WO2011121819A1

WO2011121819A1 - Loop heat pipe

Info

Publication number: WO2011121819A1
Application number: PCT/JP2010/066329
Authority: WO
Inventors: 内田　浩基; 塩賀　健司; 重憲青木; 晋尾形; 秀明長岡
Original assignee: 富士通株式会社
Priority date: 2010-03-29
Filing date: 2010-09-21
Publication date: 2011-10-06
Also published as: US20120312506A1; JP2013231597A; JPWO2011121819A1; CN102792119A

Abstract

Disclosed is a loop heat pipe which provides stable cooling performance during operation by maintaining thermal contact between an evaporator case and a wick even when a working fluid is at a high temperature and high pressure. The loop heat pipe includes an evaporator for evaporating the working fluid with heat from a heat-generating element and a condenser for condensing the evaporated working fluid, the evaporator and the condenser being coupled to each other in a loop via a coupling pipe. The evaporator has a first space and a second space. The first space has a contact surface with the heat-generating element and evaporates the working fluid fed through the coupling pipe, and the second space is provided on at least one of those surfaces that define the first space and are other than the contact surface. The evaporator is constructed to have a communication hole in the division wall that separates the first and second spaces from each other, the communication hole communicating between the first space and the second space.

Description

Loop type heat pipe

The present invention relates to a loop heat pipe used for cooling electronic devices and the like.

As a device for cooling various heating elements, an evaporator for vaporizing the working fluid (working fluid in a liquid state) with heat from the heating element, a condenser for condensing the vaporized working fluid by heat dissipation, and There is known a loop heat pipe in which a steam pipe and a liquid pipe are connected in a loop shape (see, for example, Patent Document 1).

1A to 1C are diagrams showing the structure of a conventional evaporator 1000. FIG. 1A is a cross-sectional view in the direction in which the working fluid flows, and FIGS. 1B and 1C are cross-sectional views along AA ′. Many of the heating elements 1010 such as electronic components are planar. Therefore, the heat receiving surface 1002 is a flat type so that the evaporator 1000 of the loop heat pipe is also in close contact with the heating element 1010. In order to improve the cooling performance of the loop type heat pipe, it is necessary to increase the internal volume of the evaporator 1000 as much as possible, but there is also a demand to make the outer shape as compact as possible, so a flat plate type heat pipe that satisfies both requirements is used. It is done.

In order to efficiently cool the heating element 1010 during operation (heating), it is necessary to efficiently evaporate the working liquid 1006 supplied from the liquid pipe 1003 to the evaporator 1000. Therefore, it is necessary to thermally adhere the evaporator case 1001 and the wick 1007 to efficiently transfer the heat from the evaporator case 1001 to the wick 1007 and to quickly vaporize the working fluid 1006 impregnated in the wick 1007. . The evaporated and vaporized working fluid is guided to the steam pipe 1004 through the groove 1005 formed in the wick 1007. However, when the evaporator 1000 is heated and the internal working fluid becomes high temperature, the adhesion between the evaporator case 1001 and the wick 1007 may decrease. This is shown in FIG. 1C.

1C, when the saturated vapor pressure of the working fluid exceeds the atmospheric pressure under the operating temperature of the loop heat pipe, the wall surface of the evaporator case 1001 is pressed to the outside by the internal pressure of the working fluid. Specifically, when a loop heat pipe is used at room temperature and normal pressure, an evaporator is used when a working fluid having a boiling point at room temperature or higher (eg, pentane, R141B, butane, ammonia, etc.) under atmospheric pressure is used. The case 1001 is deformed. If the shape of the evaporator is cylindrical, the internal pressure is dispersed in the circumferential direction and the expansion of the evaporator case is small. However, in the case of a flat plate heat pipe as shown in FIG. The case wall surface expands. In particular, in the case of a flat plate type evaporator due to demands for downsizing and weight reduction of electronic equipment, the evaporator body 1001 has sufficient rigidity to withstand internal pressure in order to make the evaporator body as thin as possible. It is difficult to ensure the thickness. When the evaporator case 1001 expands due to internal pressure, the adhesiveness between the contact surface of the evaporator case 1001 and the internal wick 1007 (particularly, the upper surface of the evaporator case 1001 rather than the lower surface fixed to the heating element 1010 such as a CPU). Gets worse. At a higher temperature, a gap 1020 is generated between the evaporator case 1001 and the wick 1007. In this state, heat is not transferred from the evaporator case 1001 to the wick 1007, and a problem arises that the working fluid cannot evaporate from the surface of the wick 1007 and the cooling performance deteriorates.

JP 2004-218887 A

Therefore, the present invention maintains the thermal contact between the evaporator case and the wick even when the working fluid inside the evaporator becomes high temperature and high pressure during the operation of the loop heat pipe. It is an object to provide a loop heat pipe that realizes stable cooling performance.

In order to achieve the above object, according to one aspect of the present invention, an evaporator that vaporizes a working fluid by heat from a heating element and a condenser that condenses the gasified working fluid are looped with a connecting pipe. In the connected loop heat pipe, the evaporator is
A first space having a contact surface with the heating element and evaporating the working fluid supplied from the connecting pipe;
A second space provided on at least one surface other than the contact surface among the surfaces constituting the first space;
The partition wall that separates the first space and the second space is provided with a communication hole that communicates the first space and the second space.

In another aspect of the present invention, in a loop heat pipe in which an evaporator that vaporizes the working fluid with heat from the heating element and a condenser that condenses the gasified working fluid are connected in a loop with a connecting pipe, The evaporator
A first space having a contact surface with the heating element and evaporating the working fluid supplied from the liquid pipe;
A second space which is provided on at least one surface other than the contact surface among the surfaces constituting the first space and seals a second fluid having a higher saturated vapor pressure than the working fluid at the same temperature. The configuration.

With the above-described configuration, even when the working fluid inside the evaporator becomes high temperature and high pressure during the operation of the loop heat pipe, the adhesion between the evaporator case and the wick is maintained well, and stable cooling performance is realized. be able to.

It is a figure which shows the structure of the conventional flat type evaporator used with a loop type heat pipe, and is sectional drawing along the direction through which a working fluid flows. FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. 1A, showing a state when operation is stopped. It is AA 'sectional drawing of FIG. 1A, and is a figure for demonstrating the problem at the time of the heating in the conventional flat evaporator. It is a figure showing the whole loop type heat pipe composition to which the present invention is applied. It is a figure which shows the structure of the evaporator of 1st Example, and is sectional drawing along the direction through which a working fluid flows. FIG. 3B is a sectional view taken along line AA ′ of FIG. 3A. It is a graph of the temperature-saturated vapor pressure curve of each working fluid. It is a schematic diagram for demonstrating the effect of 1st Example, and is a figure which shows the evaporator state at the time of operation stop. It is a schematic diagram for demonstrating the effect of 1st Example, and is a figure which shows the state of the evaporator at the time of a heating. It is a schematic sectional drawing which shows the example of mounting of the evaporator of 1st Example. It is a perspective view of the example of mounting of the evaporator of Drawing 6A. It is a graph which shows the effect of the loop type heat pipe using the evaporator of the 1st example. It is a figure which shows the modification 1 of the evaporator of 1st Example, and is a figure which shows the state of the evaporator at the time of operation stop. It is a figure which shows the state of the evaporator at the time of the heating in the modification 1 of FIG. 8A. It is a figure which shows the modification 2 of the evaporator of 1st Example, and is a figure which shows the state of the evaporator at the time of operation stop. It is a figure which shows the state of the evaporator at the time of the heating in the modification 2 of FIG. 9A. It is a figure which shows the structure of the evaporator of 2nd Example, and is sectional drawing along the direction through which a working fluid flows. FIG. 10B is a cross-sectional view taken along the line AA ′ of FIG. 10A. It is a schematic diagram for demonstrating the effect of 2nd Example, and is a figure which shows the state of the evaporator at the time of operation | movement stop. It is a schematic diagram for demonstrating the effect of 2nd Example, and is a figure which shows the state of the evaporator at the time of a heating. It is a figure which shows the modification 1 of 2nd Example, and is a figure which shows the state of the evaporator at the time of operation | movement stop. It is a figure which shows the state at the time of the heating in the modification 1 of FIG. 12A. It is a schematic sectional drawing which shows the example of mounting of the evaporator of 2nd Example. It is a perspective view which shows the example of mounting of the evaporator of FIG. 13A. It is a graph which shows the effect of the loop type heat pipe using the evaporator of the 2nd example.

FIG. 2 is a diagram showing an overall configuration of a loop heat pipe 1 to which the present invention is applied. The loop heat pipe 1 includes an evaporator 10 for vaporizing a working fluid in a liquid state by heat from a heating element (electronic component or the like), and a condenser 11 for condensing the working fluid in a gas state by heat dissipation. Are connected in a loop by a vapor pipe 14 for supplying the working fluid from the evaporator 10 to the condenser 11 and a liquid pipe 13 for supplying the working fluid from the condenser 11 to the evaporator 10. It is. The liquid pipe 13 and the vapor pipe 14 are combined to form a connecting pipe. In the example of FIG. 2, a cooling fan 12 is provided in the vicinity of the condensing unit 11 to promote cooling.

Note that the fluid inside the steam pipe 14 and the liquid pipe 13 is not necessarily 100% steam or 100% liquid, and both are mixed phase flows. When the loop heat pipe 1 is operating, most of the inside of the steam pipe 14 is steam, and most of the inside of the liquid pipe 13 is liquid. Therefore, for convenience, “steam pipe”, “liquid pipe” Called.

3A and 3B are diagrams showing the configuration of the evaporator 10 of the first embodiment. 3A is a cross-sectional view along the direction in which the working fluid flows, and FIG. 3B is a cross-sectional view along the line AA ′ in FIG. 3A. In the first embodiment, the evaporator 10 has an evaporation chamber (first space) 40A having a liquid supply passage 46 and a pressure adjustment chamber (second space) 40B for adjusting the pressure of the evaporation chamber, and evaporates. A pressure adjusting hole 55 that connects the evaporation chamber 40A and the pressure adjusting chamber 40B is formed in the partition wall 51 that partitions the chamber 40A and the pressure adjusting chamber 40B.

3A and 3B, the bottom surface of the evaporator case 40 is the heat receiving surface 42. The evaporator 10 is mounted on the heating element such that the heat receiving surface 42 is in contact with the heating element such as an electronic component (see FIG. 6A), and receives heat from the electronic component. A wick (porous body) 47 is in mechanical and thermal contact with the inner wall of the evaporation chamber 40A. The working fluid (liquid working fluid) 49 supplied to the evaporation chamber 40 A by the liquid pipe 13 is impregnated in the wick 47. The impregnated liquid is heated by the heat transferred from the evaporator case 40 to the wick. The inside of the evaporator 10 is maintained at the saturated vapor pressure of the working fluid, and evaporates and vaporizes when the temperature of the working fluid exceeds the boiling point at the internal saturated vapor pressure. At this time, the working fluid takes in latent heat energy. The steam that has taken in the latent heat energy passes through the groove (steam discharge groove) 45 formed in the wick 47 and flows into the steam pipe 14, and part of the steam flows into the pressure adjusting chamber 40 B through the pressure adjusting hole 55. Thereby, the evaporation chamber 40A and the pressure adjustment chamber 40B have substantially the same pressure. Note that the saturated vapor pressure in the operating temperature range of the working fluid 49 is equal to or higher than the atmospheric pressure under the environment in which the loop heat pipe 1 is used.

A specific configuration example of the evaporator 10 shown in FIGS. 3A and 3B will be described. The evaporator case 40 is a flat plate type having an overall height of 18 mm, a width of 60 mm, and a length of 70 mm. The pressure adjusting chamber 40B is provided with a pressure adjusting chamber 40B on the upper surface side of the evaporation chamber 40A, and the pressure adjusting chamber 40B constitutes a space having a height of 1 mm, a width of 56 mm, and a length of 66 mm. The pressure control chamber 40B is separated from the evaporation chamber 40A by a partition wall 51 having a thickness of 2 mm, and the partition wall 51 is provided with a pressure control hole 55 having a diameter of 1 mm leading to the vapor side of the evaporation chamber 40A. The interior dimensions of the evaporation chamber 40A are 11 mm in height, 56 mm in width, and 66 mm in length, and the overall wall thickness is 2 mm.

The material of the evaporator case 40 and the partition wall 51 is oxygen-free copper in the first embodiment. In the conventional flat plate evaporator, a material such as stainless steel having a high rigidity is often used so as to withstand a high internal pressure, but in the first embodiment, it is not always necessary to use a material having a high rigidity as will be described later. . Rather, it is preferable to use a material having a higher thermal conductivity than stainless steel so that the temperature distribution of the evaporator case 40 is uniform. For example, a material such as an aluminum alloy may be used for weight reduction.

The wick 47 disposed inside the evaporation chamber 40A is made of sintered nickel, has a porous diameter of 10 μm, and a porosity of about 50%. The outer dimensions of the wick 47 are 11 mm in height, 56 mm in width, and 50 mm in length, and the height dimension is particularly precisely manufactured so as to fit in close contact with the inner wall of the evaporation chamber 40A. Further, 15 steam passages (grooves) 45 each having a width of 1 mm and a depth of 2 mm are formed on the upper surface and the lower surface of the wick 47 (surfaces in contact with the upper surface and the lower surface of the evaporation chamber 40A) at a pitch of 3 mm. A liquid supply passage 46 having a height of 3 mm, a width of 40 mm, and a length of 40 mm is provided in the central portion of the wick 47 in order to draw the hydraulic fluid 49 supplied from the liquid pipe 13 into the wick 47.

The steam pipe 14 and the liquid pipe 13 that connect the evaporator 10 and the condensing unit 11 are both copper pipes having an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of about 300 mm. The condensing unit 11 is a copper pipe having an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 400 mm, similarly to the steam pipe 14 and the liquid pipe 13, and heat radiation fins are thermally connected around the pipe and cooled by the blower fan 12. (See FIG. 2).

In the first embodiment, n-pentane is used as the working fluid 49, but a fluid having a high vapor pressure such as butane or ammonia may be used.

FIG. 4 is a graph showing vapor pressure curves of various fluids. When n-butane is used as the working fluid 49, the boiling point under atmospheric pressure is about 36 ° C. When the loop heat pipe 1 is operated, the temperature of the working fluid 49 is in the vicinity of 50 to 70 ° C. Therefore, when butane or pentane is used as the working fluid 49, the vapor pressure becomes atmospheric pressure or higher. In the case of the conventional evaporator configuration shown in FIG. 1A, since the upper surface of the case 1001 swells due to the internal pressure of the working fluid as shown in FIG. 1C, the adhesion between the evaporator case 1000 and the wick 1007 inside deteriorates and the performance decreases. It was. On the other hand, in the first embodiment, the evaporator 10 has a double structure and the pressure adjusting chamber 40A is provided on the upper surface side of the evaporation chamber 40A so that the vapor evaporating from the surface of the wick 47 flows into the pressure adjusting chamber 40B. When the pressure adjusting hole 55 is provided in the partition wall 51, the evaporation chamber 40A and the pressure adjusting chamber 40B have the same pressure.

FIG. 5A and FIG. 5B are schematic diagrams for explaining the effects of the first embodiment. When butane is used as the working fluid 49, when the working fluid impregnated in the wick 47 is heated by heat released from the electronic component 20, the vapor pressure in the evaporation chamber 40A increases. Since the vaporized working fluid flows into the pressure adjustment chamber 40B from the pressure adjustment hole 55, the vapor pressure applied from the evaporation chamber 40A to the partition wall 51 is substantially equal to the vapor pressure applied from the pressure adjustment chamber 40B to the partition wall 51, as shown in FIG. As shown in FIG. 4, the partition wall 51 that contacts the wick 47 is not deformed by the internal pressure. On the other hand, the upper surface 53 of the evaporator case 40 (which is also the upper surface of the pressure adjusting chamber 40B in the first embodiment) has a higher butane saturated vapor pressure than the external atmospheric pressure, and thus expands outward. Then bend. However, since the partition wall 51 itself is not deformed, even when the internal pressure of the evaporation chamber 40A is increased by the vapor pressure of the working fluid 49, the evaporation chamber 40A and the wick 47 can maintain good thermal contact.

FIG. 6A and FIG. 6B are diagrams showing an example of mounting the evaporator 10 of the first embodiment. The evaporator 10 of the loop heat pipe 1 is disposed on the electronic component 20 on the printed circuit board 30 via the thermal grease 21 and is fixed to the printed circuit board 30 with an attachment screw 31. The calorific value of the evaporator 10 is about 60 W in the first embodiment. At this time, the condenser 11 (not shown) is cooled at room temperature (25 ° C.) by the blower fan (φ90 mm, 12 V drive) 12.

FIG. 7 is a graph showing the cooling performance of the loop heat pipe configured as described above. As a comparative example, a loop heat pipe incorporating the evaporator having the conventional structure shown in FIG. 1 was manufactured, and an operation experiment was performed to compare the cooling performance with the loop heat pipe 1 of the first embodiment. The horizontal axis of the graph indicates the heater heating amount (heat generation amount of the electronic component), and the vertical axis indicates the thermal resistance of the evaporator 10 and the condensing unit 11. The thermal resistance is a value obtained by dividing the difference between the temperature of the heat receiving surface 42 of the evaporator 10 and the average temperature of the condenser 11 by the amount of heat of the heating element 20. The lower the thermal resistance value, that is, the smaller the temperature difference between the heat receiving surface 42 and the condensing unit 11, the more efficiently heat is transferred from the evaporator 10 to the condensing unit 11, indicating a higher cooling performance.

In the case of a conventional loop heat pipe, the higher the heat generation amount, the higher the internal pressure of the evaporator, and the gap between the evaporator case 1001 and the wick 1007 is expanded as shown in FIG. 1C, and the cooling performance is reduced (heat resistance is increased). To do. On the other hand, in the case of the first embodiment, even when the heat generation amount is high and the temperature of the evaporator is high, the heat of the partition walls 51 and the wicks 47 in the evaporator case 40 as shown in FIG. Since it is possible to secure a state in which the contact is well maintained, it is possible to maintain high cooling performance (maintain thermal resistance low).

8A and 8B are diagrams showing a first modification of the first embodiment. In the first modification, the outer wall (for example, the upper surface) 63 of the evaporator case 60 constituting the pressure control chamber 60B is set thinner than the partition wall 61 that partitions the evaporation chamber 60A and the pressure control chamber 60B. For example, the thickness of the partition wall 61 is 2 mm, and the thickness of the upper surface 63 of the evaporator case 60 is 1 mm. When the operation is stopped, the pressure regulation chamber 60B is not deformed as shown in FIG. 8A. On the other hand, during heating, the pressure adjustment chamber 60B expands as shown in FIG. 8B. By making the outer wall surface (upper surface) 63 thinner than the inner partition wall 61, the outer wall surface 63 is deformed to the outside (atmosphere side) due to the vapor pressure flowing into the pressure regulating chamber 60B. Almost no deformation occurs. This configuration is effective in keeping the adhesion between the inner partition wall 61 and the wick 47 constant. In FIG. 8, the thickness of the outer wall 63 is ½ of the thickness of the partition wall 61. However, the thickness is not limited to this example, and the outer wall 63 can be appropriately deformed without affecting the shape of the partition wall 61. Can be set to any thickness. Depending on the type of working fluid used, for example, the thickness of the outer wall 63 can be appropriately set within the range of 1/5 to 2/3 of the thickness of the partition wall 61 (check if there is no problem in this range). Please give me).

FIG. 9A and FIG. 9B are diagrams showing a second modification of the first embodiment. In the second modification, the upper surface 73 of the evaporator case 70 and the inner partition wall 71 have the same thickness, but the partition wall 71 is slightly curved toward the evaporation chamber 70A where the wick 47 is disposed. When the operation is stopped, the pressure regulation chamber 70B is not deformed as shown in FIG. 9A. On the other hand, during heating, the pressure adjustment chamber 70B expands as shown in FIG. 9B. In this configuration, when the outer wall surface (upper surface) 73 of the evaporator case 70 is expanded outward by the steam flowing into the pressure adjusting chamber 70B from the pressure adjusting hole 75, the inner partition wall 71 is also curved to the wick 47 side. Deforms in a direction to increase As a result, a force that presses the partition wall 71 against the wick 47 works. Thereby, the adhesiveness of the partition 71 and the wick 47 further increases, and the cooling performance of the loop heat pipe is improved.

As described above, according to the configuration of the first embodiment, the cooling performance of the loop heat pipe can be improved and stabilized with a simple configuration, and a stable operation of the electronic apparatus can be realized.

10A and 10B are diagrams showing the configuration of the evaporator 80 according to the second embodiment of the present invention. 10A is a cross-sectional view along the direction in which the working fluid flows, and FIG. 10B is a cross-sectional view along the line AA ′ in FIG. 10A. In the second embodiment, the evaporator 80 has an evaporation chamber (first space) 90A having a liquid supply passage 86 and a second fluid chamber (second space) 90B having airtightness. The second fluid chamber 90B is a space for accommodating the second fluid 100 having a saturated vapor pressure higher than the saturated vapor pressure of the working fluid supplied to the evaporation chamber 90A at the same temperature. At least a part of the second fluid 100 is the liquid phase 100b. Referring to the graph of FIG. 4, when ethanol is used as the working fluid, ethanol, pentane, butane, ammonia and the like are partially sealed in a liquid phase state as the second fluid. When the working fluid is pentane, the second fluid and pentane, butane, ammonia or the like are partially sealed in a liquid phase state.

10A and 10B, the bottom surface of the evaporator case 90 is the heat receiving surface 82. The evaporator 80 is mounted on the heating element 20 so that the heat receiving surface 82 is in contact with the heating element 20 such as an electronic component, and receives heat from the electronic component (see FIGS. 11A and 11B). A wick (porous body) 47 is in mechanical and thermal contact with the inner wall of the evaporation chamber 90A. The working fluid 89 supplied to the evaporation chamber 90 A through the liquid pipe 83 is impregnated in the wick 47, heated by the heat transmitted from the evaporator case 40 to the wick 47, and vaporized. The vaporized vapor flows from the groove 45 formed in the wick 47 into the vapor pipe 84. On the other hand, when the electronic device is operated, a part of the second fluid sealed in the second fluid chamber 90B is vaporized by the heat transmitted through the evaporator case 90, and both the gas phase 100a and the liquid phase 100b exist. It is in a state.

A specific configuration example of the evaporator 80 shown in FIGS. 10A and 10B will be described. The evaporator case 80 is a flat plate having an overall height of 18 mm, a width of 60 mm, and a length of 70 mm. The double fluid structure 90B is provided on the upper surface side of the evaporation chamber 90A, and the second fluid quality 90B is a sealed space having a height of 1 mm, a width of 56 mm, and a length of 66 mm. The second fluid chamber 90B is separated from the evaporation chamber 90A by a partition wall 91 having a thickness of 2 mm. The indoor dimensions of the evaporation chamber 90A are 11 mm in height, 56 mm in width, and 66 mm in length, and the overall wall thickness is 2 mm.

The material of the evaporator case 90 and the partition wall 91 is oxygen-free copper in the second embodiment. In the conventional flat plate evaporator, a material such as stainless steel having a high rigidity is often used so as to withstand a high internal pressure, but in the second embodiment, it is not always necessary to use a material having a high rigidity as will be described later. . Rather, it is preferable to use a material having a higher thermal conductivity than stainless steel so that the evaporator case 90 has a uniform temperature. For example, a material such as an aluminum alloy may be used for weight reduction.

The wick 47 disposed inside the evaporation chamber 90A is made of sintered nickel, has a porous diameter of 10 μm, and a porosity of about 50%. The outer dimensions of the wick 47 are 11 mm in height, 56 mm in width, and 50 mm in length, and the height dimension is particularly precisely manufactured so as to fit in close contact with the inner wall of the evaporation chamber 90A. On the upper surface and the lower surface of the wick 47 (surfaces in contact with the upper surface and the lower surface of the evaporation chamber 90A), 15 steam passages (grooves) 45 each having a width of 1 mm and a depth of 2 mm are formed at a pitch of 3 mm. A liquid supply passage 86 having a height of 3 mm, a width of 40 mm, and a length of 40 mm is provided in the center of the wick 47 in order to draw the hydraulic fluid 49 supplied from the liquid pipe 13 into the wick 47.

The vapor pipe 84 and the liquid pipe 83 connecting the evaporator 80 and the condensing unit 11 (see FIG. 2) are both copper pipes having an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of about 300 mm. The condensing unit 11 is a copper pipe having an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 400 mm, like the steam pipe 84 and the liquid pipe 83, and thermally radiating fins around the pipe, and is cooled by the blower fan 12. I tried to do it.

In the second embodiment, n-pentane is used as the working fluid 89. Although the boiling point of pentane under atmospheric pressure is about 36 ° C., when the loop heat pipe 1 is operated, the temperature of the working fluid 89 is about 50 to 70 ° C., so that the vapor pressure of pentane is over atmospheric pressure. . On the other hand, 1 cc of butane is sealed in advance in the second fluid chamber 90B as the second fluid. The butane is sealed in the second fluid chamber 90B in the same manner as the working fluid of the loop heat pipe is sealed, and only the second fluid (butane) is sealed after the internal space is evacuated. The second fluid has a predominant gas phase when the heating element (electronic component) 20 is operated, but at least a part of the second fluid is in a liquid phase throughout the operation and non-operation.

FIG. 11A and FIG. 11B are schematic diagrams for explaining the effect of the second embodiment. When butane is used as the second fluid, the saturated vapor pressure of butane at the same temperature is higher than the saturated vapor pressure of n-pentane, which is the working fluid, but the second fluid chamber 90B is not deformed when the operation is stopped. At the time of heating, if the temperature of the working fluid side (evaporation chamber 90A) and the second fluid side (second fluid chamber 90B) of the evaporator case 90 is substantially the same, the partition wall 91 has a lower pressure, It is pressed to the evaporation chamber 90A side where the wick 47 is installed. Since the pressure difference between the working fluid 89 and the second fluid 100 increases as the temperature increases, the partition wall 91 comes into close contact with the wick 47 as the evaporator case 90 receives heat from the heating element 20 and becomes higher in temperature. At this time, as shown in FIG. 11B, since the difference between the second fluid chamber 90B and the atmospheric pressure is larger than the difference in internal pressure between the evaporation chamber 90A and the second fluid chamber 90B, the upper surface of the second fluid chamber 90B. 93 curves toward the outside, but the partition wall 91 also expands toward the evaporation chamber 90 A, so that the adhesion with the wick 47 is improved.

FIG. 12A and FIG. 12B are diagrams showing a modification of the evaporator of the second embodiment. In the second embodiment, the thickness of the partition wall 91 is 2 mm, which is the same as the wall thickness of the evaporator case 90. However, in the modified example, the thickness of the partition wall 91a that separates the evaporation chamber 90A and the second fluid chamber 90B of the evaporator 80a. Is thinner than the wall thickness of the evaporator case 90, for example, 1 mm. With this configuration, the second fluid chamber 90B is not deformed when the operation is stopped (FIG. 12A), but the partition wall 91a is easily deformed during heating, and the partition wall 91a and the wick 47 can be brought into close contact with each other with a stronger force. Yes (FIG. 12B).

FIG. 13A and FIG. 13B are diagrams showing an example of mounting the evaporator 80 of the second embodiment. The evaporator 80 of the loop heat pipe 1 is disposed on the electronic component 20 on the printed circuit board 30 via the thermal grease 21, and is fixed to the printed circuit board 30 by the mounting screws 31. The calorific value of the evaporator 80 is about 60 W in the second embodiment. At this time, the condensing part 11 (not shown) is cooled at room temperature (25 ° C.) by a blower fan (φ90 mm, 12 V drive) 12. The heat transferred from the heat generating component 20 to the evaporator case 90 vaporizes the working fluid impregnated in the wick 47, and the second fluid having a higher saturated vapor pressure than the working fluid sealed in the second fluid material 90B. It vaporizes and presses the partition wall 91 against the wick 47 on the evaporation chamber 90A side.

FIG. 14 is a graph showing the cooling performance of the loop heat pipe of the second embodiment. As a comparative example, a loop heat pipe incorporating the conventional wick structure shown in FIGS. 1A to 1C was manufactured, and an operation experiment was performed to compare the cooling performance with the loop heat pipe 1 of the second embodiment. The horizontal axis of the graph indicates the heater heating amount (heat generation amount of the electronic component), and the vertical axis indicates the thermal resistance of the evaporator 80 and the condensing unit 11. The thermal resistance is a value obtained by dividing the difference between the temperature of the heat receiving surface 82 of the evaporator 80 and the average temperature of the condenser 11 by the amount of heat of the heating element 20. The lower the thermal resistance value, that is, the smaller the temperature difference between the heat receiving surface 82 and the condensing unit 11, the more efficiently heat is transferred from the evaporator 80 to the condensing unit 11, indicating a higher cooling performance.

In the case of the loop type heat pipe of the prior art, the higher the heat generation amount, the higher the temperature of the evaporator. As a result, the gap between the evaporator case 1001 and the wick 1007 is enlarged as shown in FIG. Resistance increases). On the other hand, in the case of the second embodiment, as shown in FIG. 11B or FIG. 12B, the

partition walls

91, 91a in the evaporator case 90 even when the heat generation amount is high and the evaporator temperature is high. Since the thermal contact between the wick 47 and the wick 47 can be maintained in a good state, it is possible to maintain high cooling performance (maintain thermal resistance low).

In order to support such an effect, the amount of deformation of the Cu evaporator case 90 having a width of 56 mm when pentane was used as the working fluid was calculated. In the conventional configuration shown in FIG. 1, since the difference between the atmospheric pressure and the pressure in the evaporator case during LHP operation (around 70 ° C.) is 0.2 MPa (see FIG. 4), the case expands to the outside by 95 μm. Deform. As a result, it is considered that the thermal contact between the case and the wick cannot be obtained and the thermal resistance increases. On the other hand, as shown in FIG. 11, when butane is sealed in the second fluid chamber 90 B, the internal pressure of the evaporation chamber 90 A is 0.5 MPa lower than the internal pressure of the second fluid chamber 90. If there is no wick in the evaporation chamber 90A, the partition wall 91 of the evaporator case protrudes 140 μm to the evaporation chamber 90A side. However, since the wick 47 is in the evaporation chamber 90A, the partition wall 91 is pressed against the wick 47. It is considered that the adhesion is improved.

Further, as can be seen by comparing the graph of FIG. 14 and the graph of FIG. 7, when the evaporator configuration of the second embodiment is adopted, a higher cooling effect can be achieved than the evaporator configuration of the first embodiment. Can do.

In the first embodiment and the second embodiment, the second space is provided only on the upper surface of the evaporator case having a large heat conduction area, that is, the surface opposite to the heat receiving surface. The second space may be formed so as to cover one or both side walls of the (space). When the second space is formed by covering the upper surface and both side walls of the evaporation chamber (first space), a double structure is adopted over three surfaces excluding the heat receiving surface of the evaporator. In this case, the thermal adhesion between the wick and the evaporation chamber is further improved.

This international application claims the priority of patent application 2010-074443 filed in Japan on March 29, 2010, the entire contents of which are incorporated by reference into this international application.

The loop heat pipe according to the present invention can be applied to various heat generator cooling devices such as electronic devices.

1

Loop Heat Pipe

10, 80

Evaporator

13, 83

Liquid Pipe

14, 84 Steam Pipe 20 Heating Element (Electronic Device)
40, 60, 70, 90

Evaporator cases

40A, 60A, 70A, 90A Evaporation chamber (first space)
42, 82 Heat-receiving surface 47

Wick

49, 89 Working

fluid

40B, 60B, 70B Pressure adjustment chamber (second space)
51, 61, 71, 91,

91a Partition wall

55, 65, 75 Pressure adjustment hole (communication hole)
90B Second fluid chamber (second space)
100 Second fluid 100a Second fluid 100b in a gas phase Second fluid in a liquid phase

Claims

A loop heat pipe in which an evaporator that vaporizes the working fluid with heat from the heating element and a condenser that condenses the vaporized working fluid are connected in a loop with a connecting pipe,
The evaporator is
A first space having a contact surface with the heating element and evaporating the working fluid supplied from the connecting pipe;
A second space provided on at least one surface other than the contact surface among the surfaces constituting the first space;
And a partition hole separating the first space and the second space is provided with a communication hole communicating the first space and the second space.
The loop heat pipe according to claim 1, wherein the second space is formed on at least a surface of the first space opposite to a contact surface with the heating element.
The vapor pressure of the working fluid is higher than atmospheric pressure, and the thickness of the outer wall separating the second space and the atmosphere is smaller than the thickness of the partition wall separating the first space and the second space. The loop type heat pipe according to 2.
3. The loop according to claim 2, wherein a vapor pressure of the working fluid is higher than an atmospheric pressure, and a partition wall separating the first space and the second space is curved toward the first space side. Type heat pipe.
The loop type heat pipe according to claim 4, wherein the working fluid is selected from pentane, butane, and ammonia.
A loop heat pipe in which an evaporator that vaporizes the working fluid with heat from the heating element and a condenser that condenses the vaporized working fluid are connected in a loop with a connecting pipe,
The evaporator is
A first space having a contact surface with the heating element and evaporating the working fluid supplied from the liquid pipe;
A second space which is provided on at least one surface other than the contact surface among the surfaces constituting the first space and seals a second fluid having a higher saturated vapor pressure than the working fluid at the same temperature;
A loop-type heat pipe characterized by comprising:
The loop heat pipe according to claim 6, wherein at least part of the second fluid is in a liquid phase when the loop heat pipe is not in operation.
The loop heat pipe according to claim 7, wherein a thickness of a partition wall separating the first space and the second space is thinner than a thickness of an outer wall separating the second space and the atmosphere.
A porous body is provided inside the first space along the inner wall of the first space, and a passage for the working fluid supplied by the connecting pipe is formed in the porous body. The loop heat pipe according to claim 1 or 6.
The loop heat pipe according to claim 1 or 6, wherein the evaporator is made of a material having higher thermal conductivity than stainless steel.