WO2023033637A1

WO2023033637A1 - A device for non-contact induction of flow in electrically conductive liquids

Info

Publication number: WO2023033637A1
Application number: PCT/LV2021/050009
Authority: WO
Inventors: Andris BOJAREVIČS; Jurijs GEĻFGATS; Toms BEINERTS; Reinis BARANOVSKIS
Original assignee: Latvijas Universitāte
Priority date: 2021-09-03
Filing date: 2021-09-03
Publication date: 2023-03-09

Abstract

The invention relates to devices for metallurgical production, namely, for non-contact induction of flow in electrically conductive liquids. The device comprises a frame; a container for the electrically conductive liquid; rotatable permanent magnets in the form of one or more cylinders magnetized along their diameter, with the direction of the magnetization vector perpendicular to the longitudinal axis of the cylinders; the cylinders being the cylindrical magnetic dipoles; at least one drive adapted for the rotation of the rotatable permanent magnets. The cylindrical magnetic dipoles are installed in such a way that the longitudinal axis of the cylinders is perpendicular to a vertical axis of the electrically conductive liquid layer, and end surfaces of the cylindrical magnetic dipoles are parallel or perpendicular to the vertical axis of the electrically conductive liquid layer; wherein each cylindrical magnetic dipole is equipped with ferromagnetic concentrator installed symmetrically on both sides of cylindrical surface of the cylindrical magnetic dipoles, normal to the magnetization vector of the dipole, with an angle of coverage of the cylindrical surface in the range of 55-65°, the length of the concentrator not less than 1/3 of the dipole length and thickness between 1/7 and 1/5 of the diameter of the dipole.

Description

A DEVICE FOR NON-CONTACT INDUCTION OF FLOW IN ELECTRICALLY CONDUCTIVE LIQUIDS

Field of the Invention

[001] The invention relates mainly to technologies and devices for metallurgical production, but it can also be used in systems for growing semiconductor single crystals from liquid phase and in liquid power cooling systems for nuclear power units. The invention is intended to induce forcing in electrically conductive alloys for mixing, preparing, degassing and refining metals and alloys in various types of furnaces and mixers, homogenizing the composition and equalizing the melt temperature throughout the volume of the metallurgical unit.

Background Art

[002] There are various methods and devices for driving liquid metals using electromagnetic impact on molten metal using conduction [1-3] and induction [4-6] electromagnetic pumps. Conductive electromagnetic pumps [1-3] comprise a magnetic system enclosing a metal path and electrodes located on both sides of the metal path so that the vectors of the magnetic field and the electric current are perpendicular to each other. In the result of the interaction of the magnetic field and the electric current, an electromagnetic force is generated in the liquid metal, which actuates it.

[003] The common disadvantages of all conductive methods and devices are the difficulty of providing reliable stationary electrical contact between the melt and the electrodes and the need to use high electrical current values to achieve the required pump efficiency. For these reasons, the use of any variant of conductive electromagnetic control devices in metallurgy is very limited.

[004] Induction electromagnetic pumps [4-7] influence liquid metals without electrical contacts. The electromagnetic force that drives the melt results from the interaction of an external variable magnetic field with the electric currents that this field causes in the liquid metal. The most common are three-phase induction pumps powered by a three-phase AC network, which generate a traveling or rotating magnetic field in the liquid metal [8], Such pumps have a liquid metal channel with one or two inductors consisting of a laminated ferromagnetic core with the AC coils. The coils are connected to a three-phase AC network according to a traveling magnetic field pattern, similar to the coil connection in an induction motor stator.

[005] Common disadvantages of all devices using three-phase induction pumps for transporting and mixing liquid metals are their very high energy consumption, the need to use adjustable high-power sources and capacitor boxes to compensate for reactive power, and the complexity of operation and maintenance. In addition, as the gap between the inductor and the liquid metal layer (which is characteristic of metallurgical devices) increases, the efficiency of three-phase induction pumps decreases sharply.

[006] There are also known induction devices with a rotating magnetic field formed by a rotating rotor in the form of a disk or a cylinder with permanent magnets of variable polarity mounted on them [9 - 13],

[007] The common disadvantages of such known metallurgical devices are the complex configuration of the flow paths, which complicates their production and maintenance, the need for additional flow heating to prevent the melt in it from freezing, and the low efficiency with increasing gaps between rotor and liquid metal.

[008] In particular, an induction electromagnetic pump with permanent magnets [11] is known, which has a rotating cylindrical rotor with permanent magnets of variable polarity mounted on its cylindrical surface and a metal path in the form of a cylindrical annular canal enclosing the rotor. The disadvantage of such a device is the complexity of the implementation of an annular canal made of refractory materials with thin walls in metallurgical practice and its low efficiency at large (real) gaps between the rotor and the liquid metal.

[009] Solutions are also known [12, 13] which offer an aluminium alloy melting furnace equipped with an electromagnetic stirrer in the form of a rotating cylindrical rotor with permanent magnets on a surface surrounded on the outside by a half-ring canal arranged outside the furnace bath and connected with it by canals built into one of the vertical walls of the bath. Disadvantages of these solutions are the need for additional heating of the melt in the semicircular canal and the canals connecting it to the furnace bath, the risk of the melt freezing when the stirrer is switched off, the difficulty of cleaning these canals and the risk of overheating of permanent magnets mounted on the rotor, that can cause the lose of their magnetic properties.

[010] There is also known a method and device for mixing and transporting metal melts, presented in [14, 15], In accordance with the solution proposed in [14], the liquid metal is affected by a magnetic field formed by a system of cylindrical magnets magnetized along their diameter in one direction and installed parallel to each other; then these cylinders with parallel axes are synchronously rotated so that a coplanar (rotating) magnetic field is also formed in the liquid metal, inducing electric currents in the melt and, accordingly, electromagnetic forces that set it in motion, providing mixing or transportation of the liquid metal.

[Oil] This solution [14] has a number of significant disadvantages. With synchronous rotation of diametrically magnetized cylinders with induction vectors directed in one direction and parallel to each other, the efficiency of the device depends on the quality of the traveling magnetic field formed in the melt. In the proposed solution, a traveling magnetic field of the required quality will be realized only with no more than three cylinders and small values of the gap between the surface of the cylinder and the liquid metal. The general magnetic interaction directly between the cylinders of the entire system will be so great and accompanied by such large fluctuations in the magnitude of the torque that the mechanical system that drives the cylinders into rotation will be subject to heavy loads and vibrations. With a parallel arrangement of a system of diametrically magnetized cylinders on both sides of a flat layer of molten metal and their mutual synchronous unidirectional rotation, the efficiency of the device proposed in [14] will be very low due to backpressures created by opposite magnetic cylinders. Disclosure of the Invention

[012] The purpose of this invention is to eliminate the drawbacks of the prior art solutions, namely to increase the intensity of fluid motion in the melt due to the creation of intense azimuthal flows in it at increased distances between the magnets and the liquid melt and while providing the ability to regulate the speed and the direction of motion in the fluid as required in particular circumstances.

[013] The set goal is achieved

- by installing one or more rotating cylindrical magnetic dipoles from the outside of the volume with the melt (any electrically conductive liquid) with the direction of the magnetization vector perpendicular to their longitudinal axis in such a way that the longitudinal axis of the cylinders is perpendicular or parallel to the vertical axis of the metal melt layer, and their end surfaces are parallel or perpendicular to the of the metal melt layer;

- each cylindrical magnetic dipole maybe equipped with ferromagnetic concentrators installed symmetrically on both sides of its cylindrical surface normal to the dipole magnetization vector;

- the angles of coverage of the cylindrical surface of the dipole by ferromagnetic concentrators on each side are in the range of 55-65°; the length of each concentrator is at least 1/3 of the length of the cylindrical dipole, and its thickness is in the range of 1/7 and 1/5 of the diameter of the dipole;

- the geometric parameters of the device can be determined depending on the required speed of the electrically conductive liquid according to the dependencies:

where D - is the diameter of the cylindrical magnetic dipole;/- the frequency of rotation of the dipole (rev/s ); c and p, respectively, electrical conductivity and density ofthe electrically conductive liquid; B = B_r[ [L/ )] - the effective value of the magnetic field induction at a distance L from the surface of the dipole end, determined from the graph of Fig. 4; B_r - the remanence of the permanent magnet dipole material; L - the distance from the end of the dipole to the electrically conductive liquid in the container; k = 1-0.8 - an empirical arbitrary coefficient (any value of the coefficient within the range is operational and enabling, however the optimal value is selected depending on the ratio of the lengths of the dipole and the ferromagnetic concentrator).

- magnetic dipoles are preferably equipped with means for cooling them to temperatures not exceeding the operating temperature of permanent magnets;

- each dipole is preferably equipped with a drive ensuring its rotation with different speed, direction of rotation and the ability to control its operating mode from a computer according to a given program.

Brief Description of Drawings

[014] The proposed device for contactless forcing and moving of electrically conductive liquids is illustrated on the figures 1-7.

Fig. 1 shows one embodiment of the invention, with rotatable permanent magnet mounted under the bottom of the container with the melt and another adjacent to one of the vertical walls of the container.

Fig. 2 shows a cylindrical magnetic dipole with ferromagnetic concentrators.

Fig. 3 shows the calculated values of the magnetic field induction for the cases of a cylindrical dipole (a) and a dipole equipped with magnetic concentrators (b).

Fig. 4 shows the dimensionless dependence of the change in the effective value of the magnetic field induction Bin the electrically conductive liquid on the diameter D of the dipole, its magnetization Br, and on the distance L from the dipole end to the electrically conductive liquid.

Fig. 5 shows an example of the flows formed when the electrically conductive liquid is exposed to a rotating cylindrical dipole beneath the container bottom without magnetic concentrators.

Fig. 6 shows an example of the flow formed when the electrically conductive liquid is exposed to a rotating cylindrical dipole with magnetic concentrators beneath the container bottom. Fig. 7 shows the dependence of the velocity of the flows U_(p arising in the electrically conductive liquid on the number of revolutions of the dipole with ferromagnetic concentrators/during tests with permanent magnet with D = 50 mm.

Detailed Description of the Invention

[015] The device for contactless driving of electrically conductive liquids (Fig. 1) comprises a frame (1); a container (2) for the electrically conductive liquid (e.g. melt); a system of rotatable permanent magnets (3) in the form of one or more cylinders with a diameter D, magnetized along their diameter, with the direction of the vector magnetization perpendicular to the longitudinal axis (4) of the cylinders; the cylinders being the cylindrical magnetic dipoles (20); one or more drives (5) adapted for the controllable rotation of the rotatable permanent magnets (3). The container (2), the magnets (3) and the drive (5) installed on the frame (1), the magnets (3) installed nearby the container (2). In order to intensify the movement of the electrically conductive liquid in the container (2) at large distances between the electrically conductive liquid and the magnets (3), cylindrical magnetic dipoles (20) are installed in such a way thatthe longitudinal axis (4) ofthe cylinders is perpendicular to the vertical axis of the electrically conductive liquid layer, and end surfaces ofthe cylindrical magnetic dipoles (20) are parallel (e.g. Fig. 1 dipole (20) belowthe container(2)) or perpendicular (e.g. Fig. 1 dipole (20) on the right side from the container(2)) to the vertical axis of the electrically conductive liquid layer; wherein each cylindrical magnetic dipole (20) is equipped with ferromagnetic concentrator (21) (Fig. 2) installed symmetrically on both sides of cylindrical surface of the cylindrical magnetic dipoles (20), along the magnetization vector ofthe dipole (20), with an angle of coverage ofthe cylindrical surface in the range of 55-65°. The length of the concentrator (21) not less than 1/3 of the dipole (20) length and thickness between 1/7 and 1/5 ofthe diameter ofthe dipole (20). The rotation ofthe dipoles (20) is carried out using, for example, drives (5), and the speed, as well as direction of their rotation can be changed as required under the given circumstances.

[016] The presence of ferromagnetic concentrators (21) increases the area of influence ofthe magnetic field in the electrically conductive liquid and the magnitude of the magnetic induction of the field in the electrically conductive liquid (Fig. 3). The optimal dimensions of the dipoles (20) with ferromagnetic concentrators (21) are at the length of the ferromagnetic concentrators (21) h equal to at least 1/3 of the dipole (20) length H and its thickness A, equal to approximately 1/6 of the diameter D of the dipole (i.e. from 1/7 to 1/5). In this case, the geometric parameters of the entire device are determined depending on the required speed of the electrically conductive liquids

in the container (2) according to the dependences:

where D - the diameter of the cylindrical magnetic dipole (20);/- the frequency of rotation of the dipole (rps); c and p, respectively, the specific conductivity and density of the electrically conductive liquid; B = Br[f[L/Dy] - the effective value of the magnetic field induction at a distance L from the surface of the dipole (20) end, determined from the Fig. 4; Br - the magnetization of the dipole (20) material; L - the distance from the end of the dipole (20) to the electrically conductive liquid in the container (2); k = 1-0.8 - an empirical coefficient depending on the ratio of the lengths of the dipole (20) and the ferromagnetic concentrator (21).

[017] To prevent overheating of the magnetic dipoles (20) above the permissible temperature, the device can be equipped with cooling means (22) adapted for cooling the magnetic dipoles (20) to temperatures not exceeding the operating temperature of the permanent magnets (3). For instance, the cooling means (22) can be a system for supplying an air flow to areas of the device that are dangerous from the point of view of overheating. [018] The device can be installed under the bottom or at the side wall of the container (2) with the electrically conductive liquid (melt). The device is installed so that the axes of one or more cylindrical magnetic dipoles (20) are equipped with magnetic concentrators (21) are perpendicular to the plane of the container (2) and are at a distance L from the surface of the electrically conductive liquid. To achieve the required flow velocity of the electrically conductive liquid, the maximum possible distance L from the surface of the dipole (20) end to the electrically conductive liquid is calculated according to the above dependences and is determined by the size of the dipole (20) diameter, the value of the magnetization of its material, specific electrical conductivity and density of the electrically conductive liquid.

[019] The magnetic dipoles (20) are brought into rotation using some kind of drive, for example, electric drive (5). The speed and direction of rotation of the dipoles (20) with magnetic concentrators (21) are determined by the operating modes of the drives (5) independently of each other, and can be programmably controlled.

[020] When the magnetic dipoles (20) rotate with the direction of the field of magnetization vector perpendicular to their axis of rotation, the magnetic field flux from the dipole cross the electrically conductive liquid zone and, periodically changing in direction and time (Fig. 3), induce electric currents in the electrically conductive liquid. The latter, interacting with the primary magnetic field of the permanent magnets (3) of the dipole (20), excite electromagnetic forces in the electrically conductive liquid, which causes the liquid to move. Depending on the direction and speed of rotation of each of the dipoles (20), the configuration and structure of the emerging hydrodynamic flows in the electrically conductive liquid can be very diverse and is determined by the specific requirements of particular technological process.

[021] The speed of the emerging flows in the electrically conductive liquid depends on the magnitude of the magnetic field B in the liquid zone, the rotation speed (number of revolutions) of the dipoles (20), the electrical conductivity of the electrically conductive liquid, and the distance from the surface of the magnets (3) to the liquid, which should not exceed the previously calculated size L (Fig. 4). The presence of ferromagnetic concentrators (21) on the side surfaces of the cylindrical dipoles (20) significantly increases the depth of penetration of the field into the electrically conductive liquid, as well as the volume affected by the magnetic field. As a result, the efficiency of the device is considerably increased (Fig. 5-6).

[022] Tests of the claimed device were carried out on an experimental setup, in which the eutectic indium-gallium-tin alloy with a melting point of 10.6°C was used as the electrically conductive liquid. The installation was carried out with one cylindrical magnetic dipole (20) equipped with ferromagnetic concentrator (21). The dipole (20) was rotated by an electric motor. Its rotation speed was regulated by a frequency converter, which changed the frequency of the electric current supplying the electric motor.

[023] An ultrasonic Doppler anemometer was used to measure the speed of movement of the electrically conductive liquid in the container (2) at different numbers of revolutions of the magnetic dipole (20) and at different distances from the end surface of the dipole (20) end to the electrically conductive liquid.

[024] The results of measurements are shown in Fig. 7. They confirm the effectiveness of using of the proposed device for creating motion in electrically conductive liquids, in particular, liquid metals, molten semiconductor materials, etc.

[025] Moreover, the obtained experimental values of the speed rates of the liquid metal satisfactory match the calculated data, which makes it possible to assess the expected mixing rates and the required sizes of magnetic dipoles for real technological installations. In particular, the calculations indicate that in a 1.5-ton crucible with molten aluminium a device with two cylindrical magnetic dipoles (20) with a diameter of D = 150 mm at a distance between the surface of the dipoles (20) and the liquid metal A = 200 mm and the number of revolutions n = 1-1.5 rev/min will develop stirring flows with an average speed of about 0.1- 0.2 m/s, which is quite enough for intensifying melting processes and for obtaining alloys.

[026] Similar calculations of the mixing parameters of the liquid zone in solidifying steel ingots, obtained in continuous and semi-continuous casting installations, show that, provided there are no (or very weak) magnetic properties in the already solidified layer (crust) of a metal, the mixing speed can reach 0.2-0.3 m/s. The indicated mixing flow rates are quite sufficient both for homogenization of the melt in the core of the ingot and for obtaining its improved crystal structure.

[027] The use of the permanent magnets in the form of rotating cylindrical magnetic dipoles makes it possible to spread the action of the magnetic field to a significantly greater distance from the surface of the permanent magnet dipole. This circumstance makes it possible to significantly increase the permissible (from the point of view of the effectiveness of the device) wall thickness of metallurgical units and to implement in practice a number of promising metallurgical technologies. At the same time, the proposed device, in comparison with known solutions, serving for a similar purpose, is distinguished by its simplicity of design, significantly smaller dimensions and a significantly smaller amount of required expensive magnetic materials.

References

1. Birzvalk Yu.A. Basics of Theory and Calculation of DC Conduction MHD Pumps. Riga, Zinatne Publishing House, 1968, 235 p.

2. US 6732890 B2.

3. GB2317506A.

4. Voldek A.I. Induction Magnetohydrodynamics Machines with a Liquid Metal Working Body.

- Leningrad, Energy Publishing House, 1970, 272 p.

5. Peel A. A Look at the History and Some Recent Developments in the Use of Electromagnetic Devices for improving operational efficiency in the aluminium cast house. Aluminium Cast House Technology, the 8^th Australian Conference. Ed. By P.R.Whitaley, TMS, 2003, p.71-100.

6. US 3490896.

7. EP1021574 B1.

8. Verte L.A. Magnetohydrodynamics in Metallurgy. Moscow, Metallurgy Publishing House, 1975, 288 p.

9. Kalnins T. Explicit Pole MHD Pumps. Riga, Zinatne Publishing House, 1969.

10. Bucenieks I. Perspectives of using rotating permanent magnets for electromagnetic induction pump design. Magnetohydrodynamics, vol. 36 (2000), no.2, p.151-156.

11. CN101594041A.

12. EP 2206998.

13. JP 2008334089A.

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15. LV14404B.

Claims

1. A device for contactless induction of forcing in electrically conductive liquids, comprising a container (2) for the electrically conductive liquid; rotatable permanent magnets (3) in the form of one or more cylinders magnetized along their diameter, with the direction of the vector magnetization perpendicular to the longitudinal axis (4) of the cylinders; the cylinders being the cylindrical magnetic dipoles (20); at least one drive (5) adapted for the controllable rotation of the rotatable permanent magnets (3); the magnets (3) installed nearby the container (2); characterized in that cylindrical magnetic dipoles (20) are installed in such a way that the longitudinal axes (4) of the cylinders are perpendicular to a vertical axis of the electrically conductive liquid layer, and end surfaces of the cylindrical magnetic dipoles (20) are parallel or perpendicular to the vertical axis of the electrically conductive liquid layer; wherein each cylindrical magnetic dipole (20) is equipped with ferromagnetic concentrator (21) installed symmetrically on both sides of cylindrical surface of the cylindrical magnetic dipoles (20), normal to the magnetization vector of the dipole (20), with an angle of coverage of the cylindrical surface in the range of 55-65°, the length of the concentrator (21) not less than 1/3 of the dipole (20) length and thickness between 1/7 and 1/5 of the diameter of the dipole (20).

2. The device according to claim 1, characterized in that the ratio of the geometric dimensions of the elements of the device is determined by the following dependencies:

where Ucp - the required speed of the electrically conductive liquid in the container (2); D - the diameter of the cylindrical magnetic dipole (20); f - the frequency of rotation of the dipole (20), rps; o and p, respectively, specific electrical conductivity and density of the electrically conductive liquid; B = Br[f(L/D)] - the effective value of the magnetic field induction at a distance L from the surface of the dipole (20) end to the surface of the electrically conductive liquid; Br - the remanence of the dipole permanent magnet material; L is the distance from the end of the dipole (20) to the electrically conductive liquid in the container (2); k = 1-0.8 - an arbitrary coefficient depending on the ratio of the lengths of the dipole (20) and the ferromagnetic concentrator (21).

3. The device according to claims 1 or 2, characterized in that the magnetic dipoles (20) are equipped with cooling means (22) adapted for cooling the magnetic dipoles (20) to temperatures not exceeding the operating temperature of the permanent magnets (3).