Heat Transfer Materials

Abstract

The present invention is a heat transfer member which is applied to a cooling device (100), which cools an object-to-be-cooled (70) in a state of being immersed in a liquid refrigerant and promotes heat transfer to the refrigerant from the object-to-be-cooled (70). Furthermore, the object-to-be-cooled (70) is an electronic apparatus. The refrigerant is a fluorine-based insulating refrigerant having a boiling point equal to or lower than 100 °C. The refrigerant is exposed to the atmosphere. In addition, the refrigerant is a heat transfer member of which a degree of superheat dT is 10 K and heat flux q is 300 kW / m2 in a boiling curve with a lateral axis as the degree of superheat dT of the refrigerant and a vertical axis as the heat flux q. However, the degree of superheat dT is a value obtained by subtracting the saturation temperature Ts of the refrigerant from the temperature Tw of the heat transfer member. In addition, the heat flux q is the calories transferred per unit area to the refrigerant from a heat transfer portion.

Description

Heat transfer member and method for manufacturing the same CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2022-173289 filed on October 28, 2022, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a heat transfer member that is applied to a boiling cooling type cooling device.

[0003] Patent Document 1 discloses a boiling cooling type cooling device that cools an object to be cooled, such as an electronic component that generates heat during operation, while immersed in a liquid-phase refrigerant (in other words, refrigerant liquid). In the boiling cooling type cooling device, the refrigerant liquid is boiled by heat generated by the object to be cooled, and the latent heat of vaporization when the refrigerant liquid vaporizes is used to cool the object to be cooled.

[0004] The cooling device of Patent Document 1 further includes a heat transfer member that promotes heat transfer from the object to be cooled to the refrigerant, and a circulation pump that pressure-feeds the refrigerant liquid toward the heat transfer member. The heat transfer member of Patent Document 1 has a fin portion that forms a plurality of fins to increase the contact area between the heat transfer member and the refrigerant liquid.

[0005] In the cooling device of Patent Document 1, liquid refrigerant pumped from a circulation pump is forced to collide with the heat transfer member, thereby pushing out gas-phase refrigerant particles (in other words, bubbles) generated in grooves formed between adjacent fins from the grooves, thereby promoting boiling of the refrigerant near the heat transfer member and improving the cooling performance of the object to be cooled.

[0006] Japanese Patent Application Laid-Open No. 2015-220363

[0007] However, in the cooling device of Patent Document 1, the flow speed and flow direction of the refrigerant liquid pumped from the circulation pump, as well as the depth and width dimensions of each fin of the heat transfer member, are determined in order to effectively push out the air bubbles in the grooves.

[0008] Therefore, in the cooling device of Patent Document 1, if the operating conditions change, for example, if the flow velocity or flow direction of the refrigerant liquid pressure-fed from the circulation pump changes, the refrigerant liquid pressure-fed from the circulation pump may not be able to effectively push out the bubbles in the grooves. In other words, in the cooling device of Patent Document 1, if the operating conditions change, the heat transfer performance of the heat transfer member may decrease, and the cooling performance of the cooling device may decrease.

[0009] In view of the above, an object of the present disclosure is to provide a heat transfer member that can exhibit high heat transfer performance regardless of the operating conditions of a cooling device to which it is applied.

[0010] Another object of the present disclosure is to provide a method for manufacturing a heat transfer member that can exhibit high heat transfer performance regardless of the operating conditions of the cooling device to which it is applied.

[0011] In order to achieve the above-mentioned object, a heat transfer member according to one aspect of the present disclosure is a heat transfer member that is applied to a cooling device that cools an object to be cooled while immersed in a liquid-phase refrigerant, and promotes heat transfer from the object to be cooled to the refrigerant.

[0012] Furthermore, the object to be cooled is an electronic device. The refrigerant is a fluorine-based insulating refrigerant with a boiling point of 100°C or less. The refrigerant is open to the atmosphere. In addition, in a boiling curve with the degree of superheat dT of the refrigerant on the horizontal axis and the heat flux q on the vertical axis, the degree of superheat dT is 10K and the heat flux q is 300kW / m 2 It is a heat transfer member.

[0013] Here, the degree of superheat dT is the temperature Tw of the heat transfer member minus the saturation temperature Ts of the refrigerant. Also, the heat flux q is the amount of heat transferred from the heat transfer portion to the refrigerant per unit area.

[0014] According to this, when the degree of superheat dT becomes 10K in the boiling curve, the heat flux q becomes 300kW / m 2 Therefore, high heat transfer performance can be exhibited regardless of the operating conditions of the cooling device to which the present invention is applied, and as a result, the cooling device to which the present invention is applied can stably exhibit high cooling performance.

[0015] A heat transfer member according to an aspect of the present disclosure is applied to a cooling device that cools an object to be cooled while immersed in a liquid-phase refrigerant, and is a heat transfer member that promotes heat transfer from the object to be cooled to the refrigerant. Furthermore, a boiling promotion surface that promotes boiling of the refrigerant is formed on a side surface of the refrigerant that contacts the refrigerant.

[0016] In the roughness curve of the boiling promotion surface, the portions formed between adjacent peaks are defined as holes. The distance between adjacent peaks is defined as the hole width Gw. The distance between the line connecting adjacent peaks and the bottom between the adjacent peaks is defined as the hole depth Gd. The value obtained by dividing the hole depth Gd by the hole width Gw is defined as the hole aspect ratio Gd / Gw. When the number of bottoms per unit length is defined as the number of holes Ng, the number of holes with a hole aspect ratio Gd / Gw of 0.01 or more is 9 or more per mm.

[0017] According to this, the number of holes with a hole aspect ratio Gd / Gw of 0.01 or more on the refrigerant side surface is 9 or more per mm, so that, as will be described in the embodiment below, high heat transfer performance can be achieved regardless of the operating conditions of the applied cooling device, and as a result, the applied cooling device can exhibit stable high cooling performance.

[0018] Furthermore, a method for manufacturing a heat transfer member according to one aspect of the present disclosure is applicable to a cooling device that cools an object to be cooled while immersed in a liquid-phase refrigerant, and is a method for manufacturing a heat transfer member that promotes heat transfer from the object to be cooled to the refrigerant.

[0019] Furthermore, the method includes a boiling promotion surface forming step of forming a boiling promotion surface that promotes boiling of the refrigerant by shot blasting on at least a part of the refrigerant side surface that comes into contact with the refrigerant.

[0020] This allows the formation of a boiling promotion surface on the heat transfer member, thereby providing a method for manufacturing a heat transfer member that exhibits high heat transfer performance regardless of the operating conditions of the cooling device to which it is applied.

[0021] FIG. 1 is a schematic overall configuration diagram of a cooling device according to an embodiment; FIG. 2 is a schematic cross-sectional view of a cooling section according to an embodiment, taken along line II-II of FIG. 1; FIG. 3 is a schematic enlarged cross-sectional view of a heat transfer member according to an embodiment, taken along line III-III of FIG. 2; FIG. 4 is an external perspective view of a heat transfer member according to an embodiment; FIG. 5 is an enlarged arrow view taken from the direction V of FIG. 4; FIG. 6 is an explanatory diagram for explaining holes in a boiling promotion surface according to an embodiment; FIG. 7 is a boiling curve in a heat transfer member according to an embodiment; FIG. 8 is a graph showing the relationship between the hole aspect ratio according to an embodiment and the integrated value of the number of holes Ng; FIG. 9 is a graph showing the relationship between the hole width and the hole aspect ratio according to an embodiment; FIG. 10 is an external perspective view of a heat transfer member according to another embodiment;

[0022] 1 to 9, one embodiment of the present disclosure will be described. In this embodiment, a heat transfer member 80 according to the present disclosure is applied to a cooling section 30 of a cooling device 100. The cooling device 100 of this embodiment is a boiling cooling type cooling device that cools a heat generating element 70, which is an object to be cooled, while immersing it in a refrigerant liquid 40, which is a liquid-phase refrigerant.

[0023] 1 and 2, the cooling device 100 includes a circulation pump 10, a heat dissipation unit 20, and a cooling unit 30. More specifically, the cooling device 100 is formed by arranging the circulation pump 10, the heat dissipation unit 20, and the cooling unit 30 in a circulation circuit 50 that circulates a refrigerant liquid 40. The up and down arrows in FIGS. 1 and 2 indicate the vertically upward and downward directions of the properly arranged cooling unit 30, respectively.

[0024] First, the circulation pump 10 is a pumping unit that sucks in and pumps the refrigerant liquid 40 that flows out from the circulation outlet 31 of the cooling unit 30. The circulation pump 10 is an electric liquid pump that operates when supplied with power. The circulation pump 10 can be a magnet pump or a canned pump in which at least a portion of the electric motor that serves as the drive unit is sealed from the refrigerant liquid 40.

[0025] In this embodiment, a fluorine-based insulating refrigerant with a boiling point of 100°C or less is used as the refrigerant. Fluorine-based insulating refrigerants are refrigerants that have excellent insulation properties, heat transfer characteristics, and stability. More specifically, in this embodiment, Novec (a trade name and registered trademark of 3M) having a hydrofluoroether (HFE) structure is used as the refrigerant. Note that other refrigerants that may be used include Opteon (a trade name and registered trademark of Mitsui-Chemours), Galden (a trade name and registered trademark of Solvay), Asahiklin (a trade name and registered trademark of AGC), and Soluble (a trade name of Solvex).

[0026] The refrigerant inlet side of the heat radiating unit 20 is connected to the discharge port of the circulation pump 10. The heat radiating unit 20 is a heat exchange unit for radiating heat between the refrigerant liquid 40 and the atmosphere, thereby radiating the heat contained in the refrigerant liquid 40 to the atmosphere. By radiating the heat contained in the refrigerant liquid 40 to the atmosphere, the heat radiating unit 20 suppresses a temperature rise in the refrigerant liquid 40 circulating through the circulation circuit 50 and maintains the refrigerant liquid 40 in a subcooled state.

[0027] The refrigerant outlet of the heat dissipation unit 20 is connected to the circulation inlet unit 32 side of the cooling unit 30. The cooling unit 30 cools the heat generating element 70, which is the object to be cooled. As shown in the cross-sectional view of Figure 2, the cooling unit 30 has a cooling tank unit 33, a liquid storage tank unit 34, and a partition member 35. The cooling tank unit 33, the liquid storage tank unit 34, and the partition member 35 can be made of a resin material or a metal material.

[0028] The cooling tank 33 is formed in the shape of a rectangular parallelepiped container with an open top. An accommodation space 331 is formed inside the cooling tank 33 to accommodate a lower portion of the electronic board 60. The cooling tank 33 is formed with a circulation inlet 32 ​​through which the refrigerant liquid 40 flowing out from the heat dissipation unit 20 flows in, and a circulation outlet 31 through which the refrigerant liquid 40 flows out toward the suction port of the circulation pump 10. Therefore, the accommodation space 331 stores the refrigerant liquid 40.

[0029] The electronic board 60 is an electric board portion formed of a so-called rigid printed circuit board. A plurality of electronic devices including a heat generating element 70 are attached to the electronic board 60. The portion of the electronic board 60 to which the plurality of electronic devices including the heat generating element 70 are attached is the portion that is immersed in the refrigerant liquid 40 when the electronic board 60 is housed in the housing space 331. Therefore, the heat generating element 70 is housed in the internal space of the cooling tank portion 33 while being immersed in the refrigerant liquid 40.

[0030] The heat-generating element 70 is an electronic device known as a large-scale integrated circuit, specifically a central processing unit of a computer. The heat-generating element 70 generates heat during operation. When the heat-generating element 70 becomes too hot, its performance, such as its computing power, tends to deteriorate. Therefore, the cooling device 100 of this embodiment cools the heat-generating element 70 to prevent this deterioration in performance.

[0031] The heating element 70 is formed in a rectangular flat plate shape. The heating element 70 is joined to the electronic substrate 60 by soldering. Furthermore, a heat transfer member 80 is attached to the surface of the heating element 70 opposite to the surface joined to the electronic substrate 60. The heat transfer member 80 is a heat transfer section that promotes heat transfer from the heating element 70 to the refrigerant. The detailed configuration of the heat transfer member 80 will be described later.

[0032] Here, the boiling point of the refrigerant liquid 40 in this embodiment is set to a value lower than the heat generation temperature reached when the heating element 70 generates heat. Therefore, in the cooling unit 30, the refrigerant liquid 40 is boiled by the heat generated by the heating element 70, and boiling cooling is performed in which the latent heat of vaporization when the refrigerant liquid 40 vaporizes is used to cool the heating element 70.

[0033] Furthermore, in the cooling section 30 of this embodiment, the refrigerant liquid 40 in the area away from the heating element 70 is a subcooled liquid that is lower than the boiling point, and the refrigerant liquid 40 in contact with the heat transfer member 80 attached to the heating element 70 boils, which is called subcool boiling.

[0034] Refrigerant gas bubbles generated when the refrigerant liquid 40 in contact with the heat transfer member 80 boils are cooled and condensed in the subcooled liquid. Bubbles that cannot condense in the subcooled liquid are stored in the upper part of the storage space 331 and form a refrigerant gas layer 332. The refrigerant gas layer 332 contains not only the gas phase refrigerant but also the dissolved gas (specifically, air) that was dissolved in the refrigerant liquid 40. Of course, when all the bubbles have condensed, the volume of the refrigerant gas layer 332 becomes zero.

[0035] Next, the liquid storage tank 34 is formed in the shape of a rectangular parallelepiped container with an open bottom. The liquid storage tank 34 is disposed above the cooling tank 33. The upper opening of the cooling tank 33 and the lower opening of the liquid storage tank 34 are formed in shapes that fit each other.

[0036] The cooling tank 33 and the liquid storage tank 34 are integrated by bolting or other means with their openings overlapping each other. A sealing member such as a gasket (not shown) is interposed between the opening of the cooling tank 33 and the opening of the liquid storage tank 34. This prevents the refrigerant in the cooling unit 30 from leaking to the outside through a gap between the opening of the cooling tank 33 and the opening of the liquid storage tank 34.

[0037] A storage space 341 for storing the refrigerant liquid 40 is formed inside the liquid storage tank 34. An opening 342 penetrating the inside and outside of the liquid storage tank 34 is formed on the upper surface of the liquid storage tank 34. Therefore, the atmosphere can flow into the storage space 341 through the opening 342. That is, in the cooling unit 30, the refrigerant is open to the atmosphere.

[0038] The storage space 341 accommodates an upper portion of the electronic substrate 60. A connector 61 is disposed in the upper portion of the electronic substrate 60. The connector 61 is an electrical connection portion to which electrical wiring 62 is connected. The electrical wiring 62 includes a power line that serves as a transmission path for power and a signal line that serves as a transmission path for electrical signals. The electrical wiring 62 connected to the connector 61 is taken out to the outside of the cooling unit 30 through the opening 342.

[0039] The partition member 35 separates the accommodation space 331 of the cooling tank section 33 from the storage space 341 of the liquid storage tank section 34. The partition member 35 is formed in a generally flat plate shape. The outer edge of the partition member 35 is formed in a shape that fits the opening of the cooling tank section 33. The partition member 35 is fixed to the opening of the cooling tank section 33 by means of bolting, press-fitting, adhesive, or the like. The horizontally extending portion of the partition member 35 forms the bottom surface of the storage space 341.

[0040] A slit hole into which the electronic board 60 is inserted is formed in the center of the partition member 35. Support portions 351 that protrude toward the accommodation space 331 are formed around the slit hole. The electronic board 60 is sandwiched between the support portions 351 and supported so as not to come into contact with the inner wall surface of the cooling tank portion 33. The support portions 351 also function as a gas layer holder that holds the refrigerant gas layer 332 formed in the accommodation space 331.

[0041] Furthermore, a communication section 352 is formed between the partition member 35 and the electronic board 60. The communication section 352 is a refrigerant passage that connects the accommodation space 331 of the cooling tank section 33 and the storage space 341 of the liquid storage tank section 34.

[0042] As described above, the opening 342 is formed in the liquid storage tank 34, so atmospheric pressure acts on the refrigerant in the storage space 341. Therefore, when the volume of the refrigerant in the cooling tank 33 changes due to boiling or condensation of the refrigerant in the accommodation space 331, the refrigerant liquid 40 moves between the accommodation space 331 and the storage space 341 via the communication part 352.

[0043] In this way, the refrigerant liquid 40 moves between the accommodation space 331 and the storage space 341 through the communication part 352, so that the cooling tank part 33 is constantly supplied with the refrigerant liquid 40 for immersing the heating element 70.

[0044] Next, the heat transfer member 80 will be described using Figures 3 to 5. The heat transfer member 80 is formed in a flat plate shape from a material with excellent heat conductivity. The heat transfer member 80 of this embodiment is formed from a metal such as aluminum or copper. The outer surface of the heat transfer member 80 is roughly divided into a heating element side surface 81 and a refrigerant side surface 82.

[0045] The heating element side surface 81 is a flat surface of the outer circumferential surface of the heat transfer member 80 that comes into contact with the heating element 70. The heating element side surface 81 corresponds to a contact surface. The heating element side surface 81 is joined by soldering or the like to a flat surface of the heating element 70 that is opposite to the surface that is joined to the electronic board 60.

[0046] More specifically, in this embodiment, the heating element 70 and the electronic substrate 60 are joined by reflow soldering, in which paste solder is printed on the joining surfaces of at least one of the heating element 70 and the electronic substrate 60, and the printed solder is heated and melted in a reflow furnace. This allows the heating element 70 and the electronic substrate 60 to be joined over the entire joining surface.

[0047] The refrigerant-side surface 82 is a surface that comes into contact with the refrigerant liquid 40. Therefore, the refrigerant-side surface 82 is a surface of the outer circumferential surface of the heat transfer member 80 excluding the heating element-side surface 81. In other words, the refrigerant-side surface 82 includes not only a surface of the outer circumferential surface of the heat transfer member 80 that faces the heating element-side surface 81, but also a surface that intersects with the heating element-side surface 81.

[0048] Fin portions 83 are formed on the refrigerant-side surface 82 facing the heating element-side surface 81. The fin portions 83 are area-enlarging portions that increase the area of ​​the refrigerant-side surface 82 and promote heat transfer from the heating element 70 to the refrigerant. The fin portions 83 in this embodiment are formed on the refrigerant-side surface 82 facing the heating element-side surface 81, of the outer peripheral surface of the heat transfer member 80.

[0049] The fin portion 83 of this embodiment is formed by a plurality of grooves with a rectangular cross section provided on the refrigerant side surface 82 facing the heating element side surface 81. The plurality of grooves are formed to extend parallel to each other in the vertical direction. Therefore, the fin portion 83 of this embodiment forms a so-called straight fin.

[0050] Here, the height dimension from the bottom surface of each fin formed between adjacent grooves is defined as the fin height hf. The thickness dimension of each fin corresponding to the distance between adjacent grooves is defined as the fin thickness tf. The value obtained by dividing the fin height hf by the fin thickness tf is defined as the fin aspect ratio hf / tf. The distance between adjacent fins is defined as the fin spacing wf.

[0051] In this embodiment, the fin aspect ratio hf / tf is set to 1.3 or more. As a result, the area of ​​the refrigerant side surface 82 of the heat transfer member 80 of this embodiment is increased by 1.8 times or more compared to a heat transfer member without the fin portions 83. Furthermore, in this embodiment, the fin spacing wf is set to 0.2 mm or more. This prevents bubbles of refrigerant gas boiling in the fin portions 83 from remaining in the grooves.

[0052] Furthermore, in this embodiment, a boiling promotion surface 84 is formed on at least a portion of the refrigerant-side surface 82. The boiling promotion surface 84 is a surface that has been roughened on the refrigerant-side surface 82 in order to promote boiling of the refrigerant liquid 40. More specifically, as shown in FIG. 5 , the boiling promotion surface 84 is formed on the surface that forms the top of the fin portion 83 of the refrigerant-side surface 82, the side surfaces facing each other between adjacent fins, the surface that forms the bottom of the groove portion, and the side surface of the outer circumferential surface of the heat transfer member 80.

[0053] The boiling promotion surface 84 has an area larger than the area of ​​the heating element side surface 81, and is preferably formed to occupy 50% or more of the area of ​​the refrigerant side surface 82. Of course, the boiling promotion surface 84 may be formed over the entire area of ​​the refrigerant side surface 82. In addition, it is preferable that the boiling promotion surface 84 is formed over 50% or more of the fin portion 83.

[0054] Next, a detailed configuration of the boiling promotion surface 84 will be described. As described above, the boiling promotion surface 84 is a surface that has been roughened on the refrigerant side surface 82. In the heat transfer member 80, by roughening the refrigerant side surface 82, a portion that serves as a boiling starting point when the refrigerant liquid 40 boils is formed. This makes it possible to promote boiling.

[0055] Therefore, the boiling promotion surface 84 of this embodiment is roughened so that the surface roughness Rz satisfies the following formula F1.

[0056] 1≦Rz≦150 (F1) The surface roughness Rz in this embodiment is an index called ten-point average roughness.

[0057] More specifically, the surface roughness Rz is calculated by extracting a reference length from the roughness curve in a predetermined direction, calculating the sum of the average value of the absolute values ​​of the elevations of the highest to fifth peaks in the extracted portion and the average value of the absolute values ​​of the elevations of the lowest to fifth valley bottoms, and expressing this in micrometers (μm).

[0058] The roughness curve is a curve obtained by removing wavelength components of a predetermined length or more from a cross-sectional curve drawn by the flat surface on a cross section perpendicular to the flat surface. In Fig. 6, the thick line in this embodiment indicates the roughness curve Lrz of the boiling promotion surface 84.

[0059] Furthermore, in this embodiment, as shown in FIG. 6 , in the roughness curve of the boiling promotion surface 84, recesses formed between adjacent peaks 84a are defined as holes 84c. The distance between adjacent peaks 84a is defined as the hole width Gw. The distance between the line connecting adjacent peaks 84a and the valley bottom 84b between the adjacent peaks 84a is defined as the hole depth Gd. The value obtained by dividing the hole depth Gd by the hole width Gw is defined as the hole aspect ratio Gd / Gw. The number of holes 84c per unit length (1 mm in this embodiment) is defined as the number of holes Ng.

[0060] In the boiling promotion surface 84 of this embodiment, in order to effectively promote boiling, the number of holes Ng of the holes 84c that satisfy the following formula F2 is roughened so that the number of holes Ng satisfies the following formula F3.

[0061] Gd / Gw≧0.01 (F2) Ng≧9 (F3) That is, in the boiling promotion surface 84 of this embodiment, the roughening treatment is performed so that the number Ng of the holes 84c having a hole aspect ratio Gd / Gw of 0.01 or more is 9 or more per mm. The hole aspect ratio Gd / Gw may be 0.4 or less.

[0062] Furthermore, the hole width Gw may be determined so as to satisfy the following formula F4.

[0063] 315 μm≧Gw≧1.7 μm (F4) As a result of the surface roughening treatment performed on the heat transfer member 80 of this embodiment, as shown in FIG. 7 , in a boiling curve in which the horizontal axis represents the superheat dT of the refrigerant and the vertical axis represents the heat flux q, the superheat dT is 10 K and the heat flux q is 300 kW / m 2 The degree of superheat dT is a value obtained by subtracting the saturation temperature Ts of the refrigerant liquid 40 from the temperature Tw of the heat transfer member 80. The heat flux q is the amount of heat transferred from the heat transfer member 80 to the refrigerant liquid 40 per unit time.

[0064] FIG. 7 also shows, as a comparative example, the boiling curve of a heat transfer member that does not have the boiling promotion surface 84 formed thereon, that is, a heat transfer member that has not been subjected to a surface roughening treatment.

[0065] Next, a method for manufacturing the heat transfer member 80 of this embodiment will be described. First, in a material preparation step, a material for the heat transfer member 80 on which the above-described fin portion 83 is formed is prepared. In the material preparation step, a material can be prepared in which the fin portion 83 is formed by pressing or cutting a flat plate material such as aluminum or copper.

[0066] In the boiling promotion surface forming process, the boiling promotion surface 84 is formed on the material prepared in the material preparation process. In the boiling promotion surface forming process, the boiling promotion surface 84 is formed by shot blasting. Shot blasting is a processing method in which fine alumina shot material is sprayed onto the material and collided with it to form small holes in the surface of the material, thereby roughening the surface. Note that the shot material can be made of iron, stainless steel, zinc, ceramics, resin, etc.

[0067] In the boiling promotion surface forming process of this embodiment, blast material is sprayed onto the fin portion 83 from a direction perpendicular to the heat generating element side surface 81. As a result, the surfaces that form the tops of the fin portion 83 on the refrigerant side surface 82 and the surfaces that form the bottoms of the grooves become the boiling promotion surface 84. In addition, blast material is sprayed onto the heat generating element side surface 81 from four horizontal directions. As a result, the side surfaces of the outer peripheral surface of the heat transfer member 80 become the boiling promotion surface 84. Note that by spraying blast material that is sufficiently smaller than the fin spacing wf onto the fin portion 83 from various directions, the entire surface of the fin portion 83 can be roughened. As a result, the entire surface of the fin portion 83 becomes the boiling promotion surface 84.

[0068] Next, the operation of the cooling device 100 of this embodiment will be described. First, when the circulation pump 10 is operated, the circulation pump 10 sucks in and pressure-feeds the refrigerant liquid 40 that flows out from the circulation outlet 31 of the cooling unit 30. The refrigerant liquid 40 pressure-feed from the circulation pump 10 flows into the heat dissipation unit 20.

[0069] The refrigerant liquid 40 that flows into the heat dissipation unit 20 is cooled by heat exchange with the atmosphere, thereby maintaining the refrigerant liquid 40 in a subcooled state in the cooling device 100. The refrigerant liquid 40 that flows out of the heat dissipation unit 20 flows into the accommodation space 331 of the cooling unit 30 via the circulation inlet 32 ​​of the cooling unit 30.

[0070] In the cooling unit 30, the heat generated by the heating element 70 is transferred to the refrigerant liquid 40 via the heat transfer member 80. This causes the refrigerant liquid 40 near the heat transfer member 80 to boil, generating refrigerant gas bubbles. At this time, the heat generated by the heating element 70 is absorbed as latent heat of vaporization of the refrigerant liquid 40, and the heating element 70 is cooled.

[0071] The refrigerant gas bubbles rise inside the cooling tank 33 and are held below the partition member 35, forming a refrigerant gas layer 332. As described above, if all the bubbles are cooled to the subcooled liquid and condensed, the refrigerant gas layer 332 is not formed.

[0072] As described above, the cooling device 100 of this embodiment can cool the heating element 70, which is the object to be cooled, by utilizing the latent heat of vaporization of the refrigerant liquid 40. Furthermore, since the cooling device 100 of this embodiment employs the heat transfer member 80, it can exhibit stable, high cooling performance even when the operating conditions change.

[0073] More specifically, in the cooling device 100 of this embodiment, as described with reference to FIG. 7, when the degree of superheat dT becomes 10 K in the boiling curve, the heat flux q becomes 300 kW / m 2 This allows the heat transfer member 80 to exhibit high heat transfer performance regardless of the operating conditions of the cooling device 100. As a result, the cooling device 100 can stably exhibit high cooling performance.

[0074] Furthermore, the present inventors have confirmed that by performing a surface roughening treatment, i.e., by forming a boiling promotion surface 84, it is possible to form a heat transfer member 80 that exhibits high heat transfer performance, as described with reference to FIG. 7 .

[0075] Specifically, the inventors investigated the relationship between the upper limit of the hole aspect ratio and the integrated value of the number of holes Ng for six types of heat transfer members 80 that exhibit high heat transfer performance through surface roughening. The integrated value of the number of holes Ng in Fig. 8 is the integrated value of the number of holes Ng for holes 84c where the hole aspect ratio Gd / Gw is 0.01 or more and is equal to or less than the upper limit of the hole aspect ratio Gd / Gw.

[0076] As a result, it has been confirmed that a heat transfer member 80 that has a hole aspect ratio Gd / Gw of 0.01 or more and a hole number Ng of 9 or more exhibits high heat transfer performance, as shown in Fig. 8. Furthermore, as shown in Fig. 8, when the hole aspect ratio Gd / Gw exceeds 0.4, the integrated value of the hole number Ng does not change, and therefore the hole aspect ratio Gd / Gw may be set to 0.4 or less.

[0077] The inventors also investigated the distribution of the hole width Gw of six types of heat transfer members 80 that exhibit the above-mentioned high heat transfer performance by forming a boiling promotion surface 84. As a result, as shown in Fig. 9, it was confirmed that when the hole aspect ratio Gd / Gw is 0.01 or more, the heat transfer member 80 exhibits high heat transfer performance if the hole width Gw is 1.7 µm or more and 315 µm or less. This makes it possible to more reliably form a boiling promotion surface 84 that can improve heat transfer performance.

[0078] Furthermore, the heat transfer member 80 of this embodiment has the fin portion 83, which is an area-enlarged portion, and therefore can promote heat transfer from the heating element 70 to the refrigerant. Furthermore, the boiling promotion surface 84 is formed on a surface parallel to the heating element side surface 81, so even if the heat transfer member 80 has the fin portion 83, the boiling promotion surface 84 can be formed.

[0079] The manufacturing method of the heat transfer member 80 of this embodiment also includes a boiling promotion surface forming step of forming the boiling promotion surface 84 by shot blasting.

[0080] This makes it extremely easy to form the boiling promotion surface 84. Furthermore, in the boiling promotion surface forming process, the blast material is sprayed from a direction perpendicular to the heating element side surface 81, so that the boiling promotion surface 84 can be easily formed not only on the surface that forms the tops of the fin portions 83 on the coolant side surface 82, but also on the surface that forms the bottoms of the grooves.

[0081] The present disclosure is not limited to the above-described embodiments, and various modifications can be made as follows within the scope of the present disclosure.

[0082] (1) In the above embodiment, an example has been described in which the cooling device 100 is used to cool the heat-generating element 70, which is an electronic device. However, the object to be cooled is not limited to an electronic device. The cooling device 100 including the heat transfer member 80 of this embodiment can be applied to a wide range of objects that require cooling.

[0083] (2) The cooling device 100 is not limited to the configuration disclosed in the above embodiment. For example, if the refrigerant liquid 40 in the accommodation space 331 away from the heat generating element 70 can be maintained as a subcooled liquid, the circulation circuit 50, the circulation pump 10, and the heat dissipation unit 20 may be eliminated.

[0084] (3) The heat transfer member 80 is not limited to the configuration disclosed in the above embodiment.

[0085] For example, in the above embodiment, the heat transfer member 80 is fixed to the heating element 70 by soldering, but the manner of fixing the heat transfer member 80 is not limited to this. For example, the heat transfer member 80 may be fixed to the heating element 70 by fastening means such as bolts, with a sheet-like or grease-like thermally conductive material that is electrically insulating and has high thermal conductivity interposed in the gap between the heat transfer member 80 and the heating element 70.

[0086] In the above embodiment, the fin portion 83 is formed by a plurality of grooves extending in the vertical direction, but this is not limiting. For example, the fin portion 83 may be formed by a plurality of grooves extending in the vertical direction and a plurality of grooves extending in the horizontal direction, as shown in Fig. 10. In other words, the fin portion 83 may form so-called pin fins.

[0087] In the above embodiment, the fin portion 83 is formed by a plurality of grooves each having a rectangular cross section, but this is not limiting. For example, the fin portion 83 may be formed by a plurality of grooves each having a triangular or trapezoidal cross section. This makes it easier to form the boiling promotion surface 84 on the side surface between adjacent fins.

[0088] (4) In the boiling promotion surface forming step of the above embodiment, an example has been described in which shot blasting is used to form the boiling promotion surface 84, but the present invention is not limited to this. Laser processing, mechanical processing using a grinder or sander, etching, or the like may also be used as long as the boiling promotion surface 84 similar to that of the above embodiment can be formed.

[0089] (5) In the above embodiment, the cooling unit 30 includes the cooling tank 33 and the liquid storage tank 34 configured as separate bodies (i.e., separate members). However, the present invention is not limited to this. For example, the cooling tank 33 and the liquid storage tank 34 may be integrally formed.

[0090] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A heat transfer member that is applied to a cooling device (100) that cools an object to be cooled (70) while immersed in a liquid-phase refrigerant, and promotes heat transfer from the object to be cooled to the refrigerant, the object to be cooled is an electronic device, The refrigerant is a fluorine-based insulating refrigerant having a boiling point of 100° C. or less, The refrigerant is open to the atmosphere, In a boiling curve with the horizontal axis representing the degree of superheat dT of the refrigerant and the vertical axis representing the heat flux q, the degree of superheat is 10 K, and the heat flux q is 300 kW / m 2 The above heat transfer component.

2. A heat transfer member that is applied to a cooling device (100) that cools an object to be cooled (70) while immersed in a liquid-phase refrigerant, and promotes heat transfer from the object to be cooled to the refrigerant, A boiling promotion surface (84) that promotes boiling of the refrigerant is formed on the refrigerant side surface (82) that contacts the refrigerant, In the roughness curve of the boiling promotion surface, a portion formed between adjacent apexes is defined as a hole (84c), the distance between the adjacent apexes is defined as a hole width Gw, the distance between a line connecting the adjacent apexes and a bottom between the adjacent apexes is defined as a hole depth Gd, the value obtained by dividing the hole depth Gd by the hole width Gw is defined as a hole aspect ratio Gd / Gw, and the number of the holes per unit length is defined as a hole number Ng. A heat transfer member in which the number Ng of holes having a hole aspect ratio Gd / Gw of 0.01 or more is 9 or more per mm.

3. moreover, 315μm≧Gw≧1.7μm The heat transfer member according to claim 2 .

4. A contact surface (81) that contacts the object to be cooled; and an area enlarging portion (83) for enlarging the area of ​​the refrigerant side surface, 4. The heat transfer member according to claim 2, wherein the boiling promotion surface is formed on at least 50% of the area enlarged portion.