Air-cooled electromagnetic ultrasonic sensor, detection system and method

Abstract

The invention discloses an air-cooled electromagnetic ultrasonic sensor and a detection system and method, and relates to the technical field of industrial detection.The air-cooled electromagnetic ultrasonic sensor comprises a sensor body and a draught fan, the sensor body comprises a shell, a connecting block, a magnet and a coil assembly, and the connecting block, the magnet and the coil assembly are sequentially arranged in the shell in the first direction; the connecting block and the coil assembly are connected with the inner wall of the shell in a sealed mode. A first ventilation cavity, a second ventilation cavity and an air outlet channel are formed in the shell. The detection system comprises a power supply, a detector and the air-cooled electromagnetic ultrasonic sensor. The method for improving the heat resistance of the electromagnetic ultrasonic sensor comprises the steps that heat insulation is conducted on the coil assembly through the second ventilation cavity, and heat dissipation is conducted by introducing flowing air into the second ventilation cavity. The second ventilation cavity can serve as an air heat insulation layer for heat insulation, and flowing air can be introduced to take away heat of the coil assembly, so that the heat resistance of the electromagnetic ultrasonic sensor is improved.

Description

Technical Field

[0001] The present invention relates to the field of industrial detection technology, and in particular to an air-cooled electromagnetic ultrasonic sensor, a detection system and a detection method. Background Art

[0002] Electromagnetic ultrasonic nondestructive testing technology is a common means of pipeline nondestructive testing. It has many unique advantages, such as low surface requirements, non-contact measurement, and no need to consider coupling problems. When using array detection, the signal consistency between channels is good, the sensor has high stability in repeated measurements, and it is convenient for subsequent signal processing. It is easy to produce in-plane displacement and can well control the excited mode. Its principle is to excite and receive ultrasonic waves through the interaction between magnets and induction coils, and to identify and measure pipeline defects through data analysis. However, the two main components of electromagnetic ultrasonic sensors, magnets and induction coils, are prone to damage and failure under high temperature conditions. Therefore, the key to high-temperature detection is to protect the magnets and induction coils inside the sensor. At present, the magnets commonly used to make electromagnetic ultrasonic sensors are neodymium iron boron magnets with an operating temperature of 80-230℃. The induction coils are usually made of enameled wires with a maximum applicable temperature of 220℃. The coils are generally located at the bottom of the magnets, close to the object being measured, and heat is easily transferred to the coils, causing them to fail to work normally. Magnets are prone to demagnetization and demagnetization at high temperatures.

[0003] There are two main measures in the existing technology to solve the difficulties in applying electromagnetic ultrasonic sensors to high-temperature detection: one is to use high-temperature resistant coils and magnets with high residual magnetic induction intensity and high Curie point. The coils are encapsulated between heat-resistant layers, and coaxial cables using ceramic as internal insulating materials are used to withstand high temperatures; the other is to use a local active cooling method, including setting a cooling device on the upper part of the magnet to remove heat through cooling water circulation, and at the same time wrapping the coil with a ceramic layer and a polyimide film for thermal insulation; or filling the sensor cavity with circulating cooling water to wrap the magnet and the induction coil to remove heat.

[0004] However, there are many problems with the existing technology. Sensors that use physical heat insulation require high-Curie-point, high-temperature resistant magnets and coils. The magnetic induction intensity is low at high temperatures, and high requirements are placed on materials and manufacturing processes. Although water-cooled sensors with local active cooling can take away heat from the surrounding area, the heat layer between the coil and the object being measured is limited by the sensor lifting distance and thickness, and the high-temperature protection of the coil is weak. Long-term continuous measurement may damage the coil, and high requirements are placed on the coil material. In addition, the water cooling system is complex in composition, with high requirements on system pressure, sensor internal sealing, and coil waterproof protection. The cooling medium is inconvenient to carry, which increases the difficulty of on-site use. Summary of the invention

[0005] The object of the present invention is to provide an air-cooled electromagnetic ultrasonic sensor, a detection system and a detection method to solve the problems existing in the above-mentioned prior art and improve the high temperature resistance performance of the high temperature resistant electromagnetic ultrasonic sensor.

[0006] To achieve the above object, the present invention provides the following solutions: The present invention provides an air-cooled high-temperature resistant electromagnetic ultrasonic sensor, comprising a sensor body and a blower. The sensor body includes a housing, a connecting block, a magnet and a coil assembly. The connecting block, the magnet and the coil assembly are sequentially arranged in the housing along a first direction. The connecting block and the coil assembly are respectively hermetically connected to the inner wall of the housing. A first ventilation cavity, a second ventilation cavity and an air outlet duct are arranged in the housing. The first ventilation cavity surrounds the magnet. The second ventilation cavity is located on a side of the coil assembly away from the magnet. The first ventilation cavity and the second ventilation cavity are respectively communicated with the air outlet duct. The coil assembly is filled with a sealant, and the coil assembly isolates the first ventilation cavity and the second ventilation cavity. A first air inlet communicating with the first ventilation cavity, a second air inlet communicating with the second ventilation cavity and an air outlet communicating with the air outlet duct are arranged on an outer wall of the housing. The first air inlet and the second air inlet are respectively communicated with an air outlet of the blower through pipelines.

[0007] Preferably, a temperature sensor is further arranged in the second ventilation cavity.

[0008] Preferably, a first air inlet duct is further arranged in the housing. The first air inlet is communicated with the first ventilation cavity through the first air inlet duct, and the first air inlet duct is isolated from the second ventilation cavity. A second air inlet duct is further arranged in the housing. The second air inlet is communicated with the second ventilation cavity through the second air inlet duct, and the second air inlet duct is isolated from the first ventilation cavity.

[0009] Preferably, a first partition board is arranged in the housing. A top end of the first partition board is fixedly connected to the housing, and the first air inlet duct is formed between the first partition board and the inner wall of the housing.

[0010] Preferably, a wire threading pipe connected to the housing is further included. A wire placement cavity is arranged in the housing. The first ventilation cavity, the second ventilation cavity, the first air inlet duct, the second air inlet duct and the air outlet duct are respectively isolated from the wire placement cavity. The wire threading pipe is communicated with the wire placement cavity. Wires of the coil assembly and signal wires of the temperature sensor both pass through the wire placement cavity and the wire threading pipe.

[0011] Preferably, a wire harness connector is further arranged at an end of the wire threading pipe away from the housing. The wires of the coil assembly and the signal wires of the temperature sensor are respectively electrically connected to the wire harness connector.

[0012] Preferably, it further includes a heat-insulating and wear-resistant plate fixedly connected to the housing, and the second ventilation cavity is located between the coil assembly and the heat-insulating and wear-resistant plate.

[0013] The present invention also provides an electromagnetic ultrasonic detection system, including a power supply, a detector, a control unit, and the above-mentioned air-cooled high-temperature-resistant electromagnetic ultrasonic sensor. The power supply is used to supply power to the detector and the fan. The detector can provide pulse excitation for the coil windings in the coil assembly. The temperature sensor is signal-connected to the control unit, and the control unit can adjust the power of the fan according to the detection signal of the temperature sensor.

[0014] The present invention also provides a method for improving the heat resistance of an electromagnetic ultrasonic sensor: a second ventilation cavity and an air outlet duct are arranged in the electromagnetic ultrasonic sensor, and the second ventilation cavity is located on the side of the coil assembly of the electromagnetic ultrasonic sensor close to the high-temperature test piece to be measured. The second ventilation cavity communicates with the air outlet duct. The coil assembly is insulated through the second ventilation cavity, and heat dissipation is carried out by introducing flowing air into the second ventilation cavity.

[0015] Preferably, a first ventilation cavity surrounding the magnet of the electromagnetic ultrasonic sensor is arranged in the electromagnetic ultrasonic sensor, so that the first ventilation cavity communicates with the air outlet duct. The magnet is insulated through the first ventilation cavity, and heat dissipation is carried out by introducing flowing air into the first ventilation cavity.

[0016] The present invention has achieved the following technical effects compared with the prior art: The air-cooled electromagnetic ultrasonic sensor, detection system and method of the present invention improve the heat resistance of the electromagnetic ultrasonic sensor by arranging a second ventilation cavity in the electromagnetic ultrasonic sensor. The second ventilation cavity is located between the coil assembly and the high-temperature test piece to be measured. The second ventilation cavity itself can be used as an air insulation layer to improve the heat resistance of the electromagnetic ultrasonic sensor. Further, by introducing flowing air into the second ventilation cavity, the heat of the coil assembly can also be taken away, improving the heat dissipation performance, and thus improving the heat resistance of the electromagnetic ultrasonic sensor.

[0017] Further, by arranging a first ventilation cavity surrounding the magnet, the first ventilation cavity itself can be used as an air insulation layer to block the heat transfer between the housing and the magnet. By introducing flowing air into the first ventilation cavity, the heat of the magnet can also be taken away, improving the heat dissipation performance, and thus improving the heat resistance of the electromagnetic ultrasonic sensor.

[0018] Further, by arranging a temperature sensor, the temperature in the second ventilation cavity can be monitored in real time, which is convenient to adjust the output power of the fan according to the real-time temperature of the second ventilation cavity, so that the temperature in the second ventilation cavity can be maintained below the set value. Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 Structural schematic of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 1 ; Figure 2 Structural schematic of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 2 ; Figure 3 Top view of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 1 ; Figure 4 is Figure 3 A-A cross-sectional view of; Figure 5 Top view of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 2 ; Figure 6 is Figure 5 B-B cross-sectional view of; Figure 7 Partial structural schematic of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 1 ; Figure 8 Partial structural schematic of the sensor body in the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of the present invention Figure 2 ; Figure 9 Structural schematic diagram of the electromagnetic ultrasonic detection system of the present invention; In the figure: 100, sensor body; 1, housing; 2, connecting block; 3, magnet; 4, coil assembly; 5, first ventilation cavity; 6, second ventilation cavity; 7, heat-resistant and wear-resistant plate; 8, first air inlet; 9, second air inlet; 10, air outlet; 11, wire threading pipe; 12, first air inlet duct; 13, first partition; 14, second air inlet duct; 15, air outlet duct; 16, wire placement cavity; 17, wire threading partition; 18, second partition; 19, power supply; 20, fan; 21, detector; 22, control unit; 23, high-temperature test piece to be measured. Specific embodiments

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] The object of the present invention is to provide an air-cooled electromagnetic ultrasonic sensor, a detection system and a method to solve the problems existing in the above-mentioned prior art and improve the high-temperature resistance performance of the high-temperature-resistant electromagnetic ultrasonic sensor.

[0023] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Embodiment 1 As Figures 1 to 9 shown, this embodiment provides an air-cooled high-temperature-resistant electromagnetic ultrasonic sensor, which includes a sensor body 100 and a fan 20. The sensor body 100 includes a housing 1, a connection block 2, a magnet 3 and a coil assembly 4. The connection block 2, the magnet 3 and the coil assembly 4 are sequentially arranged in the housing 1 along the first direction. The connection block 2 and the coil assembly 4 are respectively hermetically connected to the inner wall of the housing 1. A first ventilation cavity 5, a second ventilation cavity 6 and an air outlet duct 15 are arranged in the housing 1. The first ventilation cavity 5 surrounds the magnet 3, and the second ventilation cavity 6 is located on the side of the coil assembly 4 away from the magnet 3. The first ventilation cavity 5 and the second ventilation cavity 6 are respectively communicated with the air outlet duct 15. The coil assembly 4 is filled with sealant, and the coil assembly 4 isolates the first ventilation cavity 5 and the second ventilation cavity 6; A first air inlet 8 communicated with the first ventilation cavity 5, a second air inlet 9 communicated with the second ventilation cavity 6 and an air outlet 10 communicated with the air outlet duct 15 are arranged on the outer wall of the housing 1; The first air inlet 8 and the second air inlet 9 are respectively communicated with the air outlet of the fan 20 through pipelines.

[0025] The air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of this embodiment further includes a temperature sensor arranged in the second ventilation cavity 6. In this embodiment, the number of both the first air inlet 8 and the second air inlet 9 is two.

[0026] In an alternative solution of this embodiment, preferably, a first air inlet duct 12 is further arranged in the housing 1. The first air inlet 8 is communicated with the first ventilation cavity 5 through the first air inlet duct 12, and the first air inlet duct 12 is isolated from the second ventilation cavity 6; A second air inlet duct 14 is further arranged in the housing 1. The second air inlet 9 is communicated with the second ventilation cavity 6 through the second air inlet duct 14, and the second air inlet duct 14 is isolated from the first ventilation cavity 5.

[0027] In an alternative embodiment of the present embodiment, preferably, a first partition 13 is provided inside the housing 1. The top end of the first partition 13 is fixedly connected to the housing 1, and the first air inlet duct 12 is formed between the first partition 13 and the inner wall of the housing 1.

[0028] In an alternative embodiment of the present embodiment, preferably, it further includes a wire threading pipe 11 connected to the housing 1. A wire placement cavity 16 is provided inside the housing 1. The first ventilation cavity 5, the second ventilation cavity 6, the first air inlet duct 12, the second air inlet duct 14, and the air outlet duct 15 are respectively isolated from the wire placement cavity 16. The wire threading pipe 11 is communicated with the wire placement cavity 16. The wires of the coil assembly 4 and the signal wires of the temperature sensor both pass through the wire placement cavity 16 and the wire threading pipe 11. In this embodiment, a part of the wire placement cavity 16 is provided between the inner wall of the housing 1 and the connecting block 2, and the other part is provided between the second partition 18 and the inner wall of the housing 1. A wire threading partition 17 is provided inside the housing 1. The wires of the coil assembly 4 and the signal wires of the temperature sensor enter the wire placement cavity 16 through the wire threading channels on the wire threading partition 17. After the wires are threaded, the wire placement cavity 16 is isolated from other cavities (including the first ventilation cavity 5, the second ventilation cavity 6, the first air inlet duct 12, the second air inlet duct 14, and the air outlet duct 15) by filling sealant in the wire threading partition 17.

[0029] In an alternative embodiment of the present embodiment, preferably, it further includes a wire harness connector provided at one end of the wire threading pipe 11 away from the housing 1. The wires of the coil assembly 4 and the signal wires of the temperature sensor are respectively electrically connected to the wire harness connector; the wire harness connector is used for electrically connecting with the wire harness connectors of other instruments, which is convenient to use.

[0030] In an alternative embodiment of the present embodiment, preferably, it further includes a heat-resistant and wear-resistant plate 7 fixedly connected to the housing 1. The second ventilation cavity 6 is located between the coil assembly 4 and the heat-resistant and wear-resistant plate 7; the heat-resistant and wear-resistant plate 7 blocks a part of the heat from entering the sensor interior through its own heat insulation performance, playing a role of static heat resistance.

[0031] The specific heat dissipation principle of the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor in this embodiment is as follows: The flowing air generated by the operation of the fan 20 is divided into two parts. One part sequentially passes through the first air inlet 8, the first air inlet duct 12, the first ventilation cavity 5, and the air outlet duct 15. The other part sequentially passes through the second air inlet 9, the second air inlet duct 14, the second ventilation cavity 6, and the air outlet duct 15. Since the first ventilation cavity 5 surrounds the magnet 3, the first ventilation cavity 5 itself can serve as an air heat insulation layer to block the heat transfer between the housing 1 and the magnet 3. By introducing flowing air into the first ventilation cavity 5, the heat of the magnet 3 can also be taken away, improving the heat dissipation performance, and thus improving the heat resistance performance of the electromagnetic ultrasonic sensor. The second ventilation cavity 6 is located between the coil assembly 4 and the high-temperature test piece 23 to be measured. The second ventilation cavity 6 itself can serve as an air heat insulation layer to improve the heat resistance performance of the electromagnetic ultrasonic sensor. By introducing flowing air into the second ventilation cavity 6, the heat of the coil assembly 4 can also be taken away, improving the heat dissipation performance, and thus improving the heat resistance performance of the electromagnetic ultrasonic sensor. The heat-resistant and wear-resistant plate 7 blocks the heat of the high-temperature test piece 23 to be measured from entering the interior of the sensor through its own heat insulation performance, playing a role in static heat resistance.

[0032] Furthermore, by setting a temperature sensor, the temperature in the second ventilation cavity 6 can be monitored in real time, facilitating the adjustment of the output power of the fan 20 according to the real-time temperature in the second ventilation cavity 6, so that the temperature in the second ventilation cavity 6 can be maintained below the set value.

[0033] It should be noted that in practical applications, based on the existing technical knowledge and the required heat dissipation amount, technical personnel can perform actual calculations on design parameters such as the thickness of the first ventilation cavity 5, the thickness of the second ventilation cavity 6, and the rotation speed of the fan 20 on the basis of the solution described in this embodiment to achieve the purpose of ensuring the heat dissipation performance and heat resistance performance. In practical applications, the magnet 3 can be a permanent magnet or an electromagnet.

[0034] Embodiment 2 As Figure 9 shown, this embodiment provides an electromagnetic ultrasonic detection system, including a power supply 19, a detector 21, a control unit 22, and the air-cooled high-temperature-resistant electromagnetic ultrasonic sensor of Embodiment 1. The power supply 19 is used to supply power to the detector 21 and the fan 20. The detector 21 can provide pulse excitation for the coil windings in the coil assembly 4. The temperature sensor is signal-connected to the control unit 22, and the control unit 22 can adjust the power of the fan 20 according to the detection signal of the temperature sensor. The temperature sensor does not require power supply. The temperature change will cause the temperature sensor to generate voltage and current signals by itself. The temperature sensor only needs to transmit the electrical signal (temperature signal) to the detector 21.

[0035] In this embodiment, the control unit 22 uses a PLC programmable controller; however, in actual applications, technicians can adaptively adjust the control unit 22 according to needs. For example, since the detector 21 has its own control circuit and chip, the control unit 22 can be integrated into the control circuit of the detector 21, or the control circuit and chip in the controller can be used as the control unit 22.

[0036] Embodiment III The present invention also provides a method for improving the heat resistance of an electromagnetic ultrasonic sensor: a second ventilation cavity 6 and an air outlet duct 15 are arranged in the electromagnetic ultrasonic sensor, and the second ventilation cavity 6 is located on the side of the coil assembly 4 of the electromagnetic ultrasonic sensor close to the high-temperature test piece 23 to be measured, and the second ventilation cavity 6 communicates with the air outlet duct 15; the coil assembly 4 is thermally insulated through the second ventilation cavity 6, and heat dissipation is carried out by introducing flowing air into the second ventilation cavity 6.

[0037] In an alternative embodiment of this embodiment, preferably, a first ventilation cavity 5 surrounding the magnet 3 of the electromagnetic ultrasonic sensor is arranged in the electromagnetic ultrasonic sensor, so that the first ventilation cavity 5 communicates with the air outlet duct 15, the magnet 3 is thermally insulated through the first ventilation cavity 5, and heat dissipation is carried out by introducing flowing air into the first ventilation cavity 5.

[0038] Specific examples are used in the present invention to elaborate on the principle and implementation manner of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An air-cooled high temperature resistant electromagnetic ultrasonic sensor, characterized in that: It includes a sensor body and a fan, the sensor body includes a shell, a connecting block, a magnet and a coil assembly, the connecting block, the magnet and the coil assembly are arranged in the shell in sequence along a first direction, the connecting block and the coil assembly are respectively sealed and connected to the inner wall of the shell, a first ventilation cavity, a second ventilation cavity and an air outlet duct are arranged in the shell, the first ventilation cavity surrounds the magnet, the second ventilation cavity is located on the side of the coil assembly away from the magnet, the first ventilation cavity and the second ventilation cavity are respectively connected to the air outlet duct, the coil assembly is filled with sealant, and the coil assembly isolates the first ventilation cavity from the second ventilation cavity; a first air inlet communicating with the first ventilation cavity, a second air inlet communicating with the second ventilation cavity and an air outlet communicating with the air outlet duct are arranged on the outer wall of the shell; the first air inlet and the second air inlet are respectively connected to the air outlet of the fan through pipelines.

2. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 1, characterized in that: Also included is a temperature sensor disposed in the second ventilation cavity.

3. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 2, characterized in that: A first air inlet duct is further provided in the shell, the first air inlet is connected to the first ventilation cavity through the first air inlet duct, and the first air inlet duct is isolated from the second ventilation cavity; A second air inlet duct is also provided in the shell, the second air inlet is communicated with the second ventilation cavity through the second air inlet duct, and the second air inlet duct is isolated from the first ventilation cavity.

4. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 3 is characterized in that: A first partition is disposed in the shell, a top end of the first partition is fixedly connected to the shell, and the first air inlet duct is formed between the first partition and an inner wall of the shell.

5. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 3, characterized in that: It also includes a wire threading tube connected to the shell, a wire placement cavity is provided in the shell, the first ventilation cavity, the second ventilation cavity, the first air inlet duct, the second air inlet duct and the air outlet duct are respectively isolated from the wire placement cavity, the wire threading tube is connected to the wire placement cavity, and the wires of the coil assembly and the signal wires of the temperature sensor pass through the wire placement cavity and the wire threading tube.

6. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 5, characterized in that: It also includes a wiring harness connector arranged at one end of the threading tube away from the shell, and the wires of the coil assembly and the signal wires of the temperature sensor are electrically connected to the wiring harness connector respectively.

7. The air-cooled high temperature resistant electromagnetic ultrasonic sensor according to claim 2, characterized in that: It also includes a heat-resistant and wear-resistant plate fixedly connected to the shell, and the second ventilation cavity is located between the coil assembly and the heat-resistant and wear-resistant plate.

8. An electromagnetic ultrasonic detection system, characterized in that: It includes a power supply, a detector, a control unit and the air-cooled high-temperature resistant electromagnetic ultrasonic sensor as described in any one of claims 2-7, the power supply is used to power the detector and the fan, the detector can provide pulse excitation for the coil winding in the coil assembly; the temperature sensor is signal-connected to the control unit, and the control unit can adjust the power of the fan according to the detection signal of the temperature sensor.

9. A method for improving the heat resistance of an electromagnetic ultrasonic sensor, characterized in that: A second ventilation cavity and an air outlet duct are arranged in the electromagnetic ultrasonic sensor, and the second ventilation cavity is located on a side of the coil assembly of the electromagnetic ultrasonic sensor close to the high-temperature test piece to be measured, and the second ventilation cavity is communicated with the air outlet duct; the coil assembly is insulated by the second ventilation cavity, and heat is dissipated by passing flowing air into the second ventilation cavity.

10. The method for improving the heat resistance of an electromagnetic ultrasonic sensor according to claim 9, characterized in that: A first ventilation cavity surrounding the magnet of the electromagnetic ultrasonic sensor is arranged in the electromagnetic ultrasonic sensor, so that the first ventilation cavity is communicated with the air outlet duct, the magnet is heat-insulated by the first ventilation cavity, and heat is dissipated by passing flowing air into the first ventilation cavity.

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