Multi-physics modeling in the electromagnetic levitation and melting of reactive metals A. A. Roy * , V. Bojarevics, K.A. Pericleous CMS, University of Greenwich *Corresponding author: A.A.Roy@gre.ac.uk Abstract: The aim of this article is to demonstrate the capability of the software for predicting free-surface motion, internal fluid flow and temperature in an electromagnetically levitated sample of liquid metal. Multi-physics solutions which demonstrate the usefulness of Comsol as a powerful MHD simulation tool have been generated to two industrial problems using the ALE moving-mesh module in combination with the Navier-Stokes, Maxwell and General Heat transfer modules. The first problem, which has relevance to continuous casting of metal ingots in a cold crucible, considers the transient free-surface motion of a semi-levitated volume of metal when its shape is confined by the field of a solenoid. The ability to establish the steady- state profile of the melt is an important factor in determining power requirements and thermal losses. This can then be fed into a 3D model (with static geometry) to include the effects of joule heating and the influence of the finger segments. The second problem is concerned with the thermo-physical property measurement of reactive molten materials using a novel technique reported in [9]. Comsol is used to predict the surface motion, centre of mass oscillations and temperature fluctuation in a metal droplet suspended in the AC field of a solenoid. Keywords: Electromagnetic levitation, MHD, free-surface 1. Introduction Electromagnetic levitation has wide-ranging applications in metal processing - shape controlling, flow suppression, casting, property measurement etc. [1]. The technology relies on the use of an induction coil carrying AC current at medium/high frequency to melt and control the shape/temperature of a metal alloy (especially in an overheated state). A well known application is that of the “cold crucible” [2] which consists of a plurality of electrically disconnected water-cooled copper segments arranged in a circle, surrounded by an induction coil. These segments enclose the charge (typically of a titanium-based composition) which is melted by Joule heating via the induced eddy currents from the alternating magnetic field of the coils. Magnetic forces limit the contact area between the melt and the segments thereby reducing unwanted heat loss. The main advantage of cold-crucibles over conventional ceramic crucibles is that reactive materials can be melted with minimum contamination [3]. Section 2.1 focuses on the use of cold- crucible technology in the continuous casting of Ti metal ingots. Scrap metal is fed (eg. with a vibrating feeder) and melted using a multi-turn water-cooled induction coil at a given rate in the “bottomless” crucible (Fig. 1). The molten volume, which is a dome-shaped on top by the EM confinement force, is drawn downwards through a water-cooled sleeve (formed by the segments) using a mechanical withdrawal system [4]. A solidification front or “crust” develops which grows according to the rate at which heat is extracted. The procedure is conducted within an evacuated chamber. The same technology can be applied to casting Si ingots [6]. Figure 1. Continuous casting of metal ingots. It is known that the field seen by the charge is largely unaffected by the presence of the withdrawal mechanism ingot Melt pool Coil Scrap Vibratory feeder