JP7477920B1 - Heat Transport Devices - Google Patents

Abstract

[Problem] To provide a device capable of efficiently transporting heat from a high-temperature heat source by thermal radiation heat transfer, thermal convection heat transfer, and boiling heat transfer. [Solution] A first heat transport device 10 comprising a substrate 12 placed in close contact with a high-temperature heat source 18, and a first unit cell 14 formed on the surface of the substrate 12, the first unit cell 14 being made of a plurality of metallic convex cells 16 regularly arranged on the substrate 12, each of the convex cells 16 satisfying the following conditions: (1) height H: 0.35 μm to 50 μm, (2) bottom width B: 0.175 to 25 μm, (3) spacing D between the convex cells 16: 0.49 μm to 50 μm. [Selected Figure] Figure 1

Description

This invention relates to a heat transport device, and in particular to a device that performs heat removal and cooling functions by being placed in close contact with a heat source.

According to thermodynamics, all power engines expel much of the energy supplied from an external source as heat. If this heat is not transported, the temperature of the materials that make up the engine will rise and the function of the heat engine will decrease or deteriorate.
Power semiconductors, integrated circuits, CPU boards, laser oscillators, relay stations, etc. incorporate various heat transport units to suppress heat generation.

A typical heat transport unit is a heat sink.
Fins are formed on the surface of a copper or aluminum plate with high thermal conductivity, and one side is bonded or joined to a heat-generating semiconductor substrate, CPU board, laser oscillator, etc.
Heat generation is suppressed by transferring the conducted heat flux to a gas or liquid refrigerant via fins.

In nuclear power plants and other facilities, turbines are rotated using the flow of heated liquid or gas, or even a liquid phase (two-phase) mixed with gas, so the heat removal caused by the high heat flux is carried out using a heat transfer mechanism that utilizes the boiling of cooling water.
As a measure against global warming, radiative cooling into space also occurs, with heat being transferred from heated homes to radiant heat through window materials.
This heat transport method has the following four mechanisms:

(1) Thermal conduction heat transfer In thermal conduction heat transfer, heat is transported from a high-temperature heat source through a solid. The thermal conductivity of the solid and the thermal resistance (gap conductance) between the solid and the high-temperature heat source determine the heat transfer characteristics.
Materials with high conductivity, such as silver, copper, or aluminum, are used, for example, in semiconductor substrates, and graphene and graphite are also beginning to be widely used as solid heat spreaders.

(2) Thermal radiation heat transfer Thermal radiation heat transfer is a heat transfer mechanism in which heat is radiated from a high-temperature heat source as electromagnetic waves. When heat is transferred to a gas phase such as air, it is accompanied by convection heat transfer, and in a vacuum, heat is transported by electromagnetic radiation.
For example, in nature, the surface of the Earth is heated by thermal radiation from the Sun through space.

This thermal radiation heat transfer follows Planck's law, and the radiated energy and electromagnetic wave wavelength are determined depending on the temperature of the high heat source.
Therefore, in order to radiate electromagnetic waves in the red-infrared-far-infrared frequency bands at low temperatures, the surface of the high-temperature source must have a special structure.
The method using a nanophotonic structure as in Non-Patent Document 1, and the method using a metamaterial as in Non-Patent Document 2, both utilize the near-field effect of electromagnetic waves.
Regarding infrared wavelength selectivity, there is research on infrared sensors and heaters that utilize photonics with micropatterns (Non-Patent Document 3) and wavelength selectivity using concave microcavities (Non-Patent Document 4), which have demonstrated the possibility of wavelength-selective thermal radiation devices at low temperatures.
In particular, as reported in Non-Patent Document 5, the reduction in emitter temperature in a recessed microcavity is only about 10% of the surface temperature of a high heat source.

(3) Thermal convection heat transfer Thermal convection heat transfer is a mechanism for transporting heat by the flow of gas or liquid through the surface of a high heat source. The heat transfer behavior is determined by the Reynolds number and Prandtl number of the gas or liquid used for cooling.
If the speed of the cooling gas or liquid is the same and the refrigerant properties are the same, the heat transfer coefficient will also be the same, so the design of the heat transfer surface shape is important for improving thermal convection heat transfer.

The heat sink is designed with protruding pillars on its surface to increase the contact area with the refrigerant and to increase the cooling capacity with low pressure loss in the clearance between the pillars (Patent Document 1).
However, when it comes to thermal convection heat transfer in a small cooling space, it is difficult to efficiently circulate refrigerant using conventional heat sinks with mm-class pillars, and recently, non-conventional devices such as heat sinks using microchannels have been proposed.
In addition, since this heat sink is a closed loop, it is not possible to directly transfer heat from the high heat source by convection using the refrigerant (Patent Document 2).
In this convective heat transfer as well, there is a need for heat transport devices based on new ideas.

(4) Boiling heat transfer Boiling heat transfer is a heat transfer mechanism that involves a phase transformation of the coolant from liquid to gas phase. In the case of cooling water, it is accompanied by a phase transformation from water to steam, realizing a heat transfer mechanism at high heat flux.
Its characteristics are described by the response of the heat flux to the degree of superheat, i.e., the boiling curve. Therefore, in order to utilize this heat transfer mechanism in a small space, it is necessary to perform convective heat transfer while repeatedly causing phase transformations in a microchannel, such as in a vapor chamber (Patent Document 3).
However, the heat transfer mechanism accompanying each phase transformation is governed by normal boiling heat transfer (Patent Document 4).

Boiling heat transfer devices with greater flexibility and capable of exceeding the critical heat flux have been developed using silicon technology (Non-Patent Document 6).
This technique has the advantage of being able to fabricate regular microstructures on silicon, but in devices that use brittle silicon, it does not provide sufficient durability for practical use.
In this boiling heat transfer, there is a need for a heat transport device having a metal microstructure that has practical durability.

Nanophotonic control of thermal radiation for energy applications／Optics Express vol.26, Issue 12, pp. 15995-16021 (2018)／Wei Li and Shanhui Fan A Review of Tunable Wavelength Selectivity of Metamaterials in Near-Field and Far-Field Radiative Thermal Transport／Materials 2018, 11(5), 862 May 22 2018／Yanpei Tian, Alok Ghanekar, Matt Ricci, Mikhail Hyde, Otto Gregory, Yi Zheng Spectral control of mid-infrared plasmon resonance and its applications / Optics Vol. 44 No. 2 (February 2015) / Tadaaki Nagao, Duy Thang DAO, Kai Chen, Satoshi Ishii Unidirectional radiative heat transfer with a spectrally selective planar absorber/emitter for high-efficiency solar thermophotovoltaic systems／Applied Physics Express 9, 112302(2016)／Asaka Kohiyama, Makoto Shimizu1, Hiroo Yugami Development of a new heat sink type radiation material / FY2012 Strategic Basic Technology Advancement Support Project Report (2013) / Okitsumo Co., Ltd., Tohoku University Boiling heat transfer of FC-72 on silicon chips with micron pin fins and submicron roughness / Transactions of the Japan Society of Mechanical Engineers, Vol. 68, No. 656 (2002) p519-p526 / Hiroshi Honda, Hiroshi Takamatsu, Jinjia Wei Patent No. 6582114 Patent No. 5778302 JP 2021-014936 A Patent No. 6623296

A common characteristic of heat transport devices, regardless of the type of heat transfer, is that they must be able to be bonded or joined to a heating surface, regardless of the size or shape of the required heat dissipation surface.
In addition, the heat transfer device must exceed the heat transfer capacity of a solid metal surface without a heat transfer device. Even if the space for heat transfer is narrow, the device must have the function of transferring heat.
Furthermore, there is a need for efficient heat transport from a high-temperature heat source to a low-temperature heat source such as a refrigerant.

In thermal radiation heat transfer, micro/nano structures are created on the surface of a heat transport device that efficiently radiate heat transferred from a high-temperature heat source as infrared or far-infrared radiation.
Heat is also transported from a relatively low-temperature, high-heat source (emitter) through gas or vacuum to an opposing object by thermal radiation.
This thermal radiation reduces the surface temperature of the heat transport device that is bonded or joined to a high heat source.

In thermal convection, the surface temperature of a heat transfer surface is rapidly reduced through a heat transport device, even under natural or forced air cooling conditions.
It improves the heat removal speed compared to metal surfaces with high thermal conductivity such as copper and aluminum.

In boiling heat transfer, the degree of superheat at the start of boiling is reduced and foaming is promoted from an early stage, allowing heat to be removed with a higher heat flux.
Even a small increase in superheat increases the heat flux, lowering the surface temperature of the heat transport device and making heat transfer from the hot heat source more efficient.
Furthermore, the critical heat flux is also increased.

In order to solve the above problems, the first heat transport device of the present invention comprises a substrate placed in close contact with a heat source, and a unit cell formed on the surface of the substrate, the unit cell being composed of a plurality of metallic convex (protruding) cells regularly arranged on a substrate, and the height H of each convex cell satisfies the condition of 0.35 μm to 50 μm.
It is desirable that the convex cell of this first heat transport device further satisfies the following condition.
Bottom width B: 0.175μm to 25μm
Distance between convex cells D: 0.49 μm to 50 μm

A second heat transport device according to the present invention comprises a substrate placed in close contact with a heat source, and a unit cell formed on the surface of the substrate, the unit cell comprising a plurality of metallic convex cells arranged in a quasi-regular pattern on the substrate, and each of the convex cells satisfies the following condition:
Average height H _ave : 0.35 μm to 50 μm
Height deviation H _dev : Within 50% of average height H _ave It is desirable that the convex cell of this second heat transport device further satisfies the following condition.
Average bottom width B _ave : 0.175 μm to 25 μm
Bottom width deviation _Bdev : Within 50% of average bottom width B Average spacing between convex cells _Dave : 0.49μm to 50μm
Spacing deviation D _dev between convex cells: within 50% of average spacing D _ave

A third heat transport device according to the present invention comprises a substrate placed in close contact with a heat source, and a metallic unit cell placed in close contact with the surface of the substrate, wherein a plurality of concave (recessed) cells are regularly arranged on the surface of the unit cell, and the height H of each concave cell satisfies the condition of 0.35 μm to 50 μm.
It is desirable that the concave cell of this third heat transport device further satisfies the following conditions.
Bottom width B: 0.175μm to 25μm
Distance between concave cells D: 0.49 μm to 50 μm

A fourth heat transport device according to the present invention comprises a substrate placed in close contact with a heat source, and a metallic unit cell placed in close contact with the surface of the substrate, wherein a plurality of concave cells are quasi-regularly arranged on the surface of the unit cell, and each concave cell satisfies the following condition:
Average height H _ave : 0.35 μm to 50 μm
Height deviation H _dev : Within 50% of average height H _ave It is desirable that the concave cell of this fourth heat transport device further satisfies the following condition.
Average bottom width B _ave : 0.175 μm to 25 μm
Bottom width deviation _Bdev : Within 50% of average bottom width B Average spacing between concave cells _Dave : 0.49μm to 50μm
Spacing deviation between concave cells D _dev : Within 50% of average spacing D _ave

A plurality of fine convex or concave cells can be formed on the surface of each of the above-mentioned convex or concave cells.
Alternatively, a tubular body may be used as the base material, and the unit cells may be formed on the outer or inner peripheral surface of the tubular body.
Furthermore, the substrate and the unit cells can be integrally formed from the same material.

The heat transport device of the present invention has a large number of microstructured convex or concave cells on its surface that satisfy the above-mentioned shape and size conditions, and therefore can efficiently transport heat conducted from a heat source via thermal radiation heat transfer, thermal convection heat transfer, and boiling heat transfer.
Furthermore, since the convex cells and the concave cells are made of metal, high durability can be achieved.

1A and 1B are a perspective view and a side view showing a first heat transport device according to the present invention; 1 is a table illustrating candidate metals, candidate polymers, candidate ceramics and inorganic materials for the substrate, and candidate metals for the cell. 1A and 1B are schematic diagrams showing an example in which the first heat transport device is used for thermal radiation heat transfer. 1A and 1B are schematic diagrams showing an example in which the first heat transport device is used for thermal convection heat transfer. 1A and 1B are schematic diagrams showing an example in which the first heat transport device is used for boiling heat transfer. 1A to 1C are diagrams illustrating variations in cell shape. This is an SEM image showing an example of cylindrical convex cells regularly arranged on a copper sheet material. 1A and 1B are a perspective view and a side view showing a second heat transport device according to the present invention. 13 is an SEM image showing the height distribution of convex cells of the second heat transport device. FIG. 13 is a diagram showing how the second unit cell of the second heat transport device is divided into a plurality of regions surrounding each convex cell on an SEM image. FIG. 13 is a diagram showing how the pitch between convex cells is calculated by plotting the central coordinates of an approximation ellipse for each region. FIG. 13 is a diagram showing a procedure for calculating the height of each convex cell. 13A and 13B are diagrams showing statistical distributions of the bottom width, the spacing between the convex cells, and the height of the convex cells included in the second heat transport device. 13 is a plan photograph showing a second heat transport device using a copper sheet as a substrate and having a plurality of protruding cells arranged in a quasi-regular array on the surface thereof. 11 is an SEM image showing a convex cell of the second heat transport device. 13 is a plan photograph showing a second heat transport device in which a stainless steel plate is used as a substrate and a plurality of protruding cells are quasi-regularly arranged on the surface of the substrate. 13 is a photograph showing a cross section of a second heat transport device in which a copper pipe is used as a substrate and a plurality of protruding cells are quasi-regularly arranged on the inner circumferential surface of the copper pipe. FIG. 13 is a diagram showing an experimental setup for infrared spectroscopy measurement of the second heat transport device. 13 is a graph showing the results of infrared spectroscopy measurement of the second heat transport device. FIG. 13 is a diagram showing an experimental setup for thermal radiation heat transfer of the second heat transport device. 13A and 13B are diagrams showing experimental results of thermal radiation heat transfer of the second heat transport device. 13 is a graph showing experimental results of thermal radiation heat transfer of the second heat transport device. FIG. 13 is a diagram showing the reduction in surface temperature in a second heat transport device that is thermally conductively coupled to a high heat source. FIG. 13 is a diagram showing an experimental setup for measuring a temperature change due to convective heat transfer under forced air cooling in the second heat transport device. 13 is a graph showing the measurement results of temperature change due to convection heat transfer under forced air cooling in the second heat transport device. FIG. 13 is a diagram showing an experimental setup for measuring a boiling curve by a second heat transport device. 13 is a graph showing the measurement results of a boiling curve using a second heat transport device. 13A and 13B are a perspective view and a cross-sectional view showing a third heat transport device according to the present invention. 13A and 13B are a perspective view and a cross-sectional view showing a fourth heat transport device according to the present invention. FIG. 13 is a cross-sectional view showing a fifth heat transport device according to the present invention. FIG. 13 is a cross-sectional view showing a sixth heat transport device according to the present invention. FIG. 2 is a diagram showing the surface characteristics of the heat transport device according to the present invention.

As shown in FIG. 1, the first heat transport device 10 according to the present invention comprises a flat substrate 12 and a first unit cell 14 formed on the surface of the substrate 12.

The substrate 12 is made of various metals, polymers, ceramics, and inorganic materials.
FIG. 2(a) shows examples of metal candidates for the substrate 12, FIG. 2(b) shows examples of polymer candidates, and FIG. 2(c) shows examples of ceramic and inorganic candidates.
In the present invention, when the thickness of the base material 12 is less than 1 mm, it is called a sheet material, and when it is 1 mm or more, it is called a plate material.

The first unit cell 14 is composed of a plurality of convex cells 16, which are regularly arranged in the vertical and horizontal directions at regular intervals. The convex cells 16 are formed to have the same shape and dimensions.
The convex cells 16 are made of, for example, a metal material as shown in FIG.
Each of the convex cells 16 is formed by, for example, laser processing, pressing, etching, blasting, plating, or the like.

Each of the convex cells 16 is fabricated to satisfy the following dimensional conditions.
(1) Height H: 0.35 μm to 50 μm
(2) Bottom width B: 0.175 to 25 μm
(3) Distance (pitch) between convex cells D: 0.49 μm to 50 μm
Here, "height H" refers to the vertical dimension from the bottom end to the tip of the convex cell 16, and "bottom width" refers to the horizontal dimension of the base portion of the convex cell.

The above dimensions are derived from the following considerations.
1) From the viewpoint of radiative heat transfer The characteristics and behavior of electromagnetic waves, including infrared rays, change depending on the wavelength (λ). Among them, λ＞0.7μm or more is near infrared, and λ＞2μm is far infrared.
In radiative heat transfer, near infrared and far infrared rays are involved in "heat transport."
For infrared lenses, the optical properties of far-infrared rays are also important.
The condition for the heat conducted through the substrate to be radiated as electromagnetic waves from the microtexture (height H) is λ>2H, where H must be 0.35 μm or more for near infrared and 1 μm or more for far infrared.
In order to obtain anti-reflection characteristics (anti-reflection) by changing the effective refractive index of the device against near-infrared and far-infrared rays propagating through air or vacuum, the first condition is required to be H>2λ. In particular, considering the far-infrared wavelength range of up to λ=25μm, H needs to be 50μm.
In addition, to obtain non-reflective characteristics, D<0.7 × λ is required, so in the near infrared, D must be 0.49 μm or less.

2) From the viewpoint of convection heat transfer In convection heat transfer, the thickness (y) of the viscous layer formed on the device surface changes depending on the speed of the refrigerant (air, water, etc.).
The convective heat transfer considered here is limited to turbulent convective heat transfer with a Reynolds number of 10,000 or less, so the viscous layer thickness is a maximum of 10 μm.
For H<y, the texture of the device does not affect the flow of the coolant.
However, in order to control the amount of heat removal, it is necessary to utilize H>y and to utilize the region where the heat conducted through the texture interferes with the flow of the refrigerant, and therefore H=50 μm is necessary.
In terms of texture, the H/B and D/B ratios are also important, with H/B>2 and D/B>2 being necessary for low pressure loss and improved heat transfer. If H is 0.35μm or more and 50μm or less, B is 0.175μm to 25μm and D is 0.49μm to 50μm.

As shown in FIG. 3, the first heat transport device 10 can be used for thermal radiation heat transfer.
That is, the first heat transport device 10 is joined or bonded onto a high-temperature heat source 18, and heat is radiated and transferred via gas or vacuum to heat the object to be radiated, thereby transporting heat over a long distance.
In particular, by changing the shape, dimensions and arrangement of the convex cells 16 of the first heat transport device 10 to control the infrared and far-infrared wavelength ranges to be absorbed and radiated, a heat radiation mechanism suited to the application can be realized.
With this heat radiation, when the temperature of the high-temperature heat source 18 is constant, the temperature of the first heat transport device 10 is reduced.

As shown in FIG. 4, the first heat transport device 10 can also be used for heat convection transfer.
By joining or adhering the first heat transport device 10 to a high-temperature heat source 18 or to a surface that is in thermal conductivity with the high-temperature heat source 18, and transferring heat by convection to a liquid or gas that acts as a refrigerant, a heat removal behavior is achieved that involves a more rapid and greater temperature drop compared to the case where the first heat transport device 10 is not provided.
In particular, the heat transmission (K) and pressure drop (p) through the first heat transport device 10 can be increased or decreased, respectively, by varying the shape, size, and arrangement of the convex cells 16 .

As shown in FIG. 5, the first heat transport device 10 can also be used for boiling heat transfer.
The first heat transport device 10 is joined or adhered to the high-temperature heat source 18 or to a surface that is in a thermally conductive state with the high-temperature heat source 18, and boiling heat is transferred to a liquid that acts as a refrigerant, thereby activating bubbling that accompanies a phase change of the liquid, and boiling heat transfer begins at a lower degree of superheat, and a steep increase in heat flux and a heat removal state that exceeds the critical heat flux are realized.
In particular, the foaming initiation superheat (ΔT _i ), the rate of heat flux increase with respect to superheat (q/ΔT) and the critical heat flux (q _c ) are decreased or increased, respectively, by changing the unit cell shape, dimensions and arrangement of the first heat transport device 10.

Although Figure 1 and Figures 3 to 5 show convex cells 16 in a truncated cone shape, the shape of the convex cells 16 is not limited, and as shown in Figure 6, various shapes such as a prism shape, a cylinder shape, a cone shape, a rounded cone shape, a pyramid shape, a polygonal pyramid shape, a truncated pyramid shape, a rectangular spire shape, and a circular spire shape are possible.
FIG. 7(a) is an SEM image showing an example of cylindrical convex cells 16 regularly arranged on a substrate 12 made of a copper sheet, and FIG. 7(b) is an enlarged view of one of the convex cells 16.

In the above, an example has been shown in which convex cells 16 of uniform shape and size are regularly arranged at equal intervals, but the present invention is not limited to this, and it is also possible to use a unit cell having convex cells 16 whose shapes, sizes, or intervals vary within a specified range.
8, the second heat transport device 20 according to the present invention comprises a flat substrate 12 and a second unit cell 24 formed on the surface of the substrate 12, and the second unit cell 24 comprises a plurality of truncated cone-shaped convex cells 16 of different shapes and dimensions. The intervals between the convex cells 16 are not uniform.
The convex cells 16 are made of, for example, a metal material as shown in FIG.
Each of the convex cells 16 is formed by, for example, laser processing, pressing, etching, blasting, plating, or the like.

Each of the convex cells 16 is fabricated to satisfy the following dimensional conditions.
(1) Average height H _ave : 0.35 μm to 50 μm
(2) Height deviation H _dev : Within 50% of the average height H _ave
(3) Average bottom width B _ave : 0.175 μm to 25 μm
(4) Bottom width deviation _Bdev : within 50% of average bottom width _Bave
(5) Average spacing between adjacent convex cells D _ave : 0.49 μm to 50 μm
(6) Spacing deviation _Ddev between adjacent convex cells: Within 50% of the average spacing _Dave . Although the shape, dimensions, and spacing of each convex cell 16 are not identical, the range of variation is within a specified range, which is defined as a "quasi-regular arrangement."
By setting the deviations of H, B, and D above to within 50% of their respective average values, the "standard deviation" that contains 66% of the total frequency is set as the acceptable range of variation.

Figure 9 is an SEM image of a partial area of a second heat transport device 20 in which multiple cone-shaped convex cells 16 are formed by plating on a substrate 12 made of copper sheet material, and shows that the multiple convex cells 16 are arranged in a quasi-regular pattern.

10, the SEM image is divided into a plurality of regions 26 surrounding each convex cell 16 by a predetermined image processing program (e.g., "ImageJ"), and a consecutive number is assigned to each region 26. After that, an approximation ellipse that best fits each region 26 is generated by the image processing program, and the base width of the convex cell 16 is calculated based on the dimensions of each ellipse.
Moreover, as shown in FIG. 11, the pitch between the convex cells 16 is calculated by plotting the central coordinates of the approximation ellipse of each region on the image program.

The height of each convex cell 16 is determined by the following procedure.
First, as shown in FIG. 12(a), an image is obtained using an SEM at 0° (viewed from directly above), and then, as shown in FIG. 12(b), the same area is tilted by 30° using the SEM and the length of each convex cell 16 is measured on the SEM.
Next, the measured height and the grayscale (8-bit value) value of the vertex position of the convex cell 16 in the image in Figure 1(a) are converted into a height value corresponding to the brightness, and the needle height distribution within the entire area of the SEM image is calculated.

FIG. 13(a) shows the statistical distribution of the bottom width of each convex cell 16 included in this second unit cell 24, FIG. 13(b) shows the statistical distribution of the spacing between each convex cell 16, and FIG. 13(c) shows the statistical distribution of the height of each convex cell 16.
The texture dimensions of this second heat transport device 20 are as follows, and satisfy the above-defined condition of quasi-ordered arrangement.
Average height H _ave = 3.0 μm
Height deviation H _dev = +0.8 μm, -0.9 μm
Average bottom width B _ave = 2 μm
Bottom width deviation B _dev = +2.5 μm, -1.5 μm
Average pitch D _ave = 2.25 μm
Pitch deviation D _dev = +1.5 μm, -1.5 μm

In order to utilize the thermal conductivity of the base material 12, a heat transport device using a copper sheet or plate material or an aluminum sheet or plate material as the base material 12 is suitable.
14 shows a second heat transport device 20, which uses a copper sheet material as the substrate 12 and has a plurality of protruding cells 16 arranged in a quasi-regular manner on its surface by plating. As shown in the figure, the entire surface appears black to the naked eye.

FIG. 15(a) shows a surface SEM image of this second heat transport device 20, in which the multiple convex cells 16 have the following average dimensions:
Average height H _ave = 3.8 μm
Average bottom width B _ave = 2 μm
Average pitch D _ave = 3 μm

FIG. 15(b) shows a surface SEM image of a second heat transport device 20 in which smaller sized convex cells 16 are arranged in a quasi-regular manner, with the multiple convex cells 16 having the following average dimensions:
Average height H _ave = 1.2 μm
Average bottom width B _ave = 0.8 μm
Average pitch D _ave = 0.9 μm

In this manner, by designing and controlling the height, bottom width, and spacing of the convex cells 16 that make up the second unit cell 24, a second heat transport device 20 having a surface texture according to the heat transfer mechanism can be fabricated.
By bonding or joining the second heat transport device 20 to the surface of the product via a thermal gap conductance determined by the thermal conductivity and plate thickness, it is possible to provide heat convection, radiation, and boiling heat transfer.

A feature of the heat transport device according to the present invention is that it can supply devices according to the area required for heat extraction and cooling, from small-area sheets and plates on a laboratory scale to large-area sheets and plates on the meter scale.
FIG. 16 shows an example of a second heat transport device 20 in which convex cells 16 are quasi-regularly created on a substrate 12 made of an A4-sized stainless steel plate.
By designing and controlling the arrangement of the protruding cells 16 formed on the surface of the substrate 12 made of stainless steel, the second heat transport device 20 can be designed to suit the heat transfer mechanism.

As shown in FIG. 17, a pipe-type heat transport device can be made by using a copper or aluminum pipe having high thermal conductivity as the substrate 12 and forming convex cells 16 regularly or quasi-regularly on its inner surface.
Again, the texture of the heat transport device can be designed and fabricated with unit cell shapes, dimensions and arrangements tailored to the application.
It is also possible to form protruding cells regularly or quasi-regularly on the outer surface of a copper or aluminum pipe serving as the substrate 12, thereby forming a pipe-type heat transport device.

[Infrared and far-infrared radiation from heat transport devices]
In a heat transport device using thermal radiation heat transfer, when the wavelength of red-infrared-far-infrared electromagnetic waves is equivalent to the dimensions of the micro- or nano-texture on the surface of the heat transport device, the device absorbs and radiates red-infrared-far-infrared radiation corresponding to the spatial frequency (hereinafter represented as λ) or wave number (the inverse of the frequency: hereinafter represented as Λ) band.
Therefore, infrared spectroscopy (FT-IR: Fast Transform-Infrared) was performed on the second heat transport device 20 shown in FIG. 9 to determine the electromagnetic wave transmittance in the red-infrared-far infrared frequency range.
FIG. 18(a) is a schematic diagram of the measurement method, FIG. 18(b) shows the appearance of an actual measurement device, and FIG. 18(c) shows the main parts of the measurement device.

FIG. 19 shows the transmittance distribution of the second heat transport device 20. As shown in FIG.
A significant drop in transmittance, in other words, two significant absorption peaks are observed, centered at Λ=1500 cm ⁻¹ and 1700 cm ⁻¹ or λ=6.67 μm and 5.90 μm.
This infrared absorption occurs due to resonance with the bottom of the second heat transport device 20 as a node and its surface as an antinode, and therefore corresponds to a wavelength twice the height of the convex cell 16 .
Since the average unit cell height is H _ave = 3.7 μm, the infrared absorption peak wavelength of the heat transport device is 7.2 μm, which is equivalent to the measured value.
The broadening of the absorption peak in FIG. 19 is due to the dispersion (H _dev ) of the heights of the convex cells 16 contained in the second unit cell 24 and the dispersion due to the quasi-ordered arrangement.

[Heat radiation transfer through air using a heat transport device]
Thermal radiation heat transfer allows heat to be transported to an object without gas convection.
Here, a heat transport device was placed on a high-temperature heat source heated to a constant temperature, and a thermal radiation heat transfer experiment was conducted in an environment where the effects of air convection were minimized.
FIG. 20(a) is a schematic diagram of the measurement method, and FIG. 20(b) shows the appearance of the actual measurement device.
In this experiment, as shown in FIG. 20(a), the second heat transport device 20 was placed on the surface of a hot plate constantly heated to 100° C., and a 2 mm-thick black polycarbonate plate (PC plate) was placed 150 mm away from the heated surface, and the temperature change on the top surface of the polycarbonate plate was measured by thermography.

First, a sample consisting only of copper sheet material was placed, and noise was removed using black shielding cloth. Air was forced to flow along the shielding cloth to remove air heated by convection heat transfer, and it was confirmed that there was no temperature rise on the top surface of the polycarbonate plate even after 600 seconds had passed.
Next, after sufficient cooling, the second heat transport device 20 was placed on the surface of a hot plate constantly heated to 100° C., and the temperature change on the upper surface of the polycarbonate plate was measured.
As shown in FIG. 21, it was confirmed that the temperature of the upper surface of the polycarbonate plate diffuses concentrically from the center, and gradually increases to a constant temperature over the entire upper surface.
As shown in FIG. 22, the temperature increased monotonically with time, and a temperature increase of about 4° C. was confirmed under these experimental conditions.

[Reduction of surface temperature in a heat transport device connected to a high heat source by thermal conduction]
In the second heat transport device 20 connected to the high heat source via the thermal conduction of the sheet material, the surface temperature is lowered below the temperature of the high heat source due to the radiative heat transfer and the convective heat transfer from the surface.
Here, as shown in FIG. 23, the second heat transport device 20 was placed on a hot plate kept at 100° C., and the temperature distribution was measured by thermography with the focus on the surface.
The hot plate temperature was measured using a thermograph and also measured separately using a thermocouple to confirm that the temperature was 100°C in advance.
As shown in the figure, the surface temperature of the hot plate is 100°C, whereas the surface temperature of the second heat transport device 20 is reduced to 50°C because heat is diffused into the air by thermal radiation and thermal convection.

[Convection heat transfer under forced air cooling using a heat transport device]
The surface temperature is reduced by heat transfer through convection from a high heat source to a gas such as air or a liquid such as water.
Here, as shown in FIG. 24, the second heat transport device 20 was placed on a hot plate kept at 50° C., and the focus was set on its surface. Under forced air cooling conditions by blowing air from an air nozzle, the change in surface temperature over time was measured by thermography.

In FIG. 25, the cooling response due to convection heat transfer measured under the same conditions is compared with that of the copper sheet material alone.
The cooling rate due to convection heat transfer is accelerated by the second heat transport device 20, and the surface temperature after 10 seconds is 42.3°C with the copper sheet material alone, a decrease of only 7.7°C, whereas with the heat transport device it is 40.8°C after 10 seconds, a decrease of 9.2°C.

[Boiling curve control using heat transport devices]
Boiling heat transfer is a heat transfer mechanism that involves a phase transformation from a liquid phase, such as cooling water, to a gas phase, such as steam, and is widely used as a heat transfer mechanism to achieve high heat flux.
The thermal engineering guideline in this case is the boiling curve, which is a diagram of the heat flux versus the degree of superheat.
When the degree of superheat of degassed pure water is increased, the state in which heat is transferred by natural convection (or forced convection) in a single phase of pure water changes to a two-phase state with bubbles (phase-transformed water vapor) generated on the heating surface, and the heat flux due to thermal convection increases sharply with the degree of superheat.
If the degree of superheat is further increased, the bubble density increases and coalesces, and the heat flux reaches a maximum at the degree of superheat where the water vapor covers the heating surface in a film-like shape (the heat flux at this time is the critical heat flux).
Any further increase in the degree of superheat would be accompanied by a rapid increase in the temperature of the material that constitutes the heating surface (burnout), so this degree of superheat and the critical heat flux determine the limits of the boiling heat transfer mechanism.

Here, using the experimental system shown in Figure 26(a), the speed of the cooling water flowing through the channel (hereinafter referred to as the Reynolds number: Re) was used as a parameter, and the heat flux accompanying the increase in superheat was measured through video observation to determine the boiling curves at each Reynolds number.
As shown in FIG. 26(b), a second heat transport device 20 was directly adhesively bonded to the surface of the tip of the copper block.

In FIG. 27, the boiling curve of only the copper block is compared with the boiling curve of the second heat transport device 20.
With only the copper block, the boiling curve is almost constant regardless of the Reynolds number. This is consistent with the conventional theory in thermal engineering that the boiling heat transfer phenomenon and the cooling water flow are independent phenomena.
On the other hand, when the second heat transport device 20 is used, as the Reynolds number of the cooling water increases, the boiling curve rises steeply at a lower degree of superheat, achieving a high increase in heat flux.

In other words, as the Reynolds number increases, the heat transfer mechanism by natural convection (or forced convection) transitions to boiling heat transfer at a lower degree of superheat, and with an increase in superheat of a few degrees Celsius, the state becomes one of boiling heat transfer with activated bubbling, and the critical heat flux also becomes greater than that of the copper block alone.
This indicates that the shape effect of the second heat transport device 20 couples the heat transfer mechanism on the device surface with the flow of cooling water, realizing a boiling heat transfer mechanism at a low degree of superheat.

In the above, a heat transport device has been described in which a plurality of protruding cells 16 are erected and arranged regularly or quasi-regularly on the surface of the substrate 12, but the present invention is not limited to this.
That is, as shown in FIG. 28, the third heat transport device 30 according to the present invention has a flat third unit cell 34 formed on the surface of a substrate 12, in which a plurality of concave cells 32 having the same shape and dimensions are regularly arranged at equal intervals vertically and horizontally.

The materials for the substrate 12 may be any of the substances shown in the tables of FIG. 2(a) to FIG. 2(c).
As the material for the third unit cell 34, the metal materials shown in the table of FIG.
When the substrate 12 and the third unit cell 34 are made of the same material (e.g., copper), there is no need to make them separate. The third heat transport device 30 can be made by forming multiple concave cells 32 in a plate material that serves as both the substrate and the unit cell.
Alternatively, the third unit cell 34 may be formed in a tubular shape, and a plurality of recessed cells 32 may be regularly formed on the inner or outer circumferential surface thereof to form the third heat transport device 30 .

The shape of the concave cells 32 is not limited to the inverted truncated cone shape shown in FIG. 28(b), and various shapes shown in FIG. 6 can be used.
Moreover, each concave cell 32 is fabricated so as to satisfy the following dimensional conditions.
(1) Height (depth): 0.35 μm to 50 μm
(2) Bottom width (opening diameter) B: 0.175 μm to 25 μm
(3) Distance between concave cells D: 0.49 μm to 50 μm
Each concave cell 32 is formed by, for example, laser processing, pressing, etching, blasting, plating, or the like.

In the above, an example has been shown in which concave cells 32 of uniform shape and dimensions are regularly arranged at equal intervals, but the present invention is not limited to this, and it is also possible to use a unit cell having concave cells 32 whose shapes, dimensions, or intervals vary within a specified range.
29, a fourth heat transport device 40 according to the present invention comprises a flat substrate 12 and a fourth unit cell 42 formed on the surface of the substrate 12, and the fourth unit cell 42 comprises a plurality of inverted truncated cone-shaped concave cells 32 of different shapes and dimensions. The intervals between the respective concave cells 32 are not uniform.

The materials for the substrate 12 may be any of the substances shown in the tables of FIG. 2(a) to FIG. 2(c).
As the material for the fourth unit cell 42, the metal materials shown in the table of FIG.
When the substrate 12 and the fourth unit cell 42 are made of the same material (e.g., copper), there is no need to make them separate. The fourth heat transport device 40 can be made by forming multiple concave cells 32 in a plate material that serves as both the substrate and the unit cell.
Alternatively, the fourth unit cell 42 may be formed in a tubular shape, and a plurality of concave cells 32 may be formed quasi-regularly on the inner or outer circumferential surface thereof to form the fourth heat transport device 40 .

The shape of the concave cells 32 is not limited to the inverted truncated cone shape shown in FIG. 29(b), and various shapes shown in FIG. 6 can be used.
Moreover, each concave cell 32 is fabricated so as to satisfy the following dimensional conditions.
(1) Average height (depth) H _ave : 0.35 μm to 50 μm
(2) Height deviation H _dev : Within 50% of the average height H _ave
(3) Average bottom width (opening diameter) B _ave : 0.175 μm to 25 μm
(4) Bottom width deviation _Bdev : within 50% of average bottom width _Bave
(5) Average spacing between adjacent concave cells D _ave : 0.49 μm to 50 μm
(6) Distance deviation D _dev between adjacent concave cells: within 50% of average distance D _ave . The concave cells 32 are produced by, for example, laser processing, pressing, etching, blasting, plating, or the like.

FIG. 30 shows a fifth heat transport device 50 according to the present invention, which comprises a substrate 12 and a fifth unit cell 52 formed on the surface thereof. The fifth unit cell 52 comprises a plurality of first convex cells 16 having a relatively large size (e.g., height H: 10 μm) and a plurality of second convex cells 54 having a finer size (e.g., height H: 1 μm) formed on the surface of the first convex cells 16 and the surface of the substrate 12.
The first convex cells 16 are formed by, for example, laser processing, pressing, or etching, and the second convex cells 54 are formed by, for example, plating or etching.

The first convex cells 16 and the second convex cells 54 may be arranged in either a regular or quasi-regular arrangement. Furthermore, the above conditions regarding the height H, bottom width B, and pitch D of at least the first convex cells 16 are applied.

FIG. 31 shows a sixth heat transport device 60 according to the present invention, which includes a substrate 12 and a sixth unit cell 62 disposed on the surface thereof.
In the sixth unit cell 62, a plurality of first concave cells 32 having a relatively large size (e.g., height H: 10 μm) are formed, and a plurality of second concave cells 64 having a finer size (e.g., height H: 1 μm) are formed on the inner surface of each of the first concave cells 32.
The first concave cells 32 are formed by, for example, laser processing, pressing, or etching, and the second concave cells 64 are formed by, for example, plating or etching.

The first concave cells 32 and the second concave cells 64 may be arranged in either a regular or quasi-regular arrangement. Furthermore, the above conditions regarding the height H, bottom width B, and pitch D of at least the first concave cells 32 are applied.

Although not shown in the drawings, a heat transport device can also be constructed by forming a plurality of finer second concave cells 64 on the surfaces of the first convex cells 16 and the substrate 12 .
Alternatively, a heat transport device can be constructed by forming a plurality of finer second convex cells 54 on the inner surface of the first concave cell 16.

[Surface characteristics of heat transport devices]
By forming unit cells having the above-mentioned convex cells 16 or concave cells 32 on the surface of the substrate 12 made of a sheet material, plate material, or pipe material, the surface properties can be changed.

For example, in the case of copper material alone, the contact angle with pure water is about 40 to 60 degrees, whereas in the case of adhesively bonding a second unit cell 24 having a convex cell 16 to a substrate 12 made of copper, the contact angle decreases to 10 to 20 degrees or even less, as shown in Figure 32(a).
That is, the heat transport device having the convex cells 16 exhibits the function of promoting hydrophilicity.

On the other hand, when the fourth unit cell 42 having the concave cells 32 is adhesively joined to the base material 12 made of aluminum, the contact angle is 90 degrees or more, as shown in FIG. 32(b).
In other words, the heat transport device having the concave cells 32 exerts the function of making the surface of a material that is originally hydrophilic water-repellent.

These findings indicate that the surface characteristics of liquids or melts, including pure water, can be controlled by designing the surface profile of the heat transport device.

10. First heat transport device
12 Substrate
14 First unit cell
16 Convex cell (first convex cell)
18 High heat source
20 Second heat transport device
24 Second unit cell
26 Regions
30 The third heat transport device
32 concave cell (first concave cell)
34 Third unit cell
40 The fourth heat transport device
42 Fourth unit cell
50 The fifth heat transport device
52 5th unit cell
54 Second convex cell
60 The 6th Heat Transport Device
62 6th unit cell
64 Second concave cell

Claims (8)

A substrate placed in close contact with a heat source;
A unit cell formed on a surface of a substrate,
The unit cell is composed of a plurality of metallic convex cells arranged quasi-regularly on a substrate,
A heat transport device, characterized in that each convex cell satisfies the following conditions:
Average height H _ave : 0.35 μm to 50 μm
Height deviation H _dev : Within 50% of average height H _ave 2. The heat transport device according to claim 1 , wherein the convex cells further satisfy the following condition:
Average bottom width B _ave : 0.175 μm to 25 μm
Bottom width deviation _Bdev : Within 50% of average bottom width _Bave Average spacing between convex cells _Dave : 0.49 μm to 50 μm
Spacing deviation D _dev between convex cells: within 50% of average spacing D _ave A substrate placed in close contact with a heat source;
A metal unit cell disposed in close contact with the surface of the substrate,
A number of concave cells are arranged quasi-regularly on the surface of the unit cell.
A heat transport device, characterized in that each concave cell satisfies the following conditions:
Average height H _ave : 0.35 μm to 50 μm
Height deviation H _dev : Within 50% of average height H _ave 4. The heat transport device according to claim 3 , wherein the concave cells further satisfy the following condition:
Average bottom width B _ave : 0.175 μm to 25 μm
Bottom width deviation _Bdev : Within 50% of average bottom width _Bave Average spacing between concave cells _Dave : 0.49 μm to 50 μm
Spacing deviation between concave cells D _dev : Within 50% of average spacing D _ave 3. The heat transport device according to claim 1 , wherein a plurality of fine convex or concave cells are formed on the surface of each of the convex cells. 5. The heat transport device according to claim 3 , wherein a plurality of fine convex or concave cells are formed on the surface of each concave cell. The substrate is a tubular body,
5. The heat transport device according to claim 1 , wherein the unit cells are formed on the outer circumferential surface or the inner circumferential surface of the tubular body. 5. The heat transport device according to claim 1 , wherein the base material and the unit cells are integrally formed from the same material.

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