JP7044314B2 - Micro-nano bubble generator and micro-nano bubble generation method - Google Patents

Description

The present invention relates to a micro-nano bubble generator for generating micro bubbles and nano bubbles (hereinafter collectively referred to as micro-nano bubbles) and a method for generating micro-nano bubbles.

Microbubbles and nanobubbles are being applied to the fields of medicine and agriculture, and are being used more and more in the engineering field as well as to improve cleaning / purifying properties and processability.
Patent Document 1 discloses a technique relating to an apparatus for generating microbubbles.

Japanese Unexamined Patent Publication No. 61-192328

There are many methods for generating microbubbles, such as swirling flow method, pressure melting method, orifice and venturi tube method, ultrasonic wave use, and micropore filter use, and various micro-bubble methods using these methods are available. A bubble generator is used.
There are many unknown parts about microbubbles and nanobubbles, and research and development on their physical characteristics, mechanism of generation (miniaturization of bubbles), functionality, specific uses, and their practical application are being actively carried out.
It is expected that microbubbles and nanobubbles will continue to be used in various fields and applications, and diversification of devices for generating microbubbles and nanobubbles is also desired.

In view of the above points, it is an object of the present invention to provide a new type of micro-nano bubble generator and a method for generating micro-nano bubbles, which have never existed before.

(Structure 1)
It is provided with a liquid supply unit that supplies a liquid for generating micro-nano bubbles and a micro-nano bubble generation unit that moves the rush piece near the interface of the liquid, and the rush frequency of the rush piece into the liquid interface is equal to or higher than a predetermined frequency. However, the micro-nano bubble generator is characterized in that the moving speed of the plunge piece is set to be equal to or higher than a predetermined speed.

(Structure 2)
The micro-nano bubble generator according to configuration 1, wherein the predetermined frequency is a frequency in the ultrasonic region under the gas-liquid mixture, or the predetermined velocity is the speed of sound under the gas-liquid mixture.

(Structure 3)
The micro-nano bubble generator according to the configuration 1 or 2, wherein the micro-nano bubble generating unit is composed of a rotating body having a plurality of plunging pieces formed on the surface thereof.

(Structure 4)
The micro-nano bubble generator according to the third configuration, wherein the liquid and the gas are sprinkled by the surface on which the plurality of plunge pieces are formed by the rotation of the rotating body to generate a high-speed gas-liquid mixed flow.

(Structure 5)
The liquid supply unit is composed of a nozzle that desires a spout at a position close to the surface of the rotating body, supplies the liquid from the nozzle, and is said to be on the rotation downstream side of the rotating body from the supply position. By covering the outer layer of the liquid flow with a flexible liquid guide member, the high-speed air-liquid mixed flow that becomes the liquid flow that winds around the surface of the rotating body is generated. The micro-nano bubble generator according to the configuration 4.

(Structure 6)
One of configurations 3 to 5, wherein the liquid supply unit is configured by a liquid container that receives all or part of the rotating body and holds the liquid in contact with the rotating body. The micro-nano bubble generator described.

(Structure 7)
The micro-nano bubble according to configuration 6, further comprising a scraping member for peeling off the liquid flow wrapped around the surface of the rotating body on the downstream side of the rotating body from the position where the rotating body comes into contact with the liquid. Generator.

(Structure 8)
The liquid supply unit is composed of a liquid container that receives all or part of the rotating body and holds the liquid in contact with the rotating body, and the liquid discharged from the liquid container by the high-speed gas-liquid mixed flow. The micro-nano bubble generator according to configuration 4 or 5, further comprising a liquid replenishment unit that supplies a liquid having a liquid discharge capacity or less, which is the maximum amount, to the liquid container.

(Structure 9)
A rotating body having a plurality of rushing pieces formed on the surface is brought into contact with the liquid interface, and the rotation of the rotating body causes the rushing piece to rush into the liquid interface at a predetermined frequency or higher, or the rushing piece of the rushing piece. A method of generating micro-nano bubbles by setting the moving speed to a predetermined speed or higher.

(Structure 10)
Due to the rotation of the rotating body, a liquid and a gas are sprinkled by the surface on which a plurality of the inrush pieces are formed to generate a high-speed gas-liquid mixed flow, and the high-speed gas-liquid mixed flow separates from the surface of the rotating body to increase the flow velocity. The method for generating micro-nano bubbles according to the configuration 9, wherein the micro-nano bubbles are generated by lowering the amount.

The micro-nano bubble generator and the method for generating micro-nano bubbles of the present invention are a new micro-nano bubble generation method that has never existed in the past, and thereby, it is possible to obtain diversification of devices for generating micro-nano bubbles and nano-bubbles.

Schematic block diagram of the micro-nano bubble generator according to the first embodiment of the present invention. A conceptual diagram illustrating the operation of the micro-nano bubble generator according to the first embodiment. Schematic block diagram showing another example of a micro-nano bubble generator Schematic block diagram of the micro-nano bubble generator according to the second embodiment of the present invention. The figure which shows the experimental apparatus which performed to confirm the behavior of the liquid inside a nozzle about the micro-nano bubble generator of Embodiment 2. A table showing the experimental results (photograph of the nozzle) for confirming the behavior of the liquid inside the nozzle. Photograph showing an experiment of another example of a micro-nano bubble generator

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. It should be noted that the following embodiment is an embodiment of the present invention and does not limit the present invention to the scope thereof.

<Embodiment 1>
FIG. 1 is a conceptual diagram showing an outline of the micro-nano bubble generator according to the first embodiment of the present invention. Further, FIG. 2 is a conceptual diagram for explaining the operation of the micro-nano bubble generator of the present embodiment.
The micro-nano bubble generator 1 of the present embodiment has a grinding wheel (rotary body) 11, a liquid container 12 for holding a liquid W for generating micro-nano bubbles, and a liquid that guards against splashes splashed by the grinding wheel 11. A splash guard 13 for returning to the inside of the container 12 is provided.

The grinding wheel 11 is a rotating body that is attached to a rotating mechanism (rotating tool or the like) (not shown) and rotates, and is arranged so as to come into contact with the liquid surface of the liquid W stored in the liquid container 12.
Abrasive grains 111 are exposed on the surface of the grinding wheel 11, and the protrusions formed by the exposed abrasive grains 111 are “rush pieces”. The uneven height of the plunge piece ranges from several μm to about 500 μm. As shown in FIG. 2, the rotation of the grinding wheel 11 causes the abrasive grains 111, which are plunging pieces, to plunge into the interface (liquid surface) of the liquid W. A large number of abrasive grains 111 are embedded in the grinding wheel, and each abrasive grain 111 rushes into the interface (liquid surface) of the liquid W one after another. As a result, the grinding wheel (rotating body) 11 functions as a "micro-nano bubble generating portion for injecting the intruding piece into the interface of the liquid".

The liquid container 12 is a tank for holding the liquid W, is configured to receive at least a part of the grinding wheel 11, and can hold the liquid level of the liquid W at a level in contact with the grinding wheel 11. As a result, the liquid container 12 functions as a liquid supply unit that supplies the liquid W to the grinding wheel 11 that is the micro-nano bubble generation unit.

The micro-nano bubble generator 1 of the present embodiment can generate micro-nano bubbles by the above-mentioned very simple configuration.
In the micro-nano bubble generator 1 of the present embodiment, the mechanism of generating micro-nano bubbles will be considered. As a mechanism for generating micro-nano bubbles in the vicinity of the point where the rotating grinding wheel 11 comes into contact with the liquid W,
Generation principle 1: Stirring of liquid W by a group of abrasive grains moving at high speed Generation principle 2: The same principle as the generation of micro-nano bubbles due to bubble collapse in a Venturi tube can be considered.

Principle of generation 1
In the vicinity of the portion where the rotating grinding wheel 11 rushes into the liquid W (on the right side in FIG. 2), the abrasive grains 111 moving at high speed come into contact with the liquid W. At this time, the liquid W is agitated while entraining air.
The abrasive grains 111 continuously enter and leave the liquid W repeatedly. Consider the frequency f when the entry / exit behavior of the abrasive grains 111 is regarded as vibration. Here, assuming that the abrasive grains 111 have a spherical shape with a uniform diameter d, the volume (d × 1 ×) in the unit plane (1 × 1) inside the grinding wheel 11 within the range of the abrasive grain size d width. 1) Assuming that the number of abrasive grains existing in the ground is Np and Vg is the abrasive grain ratio (volume percentage of the abrasive grains 111 in the entire grinding wheel 11), the average abrasive grain spacing x is expressed by the following equation 1. ..

Further, assuming that the diameter of the grinding wheel 11 is D and the rotation speed is Ns, the frequency f representing the continuous entry / exit behavior (rushing frequency) of the abrasive grains 111 into the liquid W is given by the following equation 2.

The deviation in the cutting edge height that rushes into the liquid W has a small effect and can be ignored. Therefore, for example, when "SG grindstone: # 100, structure 13" or "diamond grindstone: # 400, concentration 100" is used as the grinding wheel 11, the frequency f indicating the continuous entry / exit behavior of the abrasive grains 111 is set. In calculation, the frequency is as high as 146 kHz to 542 kHz.
At the place where the rotating grinding wheel 11 rushes into the liquid W, air is entrained and a gas-liquid mixed layer flow (high-speed gas-liquid mixed flow MF) is formed (this reduces the sound wave at that point), as described above. The frequency f is the frequency in the ultrasonic region under the gas-liquid mixture. It is considered that microbubble MB is effectively generated by this ultrasonic action (it is considered that microbubbles are generated more effectively by reaching the ultrasonic region, but even at frequencies lower than this, the abrasive moves at high speed. Microbubbles are generated by the stirring effect of plunging the liquid W into the grains 111 and stirring the liquid W while entraining air at this time).

Generation principle 2
In the Venturi tube, the speed of sound Cm of the gas-liquid mixed fluid is obtained from the following equation 3, and it is known that it is lower than that of a normal gas or liquid.

Here, p is the pressure, ρ1 is the liquid phase density, and α is the void ratio, and the gas is an ideal gas and is simplified by assuming an isothermal change. At a void ratio of 0.5 under atmospheric pressure, the speed of sound is ^about 20 m / s, which drops to the order of 101. In this region, pressure fluctuations in the Venturi tube generate microbubble MB.
In general grinding, the peripheral speed of the grinding wheel 11 is about Vs = 30 m / s, so the flow velocity of the high-speed gas-liquid mixed flow MF generated near the surface of the grinding wheel 11 so as to be caught in the grinding wheel 11 is also sonic. It is the area to reach. It is considered that the microbubble MB is generated by the sudden pressure fluctuation caused by this.
In FIGS. 1 and 2, for easy understanding, the lower end portion of the grinding wheel 11 is shown to be immersed in the liquid W, but when the grinding wheel 11 is deeply immersed in the liquid W, it is assumed that the grinding wheel 11 is immersed in the liquid W. The high-speed gas-liquid mixed flow MF formed so as to be caught in the grinding wheel 11 is less likely to occur, and efficient microbubble MB cannot be generated. In order to efficiently generate the microbubble MB, it is preferable that the contact of the grinding wheel 11 with the liquid W is several hundred μm or less.

As described above, according to the micro-nano bubble generator 1 of the present embodiment, it is possible to efficiently generate micro-bubbles with an extremely simple configuration.
The micro-nano bubble generator 1 of the present embodiment has high utility value especially in a factory or the like where machining is performed. As the processing liquid used for machining, a water-soluble processing liquid is used from the viewpoint of environmental consideration, ignition prevention and cost, and is widely used especially in grinding. On the other hand, a water-soluble processing liquid containing 95% or more of water is prone to putrefaction, and in particular, a bad odor in a factory in summer is regarded as a problem. Further, it is desirable that the water-soluble processing liquid has a high waste liquid treatment cost and can be recycled for as long as possible. In precision machining, separation work such as fine chips and machine oil in the machining fluid is indispensable, and expensive and special filtration equipment is required. To deal with such problems, the inventors are conducting research on microbubble (MB) coolant in which fine bubbles are mixed in the processing liquid, and the processing characteristics can be improved by grinding with a cBN grindstone ¹⁾ . It has been clarified that the water-soluble processing liquid used is effective in preventing spoilage and cleaning ²⁾ . 1) K. Suzuki, M. Iwai, S. Ninomiya, et al .: Effect of micro babble coolant on grinding with cBN wheel, Proc. Of ISAAT2007, (2007) 25., 2) Shinichi Ninomiya, Toshiharu Shimizu, Manabu Iwai , Suzuki Kiyoshi: Grinding Liquid Purification Effect of Micro Bubble Coolant, Journal of Abrasive Grain Processing Society, 56, 7 (2012) 465-469.
As described above, the microbubbles are effective in improving the processing characteristics of the grinding process, preventing the water-soluble processing liquid from spoiling, and cleaning the water-soluble processing liquid, and have high utility value in the factory where the machining is performed. However, when trying to use the conventional micro-bubble generator, it is necessary to newly install a device for generating the micro-bubbles and to install a supply means for supplying the micro-bubbles to a necessary place. Met.
On the other hand, in the micro-nano bubble generator 1 of the present embodiment, the grinding tool (grinding grindstone) itself used for grinding can be used, and the liquid W stored in the liquid container 12 can be used as the machining liquid itself. Therefore, it is very useful because microbubbles can be generated by using the processing machine that originally exists in the factory.

In the present embodiment, the liquid container 12 is configured to receive the lower portion of the grinding wheel 11, and includes a splash guard 13 for guarding the splashes of the grinding wheel 11 and returning it to the inside of the liquid container 12. As an example, instead of the splash guard 13, a scraping member for peeling off the liquid flow wrapped around the surface of the grinding wheel 11 may be provided. FIG. 3 shows an example of such a thing. A scraping member 121 is provided on the rotation downstream side of the grinding wheel 11 from the position where the grinding wheel 11 comes into contact with the liquid W (near the position where the rotating grinding wheel 11 rushes into the liquid W), whereby the droplets are liquid. Scattering to the outside of the container 12 is suppressed. The scraping member 121 may be arranged at a position where it is immersed in the liquid W (the high-speed gas-liquid mixed flow MF can be peeled off in the liquid, and the speed of the high-speed gas-liquid mixed flow MF drops sharply. (Pressure rise) can occur). Further, as shown in FIG. 3, a member 122 for suppressing splashes may be provided also on the upstream side of rotation.

<Embodiment 2>
FIG. 4 is a conceptual diagram showing an outline of the micro-nano bubble generator according to the second embodiment of the present invention. For the same configuration as that of the first embodiment, the same reference numerals are used, and detailed description thereof is omitted or simplified here.
The micro-nano bubble generator 1'of the present embodiment supplies the grinding grind (rotating body) 11, the liquid container 12 that holds the liquid (machining liquid) W that generated the micro-nano bubbles, and the machining fluid W to the grinding grind 11. A floating nozzle 15 is provided, and a flexible liquid guiding member 14 that covers the outer layer of the liquid flow of the working liquid W on the rotation downstream side of the grinding wheel (rotating body) 11 from the supply position of the working liquid W.

The floating nozzle 15 and the liquid guide member 14 have a configuration used in the floating nozzle method proposed by the inventors, and it has been clarified that reliable supply of processing liquid to a processing point and improvement of processing characteristics can be realized (). Shinichi Ninomiya, Manabu Iwai, Kiyoshi Suzuki: New processing liquid supply method that achieves both water saving and high efficiency / high precision processing, Journal of the Abrasive Grain Processing Society, 55, 2 (2011) 78-81.).
Since the floating nozzle 15 and the liquid guide member 14 have the same concept as the processing liquid supply method and apparatus of Japanese Patent No. 4523329, the description thereof is omitted here.

Conventionally, there was no idea of generating microbubbles based on the above floating nozzle method, but this floating nozzle 15 is referred to as the “micro-nano bubble generating portion (grinding grindstone (rotating body) 11)” described in the embodiment. The micro-nano bubble generator 1'of the second embodiment is used as a "liquid supply unit" for "".

FIG. 5A is an experimental device for an experiment conducted to confirm the behavior of the machining fluid in the nozzle portion of the micro-nano bubble generator 1 ′ of the second embodiment. FIG. 5B is an explanatory diagram (similar to FIG. 2) regarding the vicinity of the nozzle of the experimental device.
Installed at the bottom of the grinding wheel 11 using a transparent acrylic pipe at the tip of the nozzle in order to check the state of the grinding fluid near the nozzle water injection port in the minute gap between the grinding wheel 11 and the nozzle 15'closed to it. Then, the inside of the nozzle tip was visualized. The grinding wheel 11 was an SG grindstone (φ205 mm, # 100) and was rotated at 3000 rpm (V = 31.4 m / s). FIG. 6 shows an example of the result when the flow rate Q of the nozzle gap Δt (the gap between the grinding wheel 11 and the tip of the nozzle 15') and the water-soluble processing liquid (diluted by 5%) is changed. A phenomenon that seems to be a cavitation flow occurred inside the nozzle within Δt = 0.3 mm, and it was confirmed that remarkably fine bubbles were generated as the nozzle gap decreased. This phenomenon is expected to contribute to the improvement of grinding performance by cleaning the surface of the grindstone.
The mechanism by which micro-nano bubbles are generated is considered to be basically the same as that of the first embodiment.

In the present embodiment, the liquid container 12 is the processing liquid W supplied from the floating nozzle 15 to the grinding wheel 11 (the processing liquid in which microbubbles are generated as described above by being supplied to the grinding wheel 11). ) Is just a container. That is, although the liquid level in the liquid container 12 is not in contact with the grinding wheel 11 (FIG. 4) as an example, the liquid level in the liquid container 12 is brought into contact with the grinding wheel 11 to obtain the first embodiment. The same effect may be obtained.
FIG. 7A is a photograph showing an experimental state of such an experimental device. As can be seen from the photograph, high-concentration microbubbles are generated in the upper part of the liquid container with respect to the water-soluble processing liquid having a concentration of 2%.

In FIG. 7 (b), tap water is circulated by the apparatus of FIG. 7 (a), and the liquid (the liquid in which the microbubbles are almost eliminated) collected 5 minutes after the grinding wheel is stopped is collected by a beaker and the green laser beam is emitted. It is a photograph showing the result of irradiating from the side of the beaker.
The right side of the photo is the beaker of normal tap water, and the left side is the beaker of the above-collected liquid.
As can be seen from the photograph, the laser beam can be confirmed more significantly in the collected liquid than in ordinary tap water. That is, it is suggested that this method may generate not only microbubbles but also nanobubbles (existence of nanobubbles). Furthermore, by the same method, nanobubbles are generated even if pure water is used instead of tap water.

In the above embodiment, the liquid container 12 accepts a part of the grinding wheel 11, but the liquid container may accept the whole grinding wheel 11. By doing so, it is possible to more reliably prevent the droplets from jumping out of the liquid container.

In the embodiment, a liquid container is used as an example, but a liquid discharging means for supplying a liquid containing microbubbles to another device or the like may be provided (for example, a pump is used). As can be understood from the above explanations and FIG. 7A, etc., the liquid containing a large amount of microbubbles is concentrated on the upper part of the liquid, so it is preferable to configure the structure so that the liquid on the upper part is discharged.
For example, as shown in FIG. 7A, the high-speed gas-liquid mixed flow generated by being caught in the grinding wheel causes the liquid (liquid containing micro-nano bubbles) to pop out vigorously, so this is actively used. Therefore, it may be used as a liquid discharging means for efficiently collecting the ejected liquid and supplying it to another device or the like.
In this way, when the liquid discharging means for supplying the liquid containing the microbubbles to another device or the like is provided, the liquid replenishing unit for supplying the same amount of liquid as the liquid discharged by the liquid discharging means is provided. It is good to set it to.
When a liquid discharge means for discharging by the momentum of a high-speed gas-liquid mixed flow as described above is used, a liquid having a liquid discharge capacity or less, which is the maximum value of the amount of liquid discharged from the liquid container by the high-speed gas-liquid mixed flow. It is preferable to provide a liquid supply unit for supplying the liquid to the liquid container. By doing so, the level of the liquid level in the liquid container can be automatically maintained.

The micro-nano bubbles generated by using this means are described assuming that the gas dissolved in the atmosphere or liquid becomes micro-bubbles and nano-bubbles, but other desired gases (nitrogen, carbon dioxide, oxygen, ozone) are described. ) Can also be used. For example, as shown in FIG. 4, when a nozzle for supplying the processing liquid W to the grinding wheel 11 is used, micro-nano bubbles containing a large amount of each gas are formed by supplying a desired gas into the liquid in advance in the nozzle. Can be generated.

1. 1. .. .. Micro-nano bubble generator 11. .. .. Grinding wheel (micro-nano bubble generator)
111. .. .. Abrasive grains (rush pieces)
12. .. .. Liquid container (liquid supply unit)
121. .. .. Scraping member 14. .. .. Liquid-conducting member 15. .. .. Floating nozzle (liquid supply unit)

Claims (6)

A rotating body having a plurality of rush pieces having an uneven height in the range of several μm to about 500 μm is brought into contact with the liquid interface, and the rotation of the rotating body causes the rushing piece to enter the liquid interface. The step of generating micro-nano bubbles by making the frequency of the ultrasonic region or higher under the liquid mixture, or the moving speed of the plunge piece is made to be equal to or higher than the speed of sound under the gas-liquid mixture. A step to generate a micro-nano bubble by creating a high-speed gas-liquid mixed flow that reaches the speed of sound under the mixture ,
Steps to use liquids containing micro-nano bubbles based on the characteristics of micro-nano bubbles,
A method of generating micro-nano bubbles. The method for generating micro-nano bubbles according to claim 1, wherein the liquid containing the micro-nano bubbles is used for either preventing spoilage of the water-soluble processing liquid or purifying the water-soluble processing liquid. The method for generating micro-nano bubbles according to claim 1 or 2 , wherein the high-speed gas-liquid mixed flow separates from the surface of the rotating body to reduce the flow velocity to generate micro-nano bubbles. A liquid supply unit that supplies liquid to generate micro-nano bubbles,
In the vicinity of the interface of the liquid, a micro-nano bubble generator that causes gas to be sprinkled into the liquid by moving a plunging piece having an uneven height in the range of several μm to about 500 μm and bringing it into contact with the liquid.
Equipped with
A liquid in which micro-nano bubbles are generated by making the frequency of inrushing pieces into the liquid interface equal to or higher than the frequency in the ultrasonic region under the gas-liquid mixture, or the moving speed of the inrushing pieces is the gas-liquid mixture. Another device that uses the liquid that generated the micro-nano bubbles by generating a high-speed gas-liquid mixed flow that reaches the speed of sound under the gas-liquid mixture by making it higher than the speed of sound below, based on the characteristics of the micro-nano bubbles. A micro-nano bubble generator equipped with a liquid discharging means for supplying to . A micro-nano bubble generator that causes gas to flow into the liquid by moving a plunging piece having an uneven height in the range of several μm to about 500 μm and bringing it into contact with the liquid near the interface of the liquid. A micro-nano bubble generator composed of rotating bodies with multiple pieces formed on the surface,
The liquid supply unit that supplies the liquid for generating micro-nano bubbles, and is composed of a liquid container that receives all or a part of the rotating body and holds the liquid in contact with the rotating body. Liquid supply unit and
A member for returning the liquid that is scattered or wrapped around the rotating body to the inside of the liquid supply unit due to contact with the rotating body.
Equipped with
The frequency of rushing into the liquid interface should be higher than the frequency in the ultrasonic range under the gas-liquid mixture, or the moving speed of the rushing piece should be higher than the speed of sound under the gas-liquid mixture. A micro-nano bubble generator that produces a high-speed gas-liquid mixed flow that reaches the speed of sound under the gas-liquid mixture . The micro-nano bubble generator according to claim 5 , wherein the contact of the rotating body with the liquid is 100 μm or less.

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