WO2012049752A1

WO2012049752A1 - Loop-shaped heat pipe and electronic device

Info

Publication number: WO2012049752A1
Application number: PCT/JP2010/068041
Authority: WO
Inventors: 内田　浩基
Original assignee: 富士通株式会社
Priority date: 2010-10-14
Filing date: 2010-10-14
Publication date: 2012-04-19
Also published as: JPWO2012049752A1; JP5637216B2; CN103080689A; CN103080689B; US20130160974A1

Abstract

An evaporator (110) of a loop-shaped heat pipe comprises: a case (121, 122) which is provided with a fluid inlet and a steam outlet; and at least one porous body (130) which is arranged in the case and through which a liquid-phase working fluid is introduced onto the inner surface of the case. The evaporator (110) additionally comprises a liquid supply tube (140) which is arranged in the case (121, 122) and through which the working fluid is introduced from the fluid inlet to the at least one porous body (130). The liquid supply tube (140) comprises a material having a lower heat conductivity than that of a material that constitutes the case (121, 122). The vaporization of the working fluid that flows into the evaporator (110) can be prevented before the working fluid reaches the porous body (130), and therefore the steady circulation of the working fluid can be achieved.

Description

Loop heat pipe and electronic equipment

The present invention relates to a loop heat pipe and an electronic device.

A loop heat pipe is known as a device for cooling various heating elements. The loop heat pipe includes an evaporator that vaporizes the working fluid (liquid-phase working fluid) with heat from the heating element, and a condenser that condenses the vaporized working fluid (gas-phase working fluid) by heat dissipation, It has a configuration in which a steam pipe and a liquid pipe are connected in a loop. The evaporator removes heat from the heating element as the heat of vaporization of the working fluid, and also serves as a pump that drives the circulation of the working fluid.

The structure of a typical evaporator 1 is shown in FIGS. 1A-1C. FIG. 1A schematically shows a cross-sectional view of the evaporator 1 when viewed along the flow of the working fluid from the liquid pipe to the vapor pipe. 1B and 1C schematically show the AA ′ cross section of FIG. 1A for two typical evaporator structures that can be classified as cylindrical and flat, respectively.

The evaporator 10 has a metal case 20 connected to the liquid pipe 50 and the vapor pipe 55 and a porous body 30 called a wick disposed in the metal case 20. The hydraulic fluid 60a from the liquid pipe 50 flows into the liquid supply passage 31 located substantially at the center of the wick 30, and is guided to the inner wall of the metal case 20 by the capillary force of the pores in the wick 30 that is the driving force of the working fluid. It is burned. The hydraulic fluid 60a is further vaporized by the heat transmitted from the heating element to the metal case 20 to become the vapor 60b, and the vapor discharge groove (groove) 32 formed in the outer peripheral portion of the wick 30 or the inner wall of the metal case 20 is formed. It passes through and is discharged to the steam pipe 55.

In recent years, it has been studied to apply a loop heat pipe to cool electronic components such as a central processing unit (CPU) of a computer. Many electronic components have a flat heat radiation surface, as represented by an LSI package. In order to improve the adhesion between the heat radiating surface and the evaporator case 20, in the case of the cylindrical evaporator 10 ′, a flat plate portion 28 serving as a heat receiving surface is added to the case 20 as shown in FIG. 1B. On the other hand, in the case of the flat evaporator 10 ″, as shown in FIG. 1C, one surface 29 of the generally rectangular parallelepiped case 20 can be used as a heat receiving surface.

In order to improve the cooling performance of the loop heat pipe, it is effective to increase the internal volume of the evaporator. On the other hand, in order to reduce the size and weight of electronic equipment, it is necessary to make the evaporator as compact as possible. In order to increase the internal volume with a small size, particularly a thin shape, a flat plate evaporator as shown in FIG. 1C is considered preferable. In order to improve the cooling performance, it is also effective to manufacture the evaporator case with a metal, particularly, a high heat conductive metal such as copper. This is because heat is easily transferred from the heating element to the entire outer periphery of the wick, and vaporization of the working fluid is promoted. The metal case is also preferable from the viewpoint of airtight performance reliability that prevents leakage of the working fluid enclosed in the case.

However, the miniaturization of the evaporator can cause problems as shown in FIG. When heat is transferred from the heating element 70 to a portion of the evaporator case 20 adjacent to the liquid pipe 50, the working fluid 60a is heated before flowing into the liquid pipe 50 and reaching the wick 30, and boils in the portion. Thus, the bubble 60c can be generated. As shown in the enlarged schematic diagram in FIG. 2, the bubble 60 c that has entered the liquid supply passage 31 in the wick 30 generates a gas phase on both sides of the wick 30, thereby causing the normal direction toward the outer peripheral side of the wick 30. A surface tension 36 that cancels the surface tension 35 is generated. The cancellation of the surface tension means that the capillary force of the wick 30 does not work. In addition, the generation of the bubble 60c can increase the pressure in the liquid supply passage 31 and inhibit the inflow of the working fluid 60a from the liquid pipe 50. Therefore, the circulation of the working fluid is attenuated or stopped, and as a result, the cooling performance of the loop heat pipe is deteriorated and / or unstable operation is caused. This problem may be easily caused by the use of a flat plate evaporator that can use a part of the case itself as a heat receiving surface and / or the use of a metal case having a high thermal conductivity in addition to the miniaturization of the evaporator.

In relation to such problems, the end face part through which the liquid pipe passes in the case of the cylindrical evaporator is changed to metal or resin having a relatively low thermal conductivity, and the heat of the case is not directly transmitted to the liquid pipe. Techniques for doing so have been proposed. However, when the material of the evaporator case is resin, pressure resistance and long-term hermetic reliability are problems. In addition, when using a metal with low thermal conductivity, even such a metal has a thermal conductivity several tens to several hundred times that of a resin, so sufficient heat insulation cannot be obtained, and cooling performance is sufficiently lowered. Can not be suppressed.

JP 2004-218887 A JP 2009-115396 A Japanese Patent No. 3591339

Therefore, there is still a demand for a technique that can prevent the hydraulic fluid from vaporizing before reaching the wick and prevent the cooling performance of the loop heat pipe from decreasing and / or unstable operation.

According to one aspect, an evaporator of a loop heat pipe includes a case having a liquid inlet and a vapor outlet, and at least one porous member disposed in the case and guiding a liquid-phase working fluid to an inner surface of the case. Including body. The evaporator further includes a liquid supply pipe disposed in the case and guiding the working liquid from the liquid inlet into the at least one porous body. The liquid supply pipe has a material having a lower thermal conductivity than the material of the case.

According to another aspect, an electronic device including such a loop heat pipe and an electronic component thermally coupled to the evaporator is provided.

The heat transfer from the evaporator case to the working fluid flowing into the evaporator is suppressed, and the working fluid is prevented from being vaporized before reaching the wick. Therefore, the capillary force of the wick is maintained, and the stable circulation of the working fluid, and thus the efficient cooling of the electronic components in the electronic device is realized.

It is sectional drawing which shows schematically the evaporator which concerns on a prior art. It is sectional drawing which shows schematically the cylindrical evaporator which concerns on a prior art. It is sectional drawing which shows schematically the flat type evaporator which concerns on a prior art. It is sectional drawing which shows typically one problem which the evaporator which concerns on a prior art has. It is a perspective view which shows the component of the evaporator which the loop type heat pipe which concerns on one Embodiment has. It is the perspective view which looked at the manifold of Drawing 3A from another direction. It is sectional drawing which looked at the evaporator obtained from the component shown to FIG. 3A along the flow of the working fluid. It is a figure which shows the BB 'cross section of the evaporator of FIG. 3C. It is a perspective view which shows the component of the evaporator which the loop type heat pipe which concerns on other one Embodiment has. It is sectional drawing which shows the evaporator which the loop type heat pipe which concerns on other one Embodiment has. It is a perspective view which illustrates the electronic device which concerns on one Embodiment. FIG. 6B is a cross-sectional view taken along the line CC ′ of FIG. 6A. FIG. 6B is a cross-sectional view showing a cross section along DD ′ of FIG. 6A. It is typical sectional drawing which shows the structure of some Examples. It is a graph which shows the evaluation result of the structure shown in FIG.

110, 210, 310, 410

Evaporator

120, 320, 420, 520

Evaporator case

121, 221, 321, 521 First part of

case

122, 222, 322, 522 Second part of

case

130, 230, 330, 530 Porous body (wick)
140, 240, 340, 440, 540 Liquid supply pipe (140 Manifold)
142, 242, 542

Inner pipe

150, 250, 350, 450

Liquid pipe

155, 255, 355, 455

Steam pipe

160a, 360a, 460a Hydraulic fluid 400 Electronic equipment 405 Loop heat pipe 461 Condenser 463

Reservoir tank

470, 570 Electron Components 475 Wiring board

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In the drawings, various components are not necessarily drawn to the same scale. Further, the same or corresponding components are denoted by the same or similar reference numerals throughout the drawings.

First, an evaporator 110 included in a loop heat pipe according to an embodiment will be described with reference to FIGS. 3A to 3D. 3A shows the main components of the evaporator 110 in an exploded view, and FIG. 3B shows the manifold 140 shown in FIG. 3A from another direction. 3C is a cross-sectional view of the evaporator 110 obtained from the components shown in FIG. 3A when viewed along the flow of the working fluid, and FIG. 3D shows a BB ′ cross section of FIG. 3C. ing. It should be noted that FIG. 3C is not a cross-sectional view when the evaporator 110 is cut along one plane.

In the illustrated example, the evaporator 110 is a flat plate evaporator. The evaporator 110 includes a first case part 121 that communicates with the steam pipe 155 at the steam outlet 126, a second case part 122 that communicates with the liquid pipe 150 at the liquid inlet 125, and two porous bodies (wicks). ) 130 and a branch pipe (manifold) 140. The first and

second case parts

121 and 122 are connected to each other to form one evaporator case 120 that houses the wick 130 and the manifold 140. The planar dimension (dimension of the heat receiving surface) of the evaporator case 120 is determined based on the size of the heating element to be cooled. The thickness of the evaporator case 120 may be limited according to the mounting density in the electronic device. For example, when it is applied to an electronic device mounted with high density such as a server or a personal computer (PC), a thickness of about 10 mm or less may be required.

The first case part 121 has two hole parts 123 for accommodating the two wicks 130 when viewed from the second case part 122 side. The shape of the hole 123 is determined according to the outer shape of the wick 130 to be inserted, and is typically circular or elliptical. A separation wall 124 that connects the bottom surface and the top surface of the first case portion 121 exists between the two hole portions 123. The second case portion 122 can accommodate the manifold 140. However, in the present embodiment, how the evaporator case 120 is divided into two parts is not particularly limited as long as it can be connected after the wick 130 and the manifold 140 are accommodated. For example, one case portion may accommodate both the wick 130 and the manifold 140, and the other case portion may have a plate shape corresponding to one end face of the evaporator case 120. Further, the first and second case portions can be divided in the thickness direction of the flat plate evaporator 120.

Each wick 130 is generally cup-shaped, and has a cavity serving as a liquid supply passage 131 for supplying a working fluid to the wick on the inner periphery. Each wick 130 also has a plurality of steam discharge grooves (grooves) 132 on the outer periphery. The groove 132 may be formed over the entire length of the wick along the flow direction of the working fluid, in which case the end of the groove 132 on the liquid tube 150 side may be terminated by a manifold 140, as shown in FIG. 3C. In FIG. 3C, the wick 130 and the case 120 are not in contact with each other because the cross section where the groove 132 exists is shown, but the wick 130 and the case 120 are in contact with each other in the cross section where the groove 132 does not exist. . The wick 130 is preferably a resin wick, as will be described later, and is molded to have a size larger than the inner dimension of the hole 123 so as to be compressed when inserted into the hole 123 of the first case portion. . Thereby, the adhesion between the outer surface of the resin wick 130 and the inner wall of the evaporator case 120 can be enhanced, and the evaporation of the hydraulic fluid at the contact portion between the wick 130 and the case 120 can be promoted.

In order to obtain a sufficiently large capillary force, the average pore diameter of the wick 130 is preferably 15 μm or less, more preferably 5 μm or less. The porosity is preferably increased so that the hydraulic fluid does not run short at the contact portion between the wick 130 and the case 120, and is, for example, in the range of 30% or more and less than 90%.

As will be described in detail later, the manifold 140 insulates the hydraulic fluid 160a flowing from the liquid pipe 150 from the case 120 and acts as a liquid supply pipe that supplies the hydraulic fluid 160a to each wick 130. The manifold 140 has an inlet 143 provided corresponding to the liquid inlet 125 of the case 120 and two outlets 144 (FIG. 3B) for supplying hydraulic fluid to the two wicks 130. 145 inside (FIG. 3D).

The manifold 140 is preferably molded so as to come into contact with the wick 130 when accommodated in the case 120 so that the hydraulic fluid 160a from the liquid pipe 150 does not touch the case 120 before reaching the wick 130. However, if most of the space between the liquid inlet 125 of the case and the wick accommodating portion is covered with the manifold 140, boiling of the working fluid 160a before reaching the wick can be prevented. Thus, it may be allowed that a gap exists between the manifold 140 and the wick 130.

The manifold 140 has a tubular portion (inner pipe) 142 extending into the liquid pipe 150 in addition to the main body 141 arranged in the case 120 as shown in the drawing as needed. Preferably, the inner pipe 142 is formed in close contact with the inner wall of the liquid pipe 150 so that the hydraulic fluid 160a does not enter between the inner pipe 142 and the inner wall of the liquid pipe 150. The inner pipe 142 is preferably formed integrally with the main body 141.

The evaporator case 120 including the first and

second case parts

121 and 122 preferably includes a metal or an alloy in order to ensure strength and airtight reliability. The first and

second case parts

121 and 122 are joined to each other using any of various methods capable of ensuring airtight reliability, such as welding, brazing, or resin bonding. Sealed.

The evaporator case 120 also preferably includes a highly thermally conductive metal or alloy, such as oxygen-free copper, copper alloy, aluminum, or aluminum alloy, for transferring heat from the heating element to be cooled to the entire case. However, the evaporator case 120 is a metal or alloy having a relatively low thermal conductivity, such as an iron-based alloy such as stainless steel or a titanium alloy, depending on its size and / or required cooling capacity. Is also possible.

The material of the manifold 140 is selected from materials having a lower thermal conductivity than the evaporator case 120 so as to obtain a heat insulating effect. The lower the thermal conductivity of the manifold 140, the better. However, if it is 1 W / mK or less, a significant heat insulating effect can be obtained. The thermal conductivity of 1 W / mK or less is, for example, about 380 W / mK in the case of copper and about 16 W / mK in the case of stainless steel. A significant temperature difference can be created between the outer and inner walls. Therefore, the hydraulic fluid 160 a that has flowed into the case 120 is effectively insulated from the case 120, and is prevented from being vaporized before reaching the wick 130.

For example, the manifold 140 may have a resin such as a fluororesin, a nylon resin, a PEEK (polyether ether ketone) resin, a polypropylene resin, or a polyacetal resin. As an example, the thermal conductivity of MC nylon is about 0.2 W / mK, about 1/1900 of copper, and about 1/80 of stainless steel, so that a heat insulation effect can be obtained even with a thickness of 1 mm to several mm, for example. . The manifold 140 may have a porous body of resin as described above.

The wick 130 may be selected from various porous materials such as a metal wick, a carbon wick, or a resin wick, but may preferably be a resin wick. Resin wicks have the advantage of low thermal conductivity compared to other wicks, in addition to being easy to ensure adhesion to case 120. If a wick with high thermal conductivity is used, heat is transferred to the inner periphery of the wick, and bubbles are generated there, which may have the same effect as the generation of bubbles before reaching the wick. Generation of bubbles on the inner peripheral side can be prevented. Suitable materials for the resin wick include, for example, fluororesin, PEEK (polyether ether ketone) resin, polypropylene resin, polyacetal resin, and the like.

The wick 130 and at least a part of the manifold 140 may be formed of the same porous resin. In this case, for example, the wick 130 and the at least part of the manifold 140 can be integrally molded, and the remaining part of the manifold 140 can be made into a simple structure that can be easily processed.

According to the above configuration, for example, even in the case of a small flat plate evaporator, generation of bubbles due to vaporization of the hydraulic fluid before reaching the wick is suppressed or prevented, and the operation of the loop heat pipe is stabilized. Cooling performance can be maintained.

The evaporator 110 shown in FIGS. 3A-3D includes two wicks 130, but the number of wicks can be three or more. Depending on the number of wicks, the number of outlets 144 of the manifold 140 and the internal branch structure are changed.

Also, an evaporator including a single wick can be provided with a liquid supply pipe having a low thermal conductivity material corresponding to the manifold. FIG. 4 shows a loop heat pipe evaporator 210 according to another embodiment including such a single wick. In the following description of the evaporator 210, details common to the evaporator 110 shown in FIGS. 3A to 3D will not be described in detail.

The evaporator 210 includes a first case part 221 that communicates with the steam pipe 255, a second case part 222 that communicates with the liquid pipe 250, a single wick 230, and a liquid supply pipe 240. The first and

second case portions

221 and 222 are connected to each other to form one evaporator case that houses the wick 230 and the liquid supply pipe 240.

The first case part 221 has a hole part 223 for accommodating the wick 230. The second case portion 222 can accommodate the manifold 240. However, in the present embodiment, how the evaporator case is divided into two parts is not particularly limited as long as it can be connected after the wick 230 and the liquid supply pipe 240 are accommodated.

The wick 230 has a cavity serving as a liquid supply passage 231 for supplying hydraulic fluid to the wick, and has a plurality of steam discharge grooves (grooves) 232 on the outer peripheral portion. The groove 232 may be formed over the entire length of the wick 230 along the flow direction of the working fluid.

The liquid supply pipe 240 insulates the hydraulic fluid before reaching the wick from the cases (221, 222) and supplies the hydraulic fluid flowing in from the liquid pipe 250 to the wick 230. The liquid supply pipe 240 may have an inner pipe 242 extending into the liquid pipe 250 in addition to the main body 241 disposed in the case as shown in the drawing, as needed. The main body 241 of the liquid supply pipe may have an outer wall disposed along the inner wall of the case and a cavity surrounded by the outer wall. Alternatively, the liquid supply tube 240 may include one or more piping structures for distributing hydraulic fluid throughout the single wick 230.

The materials of the first case portion 221, the second case portion 222, the wick 230, and the liquid supply pipe 240 may be the same as the materials of the corresponding elements (121, 122, 130, and 140, respectively) described with respect to the evaporator 110. For example, the first and

second case portions

221 and 222 include a metal or an alloy, the wick 230 includes a porous resin, and the liquid supply pipe 240 includes a resin.

Also in the evaporator 210, as in the above-described evaporator 110, the generation of bubbles due to vaporization of the hydraulic fluid before reaching the wick can be suppressed or prevented, and the operation of the loop heat pipe can be stabilized.

However, since the evaporator 210 includes the single wick 230, it is possible to reduce the manufacturing cost by reducing the number of parts and facilitating the processing and / or assembly of the parts. On the other hand, evaporator 110 is configured to include a plurality of wicks 130 and a case hole 123 for housing the wick 130, whereby the contact area between wick 130 and case 120 can be increased. In addition, since the separation wall 124 between the plurality of holes 123 acts as a heat conduction path, the heat received from the heating element is more uniformly transmitted to the entire case. Therefore, the evaporator 110 can be more advantageous than the evaporator 210 from the viewpoint of the cooling performance of the evaporator and therefore the loop heat pipe.

Subsequently, an evaporator 310 included in a loop heat pipe according to another embodiment will be described with reference to FIG. FIG. 5 shows the evaporator 310 in a cross-sectional view similar to FIG. 3C. In the following description of the evaporator 310, details common to the evaporator 110 shown in FIGS. 3A-3D will not be described in detail.

The evaporator 310 includes a first case part 321 communicating with the vapor pipe 355, a second case part 322 communicating with the liquid pipe 350, one or more wicks 330, and a liquid supply pipe 340. The first and

second case portions

321 and 322 are connected to each other to form one evaporator case 320 that houses the wick 330 and the liquid supply pipe 340.

The wick 330 has a cavity serving as a liquid supply passage 331 for supplying the working fluid 360a to the wick, and has a plurality of vapor discharge grooves (grooves) 332 on the outer periphery.

The liquid supply pipe 340 insulates the hydraulic fluid 360 a flowing from the liquid pipe 350 from the case 320 and supplies the hydraulic fluid 360 a to the wick 330. When the evaporator 310 includes a plurality of wicks 330, the liquid supply pipe 340 has a manifold shape. The liquid supply pipe 340 may have an inner pipe (not shown) extending into the liquid pipe 350 as necessary.

The first and

second case portions

321 and 322 may be formed using different materials. The first case portion 321 that accommodates the wick 330 preferably transmits heat from the heating element to be cooled to the entire case portion, and therefore has a high thermal conductivity such as oxygen-free copper, copper alloy, aluminum, or aluminum alloy. Has metal or alloy. The second case portion 322 that accommodates the liquid supply pipe 340 includes a material having a lower thermal conductivity than the material of the first case portion 321. The material of the second case portion 322 is preferably a metal or an alloy from the viewpoint of airtight reliability of the evaporator case 320. For example, the second case portion 322 can include a metal or alloy having a relatively low thermal conductivity, such as an iron-based alloy such as stainless steel, or a titanium alloy.

The portion that divides the evaporator case 320 into the first case portion 321 and the second case portion 322 is preferably substantially coincident with the boundary between the liquid supply pipe 340 and the wick 330. This is to obtain heat conduction to the entire contact portion between the wick 330 and the case 320 and a heat insulating action to the hydraulic fluid 360a before reaching the wick.

The first and

second case portions

321 and 322 are joined to each other using any one of various methods capable of ensuring airtight reliability, such as welding, brazing, or resin bonding.

The materials of the wick 330 and the liquid supply pipe 340 may be the same as the materials of the corresponding elements described with respect to the evaporator 110 (130 and 140, respectively). For example, the wick 330 has a porous resin, and the liquid supply pipe 340 has a resin.

Also in the evaporator 310, as described with respect to the evaporator 110, it is possible to suppress or prevent the generation of bubbles due to vaporization of the hydraulic fluid before reaching the wick, and to stabilize the operation of the loop heat pipe. However, by using a material having lower thermal conductivity than the first case portion 321 for the second case portion 322, the effect of suppressing the vaporization of the hydraulic fluid before reaching the wick is enhanced, and the operation of the loop heat pipe is further stabilized. Can do. In addition, since a highly heat-conductive material can be used for the 1st case part 321, the cooling performance of a loop type heat pipe is not reduced.

Next, an electronic apparatus 400 according to an embodiment will be described with reference to FIGS. 6A-6C. 6B and 6C show an example of attachment of the evaporator to the heating element of the electronic device, respectively, in the CC ′ section and the DD ′ section in FIG. 6A. The cross section DD ′ shown in FIG. 6C passes through substantially the center of one wick and is selected as a cross section that does not include the liquid pipe and the steam pipe.

The electronic apparatus 400 includes an electronic component 470 serving as a heating element and a loop heat pipe 405 that cools the electronic component 470.

The loop heat pipe 405 includes, for example, an evaporator 410 that can be any one of the above-described

evaporators

110, 210, and 310, and a gas-phase working fluid generated by the evaporator 410, and a liquid-phase working fluid ( A condenser 461 for condensing into a working fluid. The condenser 461 is cooled by, for example, sending the air 462 from the blower to the heat dissipating fins or immersing it in a liquid cooled to room temperature or lower. The vapor-phase working fluid is supplied from the evaporator 410 to the condenser 461 through the vapor pipe 455. The working fluid from the condenser 461 is supplied to the evaporator 410 through the liquid pipe 450. The loop heat pipe 405 typically has a reservoir tank 463 in front of the evaporator 410 in the liquid tube 450 for storing a working fluid necessary for activation. The working fluid can be, for example, water, ethanol, R141B, n-pentane, acetone, butane or ammonia.

The heat generating component 470 of the electronic device is a semiconductor device such as a CPU, for example, and is mounted on a wiring substrate 475 such as a mother board of the electronic device. The attachment of the evaporator 410 onto the heat generating component 470 can be performed, for example, by screwing a pressing fitting (not shown) to the wiring board 475 or the like. Between the heat generating component 470 and the evaporator 410, for example, a good heat conductive material 480 such as thermal grease may be disposed. A plurality of heat generating components may be cooled with a single evaporator 410.

As shown in FIG. 6C, the heat generating component 470 may be disposed offset to the vapor pipe side (right side in the drawing) with respect to the evaporator 410. In other words, the evaporator 410 may be mounted on the heat generating component 470 so that the center of the heat generating component 470 is positioned on the steam pipe side from the center of the evaporator case 420. By such an offset, the distance between the heat generating component 470 and the hydraulic fluid before reaching the wick can be increased, and vaporization of the hydraulic fluid 460a before reaching the wick can be suppressed. For example, the evaporator 410 is arranged so that the manifold 440 and the heat generating component 470 do not overlap when there is a dimensional allowance.

Hereinafter, an embodiment in the case of cooling a CPU having a package size of about 30 mm × 30 mm as a heating element will be described.

The evaporator case was divided into two parts, a first part on the vapor side and a second part on the liquid side. The first part was made of oxygen-free copper and the second part was made of oxygen-free copper or stainless steel SUS304. As for the external dimensions of the evaporator case in which the first part and the second part are connected, the planar size is about 40 mm × 40 mm and the thickness is about 8 mm. Such a small and thin size enables mounting on a CPU in a high-density computer such as a server or a personal computer. Two oval holes were provided in parallel inside the first part. The width (major axis) of each hole was about 18 mm, and the height (minor axis) was about 6 mm. A porous resin (resin wick) was inserted into each of the two holes.

The wick was a porous body made of PTFE (polytetrafluoroethylene) having a length of about 30 mm. This resin wick has an average porous diameter of about 2 μm and a porosity of about 40%. Both the thickness and width of the wick were made to be about 100-200 μm larger than the size of the hole in the first portion of the case. Since the porous body made of PTFE has elasticity, the outer wall of the first part of the case and the outer periphery of the wick are brought into close contact with each other by slightly increasing the outer dimension of the wick than the wick insertion hole. Can do. An oval-shaped hole having a height of about 2 mm and a width of about 14 mm was provided in the inner peripheral portion of the resin wick so as to serve as a liquid supply passage for receiving the hydraulic fluid supplied from the liquid pipe through the manifold. A plurality of grooves (grooves) having a depth of 1 mm and a width of 1 mm were formed on the outer periphery of the wick. The working fluid vapor is generated from the surface of the groove, and the generated vapor passes through the groove and is discharged to the vapor pipe.

In the case, a resin manifold made of MC nylon was placed so that no gap was formed between the resin manifold and the resin manifold. This manifold can distribute the hydraulic fluid flowing from the liquid pipe to the two resin wicks without leaking out from the manifold. That is, the hydraulic fluid that has flowed into the evaporator is introduced into the resin wick through the resin manifold without touching the metal evaporator case. Therefore, heat transfer from the metal case to the working fluid is suppressed, and generation of bubbles can be prevented. The thickness of the wall surface of the resin manifold was about 1 mm. MC nylon has a thermal conductivity of 0.2 W / mK, which is tens to thousands of that of copper (380 W / mK) and SUS304 (16 W / mK). The effect is obtained.

Also, in some examples, the heat insulating resin of the manifold was extended to the liquid pipe side and inserted as an inner pipe inside the liquid pipe.

The assembly of the evaporator is completed by inserting a resin wick and a resin manifold into the first part and the second part of the case and sealing the first part and the second part. This sealing was performed here by laser welding.

After assembling the evaporator in this way, the evaporator, the steam pipe, the condensing part provided with the heat dissipating fins, and the liquid pipe were connected in an annular shape by welding, and the working fluid was sealed inside. As an example, a copper pipe having an outer diameter of about 4 mm and an inner diameter of about 3 mm can be used for the steam pipe and the liquid pipe. The total length of the copper pipe can be, for example, about 900 mm. Here, n-pentane was used as the working fluid. The condenser was cooled by sending air from the blower to the heat dissipating fins of the condenser.

Then, the evaporator was thermally coupled to the CPU via thermal grease (for example, W4500 manufactured by Cosmo Oil Co., Ltd.). Here, the evaporator was fixed on the CPU by screwing the pressing metal. At this time, in order to increase the distance between the hydraulic fluid flowing into the evaporator and the CPU, the center of the CPU was offset to the steam pipe side with respect to the center of the evaporator case.

The operation of the loop heat pipe configured as described above was verified by experiment. FIG. 7 shows configurations (a) to (c) whose operation has been verified.

The evaporator 510 of the configuration (a) is obtained by installing a PTFE wick 530 and an MC nylon manifold 540 inside a metal case 520 in which both the first portion 521 and the second portion 522 are made of oxygen-free copper. is there. The evaporator 510 ′ of the configuration (b) is configured such that the MC nylon manifold 540 of the configuration (a) is additionally a manifold 540 ′ in which an MC nylon inner pipe 542 is integrally formed. A 20 mm long MC nylon pipe 542 (outer diameter φ4 mm, inner diameter φ3 mm) was inserted into the tip of the liquid tube (outer diameter φ5 mm, inner diameter φ4 mm). The evaporator 510 "of the configuration (c) is obtained by changing the case 520 of the configuration (a) to a case 520" that is manufactured by using SUS304 instead of oxygen-free copper in the second part 522 ". The second portion 522 ″ made of SUS304 of the case 520 ″ was a portion of about 8 mm out of the total length of 40 mm.

The offset amount between the CPU 570 and the

evaporators

510, 510 ′, and 510 ″ is about 4 mm for all of the configurations (a) to (c). The case second portion 522 "is not overlapped.

For comparison, configurations (d) and (e) (both not shown) that do not use a resin manifold were prepared. In the configurations (d) and (e), the resin manifold 540 is simply removed from the configurations (a) and (c), respectively.

The operation of the loop heat pipe and the measurement of the heat transport resistance were measured under the same conditions for these configurations (a) to (e), using the heat generation amount of the CPU as a parameter (FIG. 8). The heat transport resistance was calculated by dividing a temperature difference obtained by subtracting the average temperature of the condenser (average value of the inlet temperature and the outlet temperature) from the temperature of the heat receiving surface of the evaporator by the CPU heating value.

In the comparative configurations (d) and (e) that do not have a resin manifold, the working fluid is boiled and vaporized in the vicinity of the evaporator portion where the working fluid flows by connecting the liquid pipe, and the circulation of the working fluid is not stable, The loop heat pipe did not operate normally.

On the other hand, in the configurations (a) to (c) having the resin manifold, stable working fluid circulation was obtained, and the loop heat pipe was able to operate normally. FIG. 8 shows the evaluation results of the heat transport resistance of each of the configurations (a) to (c). From the results shown in FIG. 8 and the comparison configurations (d) and (e) failing to operate normally, it is understood that the low thermal conductivity manifold greatly contributes to stabilization of the operation of the loop heat pipe. . Further, the combination of the manifold and the inner pipe (configuration (b)) and the combination of the manifold and the second case portion having a relatively low thermal conductivity (configuration (c)) further improve the cooling performance of the loop heat pipe. It is understood that These results mean that the loop heat pipe evaporator can be further reduced in size and thickness, and in the cooling design of high heat generation electronic components mounted on electronic devices such as high-density mounting computers, Design freedom can be increased.

Further, for example, the configurations having a metal case as the evaporator case, such as the configurations (a) to (c) described here, are excellent in pressure resistance and can prevent long-term leakage of the working fluid. A highly reliable cooling system can be provided.

As mentioned above, although embodiment was explained in full detail, this invention is not limited to specific embodiment, A various deformation | transformation and change are possible within the range of the summary described in the claim. For example, the embodiment of the flat plate evaporator has been described here, but in other evaporators such as a cylindrical evaporator, one or a plurality of liquid evaporators may be provided via a low thermal conductivity liquid supply pipe as necessary. A hydraulic fluid may be supplied to the wick.

Claims

A loop heat pipe having a liquid pipe, an evaporator, a steam pipe and a condenser connected to circulate the working fluid,
The evaporator is
A case having a liquid inlet and a vapor outlet;
At least one porous body disposed in the case and guiding a liquid-phase working fluid to the inner surface of the case;
A liquid supply pipe disposed in the case for guiding the liquid-phase working fluid from the liquid inlet into the at least one porous body;
The liquid supply pipe has a material having a lower thermal conductivity than the material of the case;
A loop-type heat pipe.
2. The loop heat pipe according to claim 1, wherein the case includes a metal or an alloy, and the liquid supply pipe includes a material having a thermal conductivity of 1 W / mK or less.
The loop heat pipe according to claim 1 or 2, wherein the case includes a metal or an alloy, and the liquid supply pipe includes a resin.
The loop heat pipe according to claim 3, wherein the liquid supply pipe has a material selected from the group consisting of a fluororesin, a nylon resin, a polyetheretherketone resin, a polypropylene resin and a polyacetal resin.
The loop heat pipe according to any one of claims 1 to 4, wherein the porous body includes a porous resin.
The loop heat pipe according to claim 5, wherein the porous resin is a porous resin made of a material selected from the group consisting of a fluororesin, a polyetheretherketone resin, a polypropylene resin, and a polyacetal resin.
The loop heat pipe according to claim 5 or 6, wherein the porous body and the liquid supply pipe have a porous resin containing the same resin.
The loop heat pipe according to any one of claims 1 to 7, wherein the liquid supply pipe extends without interruption from the liquid inlet to the at least one porous body.
The loop heat pipe according to any one of claims 1 to 8, wherein the liquid supply pipe has a tubular portion extending into the liquid pipe.
The loop heat pipe according to claim 9, wherein the tubular portion is in close contact with an inner wall of the liquid tube.
The at least one porous body has a plurality of porous bodies;
The liquid supply pipe is a manifold that distributes the liquid-phase working fluid to the plurality of porous bodies.
The loop heat pipe according to any one of claims 1 to 10, wherein
The porous body has a steam discharge groove over the entire length from the liquid pipe side to the steam pipe side on the outer periphery, and the end of the steam discharge groove on the liquid pipe side is terminated by a wall surface of the manifold. The loop heat pipe according to any one of claims 1 to 11, wherein
The loop heat pipe according to any one of claims 1 to 12, wherein the outer shape of the case is a flat plate shape.
The case includes a first part that contacts the porous body, and a second part that is located on the liquid supply port side and that accommodates at least a part of the liquid supply pipe.
The second portion includes a material having a lower thermal conductivity than the material of the first portion.
The loop type heat pipe according to any one of claims 1 to 13, wherein the heat pipe is a loop type heat pipe.
The loop heat pipe according to claim 14, wherein the first portion includes a material selected from the group consisting of oxygen-free copper, copper alloy, aluminum, and aluminum alloy.
The loop heat pipe according to claim 14 or 15, wherein the second portion includes a material selected from the group consisting of an iron-based alloy and a titanium alloy.
A loop heat pipe according to claim 1;
And an electronic component thermally coupled to the evaporator of the loop heat pipe.
The center of the electronic component is offset to the opposite side of the liquid inlet with respect to the center of the case at a joint surface between the electronic component and the case of the evaporator. Item 18. The electronic device according to Item 17.
The case of the evaporator includes a first part that comes into contact with the porous body, and a second part that is located on the liquid supply port side and includes a material having a lower thermal conductivity than the material of the first part. Have
The electronic component is bonded to the first portion;
The electronic apparatus according to claim 18, wherein