JP4278739B2 - Flat heat pipe and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat heat pipe in which a wick is disposed in a cavity.
[0002]
[Prior art]
In recent years, cooling technology for heat-generating components such as semiconductor elements mounted on electric devices such as personal computers has attracted attention. One method is a cooling technique using a heat pipe. A typical cooling method using a heat pipe is a mode in which a heat pipe is attached to a heat generating component, and heat of the heat generating component is carried to a heat radiating fin or the like through the heat pipe as a path to dissipate. There is also an electric device in which a small fan that forcibly blows air to the fins is installed.
[0003]
Briefly describing the heat pipe, the heat pipe has a hollow portion sealed inside, and a certain amount of working fluid (also referred to as hydraulic fluid) such as water or alternative chlorofluorocarbon is contained in the hollow portion. is there. 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 (vapor) in the cavity.
[0004]
In the heat pipe, the working fluid in the cavity evaporates, and the heat transfer function is activated by the movement of the vapor. For example, in the case of a straight type heat pipe, when heat is applied from one end side thereof (this part is referred to as a heat absorption part of the heat pipe), the working fluid that is in a liquid phase in the heat absorption part evaporates, and the vapor Moves to the other end, where the vapor condenses and dissipates heat (this portion is called the heat dissipating 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 dissipated to the outside.
[0005]
By the way, if the working fluid condensed in the heat radiating part does not return to the heat absorbing part, the above-described operation is not continued. Therefore, it is necessary to return (reflux) the working fluid (liquid phase) condensed in the heat radiating section to the heat absorbing section. Usually, the liquid phase of the working fluid condensed in the heat dissipation part is lowered by gravity by positioning the heat absorption part below the heat dissipation part. Such a state may be referred to as a bottom heat mode.
[0006]
When the heat dissipating part cannot be arranged above the heat absorbing part, the working fluid cannot be recirculated by the gravitational action. In view of this, a method is known in which a wick (sheet-like wick, wire, or the like) that exhibits capillary action is disposed in the cavity of the heat pipe, or a minute groove is formed in the inner wall of the cavity. In addition, the case where the heat radiating part is located below the heat absorbing part may be referred to as a top heat mode. Even when the heat dissipating part is positioned substantially horizontally with the heat absorbing part, it is difficult to expect the working fluid to recirculate due to the gravity action. In such a case, a wick is often disposed.
[0007]
[Problems to be solved by the invention]
In recent years, electrical devices such as personal computers have been remarkably downsized and improved in performance, and downsizing and space saving of a cooling mechanism for cooling heat-generating components such as CPU and MPU mounted thereon are strongly desired. Therefore, in the case of a cooling mechanism using a heat pipe, it is required to reduce the diameter of the heat pipe.
[0008]
Therefore, for example, a thin heat pipe having an outer diameter of about 3 mm has been put into practical use and has already been applied to a cooling mechanism such as a personal computer. However, depending on the space in the housing of a personal computer or the like, a heat pipe (flat heat pipe) in which the thin diameter heat pipe is further crushed to have a substantially flat cross section may be used.
[0009]
By the way, one of the advantages of using a heat pipe is that the distance between the location of the heat generating component and the heat radiation location (location where fins are arranged) can be increased to some extent. In other words, for example, heat-generating parts such as CPU and MPU cannot be located near the outer wall inside the PC main body and are often arranged at a position away from them, but in such a case, heat is generated by passing through a heat pipe. The heat of the parts can be efficiently transferred to the vicinity of the outer wall of the PC main body where the fins and fans are arranged.
[0010]
On the other hand, in the case of a portable personal computer or the like, since it is desired to reduce its size and weight, the shape of the main body portion on which heat generating components such as a CPU and MPU are mounted tends to be thinned. For this reason, the heat pipe used for the cooling mechanism of the heat-generating component often has its heat absorbing portion and heat radiating portion positioned substantially horizontally. Further, depending on the usage form of a personal computer or the like, the heat pipe may be in a top heat mode. For these reasons, a wick is often inserted into a heat pipe used in a device such as a personal computer or a fine groove is formed on the inner wall of the cavity.
[0011]
However, if the heat pipe is long to some extent, the return path of the working fluid becomes long. Therefore, in the case where the groove is formed on the inner wall of the cavity, the capillary action may be insufficient. On the other hand, even in the case of a heat pipe with a wick in the cavity, especially in the case of a flat heat pipe with a small diameter, the cross-sectional area of the cavity is small, so the steam of the working fluid becomes faster 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. In particular, in the case of a thin flat heat pipe having a thickness of about 1.5 mm or less, this tendency tends to be remarkable.
[0012]
If the working fluid is not sufficiently recirculated, a so-called dry-out phenomenon may occur, and heat transfer by the heat pipe stops or performance degradation occurs. Under such circumstances, even in the case of a thin flat heat pipe, it has been desired to develop a flat heat pipe that sufficiently maintains the reflux of the working fluid and exhibits excellent characteristics.
[0013]
[Means for Solving the Problems]
The present invention has been made in view of the above-described problems, and is intended to provide an excellent flat heat pipe that sufficiently maintains the reflux of the working fluid. That is, the flat heat pipe of the present invention has a thin container having a flat cross-sectional shape of the cavity and a sheet-like wick inserted into the container, and the sheet-like wick crosses the cavity. One substantially Ω-shaped, substantially S-shaped or substantially U-shaped is formed in the substantially central portion or end portion of the surface, and the inside of the cavity is divided into a working fluid reflux path and a steam flow path by the sheet-like wick. It is what has been done.
[0015]
Moreover, it is good to provide a gap between the sheet-like wick and the inner wall of the cavity in the major axis direction of the cavity section.
[0016]
The present inventors propose the following method as a method of manufacturing the flat heat pipe ( thin type) of the present invention described above. A step of inserting a sheet-like wick into a container pipe having a substantially cylindrical shape; a step of flattening the container base pipe in a substantially main surface direction of the sheet-like wick; and the container pipe being a heat pipe. and a step of reduction, the substantially Ω shape along the longitudinal direction in advance substantially central portion or the end portion thereof into a sheet wick, previously molded one substantially S-shaped or substantially U-shaped, that A manufacturing method is proposed.
[0017]
In the flat processing, the sheet-like wick may be crushed in the main surface direction by deformation of the container base tube.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory view schematically showing a part of the manufacturing process of the flat heat pipe of the present invention.
First, a container base pipe 200 (for example, a copper pipe) to be a heat pipe container is prepared. A sheet-like wick 10 (for example, a mesh) in which a curved portion or a bent overlap portion is formed at a substantially central portion is inserted into the container base tube 200. Some examples of sheet-like wicks are shown in FIG. 9A is a sheet-like wick formed in a substantially Ω shape, FIG. 9A is a bent form of the substantially Ω shape, FIG. 9C is a substantially S shape, and FIG. In the case of a bent form, FIG.
In the example of FIG. 1, a sheet-like wick 10 in which an Ω-shaped portion 100 is formed as a curved portion as shown in FIG. 2 is used. For example, a copper or other metal mesh may be used for the sheet-like wick 10.
[0019]
Now, after inserting the sheet-like wick 10 into the container base tube 200, the container base tube 200 is formed into a heat pipe. Here, heat pipe formation is a process of forming a hollow part sealed inside by sealing both ends of the pipe, and an appropriate amount of working fluid (not shown) such as water is injected into the hollow part prior to the sealing operation. This is a series of steps for assembling the heat pipe by a step of appropriately performing a deaeration operation, a cleaning operation, or the like in the hollow portion, although a detailed description is omitted.
[0020]
Next, flattening (pressing or the like) in the direction of the arrow shown in FIG. FIG. 1 (a) is an explanatory view showing the state after pressing, and thus a flat heat pipe 20 formed into a flat shape is obtained.
[0021]
The flattening process may be performed after a heat pipe forming process such as working fluid injection, deaeration, and welding sealing at both ends, or may be performed on the container base pipe 200 prior to the heat pipe forming process. good.
[0022]
As shown in FIG. 2, it is desirable to form the Ω-shaped portion 100 at the substantially central portion of the sheet-like wick 10. However, in some cases, the Ω-shaped portion 100 is provided at the end portion of the sheet-like wick 10. It doesn't matter.
[0023]
In the flat heat pipe 20 of the present invention described above, the Ω-shaped portion 100 of the sheet-like wick 10 extends over the entire length thereof, and is disposed at a substantially central portion of the hollow portion. When the operation test of the flat heat pipe 20 of the present invention is performed, even when the heat absorbing portion is not located below the heat radiating portion (horizontal arrangement or top heat mode), the working fluid is maintained at a high reflux and has excellent heat. It was found that the transport characteristics were realized.
[0024]
In the above-described flat heat pipe 20 of the present invention, even when the top heat mode or the heat absorbing portion and the heat radiating portion are substantially horizontally arranged, the present inventors explain the reason why the excellent heat transfer characteristics are maintained as follows. I guess.
FIG. 3 schematically shows a cross section of a flat heat pipe similar to the flat heat pipe 20 described above. This will be described with reference to this figure. A hollow portion having a flat cross section is formed inside the flat heat pipe 21, and a sheet-like wick 11 is disposed in the hollow portion, and a predetermined amount of working fluid (not shown) is accommodated therein. In the case of the present invention, the Ω-shaped portion 110 of the sheet-like wick 11 is located at substantially the center portion of the hollow portion over almost the entire length of the flat heat pipe 21.
[0025]
Therefore, the part of the Ω-shaped part 110 that mainly exhibits the wick function of moving the liquid phase part of the working fluid by capillary action is mainly the reflux path of the working fluid, and the other part is mainly the steam channel (steam channel). 30). The working fluid recirculation path and the steam flow path are divided over substantially the entire length of the flat heat pipe 21. For this reason, the movement of the liquid phase of the working fluid that goes against the flow of the working fluid vapor is less likely to be hindered by the steam. In the present invention, the inventors speculate that such a situation is a mechanism in which excellent heat transfer characteristics are maintained even when the top heat mode or the heat absorbing portion and the heat radiating portion are substantially horizontally arranged.
[0026]
7 and 8 show the manufacturing process of the conventional flat heat pipe. Compare this case with the case of the present invention.
In the case of a conventional flat heat pipe, the wick such as a sheet-like wick or a knitted fabric arranged in the cavity is likely to be disturbed in the manufacturing process. Therefore, the working fluid vapor flow path and the working fluid liquid phase In many cases, the section of the path of movement is disturbed by capillary action.
[0027]
In the example of FIG. 7, the mesh 40 is arranged along the inner wall of the container shell 41 and is crushed and flattened. However, in the case of this method, the mesh 40 tends to become confused and messy as shown in the drawing. The example of FIG. 8 shows a case where the wire wick 421 is disposed along the inner wall of the container base tube 43 by the elastic force of the spiral tape 420 wound in a spiral shape, and the container base tube 43 is crushed and flattened. However, even in this case, the wire wick 420 is easily disturbed in the crushing process.
[0028]
7 and 8, when the mesh 40 or the wire wick 420 serving as a wick is disturbed, the wick portion and the steam flow path portion are disturbed. In particular, in the case of a flat heat pipe with a small diameter, the movement of the working fluid vapor is likely to be accelerated, and it is likely that a phenomenon such as the working fluid liquid phase on the wick surface being scattered by the working fluid vapor is likely to occur. This seems to be the cause of the insufficient reflux of the working fluid.
[0029]
In contrast, in the case of the flat heat pipe 21 of the present invention as shown in FIG. 3, the Ω-shaped portion 110 mainly serving as a return path for the working fluid and the steam flow path 30 serving as a path through which much of the steam passes are flat heat pipes. Since it is divided over almost the entire length of 21, it is considered that it is hardly affected by the vapor transfer with respect to the reflux of the working fluid, and therefore, sufficient reflux is maintained and excellent heat transfer characteristics are exhibited. The vapor also passes through the curved inner side of the Ω-shaped portion 110.
[0030]
In FIG. 3, the Ω-shaped portion 110 of the sheet-like wick 11 does not necessarily have to be disposed at the central portion of the hollow portion 30. For example, it may be arranged close to the end of the cavity. In any case, it is important that the Ω-shaped portion 110 and the portion of the steam flow path are separated over almost the entire length of the flat heat pipe 21.
[0031]
Moreover, as shown in FIG. 3, it is good to leave some distance between the edge part of the sheet-like wick 11, and a cavity inner wall. It is natural that such a gap 31 also constitutes a part of the space of the cavity 30, but since there is no sheet-like wick 11, there is a meaning that more steam flow paths can be secured. As a result, improvement in heat transfer performance of the flat heat pipe can be expected.
[0032]
FIG. 4 is a conceptual diagram schematically illustrating a state in which the sheet-like wick 12 in which the Ω-shaped portion 120 is formed is deformed during flattening of a container base tube (not shown) into which the sheet-like wick 12 is inserted. In this figure, the sheet-like wick 12 is drawn with a solid line for the sake of simplicity. Now, when the container tube is crushed, the sheet-like wick 12 is also crushed to some extent so as to be pushed against its inner wall. At this time, the constricted portion of the Ω-shaped portion 120 is further deformed in the arrow direction as shown in FIG. FIG. 4 (a) shows the shape after the deformation.
[0033]
If deformed in this way, a portion corresponding to the gap 31 in FIG. 3 is secured more widely. Such desirable deformation of the sheet-like wick 12 is more likely to occur when the sheet-like wick shaped into a substantially Ω shape is used than when it is shaped into a substantially U shape.
[0034]
FIG. 5 is a diagram for explaining a part of the manufacturing process when a sheet-like wick 13 formed in a substantially S shape as shown in FIG. 6 is used as another example of the present invention. Other than the sheet-like wick 13 formed into a substantially S shape, it is the same as the example shown in FIGS. The sheet-like wick 13 inserted into the container tube 220 is subjected to a heat pipe forming process and a flattening process, and almost the entire length of the flat heat pipe 22 in which the S-shaped portion of the sheet-like wick 13 is manufactured. It is designed to be arranged in the middle part. In addition, if the sheet-like wick 13 is bent and overlapped at that portion, the capillary action is further improved.
[0035]
When performing an operation test of another example of the present invention, even when the heat absorption part is not located below the heat dissipation part (horizontal arrangement or top heat mode), the reflux of the working fluid is maintained high and excellent heat transport characteristics It was found that
[0036]
【Example】
The embodiment of the present invention is not limited to the above-described example, but here, an example of the example shown in FIGS. 1 and 2 will be described.
A net made of a metal wire made of copper having an outer diameter of 6 mm and a wall thickness of 0.25 mm and a sheet-like wick 10 of an element wire diameter of 0.1 mm was used as the container base tube 20. The flat heat pipe after flat processing has a thickness of 1 mm and a length of about 200 mm.
When this flat heat pipe was placed horizontally, a 50 mm portion was heated from one end portion and the other side was cooled and dissipated, and the temperature difference between the heating portion and the heat dissipating portion could be kept very small up to 8W. It was found that several times the heat transport characteristics were realized compared to the result of a similar test conducted with a conventional heat pipe.
[0037]
【The invention's effect】
As described above, the flat heat pipe and the manufacturing method thereof according to the present invention sufficiently maintain the reflux of the working fluid and realize excellent heat transfer characteristics.
[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 showing an example of a sheet-like wick used in the present invention.
FIG. 3 is an explanatory view showing a cross section of the flat heat pipe of the present invention.
FIG. 4 is an explanatory view showing deformation of a sheet-like wick in the manufacturing method of the present invention.
FIG. 5 is an explanatory view schematically showing a part of the manufacturing process of the flat heat pipe of the present invention.
FIG. 6 is an explanatory view schematically showing a part of the manufacturing process of the flat heat pipe of the present invention.
FIG. 7 is an explanatory view schematically showing a part of a manufacturing process of a conventional flat heat pipe.
FIG. 8 is an explanatory view schematically showing a part of a manufacturing process of a conventional flat heat pipe.
FIG. 9 is an explanatory view showing an example of a sheet-like wick used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Sheet | seat wick 200 Container base pipe 20 Flat heat pipe 100 Ω shape part 11 Sheet wick 110 Ω shape part 21 Flat heat pipe 30 Steam flow path 31 Gap 12 Sheet wick 120 Ω shape part 13 Sheet wick 22 Flat heat pipe 220 Container tube 40 Mesh 41 Container tube 420 Wire wick 421 Spiral tape 43 Container tube

Claims (6)

A container having a flat cross-sectional shape of the hollow portion and a sheet-like wick inserted into the container, and the sheet-like wick is substantially Ω-shaped at a substantially central portion or an end portion of the cross-section of the hollow portion. A thin flat heat pipe in which the inside of the hollow portion is divided into a working fluid reflux path and a steam flow path by the sheet-like wick. A container having a flat cross-sectional shape of the hollow portion and a sheet-like wick inserted into the container, and the sheet-like wick is substantially S-shaped at a substantially central portion or an end portion of the cross-section of the hollow portion. A thin flat heat pipe in which the inside of the hollow portion is divided into a working fluid reflux path and a steam flow path by the sheet-like wick. A container having a flat cross-sectional shape of the hollow portion and a sheet-like wick inserted into the container, and the sheet-like wick is substantially U-shaped at a substantially central portion or an end portion of the cross-section of the hollow portion. A thin flat heat pipe in which the inside of the hollow portion is divided into a working fluid reflux path and a steam flow path by the sheet-like wick. The thin flat heat pipe according to any one of claims 1 to 3, wherein a gap is provided between the sheet-like wick and the inner wall of the hollow portion in the major axis direction of the transverse section. A step of inserting a sheet-like wick into a container pipe having a substantially cylindrical shape, a step of flattening the sheet-like wick in a substantially main surface direction of the sheet-like wick, and a step of forming the container base pipe into a heat pipe. and a step, wherein a substantially Ω shape along the longitudinal direction in advance substantially central portion or the end portion thereof into a sheet wick, previously molded one substantially S-shaped or substantially U-shaped, claim 1 The manufacturing method of the thin flat heat pipe which manufactures the flat heat pipe as described in any of -4. The method for manufacturing a thin flat heat pipe according to claim 5, wherein, in the flattening process, the sheet-like wick is also crushed in a main surface direction by deformation of the container base tube.

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