JP2000074580A - Flat heat pipe and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a sufficient reflux of a working fluid and realize an excellent heat transfer property by forming locating parts on both ends of a wick in such a manner as to stabilize the wick in an interior of a cavity part. SOLUTION: A wick 20 having locating members 21 attached to both ends thereof is inserted in an interior of a container pipe 10 and then the container pipe 10 is subjected to a flattening work (press working) in an arrow direction. Further, the flattened container pipe 10 is subjected to a heat pipe making process in order to obtain a flat heat pipe. Here, the heat pipe making process comprises a series of steps for assembling the heat pipe by forming a closed cavity part in an interior by closing both ends of the pipe and injecting an appropriate amount of a working fluid such as water or the like in the cavity part before a closing work, and includes other steps of degassing and cleaning an interior of the cavity part or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat heat pipe having a wick disposed in a cavity.

[0002]

2. Description of the Related Art In recent years, a technique of cooling a heat-generating component such as a semiconductor element mounted on an electric device such as a personal computer has been attracting attention. One of the methods is a cooling technique using a heat pipe. As a cooling method using a heat pipe,
Typically, a heat pipe is attached to a heat-generating component, and the heat of the heat-generating component is transported to a heat-radiating fin or the like and dissipated through the heat pipe. There is also an electric device in which a small fan for forcibly blowing air to the fin or the like is installed.

[0003] The heat pipe is briefly described as follows.
The heat pipe has a cavity that is sealed inside,
A certain amount of a working fluid (also referred to as a working fluid) such as water or alternative Freon is stored in the cavity. The inside of the cavity is evacuated, so that the working fluid is easily evaporated. The working fluid exists in a mixed state of a liquid phase and a gas phase (steam) in the cavity.

[0004] In the heat pipe, the working fluid in the hollow portion evaporates, and the vapor moves, so that the heat transfer function operates.
For example, in the case of a heat pipe of a straight type, when heat is applied from one end of the heat pipe (this part is called a heat absorbing part of the heat pipe), the working fluid in a liquid phase in the heat absorbing part evaporates, and the Moves to the other end side, where the vapor condenses and radiates heat (this part is called the heat radiating part of the heat pipe). If fins or the like are attached to the heat radiating portion of the heat pipe, the heat of the working fluid vapor is easily radiated to the outside.

[0005] If the working fluid condensed in the heat radiating section does not return to the heat absorbing section, the above operation does not continue. Therefore, it is necessary to return (reflux) the working fluid (liquid phase) condensed in the heat radiating section to the heat absorbing section. Normally, the liquid phase of the working fluid condensed in the heat radiating portion is lowered by gravity by positioning the heat absorbing portion below the heat radiating portion. Such a state may be called a bottom heat mode.

If the heat radiating portion cannot be arranged above the heat absorbing portion, the working fluid cannot be recirculated by gravity.
Therefore, a method is known in which a wick (mesh, wire, or the like) that exerts a capillary action is arranged in the hollow portion of the heat pipe, or a fine groove is formed in the inner wall of the hollow portion. The case where the heat radiating portion is located below the heat absorbing portion may be referred to as a top heat mode. Even when the heat radiating section is positioned substantially horizontally with the heat absorbing section, it is difficult to expect the working fluid to return due to the effect of gravity. Therefore, in such a case, a wick is often arranged.

[0007]

In recent years, miniaturization and high performance of electric devices such as personal computers have been remarkable, and a cooling mechanism for cooling heat-generating components such as a CPU and an MPU mounted thereon has been miniaturized and saved. There is a strong demand for space. Therefore, in the case of a cooling mechanism using a heat pipe, the diameter of the heat pipe must be reduced.

Therefore, a thin heat pipe having an outer diameter of, for example, about 3 mm has been put to practical use and has already been applied to a cooling mechanism of a personal computer or the like. However, there is a case where a heat pipe having a substantially flat cross section (flat heat pipe) is used by further crushing the heat pipe having a small diameter due to the space in a housing of a personal computer or the like.

One of the advantages of using a heat pipe is that the distance between a heat-generating part and a heat-radiating point (a place where fins are disposed) can be lengthened to some extent. That is, for example, heat-generating components such as a CPU and an MPU
In many cases, the fins and fans are placed in a location away from the outer wall inside the PC main body, but away from it. It can be efficiently carried near the outer wall of the main body.

On the other hand, in the case of a portable personal computer or the like, it is desired to reduce the size and weight of the personal computer. Therefore, the main body on which heat-generating components such as a CPU and an MPU are mounted tends to be thinner. For this reason, in the heat pipe used for the cooling mechanism of the heat-generating component, the heat-absorbing portion and the heat-radiating portion are often positioned substantially horizontally. In addition, the heat pipe may be in the top heat mode depending on the use form of the personal computer or the like. Under such circumstances, a wick is often inserted into a heat pipe used for a device such as a personal computer, or a fine groove is formed on an inner wall of a hollow portion in many cases.

However, if the heat pipe is long to some extent, the flow path of the working fluid becomes long, so that the capillary action may be insufficient when the groove is formed on the inner wall of the cavity described above. On the other hand, even in the case of a heat pipe with a wick arranged in the cavity, especially in the case of a thin flat heat pipe, the cross-sectional area of the cavity is small, so the working fluid steam speeds up and moves in the opposite direction to the steam The movement of the liquid phase of the working fluid to be performed is likely to be hindered. Especially 1.5mm thickness
This tendency tends to be remarkable in the case of a thin flat heat pipe having a thickness of about the following.

If the working fluid is not sufficiently refluxed, a so-called dry-out phenomenon occurs, and heat transfer by the heat pipe is stopped or performance is deteriorated. Under such circumstances, it has been desired to develop a flat heat pipe in which even a small-sized flat heat pipe can sufficiently maintain the reflux of the working fluid and exhibit excellent characteristics.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made to provide an excellent flat heat pipe in which the recirculation of a working fluid is sufficiently maintained. That is, the flat heat pipe of the present invention has a container having a flat hollow cross-sectional shape and a wick inserted into the container. At both ends of the wick, the wick is provided inside the hollow portion. The positioning portion is formed so as to be stable.

It is preferable that the positioning portion is formed in a shape that is widened to a length of about the major axis of a cross section of the hollow portion. The wick is preferably arranged substantially at the center of the cavity except for both ends.

As the above-mentioned wick, a braid formed by a large number of fine wires, a braid formed by winding a braid formed by a large number of fine wires around a core material, and the like can be suitably applied.

As a method of manufacturing the above-mentioned flat heat pipe of the present invention, a wick whose both ends are processed to have a shape which is widened to the inner diameter of the container pipe is inserted into a container pipe having a substantially circular shape. A manufacturing method including a step of forming a heat pipe and a step of performing flattening is proposed. Heat pipe formation may be performed after flattening.

[0017]

FIG. 1 is an explanatory view schematically showing a part of a manufacturing process of a flat heat pipe according to the present invention. First, a container pipe 10 to be a heat pipe container is prepared. A wick 20 having positioning members 21 attached to both ends is inserted into the container tube 10, and the container tube 10 is flattened (pressed or the like) in the direction of the arrow shown in FIG. The flattened container pipe 10 (FIG. 1A) is converted into a heat pipe to obtain a flat heat pipe.

Here, the heat pipe is a process of sealing both ends of a tube to form a sealed cavity therein, and a working fluid such as water (not shown) in the cavity prior to the sealing operation. It means a series of steps for assembling the heat pipe by a step of appropriately performing a degassing operation, a cleaning operation, and the like in the hollow portion, etc., although a detailed explanation is omitted.

It should be noted that even if the flattening is performed after performing a heat pipe forming step such as injection of working fluid, degassing, and welding sealing of both ends, the heat pipe blank 10 may be formed prior to the heat pipe forming step. May be applied.

In this example, the positioning member 21 is separately attached to the wick 20. FIG. 2 is an explanatory diagram showing this state. In this example, a plate-shaped positioning member 21 is attached to both ends of a wick 20 (FIG. 2A) in which a thin wire is wound around a rod-shaped or tubular core 201 made of copper or the like. (FIG. 2A).

As the positioning portion, in addition to the case where a separately prepared positioning member 21 is attached as in the above-described example, for example, as shown in FIGS. 3 (A) and 3 (A), a core material on which a wick 22 is wound is provided. There is also a method of forming a positioning portion by breaking a part of the 221 and bending and expanding it.

Some examples of the form of the wick will be given. FIG. 4 shows an example of a wick. In FIG. 4, (A) shows a form in which a thin metal wire or the like is wrapped around a rod or tube made of copper or the like, and (A) shows a thin wire. Woven in a rod shape, (C) is a bundle of wires, (D)
Is a rounded mesh.

Returning to FIG. 1, in the above-mentioned flattening,
The positioning members 21 provided at both ends of the wick 20 play a role of holding the wick 20 substantially at the center of the container tube 10. For this reason, the wick 20 is arranged at a substantially central portion over substantially the entire length of the manufactured flat heat pipe.

An operation test of the flat heat pipe of the present invention manufactured by using the container shell 10 shown in FIG. As a result, even if the heat absorbing section is not located below the heat radiating section (horizontal arrangement or top heat mode),
It was found that the recirculation of the working fluid was maintained high, and excellent heat transport characteristics were realized.

The reason why the above-described flat heat pipe of the present invention maintains excellent heat transfer characteristics even in the top heat mode or when the heat absorbing portion and the heat radiating portion are arranged substantially horizontally.
The present inventors presume as follows. FIG. 5 is an explanatory diagram showing a cross-sectional view of the flat heat pipe of the present invention. Description will be made with reference to this figure.

In the flat heat pipe 3 of the present invention, the wick 30 inserted into the container 32 is positioned by the positioning portion 31 at a substantially constant position (in the case of this example, the center portion) over substantially the entire length of the flat heat pipe 3. Are located. Reference numeral 300 in the figure is a core material of the wick 30.

The wick 30 for moving the liquid phase portion of the working fluid by capillary action, ie, serves as a main circulation path of the working fluid, and the region where the wick 30 does not exist mainly serves as a steam flow path. In the case of the present invention, since the wick 30 and the steam flow path are divided at a substantially constant position over substantially the entire length of the flat heat pipe 3, the movement of the liquid phase of the working fluid reverses to the flow of the working fluid vapor. However, it is thought that it is hardly hindered by the steam. Therefore, even when the flat heat pipe 3 is used in the top heat mode or when the heat absorbing portion and the heat radiating portion are used in a substantially horizontal arrangement, the working fluid is efficiently maintained in a recirculated state, and thus excellent heat transfer is achieved. We speculate that the properties were maintained.

In Japanese Patent Publication No. 6-65554 (the present application and a part of the inventor overlap), a wick member is collected on a part of a cross section of a flat heat pipe, and the other part is used as a steam flow path. The invention is shown. On the other hand, the flat heat pipe 3 of the present invention as shown in FIG. 5 is superior in that the configuration in which the wick member 30 is located at a substantially constant position over the entire length of the flat heat pipe 3 is easily realized.

The wick 30 is not necessarily a container 32
It is not necessary to arrange it in the central part inside. For example, it may be arranged close to the end of the cavity. In any case, it is important that the wick 30 serving as a return path of the working fluid is divided so as to be arranged at a substantially constant position over almost the entire length of the flat heat pipe 3.

On the other hand, in the case of the conventional flat heat pipe, the wick arranged in the hollow portion is practically easily disturbed. This will be described with reference to FIGS. The example of FIG. 6 shows a case where the wire wick 50 is arranged along the inner wall inside the pipe 40 by the elastic force of the spirally wound spiral tape 51 and the pipe 40 is crushed and flattened. But in this case,
In the crushing step, the wire wick 50 is often disturbed as schematically shown in FIG. The example in FIG.
The mesh 52 is arranged along the inner wall of the pipe 40,
This is crushed and flattened, but also in this case, the mesh 52 is similarly disturbed during flattening, which tends to cause disorder.

When the arrangement of the wire wicks 50 and the meshes 52, which are the wicks, is disordered, as in the conventional example shown in FIGS. 6 and 7, the wick portion and the steam flow path portion are disturbed. In particular, in the case of a small-diameter flat heat pipe, the movement of the working fluid vapor is likely to be accelerated, so that it is likely that the working fluid vapor scatters the working fluid liquid phase on the wick surface. This seems to be the cause of insufficient circulation of the working fluid.

On the other hand, in the case of the flat heat pipe of the present invention, since the wick portion and the steam flow path portion are divided over substantially the entire length of the flat heat pipe, the movement of steam with respect to the reflux of the working fluid is prevented. It is considered that it is hardly affected, and therefore, sufficient reflux is maintained, and excellent heat transfer characteristics are exhibited.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be briefly described. As the container shell 10 of FIG. 1, the thickness is 0.25 mm.
And a pipe having an outer diameter of 6 mm was used. The wick 20 is formed by winding a braid having a wire diameter of 0.1 mm around a copper core material, and has an outer diameter of about 2 mm. Positioning members 21 are attached to both ends of the wick 20. Separately, anti-separation members (not shown) are also attached to prevent terminal deviation.

The positioning member 21 has a substantially rectangular shape.
The diagonal line has a length close to the inner diameter of the container shell 10. After inserting the wick 20 into the container tube 10, it is made into a heat pipe, and then pressed (flattened) to a thickness of 1 mm.
mm. The wick 20 having an outer diameter of about 2 mm was also crushed by being pressed against the inner wall of the container tube 10.

The length of the manufactured flat heat pipe is 200
mm. When the flat heat pipe was placed horizontally and a 50 mm portion was heated from one end, and the other side was cooled and radiated, the temperature difference between the heating portion and the radiating portion could be kept very small up to 8 W. It was found that the heat transfer characteristic was several times higher than the result of a similar test conducted with a conventional heat pipe.

[0036]

As described above, according to the flat heat pipe of the present invention and the method for manufacturing the same, the reflux of the working fluid is sufficiently maintained,
Excellent heat transfer characteristics are realized.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a part of a manufacturing process of a flat heat pipe of the present invention.

FIG. 2 is an explanatory view schematically showing a part of the manufacturing process of the flat heat pipe of the present invention.

FIG. 3 is an explanatory diagram showing an example of a wick and a positioning member.

FIG. 4 is an explanatory diagram showing an example of a wick.

FIG. 5 is a partial sectional view of an example of the flat heat pipe of the present invention.

FIG. 6 is an explanatory view schematically showing a part of a manufacturing process of a conventional flat heat pipe.

FIG. 7 is an explanatory view schematically showing a part of a manufacturing process of a conventional flat heat pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Container raw pipe 20 wick 21 positioning member 201 core material 22 wick 221 core material 3 flat heat pipe 30 wick 300 core material 31 positioning part 32 container 40 pipe 50 wire wick 51 spiral tape 52 mesh

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Kanichi Uejima 1-115-27 Tsukamoto, Yodogawa-ku, Osaka-shi, Japan Inside the Diamond Electric Machinery Co., Ltd. (72) Shin-ichi Kobayashi 1--15, Tsukamoto, Yodogawa-ku, Osaka-shi, Osaka Inside No. 27 Diamond Electric Co., Ltd. (72) Inventor Koji Tanaka Inside No. 15-27 Tsukamoto, Yodogawa-ku, Osaka-shi, Osaka

Claims (7)

[Claims] 1. A container having a flat hollow cross-sectional shape and a wick inserted into the container, wherein both ends of the wick are provided so that the wick is stable inside the hollow portion. A positioning part is formed,
Flat heat pipe. 2. The flat heat pipe according to claim 1, wherein the positioning portion has a shape that is widened to approximately the major axis of a cross section of the hollow portion. 3. The flat heat pipe according to claim 1, wherein the wick is arranged at a substantially central portion in the cavity except for both ends thereof. 4. The flat heat pipe according to claim 1, wherein the wick is a braid formed by a large number of fine wires. 5. The flat heat pipe according to claim 1, wherein the wick is formed by winding a braid formed by a large number of fine wires around a core material. 6. A container tube having a substantially circular shape,
A step of inserting a wick whose both ends are processed into a shape expanded to about the inner diameter of the container tube, a step of flattening the container tube, and a step of forming the container into a heat pipe. 5. The method for manufacturing a flat heat pipe according to any one of the above items 5. 7. A container tube having a substantially circular shape,
6. A process according to claim 1, further comprising the steps of: inserting a wick whose both ends are processed to have a shape expanded to about the inner diameter of the container tube, heat-forming the container, and flattening the container. A method for producing a flat heat pipe according to any one of the above.