DE102004017443B3 - Device for stirring electrically conducting liquids in a container to control material and heat exchange comprises a control/regulating unit with an interrupting unit and a computer - Google Patents

Abstract

Device for stirring electrically conducting liquids (2) in a container (3) comprises a control/regulating unit (5) with an interrupting unit (6) and a computer (7). The interrupting unit interrupts a rotating magnetic field after reaching the maximum Stokes flow region in a specified time interval. An independent claim is also included for a process for stirring electrically conducting liquids in containers using the above device.

Description

The The invention relates to a method and apparatus for stirring electrically conductive liquids in containers, in which by rotation of a magnetic field by means of centrally symmetrical opposed and outside the container Induction coils an azimuthal flow and a meridional flow in the quasi-Stokes flow regime within the conductive fluid be generated.

Become conventional permanently rotating electromagnetic fields for flow control as well as to control the fabric and heat transfer of conductive liquids in belonging shaped containers, used in particular in cylindrical containers.

Becomes an electrically conductive liquid such as a molten metal an external electromagnetic field, that in outside of the container arranged electromagnet is generated, are exposed in the melt eddy currents induced. The eddy currents in turn practice through feedback with the magnetic field a Lorentz force out to the melt. In this case, the electromagnets are made respectively two opposite ones Induction coils.

Become especially around the cylindrical one container for the Molten metal arranged several electromagnets, can be an electromagnetic Rotating field generates and stirring the molten metal to be effected, wherein a primary, the azimuthal flow arises.

The permanently rotating magnetic field at a constant angular frequency is applied to the liquid metal filled cylindrical container. The magnetic field of the induction coils induces an axially symmetric Lorentz force F _L , which is azimuthally oriented, and thus causes a rotation of the liquid. The induced Lorentz force F _L consists of two components: a time-independent and a time-dependent component oscillating at twice the frequency. The latter has a relatively small effect on the melt flow, as described in the publication Physics of Fluids, 11, 1821-1826, 1999: Nonaxisymetric flow in a finite-cylinder with a rotating magnetic field.

die Reynolds-Zahl

entsprechend der Rotation des Magnetfeldes, die relative Frequenz des Magnetfeldes ω = μ₀σωR² und das auf den Behälter bezogene Größenverhältnis

Die Hartmann-Zahl H_a und Reynolds-Zahl Re_ω können zur Taylor-Zahl Ta = Ha²Re_ω zusammengefasst werden.The interaction between a constant angular velocity or rotating magnetic field and a conducting liquid depends on various parameters, such as the material properties of the conductive liquid (kinematic viscosity ν, density ρ, electrical conductivity σ, magnetic permeability μ ₀ ), the properties of the rotating magnetic field (magnetic induction B, angular frequency of the magnetic field ω = 2πf, where f is the AC frequency, further the ratio of the number of poles to the number of phases in the respective source p), as well as the geometry of the container (height H and radius R in a cylinder) , The parameters can be divided into the following dimensionless numbers: The Hartmann number

the Reynolds number

according to the rotation of the magnetic field, the relative frequency of the magnetic field ω = μ ₀ σωR ² and the size ratio related to the container

The Hartmann number H _a and Reynolds number Re _ω can be combined to form the Taylor number Ta = Ha ² Re _ω .

festgelegt, woraus sich die folgenden azimutalen Geschwindigkeits- und Zeitskalen ergeben:

For the scaling of the speeds and times, the angular velocity of the magnetic guide

which gives the following azimuthal velocity and time scales:

The Definition of the reference speed reference speed and times for the unification of the permanently rotating magnetic field induced Vortex characteristics.

Of the Use of rotating magnetic fields for flow control and control the mass and heat transfer in conductive liquids while The solidification is in the metal and semiconductor industry meanwhile widely used, as in the publications Journal Metals, 167, 31-37 1984: Electromagnetic stirring and continuous casting Problems and goals, and Acta Astronautica, 37, 333-345, 1995: Electromagnetic field application in the process of single crystal growth under microgravity, is described. In doing so, by stirring Metal and semiconductor melts, in particular the generation of a vortex flow by a permanently rotating Magnetic field each pursued different goals.

In The metallurgy is said to stir the formation of a fine-grained Favor structure in the solidifying alloy, which is why a highly intensive flow necessary to obtain globulitic grains. During the Crystal growth, the permanently rotating magnetic field is used, on the one hand, caused by thermal convection temperature fluctuations On the other hand, the homogeneity of the melt in the vicinity of the solidification front to improve, whereby the crystal quality is increased. Both applications use the effect of the appearance of a secondary, the meridional flow in the melt due to the permanently rotating magnetic field induced azimuthal flow, as in the Cambridge University Press, 431, 2001: An Introduc tion to Magnetohydrodynamics, described as the meridional flows in the Essentially the heat / mass transfer in the liquid Determine phase of a solidifying material, as in the Publications Acta Astronautica, 37, 333-345, 1995: Electromagnetic field application in the process of single crystal growth under microgravity and Magnetohydrodynamics, 37, 337-347, 2001: Influence of alternating magnetic field on the hydrodynamics and heat / mass transfer in the processes of bulk single crystal growth.

One Another method for producing a metal strip by a continuous pouring of molten metal between two casting rolls a roll strip casting machine is described in document WO 03/024643 A2. Above the Melt bath near the respective transition melt surface / casting roll in a boiler ever a magnetic rotating field and thereby in the Melt local eddy currents generated. In the melt, a surface flow is created, which leads to the middle level, i.e. is directed to the exit plane of the metal strip. Thereby becomes an undesirable premature solidification of the molten metal along the cast roll edges prevents and the impurities and oxides are from the casting rolls transported away. The excitement of the electromagnetic rotating field carried out by multiphase alternating current with sinusoidal, rectangular or differently shaped Pulse shapes, whereby frequency and intensity are adjustable. It also can rotating permanent magnets are used, which surround the container.

Another method for continuous metal casting is in the document US Pat. No. 6,513,575 B1 described. Via a dipping pouring tube, the liquid metal is blasted into the mold. There are unwanted vibrations. The mold container is surrounded by electromagnets in this area. A static and a superimposed varying field can be generated. The field can assume different pulse shapes and be switched on and off at different times. This can be done regularly or stochastically.

The Problem is that all this, however, only to dampen the liquid Metal serves.

A device for stirring molten metal is in the document US 5 279 351 A described, wherein the metal is fed to a continuous casting process. The device consists of a plurality of induction coils, which are arranged around the container containing the metal. At least half of the induction coils caused by the electromagnetic rotating field a first rotational movement in the liquid metal, the other part causes a second rotational movement in the opposite direction of rotation, wherein the control and the phase change of the induction coils takes place in such a way that the two rotational movements of the liquid metal additionally move around the central casting axis.

Furthermore, a method and an apparatus for stirring molten aluminum alloys in the document are US 20020186616 A1 described. In this case, several, separately controllable induction coil systems are arranged around the melting vessel, which cause on the one hand circular movements of the melt and on the other cause a longitudinal movement, so that the overall result of the superposition of a spiral movement of the melt.

there always occur next to the azimuthal flow, the meridional currents and Whirling on, but in the known application solutions the meridional flow or the kinetic energy present there is not essential plays.

Of the Invention is based on the object, a method and an apparatus to stir of electrically conductive liquids in containers specify that are designed such that the kinetic energy of the meridional flow elevated and thereby the heat and / or mass transfer can be improved. It should also be guaranteed be that flow by a specification of a high magnetic number of tachyons in quasilaminaren or non-linear flow areas remains.

The object of the invention is solved by the features of claims 1 and 7. In the method of stirring electroconductive liquids in containers in which an azimuthal flow and a meridional flow are generated in the quasi-Stokes flow area inside the conducting liquid by rotation of a magnetic field by means of centrally symmetric and out-of-vessel induction coils Characteristic part of claim 1 after reaching the maximum of the Stokes flow range, the rotating magnetic field a change of switching on and off the magnetic field in a time interval .DELTA.t / At * Δt = t fm - t lam (dimensioned) (Ia) or Δt * = t fm * - t lam * (dimensionless) (Ib) and the liquid is subjected to an oscillating Lorentz force F _PRMF ,
wherein t _fm corresponds to the time t _IN1 of reaching the first minimum of the volume-average speed of the meridional flow after switching off the magnetic field to which the magnetic field is again switched on,
and wherein tlam is equal to the time t _OFF1 of reaching the first maximum of the volume average velocity of the meridional flow after the magnetic field, at which the magnetic field is first switched off, is switched on,
equivalent.

According to the invention Condition fulfilled by the switching on and off of the rotating magnetic field and Although such that the shutdown of the induced Lorentz force in the maximum of the time course of the volume-averaged meridional Speed and shutdown in the following minimum and so on continues, where t * dimensionless can be specified to an execution-independent representation for the different predetermined and possible Get applications.

advantageous Further developments of the method are the subject of the dependent claims.

als volumengemittelte azimutale Geschwindigkeit und

als volumengemittelte meridionale Geschwindigkeit mit dem Volumen V = πR²H verwendet, wobei der Zylinderbehälter den Radius R und die Höhe H aufweist.To characterize the azimuthal flow and the meridional flow, their velocities U _θ and U _rz , which are averaged over the volume V, are given by:

as volume average azimuthal velocity and

used as the volume-averaged meridional velocity with the volume V = πR ² H, wherein the cylinder container has the radius R and the height H.

With the optional specification of a high Taylor magnetic number T _a is left in the quasi-laminar and non-linear Stokes flow range.

In the Stokes flow region is then preferably worked when a periodic input and Shutdown of the rotating magnetic field is performed.

ist.For a cylinder with a size ratio of A ≠ 1, the duration of the time interval Δt / Δt * is given from the ratio Δt * = t * / fm -t * / lam (dimensionless) or non-dimensionless with Δt = t _fm -t _lam , in which

is.

wobei k nur INTEGER (ganzzahlig nach unten abgerundet) sein kann, z. B. int(1.9) = 1, wobei

sowie J₁ Bessel-Funktion erster Art und λ_k die Wurzel von J₁(x) = 0 sind,
und wird zur Speicherung in die Rechnereinheit eingegeben.The control _{equation according to the} invention for the periodic switching on / off of the Lorentz force F _PRMF is given with:

where k can only be INTEGER (rounded integer down), e.g. B. int (1.9) = 1, where

and J ₁ Bessel function of the first kind and λ _{k are} the root of J ₁ (x) = 0,
and is entered into the computer for storage.

In the apparatus for stirring electrically conductive liquids in containers in which Ro tion of a magnetic field by means of centrally symmetrically opposed and located outside the container induction coils azimuthal flow and a meridional flow in the quasi-Stokes flow region are generated within the conductive liquid is according to the characterizing part of claim 7, a control / regulating device with at least one interruption device and a computer unit, the interruption means for interrupting the rotating magnetic field after reaching the maximum of the Stokes flow range in a time interval Δt / Δt * of Δt = t fm - t lam (dimensioned) (Ia) or Δt * = t fm * - t lam * (dimensionless) (Ib) is provided,
wherein t _fm corresponds to the time t _IN1 of reaching the first minimum of the volume average velocity of the meridional flow after switching off the magnetic field to which the magnetic field is turned on again,
and wherein t _lam * the time t _OFF1 of reaching the first maximum of the volume-average speed of the meridional flow after switching on the magnetic field at which the magnetic field is first turned off,
equivalent.

advantageous Further developments of the device are the subject of the dependent claims.

Of the container is preferably cylindrical and may consist of a cylinder jacket and consist of a bottom and optionally a lid.

The Electromagnet system can have at least three pairs of induction coils each having the induction coils of a pair centrally symmetric to the central axis around the container are arranged around.

The Induction coil pairs are usually of the container shell separated by an air gap.

The Induction coil pairs are over Supply lines connected to the control / regulating device.

The control unit associated with the interruption arrangement is provided for performing the switching change .DELTA.t / .DELTA.t * of the electric current for periodically changing the Lorentz force F _PRMF and includes a controlled, the change of switching on and off performing power circuit breaker for the induction coil _pairs the interruption arrangement is designed optionally with electronic components as hardware and / or with program-technical means as software.

Of the container can be related to the thermostat, the temperature the liquid accordingly keeps the temperature preset constant or on it.

• – Eine Energieersparnis von etwa 50% bei gleicher Wirkung,
• – eine Erhöhung des relativen Verhältnisses von meridionaler zu azimutaler kinetischer Energie,
• – eine Verringerung des Turbulenzgrades, insbesondere für Verfahren zur Kristallzüchtung,
• – das Rührverfahren ist für chemische Reaktionen vorgesehen, wenn eine „unveränderliche" Grenze zwischen zwei reagierenden Flüssigkeiten bei hoher Fließgeschwindigkeit zu erreichen ist und
• – eine Erzeugung regelmäßiger Temperaturschwankungen in der Gießereitechnik, z.B. zum Schmelzen und Erstarren an der Erstarrungsfront, wobei das globulitische Dendritenwachstum frühzeitiger einsetzen soll.

The invention opens up the following possibilities:

• - an energy saving of about 50% for the same effect,
• An increase in the relative ratio of meridional to azimuthal kinetic energy,
• A reduction in the degree of turbulence, in particular for methods of crystal growth,
• - The stirring method is intended for chemical reactions, if an "immutable" boundary between two reacting liquids can be achieved at high flow rates, and
• - A generation of regular temperature fluctuations in the foundry technology, for example, for melting and solidification on the solidification front, the globulitic dendrite growth should begin earlier.

• – In der Metallurgie, insbesondere zum Rühren von Metallen, beispielsweise zur Verbesserung des Überganges von kolumnaren zu globulitischen Dendriten,
• – bei Verfahren der Kristallzüchtung, insbesondere zur Verringerung von Kristalldefekten durch Reduzierung des Turbulenzgrades und
• – in der chemischen Industrie, insbesondere zur Beseitigung von Instabilitäten zwischen zwei reagierenden chemischen Flüssigkeiten.

As a result, the invention can be used in particular in the following fields of application:

• In metallurgy, in particular for stirring metals, for example to improve the transition from columnar to globulitic dendrites,
• In crystal growing processes, in particular for reducing crystal defects by reducing the degree of turbulence and
• - in the chemical industry, in particular to eliminate instabilities between two reacting chemical liquids.

The Invention is based on an embodiment closer by means of several drawings explains: It demonstrate:

1 a schematic representation of the device according to the invention for stirring liquid metal in a closed cylindrical container in plan view,

2 a schematic representation of the apparatus for stirring liquid metal in a closed cylindrical container in side view 1 .

3 a schematic representation of the apparatus for stirring liquid metal in an open cylindrical container in side view 1 .

4 a representation of the ratio of meridional to azimuthal flow velocity as a function of time for a finite closed cylinder with the radius 25mm and a height of 50mm, at an AC frequency of 50Hz,

• a) bei geschlossenem Zylinder,
• b) bei offenem Zylinder,

5 a representation of the ratio of meridional to azimuthal flow velocity as a function of the Taylor number Ta:

• a) with the cylinder closed,
• b) with the cylinder open,

6 a representation of the time course of the dimensionless meridional volume-averaged velocities with the single elimination of the Lorentz force after t * = t * _lam = 4.5 and without elimination of the Lorentz force for closed cylinders with a radius of 25mm and a height of 50mm, at a AC frequency of 50 Hz, wherein the ratio of the poles p = 1 and the magnetic induction B equal to 1mT (Ta = 3 × 10 ⁵ ),

• a – laminare Stokessche Strömung mit t*_lam = 4,5;
• b – nicht-lineare Strömung, Spin-up t*_fm = 6,3;
• c – Spin-down ab t* = 6.3 mit einer Ausschaltung der Lorentz-Kraft nach t* = t*_lam,

7 a representation of the time course of the meridional flow during the turn-on in the spin-up phase and the turn-off in the spin-down phase

• a - laminar Stokes flow with t * _lam = 4,5;
• b - non-linear flow, spin-up t * _fm = 6.3;
• c - Spin-down from t * = 6.3 with elimination of the Lorentz force after t * = t * _lam ,

8th a representation of the time course of the ratio of the oscillating Lorentz force F _PRMF to the permanent Lorentz force F _RMF through the use of the on and off _{function according} to the invention,

9 a representation of the spatial distribution of the Lorentz force in a cylinder with a radius of 25mm and a height of 50mm at a magnetic induction of 1mT and frequency ν _B = 50Hz,

10 a representation of the time course of the volume-averaged azimuthal ( 10a ) and meridional ( 10b ) Velocities in each case depending on the permanent Lorentz force and the oscillating Lorentz force in a closed cylinder,

• a – in dem erfindungsgemäßen Zeitintervall Δt* = 1.8,
• b – in verschiedenen Zeitintervallen Δt* ≠ 1.8 und dem erfindungsgemäßen Zeitintervall Δt* = 1.8 zum Vergleich,

11 a plot of the ratio of meridional to azimuthal flow velocity as a function of time for a closed finite cylinder with a radius of 25mm and a height of 50mm at an AC frequency of 50Hz, a pole ratio p of 1, a magnetic induction of 1mT at the Taylor Number of (Ta = 3 · 10 ⁵ ) and

• a - in the time interval Δt * = 1.8 according to the invention,
• b - in different time intervals Δt * ≠ 1.8 and the time interval Δt * = 1.8 according to the invention for comparison,

12 a representation of the meridional velocity field at different times at constant Lorentz force F _L ,

13 a representation of the meridional velocity field at different times with an oscillating Lorentz force F _PRMF (with index PRMF: oscillating rotating magnetic field),

14 a representation of the concentration pattern of liquid tin (mass%) at different times at constant Lorentz force F _L ,

15 a representation of the concentration _pattern of liquid tin (mass%) at different times with oscillating Lorentz force F _PRMF and

16 a representation of the time courses of the temperature T at different points z of the central axis of the liquid metal column in a cooling from below, preferably by means of a thermostat.

The following are the 1 . 2 and 6 considered together. In the method for stirring a conductive liquid, eg, liquid tin 2 in a container 3 in which by rotation of a magnetic field by means of centrally symmetrically opposite and outside the container 3 located induction coils 11 . 12 . 13 an azimuthal flow 22 and a meridional flow 23 Flow in the quasi-Stokes flow area within the conductive fluid 2 are generated, according to the invention, after reaching the maximum of the Stokes flow range, the rotating magnetic field a change of switching on and off in a time interval .DELTA.t / .DELTA.t * of Δt = t fm - t lam (dimensioned) (Ia) or Δt * = t fm * - t lam * (dimensionless) (Ib) and the liquid 2 subjected to an oscillating Lorentz force F _PRMF ,
where t _fm , as in 6 the time t _IN1 of reaching the first minimum of the volume _average velocity U _{rzmin1 of} the meridional flow is shown 23 after switching off the magnetic field to which the magnetic field is turned on again, and
where t _lam the time t _OFF1 of reaching the first maximum of the volume- _average velocity U _{rzmax1 of} the meridional flow 23 after switching on the magnetic field to which the magnetic field is switched off for the first time,
correspond.

In 1 is a schematic representation of a device 1 for stirring a conductive liquid 2 , eg liquid tin in a container 3 shown. The device 1 essentially indicates the closed cylindrical container 3 who in 1 in plan view and in 2 is shown as a half longitudinal section with the r, z coordinates substantially at r = 0 to r = R, and an electromagnetic system 4 for generating a rotating magnetic field (RMF: rotating magnetic field) and a control / regulating device 5 with at least one interruption device 6 and a computer unit 7 on.

In detail, the container represents 3 a closed cylinder container which consists of a cylinder jacket 8th as well as from a soil 9 and a lid 10 consists.

The electromagnetic system 4 has three pairs 11 . 12 . 13 of induction coils, wherein each of the induction coils of a pair is centrally symmetric to the central axis 14 around the container 3 are arranged around. In the container 3 is the conductive liquid 2 , The induction coil pairs 11 . 12 . 13 are from the container jacket 8th through an air gap 15 arranged separately. The container 3 can on a frame 25 stand and / or with a thermostat 24 be connected. The induction coil pairs 11 . 12 . 13 are via supply lines 16 . 17 . 18 . 19 . 20 . 21 with the control device 5 connected to the computer unit 7 for controlling the oscillating rotating magnetic field. As oscillation of the rotating magnetic field, the repetitive switching change between switching on and off of the rotating magnetic field is defined.

In the control unit 5 is at least a computer and evaluation unit 7 as a computer as well as an interruption arrangement 6 to perform the switching change .DELTA.t / .DELTA.t * of the electric current for periodically changing the Lorentz force F _PRMF included. The interruption arrangement 6 can provide a controlled circuit breaker for the pairs of inductors performing the changeover from on and off 11 . 12 . 13 contain. The interruption arrangement 6 can be realized with electronic components, such as timers and gates as hardware and / or programmatic means as software.

In the 2 . 3 are schematic representations in side view of the container 3 in function of the device 1 occurring essential flows: the azimuthal flow 22 and the meridional flow 23 shown. In 3 is similar to that 2 a side view of a lid-free open container shown.

The container 3 can with the thermostat 24 related, for example, the temperature of the liquid 2 keeps constant according to the temperature specification.

The walls of the cylindrical container 3 can be considered thin walls whose conductivity is equal to that of the liquid metal 2 is identical, be formed. The lid 10 and the ground 9 of the cylindrical container 3 are electrically isolated.

In 4 Figure 12 is a plot of the ratio of meridional to azimuthal flow velocity as a function of time for a finite closed cylinder 3 with the radius 25mm and a height of 50mm at an AC frequency of 50Hz depending on the increasing Taylor number shown.

als volumengemittelte azimutale Geschwindigkeit und

als volumengemittelte meridionale Geschwindigkeit für den Zylinderbehälter 3 verwendet.After switching on the rotating magnetic field, the axisymmetric acceleration of the driven by the rotating magnetic field molten metal flow is provided. During acceleration (spin-up), the meridional flow indicates 23 different internal structures. After reaching the intended maximum speed is the kinetic energy of the meridional flow 23 at the Taylor number Ta> 10 ⁵ at 10% of the azimuthal flow, as in 4 is shown. But during the first phase of the laminar spin-up, the ratio for all Taylor magnetic numbers is 25%, as in 4 is shown. To characterize the azimuthal flow 22 and the meridional flow 23 are the volume-averaged velocities U _θ and U _rz with:

as volume average azimuthal velocity and

as volume average meridional velocity for the cylinder vessel 3 used.

As a supplement shows 5 in that, depending on the magnetic Taylor number T _a, the ratio between the meridional and the azimuthal flow strengths of the liquid 2 has its maximum in Stokes' flow. In 5 is the ratio of meridional to azimuthal flow velocity as a function of the Taylor number Ta: In 5a with closed cylinder and in 5b with the cylinder open, shown.

Of the Stokes flow range is part of the quasi-Stokesschen flow area and mainly points laminar flow conditions on. According to the invention can in quasi-Stokes flow regime be worked when a periodic disconnection and / or activation of the rotating magnetic field after reaching the maximum of Stokesschen flow area carried out becomes.

In diesem Zeitpunkt t_AUS1 ist die laminare Stokessche Strömung bei der Geschwindigkeit U_rzmax1 maximal entwickelt.In 6 are the time course of the dimensionless meridional volume-averaged velocities with the single elimination of the Lorentz force (dashed) after the first maximum of U _rz at time t * = t * / lam = 4.5 and without elimination of the rotating magnetic field (not dashed) for closed Cylinder with a radius of 25mm and a height of 50mm, at an AC frequency is 50Hz, with the ratio of the poles p = 1 and the magnetic induction B equal to 1mT (Ta = 3 x 10 ⁵ ). The 6 shows the following result: Starting from the point of view of energy saving, wherein the speeds U _rz (t) with the Lorentz force and without Lorentz force at time t * = t * / fm differ only by 15%, is the time for switching off according to the invention of the rotating magnetic field at the time

At this time t _AUS1 , the laminar Stokes flow is maximally developed at the velocity U _rzmax1 .

Starting from the same point of view, the point in time for re-engagement of the magnetic field _{according to the invention is the instant} t * / fm = 6.3, which corresponds to the first minimum U _rzmin1 in the course of the volume- _averaged meridional velocity U _rz . The next switching change with the switch-off again is after Δt * = t * / fm - t * / lam = 1.8 ± 1% at t _AUS2 = 8.2 etc.

In the 7 are representations of the time course of the meridional flow during the turn-on in the spin-up phase and the turn-off in the spin-down phase with
7a The laminar Stokes flow at t * _lam = 4.5;
7b - the non-linear flow, with spin-up at t * _fm = 6.3 and
7c - the spin-down from t * = 6.3 with an elimination of the Lorentz force after t * = t * _lam - shown.

The structure of the meridional flow 23 corresponding to the first maximum and the first minima of U _rz at the times t * _lam and t * _fm , which are based on the 6 are referred to in 7a and in 7b shown. In 7c becomes the structure of the meridional flow 23 shown according to the time t * = t * _fm . In this case, the Lorentz force is switched off after t = t _lam .

That means the 7a represents a meridional flow structure at velocity (U _rzlam / U _ref ) _max at time t _AUS1 at t _lam . The 7b shows the meridional flow structure at speed (U _rz / U _ref ) ₁ at time t _EIN1 with permanent Lorentz force and 7c represents the meridional flow structure at the velocity (U _rz / U _ref ) ₂ at the same time t _IN1 after elimination of the Lorentz force.

Auch bei einem Zylinder ohne Deckel, wie in 3 gezeigt ist, oder mit einem Größenverhältnis mit A ≠ 1 wird die Dauer des Zeitintervalls Δt* aus dem Verhältnis Δt* = t * / fm – t * / lam (dimensionslos) oder mit Δt = t_fm – t_lam (in Sekunden) vorgegeben.In 8th is the time course of the ratio of the oscillating Lorentz force F _PRMF to the permanent Lorentz force F _RMF by the use of the following inventive turn-on and turn-off (IV) shown. The first interruption (first switch off) of the magnetic field takes place at the time t _OUT1 when the maximum of the Stokes flow range is reached. The _reconnection takes place at the time t _ON1 , then again on-off at the time t _OFF2 . The interruption of the magnetic field and thus the Lorentz force takes a break of eg Δt * = 1.8 long. The number 1.8 only applies to closed cylinders 3 with size ratio

Even with a cylinder without cover, as in 3 is shown, or with a size ratio with A ≠ 1, the duration of the time interval .DELTA.t * from the ratio .DELTA.t * = t * / fm - t * / lam (dimensionless) or with .DELTA.t = t _fm - t _lam (in seconds) ,

für die periodischen Ein-/Abschaltung der Lorentz-Kraft F_PRMF,
mit

k kann nur INTEGER (ganzzahlig nach unten abgerundet) sein, z.B. int(1.9) = 1, wobei die Lorentz-Kraft F_L gleich:

sowie J₁ Bessel-Funktion erster Art und λ_k die Wurzel von J₁(x) = 0 sind.Due to the process steps set out above and the course of the quotient of the permanent and the oscillating Lorentz forces in 8th This results in a control equation that is in the computer unit 7 is saved with

for the periodic _activation / deactivation of the Lorentz force F _PRMF ,
With

k can only be INTEGER (rounded integer down), eg int (1.9) = 1, where the Lorentz force F _{L is} equal to:

and J ₁ Bessel function of the first kind and λ _{k are} the root of J ₁ (x) = 0.

The analysis of 8th shows that with oscillating rotating magnetic field 50% energy is saved.

The spatial shape of the Lorentz force F _PRMF for the selected cylindrical geometry of the container 3 is in 9 shown.

In the following, a comparison of the currents generated by a permanently rotating magnetic field and by an oscillating-rotating magnetic field is carried out:
The comparison of the integral properties of vortex flows, as generated by both types - the permanently rotating magnetic field and the oscillating - rotating magnetic field - is described in 10 shown.

The invention enables both separate liquid metal stirring operations 2 , eg, liquid tin, the following gives the following parameters: Ha = 0.71, Re _ω = 6.10 ⁵ , ω = 0.8, Ta = 3 × 10 ⁵ . It can be seen that the ratio of average time values at azimuthal velocities is 0.5 for average volume, as a consequence of an energy saving effect of 50%. But at the same time, the ratio of meridional and azimuthal flow velocities is 0.9. In addition, the ratio of meridional and azimuthal flow velocity has been improved. It is 15%, compared to the previous 11%, as in 11 is shown.

In particular, in 11b shown that at interrupts (time intervals .DELTA.t * / .DELTA.t), which are smaller or larger than the interruption of the invention (here, for example, .DELTA.t * = 1.8), no higher ratios between the meridional and azimuthal velocities U _rz / U _Θ can be measured. Only if the determined interruption .DELTA.t * / .DELTA.t in the associated switching changes is maintained is an increase in the kinetic energy of the meridional flow at the expense of the azimuthal flow achieved, and also an energy saving achieved.

The most important advantage of the control equation (IV) is the reduction of turbulence, as in the 12 and 13 is shown. The 12 shows a representation of the meridiona len velocity field at different times (50 sec, 150 sec and 280 sec) at a constant Lorentz force F _L at permanently rotating magnetic field with the formation of cylinder shell side vortex formations. In contrast, in 13 Representations of the meridional velocity field at comparatively equal times with an oscillating Lorentz force F _PRMF shown, wherein at 50 sec a laminar Stokes flow is present. In the structures at the times 150 sec and 280 sec, there is a quasi-Stokes flow, which in comparison to the analogous structures in 12 all have significantly less turbulence.

Just This reduction in turbulence is desirable in crystal growth.

Moreover, the stirring method according to the invention is suitable for the chemical industry, when an immutable boundary between two reacting liquids, for example electrolytes at high speed, is of great importance, as in US Pat 14 . 15 is shown. In the 14 a concentration pattern of liquid tin (mass%) at different times (0 sec and 300 sec) at constant Lorentz force F _L and in 15 a concentration _pattern of liquid tin (mass%) only for 300 seconds at oscillating Lorentz force F _PRMP shown. The result shows that with oscillating Lorentz force F _PRMF in 15 hardly a vertebra education exists.

One another example of the application of the method according to the invention and the device is to generate regular temperature fluctuations. The temperature fluctuations can cause the melting and solidification of the solidification front what a more timely insertion of the transition from columnar to globulitic dendrite growth can cause what in many cases the goal of using the oscillating-rotating magnetic field in foundry technology will be.

An example of temperature fluctuations controlled by an oscillating-rotating magnetic field is shown in FIG 16 shown. The temporal courses of the temperature T at different points z of the central axis of the liquid metal column are shown with a cooling from below, preferably by means of a thermostat. The cooling curves correspond to the time course of the temperature of the cooled metal 2 at different distances from the ground 9 the z axis 14 out in the cylinder 3 with adiabatic walls 8th and adiabatic lid 10 ,

• 1. Die Veringerung des Turbulenzgrades,
• 2. eine Erhöhung des Verhältnisses von meridionaler zu azimutaler kinetischer Energie und
• 3. eine Energie-Ersparnis von 50%.

Overall, the invention consists in a control of the flow of the conductive liquid 2 for the switching on / off of the rotating magnetic field in the Stokes flow range, which has the following advantages over known methods for stirring:

• 1. The reduction of the degree of turbulence,
• 2. An increase in the ratio of meridional to azimuthal kinetic energy and
• 3. an energy saving of 50%.

1

contraption

2

senior liquid

3

container

4

Electromagnetic system

5

Control / regulating device

6

Interruption device

7

computer unit

8th

cylinder surface

9

ground

10

cover

11

first Induction coil pair

12

second Induction coil pair

13

third Induction coil pair

14

central axis

15

air gap

16

First supply line

17

second supply line

18

third supply line

19

fourth supply line

20

fifth supply line

21

sixth supply line

22

azimuthal flow

23

meridional flow

24

thermostat

25

frame

Claims (17)

Method for stirring electrically conductive liquids ( 2 ) in containers ( 3 ) in which by rotation of a magnetic field by means of centrally symmetrical opposite and outside the container ( 3 ) induction coils ( 11 . 12 . 13 ) an azimuthal flow ( 22 ) and a meridional flow ( 23 ) in the quasi-Stokes flow region within the conductive liquid ( 2 ) are generated, characterized in that after reaching the maximum of the Stokes flow range, the rotating magnetic field a change of switching on and off of the magnetic field in a time interval .DELTA.t / .DELTA.t * of Δt = t fm - t lam (dimensioned) (Ia) or Δt * = t fm * -T lam * (dimensionless) (Ib) and the liquid ( 2 ) are subjected to an oscillating Lorentz force F _fm , tfm being equal to the time t _IN1 of reaching the first minimum of the volume-average velocity of the meridional flow ( 23 ) after switching off the magnetic field to which the magnetic field is switched on again, and wherein t _{lam at} the time t _OFF1 of reaching the first maximum of the volume-average speed of the meridional flow ( 23 ) after switching on the magnetic field to which the magnetic field is first turned off corresponds. Method according to claim 1, characterized in that for the characterization of the azimuthal flow ( 22 ) and the meridional flow ( 23 ) the velocities U _θ and U _rz averaged over the volume V with:

is used as the volume average meridional velocity, where V equals the volume of a cylinder vessel with V = πR ² H. Method according to at least one of the preceding claims, characterized in that with the optional specification of a high Taylor magnetic number T _{a remained} in the quasi-laminar and non-linear Stokes flow range. Method according to at least one of the preceding Claims, characterized in that in the quasi-Stokes flow region is worked when a periodic switching on and off of the rotating Magnetic field performed becomes. Method according to at least one of the preceding claims, characterized in that in the case of an open cylinder or a cylinder having a size ratio with A ≠ 1, the duration of the interrupting time interval Δt / Δt * from the ratio Δt * = t * / fm - t * / lam dimensionless) or not dimensionless with Δt = t _fm - t _{lam is} given, where

is. Method according to at least one of the preceding claims, characterized in that the following control equation (IV) for the periodic switching on / off of the Lorentz force:

where k can only be INTEGER (rounded integer down), e.g. B. int (1.9) = 1, where

and J ₁ Bessel function of the first kind and λ _{k are} the root of J ₁ (x) = 0, and used for storage in the computer unit ( 7 ) is entered. Contraption ( 1 ) for stirring electrically conductive liquids ( 2 ) in containers ( 3 ) in which by rotation of a magnetic field by means of centrally symmetrical opposite and outside the container ( 3 ) induction coils ( 11 . 12 . 13 ) an azimuthal flow ( 22 ) and a meridional flow ( 23 ) in the quasi-Stokes flow region within the conductive liquid ( 2 ), characterized in that a control device ( 5 ) with at least one interruption device ( 6 ) and a computer unit ( 7 ), the interruption device ( 6 ) for interrupting the rotating magnetic field after reaching the maximum of the Stokes flow range in a time interval .DELTA.t / .DELTA.t * of Δt = t fm - t lam (dimensioned) (Ia) or Δt * = t fm * - t lam * (dimensionless) (Ib) where t _{fm is} the _instant t _IN1 of reaching the first minimum of the volume average velocity of the meridional flow ( 23 ) after switching off the magnetic field to which the magnetic field is switched on again, and wherein t _{lam at} the time t _OFF1 of reaching the first maximum of the volume-average speed of the meridional flow ( 23 ) after switching on the magnetic field to which the magnetic field is first switched off, equivalent. Apparatus according to claim 7, characterized in that the container ( 3 ) is cylindrical and from a cylinder jacket ( 8th ) as well as from a soil ( 9 ) and optionally from a lid ( 10 ) consists. Device according to at least one of the preceding claims, characterized in that the electromagnetic system ( 4 ) at least three pairs of induction coils ( 11 . 12 . 13 ), wherein in each case the induction coils of a pair ( 11 ; 12 ; 13 ) centrally symmetrical to the central axis ( 14 ) around the container ( 3 ) are arranged around. Device according to at least one of the preceding claims, characterized in that the induction coil pairs ( 11 . 12 . 13 ) of the container shell ( 8th ) through an air gap ( 15 ) are arranged separately. Device according to at least one of the preceding claims, characterized in that the container ( 3 ) with a frame ( 25 ) and / or with a thermostat ( 24 ). Device according to at least one of the preceding claims, characterized in that the induction coil pairs ( 11 . 12 . 13 ) via supply lines ( 16 . 17 . 18 . 19 . 20 . 21 ) with the control device ( 5 ) are connected. Device according to at least one of the preceding claims, characterized in that the control device ( 5 ) associated interruption arrangement ( 6 ) is provided for performing the switching change .DELTA.t / .DELTA.t * of the electric current for periodic change and a change in the Lorentz force and a controlled, the change of switching on and off performing power circuit breaker for the induction coil pairs ( 11 . 12 . 13 ), the interruption arrangement ( 6 ) is optionally formed with electronic components as hardware and / or with program-technical means as software. Device according to at least one of the preceding claims, characterized in that the container ( 3 ) with the thermostat ( 24 ), which determines the temperature of the liquid ( 2 ) keeps constant according to the temperature specification. Use of the method and / or the device according to the preceding claims for the chemical Industry, if immutable Boundary between two reacting liquids, e.g. electrolytes is provided at high speed. Use of the method and / or the device according to the preceding claims in metallurgy to produce regular temperature fluctuations, the temperature fluctuations for melting and solidification of Lead solidification front, what a more timely beginning of the transition from columnar to globulitic dendrite growth. Use of the method and / or the device according to the preceding claims in methods of crystal growth, in particular for the reduction of crystal defects by reduction of turbulence degree.