JP2000074578A - Flat heat pipe and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a sufficient reflux of a working fluid and realize an excellent heat transfer property by providing a wick material held on both of opposing flat part inner walls of a flat container, disposed approximately in a center part of a flat part and extending approximately in a direction of a pipe axis. SOLUTION: A wick member 20 makes a working fluid move by the capillary phenomenon. A metal sheet 100 joined with the wick member 20 is rolled into a tubular shape. Then, flattening work is applied to a heat pipe 10 by a press or the like. A flat heat pipe 11 produced by applying the flattening work is constituted in such a manner that the wick member 20 contained in a cavity part is disposed almost in a constant position along a longitudinal direction of the flat heat pipe 11. That is, the wick member 20 is located approximately in a center part of the flat pipe 11 over an entire length.

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.

Accordingly, a heat pipe having a small diameter, for example, a thin heat pipe having an outer diameter of 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. For example, for portable personal computers, the thickness is 2mm
It is often used after being flattened to a thickness of 1.5 mm or less.

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
It is not always located near the outer wall inside the PC body,
Rather, it is often arranged at a position away from it. In such a case, the heat of the heat-generating component can be efficiently transferred to the vicinity of the outer wall of the personal computer main body where the fins and the fan are arranged by passing through the heat pipe.

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
In the case of a flat heat pipe as thin as the following, this tendency tends to be remarkable.

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. In other words, a flat heat pipe having a flat container and having a wick material substantially at the center of the flat portion and substantially extending in the tube axis direction, which is held on both flat inner walls of the flat container opposing each other. suggest. The flat heat pipe of the present invention is a flat heat pipe having a flat container formed by pipe-forming a metal sheet, wherein the metal sheet extends substantially in the pipe axis direction on one flat inner wall of the flat container. A structure in which a wick material is joined is proposed.

A flat heat pipe having a flat container formed by forming a metal sheet into a tube, wherein the metal sheet has a groove wick extending substantially in the pipe axis direction on one flat inner wall of the flat container. It also proposes a flat heat pipe that is formed.

It is desirable that the wick material or the groove wick is located substantially at the center of the flat portion. still,
A wick material such as a mesh may be further joined to the groove wick. Also, the wick material or groove wick may be in contact with the other flat portion inner wall.

The following method is proposed as a method for manufacturing the above-described flat heat pipe of the present invention. One of them is a step of forming a metal sheet into a tube, a step of joining a wick material extending substantially in the pipe axis direction to a part of the metal sheet prior to the tube forming, a step of forming a formed pipe into a heat pipe, Applying a flattening process to the flat heat pipe. The other is a step of forming a metal sheet into a tube, a step of forming a groove wick extending substantially in the pipe axis direction in a part of the metal sheet prior to the tube forming, a step of forming the formed pipe into a heat pipe, Applying a flattening process to the flat heat pipe.

In the above manufacturing method, the order of the step of subjecting the formed pipe to heat pipe processing and the step of subjecting the pipe to flattening are arbitrary. In addition, heat pipe processing includes work to form a cavity by sealing a pipe, work to inject a working fluid into the cavity, and other work such as vacuum degassing and cleaning the inside of the cavity. To make a heat pipe.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view schematically showing a part of an example of a manufacturing process of a flat heat pipe according to the present invention. An embodiment of the present invention will be described with reference to FIG. The metal sheet 100 assumes a copper plate etc., for example. A wick member 20 having a substantially bar-shaped outer shape is arranged and joined to a part of the main surface of the metal sheet 100. The wick member 20 is slightly shorter than the length of the metal sheet 100 in the direction in which it is arranged. This is for securing a welding margin at the time of sealing both ends of the molded pipe described later.

The wick member 20 moves the working fluid by capillary action, and various forms are known. FIG. 6 shows an example of the wick member. In the figure, (a) is a form in which a thin metal wire is wrapped around a copper rod or tube, (a) is a thin wire rod-shaped, and (c) is a bundle of wires. (D) is a rounded mesh (net).

Now, as shown in FIG. 1, the metal sheet 100 to which the wick member 20 is joined is used to roll it into a tubular shape (FIG. 2). Reference numeral 102 in FIG. 2 is a welded portion. Next, a heat pipe is formed using this tube to form a heat pipe 10.
Was manufactured. Here, the term “heat pipe” refers to a process of sealing both ends of a tube to form a sealed cavity therein, and injecting a proper amount of a working fluid such as water (not shown) into the cavity prior to the sealing operation. Although not described in detail, it means a series of steps for assembling the heat pipe by a step of appropriately performing a deaeration operation, a cleaning operation, and the like in the cavity.

Next, the heat pipe 10 is flattened by a press or the like. FIG. 2A shows a flat heat pipe 11 manufactured by performing flat processing. In the flat heat pipe 11 thus completed, the wick member 20 to be accommodated in the hollow portion is arranged at a substantially constant position along a substantially longitudinal direction of the flat heat pipe 11. That is, in this example, the wick 20 is located substantially at the center of the flat heat pipe 11 over the entire length of the flat heat pipe 11.

The position of the wick 20 only needs to be at a substantially constant position over the entire length of the flat heat pipe 11, and the position is not particularly limited to the center. However, since the flat portion (main surface portion) of the flat heat pipe 11 often serves as a heat absorbing portion or a heat radiating portion, it can be said that it is desirable to arrange the wick 20 substantially at the center as shown in the figure.

The flat heat pipe 11 of the present invention will now be described.
I tried an operation test. As a result, it has been found that even when the heat absorbing portion is not located below the heat radiating portion (horizontal arrangement or top heat mode), the reflux of the working fluid is maintained high and excellent heat transport characteristics are realized.

As shown in FIG. 2A, the wick member 20 is in contact with both upper and lower inner walls of the cavity. By doing so, the flat heat pipe 11 can have substantially symmetrical characteristics in the vertical direction in the figure.

The above-described flat heat pipe 11 of the present invention
However, the present inventors presume the reason why excellent heat transfer characteristics were maintained even in the top heat mode or in the case where the heat absorbing portion and the heat radiating portion are arranged substantially horizontally, as follows. Wick member 2 for moving the liquid phase portion of the working fluid by capillary action
The portion of 0 is a recirculation path of the working fluid. On the other hand, the steam mainly has an area where the wick member 20 does not exist as a flow path (steam flow path 101). In addition, the name of the steam flow path 101 is mainly a steam flow path,
It means. It does not mean that no steam flows to other parts. In the case of the present invention, since the wick member 20 and the steam flow path 101 are divided over substantially the entire length of the flat heat pipe 11, the movement of the liquid phase of the working fluid that is opposite to the flow of the working fluid steam is caused by the steam. Seems to be less disturbed. Therefore, the present inventors presume that excellent heat transfer characteristics are maintained even in the top heat mode or when the heat absorbing section and the heat radiating section are arranged substantially horizontally.

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 present invention is superior in practically realizing a configuration in which the wick member 20 is arranged at a substantially constant position over the entire length of the flat heat pipe, particularly at the center.

Now, other embodiments of the present invention will be described. Using a metal sheet 120 having a groove wick 30 formed at a substantially central portion as shown in FIG. 3, similarly to the above-described example, as shown in FIG. Then, it was crushed and flattened (FIG. 4 (a)). Reference numeral 122 in the drawing is a welded portion. Reference numeral 12 in the figure indicates a heat pipe before flattening, and reference numeral 13 indicates a flat heat pipe.

The flat heat pipe 13 of the present invention also has a groove wick 30 which mainly serves as a working fluid recirculation path,
A portion of the steam passage 121 through which steam mainly flows is divided over the entire length. Similar to the flat heat pipe 11 of the present invention described above, the flat heat pipe 12 was found to maintain high reflux of the working fluid and realize excellent heat transport characteristics even in the horizontal arrangement or the top heat mode.

The flat heat pipe 14 shown in FIG. 5 is an example in which both the wick member 21 and the groove wick 31 are applied. Others are the same as the above-mentioned example of the present invention. It has been found that the flat heat pipe 14 of the present invention also realizes excellent heat transport characteristics in the horizontal arrangement or the top heat mode.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention are not limited to the three examples described above, but here, examples will be described with reference to the examples shown in FIGS. The metal sheet 120 is made of copper and has a thickness of 0.25 mm. Groove wick 30 is 0.5 height
The projections are 5 mm in length and 5 mm in length, and are arranged five by five as shown in the figure. This metal sheet 120 is shown in FIG.
Formed as shown in the figure (outer diameter 6mm)
After cutting it to a length of 250 mm, forming a heat pipe such as welding sealing at both ends and injecting a working fluid, flattening is performed, and a flat heat as shown in FIG. A pipe 13 (thickness 1 mm) was obtained. The length of the manufactured flat heat pipe 13 is about 200 mm.

When the flat heat pipe 13 was placed horizontally, 50 mm portions were heated from one end, and the other side was cooled and radiated. The temperature difference between the heating portion and the radiating portion was kept very small up to 8 W. did it. 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.

[0032]

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 showing an example of a metal sheet used for manufacturing a flat heat pipe of the present invention.

FIG. 2 is an explanatory view showing a part of a manufacturing process of the flat heat pipe of the present invention and a cross section thereof.

FIG. 3 is an explanatory view showing an example of a metal sheet used for manufacturing the flat heat pipe of the present invention.

FIG. 4 is an explanatory view showing a part of a manufacturing process of the flat heat pipe of the present invention and a cross section thereof.

FIG. 5 is an explanatory view showing a cross-sectional view of the flat heat pipe of the present invention.

FIG. 6 is an explanatory view showing an example of a wick member used for the flat heat pipe of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heat pipe 100 Metal sheet 101 Steam flow path 102 Weld part 11 Flat heat pipe 20 Wick member 12 Heat pipe 120 Metal sheet 121 Steam flow path 122 Weld part 13 Flat heat pipe 30 Groove wick 14 Flat heat pipe 21 Wick member 31 Groove wick

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Ishida 1-15-27 Tsukamoto, Yodogawa-ku, Osaka-shi, Osaka Inside Diamond Electronics Co., Ltd. (72) Inventor Akemi Shuto 1-tsukamoto, Yodogawa-ku, Osaka-shi, Osaka 15-27 Diamond Electric Co., Ltd. (72) Inventor Takashi Doi 1-27 Tsukamoto, Yodogawa-ku, Osaka-shi, Osaka

Claims (8)

[Claims] 1. A flat container having a wick material, which is held on both opposed flat inner walls of the flat container and is located at a substantially central portion of the flat portion and extends substantially in a tube axis direction, Flat heat pipe. 2. A flat heat pipe having a flat container formed by forming a metal sheet into a tube, wherein the metal sheet is provided on one or both inner walls of opposed flat portions of the flat container substantially in the pipe axial direction. A flat heat pipe that holds an elongating wick. 3. A flat heat pipe having a flat container formed by forming a metal sheet into a tube, wherein the metal sheet has a groove wick extending substantially in the pipe axis direction on one flat inner wall of the flat container. Formed, flat heat pipe. 4. A flat heat pipe in which a wick material is joined to the groove wick according to claim 3. 5. The flat heat pipe according to claim 2, wherein the wick material or the groove wick is in contact with the other flat portion inner wall. 6. The wick material or the groove wick is located at a substantially central portion of a flat portion.
5. The flat heat pipe according to any one of 5. 7. A step of forming a metal sheet into a tube, a step of joining a wick material extending substantially in a tube axis direction to a part of the metal sheet prior to the tube forming, a step of forming the formed tube into a heat pipe, A flat heat pipe, comprising: flattening a flat heat pipe. 8. A step of forming a metal sheet into a tube, a step of forming a groove wick extending substantially in the direction of the tube axis in a part of the metal sheet prior to the tube forming, a step of forming the formed tube into a heat pipe, A flat heat pipe, comprising: flattening a flat heat pipe.