocation based free surface code SPHINX and the commercial package COMSOL independently confirm and extend previous findings in [4]. By including the effects of turbulence and movement of the free surface SPHINX can predict the behaviour of the droplet in dynamic regimes with and without the DC magnetic field. COMSOL is used to investigate arbitrary amplitude axial translational oscillations when the spherical droplet is displaced off its equilibrium. The results demonstrate that relatively small amplitude oscillations could cause significant variation in Joule heating and redistribution of the temperature. The effect of translational oscillations on the lumped circuit inductance is analysed. When a fixed voltage drive is applied across the terminals of the levitation coil, this effect will cause the coil current to change and a correction is needed to the electromagnetic force acting on the droplet

Modelling the formation and breakup of particle clusters in metal melt subjected to external fields

Aluminium and magnesium based metal matrix nano-composites (MMNC) with ceramic nano-reinforcements promise low weight with high durability and superior strength, desirable properties in aerospace, automobile and other applications. However, due to the small size of the particles, adhesion force between becomes significant which leads to particle agglomeration. Large clusters of nano-particles are detrimental for the final properties of the MMNC. To prevent agglomeration and to break up clusters, ultrasonic processing is used via an immersed sonotrode, or alternatively via electromagnetic vibration. The collapse of the cavitation bubbles as a result of ultra-sonication is believed to be the main mechanism of breaking up the clusters of nano-particles. The complex interaction of flow and co-joint particles subjected to the shockwave induced by cavitation is addressed in detail using a discrete-element method (DEM) code. Adhesive, elastic and frictional forces between the particles are incorporated and various models of adhesion are compared

Cold crucible melting with bottom pouring nozzle

Cold crucible melting technique with electromagnetic induction is used to obtain reactive metal castings and produce high quality metal powders for aerospace, automotive and medical applications. An important part of this technology is the nozzle used to pour the molten alloy through the bottom opening. The paper uses mathematical modelling technique, previously validated on multiple similar cases, to investigate a new type of non-consumable nozzle made of copper segments. The design of the nozzle requires to satisfy the narrow balance between the thin solidified protective layer on the wall while avoiding the blockage of the outflow if the nozzle is frozen completely. The sensitivity of the outflow to the nozzle diameter is investigated. The AC electromagnetic force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the melt shape dynamics and the heat loss to walls. The beneficial features of the cold crucible melting to purify the melt from particulate contamination are explained using the particle tracking for the full melting and pouring cycle

Demo retrofit study of a Chinese inspired cell technology

For many years, the authors have been demonstrating their cell modeling tools and cell retrofit skills using those modeling tools to present demonstration cell retrofit studies. One recent series of cell retrofit studies leads to the presentation of a cell design predicted to be able to operate at 10 kWh/kg of Al. The authors now embark on a new demonstration retrofit study this time using a Chinese cell technology inspired base case as a starting point. There are plenty of public domain information on Chinese cell technology: potshell, busbar and lining design, so that Chinese cell technology inspired base case cell design is quite similar to existing Chinese cell technologies. This first retrofit study aims at demonstrating the huge potential of productivity increase that those existing Chinese cell technologies represent without compromising the power efficiency

Vacuum arc remelting time dependent modelling

Vacuum arc remelting (VAR) aims at production of high quality, segregation-free alloys. The quality of the produced ingots depends on the operating conditions which could be monitored and analyzed using numerical modelling. The remelting process uniformity is controlled by critical medium scale time variations of the order 1-100 s, which are physically initiated by the droplet detachment and the large scale arc motion at the top of liquid pool [1,2]. The newly developed numerical modelling tools are addressing the 3-dimensional magnetohydrodynamic and thermal behaviour in the liquid zone and the adjacent ingot, electrode and crucible

Modelling the cold crucible pouring dynamics

The paper uses the mathematical modelling technique to investigate cold crucible operation with a non-consumable nozzle made of copper segments. The combination of two coils, one for the main crucible and the other for the nozzle with different power supplies, requires to superpose the effects of the two independent AC electromagnetic force fields. This leads to complex transitional flow structures and turbulence of the melt, contributing to the melt shape dynamics and the heat loss to the walls to satisfy the narrow balance between the thin solidified protective layer while avoiding the blockage of the outflow if the nozzle is frozen. The sensitivity of the outflow to the nozzle diameter is investigated. The beneficial features of the cold crucible melting to purify the melt from particulate contamination are explained using the particle tracking during the pouring process