Cavitation generation mechanism and plasma generation apparatus including cavitation generation mechanism

Abstract

To provide a cavitation generation mechanism capable of efficiently generating cavitation in a liquid by a simple mechanism and efficiently generating plasma by applying a pulse voltage between electrodes in the liquid containing bubbles mainly composed of vapor generated by the cavitation, and to provide a plasma generator including the cavitation generation mechanism.SOLUTION: The cavitation generation mechanism 3 for generating cavitation by injecting a liquid into the liquid is provided with a plurality of flow passages 31, 32 and 33 for imparting a flow having a swirl component in the same direction in the same axial direction, and the liquids flowing in the respective flow passages are merged at the outlets of the plurality of flow passages 31, 32 and 33 and injected into the liquid.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cavitation generating mechanism and a plasma generating device equipped with the cavitation generating mechanism. [Background technology]

[0002] The present applicant previously proposed a method for producing a sterilizing liquid consisting of water containing active oxygen species and nanoparticle catalysts in a stationary state by generating plasma in water containing bubbles mainly composed of water vapor by cavitation using a plasma generator that applies a pulse voltage between electrodes in the water (see Patent Document 1).

[0003] Conventionally, as cavitation generation mechanisms for causing cavitation in water, methods of agitating water with a rotor, methods of injecting water into water, and methods of installing obstacles in the water flow path have been proposed (see, for example, Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2021 / 246439 [Patent Document 2] Japanese Patent Application Publication No. 2017-176201 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-3297 [Patent Document 4] Japanese Patent Application Laid-Open No. 2024-24779 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a cavitation generation mechanism that efficiently causes cavitation in a liquid using a simple mechanism by improving the method of injecting water into a liquid as a cavitation generation mechanism for causing cavitation in water, and to provide a cavitation generation mechanism that can efficiently generate plasma by applying a pulse voltage between electrodes in a liquid containing bubbles whose main component is the resulting steam, and a plasma generating device equipped with this cavitation generation mechanism. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the cavitation generating mechanism of the present invention is a cavitation generating mechanism that generates cavitation by injecting a liquid into a liquid, and is characterized in that it has a plurality of flow paths that impart a flow having a swirling component in the same direction in the same axial direction, and the liquid that has flowed through each of the plurality of flow paths joins at the outlets of the plurality of flow paths and is injected into the liquid.

[0007] In this case, the plurality of flow paths can be provided in one nozzle.

[0008] Furthermore, the plasma generating device equipped with the cavitation generating mechanism of the present invention is characterized in that cavitation is generated by injecting a liquid into the liquid via the cavitation generating mechanism, and plasma is generated by the plasma generating device applying a pulse voltage between electrodes in the liquid containing bubbles whose main component is vapor generated by the cavitation generating mechanism. [Effects of the Invention]

[0009] The cavitation generation mechanism of the present invention and the plasma generating device equipped with the cavitation generation mechanism can efficiently cause cavitation in a liquid using a simple mechanism, and by applying a pulse voltage between electrodes in the liquid containing bubbles whose main component is the vapor generated by the cavitation, plasma can be efficiently generated. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a conceptual diagram showing an embodiment of a plasma generating device equipped with a cavitation generating mechanism of the present invention. [Figure 2] This is an explanatory diagram of the cavitation generation mechanism (convergent nozzle), where (a) is a plan view, (b) is a front view, (c) is an AA cross-sectional view of (a), and (d) is a diagram of the internal structure. [Figure 3] FIG. 10 is a diagram showing the plasma generation rate for each nozzle when the rotation angle of the flow path is changed (the relationship between the rotation angle of the flow path and the plasma generation rate). [Figure 4] These are photographs taken with a high-speed camera showing the state of bubble generation in a plasma generator for each nozzle with different rotation angles of the flow path. [Figure 5] FIG. 10 is a diagram showing the plasma generation rate for each nozzle when the rotation angle of the flow path is changed (the relationship between the voltage peak value and the plasma generation rate for each nozzle when the rotation angle of the flow path is changed). DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the cavitation generating mechanism and the plasma generating device equipped with the cavitation generating mechanism of the present invention will be described.

[0012] FIG. 1 shows an embodiment of a plasma generating device equipped with a cavitation generating mechanism of the present invention. This device is composed of a tank 1 for storing water, a rotor 2 rotated by a motor that generates a water flow in the water supplied from the tank 1, a cavitation generating mechanism 3 installed in a water flow path W connected to the rotor 2, a plasma generating device 4 that generates cavitation by injecting water into the water through the cavitation generating mechanism 3, and generates plasma by applying a pulse voltage between electrodes 41a and 41b in the water containing bubbles (cavitation bubbles) whose main component is water vapor, and a pipeline 5 that connects these mechanisms and circulates the water.

[0013] As shown in Figure 2, the cavitation generating mechanism 3 generates cavitation by injecting water into water (in this embodiment, inside the reaction chamber of the plasma generating device 4), and is equipped with multiple (two or more, in this embodiment, three) flow paths 31, 32, 33 that impart a flow with a swirling component in the same direction in the same axial direction, and the water that has flowed through each of the multiple flow paths 31, 32, 33 joins together at the outlets of the multiple flow paths 31, 32, 33 and is injected into the water.

[0014] The flow paths 31, 32, and 33 can be configured by bundling individual pipe members, for example, but here the flow paths 31, 32, and 33 are formed and integrated in one nozzle (convergent nozzle). The flow paths 31, 32, and 33 branch off from a common flow path 30 at the base end of the nozzle and merge at the tip to form a common flow path 34, with the cross-sectional area of ​​the flow path gradually decreasing toward the tip (base end: φ14 mm, tip end: φ7 mm). In this embodiment, the shapes of the flow paths 31, 32, and 33 are gradually made smaller in order to increase the flow rate when the water flowing through each flow path 31, 32, and 33 joins together and is sprayed into the water, but the shape of the flow paths and the amount of water can be set appropriately so as to obtain the required flow rate of the water when sprayed into the water. The nozzle is made of stainless steel (SUS304 in this example), iron (steel), titanium alloy. They can be made of metals such as gold, or synthetic resins (including composite materials) such as engineering plastics. For materials that are prone to chemical reactions with liquids such as water (deterioration due to oxidation, etc.), various surface treatments (such as wet processes such as plating, or surface coating treatments using dry processes such as PVD and CVD) can be used to prevent chemical reactions with liquids such as water. The nozzle can be manufactured by casting or 3D printer molding (metal materials: stainless steel (SUS316L (surgical stainless steel), SUS630), iron (maraging steel), titanium alloy, nickel-based alloy, aluminum alloy, cobalt-based alloy, synthetic resin material (including composite materials): ABS resin, PLA resin, ASA resin, PP resin, PC resin, nylon resin, acrylic resin, PETG, thermoplastic polyurethane), or by forming the inner surface into a conical surface, it can be formed by combining two components: an outer component with flow path 34 and an inner component with flow paths 30, 31, 32, and 33 (Figure 2(d)). The flow paths 31, 32, and 33 formed in the nozzle are preferably formed so that their cross-sectional shape is close to a circle (semicircle in this embodiment) because the resistance increases and the flow rate decreases as the rotation angle of the flow path for imparting a flow with a swirling component increases from 0° to 270°. The rougher the surface roughness Ra of the wall surfaces of the flow paths 31, 32, and 33 formed in the nozzle, the more water separates between the wall surface and the water flow, promoting the occurrence of cavitation. On the other hand, the rougher the surface roughness Ra, the greater the resistance and the lower the flow rate. For this reason, it is preferable to form the surface roughness Ra to be about 0.1 to 20 μm, and preferably about 1 to 10 μm.

[0015] The plasma generating device 4 is configured with electrodes 41a, 41b made of a conductor, and a pulse power supply 42 that applies a pulse voltage between the electrodes 41a, 41b, for example, a voltage equal to or higher than the discharge start voltage, with a pulse width of 1.5 μs or less and a repetition frequency of 100 kHz or more. In the insulating bubble region, the vaporized material is ionized (converted into plasma) by a high-voltage dielectric breakdown discharge caused by the pulse voltage, thereby generating in-liquid plasma (cavitation plasma; sometimes referred to as "CBP (Cavitation bubble plasma)" in this specification). The discharge form induced by the pulse voltage is preferably glow discharge, which allows the synthesis of nanoparticle catalysts in crystalline, quasicrystalline, amorphous, or other forms at low temperatures and with high energy efficiency. These nanoparticle catalysts are nanoparticles of the components of electrodes 41a and 41b. If the electrodes are metal, the nanoparticles become metal nanoparticles immediately after they are formed. Depending on the type of metal, the nanoparticles may be oxidized, or if chlorine or sulfur is present in the water, the nanoparticles may be chlorinated or sulfurized (depending on the impurity, they may form compounds with the impurity). The nanoparticle catalysts produced in this way can be used for sterilization (see Patent Document 1). The electrodes 41a and 41b are preferably arranged to face each other in a direction perpendicular to the water flow, but as long as plasma can be generated, an arrangement such as a V-shaped arrangement can also be adopted. Materials for the electrodes 41a and 41b can be selected arbitrarily depending on the application, including metals such as tungsten, copper, iron, silver, gold, and platinum, as well as aluminum, scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, gallium, germanium, yttrium, zirconium, molybdenum, technetium, ruthenium, rhodium, palladium, cadmium, indium, tin, antimony, lanthanides, hafnium, tantalum, rhenium, osmium, iridium, thallium, bismuth, and polonium, as well as conductive materials such as carbon, conductive diamond, alloys and composites thereof (including those coated with a thin film by techniques such as plating or dry coating), and oxides (including those in which the surfaces of the electrodes 41a and 41b have reacted with water).The electrodes 41a and 41b, which are arranged opposite each other, can also be made of different materials or have different sizes, such as gold and silver. The nanoparticle catalysts such as metals and metal oxides resulting from the consumption components of the electrodes 41a and 41b In addition to nanoparticles that have aggregated to form secondary particles, depending on the material of the electrodes 41a and 41b, most of the nanoparticles may end up dissolved in water due to hydrogen peroxide (H2O2) and other substances that are generated simultaneously with the nanoparticles by the in-liquid plasma (e.g., tungsten), but this is not excluded by the present invention. The shape of the electrodes 41a, 41b may be a cylinder, a rectangular cylinder, an elliptical cylinder, a cone, or a pyramid. One pair of electrodes 41a, 41b is sufficient, but two or more pairs may be installed to further improve processing efficiency. One set of plasma generator 4 is sufficient, but two or more sets may be installed to further improve processing efficiency. The polarity of the pulse voltage may be bipolar, positive, or negative. [Example]

[0016] Next, a functional test of a nozzle used in a cavitation generating mechanism, which was carried out using this device, will be described.

[0017] [About the nozzle] Table 1 shows the specifications of the nozzle for the cavitation generation mechanism. The nozzle shown in FIG. 2 is an example in which the rotation angle of the flow paths 31, 32, and 33 is 270°.

[0018] [Table 1]

[0019] [Device operating conditions] Table 2 shows the operating conditions of the device.

[0020] [Table 2]

[0021] The operating conditions of the device were as follows: The water used was ion-exchanged water, which has low conductivity (1 μS / cm) and is less likely to generate plasma, in order to more easily bring out the difference in the nozzle function used in the cavitation generation mechanism. The pump (rotor) rotation speed was set so that the flow rate of each nozzle shown in Table 1 was a constant value (18.5 L / min).

[0022] [Functional test of the nozzle for cavitation generation mechanism] Next, a function test of the nozzle of the cavitation generating mechanism was carried out in the following manner. As shown in Figures 1 and 2, a cavitation generating mechanism 3 using the nozzles shown in Table 1 was attached to a pipe 5 connected to a rotor 2, and water that passed through the cavitation generating mechanism 3 was introduced into a plasma generating device 4 equipped with electrodes 41a and 41b.

[0023] Figure 3 shows the plasma generation rate for each nozzle (the ratio of the number of pulses that generated plasma to the number of pulses applied), and Figure 4 shows a photograph taken with a high-speed camera of the bubble generation in the plasma generator (pump (rotor) rotation speed: 3600 rpm (constant)). Here, since the plasma generation rate depends on the amount of bubbles present between the electrodes and the voltage between the electrodes, instead of directly measuring the amount of bubbles, the amount of bubbles generated is indirectly measured by the plasma generation rate.

[0024] Incidentally, the function test of the nozzle of this cavitation generation mechanism was conducted by setting the operating conditions of the device to conditions that make it difficult for plasma to be generated (conditions under which the plasma generation rate of a straight nozzle in which the water sprayed into the water has no swirling component is 0%) as shown in Table 2 in order to make it easier to see the differences in the function of the nozzles used in the cavitation generation mechanism. However, even in the case of a straight nozzle, plasma can be generated as shown in Figure 5 by setting the conditions shown in Table 3 below (conditions under which plasma is easily generated).

[0025] [Table 3]

[0026] The results of the function test of the nozzle of the cavitation generation mechanism revealed the following. The plasma generation rate and the amount of bubbles generated increased as the rotation angle of the flow channel increased from 0° to 270°. This shows that in order to increase the plasma generation rate and the amount of bubbles generated, it is important to impart a swirling component to the water injected into the water by increasing the rotation angle of the flow channel. As the rotation angle of the flow path increases from 0° to 270°, resistance increases and the flow rate decreases, so in order to maintain the same flow rate (flow rate), the rotor rotation speed must be increased. The number of flow paths is important to ensure that the water flowing through multiple flow paths 31, 32, 33 joins together and is sprayed into the water, rather than having a single (straight) flow path. It is preferable to have two or more flow paths, and preferably three or more as shown in this embodiment (subject to restrictions such as the shape of the nozzle).

[0027] The cavitation generation mechanism of the present invention and the plasma generating device equipped with the cavitation generation mechanism have been described above based on their embodiments, but the present invention is not limited to these, and the configuration can be changed as appropriate within the scope of the spirit of the present invention. Specifically, water (ion-exchanged water) was used as the liquid, but depending on the application of the plasma generator, in addition to ordinary water, solutions in which solutes such as chloride salts such as sodium chloride (table salt), potassium chloride, calcium chloride, magnesium chloride, and ammonium chloride, nitrates such as potassium nitrate, sodium nitrate, and silver nitrate, magnesium sulfate, copper (II) sulfate, zinc sulfate, and ammonium sulfate, carbonates such as sodium carbonate, acetates such as sodium acetate, permanganates such as potassium permanganate, and phosphates such as sodium phosphate, potassium phosphate, and calcium phosphate are dissolved in a solvent such as water, suspensions in which insoluble or poorly soluble substances are dispersed in water, and liquids other than water such as alcohol and oil can be used, and these are not excluded. [Industrial Applicability]

[0028] The cavitation generating mechanism of the present invention and the plasma having the cavitation generating mechanism The plasma generator has a simple mechanism that efficiently causes cavitation in a liquid, and by applying a pulse voltage between electrodes in a liquid containing bubbles whose main component is the resulting vapor, it can efficiently generate plasma.Therefore, there are no restrictions on the application method or target, and the plasma generator can be widely used for a variety of purposes, such as dispersing powders, synthesizing nanoparticles, decomposing organic matter, and sterilizing microorganisms such as various plant pathogens (including viruses, bacteria, fungi, protozoa, etc.) (including preventing storage diseases that occur in agricultural products after harvest, such as vegetables, flowers, and fruit trees). [Explanation of symbols]

[0029] 1 tank 2 rotors 3. Cavitation generation mechanism (convergent nozzle) 30 Common Channel 31 Flow path 32 Flow path 33 Flow path 34 Common Channel 4. Plasma generator 41a electrode 41b Electrode 42 Pulse power supply 5 conduit W Water flow path

Claims

1. A cavitation generating mechanism that generates cavitation by injecting a liquid into a liquid, characterized in that it has multiple flow paths that impart a flow with a swirling component in the same direction along the same axis, and the liquid that has flowed through each of the multiple flow paths joins at the outlets of the multiple flow paths and is injected into the liquid.

2. 2. The cavitation generating mechanism according to claim 1, wherein the plurality of flow paths are provided in one nozzle.

3. A plasma generating device equipped with a cavitation generating mechanism, characterized in that cavitation is generated by injecting a liquid into the liquid via the cavitation generating mechanism described in claim 1 or 2, and plasma is generated by the plasma generating device applying a pulse voltage between electrodes in the liquid containing bubbles whose main component is vapor generated by the cavitation generating mechanism.

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