JP5403617B2 - Self-excited vibration heat pipe - Google Patents

Description

The present invention relates to a self-excited vibration heat pipe.
This application claims priority on February 8, 2008 based on Japanese Patent Application No. 2008-029713 for which it applied to Japan, and uses the content here.

  In recent years, with the miniaturization and high integration of electronic devices, the heat generation density of semiconductor elements and the like has increased rapidly, and there is an urgent need to establish an efficient heat removal method. However, as electronic devices such as notebook personal computers become smaller, it becomes impossible to secure a space for installing a large heat sink directly above a central processing unit (CPU) that is a heat source. In such a case, it is necessary to transport the generated heat to a place where the heat sink can be installed. For this reason, at present, wick-type heat pipes are used as heat transport means.

  About 90% of recent notebook personal computers have built-in wick heat pipes. Such a heat pipe has an outer diameter of about 3 mm and a maximum heat transport amount when installed horizontally is about 12 W. However, the wick-type heat pipe has a problem in that the heat transport capability is drastically reduced when the pipe diameter is micronized (smaller diameter).

Therefore, a self-excited vibration type heat pipe that uses a phase change that has a high heat transport capability even when micronized has recently attracted attention. However, the meandering loop type self-excited vibration heat pipe (inner diameter of about 0.5 mm to 2 mm), which is a typical example, has the problems that it is necessary to meander many pipes and that it is difficult to operate when installed horizontally. Yes (see Non-Patent Document 1).
Takao Nagasaki, “Review on Heat Transport Characteristics of Self-Excited Vibration Heat Pipe”, Heat Transfer, Vol. 44, no. 186, p. 13-17

  The present invention has been made in view of the above circumstances, and provides a self-excited vibration heat pipe capable of exhibiting a high heat transport capability even when installed horizontally without meandering the pipe. One purpose.

In order to achieve the above object, the present invention employs the following configuration.
(1) A heating unit having a wick inside; a cooling unit filled with working fluid; a linear connection between the heating unit and the cooling unit, and a flow path cut-off smaller than the flow channel cross-sectional area of the heating unit A connection channel having an area; a liquid plug protruding from the cooling unit into the connection channel and containing the working fluid; and a vapor plug in the heating unit containing the vaporized working fluid; and the liquid plug A self-excited vibration type heat pipe that self-excites in order to perform heat transfer from the heating unit to the cooling unit in the connection channel.
(2) The self-excited vibration type heat pipe may be configured as follows: the working fluid filled in the cooling unit has a free liquid level that is not constrained by internal pressure.
(3) The self-excited vibration type heat pipe may be configured as follows: the cooling unit has an opening, and the opening is provided with an adjustment unit that adjusts the internal volume of the cooling unit. It has been.
(4) The self-excited vibration type heat pipe may be configured as follows: a ratio of a cross-sectional area of the heating unit and a cross-sectional area of the connection channel is 10: 1 to 2: 1. It is.

  According to the self-excited vibration type heat pipe of the present invention, it is possible to provide a self-excited vibration type heat pipe capable of exhibiting high heat transport capability even when installed horizontally without meandering the pipe.

FIG. 1A is a schematic cross-sectional view of a self-excited vibration heat pipe according to an embodiment of the present invention. FIG. 1B is a schematic cross-sectional view of a modification of the self-excited vibration heat pipe. FIG. 1C is a schematic cross-sectional view of a modification of the self-excited vibration heat pipe. FIG. 2 is a diagram for explaining an experimental method of a self-excited vibration heat pipe, and is a schematic diagram showing an experimental apparatus. FIG. 3 is a diagram illustrating a state of occurrence of self-excited vibration in the self-excited vibration type heat pipe of Example 1, and is a graph illustrating a temporal change in temperature at a specific portion of the self-excited vibration type heat pipe. FIG. 4 is an enlarged view of FIG. FIG. 5 is a graph showing the relationship between the heat transport speed Q and the effective thermal conductivity λ _{eff in} the self-excited vibration heat pipes of Examples 1-2 and Comparative Examples 1-3. FIG. 6 is a graph showing the relationship between the heat transport rate Q and the effective thermal conductivity λ _{eff in} the self-excited vibration heat pipe of Example 1. FIG. 6 also shows the theoretical value of the thermal conductivity of the prior art heat pipe.

Explanation of symbols

1 Heat pipe (Self-excited vibration type heat pipe)
2 Heating part 3, 33, 43 Cooling part 4 Wick 5 Connection flow path 33b, 43b Opening part 34, 44 Adjustment part B Steam plug L Liquid plug M Working fluid M1 Free liquid level

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A to 1C are schematic cross-sectional views of a self-excited vibration heat pipe according to this embodiment. 1A to 1C are diagrams for explaining the structure of a self-excited vibration type heat pipe, and the size, thickness, dimensions, and the like of each part illustrated may differ from those of an actual self-excited vibration type heat pipe. is there.

A self-excited vibration heat pipe 1 shown in FIG. 1A (hereinafter sometimes referred to as a heat pipe 1) includes a working fluid M, a heating unit 2 and a cooling unit 3, a wick 4 built in the heating unit 2, and a heating. It consists of the connection flow path 5 which connects the part 2 and the cooling part 3 roughly.
In the heat pipe 1, the working fluid M flows from the cooling unit 3 into the connection flow path 5 to form a liquid plug L. In the heating unit 2, the working fluid M is vaporized to form the vapor plug B. Heat conduction is performed by the liquid plug L self-excited in the connection flow path 5.
Note that the heat pipe 1 of the present embodiment can be operated in any posture, but it is preferable to install and use it horizontally along the longitudinal direction in terms of increasing the effective thermal conductivity.

  The heating unit 2 is provided with a hollow portion 2 a that communicates with the connection channel 5. A wick 4 is disposed on the inner wall surface of the hollow portion 2a. The cooling unit 3 is a container 3a that fills the working fluid M in the example shown in FIG. 1A. The container 3a is filled with the working fluid M. The working fluid M faces the outside of the heat pipe 1 and forms a free liquid level M1 that is not restricted by the internal pressure of the heat pipe 1. Moreover, the connection flow path 5 is attached to the side wall of the container 3a. The end of the connection channel 5 on the container 3a side is an open end. The container 3a and the connection channel 5 are communicated with each other by the open end.

  The heating unit 2 and the connection channel 5 are hollow cylindrical tubes made of ceramics, glass, or metal. One end 1a of the heating unit 2 is provided with a sealing member 1c made of ceramic, glass or metal. In particular, in the present embodiment, the heating unit 2 and the connection channel 5 may each be made of borosilicate glass.

  The channel cross-sectional area of the connection channel 5 is smaller than the channel cross-sectional area of the hollow portion 2 a of the heating unit 2. In the example shown in FIGS. 1A to 1C, the cross-sectional shape of the connection channel 5 and the hollow part 2a of the heating unit 2 is substantially circular, and the inner diameter of the connection channel 5 is smaller than the inner diameter of the hollow part 2a of the heating unit 2. . Thereby, the flow path cross-sectional area of the connection flow path 5 is smaller than the hollow part 2a of the heating part 2.

The ratio of the channel cross-sectional area of the hollow portion 2a of the heating unit and the channel cross-sectional area of the connection channel 5 is preferably, for example, in the range of heating unit: connection channel = 10: 1 to 2: 1.
More specifically, when applied to water cooling of a CPU of a personal computer, the inner diameter of the hollow portion 2a of the heating unit is preferably in the range of 3 mm to 6 mm, and the inner diameter of the connection channel 5 is in the range of 0.5 mm to 3 mm. Is preferred.

  If the flow path cross-sectional area ratio, the inner diameter ratio, or the inner diameter of the heating unit 2 is smaller than the above range, the evaporation amount of the heating unit 2 cannot be obtained sufficiently, or the heating unit 2 has a low liquid holding capacity, and thus is empty. Since it will be in a state, it is not preferable. Moreover, when the flow path cross-sectional area ratio, the inner diameter ratio, or the inner diameter of the heating unit 2 exceeds the above range, the amount of fluid retained in the heating unit 2 increases, and the time from when heating is started until evaporation occurs is increased. When the low temperature working fluid flows from the cooling unit 3, the evaporation stops, and the self-excited vibration stops, and the time until the evaporation starts again by heating increases. .

  Moreover, since the heating part 2 and the connection flow path 5 have mutually different inner diameters and are substantially equal in thickness, the outer diameters are also different. For this reason, the flange part 9 is formed in the junction part 8 of the heating part 2 and the connection flow path 5. The heating unit 2 and the connection channel 5 are joined to each other through the flange portion 9. However, this configuration is merely an example. As another example, for example, the inner diameters of the heating unit 2 and the connection channel 5 are made different from each other, the wall thickness of the connection channel 5 is increased to make both outer diameters substantially equal, You may join the end surface of the heating part 2. As shown in FIG.

  Moreover, in the example shown to FIG. 1A-C, although the internal diameter of the heating part 2 and the connection flow path 5 changes abruptly on the boundary of the junction part 8, this invention is not limited to this, The heating part 2 and connection flow The inner diameter of the path 5 may be gradually changed in the vicinity of the joint 8.

As shown in FIGS. 1A to 1C, the connection channel 5 is formed in a straight line between the heating unit 2 and the cooling unit 3. Moreover, the connection flow path 5 which concerns on this invention does not need to be made into a loop shape, and the working fluid M should just oscillate in the inside of the linear connection flow path 5 at the time of the action | operation of the heat pipe 1. FIG. Here, the straight shape means that the tube is not bent into a loop shape as in the prior art but has a single tube structure. The connecting flow path 5 is preferably substantially linear, but may be somewhat curved as long as self-excited vibration is generated.
The vibration amplitude at the time of self-excited vibration of the working fluid M depends on the shape and size of the connection channel 5. For example, the inner diameter of the heating unit 2 is 5 mm, the inner diameter of the connection channel 5 is 2 mm, and the connection channel 4. When the heating unit 2 is heated with a length of 150 mm, the vibration amplitude is as large as about ± 25 to ± 50 mm. What is necessary is just to design the length of the heating part 2 and the connection flow path 5 suitably according to said vibration amplitude.

  The wick 4 may be a conventionally known wick as long as it can transport a liquid working fluid by capillary action. The wick 4 may be, for example, a metal net excellent in thermal conductivity such as copper, a cotton-like body such as glass wool, absorbent cotton, or the like. Moreover, the wick 4 may be filled in the entire region in the longitudinal direction of the heating unit 2. Or, one end of the wick 4 coincides with the joint 8 between the heating unit 2 and the connecting channel 5 so that the wick 4 is part of the longitudinal direction of the heating unit 2 (for example, about 2/3 of the entire length in the longitudinal direction). It may be filled only.

The working fluid M may be appropriately selected according to the operating temperature of the heat pipe 1. The working fluid M is preferably pure water, an organic liquid such as ethanol, a refrigerant such as Freon, or a liquefied gas such as ammonia.
Prior to the operation of the heat pipe 1, it is preferable that the connection flow path 5 and the heating unit 2 are completely filled with the working fluid degassed in advance. By heating the heating part 2 of the heat pipe 1, the working fluid M filled in the heating part 2 is vaporized to form the vapor plug B. The working fluid M is pushed out of the heating unit 2 by the steam plug B. The working fluid M remains in the connection channel 5 to form a liquid plug L. Thereafter, when the steady state is reached, evaporation and condensation of the working fluid M occur alternately in the meniscus M at the tip of the liquid plug L. For this reason, the liquid plug L self-excites in the connection flow path 5. When the connection flow path 5 is visually observed, it can be confirmed that the meniscus M, which is the gas-liquid interface between the steam plug B and the liquid plug L, reciprocates in the connection flow path 5, thereby confirming the presence or absence of self-excited vibration. Can be judged.
In addition, when the steam plug B is formed and when self-excited vibration occurs, a part of the liquid plug L is pushed out to the cooling unit 3 (container 3a), but the working fluid M filled in the container 3a is free liquid level M1. Therefore, the extruded liquid plug L can be absorbed.

The heat pipe 1 includes a working fluid M and a linear connection channel 5 that is disposed between the heating unit 2 and the cooling unit 3 and through which the working fluid M flows. The flow channel cross-sectional area of the connection flow channel 5 is smaller than the flow channel cross-sectional area of the heating unit 2, and the heating unit 2 is provided with a wick 4. For this reason, the effective thermal conductivity and the maximum heat transport amount can be significantly increased as compared with the conventional self-excited vibration heat pipe.
In particular, by providing the heating unit 2 with the wick 4, the working fluid M can be stably evaporated in the heating unit 2, and as a result, the effective thermal conductivity and the maximum heat transport amount can be further increased. it can.
In addition, the heat pipe 1 can stably maintain the self-excited vibration when installed horizontally.
Furthermore, according to said heat pipe 1, the heating part 2 and the connection flow path 5 are directly connected with each other. For this reason, a part of the liquid is supplied to the heating unit 2 every time the meniscus M at the tip of the liquid plug L comes to the joint 8 between the heating unit 2 and the connection channel 5. Accordingly, the working fluid can be held in the heating unit 2 to always evaporate. As a result, the working fluid can be stably self-excited and the effective thermal conductivity and the maximum heat transport amount can be increased.

The heat pipe 1 described above has sufficiently high performance, but if it is desired to increase the amount of heat transport, the number of pipes may be increased as necessary, and the thermal design becomes easy.
In addition, the conventional meandering loop type heat pipe could not exhibit the required performance unless meandering many times, but according to the above heat pipe, it is linear without meandering. Thus, the effective thermal conductivity and the maximum heat transport amount can be increased.
Moreover, said heat pipe 1 can be used suitably for cooling of electronic elements, such as CPU.

Next, FIG. 1B shows another example of a heat pipe. The difference between the heat pipe 31 and the heat pipe 1 shown in FIG. 1A is the configuration of the cooling unit.
The cooling part 33 of the heat pipe 31 shown in FIG. 1B is a hollow cylindrical glass tube 33a made of borosilicate glass. The inner diameter of the cooling unit 33 is larger than that of the connection channel 5. An opening 33 b is provided at one end of the glass tube 33 a, and the opening 33 b is sealed with a rubber film (adjustment unit) 34. The working fluid is filled in the cooling unit 33.
Further, a heat radiating fin 35 is provided on the outer periphery of the cooling unit 33.

  According to the heat pipe 31, a part of the liquid plug L is pushed out to the cooling unit 33 when the vapor plug B is formed and self-excited vibration is generated, but the rubber film 34 provided in the cooling unit 33. By deforming, the internal volume of the cooling part is substantially increased, and the volume of the extruded liquid plug L can be absorbed. In this example, a rubber film is used as the adjustment unit, but a diaphragm may be used instead.

Next, FIG. 1C shows still another example of the heat pipe. The difference between the heat pipe 41 and the heat pipe 31 shown in FIG. 1B is the position of the adjusting unit provided in the cooling unit.
The cooling part 43 of the heat pipe 41 shown in FIG. 1C is a hollow cylindrical glass tube 43a with one end made of borosilicate glass closed. The inner diameter of the cooling unit 43 is larger than that of the connection channel 5. An opening 43b is provided on the side surface of the glass tube 43a. The opening 43 b is sealed with a rubber film (adjustment unit) 44. The working fluid is filled in the cooling unit 43.
Further, a heat dissipating fin 45 is provided on the outer periphery of the cooling unit 43.

  According to the heat pipe 41, a part of the liquid plug L is pushed out to the cooling unit 43 when the steam plug B is formed and when self-excited vibration is generated, as in the case of the heat pipe 31. At this time, the rubber film 44 provided in the cooling unit 43 is deformed, so that the internal volume of the cooling unit 43 is substantially increased and the volume of the extruded liquid plug L can be absorbed. In this example, a rubber film is used as the adjustment unit, but a diaphragm may be used instead.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Observation of self-excited vibration: Example 1)
The characteristics of the heat pipe were evaluated by the experimental apparatus shown in FIG.
First, prepare a glass tube 13 to be a connecting flow path 5 made of borosilicate glass having an inner diameter of 2 mm and a length of 250 mm, and a glass tube 12 to be a heating unit 2 made of borosilicate glass having an inner diameter of 5 mm and a length of 150 mm. Glass tubes 12 and 13 were fused. Next, a wick 14 made of copper mesh was attached to the inner wall of the glass tube 12. The wick 14 was mounted between 100 mm from the fused part. The portion where the wick 14 was mounted was designated as the heating unit 2. Next, the one end portion 11a was sealed with a sealing member 11c made of borosilicate glass. Next, the open end 11b of the glass tube 13 serving as the connection channel was immersed in the water bath 21 to fill the interiors of the glass tubes 12 and 13 with pure water serving as the working fluid 20. Thus, the heat pipe 11 of Example 1 was manufactured.

Next, the heater 22 was attached to the heating part 2 of the heat pipe 11 over a length L of 50 mm, and the heat pipe 11 was installed almost horizontally. Further, the portion immersed in the water bath 21 was used as the cooling unit 3 of the heat pipe 11. And the temperature of the cooling water 21a in the water bath 21 was maintained at 0 degreeC. On the other hand, the heat generation amount of the heater 22 was set to such an extent that the temperature of the heating part was kept at the boiling point of pure water of 100 ° C., and the heat pipe 11 was operated.
After the heat pipe 11 was in a steady state (maximum heat transport amount 50 W), the surface temperature of each part of the heat pipe 11 and the temperature of the cooling water 21a of the water bath 21 were measured with thermocouples. The results are shown in FIGS.

  2 to 4, the temperature of the measurement location TC <b> 1 is the temperature of the heating unit 2 and the surface temperature on the one end 11 a side of the mounting portion of the heater 22. The temperature of the measurement location TC2 is the temperature of the heating unit 2 and the surface temperature on the other end 11b side of the heater 22 mounting portion. The temperature of the measurement location TC3 is the water temperature of the cooling water 22a. The temperature of the measurement location TC4 is the water temperature immediately after the exit of the open end 11b.

  As shown in FIGS. 3 to 4, TC1 and TC2 maintain about 100 ° C., and TC3 maintains about 0 ° C. On the other hand, it can be seen that TC4 has a peak periodically. The peak maximum temperature is about 10 ° C., and the peak frequency is 5 Hz. The amplitude width of the working fluid 20 is 100 mm (± 50 mm) at the maximum. Thus, in the heat pipe 11 of Example 1, self-excited vibration of the working fluid 20 was observed in a steady state.

“Measurement of heat transport rate Q and effective thermal conductivity λ _eff ”
Next, the relationship between the heat transport rate Q (heat transport amount) of the heat pipe of Example 1 and the effective thermal conductivity λ _eff was examined. In this experiment, the water temperature of the cooling water and the heating temperature of the heater were appropriately changed and measured. Further, the heat transport rate Q and the effective thermal conductivity λ _eff were obtained by the following formulas (1) and (2). The results are shown in FIG.

In the equation (1), [rho is the density of the working fluid 20 (pure water), c _p is the specific heat at constant pressure of the working fluid 20 (pure water), V is the enclosed amount of the working fluid 20, [Delta] T Is the amount of increase during the time Δt of the water temperature of the cooling section.
In Formula (2), L _Φ2 is the total length of the entire length of the connection channel and one half of the total length of the heating unit, T _H is the temperature of the heating unit, and T _L is in the water bath. D _Φ2 is the inner diameter of the connection channel.

(Example 2)
Next, a heat pipe of Example 2 was manufactured in the same manner as Example 1 except that the material of the heating side pipe and the cooling side pipe was quartz glass. Then, in the same manner as in Example 1, the relationship between the heat transport rate Q of the heat pipe of Example 2 and the effective thermal conductivity λ _eff was examined. The results are shown in FIG.

(Comparative Example 1)
Next, the heat pipe of Comparative Example 1 was manufactured in the same manner as Example 1 except that the material of the heating side pipe and the cooling side pipe was quartz glass and no wick was installed. In the same manner as in Example 1, the relationship between the heat transport rate Q of the heat pipe of Comparative Example 1 and the effective thermal conductivity λ _eff was examined. The results are shown in FIG.

(Comparative Example 2)
Next, a glass tube made of quartz glass having an inner diameter of 5 mm and a length of 400 mm was prepared, and a wick made of copper mesh was attached to the inner wall surface of the hollow portion of the glass tube. Next, one end of the pipe was sealed with a sealing member. And the hollow part was filled with the working fluid 20 (pure water). Thus, the heat pipe 11 of the comparative example 2 was manufactured.
In the same manner as in Example 1, the relationship between the heat transport rate Q of the heat pipe of Comparative Example 2 and the effective thermal conductivity λ _eff was examined. The results are shown in FIG.

(Comparative Example 3)
Next, the heat pipe of the comparative example 3 was manufactured like the comparative example 2 except not having installed the wick. In the same manner as in Example 1, the relationship between the heat transport rate Q of the heat pipe of Comparative Example 3 and the effective thermal conductivity λ _eff was examined. The results are shown in FIG.

(Evaluation)
As shown in FIG. 5, it can be seen that the heat pipe of Example 1 has a maximum heat transport rate of 33 W and an effective thermal conductivity λ _eff of 36000 W / (m · K) at the maximum.
Moreover, the heat pipe of Example 2 has the same effective thermal conductivity λ _{eff at the} same heat transport speed as that of Example 1.
On the other hand, the heat pipes of Comparative Examples 1 to 3 have a maximum heat transport rate of 10 W or less and an effective thermal conductivity λ _eff of about 100 W / (m · K) at the maximum, which is higher than that of Examples 1 and 2. It can be seen that the transport speed Q and the effective thermal conductivity λ _eff are greatly reduced.

From the results of Examples 1 and 2, a self-excited vibration type heat pipe can be configured by joining two pipes having different inner diameters and enclosing a working fluid in the hollow portion of the pipe. It can be seen that self-excited vibration can be developed even when installed.
When two pipes with different inner diameters are joined to form a heat pipe (Examples 1 and 2), the correlation between the heat transport rate and the effective thermal conductivity λ _eff becomes high and increases linearly. I understand. In Example 1, the effective thermal conductivity increased to a maximum of about 40000 W / (m · K), but this value was reduced to copper having a relatively high thermal conductivity (thermal conductivity 400 W / (m · K). )), It can be seen that the effective thermal conductivity is increased up to 100 times.
Moreover, as shown in FIGS. 3-4, it turns out that the temperature (TC1, TC2) of a heating part is maintaining the boiling-point vicinity of a working fluid (pure water). Since pure water was used this time, the temperature of the heating unit was close to 100 ° C. However, if an appropriate working fluid is selected according to the allowable temperature of the object to be cooled, efficient heat conduction can be realized.
In Example 1 above, the maximum value of the effective thermal conductivity was about 40000 W / (m · K) and the maximum value of the heat transport rate was about 50 W, but these values are not limit values. Even better results may be obtained by changing the experimental conditions.

FIG. 6 is a comparison diagram between experimental values of heat transport characteristics of the heat pipe of Example 1 and theoretical values of heat transport characteristics of the heat pipe (dream pipe) of the prior art. The relationship between Q and effective thermal conductivity (lambda) eff is shown.
This conventional heat pipe is a type of heat pipe (dream pipe) that transports heat in the axial direction by forcibly vibrating a liquid in the pipe. The effective thermal conductivity λeff of the dream pipe was calculated from the following formulas (3) and (4).


Here, λ: thermal conductivity of fluid, Pr: Prandtl number, r: pipe inner diameter, ν: kinematic viscosity of water, f: frequency, S: amplitude. This prior art dream pipe is a single-diameter pipe type that does not have a connecting channel 5 having a smaller diameter than the heating unit 2.
As shown in FIG. 6, the effective thermal conductivity of the heat pipe of Example 1 is as large as about 10 times that of the conventional dream pipe. One of the causes of this effect is that in the heat pipe of the first embodiment, the open end 11b of the glass tube 13 is opened in the water tank, so that the working fluid M in the glass tube 13 is vibrated every time the working fluid M vibrates. Is considered to be replaced with a low-temperature liquid in the water bath 21.

  According to the self-excited vibration type heat pipe of the present invention, it is possible to provide a self-excited vibration type heat pipe capable of exhibiting high heat transport capability even when installed horizontally without meandering the pipe.

Claims (4)

A heating section with a wick inside;
A cooling section filled with working fluid;
A connecting channel that connects the heating unit and the cooling unit in a straight line and has a channel cross-sectional area smaller than the channel cross-sectional area of the heating unit;
A liquid plug protruding from the cooling section into the connection flow path and containing the working fluid;
A vapor plug in the heating section containing the vaporized working fluid;
The self-excited vibration type heat pipe, wherein the liquid plug self-excites in order to perform heat transfer from the heating unit to the cooling unit in the connection channel.   2. The self-excited vibration heat pipe according to claim 1, wherein the working fluid filled in the cooling section has a free liquid level that is not constrained by internal pressure.   The self-excited vibration heat pipe according to claim 1, wherein the cooling unit has an opening, and an adjustment unit that adjusts an internal volume of the cooling unit is provided in the opening.   2. The self-excited vibration heat pipe according to claim 1, wherein a ratio of a cross-sectional area of the heating unit and a cross-sectional area of the connection channel is 10: 1 to 2: 1.