WO2008056811A1

WO2008056811A1 - Bend portion of heat insulation multiple pipe for superconducting transmission

Info

Publication number: WO2008056811A1
Application number: PCT/JP2007/072039
Authority: WO
Inventors: Yasuhide Ishiguro; Yoshikazu Kawabata; Shuichi Kusaka; Susumu Itadani; Sataro Yamaguchi
Original assignee: Jfe Steel Corporation
Priority date: 2006-11-09
Filing date: 2007-11-07
Publication date: 2008-05-15
Also published as: JP2008121746A; JP4899808B2

Abstract

Bend portion of a heat insulation multiple pipe for superconducting transmission by which heat insulation efficiency can be ensured by preventing contact of an inner pipe with an outer pipe during cooling contraction, and piping work can be carried out easily and inexpensively. In the bend portion (200) being connected with the straight pipe section (100) of a heat insulation multiple pipe for superconducting transmission in order to alter the piping direction, the inner pipe (7) and the outer pipe (6) in the bend portion are connected, respectively, with the inner pipe (2) and the outer pipe (1) in the straight pipe section on a one-to-one basis, the outside diameter of the inner pipe in the bend portion is identical to that in the straight pipe section, and the outside diameter of the outer pipe in the bend portion is larger than the outside diameter of the outer pipe to be connected in the straight pipe section.

Description

Specification Curved pipe section of heat insulation multiple pipe for superconducting power transmission

The present invention relates to a curved pipe portion of a heat insulating multiple tube for superconducting power transmission, and more specifically, has an inner tube that accommodates a superconducting cable, and one or a plurality of multiple arranged outer tubes that surround the inner tube, and are adjacent to each other. The present invention relates to a curved pipe part that is connected to a straight pipe part of a heat insulation multiple pipe for superconducting power transmission in which at least one of the inner and outer pipe gaps is a vacuum heat insulation layer, and changes the piping direction. Background art

Insulated multi-pipe for superconducting power transmission (heat-insulated multi-pipe for superconducting power transmission) has not been put to practical use because superconducting power transmission has not yet been put to practical use. According to Non-Patent Document 1, in the field test of AC superconducting transmission on the scale of 500 m, the corner part and U-shaped part as a curved pipe part that changes the wiring direction of the superconducting cable with heat insulation double tube structure The double pipe itself was bent to a large radius of curvature.

The heat-insulated multiple tube for superconducting power transmission realizes superconducting power transmission by flowing a cryogenic refrigerant such as liquid nitrogen through the gap between the outer surface of the superconducting conductor housed in the inner tube and the inner surface of the inner tube. It is important to suppress heat input from the environment. However, since the inner pipe is cooled to a very low temperature, unlike the outer pipe group on the side close to the outer environment, it contracts greatly. At this time, since the inner pipe contracts in the longitudinal direction in the straight pipe portion, if the inner pipe is connected with a bellows, the contraction can be eased and no particular problem occurs. However, for example, as shown in FIG. 4A and FIG. 4B, in the bent tube portion 200, the inner tube 2 and the outer tube 1 (shown in the case of a heat insulating double tube) are concentrically arranged in a room temperature environment. 4) If the cryogenic refrigerant 30 flows into the inner pipe 2 (FIG. 4B), the inner pipe 2 is cooled and contracts, and comes into contact with the outer pipe 1. Probability is high. When contact 4 occurs, heat is transferred from the location of contact 4 into the inner tube 2, and depending on the situation, the temperature of the superconducting conductor in the inner tube 2 exceeds the critical temperature (T c), the superconducting state collapses, and the electrical resistance However, there is a problem that superconducting power transmission cannot be realized, or that the refrigeration unit that supports the insulated multi-pipe for superconducting power transmission is heavily burdened. 4A and 4B show a spacer (low thermal conductivity spacer) 3 arranged as a means for preventing contact between the inner tube 2 and the outer tube 1 (see Patent Document 1). However, depending on the combination of the inner tube and outer tube diameters, the inner tube moves so that it sticks to the inner surface of the outer tube as the inner tube cools and contracts, and the spacer itself breaks and breaks. There is also a risk. In that case, the contact area between the inner tube and the outer tube is increased, the heat insulation efficiency is lowered, and the superconducting conductor cannot be used in the superconducting state.

One of the means for avoiding this is to increase the radius of curvature of the curved pipe part and secure a sufficient space between the inner pipe and the outer pipe, as described in Non-Patent Document 1. However, this method can be established when the system has a scale size of about 50 Om and there is room in the installation location, but it can be established in actual transmission where the transmission pipe is often bent rapidly. Is difficult.

In fields other than superconductivity, for example, in the raw material gas piping of the semiconductor industry, the outer tube of the multi-ply tube is a bellows joint and the inner tube is a normal tube. In a heat-insulated multiple tube that transports cryogenic liquid such as the inner tube and outer tube, a bellows tube is inserted into a part of the outer tube to absorb the shrinkage.

(See Patent Document 3). Non-Patent Document 1: Published by Central Research Institute of Electric Power Company “Denki Chuo Research News No. 4 1 2 (issued 0 5/6/9) J

Patent Document 1: Japanese Patent Laid-Open No. 8-6 4 8 80

Patent Document 2: Japanese Patent Application Laid-Open No. 5-104.80

Patent Document 3: Japanese Patent Laid-Open No. 2 0 0 2-7 10 5 5 Disclosure of Invention

The above prior art is insufficient to prevent the inner tube and the outer tube from contacting each other at the time of refrigerant flow in the bent tube portion of the heat insulating multiple tube for superconducting power transmission. In other words, as in Non-Patent Document 1, the means for bending the heat insulating multi-pipe itself by bending with a large radius of curvature cannot cope with the steep bend assumed for an actual transmission pipe.

In addition, as disclosed in Patent Document 1, when a spacer (low thermal conductivity spacer) is interposed between the inner tube and the outer tube, the curvature of the bent tube portion is large and the cooling shrinkage of the inner tube is large. , Su Excessive force may act on the spacer and the spacer may break. Patent literature

The method of using a bellows joint as part of the outer pipe as shown in 2 is not intended for use at cryogenic temperatures, so it may not be possible to avoid contact between the inner pipe and the outer pipe. Furthermore, since the outer diameter of the crest of the bellows joint in the bent pipe is the same as the outer diameter of the connection partner pipe in the straight pipe, the inner pipe comes into contact with the outer pipe due to cooling contraction when the cryogenic refrigerant flows. The possibility does not go down.

In Patent Document 3, a part of the bellows pipe is used for the outer pipe, and the fitting is inserted into the bellows so that the inner pipe and the outer pipe are concentrically arranged during cooling. In an actual power transmission system that is assumed to have a wide variety of pipe types and curved pipe curvatures for each pipe installation location, it is necessary to make these adjustments one by one, making piping construction more complicated and costly. Is not realistic.

In view of the problems of the prior art as described above, the present invention can prevent the contact of the inner tube to the outer tube at the time of cooling shrinkage, and can ensure the heat insulation efficiency, and the piping work can be performed easily and inexpensively. It is an object of the present invention to provide a curved pipe part of a heat insulating multiple pipe for superconducting power transmission.

The inventors diligently studied to achieve the above object, and made the present invention as follows.

That is, the present invention includes an inner tube that accommodates a superconducting cable, and one or a plurality of outer tubes that surround the inner tube, and at least one of the adjacent inner and outer tube gaps is a vacuum heat insulating layer. The superconducting power-insulated multi-tube for superconducting power transmission is connected to the straight pipe section to change the piping direction. The bent pipe section includes an inner pipe and an outer pipe respectively connected to the straight pipe section. Connected to the outer pipe on a one-to-one basis, the outer diameter of the inner pipe in the bent pipe section is the same as that in the straight pipe section, and the outer diameter of the outer pipe in the bent pipe section is the outer diameter of the connecting outer pipe in the straight pipe section. It is a curved pipe part of a heat insulating multi-pipe for superconducting power transmission characterized by being larger than the above. In the present invention, it is preferable that the bending angle of the bent tube portion is 30 degrees or more. The bending angle here means the angle of the part bent with respect to the straight pipe (that is, the inner angle is 1550 degrees or less). In the present invention, it is preferable that the pipe gap between the adjacent inner and outer pipes in the bent pipe part is 5 mm or more larger than the pipe gap between the connection partners in the straight pipe part. Further, in the present invention, in the bent pipe portion in the atmospheric environment, the inner pipe is eccentrically arranged in a direction opposite to the direction displaced when the coolant flows with respect to the outer pipe adjacent thereto. Is preferred. According to the present invention, in the curved pipe portion of the heat insulating multiple tube for superconducting power transmission, It is possible to effectively prevent the pipe from coming into contact with the outer pipe, and the piping construction of the heat insulating multi-pipe can be performed easily and inexpensively. Brief Description of Drawings

FIG. 1 is a schematic cross-sectional view in the tube axis direction showing Embodiment 1 of the present invention.

FIG. 2 is a schematic cross-sectional view in the pipe circumferential direction of the spacer arrangement portion of FIG.

FIG. 3 is a schematic cross-sectional view in the tube axis direction showing Embodiment 2 of the present invention.

4A and 4B are schematic cross-sectional views in the tube axis direction showing the conventional problems.

5A and 5B are schematic sectional views in the tube axis direction showing the conventional problems.

FIG. 6 is an explanatory view of the displacement of the inner pipe due to cooling contraction during refrigerant flow. The meanings of the symbols in each figure are as follows.

1 Outer pipe

1 c curved outer tube

2 Inner pipe

2 c inner pipe

3 Spacer (Low thermal conductivity spacer)

4 contact

5 Flange

6 Outer pipe (inside the curved pipe)

7 Inner pipe (in the curved pipe section)

8 Sue /, 1 Insulation

9 Superconducting cable

1 0 hole

2 0, 2 1, 2 2, 2 3 Arrow direction

2 5 Inner pipe body

1 0 0 Straight pipe

2 0 0 Curved Pipe BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the curved pipe portion and the straight pipe portion satisfy the following conditions (1) and (2).

(1) Inner pipe outer diameter in the curved pipe section = Inner pipe outer diameter of the connection partner in the straight pipe section

(2) Outer pipe outer diameter in the curved pipe section> Outer pipe outer diameter of the connection partner in the straight pipe section

However, the equal sign “=” in condition (1) allows an error within ± 10%. The wall thickness of the pipe in the bent pipe section and the pipe to be connected in the straight pipe section is not particularly limited. However, from the viewpoint of securing the inner pipe accommodation space and the ease of piping construction, the same thickness is used. It is preferable to make the difference between the thicknesses as small as possible if the force is different or different.

The method of connecting the outer pipe between the straight pipe section and the curved pipe section is preferably a method of fastening flanges provided at the connection ends of the pipes to be connected to each other with bolts or the like from the viewpoint of ease of piping construction.

The straight pipe part is constructed by connecting pipes with a unit length of usually 4 to 15 m by welding, flanges, etc., and at least two of the inner pipes in the straight pipe part are relayed together by bellows Although the displacement during cooling shrinkage can be reduced, there are limits to the number of bellows that can be incorporated, and the displacement due to cooling shrinkage cannot be completely absorbed when incorporated. In addition, the number is limited due to the high cost. In this respect, in the present invention, by satisfying the conditions (1) and (2), the tube gap between the inner tube and the outer tube in the bent tube portion can be expanded more than before, and the use of bellows or concentricity of multiple tubes can be achieved. Regardless of the arrangement, it is possible to avoid contact between the inner and outer tubes.

The outer diameter of the outer pipe in the bent pipe should be increased according to the degree of bending of the bent pipe (the degree of curvature) from the viewpoint of avoiding contact with the inner pipe and saving piping space. In other words, when the bend is dull (the curvature is small), the outer diameter of the outer pipe in the bent pipe is slightly larger than the outer diameter of the connecting pipe in the straight pipe, and the bend is sharp (high curvature) Therefore, it is preferable that the outer diameter of the outer pipe in the bent pipe part is considerably larger than the outer diameter of the outer pipe of the connection partner in the straight pipe part. .

Depending on the length of the straight pipe section and the bellows used for relaying the inner pipe in the straight pipe section, the appropriate value of the outer diameter of the outer pipe in the bent pipe section will change, but the conditions (1) and (2) will only be satisfied. For example, the gap between the inner pipe and the outer pipe in the bent pipe section is made larger than the gap between the inner pipe and the outer pipe of the counterpart in the straight pipe section, and the contact between the inner pipe and the outer pipe during cooling contraction is increased. Can be prevented. However, when the bending angle of the curved pipe (that is, the change angle of the piping direction) is less than 30 degrees, the inequality sign “>” is replaced with the equal sign “=” in the condition (2) (prior art However, since the amount of displacement of the inner tube in the bent tube portion during cooling contraction is small and contact with the outer tube does not occur easily, the bending angle of the bent tube portion is It is preferably 30 ° or more.

By the way, in most cases, the adiabatic multiple pipes in the bent pipe section cannot actually have an ideal concentric arrangement structure. This is because it is difficult to bend a straight pipe with a heat insulation multi-pipe structure by directly bending the heat insulation multi-pipe structure, and even if it can be made, if the bend of the bend becomes sharp, It is almost impossible to keep the tube and the outer tube out of contact.

Therefore, as an alternative, prepare straight inner pipes and outer pipes, and bend inner pipes and outer pipes that are bent so that the curvature of the pipe center axis is the same.

As shown in 5A, a method of inserting the bent tube 2c into the bent tube 1c is assumed. In practice, it is extremely difficult to perform the insertion while keeping the inner tube 2 c and the outer tube 1 c coaxial (concentric). For example, as shown in FIG. The tip end of the tube 2 hits the inner surface of the curved outer tube 1 and the insertion cannot be continued easily. If the curvature of the inner tube is smaller than that of the outer tube, it will be easier to insert, but it will not be concentric, and the inner tube will be closer to the inner surface of the outer tube. With such an arrangement, contact between the bent tube and the bent tube during cooling contraction is more likely to occur. In addition, the bent pipe has straight pipe portions at both ends, and is often difficult to insert. From this point, concentric arrangement of multiple pipes is difficult to achieve. In such an actual situation, according to the present invention, it is possible to effectively prevent the inner tube from coming into contact with the outer tube at the time of cooling contraction, even if the concentric arrangement of the multiple tubes is not taken into consideration, as described above. It can be secured.

Furthermore, in the present invention, the condition that the pipe gap between the adjacent inner and outer pipes in the bent pipe part is 5 mm or more larger than the pipe gap between the connection partners in the straight pipe part (this is a condition).

(Referred to as (3)) is preferable because the contact between the inner tube and the outer tube can be more effectively prevented. Condition (3) is that when the multiple pipes in the straight pipe part and the curved pipe part are concentrically arranged, the difference between the inner diameter of the outer pipe adjacent to the curved pipe part and the outer diameter of the inner pipe is This means that it is 1 O mm or more larger than the difference between the inner diameter of the adjacent outer pipe and the outer diameter of the inner pipe in the straight pipe section. Hereinafter, the reason why it is preferable to satisfy the condition (3) will be described. For convenience of explanation, the insulated double pipe shown in Fig. 6 is taken as an example. In this example, the bellows is not installed on the inner pipe 2 in the straight pipe section 100, so that it can cope with the most severe conditions, one end in the longitudinal direction of the pipe is a fixed end, and the other end is a free end. The length of the part 100 is L = 6 m (close to the maximum normal length of ERW steel pipe), and the pipe material is austenitic stainless steel (cooling shrinkage is larger than ferrite stainless steel). Only the inner pipe 2 and the curved inner pipe 2c are cooled and shrunk.

When cooling proceeds with the flow of the cryogenic refrigerant, the inner pipe 2 on the fixed end side contracts in the direction indicated by arrow 20 and the curved inner pipe 2 c displaces in the direction indicated by arrow 2 1. With the displacement, the inner pipe 2 on the free end side contracts in the arrow direction 22 and displaces in the arrow direction 23.

Liquid nitrogen (boiling point 7 7 K) is used as the cryogenic refrigerant, the flow direction is constant, and the shrinkage rate of the austenitic stainless steel used as the pipe material is estimated to be 1 5 X 1 0 ¹⁶ K When the contraction or displacement of the inner tube 2 and the curved inner tube 2c is calculated assuming a steady cryogenic state, the displacement of the inner tube 2 on the free end side in the direction indicated by the arrow 23 is about 7 mm. This is considered to be almost the same as the displacement of the bent tube toward the inner bend when both ends are fixed ends in Fig. 6. Since it is customary in the past that the pipe gap between adjacent pipes is kept at least 2 mm, the pipe gap in the curved pipe section is made 5 mm or more larger than the pipe gap of the connection partner in the straight pipe section. By this, it is possible to more reliably avoid contact between the inner and outer pipes adjacent in the curved pipe section.

The larger the gap between the bent pipe sections, the higher the effect of preventing the contact between the inner and outer pipes, which is preferable for realizing superconducting power transmission by ensuring the heat insulation effect. It is difficult to determine because it depends on the outer diameter of the pipe in the pipe. However, it is unlikely that extreme cases such as connecting a pipe with an outer diameter of 100 mm in the bent pipe section to a pipe with an outer diameter of 15 O mm in the straight pipe section will be possible. From the viewpoint, it is desirable that the outer diameter of the pipe in the curved pipe section is about three times or less than the outer diameter of the connecting pipe in the straight pipe section.

In addition, when the curved pipe part has a simple L-shaped structure as shown in Fig. 4A and Figure 4B, the inner pipe inside the curved pipe part is displaced in the direction toward the center of curvature of the pipe during cooling contraction, and the inner pipe of the outer pipe is bent. It tends to come into contact with the inner surface. However, considering the superconducting power transmission system as a whole, the situation is not as simple as in Fig. 4A and Fig. 4B. Every time, it is assumed that it may be bent in any direction depending on the situation affected by the multiple straight pipe of the connection partner. In order to cope with such a case, in the present invention, the condition (3) is established not only for the gap between the inner pipe and the outer pipe immediately outside the inner pipe but also for the gap between adjacent outer pipes. Is preferred.

Furthermore, when the displacement direction in which the inner pipe in the bent pipe section at the time of refrigerant flow approaches the outer pipe adjacent to this is known in advance, the inner pipe in the bent pipe section in the atmospheric environment If it is arranged eccentrically in the direction opposite to the approaching displacement direction (i.e., the direction opposite to the direction in which the inner tube is displaced when the refrigerant flows) against the outer tube, the adjacent inner and outer It is preferable because the contact between the tubes can be prevented more reliably. Example

Example 1

FIG. 1 is a schematic cross-sectional view in the tube axis direction showing a curved pipe portion having a heat insulating double pipe structure and a straight pipe portion connected thereto as Embodiment 1 of the present invention, and FIG. 2 is a spacer arrangement portion of FIG. It is a schematic sectional drawing of the pipe circumference direction. The straight pipe section on both sides of the curved pipe section 200, the inner pipe 2 and the outer pipe 1 in the 100 section are connected to the inner pipe 7 and the outer pipe 6 in the curved pipe section 200, one-to-one. The superconducting cable 9 is inserted into the tube 7. 1 and 2 show the state before the cryogenic refrigerant flows through the inner pipes 2 and 7.

The material and diameter size of the inner pipe 2 and outer pipe 1 in the straight pipe section 100 have already been optimized for use as a thermal insulation double pipe for superconducting power transmission.

Spacers (low thermal conductivity) 3 are discretely arranged in the pipe extension direction in the pipe gap between the inner pipe 2 and the outer pipe 1 to prevent mutual contact between the two pipes (curved pipe section 2 0 0 As well as within). For example, a spacer having a thickness of 2 mm made of GFRP may be used as a spacer having a square shape as shown in FIG. 2 and having a diagonal length shorter than the inner diameter of the outer tube 1. As a result, the contact point between the spacer 3 and the inner surface of the outer tube 1 can be maintained even if there is cooling shrinkage or displacement of the double tube.

(Corresponding to the heat conduction relay point from the external environment to the inner pipe 2) is limited to 2 to 3 points at most, and heat insulation performance is ensured. From the viewpoint of further preventing heat conduction, it is preferable to provide holes 10 at appropriate locations in the spacer 3 as shown in FIG.

Figure 1 shows a spacer with a spacer in the curved pipe, but it is not necessary to insert a spacer in the curved pipe. The bend angle of the bent tube part 200 is 90 degrees. The inner pipe 7 has the same material, outer diameter and wall thickness as the inner pipe 2. The outer tube 6 has an outer diameter larger than that of the outer tube 1 and is the same material and thickness as the outer tube 1. The inner pipe 7 is connected to the inner pipe 1 by welding. In addition, you can connect with a flange instead of welding. The outer pipe 6 is connected to the outer pipe 1 and the flange 5.

While the tube gap between the inner pipes 2 and 7 and the outer pipes 1 and 6 is in a vacuum state, a cryogenic refrigerant such as liquid nitrogen is gradually allowed to flow into the inner pipes 2 and 7 for further vacuuming. The thermal insulation effect can be exhibited. The inner pipes 2 and 7 are configured by winding super-insulation 8 for blocking and suppressing far-infrared energy around the outer surface of the inner pipe body 25. Super ^ Tension 8 is made by sputtering aluminum on organic resin film. In order to reduce the emissivity and suppress the heat input from the outside, a metal coating may be used instead of super-infiltration.

In the state where the inside pipes 2 and 7 are cooled to the temperature of liquid nitrogen (liquid nitrogen flows from the lower right side to the upper left side in the figure), the outer pipe 6 is hardly displaced, and the inner pipe 7 is bent due to cooling contraction. It is displaced in the direction toward the center of the index and approaches the inner curved inner surface of the outer tube 6, but the outer diameter of the outer tube 6 is made larger than the outer diameter of the outer tube 1 unlike the conventional one. The inner surface of the outer tube 6 on the inner curve side has shifted to the center of the tube axis curvature than before, and does not reach the inner tube 7.

Also, for the reasons described above, it is practically difficult to arrange the multiple pipes concentrically in the curved pipe section. Therefore, in the example of FIG. 1, the central axis of the inner pipe 7 in the curved pipe section 200 is outside. Although it is arranged at an eccentric position that is closer to the tube axis curvature center side than the center axis position of the tube 6, contact with the outer tube 6 can still be avoided during cooling contraction. In order to avoid the contact between the inner pipe 7 and the outer pipe 6 more reliably, the gap between the inner pipe 7 and the outer pipe 6 (however, in the case of mutual eccentric arrangement, so as to satisfy the above condition (3)). (Represented by the local minimum in the pipe circumferential direction) should be at least 5 mm larger than the gap between the inner pipe 2 and the outer pipe 1.

In the case of an adiabatic multi-pipe with 3 or more pipes, the illustration is omitted, but as described above, the adjacent inner and outer pipe gaps in the curved pipe part are connected to those of the connection partner in the straight pipe part. Should be larger than 5 mm. Example 2 FIG. 3 shows a second embodiment of the present invention. In the first embodiment, the displacement between the inner tube 7 and the outer tube 6 is changed in the direction of displacement of the inner tube 7 during cooling contraction (here, This is an example of a form expanded in a direction opposite to the direction in which the displacement direction is a direction toward the center of curvature of the pipe axis. According to this embodiment, contact between the inner tube 7 and the outer tube 6 can be avoided more reliably.

In addition, as a method of enlarging the pipe gap as described above, a method of increasing the curvature of the inner tube 7 and / or a method of decreasing the curvature of the inner tube 7 of the outer tube 6 compared to before the expansion ( In this method, as the outer tube 6, a tube whose diameter varies depending on the position in the tube axis direction, more specifically, a tube whose center portion in the tube axis direction is larger in diameter than both ends is used. Can be mentioned. In the example of Figure 3, these methods are used together.

Claims

The scope of the claims

1. It has an inner pipe that accommodates a superconducting cable and one or more outer pipes surrounding the soot pipe, and at least one of the adjacent inner and outer pipe gaps is a vacuum heat insulating layer. A curved pipe section that is connected to the straight pipe section of the heat insulating multiple pipe for superconducting power transmission and changes the piping direction. The inner pipe and the outer pipe of the curved pipe section are respectively connected to the inner pipe and the outer pipe of the straight pipe section. The outer diameter of the inner pipe in the curved pipe section is the same as that in the straight pipe section, and the outer diameter of the outer pipe in the curved pipe section is larger than the outer diameter of the other pipe in the straight pipe section. A curved pipe part of a heat insulating multi-pipe for superconducting power transmission characterized by being.

2. The bent pipe part according to claim 1, wherein the bent angle of the bent pipe part is 30 degrees or more.

3. The pipe according to claim 1 or 2, wherein a pipe gap between adjacent inner and outer pipes in the bent pipe part is 5 mm or more larger than a pipe gap between connection partners in the straight pipe part. Pipe part.

4. In the curved pipe part in the atmospheric environment, the inner pipe is eccentrically arranged with respect to the outer pipe adjacent to it in the direction opposite to the direction of displacement when the refrigerant flows. The curved pipe part according to any one of claims 1 to 3.