阅读说明：本技术 大功率附加场磁动力等离子体推力器阴极螺旋换热结构 (Cathode spiral heat exchange structure of high-power additional field magnetomotive plasma thruster ) 是由 李永 丛云天 汤海滨 魏延明 丁凤林 周成 王宝军 王戈 赵博强 吴延龙 李良 于 2020-05-26 设计创作，主要内容包括：本发明公开了一种大功率附加场磁动力等离子体推力器阴极螺旋换热结构,包括：阴极套筒内壁、阴极套筒外水冷套、进口管路和出口管路；其中,阴极套筒内壁与阴极套筒外水冷套通过焊接实现密封配合,阴极套筒内壁与阴极套筒外水冷套之间的区域构成冷却腔体；进口管路与阴极套筒内壁焊接,并且进口管路与冷却腔体相连通；出口管路与阴极套筒内壁焊接,并且出口管路与冷却腔体相连通；阴极套筒内壁的外表面上设有导流板,导流板在冷却腔体内引导冷却剂的流动。本发明确保阴极在高温大电流下可靠工作,同时通过引入导流板设计冷却流道,弥补了传统直通式阴极换热结构换热效率低、尺寸大、寿命短的缺陷。(The invention discloses a cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster, which comprises: the cathode sleeve comprises a cathode sleeve inner wall, a cathode sleeve outer water cooling sleeve, an inlet pipeline and an outlet pipeline; the inner wall of the cathode sleeve is in sealed fit with the water cooling jacket outside the cathode sleeve through welding, and a cooling cavity is formed in a region between the inner wall of the cathode sleeve and the water cooling jacket outside the cathode sleeve; the inlet pipeline is welded with the inner wall of the cathode sleeve and communicated with the cooling cavity; the outlet pipeline is welded with the inner wall of the cathode sleeve and communicated with the cooling cavity; and a flow guide plate is arranged on the outer surface of the inner wall of the cathode sleeve and guides the flow of the coolant in the cooling cavity. The invention ensures that the cathode works reliably under high temperature and large current, and simultaneously overcomes the defects of low heat exchange efficiency, large size and short service life of the traditional straight-through cathode heat exchange structure by introducing the guide plate to design the cooling flow channel.)

1. A cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster is characterized by comprising: the cathode sleeve comprises a cathode sleeve inner wall (1), a cathode sleeve outer water cooling sleeve (2), an inlet pipeline (51) and an outlet pipeline (52); wherein the content of the first and second substances,

the inner wall (1) of the cathode sleeve is in sealed fit with the outer water cooling sleeve (2) of the cathode sleeve through welding, and a cooling cavity (4) is formed in a region between the inner wall (1) of the cathode sleeve and the outer water cooling sleeve (2) of the cathode sleeve;

the inlet pipeline (51) is welded with the inner wall (1) of the cathode sleeve, and the inlet pipeline (51) is communicated with the cooling cavity (4);

the outlet pipeline (52) is welded with the inner wall (1) of the cathode sleeve, and the outlet pipeline (52) is communicated with the cooling cavity (4);

and a guide plate (3) is arranged on the outer surface of the inner wall (1) of the cathode sleeve, and the guide plate (3) guides the flow of the coolant in the cooling cavity (4).

2. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: cathode sleeve inner wall (1) is hollow cylinder, the one end of cathode sleeve inner wall (1) is equipped with outside bellied ladder, the surface temperature of cathode sleeve inner wall (1) changes along axial gradient, and the temperature variation range is 300 ~ 400K.

3. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the cathode sleeve outer water cooling jacket (2) is a hollow thin-wall cylinder, a first straight section is arranged at one end of the cathode sleeve outer water cooling jacket (2), a second straight section is arranged on the inner wall (1) of the cathode sleeve, and the first straight section and the second straight section are welded.

4. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the welding position of the water cooling sleeve (2) outside the cathode sleeve and the inner wall (1) of the cathode sleeve is an angle welding seam, and argon arc welding, vacuum electron beam welding and brazing are adopted for welding.

5. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the welding positions of the inlet pipeline (51) and the inner wall (1) of the cathode sleeve are pipeline and plate fillet welding seams, and electron beam welding and brazing are adopted;

and the welding position of the outlet pipeline (52) and the inner wall (1) of the cathode sleeve is a pipeline and plate fillet weld, and electron beam welding and brazing are adopted.

6. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the thinnest parts of the water cooling sleeve (2) outside the cathode sleeve and the inner wall (1) of the cathode sleeve are 3-5 mm in thickness so as to ensure the pressure resistance after integral welding, and the maximum bearable internal pressure is more than 4 MPa.

7. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the cathode sleeve inner wall (1) and the guide plate (3) have no tips, the flow resistance is reduced, and the flow speed of the coolant in the cooling cavity (4) is 0.5-2 kg/s.

8. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 1, is characterized in that: the inner wall (1) of the cathode sleeve, the water cooling sleeve (2) outside the cathode sleeve, the inlet pipeline (51) and the outlet pipeline (52) are all made of red copper.

9. The high-power additional field magnetomotive plasma thruster cathode spiral heat exchange structure according to claim 7, is characterized in that: the coolant is liquid nitrogen, liquid helium or deionized water.

Technical Field

The invention belongs to the technical field of electric propulsion power devices of spacecraft, and particularly relates to a cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster.

Background

With the requirements of applying an electric propulsion platform and a deep space exploration task to a spacecraft, various electric propulsion technical researches are developed in China and make great progress, but in view of the fact that the high-power space power supply technology of China is still in the development stage, the research on the high-power MPDT in China is started later.

In MPD, the thermal environment of the cathode is much more severe than that of the anode. Both research studies and experimental configurations indicate that the cathode of MPD suffers the most severe erosion in the harsh thermal environment of high current discharge, and therefore the cathode can be considered as a key component limiting the lifetime of the entire MPD thruster. Therefore, the design of the water cooling structure of the cathode of the MPD thruster with high power is indispensable.

The cathode adopted by the conventional electric thruster is difficult to operate for a long time in a high-current and high-heat environment, and the reliability and the service life are difficult to guarantee under the coupling action of discharge, heat radiation and ion bombardment in the MPD thruster. Therefore, the development of a novel cathode spiral heat exchange structure suitable for the high-power MPDT is a development requirement of the high-power MPDT at present, and the surface temperature of the rear end of the cathode is reduced.

Disclosure of Invention

The technical problem solved by the invention is as follows: the invention overcomes the defects of the prior art, provides a cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster, ensures the cathode to reliably work under high temperature and large current through the welding assembly of the inner wall of a cathode sleeve, a water cooling sleeve outside the cathode sleeve, a guide plate, a cooling cavity and inlet and outlet pipelines, and overcomes the defects of low heat exchange efficiency, large size and short service life of the traditional straight-through cathode heat exchange structure by introducing the guide plate to design a cooling flow channel.

The purpose of the invention is realized by the following technical scheme: a cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster comprises: the cathode sleeve comprises a cathode sleeve inner wall, a cathode sleeve outer water cooling sleeve, an inlet pipeline and an outlet pipeline; the inner wall of the cathode sleeve is in sealed fit with the water cooling jacket outside the cathode sleeve through welding, and a cooling cavity is formed in a region between the inner wall of the cathode sleeve and the water cooling jacket outside the cathode sleeve; the inlet pipeline is welded with the inner wall of the cathode sleeve and communicated with the cooling cavity; the outlet pipeline is welded with the inner wall of the cathode sleeve and communicated with the cooling cavity; and a flow guide plate is arranged on the outer surface of the inner wall of the cathode sleeve and guides the flow of the coolant in the cooling cavity.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the inner wall of the cathode sleeve is a hollow cylinder, one end of the inner wall of the cathode sleeve is provided with outwards-protruding steps, the surface temperature of the inner wall of the cathode sleeve changes along the axial gradient, and the temperature change range is 300-400K.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the water cooling sleeve outside the cathode sleeve is a hollow thin-wall cylinder, one end of the water cooling sleeve outside the cathode sleeve is provided with a first straight section, the inner wall of the cathode sleeve is provided with a second straight section, and the first straight section and the second straight section are welded.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the welding position of the water cooling sleeve outside the cathode sleeve and the inner wall of the cathode sleeve is an angle welding seam, and argon arc welding, vacuum electron beam welding and brazing are adopted for welding.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the welding position of an inlet pipeline and the inner wall of a cathode sleeve is a pipeline and plate fillet welding seam, and electron beam welding and brazing are adopted; and the welding position of the outlet pipeline and the inner wall of the cathode sleeve is a pipeline and plate fillet welding seam, and electron beam welding and brazing are adopted.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the thicknesses of the thinnest part of the inner wall of the cathode sleeve and the water cooling sleeve outside the cathode sleeve are 3-5 mm, so that the pressure resistance after integral welding is ensured, and the maximum bearable internal pressure is more than 4 MPa.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the inner wall of the cathode sleeve and the guide plate have no tips, so that the flow resistance is reduced, and the flow velocity of the coolant in the cooling cavity is 0.5-2 kg/s.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, red copper is adopted for the inner wall of the cathode sleeve, the water cooling sleeve outside the cathode sleeve, the inlet pipeline and the outlet pipeline.

In the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster, the coolant is liquid nitrogen, liquid helium or deionized water.

Compared with the prior art, the invention has the following beneficial effects:

(1) the cathode spiral heat exchange structure adopts the spiral design of the internal flow channel, ensures a longer heat exchange path, has better heat conduction capability and smaller flow resistance, and simultaneously ensures that the thermal stress at the joint of the guide plate is lower and the overall heat exchange effect is higher.

(2) The cathode spiral heat exchange structure is simple and reliable in matching, a welding connection scheme is adopted, a high-temperature and high-pressure resistant sealed cooling cavity is formed, and the cathode spiral heat exchange structure has the characteristics of strong universality and wide application range and has a very wide market application prospect.

(3) The cathode spiral heat exchange device has a compact design structure, and keeps a smaller envelope size on the premise of ensuring reliability and heat conduction capability.

(4) The welding process of the cathode spiral heat exchange structure is reliable and high-pressure resistant, the problems of process, structural strength, thermal stress and the like are fully considered in the welding of the inner wall surface and the water cooling jacket, the inlet and outlet pipelines and the inner wall surface, the cathode cooling cavity is effectively isolated from the external vacuum environment, and the problems of leakage and the like under high-pressure water flow are avoided;

(5) the cathode spiral heat exchange structure adopts materials which are easy to process and good in heat conductivity, and can realize high-efficiency heat exchange under the high-temperature condition.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 is a cross-sectional view of a cathode spiral heat exchange structure of a high-power additional field magnetomotive plasma thruster of the invention;

FIG. 2 is a left side view of the inner wall of the cathode sleeve of the present invention;

FIG. 3(a) is a front view of the inside wall of the cathode sleeve of the present invention;

FIG. 3(b) is another schematic view of the inner wall of the cathode sleeve of the present invention;

FIG. 4 is a cross-sectional view of the inner wall of the cathode sleeve at the baffle of the present invention;

FIG. 5 is a cross-sectional view of the outer water-cooled jacket of the cathode sleeve of the present invention;

FIG. 6 is an expanded view of the water cooling channel of the cathode sleeve according to the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

The cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster mainly comprises a cathode sleeve inner wall, a cathode sleeve outer water cooling sleeve, a flow guide plate, a cooling cavity and an inlet and outlet pipeline. A flow guide plate for increasing the flow path and the turbulence of the coolant is arranged in the cathode spiral heat exchange structure; the inner wall of the cathode sleeve is a cylinder, a flow guide plate is added to construct an inner flow passage, the water cooling sleeve outside the cathode sleeve is a thin-wall cylindrical table, and the outer side sealing and the matching with the inner wall surface of the cooling channel are completed through angle joint welding to finally form a whole cooling cavity; the inlet and outlet pipelines are connected with the cathode by welding. The sealing of the cooling channel in the cathode is realized through the welding connection among the inner wall of the cathode sleeve, the water cooling sleeve outside the cathode sleeve and the guide plate.

The inner wall 1 of the cathode sleeve is in sealed fit with the water cooling sleeve 2 outside the cathode sleeve through welding, a cooling cavity 4 is formed in the area between the inner wall 1 of the cathode sleeve and the water cooling sleeve, the inlet and outlet pipelines are welded with the end faces of the corresponding positions of the inner wall 1 of the cathode sleeve to achieve inlet and outlet of coolant, and meanwhile, the coolant is prevented from leaking in the cooling cavity 4.

A flow guide plate 3 is arranged on the inner wall 1 of the cathode sleeve, and the flow of the coolant is guided in a cooling cavity 4; and a coolant channel is arranged in the inlet and outlet pipeline and is communicated with a cooling cavity 4 formed between the inner wall 1 of the cathode sleeve and the water cooling jacket 2 outside the cathode sleeve, so that a closed-loop passage is realized.

As shown in fig. 1, the cathode spiral heat exchange structure of the high-power additional field magnetomotive plasma thruster comprises a cathode sleeve inner wall 1, a cathode sleeve outer water cooling jacket 2, a flow guide plate 3, a cooling cavity 4, an inlet pipeline 51 and an outlet pipeline 52. The cathode sleeve inner wall 1 and the cathode sleeve outer water cooling jacket 2 are in sealing fit through welding, a cooling cavity 4 is formed in the area between the cathode sleeve inner wall 1 and the cathode sleeve outer water cooling jacket 2, an inlet pipeline 51 is welded with the cathode sleeve inner wall 1, and the inlet pipeline 51 is communicated with the cooling cavity 4; the outlet pipeline 52 is welded with the inner wall 1 of the cathode sleeve, and the outlet pipeline 52 is communicated with the cooling cavity 4; the coolant is fed and discharged by welding the end face of the corresponding position of the cathode sleeve inner wall 1, and the coolant is prevented from leaking in the cooling cavity 4; a flow guide plate 3 is arranged on the inner wall 1 of the cathode sleeve, and the flow of the coolant is guided in a cooling cavity 4; and coolant channels are arranged in the inlet pipeline 51 and the outlet pipeline 52 and are communicated with a cooling cavity 4 formed between the inner wall 1 of the cathode sleeve and the water cooling jacket 2 outside the cathode sleeve, so that a closed-loop passage is realized.

The functional indexes of the cathode spiral heat exchange structure are verified during the test of the thruster, so that the condition that the welding position of the heat exchange structure is not leaked and the wall surface is not cracked or deformed when deionized water with the flow rate of 2kg/s and the pressure of 4MPa is introduced into the cooling cavity can be met. When the thruster works, the wall surface temperature of a central hole in the inner wall of the cathode sleeve reaches 300-400K, the cathode heat exchange structure does not have the heating concentration phenomena such as ablation, expansion crack and melting, and the temperature rise of the inlet and the outlet reaches 10-20K.

The inner wall 1 of the cathode sleeve is in sealed fit with the water cooling sleeve 2 outside the cathode sleeve through welding, a cooling cavity 4 is formed in the area between the inner wall 1 of the cathode sleeve and the water cooling sleeve, the inlet and outlet pipelines are welded with the end faces of the corresponding positions of the inner wall 1 of the cathode sleeve to achieve inlet and outlet of coolant, and meanwhile, the coolant is prevented from leaking in the cooling cavity 4.

A flow guide plate 3 is arranged on the inner wall 1 of the cathode sleeve, and the flow of the coolant is guided in a cooling cavity 4; and a coolant channel is arranged in the inlet and outlet pipeline and is communicated with a cooling cavity 4 formed between the inner wall 1 of the cathode sleeve and the water cooling jacket 2 outside the cathode sleeve, so that a closed-loop passage is realized.

Preferably, as shown in fig. 2, 3(a) and 3(b), the inner wall 1 of the cathode sleeve is a hollow cylinder, one end of the cylinder is provided with an outward convex step, the inner hollow area is in contact with the cathode through a conical surface to realize heat exchange, the temperature of the contact surface changes along the axial gradient, and the temperature change range is 300-400K.

Preferably, as shown in fig. 5, the cathode sleeve outer water cooling jacket 2 is a hollow thin-walled circular truncated cone, and the cathode sleeve outer water cooling jacket 2 and the cathode sleeve inner wall 1 are provided with straight sections with a certain length in regions where the two ends are matched, for welding connection.

Preferably, as shown in fig. 1, the welding positions a and b of the cathode sleeve outer water-cooling jacket 2 and the cathode sleeve inner wall 1 on both sides are fillet welds, and argon arc welding, vacuum electron beam welding and brazing are adopted for welding. Preferably, as shown in fig. 1, the welding position of the inlet pipe 51, the outlet pipe 52 and the inner wall 1 of the cathode sleeve is c, the pipe is welded with the plate fillet, the pipe hole is close to the outer wall, and only electron beam welding and brazing can be adopted.

Preferably, as shown in fig. 1, the thinnest portions of the water cooling jacket 2 outside the cathode sleeve and the inner wall 1 of the cathode sleeve are about 3-5 mm in thickness so as to ensure the pressure resistance after the whole welding, and the maximum bearable internal pressure is greater than 4 MPa.

Preferably, as shown in fig. 3(a), the baffle 3 is designed as a curved surface, the width of the plate is 2mm, and the adjacent distance is 5-7 mm.

Preferably, as shown in fig. 4, the baffle 3 is designed in a circular ring shape, and two sides of the inner wall surface are respectively provided with a baffle plate with a width of 4mm, and a space of 30 degrees is reserved between the baffle plate and the baffle plate.

Preferably, as shown in fig. 1, the cathode sleeve inner wall 1 and the flow guide plate 3 thereon have no tip design, so as to reduce the flow resistance, and the designed flow rate of the coolant in the cooling cavity 4 is 0.5-2 kg/s.

Preferably, as shown in fig. 2, the inner wall of the cathode sleeve is provided with a passage for the inlet and outlet pipelines and is arranged in an up-and-down symmetrical manner about the central axis.

Preferably, as shown in fig. 1, the cathode sleeve inner wall 1, the cathode sleeve outer water cooling jacket 2, the inlet pipeline 51 and the outlet pipeline 52 are made of the same material with better heat conductivity, such as red copper.

Preferably, as shown in fig. 1, the cathode coolant may use liquid nitrogen, liquid helium, or deionized water.

Preferably, fig. 6 is an expanded view of the water-cooling channel of the cathode sleeve according to the present invention. As shown in fig. 6, the cathode water cooling passages are formed by internal baffles, the flow paths being shown by the arrows. The baffle 3 comprises a first baffle 31, a second baffle 32, a third baffle 33, a fourth baffle 34, a fifth baffle 35, a sixth baffle 36, a seventh baffle 37, an eighth baffle 38, a ninth baffle 39 and a tenth baffle 30; wherein, one end of the fifth baffle 35 is connected with the front wall 11 of the cathode sleeve inner wall 1; one end of the first baffle 31 is connected with the tenth baffle 30, and a gap is reserved between the other end of the first baffle 31 and the fifth baffle 35; a gap is reserved between one end of the second baffle 32 and the tenth baffle 30, and the other end of the second baffle 32 is connected with the fifth baffle 35; one end of the third baffle 33 is connected with the tenth baffle 30, and a gap is reserved between the other end of the third baffle 33 and the fifth baffle 35; a gap is reserved between one end of the fourth baffle 34 and the tenth baffle 30, and the other end of the fourth baffle 34 is connected with the fifth baffle 35; one end of the sixth baffle plate 36 is connected with the tenth baffle plate 30, and a gap is reserved between the other end of the sixth baffle plate 36 and the fifth baffle plate 35; a gap is reserved between one end of the seventh baffle 37 and the tenth baffle 30, and the other end of the seventh baffle 37 is connected with the fifth baffle 35; one end of the eighth baffle 38 is connected with the tenth baffle 30, and a gap is left between the other end of the eighth baffle 38 and the fifth baffle 35; one end of the ninth shutter 39 is spaced apart from the tenth shutter 30, and the other end of the ninth shutter 39 is connected to the fifth shutter 35. Fig. 6 is an expanded view, and is an expanded view with the center axis of the tenth baffle 30 as a dividing line.

The longitudinal directions of the first baffle plate 31, the second baffle plate 32, the third baffle plate 33, the fourth baffle plate 34, the fifth baffle plate 35, the sixth baffle plate 36, the seventh baffle plate 37 and the eighth baffle plate 38 are all perpendicular to the longitudinal direction of the ninth baffle plate 39.

The first baffle 31 and the cathode sleeve inner wall 1 form a first channel, the first baffle 31 and the second baffle 32 form a second channel, the second baffle 32 and the third baffle 33 form a third channel, the third baffle 33 and the fourth baffle 34 form a fourth channel, the fourth baffle 34 and the cathode sleeve inner wall 1 form a fifth channel, the sixth baffle 36 and the cathode sleeve inner wall 1 form a sixth channel, the sixth baffle 36 and the seventh baffle 37 form a seventh channel, the seventh baffle 37 and the eighth baffle 38 form an eighth channel, the eighth baffle 38 and the ninth baffle 39 form a ninth channel, and the ninth baffle 39 and the cathode sleeve inner wall 1 form a tenth channel.

The cooling medium of the present embodiment enters the first channel through the inlet pipe 51, then enters the second channel, the third channel, the fourth channel, the fifth channel, the sixth channel, the seventh channel, the eighth channel, the ninth channel, and the tenth channel in this order, and finally flows to the outlet pipe 52 through the outlet.

The cathode spiral heat exchange structure adopts the internal flow channel circuitous design, ensures a longer heat exchange path, has better heat conduction capacity and smaller flow resistance, simultaneously ensures that the thermal stress at the connection part of the guide plate is lower, and has higher overall heat exchange effect.

The cathode spiral heat exchange structure is compact in design structure, small envelope size is kept on the premise of ensuring reliability and heat conduction capacity, the cathode spiral heat exchange structure is simple and reliable in matching, a welding connection scheme is adopted, a high-temperature and high-pressure resistant sealed cooling cavity is formed, and the cathode spiral heat exchange structure has the characteristics of strong universality and wide application range and has a very wide market application prospect.

The welding process of the cathode spiral heat exchange structure is reliable and high-pressure resistant, the problems of process, structural strength, thermal stress and the like are fully considered in the welding of the inner wall surface and the water cooling jacket and the welding of the inlet and outlet pipelines and the inner wall surface, and leakage under high pressure is avoided.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.