Efficient Melt Stirring Using Pulse Sequences of a Rotating Magnetic Field: Part I. Flow Field in a Liquid Metal Column

Abstract

The use of a pulsed, rotating magnetic field (RMF) is presented as an auspicious method for obtaining an intensive stirring and mixing in a pool of liquid metal; the RMF pulses within a sequence have been applied with a constant or alternating direction. The resulting flow structure in a cylindrical liquid metal column has been explored by numerical simulations and by model experiments, using the ternary alloy GaInSn. Ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the vertical velocity. Both the numerical results and the velocity measurements demonstrate the capability of the proposed stirring regimes for overcoming the limited mixing character of conventional rotary stirring. The application of a time-modulated RMF offers considerable potential for providing an optimal flow pattern in a solidifying melt, for reasons of a well-aimed modification of casting properties.

Efficient Melt Stirring Using Pulse Sequences of a Rotating Magnetic Field: Part II. Application to Solidification of Al-Si Alloys

“…A comprehensive investigation of flow structures resulting from the use of an RMF pulse sequence of constant or alternating direction has been reported in Part I of this study. [12] Numerical simulations and flow measurements presented in that article show a considerable amplification of the meridional, secondary flow without additional acceleration of the primary, rotary motion. Hence, regardless of the intensive mixing occurring in the bulk, the impact on the free surface in terms of turbulent deflections is only small.…”

“…The experimental setup used for the isothermal flow measurements is almost identical with that configuration, which has already circumstantially described in Part I of this article. [12] The ternary eutectic alloy Ga68In20Sn12 has been used as model liquid. The velocity measurements in the present article were carried out in a cylinder made from perspex with the same inner sizes as been used for the solidification experiments.…”

On an Anomaly in the Modeling of Electromagnetic Stirring in Continuous Casting

“…As we have seen, this difference does not alter the time-averaged Lorentz force when the magnetic Reynolds is small enough and only one inductor frequency is used. However, in modulated EMS, [22][23][24] magnetic fields of different frequencies are applied and it is the intention that the resulting Lorentz force should have a constant time-averaged and a time-varying component; in this case, posing the correct boundary conditions for the magnetic field is vital for obtaining meaningful results from modeling.…”

Free dendrite growth under modulated flow in pure substances: two-dimensional phase-field simulations

“…In view of the recent effort to use temporally modulated RMF's [7,3] and tailoring the flow on the macroscale, an improved understanding is also required of the impact of the flow oscillations on the dendritic microstructure. Theoretical models exist which describe the operating state of the tip [8,9,10,11] (and references therein) under steady-state conditions for the purely diffusive growth of free dendrites, and even to some extent for the presence of flow.…”

“…we consider a thermal dendrite. In analogy to [7,3], where a sequence of Lorentz-force impulses was imposed on the melt, a sequence of velocity impulses is used here to model the periodic velocity variations, which are characteristic for this kind of modulated forced convection. To our knowledge the current work is the first numerical study of the effect of periodic-flow-induced forcing on dendrite morphology that responds qualitatively to phenomena as reported by Bouissou [5].…”