WO2023167087A1

WO2023167087A1 - Cooling member, cooler, cooling device, and cooling member manufacturing method

Info

Publication number: WO2023167087A1
Application number: PCT/JP2023/006574
Authority: WO
Inventors: 昌司森; 正関口; 侑也林田
Original assignee: 国立大学法人九州大学
Priority date: 2022-03-01
Filing date: 2023-02-22
Publication date: 2023-09-07
Also published as: JP2023127436A

Abstract

Provided are a cooling member having a favorable cooling effect, a cooler, a cooling device, and a cooling member manufacturing method. The cooling member comprises integrally formed electrolytic metal foils constituted by a double-layer porous material, each layer having different mean pore sizes.

Description

Cooling member, cooler, cooling device, and method for manufacturing cooling member

The present invention relates to a cooling member, a cooler, a cooling device, and a method for manufacturing the cooling member.

A cooler that uses a boiling method that cools a heating element from the outside with a working fluid such as water is known. Boiling methods include the pool boiling method and the forced flow boiling method. Among them, the cooling mechanism for the heating element by the pool boiling method will be described. A conventional pool boiling type cooler generally comprises a container and a working fluid contained in the container, and the container has a contact portion with a heating element to be cooled. When heat is generated in the heating element and transferred to the working fluid through the contact portion, the working fluid in the vicinity of the contact portion boils. When vapor is generated by boiling, the working fluid is supplied to the contact portion due to the difference in gas-liquid density. The newly supplied working fluid thus evaporates further and removes heat from the heating element. The pool boiling type cooler does not require an external power source for circulating the liquid unlike the forced flow boiling type cooler, so it is advantageous in terms of compactness and energy saving.

However, when a large heat flux is applied to the contact area, the amount of evaporation of the working fluid increases and the contact area begins to be covered with steam. When the contact portion is completely covered with steam and becomes dry, and the working fluid is no longer supplied to the contact portion, the cooling capacity of the cooler significantly deteriorates. The heat flux in this state is called "critical heat flux (CHF)".

In order to address such a problem, in Patent Document 1, separate porous bodies are laminated to form two layers, which are provided between the heating element and the water in the cooling container, and the capillary action of the porous bodies causes the water to cool. is supplied to the heating element, and the steam generated thereby is discharged into the water in the container, thereby improving the conventional critical heat flux with a simple structure.

JP 2016-40505 A

However, in order to cope with the recent increase in the heat generation density of heat generating bodies such as electronic devices, it is desired to further improve the cooling effect of the cooler.

In order to solve such problems, it is an object of the present invention to provide a cooling member, a cooler, a cooling device, and a method of manufacturing a cooling member that have a good cooling effect.

As a result of repeated studies, the present inventors have found that the cooling member is configured by integrally forming two layers of electrolytic metal foils with different average pore sizes, and the electrolytic metal foil with a relatively small average pore size and the average pore size are relatively small. It was found that by providing the relatively large electrolytic metal foils in this order from the heating element side, the critical heat flux is improved and a cooler having a good cooling effect can be obtained.

The above problems are solved by the present invention specified as follows.
(1) A cooling member integrally formed with an electrolytic metal foil composed of two layers of porous bodies having different average pore diameters.
(2) The two layers of electrolytic metal foil supply the working fluid to the surface of the heating element by capillary action when they are provided in a container containing the working fluid so as to face the heating element. The cooling member according to (1), comprising a working fluid supply section and a steam discharge section for discharging steam generated on the surface of the heating element to the working fluid side.
(3) The cooling member according to (2), wherein each of the two layers of electrolytic metal foil has a honeycomb structure.
(4) A boiling type cooler for cooling a heating element,
a container containing a working fluid;
a cooling member according to any one of (1) to (3) provided in the container so as to face the surface of the heating element;
with
The cooling member is a cooler in which an electrolytic metal foil having a relatively small average pore size and an electrolytic metal foil having a relatively large average pore size are provided in this order from the heating element side.
(5) A working fluid introducer provided so as to be laminated on the side of the working fluid of the electrolytic metal foil having a relatively large average pore diameter, and introducing the working fluid to the electrolytic metal foil having a relatively large average pore diameter. The cooler according to (4), further comprising:
(6) the cooler according to (4) or (5);
a condenser connected to the vessel of the cooler to liquefy vaporized working fluid;
cooling system.
(7) forming a first layer of electrolytic metal foil having a relatively small average pore size by electrolytic deposition, and subsequently forming a second layer of electrolytic metal foil having a relatively large average pore size by electrolytic deposition; A method of manufacturing a cooling member in which the electrolytic metal foil composed of two layers of porous bodies with different average pore diameters is integrally formed by forming on the electrolytic metal foil.

According to the present invention, it is possible to provide a cooling member, a cooler, a cooling device, and a method of manufacturing a cooling member that have a good cooling effect.

It is a schematic diagram of the cooler 10 by a boiling system which concerns on embodiment of this invention. FIG. 3 is a schematic diagram of a boiling-type cooler 10 according to another embodiment of the present invention; 1 is a plan view of a porous body having a honeycomb structure; FIG. FIG. 3 is a schematic diagram of a boiling-type cooler 10 according to another embodiment of the present invention; 1 is a schematic diagram of a cooling device 20 having a cooler 10 according to an embodiment of the invention; FIG. It is a schematic diagram of the electrolytic deposition apparatus which concerns on a test example. (A) is an SEM cross-sectional observation photograph from directly above an electrolytic copper foil produced by applying a current of 3 A for 5 minutes, and (B) is a two-layer electrolytic copper foil produced under the conditions of (3) in the test example. It is a SEM cross-sectional observation photograph from directly above. It is an SEM cross-sectional observation photograph of a cross section of a two-layer electrolytic copper foil produced under the condition (3) of the test example. It is a schematic diagram of the pool boiling test apparatus of a test example. It is a boiling curve obtained by a test example.

Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings. It is understood that the present invention is not limited to the following embodiments, and that design changes, improvements, etc., can be made as appropriate based on the ordinary knowledge of those skilled in the art without departing from the scope of the present invention. should.

<Cooling member and cooler>
FIG. 1 is a schematic diagram of a cooling member 14 according to an embodiment of the present invention and a boil-type cooler 10 including the cooling member 14 . The cooler 10 includes a container 12 containing a working fluid 11 , and a cooling member 14 provided in the container 12 so as to be in contact with the working fluid 11 and to face the surface of the heating element 13 .

As the working fluid 11, for example, liquids having surface tension such as water, low-temperature fluids, refrigerants, and organic solvents can be used. In addition, in order to cope with the recent increase in heat generation density of heat generating elements such as electronic elements, electric An insulating fluid can also be suitably used.

The cooling member 14 is composed of a porous material. Since the cooling member 14 is made of a porous material, the working fluid 11 can be supplied to the surface of the heating element 13 by capillary action. Also, the pores of the porous body can serve as boiling nuclei near the surface of the heating element 13 .

The porous body of the cooling member 14 is made of a porous electrolytic metal foil. More specifically, the cooling member 14 has a structure in which two layers of electrolytic metal foils with different average pore sizes are integrally formed, and the electrolytic metal foil 22 with a relatively small average pore size and the electrolytic metal foil 22 with a relatively small average pore size A relatively large electrolytic metal foil 23 is provided in this order from the heating element 13 side. The first layer of the electrolytic metal foil 22 supplies the working fluid to the vicinity of the surface of the heating element 13 by capillary action when the working fluid evaporates near the surface of the heating element 13, but there is a limit mechanism of liquid supply by capillary force. Considering this, the smaller the capillary length (that is, the thickness of the first layer of electrolytic metal foil 22), the higher the limit, ie, the limit heat flux. On the other hand, vapor masses are formed on the surface of the heating element 13 under high heat flux conditions, and the volume of the vapor mass increases with time, and eventually the vapor masses are cut off from the surface of the heating element 13 . To explain the vapor mass and the vicinity of the contact portion in more detail, a liquid film of finite thickness (generally called a macro liquid film) exists between the vapor mass and the contact portion (that is, the bottom of the vapor mass). . Under such high heat flux conditions, burnout occurs when the macro-liquid film at the bottom of the vapor mass evaporates away while the vapor mass remains on the macro-liquid film. The heat flux at this time is called the critical heat flux. The thickness of the first electrodeposited metal foil 22 is preferably thin because of the limit mechanism of liquid supply by capillary force (capillary limit mechanism) as described above. Drying of the liquid tends to occur in the vicinity of the surface of the electrolytic metal foil 22, and the critical heat flux becomes small.

Therefore, in the present invention, the porous body provided in the vicinity of the surface of the heating element 13 is the electrolytic metal foil 22 having a relatively small average pore diameter, and thereon (on the working fluid side) a relatively large average pore diameter That is, an electrolytic metal foil 23 having a relatively high working fluid permeability is provided. According to such a configuration, the working fluid is abundantly supplied toward the first-layer electrolytic metal foil 22 between the first-layer electrolytic metal foil 22 and the vapor mass above it. Since the metal foil 23 exists, even if the thickness of the first electrodeposited metal foil 22 is reduced, the occurrence of liquid drying is suppressed, and the critical heat flux can be prevented from being reduced. Further, it is preferable to increase the thickness of the electrolytic metal foil 23 of the second layer because the larger the amount of liquid supplied to the electrolytic metal foil 23 of the second layer, the better. Specifically, for example, when the thickness of the first-layer electrolytic metal foil 22 is reduced to about 100 μm, the thickness of the second-layer electrolytic metal foil 23 is preferably about 1 to 2 mm or more.

The types of the electrolytic metal foils 22 and 23 are not particularly limited as long as they can be made porous by gas bubbles during electrolytic deposition as described later. Electrolytic copper foil, electrolytic copper alloy foil, electrolytic aluminum foil, Electrolytic aluminum alloy foil, electrolytic nickel foil, electrolytic nickel alloy foil, electrolytic iron foil, electrolytic iron alloy foil and the like can be used, and electrolytic copper foil and electrolytic copper alloy foil are particularly preferred. Further, as the electrolytic copper alloy foil, the copper component of the base material includes Sn, Ag, Au, Co, Cr, Fe, In, Ni, P, Si, Te, Ti, Zn, B, Mn and Zr. The copper alloy may be constituted by containing 0.001 to 4.0% by mass of one or more of them in total. Moreover, an oxide film may be formed on the surfaces of the electrolytic metal foils 22 and 23 . When the oxide film is formed, the wettability is improved, so that the working fluid can be supplied smoothly.

The cooling member 14 has a structure in which two layers of electrolytic metal foils 22 and 23 with different average pore diameters are integrally formed. Here, although the details will be described later, the term "integral formation" means that the first layer of the electrolytic metal foil 22 is first formed by electrolytic deposition under predetermined electrolytic conditions, and then the second layer is formed by changing the electrolytic conditions. of the electrolytic metal foil 23 is formed. Such an integrally formed electrolytic metal foil can be easily confirmed by observing the cross section of two layers of electrolytic metal foil, and is simply formed by stacking two layers of separately formed electrolytic metal foils. It can be easily distinguished from laminates. Specifically, in a laminate formed by stacking two layers of separately formed electrolytic metal foils, one electrolytic metal foil and the other electrolytic metal foil are only superimposed. The boundary is identified as a very sharp line, and the two layers of electrolytic metal foil are not chemically bonded at the interface. On the other hand, in the case of the structure in which two layers of electrolytic metal foil are integrally formed as in the present invention, the second layer of electrolytic metal foil is electrolytically deposited on the first electrolytic metal foil. , there is a high possibility that the boundary between them in the cross section is an indistinct line when compared with a laminate formed by stacking two layers of separately formed electrolytic metal foils. In addition, the second-layer electrolytic metal foil has a structure in which the second-layer electrolytic metal foil is deposited on the surface of the first-layer electrolytic metal foil. For this reason, it is possible to easily distinguish between the structure of a laminate in which two layers of separately formed electrolytic metal foils are laminated and the structure in which the two layers of electrolytic metal foils 22 and 23 according to the present invention are integrally formed. can.

Since the two layers of electrolytic metal foils 22 and 23 with different average pore diameters are integrally formed, air bubbles do not enter between the first and second layers of electrolytic metal foil. For this reason, in a laminated body formed by stacking two layers of separately formed electrolytic metal foils, the delivery of the working fluid between the first and second layers of the electrolytic metal foil proceeds smoothly.

As will be described later, the electrodeposited metal foils 22 and 23 become porous due to the influence of air bubbles generated during electrolytic deposition in the manufacturing method. The smaller the current value during electrolytic deposition, the smaller the size of the bubbles generated, and the deposited metal foil also becomes a dense porous body having fine pores. Thus, the pore sizes of the electrolytic metal foils 22 and 23, which are porous bodies, can be adjusted by the electrolysis conditions. The average pore diameters of the electrolytic metal foils 22 and 23 can be obtained by measuring the diameters of arbitrary 10 pores, for example, from SEM observation photographs of cross sections, and calculating the average value thereof. The first layer of electrolytic metal foil 22 provided on the heating element 13 side typically has an average pore size of 75 to 150 μm. The second-layer electrolytic metal foil 23 provided on the working fluid 11 side has an average pore diameter relatively larger than that of the first-layer electrolytic metal foil 22, typically 300 to 450 μm.

Electrolytic metal foils 22 and 23 are, as shown in FIG. A steam discharge part 17 that discharges to the fluid 11 side may be provided. An example of the porous electrolytic metal foil having the working fluid supply portion 16 and the vapor discharge portion 17 is a porous electrolytic metal foil having a honeycomb structure, as shown in the plan view of FIG. . In this case, the working fluid supply part 16 of the first-layer electrolytic metal foil 22 supplies the working fluid 11 to the vicinity of the surface of the heating element 13 by capillary action of the grid-like porous body portion around the holes of the honeycomb structure. . The vapor discharge portion 17 of the first-layer electrolytic metal foil 22 discharges the vapor generated by the heat from the heating element 13 to the second-layer electrolytic metal foil 23 side through the holes of the honeycomb structure. By supplying the working fluid 11 and discharging the steam using separate paths in this way, it is possible to suppress the occurrence of the problem that the steam covers the contact portion and limits the critical heat flux. In the second-layer electrolytic metal foil 23, the working fluid 11 is supplied to the first-layer electrolytic metal foil 22 by the lattice-like porous body portion around the holes of the honeycomb structure, similarly to the first-layer electrolytic metal foil 22. The holes of the honeycomb structure function as a steam discharge part 17 for discharging the steam discharged from the electrolytic metal foil 22 of the first layer to the side of the working fluid 11 . The second-layer electrolytic metal foil 23 has a higher permeability of the working fluid 11 than the first-layer electrolytic metal foil 22 and has a function of retaining the working fluid 11. It functions so that the working fluid 11 is rapidly supplied to the electrolytic metal foil 22 of the first layer even while the coalesced bubbles remain in the upper part.

The shape of the holes of the honeycomb structure of the electrolytic metal foils 22 and 23 can be various shapes such as polygonal, circular, and elliptical. Indicates the radius of the circle. Since the contact area of the porous body with the surface of the heating element 13 becomes large, the hole radius of the honeycomb structure for releasing the steam generated at the contact portion into the water should be small. can. In addition, since the pressure loss when passing through the porous bottom can be reduced, the gap between the holes of the honeycomb structure for releasing the steam generated at the contact portion into the water is preferably small, for example, 100 to 1000 μm. be able to.

Although FIG. 2 illustrates the working fluid supply portion 16 and the steam discharge portion 17 so as to be perpendicular to the surface of the lower heating element 13 and the upper side of the working fluid 11 side, the working fluid supply portion 16 and the steam discharge portion 17 are perpendicular to each other. is configured so that, for example, a curved path or a bent path is provided instead of being perpendicular to each other as long as it provides a path between the surface facing the surface of the heating element 13 and the surface on the side of the working fluid 11. may have been

As shown in the schematic cross-sectional view of FIG. 4, the cooler 10 is provided so as to be laminated on the working fluid 11 side of the second layer electrolytic metal foil 23 of the cooling member 14, and the working fluid 11 is electrolyzed in the second layer. It is preferable to further include a working fluid introducing body 18 having a working fluid introducing portion 19 leading to the metal foil 23 . The thickness of the electrolytic metal foils 22 and 23 of the cooling member 14 should be thin from the viewpoint of the capillary limit mechanism. There is a problem that the heat flux becomes small. On the other hand, as shown in FIG. 4, by providing a working fluid introduction body 18 for introducing the working fluid 11 to the electrolytic metal foils 22 and 23 on the electrolytic metal foils 22 and 23 (on the working fluid side), electrolysis can be performed. Between the metal foils 22, 23 and the vapor mass above them, the working fluid 11 is abundantly supplied toward the electrolytic metal foils 22, 23 and the working fluid 11 is retained above the electrolytic metal foils 22, 23. A fluid introducer 18 is present. Therefore, even if the thickness of the electrolytic metal foils 22 and 23 is reduced, it is possible to suppress the occurrence of liquid depletion and prevent the critical heat flux from becoming small. In addition, it is preferable to increase the thickness of the working fluid introducer 18 because the larger the liquid supply amount of the working fluid introducer 18 is, the better. Specifically, for example, when the thickness of each of the electrolytic metal foils 22 and 23 is reduced to about 100 μm, the thickness of the working fluid introduction body 18 is preferably about 1 mm or more.

The working fluid introduction body 18 may have a plurality of holes penetrating in the height direction, and the plurality of holes may constitute the working fluid introduction part 19 . Moreover, the plurality of holes that constitute the working fluid introduction part 19 may have a circular or polygonal cross section.

The material constituting the working fluid introducer 18 may be a porous material or a non-porous material. As a material for forming the working fluid introduction member 18, metal such as stainless steel and Teflon (registered trademark), resin, or the like can be used. In particular, by forming the working fluid introduction body 18 from metal, the wettability of the working fluid introduction body 18 is improved and the hydrophilicity is improved, so that a larger amount of the working fluid 11 is taken in and supplied to the surface of the heating element 13. It becomes possible to

Further, as another aspect of the present invention, cooling can be performed by immersing the entire heating element 13 in the working fluid 11, or partially immersing the heating element 13 from the liquid surface of the working fluid 11. . In this case, the heating element 13 may take various forms, such as a floating state or a state placed on the bottom surface of the container 12, depending on the circumstances. By attaching the cooling member 14, cooling can be performed in the same manner as in the above example.

<Method for Manufacturing Cooling Member and Cooler>
Next, a method for manufacturing a cooling member and a cooler according to an embodiment of the present invention will be described.
First, a cooling member having a configuration in which two layers of electrolytic metal foils having different average pore diameters are integrally formed is produced using an electrolytic deposition apparatus. Specifically, the anode and cathode of the electrolytic deposition apparatus are electrically connected to a power supply. A plating solution for a predetermined metal is provided in the electrolytic bath. The amount of plating solution in the electrolytic bath is not particularly limited, but may be 200 to 400 mL.
When electrolysis is performed in this state, metal ions contained in the plating solution in the electrolytic bath receive electrons on the cathode and the metal is deposited. On the other hand, hydrogen ions contained in the plating solution in the electrolytic bath receive electrons on the cathode and become hydrogen gas. The deposition reaction of these metals and the generation of hydrogen gas occur simultaneously, the hydrogen gas partially hinders the deposition reaction of the metal, and a porous structure of the metal is formed on the surface of the cathode.

After forming (electrodepositing) the first layer of electrolytic metal foil on the cathode in this manner, the current value and, if necessary, the deposition reaction time are adjusted while the plating solution in the electrolytic bath remains unchanged. Instead, a second layer of electrolytic metal foil is similarly formed (electrodeposited) on the first layer of electrolytic metal foil. By doing so, the first-layer electrolytic metal foil and the second-layer electrolytic metal foil are integrally formed. In addition, hydrogen gas can be generated more actively by increasing the current value during the electrolysis as compared to that during the production of the first electrodeposited metal foil. Therefore, the average pore diameter of the second-layer electrolytic metal foil can be made relatively larger than the average pore diameter of the first-layer electrolytic metal foil. For example, in the deposition reaction of the first electrodeposited metal foil with a relatively small average pore size, a current density of 0.38 to 0.46 A/cm ² is applied for 4 to 6 minutes, and the average pore size is relatively small. In the deposition reaction of the large second layer of electrolytic metal foil, it is preferable to apply current at a current density of 0.80 to 0.88 A/cm ² for 4 to 6 minutes or more.

Thereafter, a low current of 0.3 A is preferably applied for 30 minutes in order to increase the strength of the electrolytic metal foil, which is a porous body.
Next, the integrally formed two-layer electrolytic metal foil is peeled off from the cathode.
Finally, it is preferable to sinter at 850-950° C. for 30 minutes to 1 hour.

Next, for the desired heating element, a container is provided so that the surface thereof becomes a part of the wall surface of the container, and the two layers of electrolytic metal foils are arranged so that the first electrolytic metal foil having a relatively small average pore diameter is It is placed on the surface of the heating element so as to face the surface of the desired heating element. If necessary, a honeycomb-structured working fluid introducing member made of stainless steel or the like may be further disposed on the second layer of the electrolytic metal foil.
The container is then filled with the desired working fluid.
In this way, a boiling type cooler for cooling the heating element can be manufactured. In addition, the working fluid may be placed in the container before placing the electrolytic copper foil.

When forming two layers of electrolytic metal foil into the honeycomb structure shown in FIG. It is controlled so that electrolytic deposition does not occur only at that position. In this way, the portion where the insulating film is not placed surrounds the hole, and an electrolytic metal foil having a honeycomb structure can be produced.

<Cooling device>
FIG. 5 shows a schematic diagram of a cooling device 20 comprising a cooler 10 according to an embodiment of the invention. The cooling device 20 comprises a cooler 10 and a condenser 21 connected to the container 12 . In the condenser 21 the vaporized working fluid 11 is condensed and returned to the container 12 . The cooling device 20 does not require an external power source such as a pump, and is excellent in compactness and energy saving as a whole device.

<Application>
The cooler 10 and the cooling device 20 of the present invention can be applied to various electronic devices, nuclear reactor pressure vessels, and other general thermal devices having high heat generation densities. For example, high-performance capillary pump loops, semiconductor lasers, data center server cooling, CFC-cooled chopper controllers, and power electronic equipment can be considered. Alternatively, it can be applied to a water-cooling jacket installed on the side or bottom of a fire-resistant wall for externally cooling the fire-resistant wall of a large refuse incinerator or the like to reduce damage.

The present invention will be described in more detail below with examples, but the present invention is not limited to these.

<Test Example 1>
- Production of electrolytic copper foil -
An electrolytic deposition apparatus is shown in FIG. The electrolytic deposition apparatus had an anode (copper plate) and a cathode (disc-shaped copper plate with a diameter of 30 mm), each of which was electrically connected to a DC power supply. Each copper plate had a purity of 99.96%, a thickness of 0.3 mm, and a distance between electrodes of 2 cm.
Also, 200 mL of a plating solution containing 0.4 mol/L of CuSO ₄ and 1.5 mol/L of H ₂ SO ₄ was prepared as a copper sulfate plating bath.

When an electric current is passed through this copper sulfate plating bath, the following reactions (A) and (B) occur simultaneously at the cathode. That is, the deposition reaction of copper and the generation of hydrogen gas occur simultaneously, the deposition reaction of copper is partially hindered by the hydrogen gas, and a porous structure of copper is formed on the cathode surface.
Cu ²⁺ + 2e ⁻ → Cu (A)
2H ⁺ + 2e ^- → H ₂ (B)

First, using a DC power supply (manufactured by Nippon Stabilizer Industry Co., Ltd., maximum voltage 18 V, maximum current 100 A), disc-shaped electrolytic copper foils with a diameter of 30 mm were produced under the following conditions (1) to (5). did.
(1) A single-layer electrolytic copper foil was produced by applying a current of 3 A for 4 minutes.
(2) A single-layer electrolytic copper foil was produced by applying a current of 3 A for 12 minutes.
(3) A current of 3 A was applied for 5 minutes to prepare a first layer of electrolytic copper foil, and then a current of 6 A was applied for 5 minutes to integrally form a second layer of electrolytic copper foil on the first layer of electrolytic copper foil. .
(4) A current of 3 A was applied for 5 minutes to prepare a first layer of electrolytic copper foil, and then a current of 6 A was applied for 10 minutes to integrally form a second layer of electrolytic copper foil on the first layer of electrolytic copper foil. .
(5) A current of 3 A was applied for 5 minutes to prepare a first layer of electrolytic copper foil, and then a current of 6 A was applied for 15 minutes to integrally form a second layer of electrolytic copper foil on the first layer of electrolytic copper foil. .
Since copper and hydrogen are generated according to the chemical reaction formula shown above according to the number of flowing electrons, the experiment was conducted in the constant current mode. The applied voltage varied with the copper deposits.

Next, in order to increase the strength of the porous body, a low current of 0.3 A was applied to each of the electrolytic copper foils obtained under the conditions (1) to (5) for 30 minutes.
Next, the resulting electrolytic copper foil is peeled off from the cathode and sintered at 950°C for 30 minutes in a vacuum furnace (manufactured by Furutec Co., Ltd., maximum temperature 1200°C, furnace size: diameter 43 mm x height 60 mm). let me

Fig. 7(A) shows an SEM cross-sectional observation photograph from directly above of the electrolytic copper foil produced by applying a current of 3 A for 5 minutes. FIG. 7(B) shows a SEM cross-sectional observation photograph taken from directly above the two-layer electrolytic copper foil produced under the conditions of (3) above. Comparing these figures, the pore diameter of the porous electrodeposited copper foil formed at a current of 3A is about 150 μm, while the porous electrodeposited copper foils formed at a current of 3.0A and 6.0A, respectively, have a pore diameter of about 150 μm. It can be seen that the pore diameter is as large as about 250 μm. Therefore, it can be seen that if the current value during electrolytic deposition is large, the pore size of the porous material becomes relatively large, and as a result, the average pore size becomes relatively large.

FIG. 8 shows an SEM cross-sectional observation photograph of the two-layer electrolytic copper foil produced under the conditions of (3) above. As can be seen from FIG. 8, since the first electrodeposited copper foil and the second electrodeposited copper foil are integrally formed by electrolytic deposition, the boundary line between them is unclear. For this reason, it can be seen that the integrally formed two-layer electrolytic copper foil can be easily distinguished from a laminate formed by simply stacking two layers of separately formed electrolytic metal foils.

-Pool Boiling Test-
FIG. 9 shows a schematic diagram of the pool boiling test apparatus. The surface of the heating element was at the same height as the bottom of the pool, and the diameter of the surface of the heating element in contact with the working fluid was 30 mm. Electrodeposited copper foils prepared under the conditions (1) to (5) by the above-described electrolytic deposition method were fixed on the surface of the copper block by soldering. In addition, a copper block on which no electrolytic copper foil was provided was treated as a "bare surface" and similarly used as an experimental object.
Heating was provided by a cartridge heater embedded in the bottom of the copper block. A K-type sheath thermocouple with a diameter of 0.5 mm is placed on the central axis of the cylindrical portion of the copper block at positions 10 mm (TC1), 15 mm (TC2), 20 mm (TC3), and 25 mm (TC4) below the surface of the heating element. was installed, and the heat transfer surface temperature was calculated from the measured values of these thermocouples, and the heat flux on the surface of the heating element was calculated from the indicated temperature difference, the set distance, and the thermal conductivity of copper by Fourier's equation.
The pool was made of Pyrex (registered trademark) glass with an inner diameter of 87 mm, and internal boiling was observed. The working fluid was distilled water, the water depth was 60 mm, and the system pressure was 0.1 MPa. The generated vapor was condensed in a cooler and returned to the container.
In the experiment, heating was performed while increasing the voltage applied to the cartridge heater by about 5 V (in steps of about 0.10 MW/m ² ). Steady state was assumed to be reached and measurements were taken. The above operation was repeated until a steady state could not be maintained and the wall temperature began to rise rapidly, causing burnout. When burnout occurred, the heating was stopped immediately, and the heat flux just before that was taken as the critical heat flux.

FIG. 10 shows boiling curves obtained by the above experiment. Electrodeposited copper foil having a two-layer integrated structure formed by electrolytic deposition at current values of 3 A and 6 A has a greater heat removal capacity than a single-layer electrolytic copper foil electrodeposited at a current value of 3 A. I know you are. The factors for this are the electrolytic copper foil in the lower layer, which has fine pores in the porous body and more dendritic copper deposits are in contact with the surface of the heating element, and the structure with large gaps through which steam is easily discharged, but the liquid retention It is thought that the two-layer integrated structure with the upper electrodeposited copper foil, which has high performance, prevented the liquid from drying up on the surface of the heating element. By using the electrodeposited copper foil with the two-layer integrated structure, it was possible to achieve a maximum heat flux of 400 W/cm ² , about four times that of the bare surface.

10 Cooler 11 Working fluid 12 Container 13 Heating element 14 Cooling member 16 Working fluid supply unit 17 Steam discharge unit 18 Working fluid introduction member 19 Working fluid introduction unit 20 Cooling device 21 Capacitor 22 Electrolytic metal foil with relatively small average pore diameter (Electrodeposited copper foil for the first layer)
23 Electrolytic metal foil with relatively large average pore diameter (second-layer electrolytic copper foil)

Claims

A cooling member integrally formed with an electrolytic metal foil composed of two layers of porous bodies with different average pore diameters.
When the two layers of electrolytic metal foils are provided in a container containing a working fluid so as to face the heating element, the working fluid is supplied to the surface of the heating element by capillary action. 2. The cooling member according to claim 1, further comprising: a portion, and a steam discharge portion for discharging steam generated on the surface of the heating element toward the working fluid.
The cooling member according to claim 2, wherein each of the two layers of electrolytic metal foil has a honeycomb structure.
A boiling type cooler for cooling a heating element,
a container containing a working fluid;
a cooling member according to any one of claims 1 to 3, provided in the container so as to face the surface of the heating element;
with
The cooling member is a cooler in which an electrolytic metal foil having a relatively small average pore size and an electrolytic metal foil having a relatively large average pore size are provided in this order from the heating element side.
It further comprises a working fluid introduction member provided so as to be laminated on the working fluid side of the electrolytic metal foil having a relatively large average pore diameter, and introducing the working fluid to the electrolytic metal foil having a relatively large average pore diameter. 5. A cooler according to claim 4.
a cooler according to claim 4 or 5;
a condenser connected to the vessel of the cooler to liquefy vaporized working fluid;
cooling system with
A first layer of electrolytic metal foil having a relatively small average pore size is formed by electrolytic deposition, and then a second layer of electrolytic metal foil having a relatively large average pore size is formed by electrolytic deposition. A method for manufacturing a cooling member integrally formed with an electrolytic metal foil composed of two layers of porous bodies having different average pore diameters by forming the foil on the foil.