Parametric instability of a liquid metal sessile drop under the action of low-frequency alternating magnetic fields

A 2-D mathematical model is developed in order to simulate a parametric electromagnetic instability oscillation process of a liquid metal droplet under the action of low frequency magnetic field. The Arbitrary Lagrangian-Eulerian （ALE） method and weak form constraint boundary condition are introduced in this model for implementation of the surface tension and electromagnetic force on liquid droplet free surface. The results of the numerical calculations indicate the appearance of various regimes of oscillation. It is found that according to the magnetic field frequency various types of oscillation modes may be found. The oscillation is originated from an instability phenomenon. The stability diagram of liquid metal droplet in the parameter space of magnetic frequency and magnetic flux density is determined numerically. The diagram is very similar to that found in the so-called parametric instability.

Influence of the Slowly Rotating Transverse Magnetic Fieldon the Solidification of Metallic Alloys

In this work binary alloy of Pb-Sn is directionally solidified under transverse,slowly rotating magnetic field.For some alloys during directional solidification in the transverse magnetic field significant macrosegregation along the diameter of the ingot may appear if the growth velocity and magnetic field strength are chosen appropriately.This occurs as a result of thermoelectric current,driven by the applied temperature gradient at the solidification interface,and magnetic field interaction caused liquid phase forced convection(thermoelectrornagnetic convection). Magnetic field rotation velocity in chosen to be slow enough that induced electric current can be neglected but still fast enough not letting thermoelectromagnetic convection fully develop in the scale of crucible.In this case the effect caused by thermoelectromagnetic convection on the structure is expected to be different from the case with static magnetic field,which is already studied in many works.Newest experimental results as well as theoretical description and interpretation of the obtained results of direction solidification experiments under rotating magnetic field will be presented in this paper.Magnetic field of 0.5 T is created by rotating permanent magnet system driven by electric step motor.

Innovative Inductive Cold Crucible Configurations With Improved Efficiency

The inductive cold crucible is a very interesting tool for processing materials by magnetic field without pollution.It is more and more used in various areas like in aeronautic,photovoltaic,waste recycling industries and also for medical applications.As the cold cracible in its current state of art has a low energetic efficiency,the better comprehension of this process thanks to recently improved multiphysic modeling tools and experimental measurements gives some guidelines for experimenting new kinds of cold crucibles.These elements are presented in this paper, especially the numerical modeling and first tests operated on a'thin shaped cold crucible'which seems very promising concerning the efficiency improvement and also a better overheating of liquid charge.

Experimental Measurement of Both Kinetic and Total Mass Transfer Between Two Electromagnetically Stirred Molten Layers

In ladle metallurgical processing,two liquid layers,a metallic layer below a salty or oxide layer,are separated by an interface where mass exchanges occur by the way of a redox reaction.The mass transfer associated with such reaction is strongly dependent on the agitation of each phase as well of their interface.We use an experimental system able to melt separately metal and salt.Once these elements are molten a sampling system is used.The experimenter chooses the sampling times.Finally,the collected samples and the final metal and salt ingots are analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy(ICP-AES).During the experiments,both temperature and,intensity and frequency of the inducting current,are measured.Comparisons on experimental results are done varying the induction as well as the transferred element.

Numerical Description of Interface,Flows in an Electromagnetic Process Devoted to Liquid/Liquid Extraction

In ladle metallurgical process,two liquid layers,a metallic layer below a salty or oxide layer,are separated by an interface where mass transfers occur thanks to redox reactions.Such mass transfers are strongly dependent on the stirring of each phase.By means of induction,a cold crucible reactor can melt,confine and stir,without any physical contact,liquids at very high temperature,with opportunities for continuous treatment.To work on metal/salt couples of interest to industry,we built a facility to control and measure the full kinetic transfer of a pollutant from one layer to another.A numerical simulation of the experimental reactor is presented here.We calculate the flows in both salty and metallic layers taking into account of all the present phenomena in each liquid phase(i.e.electromagnetic stirring, buoyancy,turbulence)as well as at the interface(i.e electromagnetic shaping,viscous shear driving).The implementation of the couplings needed for the complete simulation is presented.A focus is done on the numerical description of the shear stress near the interface.Stationary flows for two inductor positions complete this short article.

Numerical Simulation of Fluid Flow Inside a Molten Liquid Metal Droplet Located in an Electromagnetic Induction Generated by Two Different Inducting Currents

Electromagnetic levitation of electrically conductive droplets by alternating magnetic fields is Sa technique used to measure the physical properties of liquid metallic alloys such as surface tension,viscosity,heat capacity.Experiments can be conducted in microgravity,to reduce electromagnetic stirring and shaping of the droplet.The inductor of the EML is composed of a single inductor which two types of voltage are imposed.This type of electrical installation generates a field to center the metallic droplet and another field to heat and excite it.We use a commercial code join to a homemade code to compute flows generated by inducting voltages recorded in the sounding rocket TEXUS-EML-2(Feb2008).In this flight,two samples(Cu75Co25 at%and A168,5Ni31,5 at%)of 8 mm diameter have been processed.

Parametric Instability of a Liquid Metal Sessile Drop Under a High Frequency Amplitude-Modulate Magnetic Field

The parametric instability behavior of a liquid mercury sessile drop under high frequency Amplitude-Modulate Magnetic Field(AMMF),i.e.a high frequency magnetic field(carder wave)modulated by a low frequency sine wave(modulate wave),is investigated experimentally.The free surface contour of the mercury drop is observed by a CCD camera while varying the frequency and amplitude of the high frequency AMMF.At a given frequency and amplitude,the edge deformations with an azimuthal wave numbers(modes n=3,4,5,6)were excited.

Experimental Investigation of the Natural and Forced Convection on Solidification of Sn-3wt.%Pb Alloy Using a Benchmark Experiment

We deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation,by means of a well-controlled solidification experiment.The experiment consists in solidifying a rectangular ingot of Sn-3wt.%Pb alloy,by using two lateral heat exchangers which allow extraction of the heat flux from one or two vertical sides of the sample.The domain is a quasi two dimensional parallepipedic ingot(100×60×10)mm.The temperature difference AT between the two lateral sides is 40 K and the cooling rate CR=0.03 K/s.The instrumentation consists in recording the instantaneous temperature maps by means of an array of 50 thermocouples in order to provide the time evolution of the isotherms.After each experiment the patterns of the segregations have been obtained by X-ray radiograph and confirmed by eutectic fraction measurements.The local solute distribution determined by means of induction coupled plasma analysis is provided.The originality of the present study is to examine the effect of the forced convection driven by a travelling magnetic field(TMF)induced by a linear inductor located on the bottom part of the sample.A periodically reversed stirring with a modulation frequency equal to 0.5 Hz stirring have been investigated.This study allows us to evaluate the evolution due to the forced convection induced by a TMF field,as well as its influence on the initial conditions,the solidification macrostructure and the segregation behavior.Measurements of the velocity field by ultrasonic Doppler velocimetry(UDV)method in a Ga-In-Sn pool were performed and transposed to the tin-lead alloy case before solidification.Post-mortem patterns of the macromesosegregations have been obtained by X-ray radiography.The results show the transport effects of the flow on both the maerosegregations and the channel formation.The reversal of the TMF produces a decrease of the level of mesosegregations,namely channel formation.