JP2024008426A - Boiling-cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiling-cooling device with a simple structure which can be hardly closed by foreign materials and can improve the performance of heat transmission.

SOLUTION: The boiling-cooling device includes: a liquid refrigerant; and a heat transmission member 5 having a heat propagation surface FT for boiling the refrigerant by heat from a heat generator. The heat propagation surface FT is arranged along a vertical line, and has a first surface 51 and a second surface 52 arranged higher in a vertical direction than the first surface 51 and recessed more than the first surface 51. The depth H3 of the second surface 52 is larger than the diameter of separated air bubbles generated by boiling of the refrigerant in a flat surface. Also, it is preferable that the heat transmission surface FT is arranged higher in the vertical direction than the second surface 52 and includes a third surface 53 recessed more than the second surface 52.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2024,JPO&INPIT

Description

TECHNICAL FIELD This disclosure relates to evaporative cooling devices.

2. Description of the Related Art Boiling cooling devices are known that cool a heating element by utilizing heat transport due to latent heat accompanying boiling of a refrigerant. An example of this device is the boiling cooling device described in Patent Document 1.

The boiling cooling device described in Patent Document 1 includes a boiling heat transfer member having a boiling heat transfer surface immersed in a refrigerant. This boiling cooling device boils the refrigerant by transmitting heat from the heating element to the refrigerant through the boiling heat transfer surface.

Further, in Patent Document 1, a plurality of holes having rough inner circumferential surfaces are provided in the boiling heat transfer surface to improve the cooling efficiency of the heating element.

JP 2017-15269 Publication

However, if the shape of the heat transfer surface is made complex and fine in order to further improve heat transfer performance, there is a risk that blockage due to foreign matter may occur during long-term use. Furthermore, it is difficult and costly to process a heat transfer surface with a complex and minute shape. Therefore, there is a need for a heat transfer surface with a simple structure that is less likely to be blocked by foreign matter and can improve heat transfer performance.

In order to solve the above problems, a boil cooling device according to a preferred embodiment of the present disclosure includes a liquid refrigerant and a heat transfer member having a heat transfer surface that boils the refrigerant using heat from a heating element. , the heat transfer surface is arranged along a vertical line, and has a first surface and a second surface arranged vertically above the first surface and recessed than the first surface, The depth of the second surface is larger than the diameter of bubbles generated by boiling of the refrigerant on the plane.

Further, a boiling cooling device according to a preferred aspect of the present disclosure includes a liquid refrigerant and a heat transfer member having a heat transfer surface that boils the refrigerant using heat from a heating element, and the heat transfer surface includes: arranged along a vertical line, including a first surface, a second surface arranged vertically above the first surface and recessed from the first surface, and a second surface arranged vertically above the second surface. , a third surface recessed than the second surface, a first step surface connecting the first surface and the second surface, and a second step surface connecting the second surface and the third surface. , and the distance along the horizontal plane from the first connecting portion between the first surface and the first stepped surface to the second connecting portion between the second surface and the second stepped surface is It is larger than the diameter of the bubbles that are released due to boiling of the refrigerant.

Further, a boiling cooling device according to a preferred aspect of the present disclosure includes a liquid refrigerant and a heat transfer member having a heat transfer surface that boils the refrigerant using heat from a heating element, and the heat transfer surface includes: a first region arranged along a vertical line and having a plurality of first recesses; and a second region arranged vertically above the first region and having a plurality of second recesses; The first opening width along the vertical line of each of the plurality of first recesses is larger than the second opening width along the vertical line of each of the plurality of second recesses.

BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective view which shows the schematic structure of the boiling cooling device based on 1st Embodiment. FIG. 2 is a sectional view of the evaporative cooling device shown in FIG. 1. FIG. FIG. 2 is a plan view of the heat transfer member shown in FIG. 1. FIG. 4 is a side view of the heat transfer member shown in FIG. 3. FIG. 5 is a partially enlarged view of the heat transfer member shown in FIG. 4. FIG. FIG. 3 is a diagram for explaining suppression of coalescence of bubbles on a heat transfer surface. FIG. 2 is a diagram for explaining the behavior of bubbles on a conventional heat transfer surface. FIG. 2 is a diagram for explaining the behavior of bubbles on a conventional heat transfer surface. It is a figure which shows the heat transfer member of a 1st modification. It is a figure which shows the heat transfer member of a 2nd modification. It is a figure which shows the heat transfer member of a 3rd modification. It is a figure which shows the heat transfer member of a 4th modification. It is a figure which shows the heat transfer member of a 5th modification. It is a figure which shows the heat transfer member of a 6th modification. It is a top view of the heat transfer member of 2nd Embodiment. 16 is a side view of the heat transfer member shown in FIG. 15. FIG. 17 is a partially enlarged view of the heat transfer member shown in FIG. 16. FIG. FIG. 3 is a diagram for explaining the generation of bubbles on a heat transfer surface. FIG. 3 is a diagram for explaining the growth of bubbles on a heat transfer surface. FIG. 3 is a diagram for explaining the growth of bubbles on a heat transfer surface. FIG. 3 is a diagram for explaining the separation of bubbles from a heat transfer surface. FIG. 6 is a diagram for explaining the action of bubbles generated in the first region of the heat transfer surface. It is a figure which shows the heat transfer member of a 7th modification. It is a figure which shows the heat transfer member of the 8th modification. It is a figure which shows the heat transfer member of a 9th modification. It is a figure which shows the heat transfer member of the 10th modification. It is a figure which shows the heat transfer member of the 11th modification. It is a figure which shows the heat transfer member of the 12th modification. It is a figure which shows the heat transfer member of the 13th modification.

Hereinafter, preferred embodiments according to the present disclosure will be described with reference to the accompanying drawings. In the drawings, the dimensions and scale of each part may differ from the actual size, and some parts are shown schematically to facilitate understanding. Further, the scope of the present disclosure is not limited to these forms unless there is a statement specifically limiting the present disclosure in the following description.

1. First embodiment 1-1. Overview of Boiling Cooling Device FIG. 1 is a perspective view showing a schematic configuration of a boiling cooling device 1 according to the first embodiment. For convenience, the following description will be made using the X-axis, Y-axis, and Z-axis, which are perpendicular to each other, as appropriate. Further, hereinafter, one direction along the X axis is the X1 direction, and the direction opposite to the X1 direction is the X2 direction. One direction along the Y axis is the Y1 direction, and the direction opposite to the Y1 direction is the Y2 direction. One direction along the Z axis is the Z1 direction, and the direction opposite to the Z1 direction is the Z2 direction. Further, the XY plane is parallel to the horizontal plane. Further, the Z axis is parallel to the vertical line, the Z1 direction corresponds to the vertically upward direction, and the Z2 direction corresponds to the vertically downward direction. Note that the direction of the Z-axis in real space is determined depending on the installation orientation of the evaporative cooling device 1. The Z axis may be inclined within a range of 45° or less with respect to the vertical line. Furthermore, "a direction along a vertical line" includes not only a direction completely parallel to a vertical line, but also a direction slightly inclined with respect to a vertical line without departing from the invention described in this specification. Furthermore, in this specification, "equal" does not only mean strictly equal, but also includes within the range of manufacturing error, etc.

The boiling cooling device 1 cools a heating element 100 shown by a two-dot chain line in FIG. The heating element 100 is, for example, a power semiconductor element such as a diode or an IGBT (Insulated Gate Bipolar Transistor). Power semiconductor elements are installed, for example, in power electronic products such as inverters or rectifiers installed in railway vehicles, automobiles, household electric machines, and the like.

In the example shown in FIG. 1, the heating element 100 has a flat shape along the XZ plane. Note that in FIG. 1, the outer shape of the heating element 100 is schematically shown. The shape of the heating element 100 shown in FIG. 1 is just an example, and it can be appropriately shaped into any desired shape. Note that the number of heating elements 100 is not limited to one, and may be two or more. When the number of heating elements 100 is two, for example, the two heating elements 100 are arranged side by side in the direction along the Y-axis so that the evaporative cooling device 1 is sandwiched therebetween. Further, the heating element 100 is not limited to a power semiconductor element, and may be any other electrical or electronic component that generates heat when driven or energized, as long as cooling is required.

FIG. 2 is a sectional view of the boiling cooling device 1 shown in FIG. The evaporative cooling device 1 shown in FIG. 2 is a loop-type thermosyphon cooler that utilizes the density difference between vaporized refrigerant RE and liquefied refrigerant RE. The boiling cooling device 1 includes a heat receiving section 10, a heat radiating section 20, a first tube section 30, and a second tube section 40.

1-1a. Heat receiving part 10
The heat receiving section 10 has a box-shaped container 11. The container 11 has a storage chamber S10 containing the refrigerant RE as an internal space. The heat receiving unit 10 heats the refrigerant RE with the heat from the heating element 100, vaporizes the refrigerant RE, and generates a gas phase refrigerant.

In the illustrated example, the container 11 has a bottom plate 111, a top plate 112, and a side wall 113. A space surrounded by the bottom plate 111, the top plate 112, and the side wall 113 is the storage chamber S10. Further, the container 11 includes a heat transfer member 5 that receives heat from the heating element 100.

Each of the bottom plate 111 and the top plate 112 is a flat plate extending along the XY plane. The bottom plate 111 and the top plate 112 are arranged parallel to each other, and the top plate 112 is arranged in the Z1 direction with respect to the bottom plate 111. Further, the top plate 112 is provided with holes for connection with the first tube section 30 and the second tube section 40. A side wall 113 is arranged between the bottom plate 111 and the top plate 112.

The side wall 113 connects the outer circumferences of the bottom plate 111 and the top plate 112 over the entire circumference. The heating element 100 comes into contact with the outer peripheral surface of the side wall 113 . In the example shown in FIG. 1, the side wall 113 is a rectangular cylinder and is composed of four flat members. Among the four flat members, the flat member that comes into contact with the heating element 100 is the heat transfer member 5 . Note that another member, adhesive, or the like may be interposed between the heating element 100 and the container 11.

The heat transfer member 5 is arranged along the Z axis. The heat transfer member 5 has a heat transfer surface FT. The heat transfer surface FT constitutes a part of the inner wall surface of the container 11. The heat transfer surface FT is exposed inside the container 11 and comes into contact with the refrigerant RE. Further, the heat transfer surface FT is arranged along the Z axis. The heat transfer surface FT transfers heat from the heating element 100 to the refrigerant RE via the heat transfer member 5. When the refrigerant RE near the heat transfer surface FT is overheated to a temperature equal to or higher than its boiling point, a plurality of bubbles B are generated on the heat transfer surface FT.

The heat transfer member 5 is made of a material with excellent thermal conductivity. Specifically, the material of the heat transfer member 5 is, for example, a metal such as aluminum and copper, or an alloy containing the metal. Further, the material of the portion of the container 11 excluding the heat transfer member 5 is not particularly limited, but similar to the material of the heat transfer member 5, for example, metals such as aluminum and copper, or alloys containing the metals, etc. .

In the example shown in FIG. 1, the heat transfer member 5 is a part of the container 11, but it may be separate from the container 11. Further, the heat transfer member 5 may be composed of one member or may be composed of a plurality of members. Moreover, the shape of the container 11 shown in FIG. 1 is an example, and it can be suitably made into a desired shape. Further, in the example shown in FIG. 2, the heat transfer member 5 has a flat plate shape, but it may have another shape, for example, a block shape. Moreover, although the shape of the accommodation chamber S10 is a square prism, this shape is only an example, and it can be appropriately set to any desired shape.

1-1b. Heat radiation part 20
The heat radiating section 20 shown in FIG. 2 is arranged in the Z1 direction with respect to the heat receiving section 10. The heat radiation section 20 includes a container 21 and a plurality of heat radiation fins 22. The container 21 has, as an internal space, a condensing chamber S20 in which the refrigerant RE is condensed and liquefied from a vaporized state. In the heat radiation section 20, the gas phase refrigerant generated in the heat receiving section 10 is condensed to generate a liquid phase refrigerant.

In the illustrated example, the container 21 has a bottom plate 211, a top plate 212, and a side wall 213. A space surrounded by the bottom plate 211, the top plate 212, and the side wall 213 is the condensing chamber S20.

Each of the bottom plate 211 and the top plate 212 is a flat plate extending along the XY plane. The bottom plate 211 and the top plate 212 are arranged parallel to each other, and the bottom plate 211 is arranged in the Z2 direction with respect to the top plate 212. Further, the bottom plate 211 is provided with holes for connection with the first tube section 30 and the second tube section 40. A side wall 13 is arranged between the bottom plate 211 and the top plate 212. The side wall 213 connects the outer circumferences of the bottom plate 211 and the top plate 212 over the entire circumference. In addition, the shape of the container 21 shown in FIG. 1 is an example, and can be suitably made into a desired shape. Moreover, although the side wall 213 is cylindrical and the condensation chamber S20 is cylindrical, these shapes are merely examples, and the shapes can be appropriately changed to a desired shape.

The container 21 is made of a material with excellent thermal conductivity. Specific materials for the container 21 include, for example, metal materials such as copper, aluminum, or alloys of any of these.

Each radiation fin 22 is thermally connected to the container 21. Each radiation fin 22 is a flat member. The plurality of radiation fins 22 are spaced apart from each other in the thickness direction. Each radiation fin 22 is formed of a material with excellent thermal conductivity. The material of the radiation fins 22 is, for example, a metal material such as copper, aluminum, or an alloy of any of these. Further, each radiation fin 22 is provided with a hole into which the container 21 is inserted. The radiation fins 22 are fixed to the container 21 by, for example, expanding the tube, press-fitting, using an adhesive, screwing, brazing, or welding. Note that another member, adhesive, or the like may be interposed between each radiation fin 22 and the container 21.

Furthermore, the shape of the radiation fins 22 is not limited to the example shown in FIG. 1, and can be appropriately formed into any desired shape. Furthermore, the radiation fins 22 may be provided as necessary, or may be omitted. However, since the heat radiation section 20 has a plurality of radiation fins 22, the gas phase refrigerant can be efficiently condensed and liquefied.

1-1c. First pipe part 30
The first pipe section 30 is a straight steam pipe connected to each of the heat receiving section 10 and the heat dissipating section 20. The first pipe section 30 has the first flow path S30 as an internal space. The first flow path S30 transports the gas phase refrigerant generated by vaporizing the refrigerant RE in the heat receiving section 10 to the heat radiating section 20. In the illustrated example, one end of the first tube section 30 is not in contact with the refrigerant RE in the storage chamber S10, and the other end of the first tube section 30 projects from the bottom plate 211 into the condensation chamber S20. Further, although the width of the first flow path S30 is constant and the cross-sectional area of the first flow path S30 is constant, these may not be constant. Moreover, although the shape of the cross section of the first flow path S30 is circular, this is just an example, and it can be appropriately set to any desired shape.

The material of the first tube portion 30 is, for example, a metal material such as copper, aluminum, or an alloy of any of these. Note that the material of the first tube portion 30 is not limited to a metal material, and may be, for example, a ceramic material or a resin material. Further, the first tube portion 30 is fixed to the top plate 112 and the bottom plate 211 by brazing or the like.

1-1d. Second pipe section 40
The second pipe section 40 is a straight liquid pipe connected to the heat receiving section 10 and the heat dissipating section 20, respectively. The second pipe portion 40 has a second flow path S40 as an internal space. The second flow path S40 transports the liquid phase refrigerant generated by condensing the gaseous phase refrigerant in the heat radiation section 20 to the heat receiving section 10. One end of the second tube section 40 is not exposed in the condensing chamber S20, and the other end of the second tube section 40 is exposed in the storage chamber S10 and is in contact with the refrigerant RE. Further, although the width of the second flow path S40 is constant and the cross-sectional area of the second flow path S40 is constant, these may not be constant. Moreover, although the shape of the cross section of the second flow path S40 is circular, this is just an example, and it can be appropriately set to any desired shape.

The material of the second tube portion 40 is, for example, a metal material such as copper, aluminum, or an alloy of any of these. Note that the material of the second tube portion 40 is not limited to a metal material, and may be, for example, a ceramic material or a resin material. Further, the second tube portion 40 is fixed to the top plate 112 and the bottom plate 211 by brazing or the like.

In such a boiling cooling device 1, the heat of the heating element 100 is transmitted to the refrigerant RE in the container 11 via the heat transfer member 5, so that the refrigerant RE boils near the heat transfer surface FT. As a result, bubbles B are generated on the heat transfer surface FT. After the generated bubbles B separate from the heat transfer surface FT due to buoyancy, they become gaseous refrigerant RE above the liquid level of the refrigerant RE. The gaseous refrigerant RE is transported from the heat receiving section 10 to the heat radiating section 20 via the first pipe section 30. The gaseous refrigerant RE transported to the heat radiation section 20 is condensed in the heat radiation section 20 and returns to liquid refrigerant RE. The liquid refrigerant RE is transported from the heat radiating section 20 to the heat receiving section 10 via the second pipe section 40.

In the boiling cooling device 1, the heating element 100 can be cooled via the heat transfer member 5 due to the phase change of the refrigerant RE near the heat transfer surface FT. Further, by repeating the vaporization of the refrigerant RE in the heat receiving section 10 and the liquefaction in the heat dissipation section 20, the heating element 100 can be continuously and stably cooled.

Note that the evaporative cooling device 1 is not limited to the configuration shown in FIG. 1, and may be, for example, a thermosiphon that is integrally configured with a heat receiving part 10, a heat radiating part 20, a first pipe part 30, and a second pipe part 40. Good too. Further, the boiling cooling device 1 may be a pool boiling type or a forced convection boiling type that forcibly generates a flow of the refrigerant RE. In the case of a forced convection boiling type, for example, a pump (not shown) is connected to the first pipe section 30.

1-2. Refrigerant RE
Refrigerant RE contains a solvent and a surfactant. The solvent is a main component of the refrigerant RE, and is typically a medium that becomes liquid at room temperature under a predetermined pressure. Specific examples of the solvent include, but are not limited to, water, alcohols such as methanol or ethanol, ketones such as acetone, glycols such as ethylene glycol, fluorocarbons such as Fluorinert, and fluorocarbons such as HFC134a. and hydrocarbons such as butane. Among these, one type can be used alone or two or more types can be used in combination in the form of a mixed solution or the like.

The surfactant is used, for example, to suppress coalescence of the bubbles B. The surfactant may be a nonionic surfactant or an ionic surfactant such as an anionic surfactant or a cationic surfactant. By using an anionic surfactant or a cationic surfactant, coalescence of the bubbles B is suppressed by, for example, a repulsive force based on the Coulomb force of the surfactant. Further, by using the nonionic surfactant, coalescence of the bubbles B is suppressed, for example, due to steric hindrance of the nonionic surfactant.

Specific examples of the surfactant include fluorine surfactants, silicone surfactants, and hydrocarbon surfactants. When the solvent contained in the refrigerant RE is water, it is preferable to use a hydrocarbon surfactant that has excellent solubility in water.

By including the surfactant in the refrigerant RE, the surface tension γ of the refrigerant RE can be reduced. Therefore, the pressure difference Δp between the inside and outside of the bubble B and the degree of superheat ΔT can be reduced. As a result, the bubbles B grow more easily. Further, by reducing the surface tension of the refrigerant RE, the adhesion force of the bubbles B to the heat transfer surface FT can be reduced. Therefore, the buoyancy required for the bubbles B to leave the heat transfer surface FT is small, so that the diameter of the bubbles B when they leave the heat transfer surface FT can be reduced.

Further, as described above, since the refrigerant RE contains a surfactant, coalescence of adjacent bubbles B is suppressed. For this reason, each bubble B generated on the heat transfer surface FT becomes easy to leave while maintaining a small diameter. As a result, the generation cycle of bubbles B can be shortened. That is, the number of bubbles B generated per unit time can be increased. Furthermore, by suppressing the coalescence of adjacent bubbles B, it is possible to suppress an increase in the area of the heat transfer surface FT in contact with each bubble B. This prevents the heat transfer surface FT from being covered for a long time by a dry area that does not contribute to heat transfer. Therefore, by including the surfactant, it is possible to improve the heat transfer characteristics of the heat transfer surface FT compared to the case where the surfactant is not included. Therefore, the cooling performance of the evaporative cooling device 1 can be improved.

Note that the surfactant may be omitted. Moreover, the refrigerant RE may contain substances such as additives other than the solvent and the surfactant. However, in this case, the substance is included in the refrigerant RE at a content rate within a range that does not adversely affect the action of the refrigerant RE.

1-3. Heat transfer member 5
FIG. 3 is a plan view of the heat transfer member 5 shown in FIG. 1. FIG. 4 is a side view of the heat transfer member 5 shown in FIG. 3. As shown in FIGS. 3 and 4, the heat transfer surface FT of the heat transfer member 5 has a height difference. Specifically, the heat transfer surface FT has a stepped shape.

The heat transfer surface FT has a plurality of vertical surfaces 51 arranged along the Z-axis and a plurality of parallel step surfaces 52 arranged along the XY plane. Note that each vertical surface 51 may be arranged completely along a vertical line, or may be slightly inclined with respect to the vertical line without departing from the invention described in this specification. Similarly, each stepped surface 52 may be arranged completely along a horizontal plane, or may be slightly inclined with respect to the horizontal plane without departing from the invention described in this specification.

Moreover, as shown in FIG. 3, each vertical plane 51 extends along the X axis. Similarly, each stepped surface 52 extends along the X-axis. Moreover, as shown in FIG. 4, each vertical surface 51 is recessed in the Y2 direction with respect to the vertical surface 51 located below.

FIG. 5 is a partially enlarged view of the heat transfer member 5 shown in FIG. 4. As shown in FIG. 5, the heat transfer surface FT of the heat transfer member 5 includes a first surface 511, a second surface 512, a third surface 513, a first step surface 521, a second step surface 522, It has a third step surface 523. Note that the first surface 511, the second surface 512, and the third surface 513 are part of the plurality of vertical surfaces 51. The first step surface 521 , the second step surface 522 , and the third step surface 523 are part of the plurality of step surfaces 52 .

The first surface 511, the second surface 512, and the third surface 513 are parallel to each other and arranged along the Z axis. The second surface 512 is arranged further in the Z1 direction than the first surface 511, and the third surface 513 is arranged further in the Z1 direction than the second surface 512. Further, the second surface 512 is more recessed in the Y2 direction than the first surface 511, and the third surface 513 is more recessed in the Y2 direction than the second surface 512. Therefore, the first surface 511, the second surface 512, and the third surface 513 are different from each other in their positions on the XY plane, particularly in their positions on the Y axis. In addition, in the illustrated example, the length W1 of the first surface 511 along the Z-axis, the length W2 of the second surface 512 along the Z-axis, and the length W3 of the third surface 513 along the Z-axis. are equal to each other.

The first step surface 521, the second step surface 522, and the third step surface 523 are parallel to each other and arranged along the XY plane. The first stepped surface 521 connects the first surface 511 and the second surface 512. The second stepped surface 522 connects the second surface 512 and the third surface 513. Further, the first stepped surface 521, the second stepped surface 522, and the third stepped surface 523 are different from each other in position on the XY plane, particularly in the Y-axis. The second step surface 522 is located in the Y2 direction with respect to the first step surface 521, and the third step surface 523 is located in the Y2 direction with respect to the second step surface 522.

The second connecting portion 502 between the second surface 512 and the second stepped surface 522 is located in the Y2 direction relative to the first connecting portion 501 between the first surface 511 and the first stepped surface 521. The third connecting portion 503 between the third surface 513 and the third step surface 523 is located further in the Y2 direction than the second connecting portion 502.

Further, in the illustrated example, the depth H2 of the second surface 512 and the depth H3 of the third surface 513 are equal to each other. The depth H2 is also the length of the second step surface 522 along the Y axis. The depth H3 is also the length of the third stepped surface 523 along the Y axis. From another perspective, the depth H2 is also the distance from the first connecting portion 501 to the second connecting portion 502 along the horizontal plane. The depth H3 is also the distance from the second connecting portion 502 to the third connecting portion 503 along the horizontal plane.

Each of the depths H2 and H3 is larger than the separation bubble diameter D _base of the bubbles B generated by boiling of the refrigerant RE on a plane. Specifically, each of the depth H2 and the depth H3 is approximately several mm. Since each of the depths H2 and H3 is larger than the detached bubble diameter D _base , coalescence of the bubbles B can be effectively suppressed. Therefore, the heat transfer performance of the heat transfer member 5 can be improved.

The detached bubble diameter D _base is the diameter of the bubble B when detached from the heat transfer surface FT. The detached bubble diameter D _base is determined, for example, by calculation using the Cole and Rohsenow equation for pure water in a reduced pressure field. The formula is expressed by the following formula (1).
D _base =1.5×10 ⁻⁴ √(σ/g(ρ _L −ρ _V ))×Ja ^5/4 ...(1)
Ja=ρ _L c _PL T _sat /ρ _V h _fg
T _sat is the saturation temperature, σ is the surface tension, ρ _L is the liquid density, ρ _V is the vapor density, c _PL is the liquid specific heat, h _fg is the latent heat of vaporization, and g is the gravity It is acceleration.

For example, when determining the separation bubble diameter D _base of pure water at a pressure of 50 kPa,
Saturation temperature _Tsat : 355 [K]
Surface tension σ: 62.4 [mN/m]
Liquid density ρ _L : 971 [kg/m ³ ]
Vapor density ρ _V : 0.309 [kg/m ³ ]
Liquid specific heat c _PL : 4.20 [kJ/kg・K]
Latent heat of vaporization h _fg : 2305 [kJ/kg]
Gravitational acceleration g=9.81 [m/s ² ]
When calculated using equation (1), the detached bubble diameter D _base is 5.24 [mm].

Note that, as described above, the addition of a surfactant to the refrigerant RE reduces the surface tension of the refrigerant RE. Therefore, for example, if the surface tension σ is 26.5 [mN/m], the detached bubble diameter D _base is 3.41 [mm].

Further, the detached bubble diameter D _base may be measured using, for example, an imaging device such as a camera. In this case, the detached bubble diameter D _base is measured in a state where forced convection does not occur in the refrigerant RE.

FIG. 6 is a diagram for explaining suppression of coalescence of bubbles B on the heat transfer surface FT. As shown in FIG. 6, for example, bubbles B01 are generated on the first surface 511. Thereafter, the bubble B01 separates from the first surface 511 and sequentially rises in the Z1 direction as a bubble B1 due to buoyancy. Similarly, bubbles B02 are generated on the second surface 512. Thereafter, the bubble B02 separates from the second surface 512 and sequentially rises in the Z1 direction as a bubble B2 due to buoyancy. Furthermore, bubbles B03 are generated on the third surface 513. Thereafter, the bubble B03 separates from the third surface 513 and sequentially rises in the Z1 direction as a bubble B3 due to buoyancy. Note that the contact portion of the bubble B01 with the first surface 511 is a dry region S1 that does not contribute to heat transfer. Similarly, the contact portion of the bubble B02 with the second surface 512 is a dry region S2 that does not contribute to heat transfer. The contact portion of the bubble B03 with the third surface 513 is a dry region S3 that does not contribute to heat transfer.

As described above, the second surface 512 is more recessed than the first surface 511 in the Y2 direction, and the third surface 513 is more recessed than the second surface 512 in the Y2 direction. Therefore, the first surface 511, the second surface 512, and the third surface 513 are located at different positions on the Y axis. As described above, each of the depths H2 and H3 is larger than the detached bubble diameter _Dbase . Therefore, the bubbles B01, B02, and B03 can be separated from each other so that they do not come into contact with each other. Therefore, coalescence of bubbles B01, B02, and B03 can be suppressed. As a result, dry regions S1, S2, and S3 that do not contribute to heat transfer are suppressed from expanding. Therefore, it is possible to improve heat transfer performance.

Further, since the positions of the first surface 511, the second surface 512, and the third surface 513 on the Y axis are different from each other, the bubbles B01, B02, and B03 rise in the Z1 direction from different positions on the Y axis due to buoyancy. Therefore, the bubble B1 is spaced apart from the bubble B02 by a distance d1. Similarly, the bubble B2 is spaced apart from the bubble B03 by a distance d2. Therefore, when the bubble B1 floats up, contact of the bubble B1 with the bubble B02 can be suppressed. Similarly, when the bubble B2 floats up, contact of the bubble B2 with the bubble B03 can be suppressed. Therefore, bubbles B1, B2, and B3 are suppressed from combining with bubbles B01, B02, and B03. As a result, the dry areas S1, S2, and S3 are prevented from expanding. Therefore, it is possible to improve heat transfer performance.

Furthermore, bubbles B01, B02, and B03 float from different positions on the Y axis. Therefore, the bubble B01 floats away from the bubble B02 by a distance d11, and the bubble B02 floats away from the bubble B03 by a distance d12. Therefore, filling of the upper part of the heat transfer surface FT with bubbles B1, B2, and B3 is suppressed. Therefore, the floating bubbles B1, B2, and B3 are suppressed from coming close to, for example, the bubble B03 located vertically most upwardly. Therefore, since the bubbles B on the heat transfer surface FT are suppressed from increasing in size, the dry areas S1, S2, and S3 are suppressed from expanding. Therefore, it is possible to improve heat transfer performance.

Further, as described above, the depths H2 and H3 are larger than the detached bubble diameter D _base , and specifically, about several mm. A simple structure in which a height difference of several millimeters is provided can suppress an increase in cost and blockage of foreign matter in a complex and minute structure. Therefore, it is possible to improve heat transfer characteristics over a long period of time with a simple configuration.

Each of FIG. 7 and FIG. 8 is a diagram for explaining the behavior of bubbles B on the conventional heat transfer surface FTx. As shown in FIGS. 7 and 8, the heat transfer surface FTx does not have a structure with a height difference. In this case, the bubbles B are likely to coalesce, and the dry region Sx that does not contribute to heat transfer is likely to expand. Specifically, when the heat transfer surface FTx is arranged along the vertical direction, the bubbles B float along the heat transfer surface FTx in the process of leaving the heat transfer surface FTx. Therefore, as shown in FIG. 7, the upper part of the heat transfer surface FTx is filled with bubbles B. Furthermore, since the bubbles B pass near the heat transfer surface FTx in the process of leaving the heat transfer surface FTx, the bubbles B are more likely to come into contact with the bubbles B formed vertically above the heat transfer surface FTx than the bubbles B. For this reason, adjacent bubbles B tend to coalesce in the upper part of the heat transfer surface FTx. As a result, the bubbles B easily coalesce, forming a large dry region Sx on the heat transfer surface FT, as shown in FIG. Since the dry region Sx does not contribute to heat transfer, the heat transfer characteristics deteriorate as a result.

On the other hand, as described above, since the heat transfer surface FT shown in FIG. 4 has a structure with a height difference, coalescence of the bubbles B is suppressed. Therefore, it is possible to improve heat transfer characteristics.

Further, the above-mentioned length W1 is preferably smaller than the detached bubble diameter D _base . Since the length W1 is smaller than the detached bubble diameter D _base , the bubbles B are prevented from coalescing in the direction along the vertical line of the first surface 511, compared to a case where the length W1 is larger. Further, from the same viewpoint, the length W2 is preferably smaller than the detached bubble diameter D _base , and the length W3 is preferably smaller than the detached bubble diameter D _base .

Further, as described above, in addition to the first surface 511 and the second surface 512, the third surface 513 is provided. By increasing the number of vertical surfaces 51, the length of each vertical surface 51 along the Z axis can be reduced. Therefore, the larger the number of vertical surfaces 51, the easier it is to make the length W1 smaller than the detached bubble diameter _Dbase . Therefore, coalescence of the bubbles B within each vertical surface 51 can be easily suppressed. In the example shown in FIG. 4, the number of vertical surfaces 51 is seven, but the number may be any number as long as it is two or more.

Note that each of the above-mentioned vertical surfaces 51 and each step surface 52 is a flat surface, but is not limited to this, and may have an uneven or curved surface.

2. Modifications The first embodiment described above can be modified, for example, in various ways as described below. Further, each modification may be combined as appropriate.

2-1. First Modified Example FIG. 9 is a diagram showing a heat transfer member 5a of a first modified example. In the heat transfer surface FTa of the heat transfer member 5a shown in FIG. 9, the depths H2 and H3 are different from each other. In the example shown in FIG. 9, the relationship between depths H2 and H3 is H3<H2. Although not shown, the relationship between the depths H2 and H3 may be H2<H3.

According to the above-described first modification, as in the first embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

2-2. Second Modified Example FIG. 10 is a diagram showing a heat transfer member 5b of a second modified example. In the heat transfer surface FTb of the heat transfer member 5ba shown in FIG. 10, the lengths W1, W2, and W3 are different from each other. In the example shown in FIG. 9, the relationship between length W1, length W2, and length W3 is W3<W2<W1. Therefore, in the second modification, the length of the vertical surface 51 along the vertical line becomes shorter as it goes vertically upward.

Also in the above-described second modification, as in the first embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

2-3. Third Modified Example FIG. 11 is a diagram showing a heat transfer member 5c of a third modified example. In the heat transfer surface FTc of the heat transfer member 5c shown in FIG. 11, the lengths W1, W2, and W3 are different from each other. In the example shown in FIG. 11, the relationship between length W1, length W2, and length W3 is W1<W2<W3. Therefore, in the third modification, for example, the length of the vertical surface 51 along the vertical line increases as it goes vertically upward.

Note that the relationship between the length W1, the length W2, and the length W3 is not limited to the relationship shown in the second modified example and the third modified example. For example, the length W2 may be the longest or the shortest. Therefore, the plurality of vertical surfaces 51 of the heat transfer surface FT may have different lengths.

Similarly to the first embodiment described above, according to the third modification described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

2-4. Fourth Modified Example FIG. 12 is a diagram showing a heat transfer member 5d of a fourth modified example. In the heat transfer surface FTd of the heat transfer member 5d in FIG. 12, the first step surface 521, the second step surface 522, and the third step surface 523 are each inclined with respect to the XY plane. Specifically, the first step surface 521 is inclined with respect to the XY plane so that the angle between the first surface 511 and the first step surface 521 is an obtuse angle. Similarly, the second step surface 522 is inclined with respect to the XY plane so that the angle between the second surface 512 and the second step surface 522 is an obtuse angle. The third step surface 523 is inclined with respect to the XY plane so that the angle formed by the third surface 513 and the third step surface 523 is an obtuse angle.

Note that the respective inclination angles of the first step surface 521, the second step surface 522, and the third step surface 523 with respect to the XY plane may be equal to or different from each other. Further, each of the inclination angles is not particularly limited, but is within a range that does not deviate from the invention described in this specification in the heat transfer member 5d in which the heat transfer surface FTd is arranged along a vertical line.

Similarly to the first embodiment described above, according to the fourth modification described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

2-5. Fifth Modification FIG. 13 is a diagram showing a heat transfer member 5e of a fifth modification. In the heat transfer surface FTe of the heat transfer member 5e in FIG. 13, the first surface 511, the second surface 512, and the third surface 513 are each inclined with respect to the Z axis. Specifically, the first surface 511 is inclined with respect to the Z axis so that the angle between the first surface 511 and the first stepped surface 521 is an obtuse angle. Similarly, the second surface 512 is inclined with respect to the Z axis so that the angle between the second surface 512 and the second step surface 522 is an obtuse angle. The third surface 513 is inclined with respect to the Z-axis so that the angle between the third surface 513 and the third stepped surface 523 is an obtuse angle.

Note that the respective inclination angles of the first surface 511, the second surface 512, and the third surface 513 with respect to the Z axis may be equal to or different from each other. Further, each of the inclination angles is not particularly limited, but is within a range that does not depart from the invention described in this specification in the heat transfer member 5e in which the heat transfer surface FTe is arranged along a vertical line.

According to the above-described fifth modification, as in the first embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

2-6. Sixth Modification Example FIG. 14 is a diagram showing a heat transfer member 5f of a sixth modification example. In the heat transfer surface FTf of the heat transfer member 5f in FIG. 14, the first surface 511, the second surface 512, and the third surface 513 are each inclined with respect to the Z axis. Moreover, the first step surface 521, the second step surface 522, and the third step surface 523 are each inclined with respect to the XY plane. Specifically, the first surface 511 and the first step surface 521 are inclined so that the angle between the first surface 511 and the first step surface 521 is an acute angle. Similarly, the second surface 512 and the second step surface 522 are inclined so that the angle between the second surface 512 and the second step surface 522 is an acute angle. The third surface 513 and the third step surface 523 are inclined so that the angle between the third surface 513 and the third step surface 523 is an acute angle.

Note that the respective inclination angles of the first surface 511, the second surface 512, and the third surface 513 with respect to the Z axis may be equal to or different from each other. Similarly, the inclination angles of the first step surface 521, the second step surface 522, and the third step surface 523 with respect to the XY plane may be equal to or different from each other. Further, each inclination angle is not particularly limited, but is within a range that does not depart from the invention described in this specification in the heat transfer member 5f in which the heat transfer surface FTe is arranged along a vertical line.

Further, in this modification, the depth H2 corresponds to the distance between the first connecting portion 501 and the second connecting portion 502 along the XY plane. The depth H3 corresponds to the distance between the second connecting portion 502 and the third connecting portion 503 along the XY plane.

In this modification, as in the first embodiment, the distance along the horizontal plane from the first connecting portion 501 to the second connecting portion 502 is larger than the detached bubble diameter D _base . Further, the distance along the horizontal plane from the second connecting portion 502 to the third connecting portion 503 is larger than the detached bubble diameter D _base . Therefore, in this modification as well, coalescence of the bubbles B can be suppressed similarly to the first embodiment. Therefore, deterioration in heat transfer performance can be suppressed. In addition, since the heat transfer surface FTf has a simple structure, it is possible to suppress an increase in cost and blockage of foreign substances for a complex and fine structure. Therefore, it is possible to improve heat transfer characteristics over a long period of time with a simple configuration. Furthermore, when the first surface 511, the second surface 512, and the third surface 513 are inclined as shown in FIG. 14, the bubbles B generated on each surface are particularly difficult to come into contact with each other, and therefore coalescence of the bubbles B is suppressed. easy to be

Similarly to the first embodiment described above, according to the above sixth modification, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

3. Second Embodiment A second embodiment of the present disclosure will be described below. In the embodiments illustrated below, for elements whose operations and functions are similar to those of the embodiments described above, the reference numerals used in the description of the embodiments described above will be used, and detailed descriptions of each will be omitted as appropriate.

3-1. Heat transfer member 5A
FIG. 15 is a plan view of a heat transfer member 5A of the second embodiment. FIG. 16 is a side view of the heat transfer member 5A shown in FIG. 15. Note that the heat transfer member 5A is arranged along the Z axis. Further, the heat transfer surface FTA of the heat transfer member 5A is arranged along the Z-axis direction. Further, in FIG. 15, illustration of bottom portions 621 and 622, which will be described later, is omitted.

As shown in FIGS. 15 and 16, the heat transfer surface FTA has a first region 61 having a plurality of first recesses 610 and a second region 62 having a plurality of second recesses 620. The second region 62 is arranged further in the Z1 direction than the first region 61.

Each first recess 610 is a groove extending along the X axis. The plurality of first recesses 610 are lined up along the Z-axis and are arranged parallel to each other at equal pitches. Note that "equal pitch" includes not only strictly equal pitch, but also within the range of manufacturing error, etc. Further, each second recess 620 is a groove extending along the X axis. The plurality of second recesses 620 are lined up along the Z-axis and arranged parallel to each other at equal pitches.

In the example shown in FIG. 16, the cross-sectional shape of each first recess 610 is V-shaped. Similarly, the cross-sectional shape of each second recess 620 is V-shaped. The plurality of first recesses 610 and the plurality of second recesses 620 are formed, for example, by machining such as cutting.

FIG. 17 is a partially enlarged view of the heat transfer member 5A shown in FIG. 16. As shown in FIG. 17, each first recess 610 has a bottom 611. As shown in FIG. The width of each first recess 610 decreases continuously toward the bottom 611. Furthermore, a connecting portion between two adjacent first recesses 610 is an apex 612 . In the first region 61, the bottom portions 611 and the apexes 612 are arranged alternately in the Z1 direction. Similarly, each second recess 620 has a bottom 621. The width of each second recess 620 continuously decreases toward the bottom 621. Furthermore, a connecting portion between two adjacent second recesses 620 is an apex 622 . In the second region 62, the bottom portions 621 and the apexes 622 are arranged alternately in the Z1 direction.

In the illustrated example, the first depth h1 of each first recess 610 is greater than the second depth h2 of each second recess 620. The first depth h1 is also the distance from the bottom 611 to the apex 612 along the XY plane. Similarly, the second depth h2 is also the distance from the bottom 621 to the apex 622 along the XY plane.

Further, the first opening width w1 of each first recess 610 along the vertical line is larger than the second opening width w2 of each second recess 620 along the vertical line. The first opening width w1 is also the distance between two adjacent vertices 612 along the Z-axis. Similarly, the second opening width w2 is also the distance between two adjacent vertices 622 along the Z-axis. Moreover, it is preferable that the first opening width w1 is smaller than the detached bubble diameter D _base . Similarly, the second opening width w2 is preferably smaller than the detached bubble diameter _Dbase .

3-2. Behavior of Bubbles FIG. 18 is a diagram for explaining the generation of bubbles B on the heat transfer surface FTA. In the following, any one of the plurality of first recesses 610 is the first recess 610_1, and one of the two first recesses 610 adjacent to the first recess 610_1. One recess 610 is a first recess 610_2, and the other first recess 610 is a first recess 610_3. Similarly, any one of the plurality of second recesses 620 is the second recess 620_1, and one of the two second recesses 620 adjacent to the second recess 620_1. The second recess 620 is the second recess 620_2, and the other second recess 620 is the second recess 620_3. Further, in FIGS. 18, 19, 20, and 21, for ease of understanding, the description will be made without considering the buoyancy force along the vertical line.

The bubbles B are generated at the bottom 611, which is the deepest position of the first recess 610_1, and at the bottom 621, which is the deepest position of the second recess 620_1. Specifically, first, as shown in FIG. 18, a nuclear bubble Bn1 is generated at the bottom 611 of the first recess 610_1. Similarly, nuclear bubbles Bn2 are generated at the bottom 621 of the second recess 620_1.

The curvature of the nuclear bubble Bn is approximately the same as the width of the groove. Therefore, as described above, since the first opening width w1 is larger than the second opening width w2, the nuclear bubble Bn1 is larger than the nuclear bubble Bn2. Therefore, by controlling the width of the groove, the size of the nuclear bubbles Bn can be controlled. Therefore, the generation cycle of the bubbles B leaving the heat transfer surface FTA can be controlled.

FIG. 19 is a diagram for explaining the growth of bubbles B on the heat transfer surface FT. As shown in FIG. 19, the growth of the contact line of the bubble B1_1 grown from the nuclear bubble Bn1 in the direction along the Z-axis is restricted by the first recess 610_1. Therefore, the adhesion force to the wall surface is limited, and the size of the bubble B1_1 to be separated is limited. Similarly, the growth of the contact line of the bubble B2_1 grown from the nuclear bubble Bn2 in the direction along the Z-axis is restricted by the second recess 620_1. Therefore, the adhesion force to the wall surface is limited, and the size of the bubble B2_1 to be separated is limited.

FIG. 20 is a diagram for explaining the growth of bubbles B on the heat transfer surface FTA. FIG. 20 shows a situation where bubbles B1_2 and B1_3 are generated after bubble B1_1 is generated. As shown in FIG. 20, as the growth of each of the bubbles B1_1, B1_2, and B1_3 progresses, the growth of the bubble B1_1 in the Z1 direction is restricted by the bubbles B1_2 and B1_3. This is because the action of the surfactant suppresses the coalescence of the bubble B1_1 with each of the bubbles B1_2 and B1_2. By restricting the growth of the bubble B1_1 in the direction along the Z-axis, the bubble B1_1 tends to grow in the direction away from the heat transfer surface FTA. Then, the bubble B1_1 sandwiched between the growing bubble B1_2 and the bubble B1_3 is deformed into a constricted shape.

Similarly, FIG. 20 shows a situation where bubbles B2_2 and B2_3 are generated after bubble B2_1 is generated. Due to the action of the surfactant, the growth of the bubble B2_1 in the direction along the Z-axis is restricted by the bubbles B2_2 and B2_3, and the bubble B2_1 tends to grow in the direction away from the heat transfer surface FTA. Then, the bubble B2_1 sandwiched between the growing bubble B2_2 and the bubble B2_3 is deformed into a constricted shape.

In this way, in addition to the heat transfer surface FTA having the first recess 610 and the second recess 620, the refrigerant RE contains a surfactant, so that the bubbles B grow more easily in the direction away from the heat transfer surface FTA. Become.

Further, as described above, the first opening width w1 is preferably smaller than the detached bubble diameter D _base . Since the first opening width w1 is smaller than the detached bubble diameter D _base , the bubble B1_1 tends to grow in the direction away from the heat transfer surface FTA due to the influence of the adjacent bubbles B1_2 and B1_3, compared to a case where the first opening width w1 is larger. For this reason, the bubbles B1_1 become easier to separate from the heat transfer surface FTA, and therefore the heat transfer performance can be improved. Similarly, the second opening width w2 is preferably smaller than the detached bubble diameter _Dbase . Since the second opening width w2 is smaller than the detached bubble diameter D _base , the bubble B2_1 tends to grow in a direction away from the heat transfer surface FTA due to the influence of the adjacent bubbles B2_2 and B2_3, compared to a case where the second opening width w2 is smaller than the detached bubble diameter D base. For this reason, the bubbles B2_1 become easier to separate from the heat transfer surface FTA, and therefore the heat transfer performance can be improved.

FIG. 21 is a diagram for explaining the separation of bubbles B from the heat transfer surface FTA. As shown in FIG. 21, as the growth of each of the bubbles B1_1, B1_2, and B1_3 progresses, the bubble B1_1 separates from the heat transfer surface FTA and separates into the bubble B1a and the bubble B1b. As described above, the constriction of the bubble B1_1 causes the bubble B1_1 to easily split into the bubble B1a and the bubble B1b. Then, the bubble B1a leaves the heat transfer surface FTA, and the bubble B1b tends to remain on the heat transfer surface FTA as a residual bubble in which a part of the bubble B1_1 remains in the first recess 610_1. Thereafter, the bubble B1b functions as a nucleus for the generation of a new bubble B1_1. Similarly, as the growth of each of the bubbles B2_1, B2_2, and B2_3 progresses, the bubble B2_1 separates from the heat transfer surface FTA and separates into the bubble B2a and the bubble B2b. Then, the bubble B2b functions as a nucleus for generating a new bubble B2_1.

By leaving the bubbles B1b and B2b on the heat transfer surface FTA, the generation cycle of the bubbles B1_1 and B2_1 can be shortened. Therefore, the number of bubbles released per unit time can be increased. Therefore, the generation cycle of bubbles B can be shortened. Therefore, the cooling performance of the evaporative cooling device 1 can be improved.

FIG. 22 is a diagram for explaining the action of the bubbles B generated in the first region 61 of the heat transfer surface FT. As described above, the second opening width w2 is smaller than the first opening width w1. Therefore, each bubble B2 generated in the plurality of second recesses 620 is smaller than each bubble B1 generated in the plurality of first recesses 610. Therefore, by providing the plurality of second recesses 620, many bubbles B2 can be efficiently removed from the heat transfer surface FTA. Therefore, the number of bubbles B2 generated per unit time can be increased, and therefore the heat transfer performance can be improved.

Further, as described above, in the configuration in which the heat transfer surface FT is arranged along a vertical line, the first region 61 where the first recess 610 is provided is more vertical than the second region 62 where the second recess 620 is provided. Located at the bottom. The first opening width w1 of the first recess 610 is larger than the second opening width w2 of the second recess 620. Therefore, large air bubbles B2 are generated in the second recess 620, and small air bubbles are generated in the first recess 610. The large bubble B2 has a higher floating speed than the small bubble B1. Therefore, the large bubble B2 rises at a higher speed due to greater buoyancy than the small bubble B1. Convection occurs when the surrounding liquid moves along with the upward movement of the large bubbles B2. The convection has the effect of peeling off the small bubbles B2 generated in the second recess 620 located vertically above the first recess 610 from the heat transfer surface FTA. Therefore, the removal of the bubbles B2 can be promoted. Moreover, the convection suppresses the filling of the bubbles B in the upper part of the heat transfer surface FTA. For this reason, it is possible to suppress the coalescence of the bubbles B in the upper part of the heat transfer surface FTA, and it is also possible to shorten the generation period of the small bubbles B2. As a result, the heat transfer performance of the heat transfer member 5 can be improved.

Further, the heat transfer surface FTA has a simple structure in which a first recess 610 and a second recess 620 are provided. For this reason, it is possible to suppress an increase in cost and blockage of foreign substances in a complex and fine structure. Therefore, it is possible to improve heat transfer characteristics over a long period of time with a simple configuration.

Further, the plurality of first recesses 610 are a plurality of grooves arranged parallel to each other, and the plurality of second recesses 620 are a plurality of grooves arranged parallel to each other. As described above, the groove can be easily formed by machining or the like. Therefore, since the first recess 610 and the second recess 620 are grooves, it is possible to improve heat transfer characteristics over a long period of time with a particularly simple configuration and at low cost.

Further, as described above, the cross-sectional shape of each first recess 610 is V-shaped, and the cross-sectional shape of each second recess 620 is V-shaped. Therefore, even if a foreign object enters the first recess 610 and the second recess 620, the foreign object easily moves along the first recess 610 and the second recess 620. Therefore, the foreign matter is easily removed from the first recess 610 and the second recess 620. Therefore, even if the evaporative cooling device 1 is used for a long period of time, the cooling performance of the evaporative cooling device 1 can be suppressed from decreasing.

Furthermore, as described above, the plurality of first recesses 610 are arranged at equal pitches, and the plurality of second recesses 620 are arranged at equal pitches. Therefore, the generation distribution of bubbles B1 and B2 on the heat transfer surface FTA can be made uniform. Furthermore, the grooves can be formed more easily than in a configuration in which the plurality of grooves are not arranged at equal pitches.

Furthermore, the second region 62 is more depressed than the first region 61 in the Y2 direction. Therefore, similarly to the first embodiment, when the bubble B1 floats, the bubble B1 is unlikely to come into contact with the bubble B2. Therefore, coalescence of the bubbles B1 and B2 is suppressed. Furthermore, filling of the upper part of the heat transfer surface FTA with bubbles B1 and B2 is suppressed.

Further, the first depth h1 is deeper than the second depth h2, and the difference between the first depth h1 and the second depth h2 is larger than the detached bubble diameter D _base . Since the difference between the first depth h1 and the second depth h2 is larger than the detached bubble diameter D _base , the bubble B1 and the bubble B2 are separated when the bubble B2 is generated and detached, as in the first embodiment. The coalescence of is suppressed. Therefore, it is possible to further improve heat transfer performance. Note that the difference between the first depth h1 and the second depth h2 is also the distance between the apex 612 and the apex 622 along the XY plane. Therefore, the distance is larger than the detached bubble diameter D _base .

Further, the ratio between the first region 61 and the second region 62 is not particularly limited, but by making the second region 62 larger than the first region 61, the number of bubbles B2 generated per unit time is increased. be able to. On the other hand, the first recess 610 only needs to exhibit the effect of convection as described above, and since the first region 61 is smaller than the second region 62, a decrease in the number of bubbles B2 generated is suppressed.

4. Modifications The second embodiment described above can be modified, for example, in various ways as described below. Further, each modification may be combined as appropriate.

4-1. Seventh Modification FIG. 23 is a diagram showing a heat transfer member 5g of a seventh modification. The heat transfer surface FTg of the heat transfer member 5g shown in FIG. 23 has a third area 63 in addition to the first area 61 and the second area 62. The third region 63 is arranged in the Z1 direction with respect to the second region 62. The third region 63 has a plurality of third recesses 630. Each third recess 630 is a groove extending along the X-axis. The plurality of third recesses 630 are lined up along the Z-axis and arranged parallel to each other at equal pitches. Moreover, the cross-sectional shape of each third recess 630 is V-shaped.

Each third recess 630 has a bottom 631 . The width of each third recess 630 continuously decreases toward the bottom 631. Further, a connecting portion between two adjacent third recesses 630 is an apex 632 . In the third region 63, the bottom portions 631 and the apexes 632 are arranged alternately in the Z1 direction.

The third depth h3 of each third recess 630 is smaller than the second depth h2. The third depth h3 is the distance from the bottom 631 to the apex 632 along the XY plane. Further, the third opening width w3 of each third recess 630 along the vertical line is equal to the second opening width w2.

Further, the third region 63 is more recessed in the Y2 direction than the second region 62. Therefore, similarly to the first embodiment, when the bubble B2 generated in the second region 62 floats, the bubble B2 is unlikely to come into contact with the bubble B3 generated in the third region 63. Therefore, the coalescence of the bubbles B2 and B3 is suppressed. In addition, filling of the upper part of the heat transfer surface FTg with bubbles B1, B2, and B3 is suppressed.

Further, the difference between the second depth h2 and the third depth h3 is larger than the detached bubble diameter D _base . Since the difference between the second depth h2 and the third depth h3 is larger than the detached bubble diameter D _base , the bubble B3 and the bubble B2 are separated when the bubble B3 is generated and detached, as in the first embodiment. The coalescence of is suppressed. Therefore, it is possible to further improve heat transfer performance.

Similarly to the second embodiment described above, according to the seventh modification described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

Note that the first opening width w1, the second opening width w2, and the third opening width w3 may be equal to or different from each other. Further, the number of regions that the "heat transfer surface" has is not particularly limited, and in addition to the "first region", "second region", and "third region", other regions may be provided.

4-2. Eighth Modification Example FIG. 24 is a diagram showing a heat transfer member 5h of an eighth modification example. In the heat transfer surface FTh of the heat transfer member 5h shown in FIG. 24, the cross-sectional shape of the plurality of first recesses 610h is rectangular. Therefore, the width of each first recess 610h is constant. Moreover, the cross-sectional shape of the plurality of second recesses 620h is rectangular. Therefore, the width of each second recess 620h is constant.

Further, a connecting portion between two adjacent first recesses 610h is a flat top surface 614. Similarly, a connecting portion between two adjacent second recesses 620h is a flat top surface 624. In the first region 61, the bottom surface 613 and the top surface 614 are arranged alternately in the Z1 direction. Similarly, in the second region 62, the bottom surface 623 and the top surface 624 are arranged alternately in the Z1 direction.

According to the above-mentioned eighth modification, as in the second embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

4-3. Ninth Modified Example FIG. 25 is a diagram showing a heat transfer member 5i of a ninth modified example. In the heat transfer surface FTi of the heat transfer member 5i shown in FIG. 24, the cross-sectional shape of the plurality of first recesses 610i is trapezoidal. Moreover, the cross-sectional shape of the plurality of second recesses 620i is trapezoidal.

Further, a connecting portion between two adjacent first recesses 610i is a flat top surface 614. Similarly, a connecting portion between two adjacent second recesses 620i is a flat top surface 624. In the first region 61, the bottom surface 613 and the top surface 614 are arranged alternately in the Z1 direction. Similarly, in the second region 62, the bottom surface 623 and the top surface 624 are arranged alternately in the Z1 direction.

Similarly to the second embodiment described above, according to the above-described ninth modification, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

Note that the cross-sectional shapes of the "first recess" and the "second recess" are not particularly limited, and may be shapes other than the cross-sectional shapes shown in FIGS. 24 and 25. Furthermore, the inner wall surfaces of the "first recess" and the "second recess" are not limited to flat surfaces, and may have an uneven or curved surface. Note that the same applies to the "third recess".

4-4. 10th Modification FIG. 26 is a diagram showing a heat transfer member 5j of a 10th modification. In the heat transfer surface FTj of the heat transfer member 5j shown in FIG. 26, the positions of the plurality of vertices 612 and the plurality of vertices 622 on the Y axis are the same.

Similarly to the second embodiment described above, according to the above tenth modification, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

4-5. Eleventh Modification FIG. 27 is a diagram showing a heat transfer member 5k of an eleventh modification. In this modification, the differences from the seventh modification will be mainly explained. In the heat transfer surface FTk of the heat transfer member 5k shown in FIG. 27, the positions of the plurality of vertices 612, the plurality of vertices 622, and the apex 632 on the Y axis are the same.

Similarly to the above-described second embodiment and seventh modification, the eleventh modification described above also has a simple structure, can suppress foreign matter clogging, and can improve heat transfer characteristics over a long period of time. .

4-6. Twelfth Modification FIG. 28 is a diagram showing a heat transfer member 5l of a twelfth modification. In this modification, the differences from the seventh modification will be mainly explained. In the heat transfer surface FTl of the heat transfer member 5l shown in FIG. 28, the first depth h1, the second depth h2, and the third depth h3 are substantially equal to each other.

Further, the distance between the apex 612 and the apex 622 along the XY plane is larger than the detached bubble diameter D _base . Similarly, the distance between the apex 622 and the apex 632 along the XY plane is larger than the detached bubble diameter D _base . Therefore, when the bubbles B are generated and separated, coalescence of the bubbles B is suppressed. Therefore, it is possible to further improve heat transfer performance.

Also in the above-described twelfth modification, as in the second embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

4-7. 13th Modification FIG. 29 is a diagram showing a heat transfer member 5m of a 13th modification. In this modification, the differences from the seventh modification will be mainly explained. In the heat transfer surface FTm of the heat transfer member 5m shown in FIG. 29, the first depth h1, the second depth h2, and the third depth h3 are substantially equal to each other. Further, the positions of the plurality of vertices 612, the plurality of vertices 622, and the plurality of vertices 632 on the Y axis are equal to each other. Further, the positions of the plurality of bottom parts 611, the plurality of bottom parts 621, and the plurality of bottom parts 631 on the Y axis are equal to each other.

Also in the above thirteenth modification, as in the second embodiment described above, clogging of foreign matter can be suppressed with a simple structure, and heat transfer characteristics can be improved over a long period of time.

Note that the first depth h1, the second depth h2, and the third depth h3 may be different from each other or may be the same.

Although the evaporative cooling device of the present invention has been described above based on the illustrated embodiments, the present invention is not limited thereto. Further, the configuration of each part of the present invention can be replaced with any configuration that exhibits the same function as in the embodiment described above, or any configuration can be added.

In the above-described embodiment, each of the "first recess", "second recess", and "third recess" is a groove, but it may not be a groove, and may be a grid-shaped hole, for example. .
In addition to cooling devices for power semiconductor devices, the present invention can be applied to a wide range of devices that utilize heat transfer by boiling phenomenon.

DESCRIPTION OF SYMBOLS 1... Boiling cooling device, 5... Heat transfer member, 10... Heat receiving part, 11... Container, 13... Side wall, 20... Heat radiating part, 21... Container, 22... Heat radiating fin, 30... First pipe part, 40... Second Pipe portion, 51... Vertical surface, 52... Step surface, 61... First region, 62... Second region, 63... Third region, 100... Heating element, 111... Bottom plate, 112... Top plate, 113... Side wall, 211 ...Bottom plate, 212...Top plate, 213...Side wall, 501...First connection part, 502...Second connection part, 503...Third connection part, 511...First surface, 512...Second surface, 513...Third surface , 521...first step surface, 522...second step surface, 523...third step surface, 610...first recess, 611...bottom, 612...apex, 613...bottom, 614...top surface, 620...second recess , 621...bottom, 622...apex, 623...bottom, 624...top, 630...third recess, 631...bottom, 632...vertex, B...bubble, Bn1...nuclear bubble, Bn2...nuclear bubble, FT...heat transfer Surface, H2...depth, H3...depth, RE...refrigerant, S10...accommodation chamber, S20...condensation chamber, S1...dry area, S2...dry area, S3...dry area, S30...first flow path , S40...Second flow path, Sx...Dry area, W1...First opening width, W2...Second opening width, d1...Distance, d2...Distance, d11...Distance, d12...Distance, h1...First depth , h2... second depth, h3... third depth, w1... first opening width, w2... second opening width, w3... third opening width.

Claims (7)

liquid refrigerant;
a heat transfer member having a heat transfer surface that boils the refrigerant with heat from a heating element;
The heat transfer surface is arranged along a vertical line,
having a first surface and a second surface disposed vertically above the first surface and recessed from the first surface;
The depth of the second surface is larger than the separation bubble diameter of bubbles generated by boiling of the refrigerant on the plane.
A boiling cooling device characterized by: The heat transfer surface further includes a third surface disposed vertically above the second surface and recessed from the second surface.
The boiling cooling device according to claim 1. liquid refrigerant;
a heat transfer member having a heat transfer surface that boils the refrigerant with heat from a heating element;
The heat transfer surface is
arranged along a vertical line,
a first surface, a second surface arranged vertically above the first surface and recessed from the first surface, and a third surface arranged vertically above the second surface and recessed from the second surface. a first step surface connecting the first surface and the second surface, and a second step surface connecting the second surface and the third surface,
The distance along the horizontal plane from the first connecting portion between the first surface and the first stepped surface to the second connecting portion between the second surface and the second stepped surface is determined by boiling of the refrigerant on the plane. Larger than the bubble diameter of the resulting bubble,
A boiling cooling device characterized by: liquid refrigerant;
a heat transfer member having a heat transfer surface that boils the refrigerant with heat from a heating element;
The heat transfer surface is arranged along a vertical line,
a first region having a plurality of first recesses, and a second region arranged vertically above the first region and having a plurality of second recesses;
The first opening width along the vertical line of each of the plurality of first recesses is larger than the second opening width along the vertical line of each of the plurality of second recesses.
A boiling cooling device characterized by: The first opening width and the second opening width are smaller than a separation bubble diameter of a bubble generated by boiling of the refrigerant on a plane.
The boiling cooling device according to claim 4. The plurality of first recesses are a plurality of grooves arranged in parallel to each other,
The plurality of second recesses are a plurality of grooves arranged in parallel to each other,
The boiling cooling device according to claim 4 or 5. the second region is more concave than the first region;
The boiling cooling device according to claim 4 or 5.

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