Refrigeration equipment and electrolysis equipment

Abstract

This realizes a cooling device with higher cooling performance. The cooling device 1 includes a chamber 10 in contact with a heat source HS, a liquid 11 that partially fills the chamber 10, a plurality of electrodes 12 immersed in the liquid 11, and a power supply 13 that applies an AC voltage to the electrodes 12. The power supply 13 generates a voltage having a voltage waveform or frequency that causes DEP resonance on the gas-liquid surface of the liquid 11.

Description

[Technical Field]

[0001] The present disclosure relates to a cooling device and an electrolyzer. [Background technology]

[0002] Vapor chambers have been proposed as devices for cooling devices that generate heat, such as power semiconductors and CPUs used in mobile terminals and the like (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-014936 [Non-patent literature]

[0004] [Non-Patent Document 1] Suraj Joottu Thiagarajan, Ronggui Yang, Charles King, Sreekant Narumanchi, "Bubble dynamics and nucleate pool boiling heat transfer on microporous copper surfaces, International Journal of Heat and Mass Transfer", Volume 89, October 2015, Pages 1297-1315 [Non-patent document 2] Masashi Mori "2020 Subsidy Program for Innovation in Alkaline Water Electrolysis Technology Using Two-Layer Porous Materials" [Non-patent document 3] Yemima Ehrnst, Peter C. Sherrell, Amgad R. Rezk,* and Leslie Y. Yeo, "Acoustically-Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes", Adv. Energy Mater., 2023 Summary of the Invention [Problem to be solved by the invention]

[0005] A typical vapor chamber consists of a hollow chamber, a liquid sealed within the chamber, and a wick with a capillary structure that runs throughout the chamber. The chamber is in contact with a heat-generating device. When the device heats up and reaches a high temperature, the liquid inside the chamber evaporates, spreads throughout the chamber, and then condenses and returns to liquid form, a process that is repeated. This dissipates heat and cools the device. After dissipating heat, the condensed liquid returns to the vicinity of the heat source, the device, by capillary action, through the gaps in the wick.

[0006] Such vapor chambers have excellent features such as high cooling efficiency and ease of miniaturization and thinning, but current vapor chambers still have room for improvement in terms of cooling performance.

[0007] The technology disclosed herein has been made in light of these circumstances, and its purpose is to realize a cooling device with higher cooling performance. [Means for solving the problem]

[0008] To solve the above problems, one embodiment of the present invention provides a cooling device that includes a chamber in contact with a heat source, a liquid that partially fills the chamber, multiple electrodes immersed in the liquid, and a power supply that applies an AC voltage to the electrodes. The power supply generates a voltage having a waveform or frequency that induces DEP resonance at the gas-liquid surface of the liquid.

[0009] In one embodiment, the waveform of the voltage generated by the power supply may be a sinusoidal waveform.

[0010] In one embodiment, the waveform of the voltage generated by the power supply may be a square waveform.

[0011] In an embodiment, the cooling device may further include a power supply control unit that controls the power supply.

[0012] In one embodiment, the liquid may be a fluorinated refrigerant.

[0013] In some embodiments, the heat source may include a power semiconductor.

[0014] Another aspect of the present invention is an electrolysis device. This device includes an electrolysis cell containing an electrolyte, a pair of electrolysis electrodes immersed in the electrolyte, an electrolysis power supply that applies a voltage to the electrolysis electrodes, a DEP electrode immersed in the electrolyte, and a DEP power supply that applies a voltage to the DEP electrode. The DEP power supply generates a voltage having a voltage waveform or frequency that causes DEP resonance on the surface of the electrolysis power supply.

[0015] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0016] According to the present invention, a cooling device with higher cooling performance can be realized. [Brief explanation of the drawings]

[0017] [Figure 1] A side view of a liquid boiling and creating bubbles when placed on a hot solid wall. [Figure 2]This is a side view of a liquid sandwiched between two parallel plate electrodes and an offset square or sine wave high voltage applied. [Figure 3] FIG. 3 is a diagram showing the relationship between frequency and amplitude regarding vibration of the gas-liquid interface in the system of FIG. 2. [Figure 4] The photographs show the gas-liquid interface when the vibration frequency is 1 Hz and 20 Hz. [Figure 5] 1 is a schematic cross-sectional view of a cooling device according to a first embodiment of the present disclosure. [Figure 6] 6 is a cross-sectional view taken along the line AA' in FIG. 5. [Figure 7] FIG. 4 is a schematic cross-sectional view of an electrolyzer according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, the embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0019] In addition, the dimensions (thickness, length, width, etc.) of each component shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple components do not necessarily represent their relative sizes, and even if a component A is depicted as being thicker than another component B in the drawings, it is possible that component A is thinner than component B.

[0020] Before describing specific embodiments, we will explain the underlying knowledge. Figure 1 is a side view of the process of bubbles forming when a liquid is filled on a high-temperature solid wall. First, small bubbles form on the solid wall, which is a thermal boundary layer (superheated liquid layer) superheated above the saturation temperature (a). The bubbles then grow due to the evaporation of a micro-liquid film several microns thick at the bottom of the bubble and the superheated liquid layer (b). The line where the three interfaces of the solid, liquid, and gas intersect is called the three-phase contact line. The formed micro-liquid film has low thermal resistance due to its thinness. However, a large temperature difference (the difference between the saturation temperature and the wall temperature, ignoring interfacial thermal resistance and vapor superheat) occurs, causing evaporation with a very high heat flux. As the liquid film evaporates, dry patches spread on the wall over time. As a result, the three-phase contact line moves outward when viewed from above. Then, as the bubble detachment process begins, the bubbles rise and assume a vertically elongated shape. At this time, the three-phase boundary line moves, causing the dry patch to become wet again (rewetting) (c). When the bubbles leave, heat transfer is promoted by convection induced by the bubbles' upward movement (d). Through these processes, the solid wall is cooled by the absorption of heat due to boiling (or more generally, phase change) and the heat transport due to liquid convection.

[0021] The faster the bubble departure frequency, the more heat can be transported, improving cooling performance. Therefore, increasing the bubble departure frequency is the key to improving cooling performance.

[0022] In pool boiling, bubbles of about 300-800 μm are generated at about 50-250 Hz. This means that the three-phase boundary line also oscillates with an amplitude of about 300-800 μm and a frequency of about 50-250 Hz. If this three-phase boundary line could be made to oscillate with a larger amplitude and higher frequency, it is expected that cooling performance could be improved. This is because the oscillation of the three-phase boundary line with a larger amplitude and higher frequency not only promotes phase change, but also causes intense convection in each phase, which is thought to promote convective heat transfer.

[0023] Therefore, it is thought that cooling performance can be improved if the three-phase field can be directly manipulated and controlled. However, even if a mechanical pump is used, it is not possible to directly control the three-phase field.

[0024] The inventors therefore considered that it would be possible to manipulate and control the three-phase boundary line by vibrating the liquid surface using dielectrophoresis (DEP) that acts on the interface under the action of an electric field.

[0025] The DEP resonance, which is the principle of the technology of the present disclosure, will be explained below. Fig. 2 is a side view of a liquid (fluorine-based refrigerant HFE7100) sandwiched between two parallel plate electrodes E1 and E2, when a high voltage of an offset square wave or sine wave is applied to these electrodes E1 and E2. When a voltage is applied, the gas-liquid interface is moved by the dielectrophoretic force F DEP This causes the sensor to vibrate vertically in a frequency range up to about 100 Hz in synchronization with the applied frequency.

[0026] Figure 3 shows the relationship between the frequency and amplitude of the vibration of the gas-liquid interface. The amplitude of the gas-liquid interface reaches a maximum of 6 mm when the frequency is 1 Hz. Thereafter, as the frequency increases, the amplitude decreases. Here, the inventors discovered that when the frequency is 20 Hz and 60 Hz, waves with a constant wavelength are generated in the horizontal direction, and the amplitude increases sharply. This is due to the electrophoretic force F DEP This phenomenon is thought to be a wave resonance caused by gravity g. Hereafter, this phenomenon will be called "DEP resonance."

[0027] Figure 4 shows photographs of the gas-liquid interface (LV interface) when the vibration frequency is 1 Hz (maximum amplitude) and 20 Hz (DEP resonance occurs). The top image shows the state when the vibration phase is 0°, and the bottom image shows the state when the vibration phase is 180°.

[0028] Furthermore, the inventors came up with the idea that by utilizing this DFP resonance, it is possible to control the three-phase field lines.

[0029] [First embodiment] 5 is a schematic cross-sectional view of a cooling device 1 according to a first embodiment of the present disclosure, with the x-axis, y-axis, and z-axis taken as shown in the figure (the same applies to FIG. 6). The cooling device 1 includes a chamber 10 in contact with a heat source HS, a liquid 11 that fills a portion of the chamber 10, a plurality of electrodes 12 immersed in the liquid 11, a power supply 13 that applies an AC voltage to the electrodes 12, and a power supply control unit 14.

[0030] The chamber 10 is a hollow box made of metal or the like. The chamber 10 is placed in contact with a heat source HS such as a CPU used in a power semiconductor or a mobile terminal. A liquid 11 is sealed in the chamber 10, forming an enclosed space.

[0031] The liquid 11 is a working fluid such as a fluorine-based refrigerant, and absorbs heat from the heat source HS, transports it to the space outside the chamber 10, and dissipates the heat.

[0032] The electrode 12 is connected to a power supply 13 and is immersed in the liquid 11. The electrode 12 generates an oscillating potential difference across the liquid 11, which in turn causes the gas-liquid surface of the liquid 11 to vibrate.

[0033] The power supply 13 applies an AC voltage to the electrode 12. The voltage generated by the power supply 13 has a voltage waveform or frequency that causes DEP resonance on the gas-liquid surface of the liquid 11.

[0034] The waveform of the voltage generated by the power supply 13 may be a sine waveform or a rectangular waveform.

[0035] The power supply control unit 14 is connected to the power supply 13 and controls the power supply 13. The power supply control unit 14 controls, for example, the period, amplitude, wavelength, and waveform of the voltage generated by the power supply 13, and the timing of starting and stopping the power supply 13. Note that the power supply control unit 14 is not necessarily required as long as the power supply 13 itself can appropriately generate a voltage having a voltage waveform or frequency that causes DEP resonance on the gas-liquid surface of the liquid 11.

[0036] 6 is a cross-sectional view taken along the line A-A' in FIG. 5. As shown in the figure, the oscillating potential difference caused by electrode 12 causes vibrations on the gas-liquid surface of liquid 11. At this time, the voltage generated by power supply 13 has a voltage waveform or frequency that causes DEP resonance on the gas-liquid surface of liquid 11, so that large-amplitude DEP resonance accompanied by waves with a constant wavelength in the lateral direction occurs on the gas-liquid surface of liquid 11. As a result, the three-phase boundary between liquid 11 and chamber 10 is driven at a high frequency and with a large amplitude.

[0037] Conventionally, the bubble separation frequency, which is the vibration frequency of the three-phase boundary line, was based on passive flow using the buoyancy of boiling and could not be controlled. In contrast, the method disclosed here uses DEP resonance to actively vibrate and control the three-phase boundary line. As a result, in addition to promoting phase change, vigorous convection occurs in each phase, promoting convective heat transfer.

[0038] The heat flux transported by the phase change has a linear relationship with the bubble point density and bubble departure frequency (see, for example, Non-Patent Document 1). For example, if this technology can increase the frequency to the same level as conventional boiling and increase the bubble point density (three-phase boundary line density) by five times (electrode size of about 100 μm), the transported heat flux will also be five times larger.

[0039] As described above, this technology achieves cooling through phase change using a new flow that differs from conventional boiling, and has the potential to significantly surpass heat transport through conventional boiling.

[0040] As described above, according to this embodiment, it is possible to realize a cooling device with higher cooling performance than conventional devices.

[0041] It is possible that the three-phase boundary line can vibrate at a higher speed than the conventional bubble separation frequency. For example, current laboratory-level verification has confirmed vibrations at frequencies of around 100 Hz and amplitudes on the order of millimeters. However, it is believed that vibrations of the same amplitude (i.e., around 300-800 μm) and frequency (i.e., around 50-250 Hz) as conventional boiling can be achieved.

[0042] The heat source HS may include a power semiconductor. To achieve carbon neutrality, various machines are being electrified. This electrification has led to a rapid increase in demand for power semiconductors that convert electrical signals. Meanwhile, power semiconductors that handle large amounts of power generate a large amount of heat due to Joule heat, making cooling them a major challenge. For these reasons, the cooling device 1 of the present disclosure is highly suitable for cooling heat sources including power semiconductors. Furthermore, typical power semiconductors are equipped with a high-voltage source that generates high voltage. If such a high-voltage source could be used for the power source 13 used to implement the cooling device 1, there would be an even greater advantage, as there would be no need to introduce an additional power supply.

[0043] [Second embodiment] 7 is a schematic cross-sectional view of an electrolyzer 2 according to a second embodiment of the present disclosure. The electrolyzer 2 includes an electrolysis tank 20 containing an electrolytic solution 21, a pair of electrolysis electrodes 22, an electrolysis power supply 23, a DEP electrode 24, and a DEP power supply 25.

[0044] The electrolysis tank 20 contains an electrolyte 21 such as an aqueous sodium hydroxide solution.

[0045] The pair of electrolysis electrodes 22 includes an anode and a cathode. The anode and cathode of the electrolysis electrodes 22 are immersed in the electrolyte 21. When the electrolysis power supply 23 applies a voltage to the electrolysis electrodes 22, a current flows between the anode and cathode of the electrolysis electrodes 22. As a result, an oxidation reaction occurs at the anode of the electrolysis electrode 22, and a reduction reaction occurs at the cathode of the electrolysis electrode 22. This causes the electrolysis of the electrolyte 21 to proceed. For example, if the electrolyte 21 is a sodium hydroxide solution, hydrogen H2 is generated at the cathode, and oxygen O2 is generated at the anode.

[0046] The DEP electrode 24 is connected to a DEP power supply 25 and is immersed in the electrolyte 21. The DEP electrode 24 generates an oscillating potential difference in the electrolyte 21, which results in the surface of the electrolysis electrode 22 vibrating.

[0047] The DEP power supply 25 applies a voltage to the DEP electrode 24. The voltage generated by the DEP power supply 25 is a voltage that causes DEP resonance on the surface of the electrolysis electrode 22. The DEP power supply 25 intermittently applies a voltage having, for example, a voltage waveform or frequency that causes DEP resonance but does not cause water electrolysis at the DEP electrode 24.

[0048] Furthermore, in order to prevent heat generation in the DEP electrode 24, an insulating coating may be applied to the DEP electrode 24 to prevent excessive current flow.

[0049] The oscillating potential difference caused by the DEP electrode 24 causes vibrations on the surface of the electrolysis electrode 22. At this time, the voltage generated by the DEP power supply 25 has a voltage waveform or frequency that causes DEP resonance on the surface of the electrolysis electrode 22, so that a large-amplitude DEP resonance accompanied by a wave with a constant wavelength in the lateral direction occurs on the surface of the electrolysis electrode 22. As a result, the three-phase field between the electrolyte 21 and the surface of the electrolysis electrode 22 is driven with high frequency and large amplitude. This promotes electrolysis of the electrolyte 21.

[0050] In the electrolysis of water, as the amount of oxygen and hydrogen gas produced increases, these gases cover the electrolysis electrodes. As a result, water cannot be supplied to the electrolysis electrodes due to mass transfer rate limitation, resulting in a limiting current density. To solve this problem, attempts have been made to promote water supply and increase the current density by installing a porous body on the electrode (see, for example, Non-Patent Document 2) or applying ultrasound (see, for example, Non-Patent Document 3).

[0051] In Non-Patent Document 1, based on the similarity between the phenomenon in which gas covers an electrode and reaches a critical current density and the phenomenon in which vapor bubbles in nucleate boiling cover a heating surface and reach a critical heat flux, a honeycomb porous body, which has been effective in improving nucleate boiling heat transfer, is applied to water electrolysis, and the critical current density is improved by promoting macroscopic water supply using capillary force.In contrast, the three-phase interface vibration by DEP disclosed herein is expected to be effective in phase change heat transport, and therefore it is thought that this effect will also be achieved in water electrolysis.

[0052] On the other hand, Non-Patent Document 2 takes a microscopic approach of promoting the supply of water molecules by applying sound waves to an electrode and disrupting the hydrogen bond network of water molecules near the electrode.In contrast, this disclosure combines both large- and small-scale approaches: promoting microscopic material transport at the three-phase boundary line using a wavy electric field, and promoting macroscopic water supply by vibrating the bubble interface.

[0053] As described above, according to this embodiment, an electrolyzer with high electrolysis performance can be realized.

[0054] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0055] For example, in cooling devices, in addition to the bubble detachment frequency, a higher bubble point density leads to higher heat transfer performance. In conventional boiling, the bubble size is naturally determined (300-800 μm). This naturally determines the upper limit of the bubble point density, but the cooling device disclosed herein does not require bubbles. Therefore, by making the electrode shape of the cooling device using DEP resonance shown in Figure 6 finer, the three-phase boundary line density can be increased.

[0056] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present disclosure. A new embodiment resulting from the combination has the combined effects of the combined embodiments and modifications.

[0057] When understanding the abstract technical ideas of the embodiments, the technical ideas should not be interpreted as being limited to the contents of the embodiments. The above-described embodiments and variations are merely illustrative examples, and many design modifications, such as changes, additions, and deletions of components, are possible. In the embodiments, the contents in which such design modifications are possible are emphasized by adding the notation "embodiment." However, design modifications are also permitted even in contents without such notation. [Industrial Applicability]

[0058] The cooling device disclosed herein can be used to cool power semiconductors used in data centers, EV batteries, and other applications. The electrolysis device disclosed herein can be used in fields requiring highly efficient electrolysis of electrolytes. The DEP resonance disclosed herein can be used to promote fuel supply in solid-fuel rockets, control the atomization and dropletization of methane fuel, and promote heat transfer in two-phase heat exchangers for fluorinated refrigerants in heat pumps. Furthermore, the DEP resonance disclosed herein can be applied to gas-liquid phase interfaces in porous media to promote the drying of batteries, food, paper, and paint. It can also be widely used to promote material synthesis in electrochemistry and promote mixing at liquid-liquid interfaces and in small-scale, low-Reynolds-number flows. [Explanation of symbols]

[0059] 1 · Cooling device, 2. Electrolyzer, 10··chamber, 11·Liquid, 12...electrode, 13...power supply, 14. Power supply control section, 20··Electrolytic bath, 21...electrolyte, 22··Electrolysis electrodes, 23. Electrolysis power source 24··DEP electrode, 25··DEP power supply, E1··Electrode, E2··Electrode, HS··Heat source.

Claims

1. a chamber in contact with a heat source; a liquid that partially fills the chamber; a plurality of electrodes immersed in the liquid; a power source that applies an AC voltage to the electrodes, The cooling device is characterized in that the power supply generates a voltage having a voltage waveform or frequency that causes DEP resonance on the gas-liquid surface of the liquid.

2. 2. The cooling device according to claim 1, wherein the waveform of the voltage generated by the power supply is a sine waveform.

3. 2. The cooling device according to claim 1, wherein the waveform of the voltage generated by the power supply is a square waveform.

4. The cooling device according to claim 1 , further comprising a power supply control unit that controls the power supply.

5. 2. The cooling device according to claim 1, wherein the liquid is a fluorine-based refrigerant.

6. The cooling device according to claim 1 , wherein the heat source includes a power semiconductor.

7. an electrolytic cell containing an electrolyte; a pair of electrolysis electrodes immersed in the electrolyte; an electrolysis power supply that applies a voltage to the electrolysis electrodes; a DEP electrode immersed in the electrolyte; a DEP power supply that applies a voltage to the DEP electrode; The electrolysis device is characterized in that the DEP power supply generates a voltage having a voltage waveform or frequency that causes DEP resonance on the surface of the electrolysis power supply.

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