US20190323780A1

US20190323780A1 - Heat pipe

Info

Publication number: US20190323780A1
Application number: US16/348,748
Authority: US
Inventors: Mohammad Shahed AHAMED; Yuji Saito
Original assignee: Fujikura Ltd
Current assignee: Fujikura Ltd
Priority date: 2016-11-22
Filing date: 2017-11-21
Publication date: 2019-10-24
Also published as: JPWO2018097131A1; CN109964093A; JP6615383B2; WO2018097131A1; TW201825850A; TWI644075B; CN109964093B

Abstract

A heat pipe includes: a container and a wick that is disposed inside the container. The container has a width, in a width direction that is orthogonal to an up-down direction and a longitudinal direction of the heat pipe, that is larger than a thickness in the up-down direction. A gap in the width direction is provided between an internal surface of the container and an external surface of the wick. A first end portion of the wick in the longitudinal direction includes concave portions depressed in the width direction at intervals in the longitudinal direction. A second end portion of the wick in the longitudinal direction does not have any concave portions. A width of the wick in the width direction is substantially equal throughout a total length of the wick in the longitudinal direction, except for a portion at which the concave portions are disposed.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed to Japanese Patent Application No. 2016-227247, filed on Nov. 22, 2016, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a heat pipe.

BACKGROUND

In the past, a heat pipe which is used for heat transport from a high temperature portion side to a low temperature portion side is known, as disclosed in Patent Document 1. In the heat pipe, a working fluid is sealed into an inside of a container, and a wick for circulating the working fluid of a liquid phase is provided on the inside of the container. An internal space of the container functions as a flow path through which the working fluid of a gas phase transfers to the low temperature portion side from the high temperature portion side, and the heat transport from the high temperature portion side to the low temperature portion side is made, by material transfer of the working fluid of the gas phase. The wick has a function of recirculating the working fluid which is condensed on the low temperature portion side to the high temperature portion side by a capillary phenomenon, and of making operation of the heat pipe maintainable.

PRIOR ART DOCUMENTS

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H11-183069
Meanwhile, in such a kind of heat pipe, there is a demand to improve the efficiency of the heat transport without increasing an occupied area, in accordance with miniaturization of a device which is mounted thereon or increase of a heating value.

SUMMARY

One or more embodiments of the present invention improve efficiency of heat transport, without increasing an occupied area of a heat pipe.
According to one or more embodiments of the present invention, there is provided a heat pipe including a container into which a working fluid is sealed, and a wick that is provided inside of the container, in which in the container, the width in a width direction which is orthogonal to both of an up-down direction and a longitudinal direction is larger than a thickness of the up-down direction, a gap in the width direction is provided between an internal surface of the container and an external surface of the wick, a plurality of concave portions that become depressed in the width direction are formed at intervals in the longitudinal direction, at a first end portion of the wick in the longitudinal direction, the concave portion is not formed at a second end portion of the wick in the longitudinal direction, and a width of the wick in the width direction is substantially equal throughout a total length of the wick in the longitudinal direction, except for a portion at which the concave portion is formed.
According to one or more embodiments, since the plurality of concave portions that become depressed in the width direction are formed at the intervals in the longitudinal direction, at the first end portion of the wick, it is possible to make a surface area of the wick large, without increasing an occupied area of the whole heat pipe.
Thereby, the working fluid with which the wick is impregnated is capable of being efficiently evaporated from the concave portion having the large surface area, and transfer of the working fluid of a gas phase to a low temperature portion side from a high temperature portion side is promoted, thereby, it is possible to improve the efficiency of heat transport.
Furthermore, the concave portion is not formed other than the first end portion, and the width of the wick in the longitudinal direction is substantially equal throughout the total length, except for the portion at which the concave portion is formed. In this manner, there is no portion of which the width of the wick is narrow other than an evaporation portion, thereby, flow resistance of the working fluid of a liquid phase does not become large. Accordingly, it is possible to efficiently transfer the working fluid of the liquid phase.
Regarding a heat pipe according to one or more embodiments of the present invention, a liquid reservoir of the working fluid, which is extended in the longitudinal direction, is formed inside of the wick, and the liquid reservoir is disposed at different position from the concave portion in the longitudinal direction, within the wick.
According to one or more embodiments, since the liquid reservoir of the working fluid, which is extended in the longitudinal direction, is formed inside of the wick, when the working fluid evaporates from the external surface of the wick, it is possible to supply the working fluid of the liquid phase from the liquid reservoir toward the external surface. Thereby, a supply quantity of the working fluid of the liquid phase to the external surface of the wick is stabilized, and the external surface of the wick is capable of being preventing from drying. Therefore, it is possible to prevent an evaporation quantity of the working fluid from being lowered by drying of the external surface of the wick, and to prevent the efficiency of the heat transport from being lowered.
Furthermore, since the liquid reservoir is disposed at the position which is different from the concave portion in the longitudinal direction, it is prevented that heat is transmitted directly to the working fluid in the liquid reservoir from a heat source. Thereby, for example, it is possible to prevent the working fluid from suddenly evaporating in the liquid reservoir, and it is possible to prevent the evaporated working fluid from flowing backward, toward the low temperature portion side in the liquid reservoir.
According to one or more embodiments of the present invention, there is provided a heat pipe including a container into which a working fluid is sealed, and a wick that is provided inside of the container, in which a gap is provided between an internal surface of the container and an external surface of the wick, an uneven portion is formed at least on the external surface at a first end portion of a longitudinal direction, within the wick, a liquid reservoir of the working fluid, which is extended in the longitudinal direction, is formed inside of the wick, and the liquid reservoir is disposed at different position from the uneven portion in the longitudinal direction.
According to one or more embodiments, in a case where the heat pipe is disposed with respect to the heat source such that the heat source is positioned in the vicinity of the uneven portion, the working fluid which receives the heat from the heat source efficiently evaporates from the external surface of the uneven portion. Furthermore, since the liquid reservoir is disposed at the position which is different from the uneven portion in the longitudinal direction, it is prevented that the heat is transmitted directly to the working fluid in the liquid reservoir from the heat source. Thereby, for example, it is possible to prevent the working fluid from suddenly evaporating in the liquid reservoir, and it is possible to prevent the evaporated working fluid from flowing backward, toward the low temperature portion side in the liquid reservoir.
Regarding a heat pipe according to one or more embodiments of the present invention, the wick is formed of a mesh material.
According to one or more embodiments, for example, the wick is capable of being formed from a plate-shaped mesh material with die cutting, and it is possible to easily form the wick, even if a shape of the uneven portion is complicated.
Regarding a heat pipe according to one or more embodiments of the present invention, the wick is joined to an upper wall and a lower wall of the container.
According to one or more embodiments, the wick is securely fixed in the container. Thereby, for example, even in a case where the heat pipe is bent, the wick transfers in the width direction within the container, and it is possible to prevent the gap from becoming narrow.
Regarding a heat pipe according to one or more embodiments of the present invention, the liquid reservoir of the working fluid, which is extended in the longitudinal direction, is formed inside of the wick, and a width of the liquid reservoir in a width direction which is orthogonal to both of the longitudinal direction and an up-down direction is smaller than a width of a portion of the wick which is adjacent to the liquid reservoir.
According to one or more embodiments, the width of the liquid reservoir is narrow to a certain extent, thereby, it is possible to cause capillary force to act on the working fluid of the liquid phase in the liquid reservoir. Therefore, due to the capillary force, it is possible to more smoothly recirculate the working fluid of the liquid phase in the liquid reservoir to the high temperature portion side from the low temperature portion side.
According to one or more embodiments of the present invention, it is possible to improve efficiency of heat transport, without increasing an occupied area of a heat pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a heat pipe according to one or more embodiments in a plane which is orthogonal to an up-down direction.

FIG. 2A is a sectional view of the heat pipe taken along A-A arrow in FIG. 1.

FIG. 2B is a sectional view of the heat pipe taken along B-B arrow in FIG. 1.

FIG. 3 is a sectional view of an uneven portion according to Modification Examples in a plane which is orthogonal to a longitudinal direction.

DETAILED DESCRIPTION

Hereinafter, a configuration of a heat pipe according to one or more embodiments will be described with reference to FIG. 1 to FIG. 3. In each drawing which is used in the following description, in order to make a shape of each member have a recognizable size, the scale thereof is appropriately changed.
As shown in FIG. 1, a heat pipe 1 includes a container 2 into which a working fluid is sealed, and a wick 3 that is provided on an inside of the container 2.

Direction Definition

Here, in the present embodiments, a positional relationship of each configuration will be described by setting an XYZ orthogonal coordinate system. An X direction is a longitudinal direction in which the heat pipe 1 and the container 2 extend. The heat pipe 1 is formed into a flat shape of which a thickness is small in a Z direction, and a width is large in a Y direction, in a cross sectional view which is orthogonal to the longitudinal direction. Hereinafter, the X direction is referred to as a longitudinal direction, the Y direction is referred to as a width direction, and the Z direction is referred to as an up-down direction.
The inside of the container 2 is hollow, and is hermetically sealed. It is possible to appropriately select a material of the container 2, by conditions such as a kind of the working fluid and a working temperature. In particular, in a case where a metal material such as copper or aluminum of which heat conductivity is high is used, it is possible to enhance heat transportability or heat diffusibility. It is possible to form the container 2, for example, using a metal tube such as a copper tube, an aluminum tube, or a stainless tube.
The container 2 is formed into the flat shape of which the width in the width direction which is orthogonal to both of the up-down direction and the longitudinal direction is larger than the thickness of the up-down direction. As an example of the size of the container 2, the width of the width direction is approximately 7 mm, a length of the longitudinal direction is approximately 100 mm, a height of the up-down direction of an internal space is approximately 0.27 mm, and a wall thickness is approximately 0.08 mm.
On the inside of the wick 3, a large number of fine pores which cause capillary force to be generated are formed. As a material of the wick 3, for example, it is possible to use a sintered body (porous sintered body) of a metal extra fine wire fiber, a metal mesh, and metal powder. In a case where the wick 3 is formed of a mesh material such as metal, it is possible to easily form the wick 3, even if the wick 3 has a complicated shape, for example, from a plate-shaped mesh material with die cutting. In a case where the wick 3 is formed of the sintered body of the metal powder, the size of the fine pore is capable of being made further smaller, and it is possible to enhance the heat transportability by causing the high capillary force to be generated.
The fine pore in the wick 3 is impregnated with the working fluid. The working fluid is a fluid which is capable of being evaporated by heating, and being condensed by heat radiation. It is possible to appropriately select the kind of the working fluid in accordance with the temperature at which the heat pipe 1 is used, or the like. As a working fluid, for example, it is possible to use water, alcohol, alternative freon, or the like. The working fluid may be sealed into the inside of the container 2, for example, in a state in which non-condensable gas such as air is degassed from the inside of the container 2 in a vacuum chamber.
As shown in FIG. 1, the wick 3 is disposed along the longitudinal direction in the container 2.
In the width direction, the width of the wick 3 is smaller than the width of the container 2, and the wick 3 is disposed at a center portion of the width direction of the container 2. Therefore, a gap S is formed in the width direction, between an external surface of the wick 3 and an internal surface of the container 2. The gaps S are provided on both sides in the width direction of the wick 3, and are extended in the longitudinal direction. The gap S becomes a circulation path for the working fluid of a gas phase. The width of the gap S in the width direction is, for example, approximately 1.7 mm.
The wick 3 is partially melted by being sintered in the container 2, and is fixed to the internal surface of the container 2. In more detail, as shown in FIG. 2A and FIG. 2B, the wick 3 is joined to an upper wall 2 a and a lower wall 2 b of the container 2. For example, in a state in which the wick 3 is disposed in the container 2, the container 2 is deformed by being compressed in the up-down direction, and the wick 3 is interposed between the upper wall 2 a and the lower wall 2 b of the container 2, thereby, the wick 3 may be fixed.
Here, in the present embodiments, as shown in FIG. 1, a plurality of concave portions 3 a 1 which become depressed in the width direction are formed at intervals in the longitudinal direction, on the external surface of the wick 3. Thereby, an uneven portion 3 a is formed on the external surface of the wick 3, the external surface forming the gap S. Hereinafter, a portion except for the concave portion 3 a 1 is referred to as a projection portion 3 a 2, within the uneven portion 3 a. The uneven portion 3 a is formed on the external surface at a first end portion 31 (end portion of a −X side, in the example shown in the drawing) in the longitudinal direction, within the wick 3. The uneven portions 3 a may be formed at both end portions of the wick 3 in the longitudinal direction. On the inside of the wick 3, a liquid reservoir 3 b of the working fluid is formed.
Due to the uneven portion 3 a, it is possible to increase a surface area of the wick 3, without increasing an occupied area of the wick 3.
The size (dimensions in the longitudinal direction and the width direction) of the concave portion 3 a 1 which forms the uneven portion 3 a is larger than an average diameter of the fine pores in the wick 3. On a surface of the uneven portion 3 a, a large number of fine pores of the wick 3 are open. It is possible to form the uneven portion 3 a, for example, when the wick 3 is formed by taking out the plate-shaped mesh material with the mold. The uneven portion 3 a may be formed to have a size such that an uneven shape thereof is visible.
The liquid reservoir 3 b is filled with the working fluid of a liquid phase. The liquid reservoir 3 b is disposed at a middle portion 33 between the first end portion 31 and a second end portion 32 of the wick 3, in the longitudinal direction, and is extended along the longitudinal direction, on the inside of the wick 3. The liquid reservoir 3 b is formed at a position which is different from the uneven portion 3 a in the longitudinal direction, within the wick 3. As shown in FIG. 1 and FIG. 2A, the liquid reservoir 3 b passes through the middle portion 33 of the wick 3 in the up-down direction. The width of the liquid reservoir 3 b in the width direction is set such that the capillary force is generated, and is, for example, approximately 0.6 mm. The width of the liquid reservoir 3 b is larger than the average diameter of the fine pores in the wick 3. In the width direction, the width of the liquid reservoir 3 b is smaller than the width of a portion of the wick 3 which is adjacent to the liquid reservoir 3 b in the width direction.
Here, as shown in FIG. 1, the width of the width direction of a portion at which the concave portion 3 a 1 is not formed within the first end portion 31, that is, the projection portion 3 a 2 is referred to as W1. The width of the width direction of the second end portion 32 is referred to as W2, and the width of the width direction of the middle portion 33 is referred to as W3. At this time, the respective dimensions of W1, W2, and W3 are substantially equal to each other. In other words, the width of the wick 3 in the width direction is substantially equal throughout the total length of the wick 3 in the longitudinal direction, except for a portion at which the concave portion 3 a 1 is formed.
In a cross section which is orthogonal to the longitudinal direction, a sectional area of the second end portion 32 becomes substantially equal in the longitudinal direction, since W2 is fixed. In the cross section which is orthogonal to the longitudinal direction, the sectional area of the middle portion 33 becomes substantially equal in the longitudinal direction, since W3, and the width of the liquid reservoir 3 b which is disposed on the inside of the middle portion 33 are fixed. In this manner, the sectional area of the second end portion 32 or the middle portion 33 is not changed in the longitudinal direction, thereby, it is possible to suppress flow resistance of the working fluid of the liquid phase so as to be small.
Next, operation of the heat pipe 1 which is configured as described above will be described.
The heat pipe 1 is attached to an electronic component or the like in a commodity (for example, a notebook PC or a mobile phone) which becomes a target of heat transport. In the example of FIG. 1, the heat pipe 1 is disposed over a high temperature portion H and a low temperature portion L which are represented by two-dot chain lines. The high temperature portion H is, for example, a heat generation portion such as a CPU, and the low temperature portion L is, for example, a heat radiation portion such as a heat sink.
In the vicinity of the high temperature portion H, the working fluid in the wick 3 evaporates by being heated through a wall surface of the container 2. Here, the first end portion 31 of the wick 3 is disposed in the vicinity of the high temperature portion H, and the uneven portion 3 a is formed at the first end portion 31. Therefore, the surface area of the wick 3 is large in the first end portion 31, and it is possible to efficiently evaporate the working fluid. The working fluid evaporates, thereby, a pressure of a gas in the vicinity of the high temperature portion H is raised. Thereby, shown by an arrow F1 in FIG. 1, the working fluid which becomes the gas phase transfers in the gap S toward the low temperature portion L side in the longitudinal direction.
The working fluid of the gas phase which reaches the vicinity of the low temperature portion L is condensed by a loss of the heat through the wall surface of the container 2, and becomes a droplet to be bonded to the wall surface of the container 2. The droplet of the working fluid soaks the fine pore in the second end portion 32 of the wick 3 due to the capillary force, as shown by an arrow F2 in FIG. 1. Here, a portion of the working fluid of the liquid phase which soaks the fine pore in the wick 3 flows into the liquid reservoir 3 b, as shown by an arrow F2′.
The working fluid of the liquid phase in the fine pore of the second end portion 32 of the wick 3, and the working fluid of the liquid phase in the liquid reservoir 3 b transfer to the high temperature portion H side of the longitudinal direction due to the capillary force. Here, since the uneven portion is not formed in the second end portion 32 and the middle portion 33, it is possible to efficiently transfer the working fluid. This is because the resistance of the working fluid becomes large, in a case where there is a spot at which the width of the wick 3 is partially narrow. Therefore, the working fluid of the liquid phase is supplied by two paths shown by arrows F3 and F4, from the fine pore in the wick 3 and the liquid reservoir 3 b to the uneven portion 3 a. The working fluid of the liquid phase which reaches the uneven portion 3 a evaporates again from the surface of the uneven portion 3 a.
The working fluid which evaporates to become the gas phase transfers to the low temperature portion L side through the gap S again. In this manner, in the heat pipe 1, phase transition between the liquid phase and the gas phase of the working fluid is repeatedly used, thereby, it is possible to repeatedly transport the heat which is recovered on the high temperature portion H side of the longitudinal direction to the low temperature portion L side.
As described above, according to the heat pipe 1 of the present embodiments, since the uneven portion 3 a is formed in the wick 3, it is possible to make the surface area of the wick 3 large, without increasing the occupied area of the whole heat pipe 1. Thereby, the working fluid with which the wick is impregnated is capable of being efficiently evaporated from the uneven portion 3 a having the large surface area, and the transfer of the working fluid of the gas phase to the low temperature portion L side from the high temperature portion H side is promoted, thereby, it is possible to improve efficiency of the heat transport.
Furthermore, the uneven portion 3 a is not formed in the second end portion 32 and the middle portion 33, and the widths W2 and W3 are substantially equal to each other, thereby, there is no portion of which the width of the wick 3 is narrow other than an evaporation portion. Accordingly, it is possible to efficiently transfer the working fluid, without making the flow resistance of the working fluid of the liquid phase large.
Since the liquid reservoir 3 b of the working fluid is formed in the middle portion 33 of the wick 3, when the working fluid evaporates from the external surface of the wick 3, it is possible to supply the working fluid of the liquid phase from the liquid reservoir 3 b toward the external surface. Thereby, a supply quantity of the working fluid of the liquid phase to the external surface of the wick 3 is stabilized, and the external surface of the wick 3 is capable of being preventing from drying. Therefore, it is possible to prevent an evaporation quantity of the working fluid from being lowered by drying of the external surface of the wick 3, and to prevent the efficiency of the heat transport from being lowered.
In a case where the heat pipe 1 is disposed with respect to a heat source such that the high temperature portion H is positioned in the vicinity of the uneven portion 3 a, the working fluid which receives the heat from the high temperature portion H efficiently evaporates from the external surface of the uneven portion 3 a. Furthermore, since the liquid reservoir 3 b is disposed at the position which is different from the uneven portion 3 a in the longitudinal direction, it is prevented that the heat is transmitted directly to the working fluid in the liquid reservoir 3 b from the heat source. Thereby, for example, it is possible to prevent the working fluid from suddenly evaporating in the liquid reservoir 3 b, and it is possible to prevent the evaporated working fluid from flowing backward, toward the low temperature portion L side in the liquid reservoir 3 b.
In a case where the mesh material is adopted as a material of the wick 3, it is possible to form the wick 3, for example, from the plate-shaped mesh material with die cutting. Thereby, even in a case where the shape of the uneven portion 3 a is complicated, it is possible to easily form the wick 3.
In the width direction, the width of the liquid reservoir 3 b is narrower than the width of the portion of the wick 3 which is adjacent to the liquid reservoir 3 b in the width direction, thereby, it is possible to cause the capillary force to act on the working fluid of the liquid phase in the liquid reservoir 3 b. Therefore, due to the capillary force, it is possible to more smoothly recirculate the working fluid of the liquid phase in the liquid reservoir 3 b to the high temperature portion H side from the low temperature portion L side.
The technical scope of the present invention is not limited to the embodiments described above, and it is possible to add various modifications thereto, within the scope without departing from the gist of the present invention.
For example, in the embodiments described above, the heat pipe 1 is extended into a straight line shape in the longitudinal direction, but the heat pipe 1 is not limited thereto, and the heat pipe 1 may be used in a bended manner. At that time, since the wick 3 is joined to the upper wall 2 a and the lower wall 2 b of the container 2, even if the heat pipe 1 is bent, the wick 3 transfers in the width direction with respect to the container 2, and it is prevented that the gap S becomes narrow. In a case where the heat pipe 1 is bent, the longitudinal direction is a direction in which a center line of the heat pipe 1 is extended, and it is possible to define the width direction as a direction which is orthogonal to both of the center line and the up-down direction.
In the example shown in FIG. 1, in a planar view which is seen from the up-down direction, a position of a center of the portion at which the uneven portion 3 a is formed within the wick 3 matches up with a position of a center of the high temperature portion H, but the present invention is not limited thereto, and the high temperature portion H may be positioned at a position shifted from the uneven portion 3 a.
In the embodiments described above, the uneven portion 3 a and the liquid reservoir 3 b are formed at positions which are different from each other in the longitudinal direction, but the present invention is not limited thereto. For example, the liquid reservoir 3 b and the uneven portion 3 a may be formed at positions which are the same in the longitudinal direction. Alternatively, a configuration in which such a liquid reservoir 3 b is not formed may be adopted.
In the embodiments described above, the uneven portion 3 a is formed only in a portion of the external surface of the wick 3, but the present invention is not limited thereto. For example, the uneven portion 3 a may be formed on the whole of the external surface of the wick 3.
The uneven portion 3 a of the embodiments described above is formed by the concave portion 3 a 1 which becomes depressed in the width direction of the wick 3, but the present invention it is not limited thereto. For example, the uneven portion 3 a may be formed by the projection portion 3 a 2 which protrudes in the width direction of the wick 3.
Moreover, the uneven portion 3 a of the embodiments described above is formed by disposing the plurality of concave portions 3 a 1 on the external surface of the wick 3, and the sizes of the respective concave portions 3 a 1 or the intervals between the concave portions 3 a 1 in the longitudinal direction are substantially equal to each other, but the present invention is not limited thereto. For example, an uneven shape in which the concave portions 3 a 1 are non-uniformly formed may be adopted such that the surface area of the wick 3 is the largest, in a portion of which the temperature is the highest within the high temperature portion H.
In the example shown in FIG. 2B, the width of the uneven portion 3 a, and the invention is not limited thereto. For example, as shown in FIG. 3, the surface area of the wick 3 may be increased, by forming the uneven portion 3 a and the concave portion 3 a 1 such that the widths are non-uniform in the up-down direction. It is possible to easily form the shape of the wick 3 shown in FIG. 3, for example, by stacking a plurality of sheet-shaped wicks of which the widths are different from each other in the up-down direction.
In addition, within the scope without departing from the gist of the present invention, it is possible to appropriately replace a configuration element in the embodiments described above with a known configuration element, and the embodiments described above may be appropriately combined with Modification Examples.

REFERENCE SIGNS LIST

- 1: heat pipe
- 2: container
- 2 a: upper wall
- 2 b: lower wall
- 3: wick
- 3 a: uneven portion
- 3 a 1: concave portion
- 3 a 2: projection portion
- 3 b: liquid reservoir
- 31: first end portion
- 32: second end portion
- 33: middle portion
- S: gap

Claims

1. A heat pipe comprising:

a container into which a working fluid is sealed; and

a wick that is disposed inside of the container, wherein

the container has a width, in a width direction that is orthogonal to both an up-down direction and a longitudinal direction of the heat pipe, that is larger than a thickness in the up-down direction,

a gap in the width direction is provided between an internal surface of the container and an external surface of the wick,

a first end portion of the wick in the longitudinal direction comprises a plurality of concave portions depressed in the width direction at intervals in the longitudinal direction,

a second end portion of the wick in the longitudinal direction does not have any concave portions, and

a width of the wick in the width direction is substantially equal throughout a total length of the wick in the longitudinal direction, except for a portion at which the plurality of concave portions is disposed.

2. The heat pipe according to claim 1,

wherein the wick further comprises a liquid reservoir of the working fluid that extends in the longitudinal direction and is disposed at a different position from any one of the plurality of concave portions in the longitudinal direction within the wick.

3. A heat pipe comprising:

a container into which a working fluid is sealed; and

a wick that is disposed inside of the container, wherein

a gap is provided between an internal surface of the container and an external surface of the wick,

at least the external surface at a first end portion of a longitudinal direction, within the wick, has an uneven portion,

a liquid reservoir of the working fluid that extends in the longitudinal direction is disposed inside of the wick at a different position from the uneven portion in the longitudinal direction.

4. The heat pipe according to claim 1, wherein the wick is made of a mesh material.

5. The heat pipe according to claim 1, wherein the wick is joined to an upper wall and a lower wall of the container.

6. The heat pipe according to claim 2, wherein

the liquid reservoir of the working fluid extending in the longitudinal direction is disposed inside of the wick, and

a width of the liquid reservoir in the width direction is smaller than a width of a portion of the wick that is adjacent to the liquid reservoir.

7. The heat pipe according to claim 3, wherein the wick is made of a mesh material.

8. The heat pipe according to claim 3, wherein the wick is joined to an upper wall and a lower wall of the container.

9. The heat pipe according to claim 3, wherein a width of the liquid reservoir in a width direction orthogonal to both the longitudinal direction and an up-down direction is smaller than a width of a portion of the wick that is adjacent to the liquid reservoir.