JPH04251189A - Micro heat pipe - Google Patents

Abstract

PURPOSE:To reduce the diameter of a fine tube container remarkably and miniaturize a heat transfer device employing a fine tube heat pipe by constituting the heat transfer deice so as to transport the amount of heat by only the axial vibration of operating fluid. CONSTITUTION:A fine tube container is characterized in that the container is formed of a continuous metallic fine tube formed so as to have a small inner diameter so that two-phase operating fluid, sealed into the container, can be moved while filling the container and a predetermined plurality of parts of the same are constituted so as to be a heat receiving section while the other predetermined plurality of parts are constituted so as to be heat reading sections and the heat receiving sections and the heat radiating sections are arranged alternately. The reduction of weight and size of the pipe is facilitated by a very easy and simple constitution and a high performance can be developed regardless of the posture of application while a micro heat pipe, high in reliability, can be constituted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention makes it possible to significantly reduce the size and weight of heat receiving and radiating devices, and to manufacture long products of thin tube heat pipes up to the ultra-thin tube class, which was previously impossible to manufacture. Concerning the structure of a capillary heat pipe that enables this.

0002

BACKGROUND OF THE INVENTION The performance of conventional heat pipes varies greatly depending on the position in which they are mounted, and they are almost inoperable, especially in top heat mode. Also, during the operation, the evaporating working fluid flow that moves at high speed from the evaporating section to the condensing section and the condensing working fluid flow that returns from the condensing section to the evaporating section are in opposite directions, making it difficult to form a thin tube due to their mutual interference. It is a thin tube with an outer diameter of about 3 mm and a length of about 400 mm.
Furthermore, the production limit for thin tube heat pipes commonly called micro heat pipes was a length of about several tens of millimeters. Another problem was that it was impossible to use it by bending it, so the degree of freedom in use was small.

[0003] In order to solve these problems, the inventor of the present invention disclosed US Pat.
A loop-type thin tube heat pipe as described in No. 49 was devised and put into practical use. Its structure is as illustrated in FIG. 2, and the loop-type thin tube container 2 is formed as a closed container with both ends of the thin tube 2 connected to each other so as to allow free circulation.
A predetermined amount of two-phase condensable working fluid is sealed inside the loop-type capillary container 2, and the inner diameter of the capillary tube 2 allows the working fluid to circulate or move while always keeping the tube closed due to the surface tension of the working fluid. The diameter is smaller than the maximum diameter that can be used, and at least one part of the loop-type fluid flow path has a circulation direction regulating means such as a check valve (in the figure, a check valve is installed). 3), at least one predetermined portion of the loop-type thin tube container 2 is provided as a heat receiving section 2-H, and at least one predetermined portion of the remaining thin tube container is provided as a heat radiating section 2-C. Most of them are characterized in that heat receiving parts 2-H and heat radiating parts 2-C are arranged alternately.

In such a loop type thin tube heat pipe, when the heat receiving section 2-H is heated by the heat receiving means H and the heat dissipating section 2-C is cooled by the heat dissipating means C, a plurality of tubes separated by the check valve 3 are connected to each other. An oscillating pressure difference is generated between the pressure chambers due to nucleate boiling occurring in the heat receiving portion 2-H, and a breathing effect occurs. Nucleate boiling in the heat receiving part 2-H causes pressure waves to propagate within the fluid, and this pressure wave causes the valve body of the check valve to vibrate, and the interaction between the vibration of the valve body and the above-mentioned breathing action causes the working fluid 4 to vibrate. generates a strong circulating propulsion force.

[0005] In this manner, the two-phase working fluid naturally circulates within the loop in a predetermined direction. Since nucleate boiling is not continuous, the circulating working fluid consists of steam bubbles 5, working fluid 4 (
(obstructed droplets) are arranged alternately and circulate. Therefore, heat is transported by sensible heat due to thermal conduction of the working fluid and latent heat of the vapor bubbles 5.

[0006] Such heat transport by the circulating flow of the working fluid enables good heat transport regardless of the mounting position of the heat pipe, and since it is a thin tube heat pipe, it can also be made smaller and lighter. It was intended to be. Furthermore, it can be used by bending it freely, greatly expanding the degree of freedom in its use.

The inventor has also devised and put into practical use a loop-type thin tube heat pipe as shown in FIG. 3 in accordance with Japanese Patent Application No. 2-319461. The loop-type capillary heat pipe is the basic structure of the loop-type capillary heat pipe shown in FIG. 2 for operation as a heat pipe, and the circulation direction regulating means (in the example shown in the figure, a check valve), which is an essential component, is removed. The other components are exactly the same. That is, in FIG. 3, the loop-type capillary container 2 has a sufficiently small inner diameter, so that the two-phase condensable working fluid sealed inside the capillary container always remains closed within the tube due to its surface tension, as shown in the figure. circulate or move in a state. Also in the loop type thin tube heat pipe, the heat receiving section 2-H and the heat dissipating section 2-C are each disposed at at least one location. However, from a practical standpoint, it is desirable that these devices be disposed in a plurality of locations, and if possible, it is more desirable that they be provided in a large number of locations. Still another condition is that the heat dissipating section 2-C is always located between the plurality of heat receiving sections 2-H. In addition, the amount of working fluid 4 sealed is normally 20% to 50% of the total internal volume of the capillary container in the loop-type capillary heat pipe shown in FIG. 2, whereas in the loop-type capillary heat pipe shown in FIG. A suitable amount of hydraulic fluid is sealed in the container, which is 30% to 95% of the internal volume.

The loop-type capillary heat pipe having such a structure is a different type of loop-type capillary heat pipe having a completely different heat transport principle from the conventional loop-type capillary heat pipe provided with a check valve. In other words, since there is no check valve, the working fluid circulates within the loop only by natural convection.
The heat circulates slowly according to the direction of natural convection, which is determined by the mounting posture of the thin tube heat pipe and the placement position between the heat receiving part and the heat radiating part. Therefore, the circulation direction of the working fluid is undefined, sometimes only in the clockwise direction in the figure, and sometimes in the counterclockwise direction, and contributing to the transport of heat is extremely small. Most of the heat transfer in the loop-type capillary heat pipe is performed by axial vibration of the working fluid.

In FIG. 3, nucleate boiling occurs in each of the heat receiving portions 2-H which receive heat from the heat receiving means H, thereby generating pressure waves and at the same time generating a group of intermittent vapor bubbles. The pressure waves generated in each heat receiving part 2-H and the pressure of the vapor bubbles sometimes simultaneously push the working fluid sealed in the narrow tube container between adjacent heat receiving parts in a closed state, sometimes simultaneously pull together, and sometimes It is pressed from one side to the other, and sometimes it is attracted from one side to the other, resulting in a vibrating state. Since the pipe line forms a loop, if there are a large number of heat receiving parts 2-H, they will amplify or interfere with each other, but as a result, the vibrations will be amplified and all the working fluid in the loop will move in the axial direction. Becomes in a vibrating state.

[0010] Such axial vibration generates a strong heat equalizing effect in the fluid using the fluid boundary layer generated on the inner surface of the pipe wall and the inner wall surface of the container as heat media, and heat is transferred from the high temperature side of the fluid to the low temperature side. Transport to the side. Therefore, the amount of heat in the high temperature part of the heat receiving part 2-H is transported by the cooling means C toward the heat radiating part 2-C which has become low temperature.

On the other hand, since the working fluid circulates slowly, the group of vapor bubbles 5 flows through the working fluid 4 in the state shown in FIG.
It is transported toward the heat radiating part 2-C by condensation, shrinks, and releases latent heat of condensation.

Therefore, the loop-type capillary heat pipe shown in FIG. 3 basically transports most of the heat as sensible heat through axial vibration of the working fluid, and secondarily transports most of the heat as latent heat through the slow circulation of vapor bubbles. Transports heat. The principle of heat transfer by axial vibration of the working fluid is described in Japanese Patent Publication No. 2-
35239, and an example is described in detail in Japanese Patent Application No. 319461/1999.

Although the loop-type capillary heat pipe without the check valve shown in FIG. 3 has a completely different operating principle from the conventional loop-type capillary heat pipe, it solves the problems of the conventional conventional heat pipe. It is similar in that it works well even under top heat and allows the heat receiving and dissipating device to be made smaller and lighter. It is also similar in that it can be used by bending it freely. Since the loop-type capillary heat pipe mainly transports heat through axial vibration of the working fluid, when the amount of working fluid enclosed is 80% or more, the heat transport capacity hardly changes in each heat receiving mode of top heat, bottom heat, and horizontal heat. In this respect, it is superior to the conventional loop-type capillary heat pipe with a check valve. However, the average heat transport performance is slightly lower.

When the amount of working fluid enclosed is less than 60%, the heat transport performance in the top heat mode and the horizontal heat mode is lower than that of the conventional thin tube heat pipe. However, in bottom heat mode, the existence of the check valve does not obstruct the rise of nucleate boiling vapor bubbles, so the amplitude of the working fluid increases significantly, and the heat transport capacity is higher than that of conventional loop type capillary heat with check valve. A major feature is that it is significantly improved compared to pipes.

[0015]

[Problem to be solved by the invention] 2 of the examples shown in FIGS. 2 and 3
All types of loop-type thin tube heat pipes have almost all of the problems of conventional ordinary heat pipes, including the fact that they operate well regardless of the position in which they are worn, and can be bent and used freely. Although it is a solution,
In order to further reduce the size and weight of heat transport devices and heat receiving and dissipating devices in response to industry demands, several issues remain.

The problem is as follows. (a) If the inner diameter is made smaller at around 1.2 mm, the defect rate of the product will increase sharply and the reliability will decrease significantly. This is because in the case of a loop-type thin tube heat pipe with a check valve, quality control is difficult because the check valve is too small. Also, as can be seen from the illustrations of the connection welds shown in Figure 4 (with check valve) and Figure 5 (without check valve), there is a check valve mounting joint, a connection joint 8 for forming a loop, and a working fluid injection thin tube. Joint 9
, the joint 10 for gas discharge capillary tubes, etc., requires a plurality or a large number of joint parts to actually manufacture a loop-type capillary heat pipe, and joints 3 and 8 each have two welded parts, joints 9 and 8, respectively.
10 requires four welding parts, and if the outer diameter is 1.6 mm or less and the inner diameter is less than 1.2 mm, the difficulty of welding increases rapidly and the reliability of the product decreases significantly. In FIGS. 4 and 5, the thin tube container is shown as a line diagram for the purpose of simplifying the drawings.

(b) Even if the diameter of the loop-type thin tube container is made smaller, the effect is often not sufficiently obtained. That is, even if the diameter of the capillary container is reduced, it is difficult to reduce the diameter of the joints, so portions with large outer diameters remain at various locations in the loop-type capillary heat pipe. In particular, caulked welds of the injection capillary and discharge capillary are left in the working fluid injection joint and the gas discharge joint, and the length thereof is as much as 15 mm. Further, the outer diameter of the joint is approximately 2 mm for a thin tube with an outer diameter of 1 mm. It is clear from FIGS. 4 and 5 that the degree of freedom in application of the loop-type thin tube heat pipe is reduced due to the remaining portions where it is difficult to reduce the outer diameter.

(c) As the diameter of the capillary container progresses from 1.6 mm in outer diameter to 1.2 mm in inner diameter, the difficulty in enclosing an appropriate amount of working fluid increases. That is, as the diameter becomes smaller, the inner tube closing force due to the surface tension of the working fluid becomes stronger, and it becomes difficult to remove air once mixed into the loop-shaped thin tube. As a countermeasure, measures have been taken to provide a joint 9 for the injection capillary tube and a joint 10 for the gas discharge capillary tube as shown in Figs. 4 and 5, but this is not perfect, and it has become difficult to fill the correct amount accurately as the diameter of the tube increases. .

[0019]

[Means for Solving the Problems] As a means for reducing the diameter of a thin tube container by solving the remaining problems while retaining the advantages of the loop-type thin tube heat pipe as described above, the present invention has been developed as shown in Figs. 4. It was decided to adopt a structure in which all the joints such as the check valve 3, the loop end connection joint 8, the working fluid injection capillary joint 9, and the gas discharge capillary joint 10 shown in FIG. 5 were abolished. That is, the loop-shaped thin tube shown in FIG. 3 is not looped, and both ends of the thin tube container are sealed. Therefore, it becomes impossible to gently circulate the working fluid during operation in the loop-type capillary heat pipe shown in FIG. 3, and the structure is such that the transport of heat is carried out only by the axial vibration of the working fluid. Due to the loss of the gentle circulation flow, the performance of the heat transport due to the latent heat of the steam bubbles 5 decreases, but this is compensated for by having a thinner tube container than in the case of a loop type, and reducing the mass of the working fluid to be vibrated. becomes smaller, and the energy loss consumed to generate vibrations is reduced and compensated for by the activation of vibrations.

FIG. 1 shows the basic structure of the micro heat pipe according to the present invention as described above. In the figure, a sealed thin tube container 1 has a length formed with a sufficiently small inner diameter so that a predetermined two-phase condensable working fluid sealed in vacuum moves inside the container in a state where the container is always filled and closed due to its surface tension. It is made up of a thin metal tube, and a plurality of predetermined parts thereof are a heat receiving part 1-H, and a plurality of other predetermined parts are a heat radiating part 1.
-C, and the heat radiating section 1-C is arranged to be located between the plurality of heat receiving sections 1-H. In the figure, broken lines H and C indicate heat receiving means and heat radiating means, respectively. Both ends 1-E of the capillary container 1 are sealed by welding after a predetermined amount of two-phase condensable working fluid is sealed inside the capillary container 1.

[0021]

[Operation] In the thin tube heat pipe configured in this way, the nucleate boiling that occurs in each heat receiving section causes axial vibration in the working fluid in the thin tube container between the heat receiving sections. Vibration causes heat to be transferred from the heat receiving part to the heat radiating part. This principle is described in detail in the operation principle of the loop-type thin tube heat pipe (type without check valve) shown in FIG.
Since it is detailed in No. 461, it will be omitted here. This heat transport by axial vibration of the working fluid is effective for thin tube heat pipes with an outer diameter of 1.6 mm or less and an inner diameter of 1.2 mm or less, and is particularly suitable for ultra-thin tube heat pipes in the micro heat pipe area. This is because the efficiency of heat transport by circulation of the working fluid deteriorates as the diameter becomes smaller due to the increase in pressure loss within the pipe, whereas the efficiency of heat transport by axial vibration deteriorates as the mass of the liquid to be vibrated decreases. This is because it becomes easier to generate vibrations, and as the diameter becomes smaller, the condition becomes better.

The most important feature of the micro heat pipe according to the present invention is that it is extremely easy to inject the working fluid. In other words, in Fig. 1 basic structure diagram, thin tube container 1
Before both terminals 1-E are welded and sealed, liquid-phase working fluid is pressurized from one terminal side, gas inside the pipe is discharged from the other terminal, and when only the liquid-phase working fluid flows out, both terminals 1-E are sealed. Just by sealing the end, impurity gases inside the thin tube container can be discharged very easily, and the full filling of the working fluid is completed. In this case, one terminal can be easily sealed by attaching a valve and closing it. After filling the volume to its full capacity, it is easy to seal one end by carrying out the evaporation method while opening and closing the valve and measuring the weight with a precision weighing scale. The amount of liquid can be precisely adjusted to the optimal amount. This method eliminates the risk of air getting into the pipe,
In addition, since it is possible to precisely adjust the amount of liquid, it is possible to accurately fill liquid even in a microtube heat pipe with an inner diameter of 0.5 mm or less.

Another effect is that the structure eliminates any joints, so it has a greater degree of freedom in use than the conventional two types of loop-type thin tubes, and can be easily attached to any device. Furthermore, the fact that there are no connecting parts means that it is highly resistant to corrosion, and there are no failures caused by poor connections, greatly improving reliability.

A further unique feature of the structure of the micro heat pipe according to the present invention is that the range of the amount of working fluid filled in for good operation is from 10% to 95% of the internal volume, which is extremely wide compared to that of a loop-type thin tube heat pipe. In addition, there is an effect that the difference in performance between the bottom heat mode and the top heat mode is extremely small in the entire range. This is because the working fluid cannot be circulated, and conversely, the energy that contributes to the generation of axial vibrations in nucleate boiling works efficiently, and it operates well even when the amount of sealed liquid is large, and the amplitude decreases when the amount of liquid is small. It is thought that it works well because it is sufficiently large. This point means that performance does not deteriorate even if the accuracy of the liquid volume ratio sealed in the thin tube container is reduced, and the work of filling the working fluid is facilitated.

[0025] In the case of a heat pipe constructed of such ultra-thin tubes, depending on the metal material used, grain boundary separation occurs in metal crystals due to severe temperature cycles over a long period of time, and a large amount of metal powder is generated. It may stay in the bent part of the thin tube container and block it. As a result of experiments, when phosphorus-deoxidized copper is used as the tube material, blockage occurs after about 300 hours of operation at 150°C. When oxygen-free copper was used, no change occurred even after 1000 hours of operation at 270°C.

The structure of the micro heat pipe according to the present invention was devised with the aim of being an ultra-thin heat pipe in the area of micro heat pipes with an inner diameter of 1.2 mm or less in a thin tube container. too,
It can be effectively applied when the length of one turn of the meandering shape is short and the distance between the heat receiving and radiating parts is short.

[0027]

[Example] A long metal thin tube having an outer diameter of 1 mm and an inner diameter of 0.7 mm was formed into an oblong spiral shape with a major axis of 38 mm and a minor axis of 18 mm to produce two meandering spiral thin tube containers having 45 turns. As a heat receiving means, a fin with a height of 13 mm has two semicircular grooves with a radius of 9 mm, and a heat receiving bottom surface of 50 mm x 50 mm.
An aluminum heat sink of mm was prepared. After assembling these by soldering as shown in Fig. 6, a predetermined ratio of HCFC142b to the internal volume is sealed in each capillary container as a working fluid, and both ends of the capillary container are sealed by welding to form a micro-tube according to the present invention. A heat pipe was constructed. In the figure, the capillary container is shown in a diagram for simplicity. In the figure, 1-1, 1-2 are thin tube containers, 1-H-1, 1-H-
2 is a heat receiving part, 1-C-1 and 1-C-2 are heat radiating parts, 1-
E and 1-E are capillary end portions. Further, the arrow C indicates the cooling air of the cooling means.

[0028] Regarding the micro heat pipe of the present invention constructed in this way, the amount of sealed liquid was varied, and the amount of heat applied to the heat receiving part was varied, and the temperature rise of the heat receiving part and the heat transport capacity were measured. The heat transport capacity is calculated using the temperature difference Δt [℃] between the heat sink heat receiving surface temperature and the cooling air temperature as the dividend, and the heat input Q [W]
Thermal resistance value R [℃/W] calculated as the quotient with
compared by. The measurement results in bottom heat mode and top heat mode at a cooling air speed of 3 m/s are shown in Tables 1 and 2 below, respectively.

[0029]

[Table 1]

[0030]

[Table 2]

The measurement results in Tables 1 and 2 clearly show the following. (a) A small heat sink of this size has a thermal resistance value of 0.0 at 50W.
Demonstrating heat dissipation performance of 7° C./W or less is in line with industry requirements. (b) Good performance is shown regardless of the amount of sealed liquid, but the performance is particularly good when the filled liquid amount is 30% to 50%. (c) Even in the top heat mode, performance comparable to that in the bottom heat mode can be obtained.

[0032]

[Effects of the Invention] As explained above, the micro heat pipe according to the present invention facilitates the production of ultra-thin tube heat pipes with an inner diameter of 1.2 mm or less, which is commonly called a micro heat pipe region, and provides a high-performance compact radiator. It makes it easier. Furthermore, unlike various conventional heat pipes, the micro heat pipe of the present invention does not deteriorate in performance in the top heat mode, so a small heat radiator using the micro heat pipe can be safely installed in equipment that undergoes rapid changes in posture. Furthermore, since the amount of liquid enclosed is extremely small, sufficient strength against centrifugal force and impact can be obtained. Furthermore, since the container does not have any welded parts, it is possible to construct a compact heat radiator that requires high reliability.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the basic structure of a micro heat pipe of the present invention.

FIG. 2 is a partially sectional plan view showing the basic structure of a loop-type capillary heat pipe that transports heat by circulating a working fluid.

FIG. 3 is a partially sectional plan view showing the structure of a loop-type capillary heat pipe that transports heat mainly by axial vibration of a working fluid.

FIG. 4 is an explanatory diagram showing connection welds for assembling the loop-type capillary heat pipe of FIG. 2;

FIG. 5 is an explanatory diagram showing connection welds for assembling the loop-type capillary heat pipe of FIG. 3;

FIG. 6 is a schematic perspective view showing the structure of a small heat radiator according to an applied embodiment of the micro heat pipe of the present invention.

[Explanation of symbols]

1 Thin tube container 1-H Heat receiving section 1-C Heat radiation section 1-E Thin tube end sealing section 2 Loop type thin tube container 3 Circulation direction regulating means (check valve) 4
Working fluid 5 Steam bubble H Heat receiving means C Heat radiating means H-S Heat receiving heat sink

Claims (3)

[Claims] Claim 1: A sealed capillary container has a sufficiently small inner diameter so that a predetermined two-phase condensable working fluid sealed under vacuum can move inside the container in a constantly filled and closed state due to its surface tension. A plurality of predetermined portions thereof are configured as a heat receiving portion and a plurality of other predetermined portions are configured as a heat dissipation portion.
A micro heat pipe characterized in that the heat radiating section is configured to be located between the plurality of heat receiving sections. 2. A sealed capillary container is a capillary container in which a long metal capillary is formed into either a meandering shape with many turns or a spiral shape, and both ends of the tube are hermetically sealed; 2. The micro heat pipe according to claim 1, wherein each predetermined portion of each turn is configured as one or more heat receiving parts and one or more heat radiating parts. [Claim 3] The long metal thin tube has an inner diameter of 1.2 mm.
2. The micro heat pipe according to claim 1, wherein the metal capillary is an oxygen-free copper capillary.