JP2000152600A - Induction-type electromagnetic drive device for conductive fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction-type electromagnetic drive device which has high mechanical strength and can be used under high temperature and high pressure while the advantages of the induction-type electromagnetic drive device which can be used in a severe environment as it does not need an electrode and which can use an AC power supply whose current is relatively low are utilized. SOLUTION: The stator 3 of an induction-type electromagnetic drive device is provided on the outer circumference of a cylindrical pipe 2 which is made of insulating material and of which a flow path is composed. The stator 3 provided on the outer circumference of the cylindrical pipe 2 has 3-phase AC windings 32 which are wound spirally in a core 30 with respective shifts of 60 deg. in order to turn the cylindrical pipe 2 with a constant angular frequency ω0 by applying distorted magnetic field (flux density B) to the outer circumference of the pipe 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductive electromagnetic drive for a conductive fluid.

[0002]

2. Description of the Related Art In a flow of a conductive fluid represented by a liquid metal, a current can flow in a working fluid.
Direct use of electromagnetic force is possible. A driving device using this electromagnetic force (including a device having a stirring function in the present specification) has many advantages such as no rotating mechanical parts, and has been studied in various countries around the world for a long time, and has now been developed. It has been put to practical use in various fields. In particular, in recent years, the use of electromagnetic force in the field of steelmaking has become popular, and there has been an increasing demand for stable operation in more severe environments.

[0003] Electromagnetic driving devices can be classified into a conduction type and an induction type. The operating principle of these driving devices is the same as that of a motor using a solid rotor, and corresponds to a DC machine and an induction machine, respectively.

[0004] Among them, the conduction type electromagnetic drive device connects a DC power supply to an electrode embedded in a duct wall surface so that a current flows in a fluid. This method is relatively simple in principle and apparatus, so that performance prediction and measurement with an experimental machine are relatively easy. However, when the temperature is high or a highly active fluid is used, the electrode is easily damaged,
There are disadvantages, such as the need for a low-voltage, large-current DC power supply.

On the other hand, in the induction type electromagnetic drive device, current is generated by electromagnetic induction by a moving magnetic field. This method is
Since no electrodes are required in principle, it is suitable for use in harsh environments. Another advantage is that a relatively low-current AC power supply can be used. For this reason, in fields such as steelmaking, inductive electromagnetic drive devices are often used.

Representative examples of the induction type electromagnetic driving device include a parallel plate type (plane sinusoidal traveling magnetic field), a concentric tube type (axially symmetric sinusoidal traveling magnetic field) and a spiral flow path type (uniform rotating magnetic field). One is. All of these standard systems are difficult to use under high temperature and high pressure. this is,
This is because the parallel-plate type flow path side wall and the spiral flow path type flow path partition wall are generally made of copper. Also, replacing them with materials of low conductivity to avoid damaging the copper walls at high temperatures results in very large losses. Such devices can be used for agitation, but are difficult to use for axial driving against pressure gradients. On the other hand, in the concentric tube type, since the electromagnetic force acts only on the portion near the outer wall, a ferromagnetic column is generally installed at the center. For this reason, loss is large at a high temperature exceeding the Curie point, and there is a problem in structural strength at a high pressure.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the electromagnetic driving device, the present invention is suitable for use in a severe environment because no electrode is required. An object of the present invention is to provide an induction-type electromagnetic drive device that has high mechanical strength and can be used under high temperature and high pressure while taking advantage of an induction-type electromagnetic drive device that can use a power supply.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, an induction-type electromagnetic drive device for a conductive fluid according to the present invention applies a twist to a magnetic field traversing a flow path of the conductive fluid, and applies a twist to a tube shaft. It is characterized by being rotated around.

In this case, an inductive electromagnetic drive device can be formed by arranging the three-phase AC stator winding spirally on the iron core.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an inductive electromagnetic drive device for a conductive fluid according to an embodiment of the present invention.

First, in order to show the basic performance of the induction type electromagnetic driving device for a conductive fluid of the present invention, a theoretical analysis of an electromagnetic field and a flow field in a circular channel is performed. Here, for simplicity, it is assumed that the magnetic Reynolds number is sufficiently small, and the induced magnetic field due to the current in the flow path is ignored. Also, assume that the flow path is sufficiently long, and ignore the end effect. The theoretical performance is shown using the results obtained.

FIG. 1 schematically shows the flow path and magnetic field distribution of the induction machine of the induction type electromagnetic drive for conductive fluid of the present invention. The flow path 1 is composed of an insulating circular tube 2 having a radius R ₀ . The stator 3 of the induction type electromagnetic driving device is installed on the outer periphery of the circular tube 2, a torsional magnetic field (magnetic flux density B) is applied from the outer periphery of the circular tube 2, and it is rotated at a constant angular frequency ω ₀ . Such a magnetic field is not only a rotating magnetic field but also a traveling magnetic field in the z direction. For this reason, the conductive fluid in the flow path 1 constituted by the circular tube 2 receives not only the rotational torque but also the electromagnetic force in the axial direction.

In the formulation, the following is assumed. (1) Magnetohydrodynamic (MHD) approximation is possible. (A) The convection current is sufficiently smaller than the conduction current and can be ignored. (B) Displacement current is negligible. (C) The electrostatic force is sufficiently smaller than the Lorentz force and can be ignored. (2) The working fluid is an incompressible Newtonian fluid, and the density ρ, viscosity η, conductivity σ, and magnetic permeability μ are constant values. (3) magnetic Reynolds number R _m is sufficiently smaller than 1. In this case, the magnetic field induced by the current in the fluid can be neglected, and the magnetic field can be approximated by the externally applied magnetic field. However, this assumption holds for a good approximation when the flow velocity is not so large for a small device. The analysis result is also useful as a first approximation for a large device.) (4) The flow path and the magnetic field application region are sufficiently long, and the end effect can be neglected (however, in many cases, the end effect cannot be ignored in an actual apparatus).

As a design target of the stator, the following magnetic flux density distribution is given on the tube wall.

[0015]

(Equation 1)

Here, ＾ indicates a dimensional variable, and k ₀ indicates a wave number in the axial direction. Here, the magnetic flux density distribution on the tube wall is expressed by the following equation (1) using an ideal stator (described later).
The analysis inside the flow path is performed assuming that the above is maintained.

From the question setting, the representative length R ₀ and the representative time T ₀
= Ω ₀ ^-1 and the representative magnetic flux density B ₀ . Also, the representative speed is set to U ₀ = R ₀ ω ₀ . These are used to evaluate each term of Ohm's law and equation of motion to obtain the following representative electric field E ₀ , representative current j ₀ and representative pressure p ₀ .

[0018]

(Equation 2)

Each variable is standardized and dimensionless using these representative quantities.

The equations governing the electromagnetic and flow fields are expressed in a dimensionless form as follows:

[0021]

(Equation 3)

The dimensionless parameters that appear in the equations and boundary conditions are:

[0023]

(Equation 4)

The parameter α is the ratio of the circumference of the flow path 1 formed by the circular tube 2 to the axial wavelength of the magnetic field, and represents the degree of twist of the magnetic field. Here, it is called “torsion ratio”. The square of the Hartmann number, Ha ^2, is a value obtained by evaluating the ratio of Lorentz force to viscous force in the mainstream, and the thickness of the boundary layer is characterized by Ha ⁻¹ . The interaction parameter (Stewart number) N is a value that evaluates the ratio of the Lorentz force to the inertia force in the mainstream, and is a parameter that characterizes the effect of inertia. Magnetic Reynolds number R _m is a value obtained by evaluating the ratio of the induced magnetic field and the external magnetic field due to the flow path within the current, a parameter characterizing the effect of the induced magnetic field. Here, the magnetic Reynolds number is R _m <<
Since the case of 1 is considered, Ampere's law equation (4)
Is approximated as:

[0025]

(Equation 5)

Therefore, a scalar potential に 関 す る with respect to the magnetic flux density B is defined as follows.

[0027]

(Equation 6)

Substituting into Gauss's law equation (3),

[0029]

Equation 7

From the first equation of equation (10), the boundary condition is

[0031]

(Equation 8)

The electric field E is set as follows.

[0033]

[Equation 9]

[0034] Here, e _z is a unit vector in the axial direction of the tube. The first term on the right side represents an electrostatic field, and the second term represents an induced electromotive force generated by a magnetic field traveling in the z direction. (Here, when observing from a coordinate system that moves with the traveling magnetic field,

[0035]

(Equation 10)

## EQU1 ## The electric field in that case can be represented only by the scalar potential φ. When this is rewritten into an electric field in a stationary coordinate system by Lorentz transformation, the equation (1) is obtained.
6) is obtained. ) Substituting equations (13) and (16) into Faraday's law (5),

[0037]

[Equation 11]

Is obtained. If the end effect is negligible, the above equation is automatically satisfied. Equation (1) is given by Ohm's law (7).
3) Substituting equation (16) gives

[0039]

(Equation 12)

Substituting this into the law of conservation of charge (6) gives

[0041]

(Equation 13)

Equation (18) is added to the second equation of boundary condition equation (10).
And considering the fluid adhesion condition u = 0,

[0043]

(Equation 14)

Equations (14) and (15) are boundary value problems of independent differential equations, and ψ can be obtained prior to other unknown variables. When the obtained ψ is treated as a known function, Equations (8), (9) and (19) can be expressed as u, p,
It becomes a closed simultaneous differential equation with respect to φ, and the boundary condition is given by the third expression of Expression (10) and Expression (20). However, B and j are given by using equations (13) and (18) as auxiliary equations.

The solution after a sufficient time has elapsed is a periodic solution for t. However, since the flow field and the electric field are governed by nonlinear equations, variable separation using complex amplitude is not possible. Considering that the magnetic field is twisted, the independent variables are replaced as follows.

[0046]

(Equation 15)

Considering the converted independent variables, if the flow is laminar, there is a steady solution. If the end effect can be ignored, the variables except for the pressure p do not depend on Z.

[0048]

(Equation 16)

Can be placed. With this conversion,
The unsteady three-dimensional problem for (r, θ, z; t) is (R,
The result is a stationary two-dimensional problem concerning (i). (If the end effect is considered, it becomes a stationary three-dimensional problem with respect to (R, Θ, Z).) The result obtained as a function of the independent variable (R, Θ) is obtained at any time t and any cross section z. In the r-θ plane. However, it is necessary to convert Θ into θ by using the third expression of Expression (21).

When Expressions (14) and (15) are represented by (R, Θ),

[0051]

(Equation 17)

When Expressions (19) and (20) are represented by (R, Θ),

[0053]

(Equation 18)

The expressions (8), (9) and (10)
Is represented by (R, Θ),

[0055]

(Equation 19)

If one is interested in the transient behavior until the steady state is reached, the derivative term relating to T may be added to the inertia terms of the equations of motion (29) to (31).

Equations (24) to (33) are closed equations. Therefore, a solution can be obtained without explicitly seeking the magnetic flux density and electric field. If the distribution of magnetic flux density and electric field is required, it can be calculated by the following equation.

[0058]

(Equation 20)

Incidentally, the magnetic flux density does not depend on the flow velocity, but is given by the solutions of the equations (24) and (25). The scalar potential ψ is set as follows.

[0060]

(Equation 21)

By substituting into equations (24) and (25),

[0062]

(Equation 22)

The solution is a first-order modified Bessel function of the first kind I
_It is expressed as follows using ₁ (x).

[0064]

(Equation 23)

Although the potential φ depends on the flow velocity, an analytical solution can be easily obtained since u = 0 at the start. In this case, φ is set as follows.

[0066]

(Equation 24)

Substituting into equations (26) and (27), u = 0
Then

[0068]

(Equation 25)

The solution is a modified Bessel function of the first kind I ₁ (x) and its derivative I ₁ ′ (x) = dI ₁ / dx = I ₀ (x) −I ₁
It is expressed as follows using (x) / x.

[0070]

(Equation 26)

The average of the driving force at the start in the 始 動 direction (the same as the average in real time) is

[0072]

[Equation 27]

The average in the cross section of the driving force is

[0074]

(Equation 28)

[0075]

(Equation 29)

In general, when the induction machine reaches a certain speed, it is synchronized and j = 0. Here, the following rigid body motion is assumed as the synchronization speed.

[0077]

[Equation 30]

In this case, the following synchronization condition is immediately obtained from Ohm's law equation (33).

[0079]

(Equation 31)

Is derived. The above equation indicates that the synchronization speed is not uniquely determined. This is a remarkable fact when a rotating torsional magnetic field is used, and is important in discussing the performance of a driving device. In the actual flow in the flow path 1 constituted by the circular pipe 2, the adhesive condition expression (32)
Must be satisfied, there is no rigid body motion as in equation (46). (When using a rotating torsional magnetic field for the levitation of a metal lump, the above-mentioned non-unique synchronization conditions must be considered. If the synchronization speed is reached, the levitation force will not work. Therefore, it is expected that the synchronization condition will be modified by the influence of the boundary layer to obtain uniqueness.

When the inertia of the fluid is large to some extent, the fluid cannot follow the torsion of the magnetic field and tends to go straight. Even in this case, the swirling component of the flow velocity cannot be ignored, but it is expected that there is a condition range that can be approximately handled as an axisymmetric flow u = (0, uθ (R), u _z (R)).

[0082]

(Equation 32)

Here, φ is set as follows.

[0084]

(Equation 33)

[0085]

(Equation 34)

Further, by substituting equation (48) into equations of motion (30) and (31) and taking the circumferential average (same as the real-time average),

[0087]

(Equation 35)

The boundary conditions are obtained from the equations (27) and (32).

[0089]

(Equation 36)

In the central region, the viscous term is a minute term of about Ha- ² and can be ignored. The solution in that case is

[0091]

[Equation 37]

Here, a is an unknown constant.

[0093]

(Equation 38)

Here, f 'indicates df / dR when the tube wall R = 1. The solution satisfying the second and third expressions of the boundary condition expression (52) is

[0095]

(Equation 39)

From the connection conditions of the central area solution (53) and the boundary layer solution (56),

[0097]

(Equation 40)

[0098] The solution is
Expressed in the form of on (first term only),

[0099]

(Equation 41)

Incidentally, in an actual induction type electromagnetic drive device, the stator is formed by winding a thin winding around an iron core multiple times. Here, the winding is replaced with a current sheet for simplicity. In this case, the tube wall composed channel 1 by circular pipe 2, a current sheet, all core inner wall concentric cylinder, the tube wall and the current sheet in the flow channel 1 is sufficiently than the flow path inner diameter 2R ₀ Shall be thin. The material of the iron core disposed outside the current sheet is ideal, and has a very high magnetic permeability and a very low conductivity. Applying Ampere's law across the current sheet,

[0101]

(Equation 42)

Stator design target equation (1) and charge conservation law

[0103]

(Equation 43)

In order to satisfy

[0105]

(Equation 44)

Equation (62) indicates that the current of the current sheet is independent of the location,

[0107]

(Equation 45)

The above-described magnetic field can be generated by spirally winding the three-phase AC stator windings at an angle of 60 °. It is the same as the stator of the three-phase two-pole induction motor, except that the core groove and the winding are spiral.

[0109]

FIG. 3 shows an embodiment of an induction type electromagnetic driving device for a conductive fluid according to the present invention. This induction type electromagnetic drive device comprises a stator 3
And twisted magnetic field (magnetic flux density B) from the outer circumference of the circular tube 2
So that the stator 3 installed on the outer periphery of the circular tube 2 is shifted by 60 ° from the three-phase AC winding 32 to the iron core 30 so that it can be rotated at a constant angular frequency ω _0. It is configured to be wound spirally. In this case, the iron core 30 is formed by laminating a donut-shaped electromagnetic steel plate 31 having a required thickness (thin plate) in which recesses 31a are formed at intervals of 60 ° by pressing or the like while being shifted by a predetermined angle. A simple and accurate spiral groove 30a for inserting
By inserting the windings 32 into the concave grooves 30a, the three-phase alternating-current windings 32 can be spirally arranged by being shifted by 60 °. Then, as shown in FIG. 3B, the winding 32 is, for example, a first phase 32.
a, the second phase 32b and the third phase 32c are arranged in order. (Note that the circles in the figure indicate the direction of the current.) This makes it possible to apply a twist to the magnetic field crossing the flow path 1 and rotate it around the tube axis.
Electromagnetic force can be applied to the entire flow path 1, and the loss is small even if the pipe wall of the circular pipe 2 constituting the flow path 1 is an insulator, so that the material of the pipe wall is restricted. It has high mechanical strength and can be used under high temperature and high pressure.

The inductive electromagnetic drive device for a conductive fluid according to the present invention can be specifically applied to the following uses. When this induction-type electromagnetic drive device is attached to the immersion nozzle of a continuous casting machine, it is possible to control the flow rate in a non-contact manner, and in principle, it is possible to completely stop the inflow or reverse the flow. At the same time, a swirling flow can be provided in the immersion nozzle. It is expected that the flow in the mold is stabilized by the swirling flow. This induction type electromagnetic drive device is excellent in durability and mechanical strength. Further, when this induction type electromagnetic drive device is attached to a groove type induction furnace, the fluid heated by induction heating is discharged from the groove at a high speed. Thereby, it is expected that the inclusions are prevented from adhering to the inner wall of the groove, and the maintenance labor is remarkably reduced. Further, the temperature in the furnace is made uniform. Further, the induction type electromagnetic drive device can be applied to a levitation device. In this case, the lump of the molten metal floats and is held in the air.

[0111]

The inductive electromagnetic drive device for a conductive fluid according to the present invention applies a twist to a magnetic field traversing the flow path of the conductive fluid and rotates the magnetic field around the pipe axis. Electromagnetic force can act on the whole road,
Since the loss is small even when the flow path pipe wall is an insulator, the material of the flow path pipe wall is not restricted, the mechanical strength is high, and it can be used under high temperature and high pressure.

Further, by forming a three-phase AC stator winding spirally on an iron core to constitute an induction type electromagnetic drive device,
Since the three-phase alternating current of the stator maintains a phase difference of exactly 120 °, power loss can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an induction type electromagnetic driving device for a conductive fluid according to the present invention.

FIG. 2 is a graph showing a torsional ratio dependence of a starting driving force.

3A and 3B are explanatory views showing an embodiment of an induction type electromagnetic driving device for a conductive fluid of the present invention, wherein FIG.
(B) is a plan view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow path 2 Circular tube 3 Stator 30 Iron core 31 Magnetic steel sheet 32 Winding B Magnetic flux density of a torsion magnetic field

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) F27D 11/06 F27D 11/06 B (71) Applicant 591026274 Fuji Electric Engineering Co., Ltd. Kashiwa, Nishiyodogawa-ku, Osaka-shi, Osaka 1-10-3 Sato (72) Inventor Kazuyuki Ueno 2-1-1 Katahira Research Institute, Tohoku University, Aoba-ku, Sendai, Miyagi Prefecture (72) Inventor Shinichi Kamiyama Ochiai-san, Aoba-ku, Sendai, Miyagi Prefecture 10-18 F term (reference) 4E004 MB11 4E014 LA17 4K063 AA00 AA12 AA19 BA02 BA03 CA06 FA35

Claims (2)

[Claims] 1. An inductive electromagnetic drive device for a conductive fluid, wherein a torsion is applied to a magnetic field traversing a flow path of the conductive fluid, and the magnetic field is rotated about a tube axis. 2. The induction type electromagnetic drive device for a conductive fluid according to claim 1, wherein a three-phase AC stator winding is spirally disposed on the iron core.