Evaporation surface structure of cooling device, manufacturing method thereof, cooling device and heat pipe

Abstract

To provide an evaporation face structure or the like of a cooling device which is remarkably improved in cooling performance by effectively increasing a surface area without largely lowering the heat conductivity of a sintered body layer.SOLUTION: An evaporation face structure of a cooling device 1 of this invention comprises an evaporation part 5 for evaporating a liquid-phase working fluid, and phase-changing it to a gas phase, and a condensation part 7 arranged in a position separated from the evaporation part 5, and phase-changing the gas-phase working fluid to a liquid phase by condensing the gas-phase working fluid at a container 3 having an internal space S into which the working fluid is sealed. A sintered body layer 9 formed by sintering metal particles is arranged at an inner face of the evaporation part 5 of the container 3, the sintered body layer 9 has a sintered aggregation part 15 in which a plurality of minute air gaps 19 are formed at least on a surface, and whose air gap rate is equal to or higher than 50%, and in the sintered aggregation part 15, a plurality of cracked coarse air gaps 17 whose air gap sizes are larger than the minute air gaps 19, and whose air gap rates are 100% are partially formed at least on a surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an evaporation surface structure of a cooling device, and more particularly to an evaporation surface structure of a cooling device such as a boiling type cooling device for cooling electric / electronic components and a heat pipe having heat transport properties, a manufacturing method thereof, and a cooling device and a heat pipe. [Background technology]

[0002] In recent years, electronic components such as semiconductor elements mounted on electric and electronic devices such as laptops, digital cameras, and mobile phones tend to generate more heat due to high density mounting associated with higher functionality, so it is important to adopt a configuration that can cool them efficiently. One method for cooling electronic components is to use the latent heat of vaporization when a refrigerant (fluid) sealed in a container evaporates and boils. When this container is connected to or contacted with a heat generating body, the liquid phase refrigerant evaporates and changes phase to gas phase, absorbing heat as latent heat of vaporization and cooling the heat generating body. Examples of such cooling devices include heat pipes and boiling type cooling devices (CVC).

[0003] For example, a heat pipe generally includes a tubular vessel (container) having an internal space in which a working fluid is sealed. The tubular vessel has an evaporator at one end for evaporating the liquid phase working fluid to change it to a gas phase working fluid, and a condenser at the other end for condensing the gas phase working fluid to change it to a liquid phase working fluid. The working fluid that has changed from liquid to gas phase in the evaporator flows from the evaporator to the condenser. The working fluid that has changed from gas to liquid phase in the condenser flows from the condenser to the evaporator. In this way, a circulating flow of the working fluid is formed between the evaporator and the condenser in the tubular vessel, thereby transporting heat between the evaporator and the condenser in the tubular vessel.

[0004] A CVC has a structure in which a fluid is enclosed in a roughly rectangular or flat container, and the inner surface of the container, which is attached in contact with a heat generating element such as an electronic component, becomes the evaporating surface of the evaporator. The enclosed fluid evaporates due to heat received from the heat generating element in the evaporator, and the gas phase fluid is cooled by a cooling pipe or heat pipe that penetrates a condenser located above the evaporator and changes to a liquid phase.

[0005] As an example of the structure of the evaporation surface in a conventional cooling device, a wick structure (hereinafter sometimes referred to as a "sintered body layer") made of a sintered body of granular metal powder is provided in the evaporation part of a container. The sintered body layer constituting the evaporation part has excellent retention power for liquid phase working fluid.

[0006] In order to reduce the thermal resistance on the evaporation surface, metal powder such as copper powder is used as the metal particles forming the wick structure. For example, Patent Document 1 discloses a heat pipe that includes a metal powder layer made of metal powder adhered only to the groove wall surface of a groove wick that constitutes a wick at least in the evaporation section among the evaporation section, the heat insulating section, and the condensation section, and that forms a porous wick made of a sintered body of metal powder. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5759606 Summary of the Invention [Problem to be solved by the invention]

[0008] The cooling performance of heat pipes, CVCs, etc. is greatly affected by the thermal conductivity and surface area of ​​the metal powder layer (sintered body layer) made of a sintered body on the inner wall of the evaporation section. In general, the higher the porosity (air porosity) of the sintered body layer, the larger the surface area, and the larger the bonding area between the metal powder particles, the higher the thermal conductivity. However, since there is usually a trade-off between the porosity and the bonding area between the metal powder particles, as described in Patent Document 1, it is difficult to achieve both of these two characteristics in a heat pipe configuration in which a wick structure is simply formed by sintering and bonding metal powder particles. For this reason, there is a demand for further improvement in cooling performance by optimizing at least the surface structure (evaporation surface structure) of the sintered body layer, which is the wick structure formed on the inner surface of the evaporation section.

[0009] A conventional method for manufacturing an evaporation surface structure includes, for example, a method in which a powder of a soluble salt such as table salt (NaCl) and a copper powder are mixed and baked (sintered) on the inner surface of the evaporation part of a container, and then NaCl is dissolved with water to obtain a sintered body layer with controlled void size, etc. However, the sintered body layer thus obtained cannot completely dissolve and remove NaCl with water, and a trace amount of NaCl remains, which may cause deterioration of the product and a decrease in quality. This method also requires sintering at a temperature lower than 801°C, which is the melting point of NaCl. However, even if metal particles made of a metal such as copper having a general particle size (for example, a particle size of the order of μm or more) are used, the melting point of the metal particles (for example, the melting point of copper (bulk material): 1085°C) is generally higher than the melting point of NaCl. Therefore, even if such metal particles are heated at a temperature of, for example, about 700°C, solid-phase sintering does not proceed sufficiently, and the metal particles are not bonded to each other, or even if they are bonded, a sufficient bonding area between the metal particles is not obtained.

[0010] In order to solve these problems, the present invention aims to provide an evaporative surface structure for a cooling device, a manufacturing method thereof, and a cooling device and heat pipe, which effectively increase the surface area and significantly improve cooling performance without significantly reducing the thermal conductivity of the sintered layer by optimizing the properties of at least the surface of the sintered layer. [Means for solving the problem]

[0011] In order to achieve the above object, the gist of the present invention is as follows. (1) An evaporation surface structure of a cooling device comprising a container having an internal space in which a working fluid is sealed, an evaporation section which evaporates the working fluid in a liquid phase and changes the phase to a gas phase, and a condensation section which is disposed at a position spaced apart from the evaporation section and condenses the working fluid in the gas phase and changes the phase to a liquid phase, the evaporation surface structure of a cooling device comprising: an inner surface of the evaporation section of the container having a sintered body layer formed by sintering metal particles, the sintered body layer having a sintered aggregate portion having a porosity of 50% or more and having a plurality of microvoids formed at least on its surface, the sintered aggregate portion having a plurality of crack-like coarse voids which are larger in void size than the microvoids and have a porosity of 100% partially formed at least on its surface. (2) The evaporative surface structure of a cooling device described in (1), in which the sintered layer is composed of metal particles having a particle diameter of 40 nm or more and 50 μm or less bonded together, the overall porosity is 50 to 95%, the metal particles and the minute voids that constitute the sintered aggregate are randomly arranged, and when the average diameter of the bonded metal particles is Da and the bonding width of the bonding parts between the metal particles is W, the average diameter Da of the metal particles and the bonding width W of the bonding parts between the metal particles satisfy the inequality W / Da>0.5. (3) The evaporation surface structure of a cooling device according to (1) or (2), wherein the plurality of coarse voids are randomly formed in the sintered aggregate portion. (4) The evaporation surface structure of a cooling device according to (1), (2) or (3), wherein the porosity of the sintered aggregate portion is smaller than the porosity of the entire sintered body layer. (5) The evaporation surface structure of a cooling device according to any one of (1) to (4), wherein the sintered body layer has a thickness of 50 to 2000 μm. (6) The evaporation surface structure of a cooling device according to any one of (1) to (5), wherein the sintered body layer has a bridge structure connecting a plurality of the sintered aggregate portions to each other. (7) A cooling device having the evaporation surface structure described in any one of (1) to (6). (8) A heat pipe having an evaporation surface structure according to any one of (1) to (6). (9) A method for manufacturing an evaporation surface structure according to any one of (1) to (6), The method for manufacturing an evaporation surface structure includes a particle layer formation step of forming a layer of metal particles having an average particle diameter of 250 nm or less on the inner surface of the container, and a sintering step of sintering the formed layer of metal particles in a reducing atmosphere at a temperature of 300°C or more and 1050°C or less. (10) The method for manufacturing an evaporation surface structure according to (9), wherein the sintering step is performed at a sintering temperature of 700° C. or less. Effect of the Invention

[0012] According to the present invention, it is possible to provide a novel evaporative surface structure for a cooling device, in which the surface area is effectively increased and cooling performance is significantly improved without significantly reducing the thermal conductivity of the sintered body layer by optimizing at least the surface properties of the sintered body layer, as well as a manufacturing method thereof, a cooling device, and a heat pipe. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a longitudinal sectional view of a heat pipe, which is a cooling device having an evaporation surface structure according to the present invention. [Diagram 2] FIG. 2 is an optical microscope photograph (magnification: 50 times) of the surface of the sintered body layer constituting the evaporation surface structure produced in Example 1. [Diagram 3] FIG. 3 shows the surface condition of the sintered body layer constituting the evaporation surface structure produced in Example 1, where FIG. 3(a) is a surface SEM photograph (magnification: 5000x) of a region including a sintered aggregate portion and a coarse void in the sintered body layer, FIG. 3(b) is an enlarged SEM photograph (magnification: 10000x) of the coarse void shown in FIG. 3(a), and FIG. 3(c) is an enlarged SEM photograph (magnification: 10000x) of a sintered aggregate portion in the sintered body layer. [Figure 4] FIG. 4 is a diagram for explaining the relationship between the average diameter Da of the joined metal particles that compose the sintered aggregate portion and the joint width W of the joints between the metal particles. [Diagram 5]FIG. 5 is a halo image of the surface of the sintered body layer constituting the evaporation surface structure produced in Example 1. [Figure 6] FIG. 6 is an optical microscope photograph (magnification: 50 times) of the surface of the sintered body layer constituting the evaporation surface structure produced in Comparative Example 1. [Figure 7] FIG. 7 is a graph showing the results of measuring the heat flux and heat transfer coefficient of the evaporation surface (boiling surface) for the evaporation surface structures produced in Example 1 and Comparative Example 1. [Figure 8] FIG. 8 is a graph showing the results of measuring the heat input and thermal resistance of the heat pipes produced in Example 2 and Comparative Example 2. [Figure 9] FIG. 9 is a perspective view showing an example of a CVC device, which is a cooling device having an evaporation surface structure according to the present invention. [Figure 10] FIG. 10 is an optical microscope photograph (magnification: 50 times) of the surface of the sintered body layer constituting the evaporation surface structure produced in Example 3. [Figure 11] FIG. 11 is an enlarged SEM photograph (magnification: 1000 times) of the sintered body layer constituting the evaporation surface structure produced in Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, the evaporation surface structure of the cooling device according to the present invention will be described in detail below.

[0015] <Evaporation surface structure> The evaporation surface structure of a cooling device according to the present invention is provided with a container having an internal space in which a working fluid is sealed, an evaporation section which evaporates the liquid phase working fluid to change it to a gas phase, and a condensation section which is arranged at a position spaced apart from the evaporation section and condenses the gas phase working fluid to change it to a liquid phase, in which the inner surface of the evaporation section of the container has a sintered body layer formed by sintering metal particles, and the sintered body layer has a sintered aggregate section having a porosity of 50% or more and having a plurality of microvoids formed at least on its surface, and the sintered aggregate section has a plurality of crack-like coarse voids partially formed at least on its surface, the void size of which is larger than the microvoids and has a porosity of 100%.

[0016] Fig. 1 is a diagram showing the internal structure of a heat pipe, which is a cooling device according to one embodiment of the present invention. Fig. 2 is an optical microscope photograph (magnification: 50 times) of the surface of a sintered body layer constituting an evaporation surface structure according to one embodiment of the present invention (Example 1), and Fig. 3 is an SEM photograph showing the surface state of the same embodiment (Example 1) as Fig. 2. The heat pipe 1 shown in FIG. 1 is provided with a container 3 having an internal space in which a working fluid is sealed, an evaporator section 5 which evaporates the working fluid in a liquid phase and changes the phase to a gas phase, and a condenser section 7 which is disposed at a position spaced apart from the evaporator section 5 and condenses the working fluid in a gas phase and changes the phase to a liquid phase.

[0017] In the evaporation surface structure of the heat pipe 1, which is a cooling device of the present invention, the inner surface of the evaporation section 5 of the container 3 has a sintered body layer 9 formed by sintering metal particles, and the sintered body layer 9 has a sintered aggregate 15 with a porosity of 50% or more and a plurality of microvoids 19 formed at least on the surface, as shown in Figures 2 and 3, and the sintered aggregate 15 has a plurality of crack-like coarse voids 17 with a void size larger than the microvoids 19 and a porosity of 100% partially formed at least on the surface. In the present invention, the "coarse void" refers to a crack-like void in a portion where the sintered aggregate is interrupted over a width of about 50 to 600 μm. In addition, the "microvoid" refers to a void of about 50 μm or smaller size that exists between metal particles in the sintered aggregate.

[0018] The evaporation surface structure of the present invention has a sintered assembly 15 formed by sintering metal particles in the sintered body layer 9, and therefore exhibits high thermal conductivity. Moreover, the sintered assembly 15 has a large surface area with a plurality of microvoids 19 and a porosity of 50% or more, so that the contact area with the refrigerant (fluid) is also large. Due to these characteristics, the evaporation surface structure of this embodiment can improve the performance of the heat pipe 1, which is a cooling device. Since the sintered assembly 15 has a plurality of microvoids 19, the evaporation surface structure is also excellent in fluid retention. In addition, since a plurality of crack-like coarse voids 17, which are larger in void size than the microvoids 19 and have a porosity of 100%, are also partially formed in the sintered assembly 15, the fluid can smoothly penetrate and move in the sintered body layer 9. Moreover, in the evaporation surface structure of this embodiment, the fluid is less likely to dry out, in which the fluid evaporates all at once and dries up, because the microvoids 19 and the coarse voids 17 differ in ease of evaporation. Due to these characteristics, the evaporation surface structure of this embodiment can significantly improve the performance of the cooling device.

[0019] For example, in the evaporation surface structure of the embodiment shown in FIG. 2, at least the surface of the sintered body layer 9 formed on the inner surface of the evaporation part of the container has a sintered assembly 15, and a plurality of crack-like coarse voids 17 with a porosity of 100% are partially formed on the surface. In addition, the sintered assembly 15 has a plurality of minute voids 19, and a large number of minute irregularities are present on the surface. With such a structure, the fluid flows smoothly in the sintered body layer 9 and is difficult to run out, and the contact area between the sintered body layer 9 and the fluid is also large, resulting in excellent cooling performance. In the evaporation surface structure of this embodiment, the coarse voids 17 are also formed randomly in the sintered assembly 15, so that the cooling medium (fluid) easily permeates from the surface of the sintered body layer 9 into the minute voids 19 present inside. The coarse voids 17 also have various shapes with a width of about 50 to 600 μm and a length of about 100 to 1000 μm, particularly about a width of about 100 to 400 μm and a length of about 100 to 600 μm. On the other hand, the sintered aggregates 15 also have various shapes with sizes from slightly less than 50 μm to more than 1000 μm, particularly from about 100 to 800 μm. Such random arrangement, shape, and size of the sintered body layer allows the fluid to flow evenly and smoothly through the sintered body layer, resulting in better cooling performance. The evaporation surface structure of the present invention is not limited to the embodiment shown in FIG. 2, and there are no particular limitations on the size or shape of the sintered aggregates and the coarse voids. For example, the sintered aggregates and the coarse voids may each be three-dimensionally continuous to form a co-continuous structure.

[0020] (Microstructure of sintered aggregate) FIG. 4 is a diagram illustrating the relationship between the average diameter Da of the joined metal particles 21a1, 21a2 that form the sintered aggregate and the joint width W of the joint between the metal particles 21a1, 21a2. In the evaporation surface structure of this embodiment, the sintered layer 9 is formed by bonding together metal particles having a particle diameter of 40 nm or more and 50 μm or less, the overall porosity is 50 to 95%, the metal particles 21 and microvoids that constitute the sintered aggregate portion 15 are randomly arranged, and when the average diameter of the bonded metal particles 21 is Da and the bonding width of the bonding portions between the metal particles 21a1 and 21a2 is W, it is preferable that the average diameter Da of the metal particles 21 and the bonding width W of the bonding portions between the metal particles 21a1 and 21a2 satisfy the inequality relationship W / Da>0.5.

[0021] The evaporation surface structure of the present invention is manufactured by sintering metal particles having an average particle diameter of, for example, about 250 nm or less, particularly about 100 nm or less, as described later. In the above embodiment, the metal particles in the sintered body layer 9 have a relatively large particle diameter (diameter) of 40 nm to 50 μm, particularly 100 nm to 20 μm. Moreover, the metal particles are bonded to each other with their outer surfaces in contact with each other, and a columnar structure as observed in FIG. 3 is also formed. In a preferred embodiment of the present invention, the width (bonding width) W of the bonding portion is configured to be larger than half the average diameter Da of the metal particles 21 in the sintered body layer 9, so that the metal particles 21a1 and 21a2 are strongly bonded to each other, and a heat conduction path through the bonding portion having a relatively large bonding area can be formed. Therefore, the evaporation surface structure of such an embodiment has a higher thermal conductivity, and therefore the cooling performance is improved. In a more preferred evaporation surface structure of this embodiment, the metal particles in the sintered layer have an average particle size (diameter) Da of 40 nm or more and 50 μm or less, particularly 500 nm or more and 20 μm or less, and optionally 100 nm or more and 5 μm or less, and the joint width W of the joint between the metal particles is more than 0.5 times Da, particularly 0.8 times or more.

[0022] In the preferred embodiment as described above, the porosity of the entire sintered body layer 9 is as high as 50 to 95%, and the surface area is large. Moreover, as shown in FIG. 3, the metal particles and the minute voids 19 are randomly arranged in the sintered assembly portion 15, so that the fluid is particularly likely to come into contact with the metal particles in the dense portion and evaporate easily. Therefore, compared with an evaporation surface arranged in a regular manner, a high cooling performance can be achieved even if the surface area is the same. In addition, the fluid in the evaporation portion does not evaporate all at once, so that dryout can be prevented. In a more preferred evaporation surface structure of the present invention, the porosity of the entire sintered body layer is 50 to 85%, particularly 60 to 75%. The evaporation surface structure of the present invention is not limited to the embodiment shown in FIG. 3, and the structure of the sintered body, the length of the joint of the metal particles, and the like are not particularly limited. For example, the metal particles forming the sintered body and the voids thereof may be three-dimensionally continuous, forming a co-continuous structure.

[0023] (Macrostructure of sintered layer) In the evaporation surface structure of the present invention, it is also preferable that the above-mentioned multiple coarse voids 17 are randomly formed in the sintered aggregate 15 as shown in FIG. 2. This structure creates some parts where the bonded metal particles are more likely to come into contact with the refrigerant, making it possible to further improve the cooling performance. In addition, in the evaporation surface structure of the present invention, it is preferable that the porosity of the sintered aggregate is smaller than the porosity of the entire sintered body layer. This means that the sintered body layer has coarse voids, etc., and similar to the random structure of the sintered aggregate as described above, it exhibits high cooling performance and has the effect of preventing dryout. In addition, there is an advantage that the fluid can easily flow through the evaporation part through such coarse voids.

[0024] In another preferred embodiment of the evaporation surface structure of the present invention, the thickness of the sintered body layer is 50 to 2000 μm, further 100 to 1500 μm, particularly 300 to 1000 μm. In many cooling devices, a sintered body is formed in a capillary structure for returning the fluid condensed in the condenser to the evaporation section, and if the thickness of the sintered body layer is 2000 μm or less, there is no risk of the flow of the fluid being obstructed there. In addition, if the thickness of the sintered body layer is 50 μm or more, microvoids and coarse voids are easily formed in the layer. Moreover, a three-dimensional structure in which the metal particles and the voids are connected to each other is easily generated. As a result, the contact area between the fluid and the metal particles is also increased, and the heat conduction through the metal particles is also improved. The evaporation surface structure of the present invention may also have a co-continuous structure in which both the sintered aggregate portion and the coarse voids are connected to each other.

[0025] Fig. 10 is an optical microscope photograph (magnification: 50 times) of the surface of the sintered body layer constituting the evaporation surface structure of yet another embodiment (Example 3) of the present invention, and Fig. 11 is an SEM photograph showing the surface state of the same embodiment (Example 3) as Fig. 10. In this embodiment, as shown in Figs. 10 and 11, the sintered body layer 9 has a bridge structure 22 that connects multiple sintered body aggregates 15, 15 to each other. In one preferred embodiment of the evaporation surface structure of the present invention, such bridge structures 22 connect multiple sintered body aggregates 15, 15 across the coarse voids 17, so that more heat conduction paths are formed and the flow of fluid is further agitated, resulting in an effect of reducing thermal resistance.

[0026] (Evaporation surface structure material) The evaporation surface structure of the present invention has a sintered layer formed by sintering metal particles, and is not particularly limited in material as long as it has the above-mentioned structure. As the metal particles, any material can be selected from various metal materials such as copper, aluminum, tin, silver, gold, iron, nickel, cobalt, stainless steel, titanium, and alloys thereof, such as brass, depending on the intended cooling device. Among the above, metals with high thermal conductivity, such as copper, copper alloys, aluminum, and aluminum alloys, are preferred, but tin, tin alloys, titanium, titanium alloys, nickel, and nickel alloys may also be used. The same applies to the material of the container.

[0027] <Method of manufacturing the evaporation surface structure> The evaporation surface structure of the present invention as described above can be produced, for example, by a manufacturing method including a particle layer forming step of forming a layer of metal particles having an average particle diameter of 250 nm or less on the inner surface of a container, and a sintering step of sintering the formed layer of metal particles at a temperature of 300°C to 1050°C in a reducing atmosphere. In general, metal particles having an average particle diameter of 250 nm or less can be bonded together to become giant and form a three-dimensional structure even in a temperature environment below the melting point, and are therefore useful as raw materials for producing the evaporation surface structure of the present invention. There is no particular restriction on the material of the metal particles, and any metal particles may be used depending on the purpose. However, for the reasons described above, copper, copper alloy, aluminum, aluminum alloy particles, and the like, especially copper particles, are preferred.

[0028] When the above-mentioned metal particles (metal nanoparticles) having an average particle size of 250 nm or less, particularly 100 nm or less, are sintered in a reducing atmosphere at a temperature of 300 to 1050°C while optionally applying pressure, the particles fuse or bond together. As a result, the metal particles aggregate to form a particle size of 40 nm to 50 μm, particularly 100 nm to 20 μm, and bond together to form the above-mentioned sintered body layer having voids.

[0029] The sintering temperature is preferably 700°C or lower, particularly 650°C or lower. When sintering is performed at such a relatively low temperature, the metal particles are bonded together while maintaining a finely intertwined structure, and an evaporation surface structure with a large surface area can be obtained. However, the sintering temperature can be arbitrarily changed depending on the desired evaporation surface structure and the type of metal particles used as the raw material, and can be, for example, higher than 700°C and 1050°C or lower, particularly within the range of 900 to 1000°C. In particular, when forming a bridge structure 22 that connects a plurality of sintered aggregates 15, 15, the sintering temperature is preferably 800°C or higher, and more preferably 900°C or higher.

[0030] There is no particular limitation on the sintering method in a reducing atmosphere in the sintering step, and various known methods can be used. Examples include, but are not limited to, sintering in a gas containing hydrogen, hydrocarbon, carbon monoxide, etc. From the viewpoints of safety and cost, it is preferable to perform sintering under a flow of hydrogen / nitrogen mixed gas.

[0031] <Cooling device> In the evaporation surface structure of this embodiment, the surface area can be effectively increased without significantly decreasing the thermal conductivity of the sintered body layer, thereby significantly improving the cooling performance. Another advantage is that the fluid is less likely to dry out. Therefore, a cooling device having the evaporation surface structure of this embodiment exhibits excellent cooling performance. This embodiment also includes a cooling device having the above-mentioned evaporation surface structure.

[0032] There is no particular limitation on the cooling device to which the evaporation surface structure of this embodiment can be applied. The evaporation surface structure of this embodiment can be fabricated on the evaporation surface of various devices ranging from small to large cooling devices. Therefore, it is particularly suitable for use in devices that cool electric and electronic components. In addition, since dry-out is unlikely to occur, it is suitable as an evaporation surface structure for a boiling type cooling device (CVC) or a heat pipe. In particular, it is suitable as an evaporation surface structure in a wick structure of a heat pipe.

[0033] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. EXAMPLES

[0034] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0035] (Example 1, Comparative Example 1) A copper powder having an average particle size of 100 nm was placed on a copper plate (25 mm x 25 mm x 3 mm) to form a layer, which was then sintered at 620°C for 2 hours under pressure in a reducing atmosphere of hydrogen / nitrogen mixed gas to produce an evaporation surface structure (Example 1). In the resulting evaporation surface structure, a sintered body layer having an average thickness of 312 μm was formed. An optical microscope photograph of the sintered body layer is shown in FIG. 2, and an SEM photograph is shown in FIG. 3.

[0036] The evaporation surface structure of Example 1 had a sintered aggregate 15 in which a plurality of microvoids were formed, as shown in FIG. 2. A plurality of crack-like coarse voids 17, which were larger in void size than the microvoids 19 and had a porosity of 100%, were partially formed on the surface of the sintered aggregate 15. The coarse voids 17 were also randomly formed in the sintered aggregate 15. When the porosity was calculated from the mass and volume, the porosity of the sintered body layer was about 60%, and the porosity of the sintered aggregate 15 was about 45%. In addition, as shown in FIG. 3, the metal particles 21 in the sintered body layer had a diameter of about 100 nm or more and 5 μm or less, and most of them had a diameter of 1 μm or more, which was larger than the copper powder used as the raw material. The metal particles 21a1 and 21a2 were bonded to each other over a wide area, and some of them had a columnar shape. When the average diameter Da of these metal particles 21a1, 21a2 and the joint width W of the joint were measured, Da was 2.2 μm and W was an average of 1.4 μm, satisfying the inequality relationship W / Da>0.5. When a halo image was taken of the sintered aggregate of this evaporation surface structure, a dot-like image was observed as shown in Figure 5. This revealed that there was no periodicity in the sintered aggregate 15, that is, the metal particles 21 and the minute voids 19 were randomly arranged.

[0037] A sintered layer having an average thickness of 375 μm was formed on a copper plate by the same procedure as in Example 1, except that copper powder with an average particle diameter of 20 μm was used (Comparative Example 1). An optical microscope photograph of the obtained sintered layer is shown in FIG. 6. In the evaporation surface structure of this comparative example, copper particles with a particle diameter of about 20 μm were simply randomly arranged, and no sintered aggregates with microvoids formed therein or large voids formed randomly in the sintered aggregates were observed.

[0038] Using each of the sintered copper plates (heat transfer members) prepared above, the heat flux and heat transfer coefficient of the boiling surface were measured. The measurements were performed using this sintered copper plate on the boiling surface of the boiling cooling device shown in Figure 9. The container temperature on the boiling surface was Tc (K), the vapor temperature of the liquid F (1) filled inside the container was Tv (K), the heat input to the heater was Q (W), and the projected area of ​​the boiling surface was S (m 2 ), Q / {(Tc-Tv) S} is the heat transfer coefficient (W / m 2 The results are shown in Figure 7.

[0039] 7, the heat transfer member of Example 1, which has an evaporation surface structure satisfying the requirements of the present invention, exhibited a higher heat transfer coefficient than the heat transfer member of Comparative Example 1. This result shows that the evaporation surface structure of the present invention has excellent thermal conductivity and can exhibit good cooling performance.

[0040] (Example 2, Comparative Example 2) Using the same method as in Example 1, a cylindrical heat pipe 1 having a length of 400 mm, a diameter (inner diameter) of 8 mm, and an internal structure shown in FIG. 1 was prepared. Specifically, a core rod was inserted into the cylindrical container 3, and the copper powder used in Example 1 was then loaded into the gap. Then, after sintering the copper powder in the same manner as in Example 1, the core rod was pulled out of the container 3 to form a sintered body layer 9. Next, a heat pipe was produced by sealing only one end and injecting water, which is a liquid phase working fluid, from the other end and sealing the other end (Example 2). The heat pipe in Example 2 had an evaporation surface structure formed on the inner circumferential surface that satisfied the provisions of the present invention, similar to Example 1.

[0041] A heat pipe was produced in the same manner as in Example 2, except that copper powder with an average particle size of 100 μm was used (Comparative Example 2). The heat pipe of Comparative Example 2 had the same evaporation surface structure formed on the inner circumferential surface as that of Comparative Example 1. The average thickness of the sintered body layer was about 417 μm.

[0042] The performance of each heat pipe fabricated above was evaluated under the following conditions. The measurement results of the maximum heat transfer rate Qmax are shown in Figure 8. (Performance evaluation) 1. A heating element (heat output 50W to 250W) was attached to the outer surface of the evaporation section (heat receiving section), which is one end of the heat pipe. 2. A heat exchange means was attached to the condensation section (heat dissipation section), which is the other end of the heat pipe. 3. The intermediate section between the evaporation section and the condensation section was insulated by installing insulation material. 4. With the heater installed horizontally, the heat input to the evaporator section was gradually increased from 50 W, and the amount of heat input when the difference between the heater temperature and the condenser temperature was minimized was measured. This measured heat input was taken as the maximum heat transport rate Qmax (W). 5. The difference between the heater temperature and the condenser temperature was measured and divided by the heat input to obtain the thermal resistance (℃ / W).

[0043] As shown in FIG. 8, it was found that the heat pipe of Example 2 having the evaporation surface structure of the present invention has the advantage of having a smaller maximum heat transport amount at low heat input and a lower thermal resistance than the heat pipe of Comparative Example 2.

[0044] Example 3 An evaporation surface structure was produced in the same manner as in Example 1, except that the sintering temperature was 950° C. An optical microscope photograph of the sintered body layer 9 of the obtained evaporation surface structure is shown in FIG.

[0045] The evaporation surface structure of Example 3 had a sintered aggregate 15 in which a plurality of microvoids were formed, as shown in FIG. 10. A plurality of crack-like coarse voids 17, which were larger in void size than the microvoids and had a porosity of 100%, were partially formed on the surface of the sintered aggregate 15. The coarse voids 17 were also randomly formed in the sintered aggregate 15. When the porosity was calculated from the mass and volume, the porosity of the sintered body layer 9 was about 80%, and the porosity of the sintered body aggregate 15 was about 50%. The average thickness of the sintered body layer 9 was about 1400 μm.

[0046] 10 and 11, in the sintered body layer 9 of Example 3 sintered at 950°C, bridge structures 22 were observed connecting a plurality of sintered aggregates 15, 15 across the large voids 17. In the evaporation surface structure of this example, the bridge structures 22 connect the sintered aggregates 15, 15 to each other, forming more heat conduction paths and further stirring the fluid flow, resulting in an effect of reducing thermal resistance.

[0047] As shown in Figure 11, the metal particles in the sintered layer generally had diameters of 500 nm to several tens of μm, especially 20 μm or less, which was larger than the copper powder used as the raw material. The metal particles were bonded to each other over a wide area, and some of them had a columnar shape. When the average diameter Da of these metal particles and the joint width W of the joint were measured, Da was 18.8 μm and W was 13.2 μm on average, satisfying the inequality W / Da>0.5.

[0048] As described above, according to the present invention, an evaporation surface structure was obtained, which has a sintered aggregate having a porosity of 50% or more and a sintered body layer on the surface of the sintered aggregate, in which a plurality of crack-like coarse voids, the void size of which is larger than the microvoids and the porosity of which is 100%, are partially formed. It was shown that such an evaporation surface structure of the present invention exhibits high thermal conductivity and low thermal resistance, and can provide excellent cooling performance. [Explanation of symbols]

[0049] 1. Heat pipe (or cooling device) 3. Container 5 Evaporation section 7 Condenser 9 Sintered layer 11 Middle section 13 Groove 15 Sintering assembly 17 Coarse void 19 Micro void 21, 21a1, 21a2 Metal particles 22 Bridge structure L Longitudinal direction of tubular container S interior space Da is the average diameter of the bonded metal particles W Joint width of joint

Claims

1. A container having an internal space in which a working fluid is sealed, An evaporation section that evaporates the working fluid in a liquid phase and changes the phase to a gas phase; a condensation section disposed at a position separated from the evaporation section and configured to condense the working fluid in a gas phase to change the working fluid into a liquid phase; In a cooling device, an evaporation surface structure comprising: a sintered layer formed by sintering metal particles on an inner surface of the evaporation portion of the container; The sintered body layer has a sintered aggregate portion on at least a surface thereof, in which a plurality of microvoids having a size of 50 μm or less are formed, and the porosity is 50% or more; The sintered aggregate portion has a void size larger than the microvoids, a void ratio of 100%, and a plurality of crack-like coarse voids having a width of 50 to 600 μm and a length of 100 to 1000 μm partially formed at least on the surface, in an evaporation surface structure of a cooling device.

2. the sintered layer is formed by bonding metal particles having a particle diameter of 40 nm or more and 50 μm or less, and has an overall porosity of 50 to 95%, The metal particles and the minute voids constituting the sintered aggregate are randomly arranged, When the average diameter of the joined metal particles is Da and the joining width of the joint between the metal particles is W, the average diameter Da of the metal particles and the joining width W of the joint between the metal particles are expressed as follows: W / Da>0.5 The evaporation surface structure of the cooling device according to claim 1 , which satisfies the inequality relationship:

3. The evaporation surface structure of a cooling device according to claim 1 , wherein the plurality of large voids are randomly formed in the sintered aggregate portion.

4. 4. The evaporation surface structure of a cooling device according to claim 1, wherein the porosity of the sintered aggregate portion is smaller than the porosity of the entire sintered body layer.

5. The evaporation surface structure of a cooling device according to any one of claims 1 to 4, wherein the sintered layer has a thickness of 50 to 2000 µm.

6. The evaporation surface structure of a cooling device according to any one of claims 1 to 5, wherein the sintered body layer has a bridge structure connecting a plurality of the sintered aggregate portions to each other.

7. A cooling device comprising the evaporation surface structure according to any one of claims 1 to 6.

8. A heat pipe comprising the evaporation surface structure according to any one of claims 1 to 6.

9. A method for manufacturing an evaporation surface structure according to any one of claims 1 to 6, comprising the steps of: A manufacturing method for an evaporation surface structure, comprising: a particle layer forming step of forming a layer of metal particles having an average particle diameter of 250 nm or less on the inner surface of the container; and a sintering step of sintering the formed layer of metal particles in a reducing atmosphere at a temperature of 300°C or more and 1050°C or less.

10. The method for manufacturing an evaporation surface structure according to claim 9 , wherein the sintering step is performed at a sintering temperature of 700° C. or less.

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