WO2007065937A1

WO2007065937A1 - Method and device for electromagnetically influencing the flow conditions in fluids of low electrical conductivity and high viscosity

Info

Publication number: WO2007065937A1
Application number: PCT/EP2006/069457
Authority: WO
Inventors: Bernd Halbedel; Dagmar Hülsenberg; Uwe Krieger; Ulrich Lüdtke; Gunter Carl; Hans-Jürgen LINZ
Original assignee: Technische Universität Ilmenau; Jsj Jodeit Gmbh
Priority date: 2005-12-08
Filing date: 2006-12-08
Publication date: 2007-06-14
Also published as: DE102005058729A1; EP1957416A1

Abstract

The invention relates to a method and device for electromagnetically influencing the flow conditions of flowing fluids of low electrical conductivity and high viscosity - preferably glass melts - in channels of any desired cross section. For this purpose, Lorentz forces that are perpendicular to the main direction of flow but axially opposed from portion to portion are generated, resulting from the simultaneous compression of alternating electric and magnetic fields that are vectorially directed perpendicularly to one another and have the same temporal behaviour. By means of electrodes (3a, 3b) that are in contact with the fluid, the alternating electric fields produce in the fluid electric current density distributions that are directed perpendicularly to the main direction of flow of the fluid. The alternating magnetic fields are generated by an external coreless coil system which encloses the fluid and the electrodes and the field lines of which in the fluid are primarily directed parallel to the main flow. The Lorentz forces impress on the main flow flow components that are oppositely directed from portion to portion and, because of the great velocity gradients induced between these axial portions, even out the local and temporal distribution of the chemical composition and the temperature in the fluid independently of gravitational force, and also change the residence time of the fluid in the channel in a controlled manner.

Description

Method and device for electromagnetic

Influencing the flow conditions in low electrically conductive and highly viscous fluids

The present invention relates to a method and a device for carrying out the method

Gravitationally independent electromagnetic influence on the flow conditions of low electrically conductive and highly viscous fluids - preferably glass melts - in channels of any cross-section.

In practice, the flow in a glass melting unit takes place primarily by convection, which occurs under the influence of gravity due to density differences as a result of temperature gradients in the melt. It is often reinforced with the help of an additional electric heater (EZH). However, the force effect generated is always linked to the presence and direction of gravity, or in the opposite direction, and to the presence of temperature gradients. Due to the required gradients, thermal homogenization of the melt is never possible and chemical homogenization is linked to long process times. In addition, local hypothermia or overheating of the melt and the associated reboiling can occur.

Another applied flow control is mechanical stirring. It takes place with the help of different types of Ruhrers and with glass melts at different positions in the melting unit. For example, a rod stirrer can use high speeds and the resulting shear forces to pull apart an existing streak, increasing their surface area and reducing the chemical gradients. th necessary diffusion is favored (see DE 100 57 285).

Spiral stirrers are primarily used to improve thermal homogeneity because they ensure high material transport [1]. Therefore, they are also particularly suitable for coloring glass in the feeder of glass melting plants (feeder area) (SU 1 011 564). On the other hand, blade stirrers generate the shear forces through different speeds along a blade (DD 296 798, DD 274 812, EP 0 504 774).

Despite frequent use, the use of mechanical stirrers often does not guarantee the desired improvement in the homogeneity of the glass melts, because on the one hand the abrasion products of the stirrers cause colorings, crystal germs and other impurities [1] and on the other hand the risk of thermal reboiling through local undercooling and reheating Melt exists [2]. Furthermore, these stirrers have limited operating times and call due to the often necessary use of precious metals

(Platinum, platinum-rhodium) high operating costs. GB 1289317 and DE 2056445 describe a method and a device for producing glass in which electromagnetic forces are used to stir glass melts, in particular during the casting process or refining, which result from the interaction of the heating current with a perpendicular to it standing external magnetic field result.

Here, alternating currents with a frequency of 50 Hz and alternating magnetic fields of the same frequency are used. The phase position does not necessarily have to match. The magnetic field is generated by one or more single-phase and three-phase iron-bearing alternating current magnets, which are externally adapted to the melting vessels. Different flows are to be realized by separately controlling individual magnets. In order to achieve sufficient stirring effects, it is recommended that the ratio of the electromagnetic force to the convection force according to equation (1)

B

> 1: D

adjust. Designate it:

j - the electrical current density in the melt, B - the magnetic flux density,

g - gravitational acceleration,

P _F - the density of the glass melt,

ß _F - the thermal volume expansion coefficient of the melt

Δi3- - the temperature gradient in the melt.

Although the advantageous use of Lorentz forces for influencing the flow of glass melts is already proposed here, the proposed devices and methods only allow a change in the flow in or against gravity. A significant improvement in the color characteristics of UV-absorbing glasses is also achieved according to [3] if an alternating current is passed through the melt via top electrodes and a magnetic alternating field penetrates the melting vessel perpendicular to it. The better distribution of the coloring glass components (Cr ³ VCr ⁶⁺ -; Fe ³⁺ - ions) is based on the volume force density generated electromagnetically - hereinafter referred to as Lorentz force density - - A -

(2)

^L dV with f _L - Lorentz force density,

F _L - Lorentz force,

V - volume element, resulting flow in the glass melt is returned. The flow rates achieved should have been up to 12 cm / s with a magnetic induction of 0.15 T. No information is available on the current densities j in the melt.

In addition, from [4] further results on electromagnetic stirring in a small-scale plant (channel melter with 0.8 m ³ capacity) are known. Two horseshoe-shaped alternating current magnets are attached opposite each other on the side walls of the channel melter, so that the magnetic field must close across the melting channel. In the area of the action of the magnetic fields of the AC magnets, three electrodes are centered in the melting channel with one

Positioned a certain distance, so that the electric current field between the electrodes crossed with the magnetic field penetrating into the melt and finite Lorentz force densities are generated, which in turn initiate flows in the channel cross section. The effect of this flow is said to contribute to the homogenization of the melt. The effects are demonstrated on the basis of refractive index measurements on samples from the cooled melt. The average induction in the glass melt is between 0.015 T to 0.249 T. In SU 81 49 04 a method for improving the refining and homogenization of particularly highly viscous molten glass (up to 500 Pas at temperatures of 1250 ⁰ C to 1460 ° C) is proposed in a special melting unit, wherein a flow of the order of 4 to 5 cm / s and their change (e.g. every 3 to 5 min) between the horizontal and vertical direction (= parallel to gravity) is forced by means of corresponding Lorentz force densities acting in the melt. For this there are 3 pairs of electrodes in the melt, with which current density distributions of depending on the type of glass

10 to about 50 mA / mm ² and an electromagnet on the outside of the melting unit, which generates a magnetic field that is perpendicular to the current density and synchronous in time (flux density up to 40 mT). The changes of direction, for example from horizontal to vertical flow, are determined by the

Switching of the electrodes and the electromagnet made by means of a device not described in detail. Due to the Lorentz force distribution generated in each case, the flow is designed in different directions, so that separate work steps are required which are used for refining or for homogenizing the glass melt. The duration of the electromagnetic refining and homogenization procedures is up to several hours (1 to 3 hours). The improvement in glass quality due to the electromagnetically initiated flows was demonstrated by the decrease in the bubble content of glass samples compared to traditionally produced glasses (without magnetic stirring). The following procedures are given as examples for various glass compositions (in% by mass): • 31.04% S iO ₂ ; 65.57% PbO; 2.64% Na ₂ O; 0.5% As ₂ O ₃ and 0.25%

Sb ₂ O ₃ ;

Melting: 1350 ⁰ C, 3 h

Purification: 1480 ⁰ C (30 Pas); 50 mA / mm ² ; 50 mT; Change of direction every 5 min; 15 min total homogenization time: 1240 ⁰ C (50 - 70 Pas); 50 mA / mm ² ; 50 mT;

Change of direction every 5 min; 90 min total duration • 65.15% SiO ₂ ; 12.11% B ₂ O ₃ ; 3.19% Al ₂ O ₃ ; 1.56% BaO; 1.20% CaO;

0.50% MgO; 6.10% K ₂ O; 9.89% Na ₂ O and 0.30% As ₂ O ₃ ;

Melting: 1380 ⁰ C - 1420 ° C, 3 h

Affine: 1440 ⁰ C - 1460 ° C (20-25 Pas); 20 mA / mm ² ;

40m T; Change of direction every 2.5 min;

15 min total duration

Homogenize: 1280 ° C - 1260 ⁰ C (225 - 230 Pas);

50 mA / mm ² ; 40 mT; Change of direction every 5 min; 90 min total duration

42.80% SiO ₂ ; 45.00% PbO; 10.40% K ₂ O; 1.50% Na ₂ O; 0.30% As ₂ O ₃ melting: 1380 ° C, 3 h

Purification: 1450 ° C (20 Pas); 30 mA / mm ² ; 50m T;

Change of direction every 5 min; 30 min total homogenization time: 1280 ⁰ C (120 Pas); 30 mA / mm ² ; 50 mT;

Change of direction every 5 min; 60 min total duration

SU 10 244 23 also describes a method for improving the homogeneity of glass melts with the help of Lorentz forces, with a low-frequency magnetic field (0.2-0.6

T; 50 Hz) and briefly (0.5 - 2.5 s) another, but higher-frequency magnetic field (0.01 - 0.03 T, 19 - 250 kHz) with an electrical current density (synchronous with the basic field) penetrate melted glass. The time for the electromagnetic homogenization procedure is 15 minutes to 60 minutes. This melting process is intended in particular for

Production of optical glasses may be suitable. JP 2000-128547, on the other hand, describes electromagnetically initiated stirring effects in glass melts of a certain composition, the melting state of which is generated in an inductively heated platinum crucible. A magnetic field - presumably constant field - with an intensity in the range of 0.1 T to 8 T is applied perpendicular or parallel to the crucible axis. The exposure time of the magnetic field is 2 to 5 hours. The composition of the glass melts should contain at least one of the known network-forming oxides SiC> 2, B2O3, P2O5 or GeC> 2. The proportion of these network formers - individually or in total - must, however, be less than 30 mol%. No reference is made to the generation of an electrical current density in the melt via electrodes. It can therefore be assumed that no ion current initiated from outside (ie impressed via electrodes or electrically induced) flows in the melt. Nevertheless, an additional flow is found. The influence of these electromagnetically induced flows has been demonstrated in laboratory experiments under defined operating conditions by measuring the changed temperature distributions. In particular, glasses with high homogeneity and transmission for optical applications (optical fibers, laser glasses, glasses with extremely high refractive index, IR glasses, ...) should be able to be produced without mechanical stirring. For example, two-hour melting procedures with 2 T are given with the following compositions (in mol%):

• 77.80% TeO ₂ ; 3.10% PbO; 14.10% B ₂ O ₃ ; 1.60% Bi ₂ O ₃ ; 1.6% WO ₃ ;

1.8% Al ₂ O ₃ at 900 ⁰ C (→ high-index tellurite glasses),

• 51.00% ZrF ₄ ; 20.00% BaF ₂ ; 4.50% LaF ₃ ; 4.50% AlF ₃ ; 20.00% NaF ₂ at 900 ⁰ C (→ zirconium fluoride glasses for light guides),

• 21, 60% Bi ₂ O ₃ ; 44.80% PbO; 13, 60% Ga ₂ O ₃ ; 20.00% GeO ₂ at 1000 - 1250 ° C (→ Germanate glasses). This publication does not contain any explanation of the causes of the effects achieved. The inductive heating of the crucible wall presumably produces a strong local heating of the melt in the outer areas, as a result of which an intensive

Convection occurs in the melt. As a result of the very low network component of semiconducting or highly ion-conducting glasses, this flow also represents a direct current. The crossing of this natural direct current with a sufficiently strong static magnetic field leads to a constant and unidirectional Lorentz force that changes the existing convection current , so that the observed homogenization effects arise. But here, too, the electromechanical flow control depends on convection and thus on the presence of gravity and a temperature gradient. Under no circumstances is thermal homogenization achieved.

This also applies to the method proposed in DE 10 2004 015 055 A1 and the associated arrangement for specifically influencing the flow of a glass melt during the transfer from the melting furnace in a processing process. The Lorentz forces can only be generated in or against gravity or the main flow. DE 31 05 070 A1 describes a process for the production of

Glass fibers are proposed, the radial distribution of the thermally ionized dopants being changed with radially acting electrical and / or electromagnetic field forces which act on a melted glass mixture mixed with dopants, and thus the refractive index distribution over the fiber cross section being set in a targeted manner. The electric field is between a central electrode immersed in the glass mixture, which is just before the melt solidifies is removed again and an outer electrode, which is arranged concentrically to the center electrode and surrounds the glass mixture, is impressed. In order to avoid contamination due to corrosion of the electrodes, a coil (toroid) can be arranged around the glass mixture, which generates an axial magnetic field. In this case the glass mixture must be turned. Then the induced should be radial

acting Lorentz force change the radial ion distribution. One promises stronger effects if one combines the axial magnetic field with the radial electrical field.

In none of the cases shown is a flow generated in the glass, but the thermal diffusion of the ions is directed by the generated field forces. It should also be noted that the field forces act on both the cations and the anions. However, due to the charge of the ions, this effect is directed in the opposite direction, so that the glass segregates and is not homogenized. The effect of these decisively disadvantageous effects does not diminish when using asymmetrical alternating fields, the half wave of which is suppressed to 20%.

In US 6 849 121 B1 are generated in a rotationally symmetrical graphite crucible by generating a tangent Lorentz force distribution by means of a radial

Current density distribution, which is impressed between a graphite electrode of small diameter and the graphite crucible itself by applying a DC voltage, and the superimposition with an axial magnetic field, generated by means of a solenoid coil arrangement surrounding the crucible, forces tangential flows in the melt which are intended to chemically homogenize the melt and thus allow uniform crystal growth at the lower crucible outlet. The use of constant fields is generally not advisable for glass melts, since the electric field forces dissociation. Furthermore, there is no main flow in the axial direction in this process. Likewise, due to the electrical conductivity of the crucible bottom, axially directed current density distributions are formed between the center electrode and the crucible. This means that, particularly in the area of the crucible bottom, where the crystals form, there are no tangential Lorentz forces and thus in extreme cases

(Current density parallel to the magnetic field) no tangential flows can arise. Furthermore, due to the thin center electrode, only small current densities in the melt can be realized with the proposed arrangement, since a surface current limit density of the electrodes of <2 A / cm ² must be maintained. Exceeding this would increase electrode corrosion exponentially, making the formation of pure crystals impossible. However, small current densities result in correspondingly low flux densities, which are also generated by conventional solenoid windings

Lorentz forces (cf. Eq. (2), which in turn only result in small flows in the melt and thus inadequate homogenization of the melt. This means that expensive high-field magnet systems had to be used in order to achieve sufficient effects.

Similar arrangements are also proposed in EP 0500 970 A1 for power generation. However, due to the movement of a low electrically conductive, but low viscous fluid (e.g. sea water) through the strong DC field (10 to 20 T) of a superconducting solenoid magnet in the fluid, an electrical current density - anologically known MHD genes - rators - induced and not induced by an external magnetic field or impressed via electrodes.

Patent application PCT / FR2004 / 050319 (WO 2005/008157 A2) describes a method which is based on the principle of

Induction crucible furnace works. In this method, a second galvanically isolated but inductively coupled inductor is used, which generates an oppositely directed, also high-frequency electromagnetic field (0.1 MHz <f <20 MHz), which also penetrates the melt. The electromagnetic force effect, which results from the interaction of the eddy currents induced in the melt and the overlapping inductor fields, creates one

Changes in the geometry of the enamel surface and a more intensive, turbulent mixing, which changes the

Improved melting behavior of introduced glass powder. The effects can be achieved with a phase shift of the two inductor systems of 20 ° to 40 °. However, due to the low electrical conductivity of glass melts and the high losses as well as the high technical complexity for the electrical power supply of the inductor system, the geometrical dimensions of the melting unit that can be realized are severely restricted (diameter of the

10 cm). Another disadvantage of this method is that a continuous operation of the manufacturing process has not yet been realized.

In national as well as in international practice, glass melting plants with the previously known devices for influencing electromagnetic flow are currently not used, since the effects that can be achieved with them are not sufficient. The main reason for this is insufficient mixing and homogenization the melt due to insufficient gradients of the velocity in the fluid volume. In addition, the exponential temperature dependencies of the properties (viscosity, electrical conductivity) of glass melts lead to a difficult to control flow control or regulation, especially in the case of inhomogeneous glass melts.

Another cause for the previously unrealized

Use is inadequate and / or diffuse penetration of the melt with the externally generated magnetic fields, so that the vectorial connection with the electrical current density in the melt does not lead to the maximum possible Lorentz force density. Furthermore, the expenditure for generating the required external magnetic field is too high. This is especially true for high field magnets. As a result, the effects achieved cannot be implemented in a value-adding manner. In addition, the measures to influence electromagnetic currents sometimes lead to disadvantageous side effects:

Reboiling as a result of local overheating due to the uneven distribution of the impressed electrical current densities, which can be increased by the exponential increase in the electrical conductivity of glass melts with temperature.

• Bulging / breakthrough of the batch ceiling in the case of fully electric melts (VES) above the bottom electrodes (bottom electrodes) as a result of the strong Lorentz forces near the electrodes and directed upwards and the resulting increase in heat radiation and vault damage.

The currently used technologies for influencing the flow (convection, mechanical stirring) have the disadvantage that the properties of the glass melt immediately before Leaving the melting unit are insufficiently controllable. Problems to be mentioned are:

• Flow control / portioning of the melt based on empirical approaches

• insufficient chemical and thermal homogeneity of the

melt

• Crystallizations in the melt.

For the subsequent shaping, this may mean long running-in times for the process, large tolerances in the dimensional accuracy and in the properties of the manufactured product. However, the increasing demands on technical glasses and the trend towards cost reduction require a constant improvement in glass production. It is the same

Melting of new, especially high-melting glass compositions is necessary. In order to be able to guarantee the required quality of the glass product in the future, the options for influencing the flow conditions in a melting unit are of great importance.

The object of the invention is therefore to provide a method and a device suitable for carrying out the method for the electromagnetic influencing of the flow conditions of primarily glass melts or other slightly electrically conductive, viscous fluids in channels of any cross section, the flow influences from gravity independently, in sections, efficiently , specifically controllable and tool-free. This is intended on the one hand to minimize the diffusion times characteristic of chemical homogenization in laminar flows (by maximizing the interface of the inhomogeneities) and on the other hand to simultaneously minimize the temperature gradients and to set the residence time of the fluid in the channel can. Furthermore, the homogenization (thermal and chemical) should take place over the entire flow cross-section and flow control or regulation should be possible by changing the dwell time.

According to the invention, this object is achieved by a method and devices as claimed in claims 1 and 18. Preferred refinements of the method according to the invention are characterized in claims 2 to 16, while preferred refinements of the devices are given in claims 19 to 33. A device according to the invention is characterized in that the wall of the channel, which is in direct contact with the fluid, is partially or completely electrically conductive, and an inner electrode is arranged centrally in the channel and, like the outer electrode, is partially or completely electrically conductive , so that when an AC voltage is applied to these outer and inner electrodes, the fluid is partially or completely penetrated by a primarily radial current density distribution over the length of the channel.

In order to generate an alternating magnetic field in the fluid in this channel, at least two (or a multiple thereof) ironless magnetic coils are preferably positioned in a Helmholtz arrangement concentrically around the channel in the method according to the invention. These magnetic coils are fed with coil currents which are analogous to the electrode current with respect to the temporal behavior, but are partially phase-shifted by 180 ° with respect to one another, so that the channel cross-section is penetrated by an axially but sectionally opposite magnetic field. As a result, the electrical flow field j and the magnetic field B are perpendicular to each other in the fluid and here give the maximum possible according to equation (2)

Lorentz force distribution F _L , which, however, is aligned alternately in sections - just like the magnetic field - tangentially to the current density distribution in a positive or negative direction and thus also produces locally alternating tangential velocity components in the fluid.

This means that, compared to Lorentz force distributions in the same direction, conditions of current (fluid density, flux density of the coils), which are otherwise the same, can achieve significantly higher velocity gradients in the fluid. This leads to an efficient homogenization (chemical and thermal) of the fluid and, at the same time, to an increase in the residence time due to the superimposition of the tangential flow components with the axial component from the main flow of the fluid. The homogenization and the dwell time of the fluid in the channel can be varied, adjusted and adjusted via the size of the electrode current, the size of the coil current and / or their phase relationship to one another, regardless of other process parameters, and can also be controlled if appropriate flow measuring devices are available.

The arrangement of the magnetic coils according to the Helmholtz condition (coil radius = coil spacing) ensures a sufficiently uniform distribution of the magnetic field over the entire channel cross section with minimal use of line material for these magnetic coils. If necessary, it makes sense to route the supply and discharge lines for the electrical supply of the electrodes with positive and negative winding senses around the flow channel, so that a locally distributed but oppositely flowing coil arrangement is created, which also generates alternating magnetic fields in their direction.

It is also possible to feed all magnetic coils with the same current directions, so that a magnetic field axially penetrating the channel and the fluid in one direction

arises, but to segment the inner and outer electrodes, to electrically isolate the segments from each other and to switch the opposite electrode segments alternately, so that sections of the fluid alternating radially outward or radially inward are produced, which in turn are caused by the vectorial

Generate a link with the axial magnetic field for current density distribution to generate tangential Lorentz forces, which act in sections in positive and negative directions, and thus also generate alternating, tangential velocity components in the fluid.

With the proposed method and the device according to the invention, flows perpendicular to the main flow direction are generated over the length of a flow channel, regardless of the force of gravity, but in sections opposite flows, thus maximizing the speed gradients, particularly in the transition zones of the partial sections. The magnet coils or parts thereof can be adapted electrically to the available current sources (medium frequency generator, frequency converter) in series or in parallel and with respect to the current direction in the magnet coils the requirements are connected in the same or opposite way.

In the case of high-melting fluids and corresponding quality requirements, the inner and outer electrodes (channel walls) must be made of appropriate platinum alloys due to the required temperature resistance. As a result, frequencies> 1 kHz must preferably be used to avoid platinum corrosion for the coil and electrode current. For other electrode materials

(Molybdenum, tin dioxide, ... copper), the existing network frequencies (50/60 Hz) can be used.

Another effect of the impressed electrical current density j is that the fluid is additionally electrically heated directly. The heating power P _H inevitably generated directly in the fluid according to equation (3)

P _H = —V (3) σ with P _H - heating power and

σ - electrical conductivity of the fluid can, on the one hand, be reduced if necessary and the associated reduction in the Lorentz force density can be compensated for by a proportional increase in the magnetic flux density (a reduction in the current density j to half results in a reduction in the additional heating power to H) in order to ensure the same Lorentz force distribution in this case, only a doubling of the magnetic flux density is necessary) or on the other hand to compensate for the increased heat loss due to the modified flow conditions can be used. These options are particularly advantageous for glass melts.

The application of the invention in particular brings advantages for glass melting techniques with an electrically heated vertical outlet channel and plunger (plunger) for flow control for the production of high-melting, low-alkali or free of borosilicate glasses. As a rule, only the plunger is to be used as the center electrode and that

Adapt the magnet system as a module to the systems. Furthermore, with the electromagnetic flow control according to the invention, new glasses are used, which are conventional

Manufacturing techniques for phase separation or crystallization tend to be produced.

Of course, due to the independence of gravity, it is also within the scope of the invention to arrange the flow channel with the described variants of the magnet and electrode system at any angle to gravity up to the horizontal position or to carry out the method according to the invention under μ-gravimetric conditions (space, parabolic flight, etc.) . The tangential flows are also generated electromagnetically. The proposed method and the associated device is particularly suitable for the production of technical glasses, glasses for flat screens based on LCD and plasma, optical glasses, glass silk, container glasses and others. In addition, some special glasses can only be melted homogeneously with the help of the solution according to the invention. Another advantage of the invention is that the quality of the glasses to be produced can be increased significantly and that a more precise metering of the fluid and the associated going to be less wall thickness tolerances of the final products.

Further advantages, details and developments of the present invention result from the following description of preferred embodiments, with reference to the drawing. FIG. 1 shows a cross section and a section from the FIG

Longitudinal section of a device according to the invention according to a first embodiment;

Figure 2 - a cross section and a section of the

Longitudinal section of a device according to the invention according to a second embodiment;

Figure 3 - the distribution of the magnetic flux density in

2 shows a section of the device according to FIG. 2 with a magnetic flooding of 2500 A,

Scale in T

Figure 4 - the distribution of the current density in the annular gap

Device according to Figure 2 at an electrode voltage of 130 V and a medium electrical

Conductivity of the glass melt of 1 S / m, scale in A / m ²

Figure 5 - the distribution of the Lorentz force in the annular gap

Device according to FIG. 2 with an electrode voltage of 130 V, an average electrical conductivity of the glass melt of 1 S / m and a magnetic flooding of 2500 A, scale in N / m ³ Figure 6 - Principle of a flow control connected to the device according to the invention; Figure 7 - the device according to the invention with a representation of the electrode supply and discharge;

Figure 8 - a cross section and a section of the

Longitudinal section of an inventive

Device with segmented and alternating electrodes.

FIG. 1 shows a device according to the invention in accordance with a first embodiment for influencing electromagnetic flow for a device, in particular under the effect of

Gravity g emerging glass melt (4) shown in a vertical, rotationally symmetrical channel. The main flow of the fluid can also be forced with a pressure (pump) - especially when the channel is arranged horizontally.

In any case, the magnet system (1) is positioned concentrically around the fluid-carrying channel. There is thermal insulation (2) between the outer electrode (3a) of the electrode system (3), which also represents the channel wall, and the magnet system (1). In the case of hot fluids, such as glass melts, it is advisable to reduce the high temperatures by means of thermal insulation (2) in the form of refractory materials common in glass melting plant construction to temperatures below the permissible operating temperatures of the electrical conductor materials (copper) used for the magnetic coils. To design this thermal insulation is to consider the heat transport through conduction and radiation. This requirement does not apply to cold fluids. The coil cross sections of the magnet system can thus be chosen to be smaller. In the best case, the magnet coil and channel cross sections are identical, apart from the space required for the electrical insulation between the magnet coils and the outer electrode.

The inner electrode (3b) is arranged concentrically to the outer electrode (3a) of the electrode system (3) in the middle of the fluid-carrying channel. The outer and inner electrodes can be made of a platinum alloy, for example. The fluid (glass melt) (4) moves between the outer and inner electrodes in the direction of §.

The magnet system (1) consists of ironless ring coils, which are alternately switched against each other. One recognizes the partial magnetic fields (5) that counteract in sections or the Lorentz forces and velocity components in the fluid that alternate in sections in the positive or negative tangential direction. This results in theoretically twice the speed gradient under otherwise identical conditions - particularly advantageous for the inhomogeneities present in highly viscous, laminar flowing fluids

(Streaks) dissolve effectively.

The magnetic coils with the radius r ₀ are arranged concentrically around the channel at a distance 2d. The penetration of the fluid volume with the magnetic field generated by the magnet system (1) is shown in principle with the drawn magnetic field lines (5). The coil cross-sections can be circular or polygonal. The intensity of the magnetic field in the coil cross-section depends on the flux through the magnetic coils w * I and on the mean radius r _{0 of} the pair of coils. Equation (4) applies to the z component of induction on the z axis (= coil axis, direction opposite g):

£ _z (2.0) = - μ ₀ r ₀ ² iW - + - A)

2 (r ^> ₊ (d _{+ z} yy (r ^> ₊ (d - _z yy where 2d - the coil distance,

μo - the absolute permeability,

r ₀ - the coil radius,

w - the number of turns of the coil and

I - denote the coil current. Accordingly, with a preferred use of a Helmholtz coil arrangement with radii ro und 20 mm and floodings of w * I = 1000 A, induction B _z (z, 0)> 40 mT can be generated in each section. As the magnet coil radii become larger, the magnetic flux densities generated become significantly smaller. This can be compensated for by a higher magnetic flux through the coils by changing the number of coil turns w and / or the coil current I.

Are conductive areas in the magnet system, e.g. B. the electrodes and the fluid, the magnetic field is weakened depending on the size of the frequency of the magnetic field and the electrical conductivity and permeability of these areas. The reduction due to shielding is characterized by the depth of penetration δ of the magnetic field. Equation (5) applies to the depth of penetration:

where f - the frequency of the electromagnetic field, μ - the permeability and

σ - denote the electrical conductivity. It decreases exponentially with increasing frequency, permeability and electrical conductivity. Table 1 shows the electromagnetic penetration depth for dispersion-enhanced platinum to illustrate the relationships

(DVS platinum) and for a glass melt with an electrical conductivity of 1 S / m at various possible relative permeabilities depending on the frequency f of the magnetic field.

It can be seen that glasses - even with 1 different relative permeabilities - are always sufficiently penetrated by higher-frequency magnetic fields, but at frequencies> 5 kHz the magnetic field in areas with metallic conductivities and thicknesses of approx. 1 mm For example, the channel walls or external electrodes in the case of glass melts must decay to more than 1 / eth part of its original intensity. The frequency of the electrode and coil current must therefore be set so that minimal electrode corrosion occurs, but the magnetic induction in the fluid is reduced to a maximum of 50% of the induction without shielding due to the shielding effect of the outer electrode. Table 1: Penetration depth δ of DVS platinum and a glass melt as a function of the magnetic field frequency f

If an alternating voltage is applied to the electrode system (3), a radial current density distribution results in the glass melt. With a fixed electrode voltage, the magnitude of the current density depends on the electrical resistance between the electrodes. This is determined by the electrical conductivity of the glass melt and the geometry of the annular gap. Taking into account the additional heating power (see Eq. 3), current densities of up to 100 mA / mm ^{2 are} possible in glass melts. If the temporal behavior of current density and magnetic field are synchronous, a tangential Lorentz force density distribution is generated in the fluid, which forces a tangential flow. At j = 100 mA / mm ² and B = 40 mT, these Lorentz force densities are up to +4000 N / m ³ in the positive tangential direction and -4000 N / m ³ in the negative tangential direction. The difference in the electromagnetically generated force densities from section to section is therefore 8000 N / m ³ . In comparison, the volume force, which acts on a leaking glass melt due to gravity, is only approx. 2300 N / m ³ .

FIG. 2 illustrates a second embodiment of a device for electromagnetic currents according to the invention. influence with alternating counter

Solenoids.

In order to achieve a complete and almost uniform magnetic penetration of the fluid volume, it has proven to be expedient not to switch individual magnet coils, but rather magnet coil groups of at least 2 magnet coils per group with respect to the current direction, as is shown in the second exemplary embodiment in FIG. 2.

Here, the magnetic coils in Helmholtz arrangement are switched in pairs. The inner diameter of the outer electrode is 40 mm, the outer diameter of the inner electrode is 20 mm. 6 water-cooled magnetic coils with a number of turns w = 1, a center diameter of 120 mm and a center position of 60 mm are arranged concentrically. The conductor cross section of the magnetic coils is hollow and rectangular (external dimensions: 15 mm x 10 mm). The solenoids are connected in series and in pairs. A current of 2500 A flows through them at a frequency of 1 kHz. With this flooding, the basic field line image (5) shown in FIG. 2 is created.

FIG. 3 shows the numerically calculated distribution of the magnetic flux density in a device according to FIG. 2 at the time of the maximum of the coil current. It can be seen that the magnetic field penetrates the glass melt completely, sufficiently strongly (up to 10 mT) and evenly in sections. The calculated current density distribution (see FIG. 4) is radial. The current densities are greatest at the inner electrode (3b). They are 20 mA / mm ^{2 here} and 10 mA / mm on the outer electrode (3a). The electrode voltage is 130 V. The The heating power of the electrode current in the electrodes is negligible. The eddy current losses due to the magnetic field in the electrodes and in the melt are also negligible. The required performance of the

Magnetic coils is 4 kW.

The mean Lorentz force densities (see FIG. 5) in one

The device according to FIG. 2 has three sections (-640 / + 480 / -640) N / m ³ . This creates a tangential flow of (-0, 4 / + 0, 3 / + 0, 4) mm / s with alternating direction in the annular gap sections, which results in an average velocity gradient of approx. 5.8 -l / ms. This leads to rapid and good thermal and chemical homogenization of the melt.

If the annular gap through which the fluid flows is open at the lower end, the fluid runs out of the channel in a spiral. The outlet speed of the fluid is expediently controlled via the size of the tangential speed component in the lower annular gap section, which in turn depends on the size of the electrode current and / or the magnetic field. For this purpose, it makes sense to separate and electrically isolate the lower area of the outer and inner electrodes from the upper area, so that the average outlet speed of the fluid is controlled via the electrode current which is supplied to this annular gap section. Likewise, the lower pair of magnetic coils can be disconnected from the power supply of the magnet system and supplied separately, so that the control of the medium outflow speed of the fluid takes place via the size of the magnetic flux density in this lower area. In the upper sections, the electromagnetic homogenization of the

Melt can be adjusted. In order to maximize the control range of the average outlet speed of the fluid, it is expedient to use both possibilities, the separate electrical supply of the electrode and magnetic subsystems being able to take place via synchronized current sources (frequency converters).

FIG. 6 shows the principle of a flow control connected to the device according to the invention. To regulate the average outlet speed of the

A flow measuring device (7) is provided in the flow channel for fluids. The actual value measured with this flow measuring device is matched to the predetermined setpoint by means of a current control (10) of the synchronized current sources (8) and (9). Depending on the type of fluid, suitable flow meters are, for example, but not exclusively, orifices known from the prior art (cold, high-viscosity fluids), vane anemometers (cold, low-viscosity fluids) or Lorentz force anemometers (hot ones

Fluids).

FIG. 7 shows the supply line guide (11) for realizing the locally distributed coil arrangement according to the invention, through which alternating directions flow, with an exemplary number of coil turns of 2. The electrical lead of the outer electrode is in this case with a positive winding sense and the lead of the inner electrode with a negative winding sense is guided in a coil-like manner around the flow channel. Such designs can advantageously be used with high electrode currents (electrically heated feeders from glass melting plants) and / or with flow channels which allow immediate wrapping - that is, without large distances. FIG. 8 shows the cross section and a section from the longitudinal section of a device according to the invention with segmented and alternating electrodes (12a, 12b) and the method that can be carried out with it. The radial current density distributions that are achieved in this way, alternating outwards and inwards, generate tangential Lorentz forces that act in sections in positive and negative directions and thus also locally changing tangential velocity components in the fluid.

In this case, greater speed gradients can be achieved if the ratios of the electrical resistances between the inner and outer electrode segments to neighboring segments are less than 1, since the reversal of the electrical field does not require a return, like the magnetic field, for physical reasons, and consequently the field reversal can take place over much smaller distances .

In the method according to the invention, the aim is to load the magnet systems up to the maximum current, since the greatest magnetic flux density, the highest Lorentz force or the greatest change in the current conditions can be achieved thereby. The inductor current also leads to heating of the

Inductor coil, which leads to destruction if a limit temperature is exceeded. Therefore, the inductor coil can be forced-cooled (water cooling) and provided with a temperature monitor. This enables operation with maximum inductor current and consequently maximum

Realizable magnetic field. Bibliography

[1] - Sims, R .: Stirring in a glass - a technology overview,

Proceedings 75th Glass Technology Conference, pp. 117-121,

German Glass Technology Society, 2001

[2] - Voss, H. J .: Electrically heated glass melting furnaces -

Current status against the background of energy, environment, flexibility and operational security. Glass Be.

Technol., 70, 1997, No. 5, N61-N68

[3] - Osmanis, A. D .; u.a .: Influence of stirring one

Melt in the electromagnetic field on the spectral and color characteristics of chrome-containing glasses. (Orig.

Russ.) In: Proceedings 12th Riga Symposium on

Magnetohydrodynamics 1987, pp. 179-183

[4] - Osmanis, A. D .; u.a .: Intensification of the processes of the glass melt in the electromagnetic field. (Orig. Russ.)

In: Reference book on scientific work, inorganic glasses, coatings and materials, Riga 1987, pp. 123-130

Reference list

1 - magnet system

2 - thermal insulation

3 - electrode system

3a - outer electrode

3b - inner electrode

4 - fluid (glass melt)

5 - magnetic field lines (basic sales)

6 - Electromagnetically initiated flow pattern

7 - flow measuring device

8 - synchronized power source for the magnet system

9 - synchronized power source for the electrode system

10 - Current regulation

11 - supply lines

12 - electrode segments

12a - electrode segment of the outer electrode

12b - electrode segment of the inner electrode B - magnetic induction

B _z - z component of magnetic induction

2d - coil spacing

f - frequency of the electromagnetic field

F _L - Lorentz force

f _L - Lorentz force density

g - gravitational acceleration

I - coil current

j - current density

P _H - heating power

r ₀ - coil radius

V - volume element

v _t - tangential velocity component

w - number of coil turns

δ - depth of penetration

μ - permeability

μo - absolute permeability

σ - electrical conductivity

Claims

1. Method for the electromagnetic influencing of the flow conditions of flowing, low electrically conductive and highly viscous fluids - preferably glass melts - in channels of any cross-section, in which the

Main flow direction vertical, but axially oppositely directed Lorentz forces are generated, which result from the simultaneous impressing of vectorially perpendicular electric and magnetic alternating fields of the same temporal behavior, whereby

the electrical alternating fields generate electrical current density distributions in the fluid via electrodes which are in contact with the fluid and which are directed perpendicular to the main flow direction of the fluid,

- The alternating magnetic fields are generated by an external ironless coil system enclosing the fluid and the electrodes, whose field lines in the fluid are primarily directed parallel to the main flow and

- the direction of one of the two fields by 180 °

is rotated in sections,

and wherein the Lorenz forces of the main flow impress sections of oppositely directed flow components, which as a result of the axial between them

High velocity gradients caused by sections of gravity-independent change the local and temporal distribution of the chemical composition and the temperature in the fluid, as well as the controlled residence time of the fluid in the channel.

2. The method according to claim 1, characterized in that the frequency of the alternating fields and the frequency of electrode and coil current is set so that minimal electrode corrosion occurs and at the same time the magnetic induction in the fluid by the shielding effect of the outer electrode by a maximum 50% of the

Induction without shielding is reduced.

3. The method according to claim 1 or 2, characterized in that the necessary magnetic flux is set via the height of the coil current, the effective value of the magnetic flux density on the inner electrode of the channel is at least 10 mT.

4. The method according to any one of claims 1 to 3, characterized

characterized in that the homogenization of the fluid can be changed via the size of the flow components which are directed perpendicularly but axially in sections to the main flow direction.

5. The method according to any one of claims 1 to 4, characterized

characterized in that the fluid is stirred and homogenized with the channel closed.

6. The method according to any one of claims 1 to 5, characterized

characterized in that the fluid enters axially on one channel side and exits on the other channel side with a helical flow.

7. The method according to any one of claims 1 to 6, characterized

characterized in that the size of the flow components perpendicular to the main flow direction in one or several sections, the residence time of the fluid in the channel and thus its flow can be changed.

8. The method according to any one of claims 1 to 7, characterized

characterized that the stirring effect and the medium

Exit velocity of the fluid can be controlled and regulated relative to one another via the size of the electrode currents, the size of the coil currents and / or their phase relationship.

9. The method according to claim 7, characterized in that the average exit velocity of the fluid over the

Size of an area of the outer and inner electrodes which is separate and separately supplied from the power supply of the outer and inner electrodes is controlled, the electrical operating parameters of the other electrode system part and the magnetic coils being kept constant.

10. The method according to claim 7, characterized in that the average outlet speed of the fluid is controlled via the size of the coil current of the magnet coils separated and separately supplied from the power supply of the other magnet coils, the electrical

Operating parameters of the electrode system and the other solenoids are kept constant.

11. The method according to claim 7, characterized in that the average exit velocity of the fluid both via the size of the electrode currents of a separate and separately supplied from the outer and inner electrodes

Range and the size of the coil currents of the solenoids separated and separately supplied from the power supply of the other solenoids is controlled, the electrical operating parameters of the other electrode system part and the other solenoid coils are kept constant.

12. The method according to any one of claims 1 to 11, characterized

characterized in that the average exit velocity of the fluid is recorded with a flow measuring device (6).

13. The method according to any one of claims 1 to 12, characterized

characterized in that the average exit velocity of the fluid from the channel is adapted online to the subsequent processing process.

14. The method according to any one of claims 1 to 13, characterized

characterized in that the stirring or homogenization times are determined by the closing times of the channel.

15. The method according to any one of claims 1 to 14, characterized

characterized in that the changed heat loss resulting from the modified flow conditions is compensated by the heating effect of the electrical current density in the fluid.

16. The method according to any one of claims 1 to 15, characterized

characterized in that the maximum current for the magnet system is controlled and limited by temperature measurement.

17. Device for electromagnetic interference

Flow conditions of flowing low electrically conductive and highly viscous fluids - preferably glass melt - in channels of any cross-section with a magnet system (1) surrounding the channel, consisting of at least two ironless magnet coils, which are positioned concentrically around the channel and an electrode system (3) with an outer electrode (3a) and an inner electrode arranged in the center and concentrically in the channel ( 3b), characterized in that the magnetic coils are connected in opposite sections in sections.

18. Device for electromagnetic interference

Flow conditions of flowing low electrically conductive and highly viscous fluids - preferably glass melts - in channels of any cross-section with a magnet system (1) surrounding the channel made of at least two ironless magnet coils, which are positioned concentrically around the channel, and an electrode system (3) with an outer electrode ( 3a) and an inner electrode (3b) arranged centrally and concentrically in the channel, characterized in that the magnetic coils are connected in the same way, that the outer electrode (3a) and the inner electrode consist of individual segments, the individual

Segments are electrically insulated from one another and adjacent electrode segments are alternately connected in opposition.

19. The device according to claim 17, characterized in that the magnetic coils are connected individually or in groups with the opposite current direction.

20. Device according to one of claims 17 to 19, characterized in that the channel is a tube in which a second tube with a smaller diameter is arranged concentrically, that the tubes as an outer or inner electrode are formed and that the fluid flows in the annular gap between these tubes in an axial direction.

21. Device according to one of claims 17 to 20, characterized in that the magnetic coils are arranged according to the Helmholtz condition.

22. Device according to one of claims 17 to 21, characterized in that the magnetic coils are arranged distributed over a partial region of the channel or over the entire channel length.

23. Device according to one of claims 17 to 22, characterized in that the magnetic coils each consist of a turn, the cross section of which is preferably designed as a flat rectangular waveguide.

24. Device according to one of claims 17 to 23, characterized in that the magnetic coils are formed from the electrical supply and discharge lines of the electrode system.

25. Device according to one of claims 17 to 24, characterized in that water cooling is provided for the windings of the magnetic coils.

26. Device according to one of claims 17 to 25, characterized in that the electrode system (3) consists of platinum, platinum alloys, molybdenum or tin dioxide.

27. Device according to one of claims 17 to 26, characterized in that the electrode and the magnet system are fed by a current source and the adaptation the voltages or currents take place via inductive transformers.

28. Device according to one of claims 17 to 26, characterized in that the electrode and the magnet system are fed by two electrically isolated, but time-synchronized current sources.

29. Device according to one of claims 17 to 28, characterized in that the flow channel can be closed on one side.

30. Device according to one of claims 17 to 29, characterized in that a flow measuring device (7) is arranged in the channel, preferably at the channel end

31. Device according to one of claims 17 to 30, characterized in that temperature sensors are arranged in the magnet system.

32. Device according to one of claims 17 to 31, characterized in that a region of the outer and inner electrodes is separated from the other, is electrically insulated and is supplied electrically separately with a synchronized current source.

33. Device according to one of claims 17 to 32, characterized in that coils are galvanically isolated from the power supply of the other coils and are separately supplied electrically with a synchronized current source.