JP7170337B2 - Variable magnetic field generation system and static magnetic refrigeration system using the same - Google Patents

Description

The present invention relates to a system for generating a varying magnetic field using superconducting coils and a static magnetic refrigeration system using the system.

2. Description of the Related Art Conventionally, a magnetic refrigerator using a magnetic material that generates heat and absorbs heat in response to a magnetic field (hereinafter referred to as "magnetic working material") is known as a refrigerator that is applied to cryogenic temperatures below liquid helium.
For example, Patent Literature 1 discloses a stationary magnetic refrigerator in which a magnetic working material is arranged in the central portion of a superconducting coil and a magnetic shield is reciprocated in the space between the superconducting coil and the magnetic working material. . In this technology, refrigeration is realized by changing heat generation/absorption of the magnetic working material by applying or blocking a magnetic field to the magnetic working material according to the reciprocating motion of the magnetic shield.
Further, Patent Document 2 discloses a magnetic refrigerator having a structure in which a superconducting coil and a magnetic shield are stacked and a magnetic working material is arranged inside. In this technology, by reciprocating the magnetic shield and switching between a state in which it is arranged inside the superconducting coil and a state in which it is arranged inside the magnetic shield, the heat generation/absorption of the magnetic working material is changed, and refrigeration is performed. Realize
Both technologies utilize superconducting coils. Since superelectric coils can generate strong magnetic fields, they are applied to medical diagnostic imaging equipment and magnetic levitation trains for transportation. A technology called SMES (Superconducting Magnetic Energy Storage) is also known as a system using superelectric coils. That is, since superconductivity has the characteristic of zero electrical resistance, when both ends of the coil are closed to form a closed circuit with current flowing through the coil, the current continues to flow through the coil without attenuation. The magnetic field created by continues to occur. SMES is a technique for storing power as magnetic energy in this way.

JP-A-4-273956 JP-A-4-327479

In conventional magnetic refrigeration technology, the generation of a magnetic field by a superconducting coil requires cooling to maintain the superconducting state. Alternatively, energy is required for the reciprocating motion of the magnetic working material itself, leaving room for improvement in energy efficiency as a whole. Therefore, there has been a demand for a technique for changing the magnetic field acting on the magnetic working material while saving energy.
The technology to change the magnetic field is expected to be applied not only to magnetic refrigeration but also to a wide range of fields.
SUMMARY OF THE INVENTION In view of such problems, it is an object of the present invention to provide an energy-saving technique for varying a magnetic field, and to provide a magnetic refrigeration technique utilizing the technique.

The present invention
A fluctuating magnetic field generation system that generates a fluctuating magnetic field by a plurality of superconducting coils,
a plurality of superconducting coils;
an initial charging circuit that connects and disconnects the superconducting coil and a power supply;
an energy transfer circuit capable of arbitrarily changing the current flowing through each of the plurality of superconducting coils while being disconnected from the power source;
a control unit that controls the initial charging circuit and the energy transfer circuit;
The control unit
an initial charging control unit that connects the superconducting coil to a power source and controls an initial charging circuit to disconnect the power source after initial charging with a predetermined current is achieved;
an energy transfer controller for controlling the energy transfer circuit to vary the current flowing through each of the superconducting coils in a preset sequence after the initial charging is achieved. can be done.

According to the present invention, the magnetic field generated in each superconducting coil can be varied by transferring the energy initially charged in the superconducting coils between the superconducting coils. Therefore, it is possible to suppress the supply of energy from the outside for generating the fluctuating magnetic field to the extent that it is almost unnecessary.

In the variable magnetic field generation system of the present invention,
An even number of the plurality of superconducting coils may be provided.

Although the number of superconducting coils is arbitrary, when an even number of superconducting coils are provided, the superconducting coils can be arranged in a well-balanced manner. By doing so, it is possible to reduce the size of the entire system, and to arrange the magnetic fields generated by the superconducting coils in a well-balanced manner. The arrangement is more preferably point-symmetrical or line-symmetrical.

A variable magnetic field generation system of the present invention,
The plurality of superconducting coils are provided with three or more,
The energy transfer control unit may apply a current in the opposite direction to adjacent superconducting coils.

By doing so, the magnetic fields generated by the superconducting coils through which currents flow in opposite directions cancel each other out, and leakage of the magnetic field to the outside can be suppressed.
A superconducting coil that allows a current to flow in the opposite direction can be arbitrarily selected. It is not always necessary to select the one with the shortest mutual distance. The above-mentioned "proximity" means within a range in which interaction that cancels out the magnetic fields can be obtained. Also, the number of superconducting coils through which a current is passed can be set arbitrarily, but if the number is even, there is an advantage that the interaction of canceling out the magnetic fields can be obtained relatively effectively.

In the variable magnetic field generation system of the present invention,
The energy transfer control unit may group a predetermined number of the plurality of superconducting coils, and sequentially apply the maximum current to each superconducting coil in the group.

By doing so, the current flowing through each superconducting coil changes between the maximum and zero, so that the maximum magnetic field fluctuation can be obtained.
The predetermined number of groups can be determined arbitrarily. For example, all of a plurality of superconducting coils may be considered as one group. You may divide these into the same number of groups of 2 or 3 or more. They may also be divided into different numbers of groups.

In the variable magnetic field generation system of the present invention,
The predetermined current in the initial charging is the current required to store the magnetic energy in the entirety of the plurality of superconducting coils in a reference state in which 100% of the current flows through a predetermined number of the plurality of superconducting coils corresponding to a part of the plurality of superconducting coils. It may be a value.

The energy stored in the superconducting coil is given by 0.5Li ² where L is the reactance and i is the current. Therefore, assuming that there are M superconducting coils in total in a reference state in which 100% current is passed through a predetermined number n of coils, the current value per coil is the maximum current×(n/M) ^{0 .5} . By doing so, the necessary energy can be stored in the superconducting coil in advance in just the right amount.

The present invention can be configured as a variable magnetic field generation system, or as various systems using this system.
For example, the present invention provides
A stationary magnetic refrigeration system using the magnetocaloric effect,
A varying magnetic field generating system according to any of the above;
A static magnetic refrigeration system comprising a heat exchanger made of a magnetic working material that generates heat/absorption due to fluctuations in the magnetic field and is disposed inside at least one of the superconducting coils.

As described above, the fluctuating magnetic field generating system of the present invention can fluctuate the magnetic field while saving energy, so that magnetic refrigeration can be realized while saving energy.
Various substances other than gadolinium can be used as the magnetic working substance in the present invention. Also, the shape of the heat exchange body can be arbitrarily determined. The heat exchange body may be composed of a lump of the magnetic working material, or may be composed of fine wires using the magnetic working material woven into a mesh. Such thin wires may be manufactured by, for example, a so-called powder-in-tube manufacturing technique in which a magnetic working material is wrapped in copper or other metal with good thermal conductivity.

In the stationary magnetic refrigeration system of the present invention,
The magnetic working material may be arranged inside all of the plurality of superconducting coils.

By doing so, the fluctuating magnetic field generated in each superconducting coil can be efficiently used for refrigeration.

The present invention does not need to have all of the various features described above, and can be configured by omitting or combining some of them as appropriate. Moreover, the present invention can be configured as various systems using a variable magnetic field generation system in addition to the static magnetic refrigeration system. Furthermore, the present invention may be configured in aspects such as a method for generating a varying magnetic field and a static magnetic refrigeration method.

1 is an explanatory diagram showing the configuration of a static magnetic refrigeration system; FIG. FIG. 4 is an explanatory diagram showing a sequence (1) of energy transfer; FIG. 4 is an explanatory diagram showing a sequence (2) of energy transfer; FIG. 2 is an explanatory diagram showing the arrangement of superconducting coils; It is explanatory drawing which shows the result (1) of magnetic field analysis. It is explanatory drawing which shows the result (2) of magnetic field analysis. It is explanatory drawing which shows the result (3) of magnetic field analysis. It is explanatory drawing which shows the result (4) of magnetic field analysis.

Embodiments of the present invention will now be described with reference to the configuration of a static magnetic refrigeration system using a superconducting coil and a magnetic working material. This is a structural example of a system for recondensing hydrogen and storing it as liquid hydrogen. It is a system that performs refrigeration at extremely low temperatures.

FIG. 1 is an explanatory diagram showing the configuration of a static magnetic refrigeration system.
Four cooling devices 50 using superconducting coils are installed in the sealed container 40 . The structure of the cooling device 50 is shown in the lower right.
In the cooling device 50 , a superconducting coil 51 is installed inside the sealed container 40 . The superconducting coil 51 is cooled to realize superconductivity, but this cooling mechanism is omitted from the drawing to avoid complication of the drawing.
In the internal space of the superconducting coil 51, a magnetic working material 52 that generates heat/absorbs heat according to the state of the magnetic field is installed. In this embodiment, the shape is cylindrical, but it may be any shape. The magnetic working material 52 can be composed of various materials, but in this embodiment, a gadolinium alloy (eg, Gd ₅ Ge ₄ ) is used. A fine wire is produced by a so-called powder-in-tube manufacturing technique in which gadolinium alloy powder is filled in a hollow fine wire made of a material having good thermal conductivity such as copper. can be configured. It is not limited to such a configuration, and may be composed of gadolinium lumps or the like.
A heat transfer post 54 is provided in contact with the magnetic working material 52 . The heat transfer post 54 can be constructed of a solid that conducts heat well. When the magnetic working material 52 generates heat/endotherm under the action of the magnetic field, the corresponding heat is transferred through the heat transfer column 54 . An exhaust heat cooling device 55 is attached to the upper end of the heat transfer column 54 . When the magnetic working material 52 is in an exothermic state, the heat is transferred to the exhaust heat cooling device 55 through the heat transfer column 54 and discharged from the sealed container 40 to the outside. A thermal switch 53 is attached in the middle of the heat transfer column 54 . The thermal switch 53 is an element that transfers heat only in one direction from the thermal switch 53 to the heat transfer column 54 . Since the thermal switch 53 can use various well-known elements, detailed description thereof will be omitted. By providing the thermal switch 53, when the magnetic working material 52 absorbs heat, heat flows from the thermal switch 53 through the exhaust heat cooling device 55, and the condenser 57 that liquefies the hydrogen gas is cooled.
A hydrogen storage tank 56 is attached to the lower portion of the cooling device 50 . When hydrogen is supplied to the cooling device 50 , the hydrogen is reliquefied by coming into contact with the condensation section 57 that has been cooled down by magnetic refrigeration, and is stored in the hydrogen storage tank 56 as a liquid.
In the above configuration, the heat transfer column 54 may be configured by a pipe in which a heat exchange medium is sealed so as to circulate inside. In this case, the thermal switch 53 may be a switch for switching the circulation direction of the medium.

The four cooling devices 50 described above are arranged inside the sealed container 40 . The number and arrangement of the cooling devices 50 can be arbitrarily determined. Considering the overall balance, etc., it is preferable to prepare an even number of cooling devices 50 .

Each cooling device 50 is connected to an initial charging circuit 22 for connecting and disconnecting the superconducting coil 51 and the power supply 24 . In this embodiment, grid power is used as the power supply 24, but the power supply is not limited to this.
Each cooling device 50 is connected to an energy transfer circuit 20 that can arbitrarily change the current flowing through the four superconducting coils 51 while being disconnected from the power supply 24 . The energy transfer circuit 20 is composed of a plurality of switches that can arbitrarily connect and disconnect both ends of the superconducting coil 51 . In this embodiment, the circuit configuration is such that the direction of the current flowing through the superconducting coil 51 can be reversed.

The operation of initial charging circuit 22 and energy transfer circuit 20 is controlled by controller 10 . The control device 10 can be configured as a computer having an internal CPU and memory. In this embodiment, the control device 10 is configured by software by installing a computer program for realizing the functions shown in the figure, but all or part of these functions are configured by hardware such as ASIC. You may

The setting input unit 11 has a function of inputting instructions from the operator. In this embodiment, for example, settings such as a current value to be supplied to the superconducting coils 51 in the initial charging and a sequence of energy transfer between the superconducting coils 51 after the completion of charging are input.
The initial charging control unit 12 connects the superconducting coil 51 and the power supply 24 , disconnects the superconducting coil 51 from the power supply 24 when a predetermined current flows through the superconducting coil 51 , and connects both ends of the superconducting coil 51 . Since the superconducting coil 51 has a characteristic of zero electrical resistance, a current of a predetermined value continues to flow due to initial charging.
After the initial charging is completed, the energy transfer control section 13 changes the current flowing through each superconducting coil 51 according to a predetermined sequence. By doing so, the magnetic field generated by each superconducting coil 51 can be varied.

In this embodiment, by changing the current flowing through the four superconducting coils 51, the magnetic field generated by each superconducting coil 51 is changed, and as a result, the heat generation/heat absorption of the magnetic working material 52 is changed, and cooling is performed. come true. An example of a sequence for varying this magnetic field will be described below.
FIG. 2 is an explanatory diagram showing the energy transfer sequence (1). FIG. 2(a) shows the state of the current and energy of each superconducting coil when the initial charging is completed. For the four superconducting coils A to D in the figure, the hatched graph on the left represents current, and the filled graph on the right represents energy. The state of FIG. 2(a) is equivalent to the four superconducting coils A to D, and shows a state in which about 50% of the maximum current is flowing. Since the energy stored in the superconducting coil 51 is proportional to the square of the current, the energy is 25% when the current is 50%.

FIG. 2(b) shows a state in which all energy is transferred to the superconducting coil A as one step of energy transfer. That is, 100% of the current is passed through the superconducting coil A and 100% of the energy is transferred, while the superconducting coils B to D are in a state of zero current and zero energy. Also in the state of FIG. 2(b), the total energy is the same as in the state of FIG. 2(a).
Similarly, FIG. 2(c) shows a state in which all energy is transferred to superconducting coil B, FIG. 2(d) shows a state in which all energy is transferred to superconducting coil C, and FIG. It represents a state in which energy is transferred. After FIG. 2(e), the steps after FIG. 2(b) are repeatedly executed.
In the sequence shown in FIG. 2, as shown in FIGS. 2(b) to 2(e), the four superconducting coils are in a transfer state in which a 100% current is supplied to each of the four superconducting coils in order.
According to such a sequence, a magnetic field with energy of 100% and a magnetic field of zero energy are generated in each superconducting coil, so that a large magnetic field fluctuation can be generated, resulting in a temperature change of the magnetic working material. has the advantage of being able to increase

In the sequence of FIG. 2, initial charging is performed on the assumption that 100% energy is transferred to one superconducting coil. Therefore, in order to realize a state in which 100% energy is evenly divided into four coils, that is, a state of 25% energy per coil, the initial charge is a state in which 50% of the current is passed through each superconducting coil. .

FIG. 3 is an explanatory diagram showing the energy transfer sequence (2). FIG. 3(a) showed the initial charging. In this example, superconducting coils A to D each carry approximately 70% of the current and store 50% of the energy.
FIG. 3(b) shows a state in which 100% current is passed through the superconducting coils A and C and 100% energy is transferred as one step of energy transfer. In FIG. 3(c), 100% of the current is then applied to the superconducting coils B and D to transfer 100% of the energy. Thus, in the sequence of FIG. 3, two coils are paired to transfer 100% current and 100% energy.
In the sequence of FIG. 3, 200% of the energy is required in total to transfer 100% of the energy to the two superconducting coils. In the initial charge, since this is stored in four superconducting coils, 50% of the energy is stored in one superconducting coil, and about 70% of the current flows.

3(b) and 3(c), the superconducting coils A, B and C, D have different hatching gradients. This indicates that the direction of the current is reversed. That is, in FIG. 3(b), the superconducting coils A and C are supplied with opposite currents, and in FIG. 3(c), the superconducting coils B and D are supplied with opposite currents. By passing currents in opposite directions in this way, the magnetic fields generated in the superconducting coil cancel each other out, making it possible to suppress leakage of the magnetic field to the outside.

Analysis results of the magnetic field generated by the current flowing through the superconducting coil will be described below.
FIG. 4 is an explanatory diagram showing the arrangement of superconducting coils. A plan view is shown in FIG. 4(a), and a perspective view is shown in FIG. 4(b).
In this analysis, the inner diameter d1 of the superconducting coil is 100 mm, the outer diameter d2 is 200 mm, the height h is 100 mm, the spacing dx in the x direction and the spacing d2 in the y direction are each 50 mm, the number of coil turns is 500, and the current value is 600 A. was analyzed as

FIG. 5 is an explanatory diagram showing the result (1) of the magnetic field analysis. The uppermost figure shows a state in which only the superconducting coil A is energized. The results of the magnetic field analysis of the region S between the superconducting coils A and B and the superconducting coils C and D are shown in the middle row. It can be seen that the influence of the superconducting coil A appears in the region S. The lower part shows a graph showing the strength of the magnetic field in the horizontal direction in the middle part. A slightly darker portion in the middle diagram corresponds to the vicinity of x=0.1 in the lower graph, that is, the area where the absolute value of the magnetic field is the largest.

FIG. 6 is an explanatory diagram showing the result (2) of the magnetic field analysis. The uppermost figure shows the state of energization to four superconducting coils. The superconducting coils A and D and the superconducting coils B and C pass 50% of the current in opposite directions.
The middle row shows the magnetic field analysis results of the region S between the superconducting coils. As can be seen from the comparison with FIG. 5, the effect of the magnetic field generated by the superconducting coil does not appear to be significant. A graph showing the strength of the magnetic field in the region S is shown in the lower part. As shown in the figure, although the magnetic field fluctuates violently, the range is within plus or minus 0.2 T, so it can be evaluated that the strength of the magnetic field is approximately zero. In this way, by reversing the direction in which the current flows through the superconducting coil, the magnetic fields cancel each other out, so it is thought that leakage of the magnetic field to the outside can be reduced.

FIG. 7 is an explanatory diagram showing the result (3) of the magnetic field analysis. The top row represents the state of energization, and since all the superconducting coils are represented with the same density, it can be seen that the current is flowing in the same direction. The initial charge state corresponds to this. The middle row shows the magnetic field analysis results of the region S between the superconducting coils. Dark colored portions appear between superconducting coils A and C and between superconducting coils B and D, indicating that the magnetic field is greatly affected. A graph showing the strength of the magnetic field is shown at the bottom. It can be seen that there are two places where the absolute value of the magnetic field is large, corresponding to the middle figure.

FIG. 8 is an explanatory diagram showing the result (4) of the magnetic field analysis. The top row shows the state of energization to the four superconducting coils. As shown in FIG. However, the current value is larger than that in FIG. 6, and 100% of the current is supplied.
The middle row shows the magnetic field analysis results of the region S between the superconducting coils. As in FIG. 6, it does not appear that the influence of the magnetic field generated by the superconducting coil is significant. A graph showing the strength of the magnetic field in the region S is shown in the lower part. Similar to FIG. 6, the strength of the magnetic field can be estimated to be approximately zero. In this way, by reversing the direction in which the current flows through the superconducting coil, the magnetic fields cancel each other out even when the current value is large, so it is thought that leakage of the magnetic field to the outside can be reduced.

According to the above analysis results, it can be seen that the magnetic field outside the coil is greatly affected by the energization state of the superconducting coil. In general, it is considered preferable that the leakage of the magnetic field to the outside is small. From this point of view, it can be said that it is preferable to pass currents in opposite directions to the two superconducting coils as shown in FIGS. .
However, the energization of the superconducting coil may be arbitrarily determined in consideration of other factors. At this time, as shown by the analysis results, the external magnetic field is affected, so it is preferable to determine the energization of the superconducting coil in consideration of such influence.

According to the stationary magnetic refrigeration system of the embodiment described above, the magnetic field of the superconducting coil can be changed by transferring the energy stored in the superconducting coil by the initial charge. Since it is almost unnecessary to supply energy from the outside, it has the advantage of being able to generate a fluctuating magnetic field with very low energy consumption.
In addition, the static magnetic refrigeration system using this does not require the drive mechanism required in the conventional magnetic refrigeration system, that is, the mechanism for reciprocating the magnetic shield or the magnetic working material. No energy is required to do so. Furthermore, since no drive mechanism is required, there is also the advantage that the structure can be simplified.

All of the various features described above are not necessarily provided, and some of them can be omitted or combined as appropriate.
Moreover, the present invention is not limited to the above-described embodiments, and various modifications can be configured. In the embodiments, an example as a stationary magnetic refrigeration system was shown, but the present invention can also be used for other applications. Such applications may include, for example, refrigeration or cooling systems not intended to condense hydrogen, such as fusion coils and cooling systems for power stabilization and storage systems. Also, the variable magnetic field may be applied to magnetization of permanent magnets.

INDUSTRIAL APPLICABILITY The present invention can be applied to generation of a varying magnetic field using superconducting coils and static magnetic refrigeration using the same.

10 Control device 11 Setting input unit 12 Initial charging control unit 13 Energy transfer control unit 20 Energy transfer circuit 22 Initial charging circuit 24 Power source 40 Sealed container 50 Cooling device 51 Superconducting coil 52 Magnetic working material 53 Thermal switch 54 Heat transfer column 55 Exhaust heat cooling device 56 hydrogen storage tank 57 condenser

Claims (6)

A stationary magnetic refrigeration system using the magnetocaloric effect,
a plurality of superconducting coils;
an initial charging circuit that connects and disconnects the superconducting coil and a power supply;
an energy transfer circuit capable of arbitrarily changing the current flowing through each of the plurality of superconducting coils while being disconnected from the power supply;
a controller for controlling the initial charging circuit and the energy transfer circuit;
a magnetic working material that generates heat/absorbs heat due to fluctuations in the magnetic field and is placed inside at least one of the superconducting coils;
The control unit
an initial charging control unit that connects the superconducting coil to a power source and controls an initial charging circuit to disconnect the power source after initial charging with a predetermined current is achieved;
an energy transfer controller for controlling said energy transfer circuit to vary the current through each of said superconducting coils in a preset sequence after said initial charge is achieved. The stationary magnetic refrigeration system of claim 1, wherein
The stationary magnetic refrigeration system, wherein an even number of the plurality of superconducting coils are provided. The stationary magnetic refrigeration system according to claim 1 or 2,
The plurality of superconducting coils are provided with three or more,
The energy transfer control unit is a static magnetic refrigeration system in which a current is applied in the opposite direction to the adjacent superconducting coil. The stationary magnetic refrigeration system according to claim 1 or 2,
The energy transfer control unit groups a predetermined number of the plurality of superconducting coils and sequentially applies a maximum current to each superconducting coil in the group. The stationary magnetic refrigeration system according to any one of claims 1 to 4,
The predetermined current in the initial charging is the current required to store the magnetic energy in the entirety of the plurality of superconducting coils in a reference state in which 100% of the current flows through a predetermined number of the plurality of superconducting coils corresponding to a part of the plurality of superconducting coils. stationary magnetic refrigeration system that is value. The stationary magnetic refrigeration system of claim 1, wherein
The stationary magnetic refrigeration system, wherein the magnetic working material is arranged inside all of the plurality of superconducting coils.

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