HEAT PIPE AND MANUFACTURING METHOD OF HEAT PIPE

Description

TECHNICAL FIELD

The present invention relates to a heat pipe and a manufacturing method of a heat pipe. Priority is claimed on Japanese Patent Application No. 2021-186955 filed on Nov. 17, 2021, the content of which is incorporated herein by reference.

PATENT LITERATURE

Patent Document 1

Japanese Unexamined Patent Application, First Publication No. 2015-135211

Incidentally, the heat pipe as described in Patent Document 1 or the like is required to have a high heat transport capacity.

SUMMARY

One or more embodiments of the present invention provide a heat pipe with an improved heat transport capacity.

A heat pipe according to one or more embodiments of the present invention includes a container having an internal space and an inner circumferential surface facing the internal space and in which a working fluid is sealed, and a first wick portion accommodated in the internal space, in which a vapor flow path is formed in the internal space, the container has a second wick portion including a plurality of grooves formed on the inner circumferential surface of the container, the first wick portion includes a pore layer having a smaller effective pore radius than the second wick portion and a holding layer holding the pore layer, and the first wick portion is in contact with the vapor flow path and the second wick portion.

According to the above-described embodiments of the present invention, the heat pipe has the first wick portion including the pore layer having a smaller effective pore radius than the second wick portion. Therefore, it is possible to improve a magnitude of a capillary force applied to the working fluid (liquid). Also, the heat pipe has the second wick portion including the plurality of grooves. Thereby, it is possible to increase a transmittance of the second wick portion and it is possible to suppress flow resistance applied to the working fluid (liquid). Therefore, it is possible to improve a heat transport capacity of the heat pipe.

Here, the pore layer may be a sintered body of a powder.

Also, the holding layer may be a mesh body.

Also, the pore layer and the holding layer may be joined to each other by sintering.

Also, the holding layer may be in contact with the second wick portion, and the pore layer may be in contact with the vapor flow path.

Also, a manufacturing method of a heat pipe according to one or more embodiments of the present invention includes a preparation step of preparing a container, in which a plurality of grooves are formed on an inner circumferential surface, and a holding layer, a first sintering step of forming a first wick portion by joining a pore layer onto the holding layer by sintering, and a second sintering step of joining the first wick portion onto the inner circumferential surface of the container by sintering.

According to the above-described embodiments of the present invention, it is possible to manufacture the heat pipe including both the plurality of grooves and the pore layer. Therefore, it is possible to manufacture a heat pipe with an improved heat transport capacity.

According to above-described embodiments of the present invention, it is possible to provide a heat pipe with an improved heat transport capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a heat pipe according to one or more embodiments of the present invention.

FIG. 2 is a cross-sectional view taken along line II-II illustrated in FIG. 1.

FIG. 3 is an enlarged view of a part of the heat pipe illustrated in FIG. 2.

FIG. 4A is a view illustrating a part of steps of manufacturing the heat pipe according to one or more embodiments of the present invention.

FIG. 4B is a view illustrating a step following FIG. 4A.

FIG. 4C is a view illustrating a step following FIG. 4B.

DETAILED DESCRIPTION

Hereinafter, a heat pipe 1 according to one or more embodiments of the present invention will be described on the basis of the drawings.

As illustrated in FIGS. 1 and 2, the heat pipe 1 includes a container 10 having an internal space S and a first wick portion W1 accommodated in the internal space S. In one or more embodiments, the container 10 has an elongated shape extending in one direction. A working fluid F is sealed in the container 10.

Definition of Directions

Here, in one or more embodiments, a direction parallel to a central axis O of the container 10 is referred to as a Z direction or a longitudinal direction Z. One direction in the longitudinal direction Z is referred to as a +Z direction. A direction opposite to the +Z direction is referred to as a-Z direction. A cross section perpendicular to the longitudinal direction Z is referred to as a cross section. A direction orthogonal to the central axis O of the container 10 when viewed from the longitudinal direction Z is referred to as a radial direction. In the radial direction, a direction approaching the central axis O is referred to as a radially inward direction, and a direction away from the central axis O is referred to as a radially outward direction. A direction of revolving around the central axis O when viewed from the longitudinal direction Z is referred to as a circumferential direction.

The working fluid F is a well-known phase-change material, and changes a phase between a gas phase and a liquid phase inside the container 10. For example, water (pure water), alcohol, ammonia, or the like may be employed as the working fluid F. In the present specification, the working fluid in a gas phase may be referred to as a “vapor F1,” and the working fluid in a liquid phase may be referred to as a “liquid F2”. Also, when the gas phase and the liquid phase are not particularly distinguished, they may be simply referred to as the working fluid F.

The container 10 is a sealed hollow container. In one or more embodiments, more specifically, the container 10 includes a pipe portion 10A and a pair of closing portions 10B. The pipe portion 10A is a cylindrical member and extends in the longitudinal direction Z. The pair of closing portions 10B closes both end portions of the pipe portion 10A in the longitudinal direction Z. A space surrounded by the pipe portion 10A and the pair of closing portions 10B corresponds to the internal space S of the container 10. A diameter of the container 10 (the pipe portion 10A) is in a range of, for example, 2 to 5 mm. The container 10 (the pipe portion 10A) has an inner circumferential surface 10a facing inward in the radial direction. The inner circumferential surface 10a faces the internal space S of the container 10.

A vapor flow path G is formed in the internal space S. The vapor flow path G is a space through which the vapor F1 flows. In one or more embodiments, more specifically, a portion (space) of the internal space S excluding the first wick portion W1 corresponds to the vapor flow path G. The vapor F1 flows through the vapor flow path G mainly in the longitudinal direction Z.

The container 10 has a plurality of grooves 11 that are recessed outward in the radial direction from the inner circumferential surface 10a. The grooves 11 each extend over the entire length of the inner circumferential surface 10a in the longitudinal direction Z. In one or more embodiments, the plurality of grooves 11 are disposed at intervals throughout the inner circumferential surface 10a in the circumferential direction. A protrusion 12 is formed between two grooves 11 adjacent in the circumferential direction. The protrusions 12 are each in contact with the first wick portion W1.

In the present specification, the plurality of grooves 11 and the plurality of protrusions 12 may be collectively referred to as a second wick portion W2. Also, the first wick portion W1 and the second wick portion W2 may be collectively referred to as a wick portion W. The wick portion W is a portion through which the liquid F2 flows. The wick portion W generates a capillary force with respect to the liquid F2, and thereby the liquid F2 flows through the wick portion W mainly in the longitudinal direction Z. Although details will be described later, the working fluid F moves between the wick portion W and the vapor flow path G while being accompanied by a phase change between the vapor F1 and the liquid F2.

The grooves 11 according to one or more embodiments are each formed in a rectangular shape in a cross-sectional view. A dimension of the groove 11 in the circumferential direction is in a range of, for example, 0.05 to 0.2 mm. A dimension of the groove 11 in the radial direction is in a range of, for example, 0.05 to 0.2 mm. A transmittance of the groove 11 is in a range of, for example, 5.0 to 30.0×10−10 m2. An effective pore radius of the groove 11 is in a range of, for example, 0.05 to 0.2×10−3 m. Note that, in the present specification, the “effective pore radius” means an effective radius (capillary radius) of a groove, a pore, a gap, or the like that generates a capillary force with respect to the liquid F2.

The first wick portion W1 according to one or more embodiments has a layer shape (sheet shape) extending in the circumferential direction. The first wick portion W1 extends over the entire length of the container 10 in the longitudinal direction Z. The first wick portion W1 is in contact with the vapor flow path G and the second wick portion W2 (the protrusion 12) (see also FIG. 3). The first wick portion W1 and the second wick portion W2 (the protrusion 12) may be joined to each other by sintering. As illustrated in the example of FIG. 2, the first wick portion W1 may not have to cover the entire second wick portion W2 in the circumferential direction. In other words, a part of the second wick portion W2 in the circumferential direction may be exposed to the vapor flow path G.

The first wick portion W1 includes a pore layer 20 and a holding layer 30 (see also FIG. 3). The pore layer 20 and the holding layer 30 are adjacent to each other in the radial direction. The pore layer 20 and the holding layer 30 may be joined to each other by sintering. In one or more embodiments, the pore layer 20 is positioned on a radially inner side of the holding layer 30. That is, the pore layer 20 is in contact with the vapor flow path G, and the holding layer 30 is in contact with the second wick portion W2. However, the pore layer 20 may be positioned on a radially outer side of the holding layer 30. That is, the pore layer 20 may be in contact with the second wick portion W2, and the holding layer 30 may be in contact with the vapor flow path G.

The pore layer 20 has a smaller effective pore radius than the second wick portion W2. The pore layer 20 according to one or more embodiments is a sintered body formed by sintering a powder, and an effective pore radius of the pore layer 20 is in a range of, for example, 0.001 to 0.05×10-3 m. As the powder forming the pore layer 20, for example, a metal powder such as a copper powder may be used. A diameter of the powder forming the pore layer 20 is in a range of, for example, 1 to 200 μm. However, if the diameter of the powder is excessively large, there is a likelihood that the capillary force generated by the pore layer 20 will be reduced. On the other hand, if the diameter of the powder is excessively small, there is a likelihood that the powder will melt during sintering. Also, if the diameter of the powder is excessively small, flow resistance in the pore layer 20 increases excessively, and movement of the working fluid F from the wick portion W toward the vapor flow path G may be hindered. Therefore, the diameter of the powder is preferably in a range of 5 to 50 μm. A transmittance of the pore layer 20 is in a range of, for example, 0.001 to 0.1×10−10 m2.

The holding layer 30 supports the pore layer 20 and suppresses falling off of the pore layer 20 or a powder or the like forming the pore layer 20 into the grooves 11 or the vapor flow path G. The holding layer 30 has a larger effective pore radius than the pore layer 20. The holding layer 30 according to one or more embodiments is a mesh body having a plurality of wire bodies, and an effective pore radius of the holding layer 30 is in a range of, for example, 0.05 to 0.5×10−3 m. As the wire bodies forming the holding layer 30, metal wires such as, for example, copper wires may be used. A diameter of the wire body forming the holding layer 30 is in a range of, for example, 10 to 100 μm. A transmittance of the holding layer 30 is in a range of, for example, 1.0 to 10.0×10−10 m2.

Next, an example of a manufacturing method of the heat pipe 1 according to one or more embodiments will be described.

The manufacturing method of the heat pipe 1 according to one or more embodiments includes a preparation step, a first sintering step, and a second sintering step.

In the preparation step, the container 10 and the holding layer 30 described above are prepared. As illustrated in FIG. 4A, the holding layer 30 has a flat plate shape in the preparation step.

In the first sintering step, the pore layer 20 is joined onto the holding layer 30 by sintering to form the first wick portion W1 as illustrated in FIG. 4B. In one or more embodiments, more specifically, the powder is sintered on the holding layer 30. Thereby, formation of the pore layer 20 and joining of the pore layer 20 and the holding layer 30 are performed simultaneously by sintering. However, the pore layer 20 having a flat plate shape may be prepared in advance, and the prepared pore layer 20 may be joined onto the holding layer 30 by sintering. Also, in the first sintering step, the pore layer 20 and the holding layer 30 may be pressed together by a press member (not illustrated) or the like. In this case, it is possible to join the pore layer 20 and the holding layer 30 more reliably.

In the second sintering step according to one or more embodiments, the first wick portion W1 formed in the first sintering step is bent into a cylindrical shape and inserted into the container 10 as illustrated in FIG. 4C. Next, the first wick portion W1 is joined onto the inner circumferential surface 10a (the second wick portion W2) of the container 10 by sintering.

Through the steps described above, the heat pipe 1 according to one or more embodiments is manufactured.

Next, an operation of the heat pipe 1 configured as above will be described.

The heat pipe 1 is a heat dissipation module that receives heat from a heat source H and releases the received heat to the outside. Hereinafter, it is assumed that the heat source H is in contact with a −Z end portion of the container 10 (see FIG. 1). Also, for ease of explanation, the −Z side of the heat pipe 1 may be referred to as a high temperature side, and a +Z side of the heat pipe 1 may be referred to as a low temperature side.

As illustrated in FIG. 1, the liquid F2 that has permeated into the wick portion W is evaporated by the heat received from the heat source H, changes its phase into the vapor F1, and is directed toward the vapor flow path G (S1). The vapor F1 flows through the vapor flow path G toward the low temperature side in which a pressure and temperature are lower than those of the high temperature side (S2). As the vapor F1 flows toward the lower temperature side, it dissipates heat to the container 10 and the temperature decreases. The vapor F1 eventually condenses and changes its phase into the liquid F2, and the liquid F2 permeates into the wick portion W (S3). The liquid F2 that has permeated into the wick portion W flows back to the high temperature side due to a capillary force of the wick portion W (S4). When the cycles S1 to S4 are repeated, it is possible for the heat pipe 1 to continue to absorb heat from the heat source H and continue to release the absorbed heat to the outside.

Here, the first wick portion W1 according to one or more embodiments includes the pore layer 20 having a smaller effective pore radius than the second wick portion W2. Thereby, a capillary force applied to the liquid F2 is improved in the first wick portion W1, and it is possible to improve a heat transport capacity of the heat pipe 1. Particularly, when the pore layer 20 is a sintered body of a powder, it is possible to make the effective pore radius of the pore layer 20 smaller more reliably than when the pore layer 20 is formed of, for example, twisted wires or braided wires. Thereby, it is possible to improve the heat transport capacity of the heat pipe 1 more reliably.

Also, the second wick portion W2 according to one or more embodiments includes the plurality of grooves 11. Thereby, it is possible to increase a transmittance of the second wick portion W2 compared to a case in which the second wick portion W2 is, for example, a sintered body of a powder or a mesh body. Thereby, flow resistance applied to the liquid F2 is reduced, and it is possible to improve the heat transport capacity of the heat pipe 1.

In this way, when the heat pipe 1 includes both the second wick portion W2 having a high transmittance and the first wick portion W1 (the pore layer 20) having a smaller effective pore radius than the second wick portion W2, it is possible to effectively improve the heat transport capability of the heat pipe 1.

Also, the heat pipe 1 according to one or more embodiments includes the holding layer 30 that holds the pore layer 20. Thereby, falling off of the pore layer 20 or the powder or the like forming the pore layer 20 into the grooves 11 or the vapor flow path G and clogging the grooves 11 or the vapor flow path G do not easily occur. Particularly, when the holding layer 30 is a mesh body, since it is possible for the holding layer 30 to easily hold the powder even if the pore layer 20 is formed of a powder with a small diameter or the like, it is possible to suppress clogging of the grooves 11 or the vapor flow path G more effectively suppressed. Also, if the pore layer 20 and the holding layer 30 are joined by sintering, it is possible to suppress clogging of the grooves 11 or the vapor flow path G more reliably suppressed.

Incidentally, as a structure constituting a general wick, twisted wires, braided wires, or the like may also be mentioned in addition to the sintered body of a powder, the mesh body, and the grooves described above. However, since the wick using twisted wires or braided wires is difficult to maintain a strength of the twist and a shape of the braid constant during manufacturing, variations are likely to occur in a shape of the wick. Such variations in a shape of the wick tend to cause variations in the heat transport capacity of the heat pipe.

In contrast, the second wick portion W2 according to one or more embodiments is a wick formed by the grooves 11. Therefore, it is possible to suppress variations in a shape of the second wick portion W2 during manufacturing compared to a case in which, for example, the second wick portion W2 is a wick formed of twisted wires or a braided wires. Thereby, it is possible to suppress variations in the heat transport capacity of the heat pipe 1. Particularly, if the pore layer 20 is a sintered body of a powder, since it is also possible to suppress variations in a shape of the pore layer 20, it is possible to suppress variations in the heat transport capacity of the heat pipe 1 more effectively. Similarly, if the holding layer 30 is a mesh body, since it is possible to suppress variations in a shape of the holding layer 30, it is possible to suppress variations in the heat transport capacity of the heat pipe 1 more reliably.

As described above, the heat pipe 1 according to one or more embodiments includes the container 10 having the internal space S and the inner circumferential surface 10a facing the internal space S and in which the working fluid F is sealed, and the first wick portion W1 accommodated in the internal space S, in which the vapor flow path G is formed in the internal space S, the container 10 has the second wick portion W2 including the plurality of grooves 11 formed on the inner circumferential surface 10a of the container 10, the first wick portion W1 includes the pore layer 20 having a smaller effective pore radius than the second wick portion W2 and the holding layer 30 holding the pore layer 20, and the first wick portion W1 is in contact with the vapor flow path G and the second wick portion W2.

According to this configuration, the heat pipe 1 has the first wick portion W1 including the pore layer 20 having a smaller effective pore radius than the second wick portion W2. Therefore, it is possible to improve a magnitude of the capillary force applied to the liquid F2. Also, the heat pipe 1 has the second wick portion W2 including the plurality of grooves 11. Thereby, it is possible to increase a transmittance of the second wick portion W2 and it is possible to suppress flow resistance applied to the liquid F2. Therefore, it is possible to improve the heat transport capacity of the heat pipe 1.

Also, the pore layer 20 is a sintered body of a powder. With this configuration, it is possible to make the effective pore radius of the pore layer 20 smaller more reliably. Therefore, it is possible to improve the heat transport capacity of the heat pipe 1 more reliably.

Also, the holding layer 30 is a mesh body. With this configuration, clogging of the grooves 11 or the vapor flow path G due to the pore layer 20 or the powder or the like forming the pore layer 20 falling into the grooves 11 or the vapor flow path G does not easily occur.

Also, the pore layer 20 and the holding layer 30 may be joined to each other by sintering. According to this configuration, the pore layer 20 or the powder or the like forming the pore layer 20 are more reliably held by the holding layer 30.

Also, the holding layer 30 is in contact with the second wick portion W2, and the pore layer 20 is in contact with the vapor flow path G. In other words, the pore layer 20 is positioned on a radially inner side of the holding layer 30. With this configuration, it is possible to suppress falling off of the powder or the like forming the pore layer 20 toward the grooves 11 in which clogging is particularly likely to occur.

Also, the manufacturing method of the heat pipe 1 according to one or more embodiments includes the preparation step of preparing the container 10, in which the plurality of grooves 11 are formed on the inner circumferential surface 10a, and the holding layer 30, the first sintering step of forming the first wick portion W1 by joining the pore layer 20 onto the holding layer 30 by sintering, and the second sintering step of joining the first wick portion W1 onto the inner circumferential surface 10a (the second wick portion W2) of the container 10 by sintering.

With this configuration, it is possible to manufacture the heat pipe 1 having both the second wick portion W2 including the plurality of grooves 11 and the first wick portion W1 including the pore layer 20 having a smaller effective pore radius than the second wick portion W2. Therefore, it is possible to manufacture a heat pipe with an improved heat transport capacity. Also, since the pore layer 20, the holding layer 30, and the second wick portion W2 are joined to each other by sintering, it is possible to suppress falling off of the first wick portion W1 into the vapor flow path G, or falling off of the pore layer 20 or the powder or the like forming the pore layer 20 into the grooves 11.

Note that, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications may be made within a range not departing from the meaning of the present invention.

For example, a shape of the container 10 (the pipe portion 10A) is not limited to a cylindrical shape. A shape of the pipe portion 10A may be changed as appropriate as long as it is possible to accommodate the working fluid F and the first wick portion W1 in the internal space S. For example, a shape of the pipe portion 10A may be elliptical, oval, rectangular, or the like in a cross-sectional view.

Also, a diameter of the container 10 may be less than 2 mm or larger than 5 mm.

Also, the plurality of grooves 11 may not be disposed throughout the inner circumferential surface 10a of the container 10 in the circumferential direction. In other words, the second wick portion W2 may not need to extend throughout the inner circumferential surface 10a in the circumferential direction.

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.

REFERENCE SIGNS LIST

• • 1 Heat pipe
  • 10 Container
  • 10a Inner circumferential surface
  • 11 Groove
  • 20 Pore layer
  • 30 Holding layer
  • F1 Vapor (working fluid)
  • F2 Liquid (working fluid)
  • S Internal space
  • G Vapor flow path
  • W1 First wick portion
  • W2 Second wick portion