JP2017009165A - Heat exchanger and magnetic heat pump device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat exchanger capable of improving heat exchange efficiency.SOLUTION: An MCM heat exchanger 10 used in a magnetic heat pump device includes a plurality of plate materials 11 constituted by a magnetocaloric effect material, and a container 12 storing the plate materials 11, and the container 12 has a first opening 131 through which a liquid medium flows into the container 12 or flows out of the container 12, and a second opening 141 through which the liquid medium flows out of the container 12 or flows into the container 12. An extension direction of the plate materials 11 is substantially parallel to a first direction CL from the first opening 131 to the second opening 141, and the plate materials 11 are arranged at an interval from one another in a second direction substantially orthogonal to the first direction CL. A pitch of the plate materials 11 is narrowest at a portion closest to a virtual straight line VL which connects the first opening 131 and the second opening 141.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a heat exchanger used in a magnetic heat pump apparatus using a magnetocaloric effect, and a magnetic heat pump apparatus including the heat exchanger.

  A magnetic refrigeration device including a heat exchanger filled with magnetic material for magnetic refrigeration that is substantially spherical particles is known (see, for example, Patent Document 1 (paragraphs [0038] to [0039], FIG. 2)). This heat exchanger has one opening connected to the low temperature side heat exchange part via piping and the other opening connected to the high temperature side heat exchange part via another pipe.

JP 2010-77484 A

  The cross-sectional area of the heat exchanger is relatively large compared to the cross-sectional area of each opening. For this reason, there is a problem that the flow rate of the liquid refrigerant decreases as the distance from the central axis of the opening increases, and the liquid refrigerant does not flow uniformly inside the heat exchanger, resulting in a decrease in heat exchange efficiency.

  The problem to be solved by the present invention is to provide a heat exchanger capable of improving the heat exchange efficiency and a magnetic heat pump apparatus including the heat exchanger.

  [1] A heat exchanger according to the present invention is a heat exchanger used in a magnetic heat pump device, and includes a plurality of plate members made of a magnetocaloric effect material, and a container that stores the plurality of plate members. The container has a first opening through which fluid flows into or out of the container, and a second opening through which the fluid flows out of or into the container; The extending direction of the plurality of plate members is substantially parallel to the first direction from the first opening toward the second opening, and the plurality of plate members are in the first direction. In a second direction substantially orthogonal to each other, and the pitch of the plate members is closest to an imaginary straight line connecting the first opening and the second opening, The narrowest heat exchanger.

  [2] In the above invention, the pitch of the plate material may gradually or stepwise increase as the distance from the virtual straight line increases.

  [3] In the above invention, the first opening may overlap at least a part of the second opening in the first direction.

  [4] In the above invention, the container includes a first wall in which the first opening is formed, and a second wall in which the second opening is formed, and the first wall The opening may be provided substantially at the center of the first wall, and the second opening may be provided substantially at the center of the second wall.

  [5] A magnetic heat pump device according to the present invention includes at least one heat exchanger, a magnetic field changing means for applying a magnetic field to the magnetocaloric effect material and changing the magnitude of the magnetic field, and a pipe. The first and second external heat exchangers respectively connected to the container and the fluid is supplied from the container to the first or second external heat exchanger in conjunction with the operation of the magnetic field changing means. And a fluid heat supply device.

  According to the present invention, the pitch of the plate material is narrowest closest to the virtual straight line. Thereby, since the flow velocity of the fluid in the container is made uniform, the heat exchange efficiency of the heat exchanger can be improved.

FIG. 1 is a diagram showing an overall configuration of a magnetic heat pump device according to an embodiment of the present invention, and shows a state where a piston is in a first position. FIG. 2 is a diagram illustrating the overall configuration of the magnetic heat pump device according to the embodiment of the present invention, and is a diagram illustrating a state where the piston is in the second position. FIG. 3 is a cross-sectional view of the MCM heat exchanger according to the embodiment of the present invention, and is a view cut along the flow direction of the liquid medium. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a cross-sectional view showing a modification of the MCM heat exchanger in the embodiment of the present invention. FIG. 7 is a perspective view showing a modification of the plate material in the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 and 2 are diagrams showing the overall configuration of the magnetic heat pump apparatus in the present embodiment, and FIGS. 3 to 5 are views showing an MCM heat exchanger in the present embodiment.

  The magnetic heat pump device 1 in the present embodiment is a heat pump device using a magnetocaloric effect, and as shown in FIGS. 1 and 2, first and second MCM heat exchangers 10 and 20, The piston 30, the permanent magnet 40, the low temperature side heat exchanger 50, the high temperature side heat exchanger 60, the pump 70, the pipes 81 to 84, and the switching valve 90 are provided.

  The first and second MCM heat exchangers 10 and 20 in the present embodiment correspond to an example of a heat exchanger in the present invention, and the piston 30 and the permanent magnet 40 in the present embodiment serve as an example of a magnetic changing unit in the present invention. The low temperature side heat exchanger 50 and the high temperature side heat exchanger 60 correspond to an example of the first and second external heat exchangers in the present invention, and the pipes 81 to 84 in the present embodiment are the pipes in the present invention. It corresponds to an example, and the pump 70 and the switching valve 90 in the present embodiment correspond to an example of the fluid supply means in the present invention.

  As shown in FIGS. 3 to 5, the first MCM heat exchanger 10 includes a plurality of plate members 11 and a container 12 that houses the plate members 11. In addition, since the structure of the 1st MCM heat exchanger 10 and the 2nd MCM heat exchanger 20 is the same, the structure of the 1st MCM heat exchanger 10 is demonstrated in detail below, and 2nd MCM heat exchanger 10 is demonstrated. Description of the configuration of the heat exchanger 20 is omitted.

  Each plate member 11 is composed of a member obtained by forming a magnetocaloric effect material (MCM) having a magnetocaloric effect into a plate shape by plastic working or the like. When a magnetic field is applied to the plate material 11 composed of this MCM, the magnetic entropy is reduced by aligning the electron spin, and the plate material 11 generates heat and the temperature rises. On the other hand, when the magnetic field is removed from the plate material 11, the electron spin becomes messy and the magnetic entropy increases, and the plate material 11 absorbs heat and the temperature decreases. Note that the plate-like shape in the present embodiment includes a foil material having a thickness of about 0.1 mm.

  The MCM constituting the plate material 11 is not particularly limited as long as it is a magnetic material. For example, the MCM has a Curie temperature (Curie point) in a room temperature range of about 10 ° C. to 30 ° C. and exhibits a high magnetocaloric effect in the room temperature range. It is preferable that it is a magnetic body. Specific examples of such MCMs include gadolinium (Gd), gadolinium alloys, lanthanum-iron-silicon (La-Fe-Si) compounds, and the like.

  The several board | plate material 11 is accommodated in the container 12 of the 1st MCM heat exchanger 10, as shown in FIGS. The container 12 has a box shape having a front wall 13, a rear wall 14, a first side wall 15, and a second side wall 16. The plurality of plate members 11 are accommodated in the internal space 121 of the container 12 while being supported by the first and second side walls 15 and 16.

  In the present embodiment, the container 12 has a rectangular cross-sectional shape. However, the present invention is not particularly limited thereto, and for example, the container 15 may have a circular cross-sectional shape. The front wall 13 in the present embodiment corresponds to an example of the first wall in the present invention, and the rear wall 14 in the present embodiment corresponds to an example of the second wall in the present invention.

  A first opening 131 is formed in the front wall 13 of the container 12. The first opening 131 penetrates the front wall 13 along the flow direction CL of the liquid medium in the container 12 (that is, the direction from the first opening 131 toward the second opening 141, the X direction in the figure). The front wall 13 is disposed substantially at the center. As shown in FIG. 1, the first opening 131 communicates with the low temperature side heat exchanger 50 via the first low temperature side pipe 81.

  A second opening 141 is also formed in the rear wall 14 of the container 12. The second opening 141 passes through the rear wall 14 along the above-described flow direction CL, and is disposed substantially at the center of the rear wall 14. As shown in FIG. 2, the second opening 141 communicates with the high temperature side heat exchanger 60 via the first high temperature side pipe 83.

  In the present embodiment, the entire first opening 131 overlaps the entire second opening 141 when viewed along the above-described distribution direction CL. The positional relationship between the first opening and the second opening when viewed along the distribution direction CL is not particularly limited as long as the first opening and the second opening partially overlap. .

  Both the first side wall 15 and the second side wall 16 are side walls extending substantially parallel to the flow direction CL. The first and second side walls 15 and 16 are interposed between the front wall 13 and the rear wall 14 and face each other.

  A plurality of first grooves 151 are formed on the inner side surface of the first side wall 15. Each first groove 151 is a linear groove extending along the flow direction RL. The plurality of first grooves 151 are arranged with a space therebetween in a direction substantially perpendicular to the flow direction CL (Z direction in the drawing). In the present embodiment, the pitch between the first grooves 151 adjacent to each other is the narrowest closest to the virtual straight line VL connecting the first opening 131 and the second opening 141, whereas the virtual straight line It is the farthest and widest from the VL.

  A plurality of second grooves 161 are also formed on the inner surface of the second side wall 16. Each second groove 161 is a linear groove extending along the flow direction RL. The plurality of second grooves 161 are arranged at intervals from each other in a direction (Z direction in the drawing) substantially orthogonal to the flow direction CL. In the present embodiment, the pitch between the second grooves 161 adjacent to each other is the narrowest closest to the virtual straight line VL, but is the widest farthest from the virtual straight line VL.

  Each plate member 11 is accommodated in the internal space 121 of the container 12 so that the plane direction (XY plane direction in the drawing) of the plate member 11 is substantially parallel to the flow direction CL. And while the one side edge part of the board | plate material 11 is inserted in the 1st groove | channel 151, and the other side edge part of the said board | plate material 11 is inserted in the 2nd groove | channel 161, the board | plate material 11 is container 12 Are supported by the inner surfaces of the side walls 15 and 16, respectively.

  At this time, as described above, the first grooves 151 are spaced apart from each other, and the second grooves 161 are also spaced apart from each other. For this reason, in the state where the plurality of plate members 11 are supported by the container 12, a gap 17 is formed between the plate members 11 adjacent to each other.

In the present embodiment, the pitch between the first grooves 151 adjacent to each other gradually increases as the distance from the virtual straight line VL increases, and the pitch between the second grooves 161 adjacent to each other also increases. It gradually widens away from VL. For this reason, the pitch between the plurality of plate members 11 is the narrowest closest to the virtual straight line VL (pitch P _min in the figure), but is the widest farthest from the virtual straight line VL (see FIG. Middle pitch P _max ).

  Thus, in the present embodiment, the pitch of the plate material 11 gradually increases as the distance from the virtual straight line VL increases. For this reason, at a position close to the virtual straight line VL in the internal space 121 of the container 12, the pressure loss of the liquid medium increases and the flow speed of the liquid medium decreases. On the other hand, at a position away from the virtual straight line VL in the internal space 121 of the container 12, the pressure loss of the liquid medium is reduced and the flow speed of the liquid medium is increased. Thereby, since the flow velocity of the liquid medium in the container 12 is made uniform, the heat exchange efficiency of the first MCM heat exchanger 10 is improved.

  In this example, the “position close to the virtual straight line VL in the internal space 121 of the container 12” means a virtual straight line in the internal space 121 in the radial direction (Z direction in the drawing) centered on the virtual straight line VL. It means a position close to VL. Further, “a position away from the virtual straight line VL in the internal space 121 of the container 12” means that it is separated from the virtual straight line VL in the internal space 121 in the radial direction (Z direction in the drawing) centered on the virtual straight line VL. Means the position.

  FIG. 6 is a cross-sectional view showing a modification of the MCM heat exchanger in the present embodiment.

  In addition, as shown in FIG. 6, the pitch between the plate members 11 adjacent to each other may gradually increase as the distance from the virtual straight line VL increases. Also in the case of this modified example, since the flow rate of the liquid medium in the container 12 is made uniform, the heat exchange efficiency of the first MCM heat exchanger 10 is improved.

  FIG. 7 is a view showing a modification of the plate material in the present embodiment.

  Further, the shape of the plate member 11 is not particularly limited to the above shape. For example, as shown in FIG. 7, the plate material 11 </ b> B may have a shape folded in two at the bent portion 111. In this case, the bent portion 111 is inserted into the first groove 151, and the side end of the plate member 11 </ b> B opposite to the bent portion 111 is inserted into the second groove 161. 11B is supported on the side walls 15 and 16 of the container 12.

  As shown in FIG. 2, the container 22 of the second MCM heat exchanger 20 is also a box type having a front wall, a rear wall, and a pair of side walls, like the container 12 of the first MCM heat exchanger 10. It has a shape, and a plurality of plate members 21 are accommodated therein. The plate member 21 of the second MCM heat exchanger 20 has the same configuration as the plate member 11 of the first MCM heat exchanger 10.

  A first opening 231 is formed in the front wall of the container 22, and the first opening 231 communicates with the low temperature side heat exchanger 50 via the second low temperature side pipe 82. A second opening 241 is also formed in the rear wall of the container 22, and the second opening 241 communicates with the high temperature side heat exchanger 60 via the second high temperature side pipe 84.

  Similarly to the container 12 of the first MCM heat exchanger 10, a plurality of grooves are formed on the inner side surfaces of the pair of side walls of the container 22 so as to face each other. Supported by 22 side walls. At this time, in the present embodiment, like the first MCM heat exchanger 10, a plurality of grooves are formed on the inner surface of the side wall so that the pitch of the grooves gradually increases as the distance from the center of the container 22 increases. Therefore, the pitch of the plate material 21 gradually increases as the distance from the center of the container 22 increases.

  For example, when the air conditioner using the magnetic heat pump device 1 in the present embodiment functions as cooling, the room is cooled by exchanging heat between the low temperature side heat exchanger 50 and the indoor air, The heat is radiated to the outside by performing heat exchange between the high temperature side heat exchanger 60 and the outside.

  On the other hand, when the air conditioner functions as heating, the room is warmed by exchanging heat between the high temperature side heat exchanger 60 and the indoor air, and the low temperature side heat exchanger 50 and the outdoor side. Heat is absorbed from outside by exchanging heat with other air.

  As described above, a circulation path including the four heat exchangers 10, 20, 50, 60 is formed by the two low temperature side pipes 81, 82 and the two high temperature side pipes 83, 84. A liquid medium is pumped into the circulation path. Specific examples of the liquid medium include liquids such as water, antifreeze, ethanol solution, or a mixture thereof. The liquid medium in the present embodiment corresponds to an example of a fluid in the present invention.

  The two MCM heat exchangers 10 and 20 are accommodated inside the piston 30. The piston 30 can reciprocate between the pair of permanent magnets 40 by an actuator 35. Specifically, the piston 30 can reciprocate between a “first position” as shown in FIG. 1 and a “second position” as shown in FIG. . As an example of the actuator 35, for example, a motor or an air cylinder provided with a ball screw mechanism can be exemplified.

  Here, the “first position” refers to a piston in which the first MCM heat exchanger 10 is not interposed between the permanent magnets 40 and the second MCM heat exchanger 20 is interposed between the permanent magnets 40. 30 positions. On the other hand, the “second position” is a piston in which the first MCM heat exchanger 10 is interposed between the permanent magnets 40 and the second MCM heat exchanger 20 is not interposed between the permanent magnets 40. 30 positions.

  Note that the permanent magnet 40 may be reciprocated by the actuator 35 instead of the first and second MCM heat exchangers 10 and 20. Alternatively, an electromagnet having a coil may be used in place of the permanent magnet 40. In this case, a mechanism for moving the MCM heat exchangers 10, 20 or the magnet becomes unnecessary. In addition, when an electromagnet having a coil is used, the magnitude of the magnetic field applied to the plates 11 and 21 is changed instead of applying / removing the magnetic field to the plates 11 and 21 of the MCM heat exchangers 10 and 20. May be.

  The switching valve 90 is provided in the first high temperature side pipe 83 and the second high temperature side pipe 84. The switching valve 90 switches the liquid medium supply destination by the pump 70 to the first MCM heat exchanger 10 or the second MCM heat exchanger 20 in conjunction with the operation of the piston 30 described above, The connection destination of the high temperature side heat exchanger 60 can be switched to the second MCM heat exchanger 20 or the first MCM heat exchanger 10.

  Next, operation | movement of the magnetic heat pump apparatus 1 in this embodiment is demonstrated, referring FIG.1 and FIG.2.

  First, when the piston 30 is moved to the “first position” shown in FIG. 1, the plate material 11 of the first MCM heat exchanger 10 is demagnetized to lower the temperature, while the second MCM heat exchanger 20. The plate material 21 is magnetized and the temperature rises.

  At the same time, the switching valve 90 causes the pump 70 → the first high temperature side pipe 83 → the first MCM heat exchanger 10 → the first low temperature side pipe 81 → the low temperature side heat exchanger 50 → the second low temperature side pipe. A first path consisting of 82 → second MCM heat exchanger 20 → second high temperature side pipe 84 → high temperature side heat exchanger 60 → pump 70 is formed.

  For this reason, the liquid medium is cooled by the plate material 11 of the first MCM heat exchanger 10 whose temperature has decreased due to demagnetization, the liquid medium is supplied to the low temperature side heat exchanger 50, and the low temperature side heat exchanger 50 is To be cooled.

  At this time, the liquid medium passes through the gap 17 formed between the plate members 11 and contacts the plate member 11 inside the first MCM heat exchanger 10, so that the liquid medium is cooled by the plate member 11. . In the present embodiment, the pitch between the plate members 11 adjacent to each other gradually increases as the distance from the virtual straight line VL increases, so that the flow velocity of the liquid medium in the container 12 is made uniform.

  On the other hand, the liquid medium is heated by the plate material 21 of the second MCM heat exchanger 20 that has been magnetized and the temperature has risen, and the liquid medium is supplied to the high temperature side heat exchanger 60, and the high temperature side heat exchanger 60. Is heated.

  At this time, inside the second MCM heat exchanger 20, the liquid medium passes through the gap formed between the plate materials 21 and comes into contact with the plate material 21, so that the liquid medium is heated by the plate material 21. In the present embodiment, the pitch between the plate members 21 adjacent to each other gradually increases as the distance from the center of the container 22 increases, so that the flow velocity of the liquid medium in the container 22 is made uniform. .

  Next, when the piston 30 is moved to the “second position” shown in FIG. 2, the plate material 11 of the first MCM heat exchanger 10 is magnetized and the temperature rises, while the second MCM heat exchanger The 20 plate materials 21 are demagnetized and the temperature is lowered.

  At the same time, the switching valve 90 causes the pump 70 → second high temperature side pipe 84 → second MCM heat exchanger 20 → second low temperature side pipe 82 → low temperature side heat exchanger 50 → first low temperature side pipe. A second path consisting of 81 → first MCM heat exchanger 10 → first high temperature side pipe 83 → high temperature side heat exchanger 60 → pump 70 is formed.

  For this reason, the liquid medium is cooled by the plate material 21 of the second MCM heat exchanger 20 whose temperature has decreased due to demagnetization, the liquid medium is supplied to the low temperature side heat exchanger 50, and the low temperature side heat exchanger 50 is To be cooled.

  At this time, in the second MCM heat exchanger 20, the liquid medium passes through a gap formed between the plate materials 21 and comes into contact with the plate material 21, whereby the liquid medium is cooled by the plate material 21. In the present embodiment, the pitch between the plate members 21 adjacent to each other gradually increases as the distance from the center of the container 22 increases, so that the flow velocity of the liquid medium in the container 22 is made uniform. .

  On the other hand, the liquid medium is heated by the plate material 11 of the first MCM heat exchanger 10 that has been magnetized and the temperature is increased, and the liquid medium is supplied to the high temperature side heat exchanger 60, and the high temperature side heat exchanger 60 is Heated.

  At this time, in the first MCM heat exchanger 10, the liquid medium passes through the gap 17 formed between the plates 11 and comes into contact with the plates 11, so that the liquid medium is heated by the plates 11. . In the present embodiment, the pitch between the plate members 11 adjacent to each other gradually increases as the distance from the virtual straight line VL increases, so that the flow velocity of the liquid medium in the container 12 is made uniform.

  Then, the reciprocating movement between the “first position” and the “second position” of the piston 30 described above is repeated, and the plate members 11 and 21 in the first and second MCM heat exchangers 10 and 20 are repeated. By repeating the application / removal of the magnetic field, the cooling of the low temperature side heat exchanger 50 and the heating of the high temperature side heat exchanger 60 are continued.

  As described above, in the present embodiment, in the first MCM heat exchanger 10, the pitch between the plurality of plate members 11 is the narrowest closest to the virtual straight line VL. For this reason, since the flow velocity of the liquid medium in the container 12 is made uniform, the heat exchange efficiency of the first MCM heat exchanger 10 can be improved.

  In the second MCM heat exchanger 20 as well, the pitch between the adjacent plate members 21 is narrowest closest to the virtual straight line. For this reason, since the flow velocity of the liquid medium in the container 22 is made uniform, the heat exchange efficiency of the second MCM heat exchanger 20 can be improved.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  The configuration of the magnetic heat pump device described above is an example, and the heat exchanger according to the present invention may be applied to other magnetic heat pump devices of an AMR (Active Magnetic Refrigerataion) system.

  For example, the magnetic heat pump device includes a first MCM heat exchanger, a magnetic field changing unit that applies a magnetic field to the MCM and changes the magnitude of the magnetic field, and a first connected to the MCM heat exchanger via a pipe. And a second external heat exchanger and fluid supply means for supplying fluid from the MCM heat exchanger to the first or second external heat exchanger in conjunction with the operation of the magnetic field changing means.

  Moreover, although the above-mentioned embodiment demonstrated the example which applied the magnetic heat pump apparatus to air conditioners, such as home use or a motor vehicle, it is not specifically limited to this. For example, by selecting an MCM having an appropriate Curie temperature according to the application, the magnetic heat pump device according to the present invention can be applied to an application in a cryogenic temperature region such as a refrigerator or an application in a certain high temperature region. May be.

DESCRIPTION OF SYMBOLS 1 ... Magnetic heat pump apparatus 10 ... 1st MCM heat exchanger 11, 11B ... Plate material 111 ... Bending part 12 ... Container 121 ... Internal space
13 ... Front wall
131 ... 1st opening
14 ... Back wall
141 ... second opening
15 ... 1st side wall
151: First groove
16 ... second side wall
161 ... second groove 17 ... gap 20 ... second MCM heat exchanger 21 ... plate material 22 ... container 221 ... internal space 23 ... front wall
231 ... 1st opening 24 ... Rear wall
241 ... Second opening 30 ... Piston 35 ... Actuator 40 ... Permanent magnet 50 ... Low temperature side heat exchanger 60 ... High temperature side heat exchanger 70 ... Pump 81-82 ... First to second low temperature side pipes 83-84 ... 3rd-4th high temperature side piping 90 ... Switching valve

Claims (5)

A heat exchanger used in a magnetic heat pump device,
A plurality of plates made of magnetocaloric effect material;
A container for accommodating a plurality of the plate members,
The container is
A first opening through which fluid flows into or out of the container;
A second opening through which the fluid flows out of or into the container;
The extending direction of the plurality of plate members is substantially parallel to a first direction from the first opening toward the second opening,
The plurality of plate members are disposed at a distance from each other in a second direction substantially orthogonal to the first direction,
The pitch of the said board | plate material is the heat exchanger which is the narrowest at the nearest of the virtual straight line which connects the said 1st opening and the said 2nd opening. The heat exchanger according to claim 1,
The pitch of the said board | plate material is a heat exchanger which spreads gradually or in steps as it leaves | separates from the said virtual straight line. The heat exchanger according to claim 1 or 2,
The heat exchanger in which the first opening overlaps at least a part of the second opening in the first direction. It is a heat exchanger as described in any one of Claims 1-3,
The container is
A first wall in which the first opening is formed;
A second wall in which the second opening is formed,
The first opening is provided substantially in the center of the first wall;
The heat exchanger in which the second opening is also provided substantially at the center of the second wall. At least one heat exchanger according to any one of claims 1 to 4;
A magnetic field changing means for applying a magnetic field to the magnetocaloric effect material and changing the magnitude of the magnetic field;
First and second external heat exchangers respectively connected to the vessel via piping;
And a fluid supply means for supplying the fluid from the container to the first or second external heat exchanger in conjunction with the operation of the magnetic field changing means.

Images