JP4382891B2 - 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. Therefore, there are known methods of disposing a wick (mesh, wire, etc.) that develops a capillary action in the cavity of the heat pipe or forming a fine groove on 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, a thin heat pipe, 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. For example, in the case of a portable personal computer, it is often used after being flattened to a thickness of about 2 mm and further to a thickness of 1.5 mm or less.
[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. That is, for example, a heat generating component such as a CPU or MPU is not necessarily arranged near the outer wall inside the personal computer body, but rather is often arranged at a position away from it. In such a case, by passing through the heat pipe, the heat of the heat generating component can be efficiently carried to the vicinity of the outer wall of the personal computer main body where the fins and the fan 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]
Thus, if the working fluid is not sufficiently recirculated, a so-called dry-out phenomenon occurs, 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, there is provided a flat heat pipe having a flat container formed by the tube molding a metal sheet, the metal sheet is substantially axial direction of the tube on one of the flat inner wall of the flat container An extending groove wick portion is formed, a wick material extending substantially in the tube axis direction is joined to a position facing the groove wick portion, and the wick material is joined to the tip of the groove wick portion . We propose a configuration with
[0015]
It is desirable that the wick material and the groove wick are located at a substantially central portion of the flat portion .
[0016]
The following method is proposed as a method for manufacturing the flat heat pipe of the present invention described above. A step of forming a metal sheet into a tube, a step of forming a groove wick portion extending substantially in the tube axis direction in a part of the metal sheet prior to the tube forming, and a portion of the metal sheet when the tube is formed Is a method of manufacturing a flat heat pipe having a step of joining a wick material extending substantially in the tube axis direction to a position facing the groove wick portion, a step of forming a formed tube into a heat pipe, and a step of flattening the tube. .
[0017]
In the said manufacturing method, the order of the process which heat-processes to the shape | molded pipe | tube, and the process of flattening a pipe | tube is arbitrary. Heat pipe processing includes the work of sealing the tube to form a cavity, the work of injecting a working fluid into the cavity, and the work of vacuum degassing and cleaning the cavity. Refers to heat pipes.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view schematically showing a part of a manufacturing process example of a flat heat pipe of the present invention. An embodiment of the present invention will be described with reference to this figure.
The metal sheet 100 assumes a copper plate etc., for example. A wick member 20 whose outer shape is substantially rod-shaped is disposed 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 disposed. This meaning is to secure a welding margin at the time of sealing work at both ends of the molded pipe described later.
[0019]
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 wound around a copper rod or tube, (i) is a thin wire rod knitted, and (c) is a bundle of wires. (D) is a rounded mesh.
[0020]
Now, using the metal sheet 100 to which the wick member 20 is joined as shown in FIG. 1, it is rolled into a tubular shape (FIG. 2). The code | symbol 102 in FIG. 2 is a welding part. Subsequently, this pipe was used to form a heat pipe to produce a heat pipe 10. Here, heat pipe formation is a process of forming a hollow portion sealed inside by sealing both ends of the tube, and an appropriate amount of working fluid (not shown) such as water is injected into the hollow portion 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.
[0021]
Next, the heat pipe 10 is flattened by a press or the like. FIG. 2 (a) shows a flat heat pipe 11 manufactured by flattening. In the flat heat pipe 11 thus completed, the wick member 20 that fits in the hollow portion is arranged at a substantially constant position along the substantially longitudinal direction of the flat heat pipe 11. In other words, in this example, the wick 20 is positioned substantially at the center of the flat heat pipe 11 over the entire length of the flat heat pipe 11.
[0022]
The position of the wick 20 only needs to be present 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 part (main surface part) of the flat heat pipe 11 is often a heat absorbing part or a heat radiating part, it can be said that it is desirable to arrange the wick 20 almost at the center as shown.
[0023]
Now, an operation test of the flat heat pipe 11 of the present invention was performed. As a result, it was found that even when the heat absorbing part is not located below the heat radiating part (horizontal arrangement or top heat mode), the working fluid is maintained at a high reflux and excellent heat transport characteristics are realized.
[0024]
As shown in FIG. 2A, the wick member 20 is in contact with both the upper and lower inner walls of the hollow portion. By carrying out like this, this flat heat pipe 11 can be made into the thing by which the characteristic became substantially symmetrical in the up-down direction in a figure.
[0025]
In the above-described flat heat pipe 11 of the present invention, the reason why the excellent heat transfer characteristics are maintained even when the top heat mode or the heat absorbing portion and the heat radiating portion are arranged substantially horizontally is as follows. I guess.
The portion of the wick member 20 that moves the liquid phase portion of the working fluid by capillary action serves as a return path for the working fluid. On the other hand, steam mainly passes through the area where the wick member 20 does not exist (steam). The flow path 101). In addition, the designation | designated with the steam flow path 101 means that the part becomes a flow path of steam mainly. 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 almost the entire length of the flat heat pipe 11, the movement of the liquid phase of the working fluid that goes against the steam flow of the working fluid It seems to be difficult to be disturbed by. Therefore, the present inventors speculate that excellent heat transfer characteristics are maintained even when the top heat mode or the heat absorbing portion and the heat radiating portion are arranged substantially horizontally.
[0026]
By the way, Japanese Patent Publication No. 6-65954 (a part of the present invention overlaps with the present inventor) shows an invention in which a wick member is collected in a part of a cross section of a flat heat pipe and the other part is a steam channel. Has been. On the other hand, the present invention has an advantage in practically realizing a configuration in which the wick member 20 is disposed at a substantially constant position, particularly in the central portion, over the entire length of the flat heat pipe.
[0027]
Now, other embodiments of the present invention will be described briefly.
Using the metal sheet 120 having the groove wick 30 formed substantially at the center as shown in FIG. 3, as in the above example, it is rolled into a pipe as shown in FIG. After that, it was crushed and flattened (FIG. 4 (a)). The code | symbol 122 in a figure is a welding part. Reference numeral 12 in the figure denotes a heat pipe before flattening, and reference numeral 13 denotes a flat heat pipe.
[0028]
The flat heat pipe 13 of the present invention is also divided over the entire length of the groove wick 30 that mainly serves as a return path for the working fluid and the portion of the steam channel 121 through which steam mainly flows. It has been found that the flat heat pipe 12 also achieves excellent heat transport characteristics while maintaining a high reflux of the working fluid even in the horizontal arrangement or the top heat mode, like the flat heat pipe 11 of the present invention described above.
[0029]
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 this 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]
【Example】
Although the embodiment of the present invention is not limited to the above-described three examples, here, examples will be described for the examples shown in FIGS.
The metal sheet 120 is made of copper and has a thickness of 0.25 mm. The groove wick 30 is formed by aligning five protrusions each having a height of 0.5 mm and a length of 5 mm as illustrated. As shown in FIG. 4A, this metal sheet 120 is formed into a pipe shape (outer diameter 6 mm), cut into a length of 250 mm, and weld sealed at both ends, injection of working fluid, etc. After heat pipe formation, flat processing was performed to obtain a flat heat pipe 13 (thickness 1 mm) as shown in FIG. The length of the manufactured flat heat pipe 13 is about 200 mm.
[0031]
When this flat heat pipe 13 was placed horizontally, the 50 mm portion was heated from one end thereof, and the other side was cooled and dissipated, and the temperature difference between the heating portion and the heat radiating 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.
[0032]
【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 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 a 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 the 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 in 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 Welding part 11 Flat heat pipe 20 Wick member 12 Heat pipe 120 Metal sheet 121 Steam flow path 122 Welding part 13 Flat heat pipe 30 Groove wick 14 Flat heat pipe 21 Wick member 31 Groove wick

Claims (3)

A flat heat pipe having a flat container formed by tube-forming a metal sheet, wherein the metal sheet is formed with a groove wick portion extending substantially in the tube axis direction on the inner wall of one flat portion of the flat container. A flat heat pipe in which a wick material extending substantially in the tube axis direction is joined to a position facing the groove wick portion, and further, the wick material is joined to the tip of the groove wick portion . The flat heat pipe according to claim 1, wherein the wick material and the groove wick are located at a substantially central portion of the flat portion . 3. A method of manufacturing a flat heat pipe according to claim 1 or 2, wherein a step of forming a metal sheet in a tube, and a groove extending substantially in the tube axis direction in a part of the metal sheet prior to the tube forming. A step of forming a wick portion, a step of joining a wick material extending substantially in the tube axis direction to a position facing the groove wick portion when a tube is formed as a part of the metal sheet, and forming the pipe into a heat pipe A method for manufacturing a flat heat pipe, comprising: a step of flattening a pipe.

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