Microbubble generating device and microbubble generating method

Abstract

To provide a technology to efficiently generate fine bubbles using a porous body.SOLUTION: A fine bubble generation device where fine bubbles are generated in liquid includes: a porous body provided with a first surface having a plurality of pores being in contact with the liquid and generating the fine bubbles; a gas supply mechanism to supply a gas to the porous body; and a liquid oscillation mechanism to oscillate the liquid being in contact with the first surface in a direction along the first surface. In the device, the gas supplied to the porous body is released into the liquid via the plurality of pores during the oscillation of the liquid by the liquid oscillation mechanism.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a microbubble generating device and a method for generating microbubbles. [Background technology]

[0002] In recent years, the usefulness of technologies using fine bubbles less than 100 μm in diameter, known as fine bubbles, has been attracting attention. Fine bubbles include, for example, ultrafine bubbles less than 1 μm in diameter and microbubbles greater than 1 μm in diameter. By miniaturizing bubbles, for example, it is expected that gas-liquid reactions will be promoted in chemical reactions such as organic synthesis, and oxygen supply will be more efficient in culturing microorganisms and animal cells. Other applications of fine bubble technologies are being explored, including cleaning technologies using liquids containing fine bubbles, water sterilization and deodorization, ozonated water generation, health and medical equipment, water purification in lakes and aquaculture facilities, various wastewater treatment processes in factories and livestock farms, and functional water production. Accordingly, the market for devices that generate microbubbles and ultrafine bubbles has expanded in recent years.

[0003] The micro-bubble generator disclosed in Patent Document 1 includes a fluid swirling chamber defined by a tubular member having a cylindrical inner circumferential surface, a first end wall member closing one end of the tubular member, and a second end wall member closing the other end of the tubular member; a fluid inlet port for introducing a gas-liquid mixture into the fluid swirling chamber; and a fluid outlet port for discharging the gas-liquid mixture from the fluid swirling chamber. In this gas swirling shearing device, the fluid inlet port is located closer to the second end wall member than the axial center of the tubular member. The fluid outlet port penetrates the second end wall member along the central axis of the inner circumferential surface of the tubular member. The gas-liquid mixture introduced into the fluid swirling chamber swirls toward the first end wall member, which does not have an outlet port. The gas-liquid mixture then reverses direction while being directed by the first end wall toward the radial center of the fluid swirling chamber, further increasing its swirling velocity, toward the second end wall member, and is then discharged to the outside through the fluid outlet port. This document describes that at this time, the shear force on the gas contained in the liquid increases, accelerating the reduction to fine particles.

[0004] The ultrafine bubble generator disclosed in Patent Document 2 includes a cylindrical casing having a liquid inlet at one end and a liquid outlet at the other end, and includes: a flow rate increasing section for increasing the flow rate of the liquid introduced from the inlet toward the outlet; a gas suction section for drawing gas from the outside into the casing, whose pressure has been reduced by the liquid flow accelerated by the flow rate increasing section; and an ultrafine bubble-containing liquid generating section for shearing the gas drawn in by the gas suction section with the accelerated liquid flow to generate a liquid containing ultrafine bubbles. The gas suction section of this ultrafine bubble generator is provided with a pulsation suppressor for suppressing pulsation of the drawn gas. This document states that the provision of the pulsation suppressor reduces gas pulsation, enabling stable generation of ultrafine bubbles and reducing vibration and noise.

[0005] The bubble generation device disclosed in Patent Document 3 includes a gas flow path whose downstream end is placed in liquid, and a gas pressure control device that reduces the pressure inside the gas flow path to suck in liquid from the downstream end so that the liquid mixes with the gas in the gas flow path, and then pressurizes the gas flow path to eject the liquid in the gas flow path and the gas mixed with the liquid from the downstream end into the liquid.This document states that during each of the processes of depressurizing and pressurizing the gas flow path, a stirring force or the like can be applied to the bubbles generated in the gas flow path, thereby efficiently breaking down the bubbles into finer sizes.

[0006] The bubble generating device disclosed in Patent Document 4 includes a gas supply source, a gas flow path that guides the gas supplied by the gas supply source into a liquid, a porous member disposed at the outlet of the gas flow path, and a vibration source that applies vibrations to the liquid-side surface of the porous member. In this bubble generating device, the gas introduced into the fluid from the flow path passes through the porous member, forming microbubbles that are then introduced into the liquid. The vibration source then vibrates the surface of the porous member, causing the microbubbles to quickly drop off from the surface of the porous member. This document states that this configuration enables efficient generation of microbubbles in a liquid. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-272719 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-028340 [Patent Document 3] Japanese Patent Application Publication No. 2017-023996 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-265939 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, in devices configured to generate bubbles in a liquid by passing a gas through a porous body (e.g., Patent Document 4), the diameter of the bubbles generated tends to be larger than in devices with other configurations (e.g., Patent Documents 1 to 3).

[0009] Therefore, the present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a technology for more efficiently generating fine bubbles using a porous body. [Means for solving the problem]

[0010] The microbubble generator disclosed herein is a device for generating microbubbles in a liquid. This device includes a porous body having a first surface that contacts the liquid and has a plurality of pores that generate the microbubbles, a gas supply mechanism that supplies gas to the porous body, and a liquid agitation mechanism that agitates the liquid in contact with the first surface in a direction along the first surface. This device is configured so that the gas supplied to the porous body is released into the liquid through the plurality of pores while the liquid is agitated by the liquid agitation mechanism.

[0011] In the micro-bubble generator having such a configuration, while the liquid is oscillating along the first surface of the porous body, shear force can be generated on the first surface by the oscillating liquid, which allows for more efficient generation of micro-bubbles.

[0012] In a preferred embodiment of this device, the porous body is configured in a cylindrical shape with both ends open. The inner surface of the porous body is the first surface having the plurality of pores, which are a plurality of through-holes. The gas supply mechanism is configured to supply the gas from the outer surface side of the porous body. This configuration can better achieve the effects of the technology disclosed herein.

[0013] In another preferred embodiment of this device, the gas supply mechanism has a cylindrical gas supply pipe with both ends open, and the porous body is disposed therein. The gas supply mechanism is configured to supply the gas between the inner wall surface of the gas supply pipe and the outer surface of the porous body. This configuration makes it possible to generate fine bubbles more efficiently and to suppress leakage of liquid from the inside to the outside of the porous body.

[0014] In another preferred embodiment of this device, the porous body is cylindrical with one end closed and the other end open. The outer surface of the porous body is the first surface having the plurality of pores, which are a plurality of through-holes. The gas supply mechanism is configured to supply the gas from the inner surface side of the porous body. This configuration can better achieve the effects of the technology disclosed herein.

[0015] In another preferred aspect of the device, the gas supply mechanism is configured to be able to switch between starting and stopping the supply of gas depending on the state of the oscillation. With this configuration, the efficiency of generating microbubbles can be increased and the size of the microbubbles can be made smaller.

[0016] In another preferred embodiment of this device, the gas supply mechanism includes a gas supply source, a pipe that serves as a gas flow path from the gas supply source to the porous body, and a valve provided on the pipe. The gas supply mechanism is configured to start and stop supplying the gas to the porous body by opening and closing the valve depending on the state of the oscillation. This configuration can further improve the efficiency of generating fine bubbles.

[0017] In another preferred embodiment of this device, the liquid oscillating mechanism is configured to oscillate the liquid in a direction from one end of the cylindrical porous body to the other end and from the other end to the one end. As described above, both ends of the cylindrical porous body are open. Therefore, with this configuration, the generated microbubbles can be efficiently discharged to the outside of the porous body from either end.

[0018] In another preferred aspect of this device, the liquid oscillating mechanism includes a container for storing the liquid, a pressure reducing device, a pressurizing device, an air storage chamber, a valve, and piping. One end of the porous body is connected to the container via the piping, and the other end of the porous body is connected to the air storage chamber. The air storage chamber is connected to the pressure reducing device and the pressurizing device. The connection between the air storage chamber and the pressure reducing device and the connection between the air storage chamber and the pressurizing device are configured to be switchable by the valve. The liquid oscillating mechanism is configured to suck the liquid into the porous body from the one end when the pressure inside the porous body is reduced via the connection between the air storage chamber and the pressure reducing device, and to discharge the liquid from the one end to the outside of the porous body when the pressure inside the porous body is increased via the connection between the air storage chamber and the pressurizing device, and to oscillate the liquid by alternately repeating the suction and discharge. With this configuration, the liquid can be smoothly sucked in and discharged from the end portion, and as a result, fine bubbles can be generated more efficiently.

[0019] In another preferred aspect of this device, the liquid oscillating mechanism includes a container for storing the liquid, a pressure reducing device, a pressurizing device, an air storage chamber, and a valve. The container is connected to the air storage chamber. The porous body is disposed within the air storage chamber. The air storage chamber is connected to the pressure reducing device and the pressurizing device, and the connection between the air storage chamber and the pressure reducing device and the connection between the air storage chamber and the pressurizing device are configured to be switchable by the valve. The liquid oscillating mechanism is configured to suck the liquid from the container into the air storage chamber when the pressure inside the air storage chamber is reduced, and to discharge the liquid from the air storage chamber into the container when the pressure inside the air storage chamber is increased, alternately repeating the suction and discharge, thereby oscillating the liquid. With this configuration, it is possible to suppress the coalescence of bubbles in the flow path, and to generate fine bubbles more efficiently.

[0020] In another preferred embodiment of this device, the liquid agitation mechanism includes a container that contains the liquid and serves as a supply source for the liquid to the porous body, and that collects the gas released from the porous body. The container is disposed above the porous body. With this configuration, gravity can be used to supply the liquid to the porous body. Therefore, in addition to the effects of the technology disclosed herein, the effect of simplifying the device can be achieved.

[0021] In another preferred aspect of this device, the liquid oscillating mechanism includes a container for containing the liquid, a pressurizing device, an air storage chamber, a valve, and a pipe. The porous body is arranged so that one end is on the upper side and the other end is on the lower side. The container is arranged above the one end of the porous body and is connected to the one end via the pipe. The air storage chamber is connected to the other end of the porous body via the pipe and is connected to the pressurizing device. The valve allows for switchable connection and disconnection between the air storage chamber and the pressurizing device. The liquid oscillating mechanism is configured to suck the liquid into the porous body from the one end when the air storage chamber is not connected to the pressurizing device, and to discharge the liquid from the one end to the outside of the porous body when the air storage chamber is connected to the pressurizing device and the inside of the porous body is pressurized, alternately repeating the suction and discharge, thereby oscillating the liquid. This configuration can achieve the effect of further simplifying the device configuration in addition to the effect of the technology disclosed herein.

[0022] In another preferred embodiment of this device, the liquid agitation mechanism is configured to adjust the average Reynolds number of the liquid during the agitation to not more than 8000. With this configuration, fine bubbles can be generated more efficiently.

[0023] In another preferred embodiment of this device, the porous body has an average pore size of less than 10 μm. With this configuration, fine bubbles can be generated more efficiently.

[0024] Furthermore, there is provided a method for generating microbubbles in a liquid using the microbubble generator described above. With this method, the size of the microbubbles can be made smaller. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a micro-bubble generating device according to the first embodiment. [Figure 2] FIG. 2 is an enlarged view of the porous body 110 and its vicinity in FIG. [Figure 3] FIG. 3 is a flow chart illustrating the operation of the micro-bubble generating device 100. [Figure 4] FIG. 4 is a schematic diagram of the air bubble generating device 2 of Test Example 2. [Figure 5] FIG. 5 is a schematic diagram of the air bubble generating device 3 of Test Example 3. [Figure 6] FIG. 6 is a schematic diagram of a micro-bubble generating device according to the second embodiment. [Figure 7] FIG. 7 is a schematic diagram of a micro-bubble generating device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the technology disclosed herein will be described. Matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In this specification, the notation "A to B" indicating a numerical range means "A or more and B or less," as well as "greater than A and less than B," "greater than A and B or less," and "greater than A and less than B." The arrow U in each figure indicates an upward direction in the direction of gravity. The arrow D in each figure indicates a downward direction in the direction of gravity.

[0027] In this specification, "fine bubbles" may include fine bubbles. Fine bubbles are defined as bubbles with a diameter of less than 100 μm according to the International Organization for Standardization (ISO) standard (ISO 20480-1:2017). Fine bubbles also encompass microbubbles and ultrafine bubbles. According to the above standard, microbubbles are defined as bubbles with a diameter of 1 μm or more and less than 100 μm. According to the above standard, ultrafine bubbles are defined as bubbles with a diameter of less than 1 μm.

[0028] As used herein, "fine bubbles" refers to bubbles with an average bubble diameter of 150 μm or less (preferably 125 μm or less, more preferably 115 μm or less, even more preferably 110 μm or less, and particularly preferably 100 μm or less). As used herein, the term "average bubble diameter" refers to the bubble diameter (D ) at which the cumulative number of bubbles from the smallest diameter is 50%, as calculated by randomly selecting 100 to 500 bubbles (e.g., 200 to 300 bubbles) from an image captured using a commercially available digital imaging device (e.g., a high-speed camera) and analyzing the images using "ImageJ," a free image analysis software developed by the National Institutes of Health. 50 )

[0029] With respect to "fine bubbles" in this specification, the mode diameter is, for example, 150 μm or less, preferably 125 μm or less, more preferably 100 μm or less, even more preferably 75 μm or less, and particularly preferably 50 μm or less. Although not particularly limited, the mode diameter is generally 5 μm or more, and may be 10 μm or more. In this specification, the "mode diameter" refers to the most frequent bubble diameter calculated by randomly selecting 100 to 500 (e.g., 200 to 300) bubbles from an image acquired using a commercially available digital imaging device (e.g., a high-speed camera) and analyzing the images using the image analysis software "ImageJ."

[0030] With respect to "fine bubbles" herein, the Sauter diameter is, for example, 300 μm or less, preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. While not particularly limited, the Sauter diameter is generally 30 μm or more, and may be 50 μm or more. In this specification, the term "Sauter diameter" refers to a value obtained by randomly selecting 100 to 500 bubbles (e.g., 200 to 300 bubbles) from an image acquired using a commercially available digital imaging device (e.g., a high-speed camera) and calculating the ratio of the sum of the volumes to the sum of the surface areas of the selected bubbles. The image analysis software "ImageJ" can be used to calculate the Sauter diameter.

[0031] First Embodiment FIG. 1 is a schematic diagram of a micro-bubble generator according to a first embodiment. FIG. 2 is an enlarged view of the vicinity of a porous body 110 in FIG. 1. The micro-bubble generator 100 (hereinafter simply referred to as the "device 100") is a device that generates micro-bubbles in a liquid. As shown in FIG. 1, the device 100 includes a porous body 110, a gas supply mechanism 120, and a liquid oscillation mechanism 130. The device 100 is configured to release gas G supplied to the porous body 110 into the liquid LQ through a plurality of pores MP while the liquid LQ is being oscillated by the liquid oscillation mechanism 130. While the liquid LQ is oscillating along the first surface, shear force may be generated on the first surface due to the oscillation of the liquid LQ. This allows micro-bubbles to be generated more efficiently. For example, by releasing gas G into the liquid LQ through a plurality of pores MP during this oscillation, the size of the micro-bubbles generated by the shear force can be reduced. Furthermore, the bubble diameter distribution of the generated fine bubbles can be made narrower.

[0032] The oscillation of the liquid LQ refers to, for example, the motion of the liquid LQ alternately and continuously repeating a flow of the liquid LQ from any point P to any other point Q on the first surface of the porous body 110 and a flow from point Q to point P. The period during which the liquid LQ is oscillating refers, for example, to the period during which the liquid LQ flows from point P to point Q and the period during which it flows from point Q to point P. The flow velocity of the liquid LQ becomes zero at the time when the flow from point P to point Q switches to the flow from point Q to point P and at the time when the flow from point Q to point P switches to the flow from point P to point Q. For this reason, these two time points are excluded from "the period during which the liquid LQ is oscillating."

[0033] The porous body 110 has, for example, a first surface having a plurality of pores that come into contact with the liquid LQ and generate fine bubbles FB. As shown in FIGS. 1 and 2, the porous body 110 is configured in a cylindrical (hollow cylindrical) shape with both ends (ends 11A and 11B in FIG. 2) open. In this embodiment, the inner surface 111 of the porous body 110 is the first surface. As shown in FIG. 2, the inner surface 111 has a plurality of pores MP. The plurality of pores MP may be a plurality of through-holes. In this embodiment, the gas supply mechanism 120 is configured to supply the gas G from the outer surface side 112 of the porous body 110. The gas supply mechanism 120 will be described in further detail below. In the embodiment shown in FIG. 2, the point P is located on the inner surface 111 at the end 11B on the gas storage chamber 138 side, and the point Q is located on the inner surface 111 at the end 11A on the container side 131.

[0034] As shown in FIG. 2, the porous body 110 is provided with O-rings 91 and 92. The O-ring 91 is made of, for example, resin, and is attached to one end 11A side of the porous body 110. The O-ring 92 is attached to the other end 11B side of the porous body 110. In this embodiment, the O-rings 91 and 92 are sandwiched between the pipe 139 (here, the third pipe 13Z) of the liquid oscillation mechanism 130 and the gas supply pipe 126 of the gas supply mechanism 120. This interconnects the porous body 110, the pipe 139 (here, the third pipe 13Z), and the gas supply pipe 126. This allows the gas G to be supplied to the outer surface 112 of the porous body 110, and causes the liquid LQ to flow through the lumen of the porous body 110.

[0035] The average pore diameter of the porous body 110 is appropriately set depending on the desired diameter of the microbubbles and is not particularly limited. The average pore diameter is, for example, 20 μm or less, and may be 15 μm or less, or 10 μm or less. The smaller the average pore diameter, the smaller the microbubbles that can be generated. From this perspective, the average pore diameter is preferably less than 10 μm, more preferably 7 μm or less, and even more preferably 5 μm or less. On the other hand, if the average pore diameter is too small, the supplied gas cannot pass through, and there is a risk that microbubbles will not be properly formed. From this perspective, the average pore diameter is, for example, 0.05 μm or more, preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more.

[0036] The average pore diameter can be measured by mercury intrusion porosimetry using a mercury porosimeter. A commercially available conventional mercury porosimeter can be used, and an example is the "AutoPore IV 9500" manufactured by Micrometrics. The nominal value of the manufacturer or the like may be used as the average pore diameter.

[0037] The porous body 110 may be made of, for example, ceramic. Examples of ceramics that make up the porous body 110 include alumina (Al2O3), zirconia (ZrO2), magnesia (MgO), silica (SiO2), titania (TiO2), zircon (ZrSiO4), and mullite (Al6O 13Examples of suitable ceramics include oxide ceramics such as silicon nitride (SiN), boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC), and boron carbonitride (BCN). The ceramic may be a single ceramic or a composite material containing two or more of the above-mentioned ceramics. Alumina, boehmite, silica, and titania are preferred ceramics, because they are stable in quality, inexpensive, and readily available. The parenthesized chemical formulas accompanying each ceramic indicate typical compositions of the ceramic, but are not intended to limit the ceramic composition to those chemical formulas. While ceramics are used as an example of the material for the porous body 110, the material is not limited thereto. The porous body 110 may be made of, for example, metal or resin.

[0038] The gas supply mechanism 120 is, for example, a mechanism for supplying gas G to the porous body 110. The type of gas G is not particularly limited and is appropriately selected depending on the type of desired microbubbles. The gas G may be, for example, air, oxygen gas, ozone, hydrogen gas, nitrogen gas, carbon dioxide gas, etc., and is air in this example.

[0039] In this embodiment, the gas supply mechanism 120 is configured to be able to switch between starting and stopping the supply of gas G depending on the state of oscillation of the liquid LQ. As will be described later, the operation of the gas supply mechanism 120 and the operation of the liquid oscillation mechanism 130 are controlled by a control unit. For this reason, for example, a program for switching between starting and stopping the supply of gas G depending on the operation of the liquid oscillation mechanism 130 may be predefined in the control unit. This makes it possible to switch between starting and stopping the supply of gas G depending on the state of oscillation of the liquid LQ. An example of such a program is a program that supplies gas G to the porous body 110 only during a predetermined period of time during which the liquid LQ oscillates, and stops the supply of gas G during periods other than the predetermined period. By supplying gas G during a specific period of time during which the liquid LQ oscillates, the efficiency of generating microbubbles can be increased and the size of the microbubbles can be further reduced. An example of the predetermined period is the period during which the porous body 110 flows from end 11B to end 11A. During this period, the liquid LQ flows within the porous body 110 in a direction toward the container 131. By supplying the gas G during the period in which the direction in which the generated micro-bubbles are discharged to the outside of the porous body 110 coincides with the direction in which the liquid LQ flows, micro-bubbles can be generated more efficiently.

[0040] As shown in FIG. 1 , the gas supply mechanism 120 includes a supply source 121, a regulator 122, a flow meter 123, a pressure gauge 124, a valve 125, a gas supply pipe 126, and a pipe 127. The supply source 121 is a supply source of gas G, such as a gas cylinder. The regulator 122 is, for example, a pressure regulator that adjusts the supply pressure of gas G supplied from the supply source 121. The flow meter 123 is a measuring instrument that measures the flow rate of gas G in the pipe 127 (the supply amount of gas G). The pressure gauge 124 is a measuring instrument that measures the pressure of gas G in the pipe 127 (the supply pressure of gas G). The valve 125 is provided on the pipe 127. The valve 125 switches, for example, between starting and stopping the supply of gas G to the porous body 110. In this embodiment, the valve 125 switches between starting and stopping the supply of gas G to the gas supply pipe 126. The valve 125 is preferably an electrically controllable valve such as a solenoid valve. As shown in Fig. 1, the supply source 121, the regulator 122, the flow meter 123, the pressure meter 124, the valve 125, and the gas supply pipe 126 are interconnected via a pipe 127. The pipe 127 serves as a flow path for the gas G from the supply source 121 to the porous body 110.

[0041] In this embodiment, the gas supply mechanism 120 is configured to switch between starting and stopping the supply of gas G to the porous body 110 by opening and closing the valve 125 in accordance with the state of oscillation of the liquid LQ. For example, a program that opens and closes the valve 125 in accordance with the operation of the liquid oscillation mechanism 130 and switches between starting and stopping the supply of gas G may be defined in advance in the control unit. This makes it possible to switch between starting and stopping the supply of gas G in accordance with the state of oscillation of the liquid LQ. Furthermore, the efficiency of generating fine bubbles can be further improved.

[0042] In this embodiment, as described above, the gas supply mechanism 120 has a gas supply pipe 126. Furthermore, in this embodiment, the gas supply mechanism 120 is configured to supply gas G between the inner wall surface of the gas supply pipe 126 and the outer surface 112 of the porous body 110. As shown in FIGS. 1 and 2, the gas supply pipe 126 is a cylindrical (hollow cylindrical) pipe with both ends (ends 12A and 12B in FIG. 2) open, and the porous body 110 can be placed inside the gas supply pipe 126. When the porous body 110 is placed inside the gas supply pipe 126, a gap is formed between the inner wall surface of the gas supply pipe 126 and the outer surface 112 of the porous body 110. Gas G is supplied into this gap. In this embodiment, the gas supply pipe 126 has supply holes 12P and exhaust holes 12Q in its wall. The supply holes 12P and exhaust holes 12Q are, for example, through-holes that connect the inside and outside of the gas supply pipe 126. The supply hole 12P is connected to, for example, a pipe 127 (see FIG. 1). The gas G is supplied to the gas supply pipe 126 via the pipe 127 and the supply hole 12P. For example, a sealing plug 128 is attached to the exhaust hole 12Q. By removing the sealing plug 128, for example, the gas G in the gas supply pipe 126 can be discharged to the outside of the supply pipe 126. For example, the sealing plug 128 can be removed when the internal pressure of the gas supply pipe 126 becomes too high. The gas supply mechanism 120 includes the gas supply pipe 126, and gas G is supplied between the inner wall surface of the gas supply pipe 126 and the outer surface of the porous body 110, thereby more efficiently supplying the gas G to the porous body 110. Furthermore, even if the supply of gas G is stopped, the gas G may remain in the gas supply pipe 126. Therefore, by using the gas supply pipe 126, leakage of the liquid LQ to the outside via the pores MP (here, the through holes) of the porous body 110 can be more effectively suppressed.

[0043] Regarding the arrangement of the porous body 110 inside the gas supply pipe 126, as shown in FIG. 2, a connecting member 93 is attached to the end 12A of the gas supply pipe 126, and a connecting member 94 is attached to the end 12B. The connecting members 93 and 94 are, for example, members that connect the gas supply pipe 126, the porous body 110, and the third pipe 13Z. As shown in FIG. 2, the outer peripheries of the ends 12A and 12B and the inner peripheries of the connecting members 93 and 94 are threaded, thereby attaching the connecting members 93 and 94 to the gas supply pipe 126. The connecting members 93 and 94 also have through-holes through which the third pipe 13Z is inserted. In this embodiment, the third pipe 13Z is provided with locking portions Z1 and Z2, which are ring-shaped protrusions, along its outer periphery. The locking portions Z1 and Z2 come into contact with the periphery of the through holes of the connecting members 93 and 94, whereby the third pipe 13Z and the connecting members 93 and 94 are connected to each other.

[0044] As shown in FIG. 2, the gas supply pipe 126 has a holding portion 1261 provided on the end 12A side and a holding portion 1262 provided on the end 12B side. The holding portions 1261 and 1262 are, for example, portions that hold the porous body 110 inside the gas supply pipe 126. As shown in FIG. 2, the holding portions 1261 and 1262 have through-holes. As shown in FIG. 2, the porous body 110 is inserted into the through-holes of the holding portions 1261 and 1262, and a connecting member 93 to which the third pipe 13Z is attached is attached, with an O-ring 91 placed on the surface of the holding portion 1261 on the end 12A side. A connecting member 94 to which the third pipe 13Z is attached is attached, with an O-ring 92 placed on the surface of the holding portion 1262 on the end 12B side. This positions the porous body 110 inside the gas supply pipe 126, and connects the gas supply pipe 126, the porous body 110, and the third pipe 13Z. The liquid LQ is configured to flow through the inner cavity of the porous body 110 via this connection.

[0045] The liquid oscillation mechanism 130 is, for example, a mechanism that oscillates the liquid LQ that is in contact with the first surface (here, the inner surface 111) in a direction along the first surface. There are no particular limitations on the type of liquid LQ. Here, the liquid LQ may be water.

[0046] The liquid oscillation mechanism 130 is configured to oscillate the liquid LQ, for example, in a direction K1 from one end 11A to the other end 11B of the porous body 110, and in a direction K2 from the other end 11B to the one end 11A. In this embodiment, the liquid oscillation mechanism 130 is configured to oscillate the liquid LQ along the inner surface 111 of the porous body 110, in the direction K1 from the end 11A to the end 11B, and in the direction K2 from the end 11B to the end 11A. As shown in FIG. 2, the end 11A and the end 11B are open ends. Therefore, by oscillating the liquid LQ between the end 11A and the end 11B, it is possible to efficiently discharge microbubbles generated from either the end 11A or the end 11B (here, the end 11A) to the outside of the porous body 110.

[0047] As shown in FIG. 1, the liquid shaking mechanism 130 includes a container 131, a pressure reducing device 132, a pressurizing device 133, a regulator 134, a flow meter 135, a pressure gauge 136, a valve 137, an air storage chamber 138, and a pipe 139. The pipe 139 includes a first pipe 13X, a second pipe 13Y, and a third pipe 13Z. As shown in FIG. 2, the pressurizing device 133, the regulator 134, the flow meter 135, the pressure gauge 136, and the valve 137 are connected via the first pipe 13X. This connection is also referred to as the "pressurizing line" below. The pressure reducing device 132 and the valve 137 are connected via the second pipe 13Y. This connection is also referred to as the "pressurizing line" below. Furthermore, one end 11A of the porous body 110 is connected to the container 131 via a third pipe 13Z, and the other end 11B of the porous body 110 is connected to the air accumulation chamber 138. The third pipe 13Z serves as a flow path for the liquid LQ that runs from the container 131 through the inner cavity of the porous body 110 to the air accumulation chamber 138. In this embodiment, the porous body 110 is arranged so that the end 11A is on the lower side and the end 11B is on the upper side (see FIG. 2). Furthermore, as shown in FIG. 1, the container 131 is arranged below the end 11A of the porous body 110.

[0048] The container 131 contains, for example, a liquid LQ. The container 131 is, for example, a supply source of the liquid LQ to the porous body 110. The container 131 can also serve as a recovery unit that recovers the gas G (fine bubbles FB) released from the porous body 110. The pressure reducing device 132 is a device that reduces the pressure inside the air accumulation chamber 138 and the porous body 110 via the second pipe 13Y and the third pipe 13Z, and is, for example, a vacuum pump. The pressurizing device 133 is a device that pressurizes the air accumulation chamber 138 and the porous body 110 via the first pipe 13X and the third pipe 13Z, and is, for example, an air compressor. The regulator 134 is, for example, a pressure regulator that adjusts the supply pressure of the air supplied from the pressurizing device 133. The flow meter 135 is a measuring instrument that measures the flow rate (supply amount) of air through the first pipe 13X. The pressure gauge 136 is a measuring instrument that measures the pressure (supply pressure) of the air in the first pipe 13X. The valve 137 is provided at the junction of the first pipe 13X, the second pipe 13Y, and the third pipe 13Z. The valve 137 is configured to be switchable between the connection between the air storage chamber 138 and the decompression equipment 132 and the connection between the air storage chamber 138 and the pressurization equipment 133. The valve 137 is preferably an electrically controllable valve such as a solenoid valve.

[0049] In this embodiment, the gas storage chamber 138 is a cylindrical (hollow cylindrical) tube that is open at both ends (the end 13A and the other end in FIG. 2). The gas storage chamber 138 is configured to be able to draw in and discharge the liquid LQ contained in the container 131. In this embodiment, the gas storage chamber 138 is provided with a first connection hole 13R and a second connection hole (not shown). As shown in FIG. 2, the first connection hole 13R is provided at one end 13A of the gas storage chamber 138 (the end on the porous body 110 side in FIG. 2). Furthermore, the second connection hole is provided at the other end of the gas storage chamber 138 (the end on the valve 137 side in FIG. 1). In this embodiment, the valve 137, the gas storage chamber 138, the gas supply pipe 126, the porous body 110, and the container 131 are connected to a third pipe 13Z. The liquid LQ flows through the inner cavity of the porous body 110 via this connection, and is configured so that the liquid LQ can be sucked into and discharged from the gas accumulation chamber 138.

[0050] In this embodiment, the liquid oscillation mechanism 130 draws the liquid LQ into the porous body 110 from one end 11A when the pressure inside the porous body 110 is reduced via the connection between the air accumulation chamber 138 and the pressure reduction equipment 132. Furthermore, the liquid oscillation mechanism 130 discharges the liquid LQ from one end 11A to the outside of the porous body 110 when the pressure inside the porous body 110 is increased via the connection between the air accumulation chamber 138 and the pressure reduction equipment 133. The liquid oscillation mechanism 130 is configured to alternately repeat the suction and discharge, thereby oscillating the liquid LQ. In this embodiment, as described above, the end 11A of the porous body 110 is connected to the container 131. Therefore, the suction and discharge of the liquid LQ at the end 11A can be performed smoothly, and as a result, fine bubbles can be generated more efficiently.

[0051] The liquid agitation mechanism 130 is preferably configured to adjust the average Reynolds number Re of the liquid LQ during agitation of the liquid LQ to 8000 or less. In this specification, the average Reynolds number Re of the liquid LQ is calculated using the following formula (1): Re=ρUD / μ (1) In the above formula (1), ρ is the viscosity of the liquid LQ (kg / cm 3 ) and when the liquid LQ is water, ρ = 998.2 (kg / cm 3 ) where U is the viscosity coefficient (Pa s) of the liquid LQ, and when the liquid LQ is water, U = 0.001 (Pa s). D is the inner diameter (m) of the porous body 110. U is the cross-sectional average flow velocity (m / s). The cross-sectional average flow velocity U can be calculated, for example, by dividing the amount of displacement (m) of the liquid surface of the liquid LQ during the period in which the liquid LQ is discharged from the porous body 110 (here, the amount of displacement (m) of the liquid surface in the air accumulation chamber 138) by that period (s). By setting the average Reynolds number Re in the above range, it is possible to generate fine bubbles more efficiently.

[0052] The average Reynolds number Re of the liquid LQ can be set appropriately depending on the desired bubble diameter of the microbubbles, the bubble diameter distribution of the microbubbles, the amount of microbubbles generated, and the like. While not particularly limited, the average Reynolds number Re may be, for example, 1000 or more. The average Reynolds number Re may be, for example, 2300 or less or less than 2300. The average Reynolds number Re can be set appropriately by, for example, changing the level of pressurization by the pressurizing equipment 133, the timing of opening the valve 137, the inner diameter of the porous body 110, and the like. In this specification, a flow region where the average Reynolds number Re is less than 2300 is defined as a "laminar flow region," a flow region where the average Reynolds number Re is 2300 or more but less than 4000 is defined as a "transition region," and a flow region where the average Reynolds number Re is 4000 or more is defined as a "turbulent flow region."

[0053] Although not shown in the figures, a series of operations of device 100 is controlled by a control unit. The series of operations of device 100 can be controlled, for example, by a computer running in accordance with a predetermined program. Each function of the control unit can be processed by, for example, hardware such as an arithmetic unit (also referred to as a processor, CPU (Central Processing Unit), or MPU (Micro-processing unit)) and a storage unit (memory, hard disk, etc.) of each computer constituting the control unit working in cooperation with software. The configuration of the control unit does not characterize the technology disclosed herein, so a description thereof will be omitted here.

[0054] FIG. 3 is a flow diagram illustrating the operation of the micro-bubble generator 100. Before executing the control flow shown in FIG. 3, the porous body 110, the gas supply mechanism 120, and the liquid agitation mechanism 130 are connected. For example, first, the porous body 110 and the liquid agitation mechanism 130 are connected. For example, the porous body 110 is accommodated inside the gas supply pipe 126, and the gas accumulation chamber 138, the porous body 110, and the container 131 are connected via the third pipe 13Z. At this time, the end 11A of the porous body 110 is connected to the container 131 via the third pipe 13Z. Here, the tip of the third pipe 13Z attached to the end 11A is placed in the liquid LQ accommodated in the container 131. Next, the third pipe 13Z attached to the end of the gas accumulation chamber 138 (the end on the valve 137 side in FIG. 1) is connected to the valve 137. It is preferable to connect the valve 137 to the pressurizing equipment 133, the regulator 134, the flow meter 135, and the pressure gauge 136 in advance via the first pipe 13X to construct a pressurization line. It is also preferable to connect the valve 137 to the depressurization equipment 132 in advance via the second pipe 13Y to construct a depressurization line.

[0055] Next, the porous body 110 is connected to the gas supply mechanism 120. A pipe 127 is connected to the porous body 110 (here, the porous body 110 disposed inside the gas supply pipe 126) to which the third pipe 13Z is connected as described above. Here, the pipe 127 is connected to the supply hole 12P of the gas supply pipe 126. It is preferable that the supply source 121, the regulator 122, the flow meter 123, the pressure gauge 124, and the valve 125 are connected to the pipe 127 in advance.

[0056] After the various parts of the apparatus 100 are connected, the control flow shown in FIG. 3 is executed. In this control flow, first, the porous body 110 is connected to a decompression line (step S1). Here, for example, the valve 137 is switched to the decompression line side. Next, the pressure inside the third pipe 13Z is reduced (step S2). For example, by turning on the switch of the decompression equipment 133 and sucking the air inside the air storage chamber 138 through the third pipe 13Z, it is possible to reduce the pressure inside the air storage chamber 138 and the inner cavity of the porous body 110. Then, the liquid LQ inside the container 131 is sucked through the third pipe 13Z and flows into the inner cavity of the porous body 110 (step S3). Then, the liquid LQ is sucked into the air storage chamber 138. As a result, the liquid level of the liquid LQ inside the air storage chamber 138 rises.

[0057] Next, it is determined whether the liquid level of the sucked liquid LQ has reached a predetermined height (step S4). In this embodiment, it is determined whether the liquid level of the liquid LQ in the air accumulation chamber 138 has reached height H1. If there is a liquid level of the liquid LQ in the air accumulation chamber 138, it can be confirmed that at least the inner cavity of the porous body 110 is filled with the liquid LQ. By using the fact that the liquid level of the liquid LQ has reached height H1 in the air accumulation chamber 138 as the criterion for determination in step S4, it is possible to sufficiently fill the cylinder (inner cavity) of the porous body 110 with the liquid LQ, for example. Note that height H1 can be set appropriately depending on the volume of the cylinder (inner cavity) of the porous body 110.

[0058] If it is determined in step S4 that the liquid level of the liquid LQ has reached a predetermined height (here, height H1) (Yes), the porous body 110 is connected to the pressurized line (step S5). Here, for example, the valve 137 is switched to the pressurized line side. At the same time, the switch of the pressurizing equipment 133 is turned on to pressurize the inside of the air accumulation chamber 138 (step S6). At this time, air supplied from the pressurizing equipment 133 into the air accumulation chamber 138 lowers the liquid level of the liquid LQ, and the liquid is discharged from the air accumulation chamber 138 and the inner cavity of the porous body 110 into the container 131 (step S7). On the other hand, if it is not determined in step S4 that the liquid LQ has reached the predetermined height (here, height H1) (No), the process returns to step S3, as shown in FIG. 3.

[0059] Next, the valve 125 of the gas supply mechanism 120 is opened (step S8). By opening the valve 125, it is possible to supply the gas G adjusted to a predetermined supply pressure to the porous body 110. When the gas G is supplied to the porous body 110, as described above, the liquid LQ is discharged from the inner cavity of the porous body 110 toward the container 131. At this time, a shear force is generated on the inner surface 111 of the porous body 110 in a direction along the inner surface 111 due to the discharge of the liquid LQ. By supplying the gas G at a predetermined supply pressure at this timing, the gas G enters the inner cavity of the porous body 110 through the pores MP. This makes it possible to generate fine bubbles (step S9).

[0060] The timing for opening the valve 125 in step S8 is not particularly limited and can be set appropriately depending on the operating conditions of the device 100. This timing can be set, for example, at the same time as the pressurization of the air accumulation chamber 138 in step S6. By opening the valve 125 at the same time as the pressurization of the air accumulation chamber 138, the period during which fine bubbles are generated can be extended, and ultimately the efficiency of generating fine bubbles can be improved.

[0061] Next, it is determined whether the liquid level of the discharged liquid LQ has reached a predetermined height (step S10). In this embodiment, it is determined whether the liquid level of the liquid LQ in the air accumulation chamber 138 has reached height H2. Height H2 can be set closer to the container 131 than the height H1 described above. By using the fact that the liquid level of the liquid LQ has reached height H2 in the air accumulation chamber 138 as the criterion for determination in step S4, it is possible, for example, to prevent the gas in the air accumulation chamber 138 from being discharged into the container 131 through the cylinder (lumen) of the porous body 110.

[0062] If it is determined in step S10 that the liquid level of the liquid LQ has reached a predetermined height (here, height H2) (Yes), the valve 125 is closed (step S11). Closing the valve 125 stops the supply of gas G to the gas supply pipe 126, and so micro-bubbles will soon cease to be generated. After step S11, the process returns to step S1 (RETURN), and the control flow shown in FIG. 3 is repeated. On the other hand, if it is not determined in step S10 that the liquid level of the liquid LQ has reached a predetermined height (here, height H2) (No), the process returns to step S7, as shown in FIG. 3.

[0063] The technology disclosed herein provides a method for generating microscopic bubbles in a liquid LQ using the device 100. By using this method, it is possible to generate microscopic bubbles more efficiently.

[0064] The first embodiment of the micro-bubble generator disclosed herein has been described above with reference to FIGS. 1 to 3. However, the micro-bubble generator disclosed herein is not limited to this and may include other modifications. For example, in the apparatus 100 configured as described above, the gas supply mechanism 120 switches between starting and stopping the supply of gas G depending on the state of oscillation of the liquid LQ. However, the present invention is not limited to this. For example, the gas supply mechanism 120 may be configured to adjust the supply pressure of gas G depending on the state of oscillation of the liquid LQ. For example, in the first embodiment, gas G may be supplied at supply pressure P1 while gas G is being supplied to the porous body 110, and gas G may be supplied at supply pressure P2 (P2 > 0) lower than supply pressure P1 while the supply of gas G is stopped. By changing the supply pressure of gas G depending on the state of oscillation of the liquid LQ, micro-bubbles can be generated more efficiently. The supply pressure P1 is not particularly limited as long as it is large enough to generate fine bubbles, and can be set appropriately depending on the average pore diameter of the porous body 110, the desired size of the fine bubbles, the desired amount of the fine bubbles, etc. The supply pressure P2 is not particularly limited as long as it is large enough to prevent the liquid LQ from leaking to the outside through the pores MP (through holes in this case) of the porous body 110 and to prevent the generation of fine bubbles.

[0065] Furthermore, in the operation of the apparatus 100 configured as described above, the switching to the decompression line side and the switching to the pressurized line side by the valve 137 and the opening and closing of the valve 125 are performed at the same time. However, this is not limited to this. Depending on the operating conditions of the apparatus 100, the liquid LQ may have infiltrated into the pores MP of the porous body 110. Even if the valve 125 is opened to supply the gas G in this state, the liquid LQ that has infiltrated into the pores MP must first be discharged, and fine bubbles cannot be generated for the period required for such discharge of the liquid LQ. In this case, the timing of discharging the liquid LQ from the lumen of the porous body 110 and the timing of generating the fine bubbles cannot be synchronized, which can make it difficult to control the bubble diameter. In such a case, the timing of switching the valve 137 to the pressurized line side and the timing of opening the valve 125 to supply the gas G may be set to be different. For example, the valve 137 may be switched to the pressurized line side first, and after the discharge of the liquid LQ begins, the valve 125 may be opened to supply the gas G to the porous body.

[0066] Next, a test example relating to the first embodiment of the technology disclosed herein will be described. Note that the test example shown below is not intended to limit the technology disclosed herein.

[0067] <Test 1> In Test 1, microbubbles were generated using the microbubble generator according to the first embodiment. The configuration of the device used in Test 1 is as shown in Figures 1 and 2. Therefore, the reference numbers attached to the names of the devices below are the numbers shown in Figure 1 or 2.

[0068] -Example 1 (Example 1A to Example 1D)- A porous body with an average pore diameter of 0.5 μm, a porosity of 36%, and mainly composed of alumina was used as the porous body 110. First, a third pipe 13Z was connected to the inside of the cylindrical porous body 110 so that the liquid LQ (water) circulated. Next, an air accumulation chamber 138 was provided in the upper section of the third pipe 13Z (the upper section of the porous body 110). Furthermore, a pressurization device 133 (air compressor) and a decompression device 132 (vacuum pump) were attached to the air accumulation chamber 138, and a valve 137 (solenoid valve) was used to switch between the pressurization line and the decompression line. The third pipe 13Z on the lower section (tip) side of the porous body 110 was placed in a container 131 and immersed in the liquid LQ.

[0069] Next, a pipe 127 was connected to the gas supply pipe 126 so that gas G (air) could be supplied from the outer surface 112 of the porous body 110, and air was supplied from the outer surface 112 of the porous body 110 to the inner surface 111 side through the pores MP (through holes). A regulator 122, a flow meter 123, a pressure meter 124, and a valve 125 (solenoid valve) were connected to the middle of the pipe 127 so that the timing of supplying the gas G could be controlled.

[0070] In order to accelerate the vertical movement of the liquid LQ in the lumen of the porous body 110, first, the air in the air storage chamber 138 was sucked by the decompression equipment 132 until the entire lumen of the porous body 110 was immersed in the liquid LQ (here, up to height H1 of the air storage chamber 138). Next, the valve 137 was switched to the pressurization equipment 133 side to send air into the air storage chamber 138, thereby lowering the liquid level of the liquid LQ to height H2 of the air storage chamber 138 and pushing out the liquid LQ from the lumen of the porous body 110. By repeatedly decompressing and pressurizing the air storage chamber 138 in this manner, the liquid LQ in the lumen of the porous body 110 was accelerated to move up and down. At the timing when the liquid LQ in the lumen of the porous body 110 was being pushed down, the valve 125 was opened and the gas G was supplied. The time for which the valve 125 was kept open was set to be the same as the time for which the liquid LQ was discharged from the porous body 110. Furthermore, the timing at which the valve 125 is opened and the timing at which the valve 137 is switched to the pressurized line side are set to be the same.

[0071] Then, an image of the bubbles released from the porous body 110 into the liquid LQ in the container 131 was taken using a high-speed camera. After that, using the image analysis software "ImageJ", 300 bubbles were randomly selected from the acquired image, and the Sauter diameter (μm), number-average diameter (μm), and D 10 (μm), D 50 (μm), and D 90 The coefficient of variation (CV value) (%) of the number-average diameter was also calculated. The results are shown in the corresponding columns in Table 1. The Sauter diameter (μm) is a value obtained by calculating the ratio of the sum of the volumes of the bubbles analyzed to the sum of the surface areas. The number-average diameter (μm) is the arithmetic mean value of the diameters of the bubbles analyzed. D 10 (μm) is the bubble diameter that is 10% of the total diameter of the bubbles analyzed, starting from the smallest. 50 (μm) is the bubble diameter at which the cumulative diameter from the smallest bubble of the analyzed bubbles is 50%. 90 (μm) is the bubble diameter at which the cumulative diameter of the bubbles analyzed is 90% from the smallest.

[0072] Here, the conditions were set so that the average Reynolds number Re and the Sauter diameter of the bubbles generated from the porous body when the porous body was used would be the values ​​shown in the corresponding columns of Table 1. The Reynolds number Re listed in Table 1 is a value calculated based on the above formula (1). Regarding these conditions, the corresponding columns of Table 1 show the porous body conditions for each example, including the average pore diameter (μm), inner diameter (mm), and length (mm); the liquid conditions for each example, including the flow rate (L / min), average Reynolds number Re, fluid field, pressure (MPa), solenoid valve opening (%), and cycle (Hz); and the gas conditions for each example, including the average supply pressure (MPa) and solenoid valve opening (%). The liquid and gas conditions listed in Table 1 were set so that the bubble diameter of the bubbles generated in each example would be smallest.

[0073] The "solenoid valve opening degree (%)" in Table 1 for liquid conditions is the percentage (%) of the period during which the valve 137 was connected to the pressurized line, when one oscillation cycle is taken as 100%. Also, the "solenoid valve opening degree (%)" in Table 1 for the supply of gas G is the percentage (%) of the period during which the valve 125 was open, when one oscillation cycle is taken as 100%. When the solenoid valve opening degree was 50% for both the supply of gas G and the oscillation of liquid LQ, the valve was connected to the pressurized line and gas G was supplied for 50% of one oscillation cycle (half cycle). When the solenoid valve opening degree was 20% for both the supply of gas G and the oscillation of liquid LQ, the valve was connected to the pressurized line and gas G was supplied for 20% of one oscillation cycle. Moreover, here, one period of oscillation of the liquid LQ is defined as the time period during which the liquid level of the liquid LQ drops from height H1 in the air storage chamber 138 to height H2, and then rises from height H2 to height H1.

[0074] -Example 2 (Example 2A to Example 2C)- A porous body having an average pore size of 1 μm and a porosity of 38% was used as the porous body 110. Data for each example was obtained using the same materials and procedures as in Example 1. The data and conditions are shown in the corresponding columns of Table 1.

[0075] -Example 3 (Example 3A to Example 3D)- A porous body having an average pore size of 3 μm and a porosity of 40% was used as the porous body 110. Data for each example was obtained using the same materials and procedures as in Example 1. The data and conditions are shown in the corresponding columns of Table 1.

[0076] In Example 3B, the time period during which the valve 125 was open was set to be shorter than the time period during which the liquid LQ was discharged from the porous body 110. The timing at which the valve 125 was opened was made different from the timing at which the valve 137 was switched to the pressurized line side. In this example, the valve 125 was kept open only for the period immediately after the valve 137 was switched to the pressurized line side, thereby generating bubbles. If one oscillation cycle is taken as 100%, the period during which the valve 125 was kept open was 1%.

[0077] Example 4 (Example 4A and Example 4B) A porous body having an average pore size of 10 μm and a porosity of 42% was used as the porous body 110. Data for each example was obtained using the same materials and procedures as in Example 1. The data and conditions are shown in the corresponding columns of Table 1.

[0078] [Table 1]

[0079] <Test 2 (comparison test)> In Test 2, bubbles were generated using a liquid circulation type (inline type) bubble generator. FIG. 4 is a schematic diagram of the bubble generator 2 of Test Example 2. As shown in FIG. 4, a cylindrical porous body 21 was connected to a liquid feed pump 22b via a pipe 22a so that the liquid LQ circulated inside the porous body 21. The tip of the pipe 22a on the liquid feed pump 22b side was immersed in the liquid LQ in a container 23 so that the liquid LQ circulated inside the porous body 21 at a constant speed. A voltage regulator 22c that adjusted the voltage of the liquid feed pump 22b was connected to the liquid feed pump 22b. In addition, a pressure gauge 22d, a valve 22e (ball valve), and a pressure gauge 22f were connected to the pipe 22a. A pipe 24 was further connected to the porous body 21 so that the liquid LQ could be discharged into the container 23 via the pipe 24. Then, porous body 21 was housed in gas supply pipe 25a, and piping 25b was connected to gas supply pipe 25a so that gas G could be supplied from the outer surface of porous body 21. Pipe 25b was connected to gas G supply source 25c, regulator 25d, flow meter 25e, and pressure meter 25f. With this configuration, gas G was supplied from the outer surface of porous body 21 through the pores to the inner surface, and bubbles were generated.

[0080] Comparative Example 1 (Comparative Example 1A to Comparative Example 1E) A porous body having an average pore diameter of 0.5 μm and a porosity of 36% was used as the porous body 21. Gas G was supplied to the porous body 21 to generate bubbles. The Reynolds number Re was set to a desired value by adjusting the voltage of the liquid supply pump 22b and the opening of the pipe 22a by the valve 22e. The Reynolds number Re is shown in the corresponding column in Table 2. The supply pressure of the gas G was also adjusted using the regulator 25d. The supply pressure was set to the lower limit pressure value at which bubbles were generated from the porous body 21 for each Reynolds number Re shown in Table 2.

[0081] Then, an image of the bubbles released from the porous body 21 into the liquid LQ in the container 23 was taken using a high-speed camera. After that, using the same method as in Test 1 above, the Sauter diameter (μm), number-average diameter (μm), coefficient of variation (CV value) (%) of the number-average diameter of the bubbles, and D 10 (μm), D50 (μm), and D 90 The results are shown in the corresponding columns in Table 2.

[0082] In addition, Table 2 also lists the porous body conditions, liquid conditions, and gas conditions for each example.

[0083] Comparative Example 2 (Comparative Example 2A to Comparative Example 2E) A porous body having an average pore size of 1 μm and a porosity of 38% was used as the porous body 21. Data for each example was obtained using the same members and procedures as in Comparative Example 1. The data and conditions are shown in the corresponding columns of Table 2.

[0084] -Comparative Example 3 (Comparative Example 3A~Comparative Example 3E)- A porous body having an average pore size of 3 μm and a porosity of 40% was used as the porous body 21. Data for each example was obtained using the same members and procedures as in Comparative Example 1. The data and conditions are shown in the corresponding columns of Table 2.

[0085] Comparative Example 4 (Comparative Example 4A to Comparative Example 4D) A porous body with an average pore size of 10 μm and a porosity of 42% was used as the porous body 21. Data for each example was obtained using the same materials and procedures as in Comparative Example 1. The data and conditions are shown in the corresponding columns in Table 2. In Comparative Example 4A, the bubbles that were generated coalesced, and data could not be obtained. The "-" in the "Bubble Properties" column for Comparative Example 4A in Table 2 indicates that data could not be obtained.

[0086] [Table 2-1] [Table 2-2]

[0087] <Test 3 (comparison test)> In Test 3, bubbles were generated using an immersion-type bubble generator. FIG. 5 is a schematic diagram of the bubble generator 3 of Test Example 3. As shown in FIG. 5, a pipe 32 was connected to a cylindrical porous body 31 so that gas G circulated inside the porous body 31. The porous body 31 connected to the pipe 32 was immersed in liquid LQ (water) in a container 33. Then, gas G was supplied to the inside of the porous body 31 via the pipe 32. Gas G was released from the inside to the outside of the porous body 31 through the pores into the liquid LQ, thereby generating bubbles from the outer surface of the porous body 31. A gas G supply source 34, a regulator 35, a flow meter 36, and a pressure gauge 37 were connected to the pipe 32.

[0088] -Comparative Example 5- A porous body having an average pore diameter of 0.5 μm and a porosity of 36% was used as the porous body 31. Gas G was supplied to the porous body 31 to generate bubbles. The supply pressure of gas G was adjusted using a regulator 35. This supply pressure was set to the lower limit pressure value at which bubbles were generated from the porous body 31. Table 3 shows the porous body conditions and gas supply conditions for this example.

[0089] Then, an image of the bubbles released from the porous body 31 into the liquid LQ in the container 33 was taken using a high-speed camera. After that, using the same method as in Test 1 above, the Sauter diameter (μm), number-average diameter (μm), coefficient of variation (CV value) (%) of the number-average diameter of the bubbles, and D 10 (μm), D 50 (μm), and D 90 The results are shown in the corresponding columns in Table 3.

[0090] -Comparative Example 6- A porous body having an average pore size of 1 μm and a porosity of 38% was used as the porous body 31. Data for each example was obtained using the same members and procedures as in Comparative Example 5. The data and conditions are shown in the corresponding columns of Table 3.

[0091] -Comparative Example 7- A porous body having an average pore size of 3 μm and a porosity of 40% was used as the porous body 31. Data for each example was obtained using the same members and procedures as in Comparative Example 5. The data and conditions are shown in the corresponding columns of Table 3.

[0092] [Table 3]

[0093] From the results shown in Tables 1 to 3, it was found that fine bubbles can be generated by using the fine-bubble generator 100, which is equipped with a porous body 110, a gas supply mechanism 120, and a liquid agitation mechanism 130, and is configured so that the gas G supplied to the porous body 110 is released into the liquid LQ through the plurality of pores MP while the liquid LQ is agitated. In particular, it was found that in the laminar flow region where the average Reynolds number Re is less than 2300, when the device 100 is used, finer bubbles can be generated than when the other devices 2 and 3 are used. This shows that the device 100 can generate fine bubbles more efficiently.

[0094] Second Embodiment Fig. 6 is a schematic diagram of a micro-bubble generator according to the second embodiment. As shown in Fig. 6, a micro-bubble generator 200 (hereinafter simply referred to as "device 200") includes a porous body 210, a gas supply mechanism 220, and a liquid shaking mechanism 230. Hereinafter, explanations of matters common to the first embodiment and matters different from the first embodiment that do not characterize the technology disclosed herein may be omitted.

[0095] The porous body 210 has, for example, a first surface having a plurality of pores that come into contact with the liquid LQ and generate fine bubbles FB. As shown in FIG. 6, the porous body 210 is configured in a cylindrical (hollow cylindrical) shape with one end (end 21A in FIG. 6) closed and the other end (end 21B in FIG. 6) open. In this embodiment, the outer surface 212 of the porous body 210 is the first surface. Here, the outer surface 212 has a plurality of pores MP. The plurality of pores MP may be a plurality of through-holes. In this embodiment, the gas supply mechanism 220 is configured to supply the gas G from the inner surface side 211 of the porous body 210. Note that in the embodiment shown in FIG. 6, the point Q is located on the outer surface 212 at the end 21A of the container side 231, and the point P is located on the outer surface 212 at the opposite end 21B. This configuration also makes it possible to generate fine bubbles more efficiently.

[0096] The porous body 210 includes, for example, a support member 290. The support member 290 is attached, for example, to the end portion 21B of the porous body 210. As shown in Fig. 6, the support member 290 is connected to a pipe 227 of the gas supply mechanism 220. The support member 290 has, for example, a through-hole, and is configured so that the gas G is supplied to the inner surface side (inner cavity) of the porous body 210 by attaching the pipe 227 to the through-hole.

[0097] As shown in Fig. 6, the gas supply mechanism 220 includes a supply source 221, a regulator 222, a flow meter 223, a pressure gauge 224, a valve 225, and a pipe 227. As shown in Fig. 2, the supply source 221, the regulator 222, the flow meter 223, the pressure gauge 224, and the valve 225 are connected to one another via the pipe 227. As shown in Fig. 6, the pipe 227 passes through a through-hole 238h provided in the gas storage chamber 238 and is connected to the end 21B of the porous body 210. The pipe 227 serves as a flow path for the gas G from the supply source 221 to the porous body 210.

[0098] In this embodiment, the liquid swaying mechanism 230 is configured to sway the liquid LQ along the outer surface 212 of the porous body 210 in a direction L1 from one end 21A to the other end 21B, and in a direction L2 from the other end 21B to the one end 21A. As shown in FIG. 6, the porous body 210 is contained in a cylindrical air accumulation chamber 238. For this reason, it is preferable to sway the liquid LQ in a direction L1 from the first connection hole 23R to the second connection hole 23S (a direction from the end 23A to the end 23B), and in a direction L2 from the second connection hole 23S of the air accumulation chamber 238 to the first connection hole 23R (a direction from the end 23B to the end 23A).

[0099] As shown in FIG. 6, the liquid oscillation mechanism 230 includes a container 231, a pressure reducing device 232, a pressurizing device 233, a regulator 234, a flow meter 235, a pressure gauge 236, a valve 237, an air storage chamber 238, and a pipe 239. The pipe 239 includes a first pipe 23X, a second pipe 23Y, and a third pipe 23Z. As shown in FIG. 6, the liquid oscillation mechanism 230 includes a pressurization line via the first pipe 23X and a depressurization line via the second pipe 23Y. The third pipe 23Z is connected to the first connection hole 23R and the second connection hole 23S of the air storage chamber 238, respectively. The tip of the third pipe 23Z connected to the first connection hole 23R is disposed in the liquid in the container 231. In this embodiment, the third pipe 23Z and the air accumulation chamber 238 form a flow path for the liquid LQ along the outer surface 212 of the porous body 110. In this embodiment, the porous body 210 is arranged so that the end 21A is on the lower side and the end 21B is on the upper side. In addition, as shown in Fig. 6, the container 231 is arranged below the end 21A of the porous body 210.

[0100] In this embodiment, when the pressure inside the gas storage chamber 238 is reduced, the liquid agitation mechanism 230 draws the liquid LQ from the container 231 into the gas storage chamber 238. Furthermore, when the pressure inside the gas storage chamber 238 is increased, the liquid agitation mechanism 230 discharges the liquid LQ from the gas storage chamber 238 into the container 231. The liquid agitation mechanism 230 is configured to agitate the liquid LQ by alternately repeating this suction and discharge. In this embodiment, as described above, the porous body 210 is accommodated in the gas storage chamber 238. This configuration increases the bubble generation space compared to the embodiment of FIG. 2, which is preferable from the perspective of suppressing bubble coalescence within the flow path. Therefore, it is expected that porous bodies with larger average pore diameters can be used and that operation at a higher supply gas flow rate will become possible. Consequently, this configuration can achieve effects such as promoting the miniaturization of bubbles per porous body, increasing the amount of gas generated, and reducing the gas supply pressure.

[0101] The operation of the apparatus 200 will be described below with reference to FIG. 3. Before executing the control flow shown in FIG. 3, the porous body 210, the gas supply mechanism 220, and the liquid agitation mechanism 230 are connected. For example, the porous body 210 and the liquid agitation mechanism 230 are first connected. For example, the porous body 210 is accommodated inside the gas accumulation chamber 238, and the gas accumulation chamber 238 is connected to the container 231 and the gas accumulation chamber 238 is connected to the valve 237 via the third pipe 23Z. At this time, the tip of the third pipe 23Z attached to the first connection hole 23R is placed in the liquid LQ accommodated in the container 231. Next, the first pipe 23X and the second pipe 23Y are connected to the valve 237, and a pressurized line and a depressurized line are established.

[0102] Next, the porous body 210 is connected to the gas supply mechanism 220. As described above, the piping 227 is connected to the porous body 210 placed inside the gas storage chamber 238. Here, the piping 227 is connected to the support member 290 attached to the end 21B of the porous body 210.

[0103] Once the various parts of the device 200 have been connected, the control flow shown in Fig. 3 is executed. In this control flow, first, the air accumulation chamber 238 is connected to a decompression line (step S1). Next, the pressure inside the third piping 23Z is reduced (step S2). For example, the pressure inside the air accumulation chamber 238 can be reduced by turning on the switch of the decompression equipment 233 and sucking the air inside the air accumulation chamber 238 through the third piping 23Z. Then, the liquid LQ inside the container 231 is sucked through the third piping 23Z and flows into the air accumulation chamber 238 (step S3). As a result, the liquid level of the liquid LQ inside the air accumulation chamber 238 rises.

[0104] Next, it is determined whether the liquid level of the sucked liquid LQ has reached a predetermined height (step S4). In this embodiment, it is determined whether the liquid level of the liquid LQ in the air accumulation chamber 238 has reached height H3. In this embodiment, height H3 can be set closer to the end 23B of the air accumulation chamber 238 than the end 21B of the porous body 210.

[0105] If it is determined in step S4 that the liquid level of the liquid LQ has reached a predetermined height (here, height H3) (Yes), the porous body 210 is connected to the pressurized line (step S5). Here, for example, the valve 237 is switched to the pressurized line side. At the same time, the switch of the pressurizing equipment 233 is turned on to pressurize the inside of the air accumulation chamber 238 (step S6). At this time, air supplied from the pressurizing equipment 233 into the air accumulation chamber 238 lowers the liquid level of the liquid LQ, and the liquid is discharged from the air accumulation chamber 238 into the container 231 (step S7). On the other hand, if it is not determined in step S4 that the liquid LQ has reached the predetermined height (No), the process returns to step S3.

[0106] Next, the valve 225 of the gas supply mechanism 220 is opened (step S8). By opening the valve 225, the gas G can be supplied to the porous body 210. When the gas G is supplied to the porous body 210, the liquid LQ is discharged from the gas accumulation chamber 238 toward the container 231, as described above. At this time, a shear force is generated in the direction along the outer surface 212 of the porous body 210 due to the discharge of the liquid LQ. At this timing, the gas G is supplied to the inner surface 211 side of the porous body 210 at a predetermined supply pressure, whereby the gas G is released to the outside of the porous body 210 through the pores MP, and fine bubbles can be generated (step S9). Note that the timing for opening the valve 225 in step S8 is not particularly limited and can be set appropriately depending on the operating conditions of the apparatus 200.

[0107] Next, it is determined whether the liquid level of the discharged liquid LQ has reached a predetermined height (step S10). In this embodiment, the criterion for proceeding to the next step is that the liquid level of the liquid LQ in the air storage chamber 138 has reached height H4. Height H4 can be set closer to the container 131 than the above-mentioned height H3. Height H4 can be set, for example, closer to the end 23B of the air storage chamber 238 than the end 21B of the porous body 210. By using the liquid level of the liquid LQ being height H4 in the air storage chamber 138 as the criterion for determination in step S4, it is possible, for example, to prevent the gas in the air storage chamber 238 from being discharged into the container 131 through the cylinder (lumen) of the porous body 110.

[0108] If it is determined in step S10 that the liquid level of the liquid LQ has reached a predetermined height (here, height H4) (Yes), the valve 225 is closed (step S11). Closing the valve 225 stops the supply of gas G to the air accumulation chamber 238, and so the generation of fine bubbles gradually ceases. After step S11, the process returns to step S1 (RETURN), and the control flow shown in FIG. 3 is repeated. On the other hand, if it is not determined in step S10 that the liquid level of the liquid LQ has reached a predetermined height (here, height H4) (No), the process returns to step S7.

[0109] Third Embodiment In the first and second embodiments, the collection unit (container 131 in the first embodiment, container 231 in the second embodiment) that collects gas (here, microbubbles) released from the porous body that serves as the bubble generation unit is located below the location where the porous body 110 or 210 is located. However, this is not limited to this. The collection unit may be located above the location where the bubble generation unit is located. FIG. 7 is a schematic diagram of a microbubble generation device according to a third embodiment. As shown in FIG. 7, a microbubble generation device 300 (hereinafter simply referred to as "device 300") includes a porous body 310, a gas supply mechanism 320, and a liquid shaking mechanism 330. Hereinafter, explanations of matters common to the first embodiment and matters different from the first embodiment that do not characterize the technology disclosed herein may be omitted.

[0110] 7, the porous body 310 is arranged so that one end 31A is on the upper side and the other end 31B is on the lower side. In this embodiment, the end 31A of the porous body 310 is connected to the container 331 via a pipe 339 (here, the third pipe 33Z). In addition, the end 31B is connected to the air storage chamber 338 via a pipe 339 (here, the third pipe 33Z).

[0111] In this embodiment, the liquid oscillation mechanism 330 is configured to oscillate the liquid LQ along the inner surface 311 of the porous body 310 in a direction M1 from one end 31A to the other end 31B and in a direction M2 from the other end 31B to the one end 31A. As shown in FIG. 7 , the liquid oscillation mechanism 330 includes a container 331, a pressurizing device 333, a regulator 334, a flow meter 335, a pressure gauge 336, a first valve 3371, a second valve 3372, an air storage chamber 338, and a pipe 339. The pipe 339 includes, for example, a first pipe 33X and a third pipe 33Z. In this embodiment, the container 331 is disposed above the end 31A of the porous body 310 and is connected to the end 31A via the third pipe 33Z. The tip of the third pipe 33Z connected to the end 31A is disposed in the liquid LQ inside the container 331. In this embodiment, the gas accumulation chamber 338 is connected to the end 31B of the porous body 310 via the third pipe 33Z. As shown in Fig. 7, the end 31B of the porous body 310 and the first connection hole 33R of the gas accumulation chamber 338 are connected via the third pipe 33Z. In the embodiment shown in Fig. 7, the path of the liquid LQ runs from the container 331 through the lumen of the porous body 310 to the gas accumulation chamber 338 via the third pipe 33Z.

[0112] In this embodiment, the supply state of the liquid LQ from the container 331 to the porous body 310 is configured to be switched by a first valve 3371 (for example, a ball valve). The first valve 3371 is disposed on the third pipe 33Z, for example. Here, by opening the first valve 3371, the liquid LQ in the container 331 flows into the third pipe 33Z by gravity, passes through the inner cavity of the porous body 310, and reaches the air accumulation chamber 338. Furthermore, by closing the first valve 3371, for example, the supply of the liquid LQ to the porous body 310 can be stopped, and ultimately the operation of the apparatus 300 can be stopped.

[0113] In this embodiment, the air accumulation chamber 338 is further connected to the pressurizing equipment 333 via a first pipe 33X. For example, in the liquid shaking mechanism 330, a pressurizing line is constructed via the first pipe 33X. As shown in FIG. 7, the first pipe 33X is connected to the second connection hole 33S of the air accumulation chamber 338.

[0114] In this embodiment, the connection and disconnection between the air storage chamber 338 and the pressurizing device 333 can be switched by a second valve 3372 (for example, a solenoid valve). The second valve 3372 is arranged, for example, on the first pipe 33X. Here, by opening the second valve 3372, the air storage chamber 338 and the pressurizing device 333 are connected, and the inside of the air storage chamber 338 is pressurized. In addition, by closing the second valve 3372, the air storage chamber 338 and the pressurizing device 333 are disconnected.

[0115] In this embodiment, the liquid agitation mechanism 330 draws the liquid LQ into the porous body 310 from the end 31A when the air accumulation chamber 338 and the pressurizing equipment 333 are not connected. Furthermore, when the air accumulation chamber 338 and the pressurizing equipment 333 are connected and the inside of the porous body 310 is pressurized, the liquid agitation mechanism 330 discharges the liquid LQ from the end 31A to the outside of the porous body 310. The liquid agitation mechanism 330 is configured to agitate the liquid LQ by alternately repeating this suction and discharge. In this embodiment, as described above, the container 331 is disposed above the porous body 310. With this configuration, the liquid LQ can be supplied from the container 331 into the porous body 310 by gravity, and the installation of the pressure-reducing equipment used in the embodiments of FIGS. 2 and 6 can be omitted. Therefore, the device 300 can achieve the effect of simplifying the device configuration in addition to the effect of the technology disclosed herein.

[0116] Next, a test example relating to the third embodiment of the technology disclosed herein will be described. Note that the test example shown below is not intended to limit the technology disclosed herein.

[0117] <Test 4> In Test 4, microbubbles were generated using the microbubble generator according to the third embodiment. The configuration of the device used in Test 4 is as shown in Figure 7. Therefore, the reference numbers attached to the names of the devices below are the numbers shown in Figure 7.

[0118] -Examples 31 to 33- The porous body 310 used was a porous body mainly composed of alumina with an average pore diameter of 0.5 μm and a porosity of 36%. First, a third pipe 33Z was connected to the ends 31A and 31B of the cylindrical porous body 310 so that the liquid LQ (water) circulated inside the porous body 310. Next, an empty container 331 was provided in the upper section of the third pipe 33Z on the end 31A side (the upper section of the porous body 310). Furthermore, an air storage chamber 338 was connected to the third pipe 33Z on the end 31B side. Furthermore, a pressurizing device 333 (air compressor) was attached to the air storage chamber 338, and a second valve 3372 (solenoid valve) was used to switch between connection and disconnection between the air storage chamber 338 and the pressurizing device 333.

[0119] Next, a pipe 327 was connected to the gas supply pipe 326 so that gas G (air) could be supplied from the outer surface 312 of the porous body 310, and air was supplied from a supply source 321 from the outer surface 312 of the porous body 310 through the pores (through holes) to the inner surface 311. A regulator 322, a flow meter 323, a pressure meter 324, and a valve 325 (solenoid valve) were connected to the middle of the pipe 327 so that the timing of the supply of gas G could be controlled.

[0120] Next, it was confirmed that the first valve 3371 was closed, and the liquid LQ was poured into the container 331. Next, the valve 325 of the gas supply mechanism 320 and the second valve 3372 of the liquid shaking mechanism 330 were opened. Next, the first valve 3371 was gradually opened, and the liquid LQ in the container 331 was allowed to flow into the third pipe 33Z. When the liquid level of the liquid LQ reached height H5 in the air storage chamber 338, the aperture (%) of the second valve 3372 was set to a predetermined aperture, and the pressurizing force (MPa) of the pressurizing equipment 333 was adjusted so that the liquid level of the liquid LQ moved up and down between heights H5 and H6 in the air storage chamber 338. The average Reynolds number Re in each example is shown in the corresponding column of Table 4. Note that, as shown in FIG. 7, height H5 was set to a position higher than height H6 in the air storage chamber 338 (here, on the first pipe 33X side). The opening (%) of the second valve 3372 and the pressurizing force (MPa) by the pressurizing equipment 333 in each example are as shown in the "Solenoid valve opening (%)" and "Pressure (MPa)" columns under liquid conditions in Table 4. The "Solenoid valve opening (%)" under liquid conditions in Table 4 is the ratio (%) of the period during which the second valve 3372 is connected to the pressurizing line, with one oscillation cycle being taken as 100%. Here, one oscillation cycle of the liquid LQ is defined as the period during which the liquid level of the liquid LQ drops from height H5 in the air storage chamber 338 to height H6, and then rises from height H6 to height H5.

[0121] Furthermore, the opening (%) of valve 327 of gas supply mechanism 320 was set to a predetermined opening, and the supply pressure (MPa) of gas G was adjusted to generate bubbles. The opening (%) of valve 327 and the supply pressure (MPa) of gas G in each example are as shown in the "Solenoid valve opening (%)" and "Pressure (MPa)" columns under gas conditions in Table 4. The "Solenoid valve opening (%)" under gas conditions in Table 4 is the percentage (%) of the period during which valve 327 was open, assuming one oscillation cycle to be 100%.

[0122] In Examples 31 and 33, the solenoid valve opening degree for the liquid condition was 20% and the solenoid valve opening degree for the gas condition was 99%, which means that the connection to the pressurized line was maintained for 20% of one oscillation cycle and that the entire oscillation cycle was in a state of supplying gas G. In Example 32, the solenoid valve opening degree for the liquid condition and the solenoid valve opening degree for the gas condition were both 20%, which means that the connection to the pressurized line was maintained for 20% of one oscillation cycle and that the gas G was supplied.

[0123] An image of the bubbles released from the porous body 310 into the liquid LQ in the container 331 was taken using a high-speed camera. After that, using the same method as in Test 1 above, the Sauter diameter (μm), number-average diameter (μm), coefficient of variation (CV value) (%) of the number-average diameter of the bubbles, and D 10 (μm), D 50 (μm), and D 90 The results are shown in the corresponding columns in Table 4.

[0124] [Table 4]

[0125] The results shown in Table 4 demonstrate that fine bubbles FB can be generated by using the fine-bubble generator 300 according to the third embodiment. As described above, the device 300 does not have the pressure-reducing equipment that is provided in the fine-bubble generators of the first and second embodiments. However, Test 4 demonstrates that even when using a device 300 equipped with a liquid-swaying mechanism 330 that does not have a pressure-reducing equipment, the liquid LQ can be drawn into the porous body 310 by gravity by locating the container 331 containing the liquid LQ above the porous body 310.

[0126] As described above, this embodiment is provided with a container 331. The container 331 stores the liquid LQ and is the supply source of the liquid LQ to the porous body 310. The container 331 is arranged above the porous body 310. In the device 300 configured as described above, the container 331, which is the supply source of the liquid LQ, is arranged above the porous body 310, which generates the fine bubbles FB, and thus gravity can be used to supply the liquid LQ to the porous body 310. For this reason, even when a liquid shaking mechanism 330 that does not have a pressure-reducing device is used, the effects of the technology disclosed herein can be realized. Furthermore, the effect of simplifying the device by omitting the pressure-reducing device can be realized.

[0127] The third embodiment has been described above using an example in which the first surface (gas generating surface) of the porous body is the inner surface. However, the present invention is not limited to this. Even when the first surface (gas generating surface) of the porous body is the outer surface, the same effects as those described above can be achieved.

[0128] The technology disclosed herein encompasses the manufacturing methods described in items 1 to 14 below.

[0129] [Item 1] A microbubble generator that generates microbubbles in a liquid, a porous body having a first surface that contacts the liquid and has a plurality of pores that generate the microbubbles; a gas supply mechanism for supplying a gas to the porous body; a liquid oscillation mechanism that oscillates the liquid in contact with the first surface in a direction along the first surface; It is equipped with A micro-bubble generating device configured to release the gas supplied to the porous body into the liquid through the plurality of pores while the liquid is being agitated by the liquid agitation mechanism. [Item 2] the porous body is configured in a cylindrical shape with both ends open, and the inner surface of the porous body is the first surface having the plurality of pores which are a plurality of through holes; Item 2. The micro-bubble generating device according to item 1, wherein the gas supply mechanism is configured to supply the gas from the outer surface side of the porous body. [Item 3] Item 3. The fine-bubble generator according to item 2, wherein the gas supply mechanism has a cylindrical gas supply pipe with both ends open, inside which the porous body is disposed, and is configured to supply the gas between the inner wall surface of the gas supply pipe and the outer surface of the porous body. [Item 4] the porous body is configured in a cylindrical shape with one end closed and the other end open, and the outer surface of the porous body is the first surface having the plurality of pores which are a plurality of through holes; Item 2. The micro-bubble generating device according to item 1, wherein the gas supply mechanism is configured to supply the gas from the inner surface side of the porous body. [Item 5] 5. The micro-bubble generating device according to any one of items 1 to 4, wherein the gas supply mechanism is configured to be able to switch between starting and stopping the supply of the gas depending on the state of the oscillation. [Item 6] The micro-bubble generator according to any one of items 1 to 5, wherein the gas supply mechanism includes a gas supply source, a pipe that serves as a gas flow path from the gas supply source to the porous body, and a valve provided on the pipe, and is configured to start and stop supplying the gas to the porous body by opening and closing the valve depending on the state of the oscillation. [Item 7] 7. The micro-bubble generator according to any one of items 2 to 6, wherein the liquid oscillating mechanism is configured to oscillate the liquid in a direction from one end of the cylindrical porous body to the other end and in a direction from the other end to the one end. [Item 8] the liquid agitation mechanism includes a container for storing the liquid, a pressure reducing device, a pressure increasing device, an air storage chamber, a valve, and piping; one end of the porous body is connected to the container via the piping, and the other end of the porous body is connected to the air storage chamber; the air storage chamber is connected to the pressure reduction equipment and the pressurization equipment, and the connection between the air storage chamber and the pressure reduction equipment and the connection between the air storage chamber and the pressurization equipment are switchable by the valve; The liquid shaking mechanism includes: The fine-bubble generator according to any one of items 2, 3, and 5 to 7, is configured to suck the liquid into the porous body from the one end when the inside of the porous body is depressurized via the connection between the air storage chamber and the depressurization equipment, and to discharge the liquid from the one end to the outside of the porous body when the inside of the porous body is pressurized via the connection between the air storage chamber and the pressurization equipment, by alternately repeating the suction and discharge, thereby oscillating the liquid. [Item 9] the liquid agitation mechanism includes a container for storing the liquid, a pressure reducing device, a pressure increasing device, an air storage chamber, and a valve; The container is connected to the air storage chamber, The porous body is disposed in the air storage chamber, the air storage chamber is connected to the pressure reduction equipment and the pressurization equipment, and the connection between the air storage chamber and the pressure reduction equipment and the connection between the air storage chamber and the pressurization equipment are switchable by the valve; The liquid shaking mechanism includes: The fine-bubble generation device according to any one of items 4 to 7, wherein the device is configured to suck the liquid from the container into the air storage chamber when the pressure inside the air storage chamber is reduced, and to discharge the liquid from the air storage chamber into the container when the pressure inside the air storage chamber is increased, and to oscillate the liquid by alternately repeating the suction and discharge. [Item 10] the liquid agitation mechanism includes a container that contains the liquid and is a supply source of the liquid to the porous body, and that collects the gas released from the porous body; 8. The fine-bubble generating device according to any one of items 1 to 7, wherein the container is placed above the porous body. [Item 11] the liquid agitation mechanism includes a container for storing the liquid, a pressurizing device, an air storage chamber, a valve, and piping; the porous body is arranged so that one end is on the upper side and the other end is on the lower side, the container is disposed above the one end of the porous body and is connected to the one end via the piping; the air storage chamber is connected to the other end of the porous body via the piping and is also connected to the pressurizing equipment; The connection and disconnection between the air storage chamber and the pressurizing equipment can be switched by the valve, The liquid shaking mechanism includes: The fine-bubble generator according to any one of items 2, 3, and 5 to 7, is configured to suck the liquid into the porous body from the one end when the air storage chamber and the pressurizing equipment are not connected, and to discharge the liquid from the one end to the outside of the porous body when the air storage chamber and the pressurizing equipment are connected and the inside of the porous body is pressurized, by alternately repeating the suction and discharge. [Item 12] 12. The micro-bubble generator according to any one of items 1 to 11, wherein the liquid agitation mechanism is configured to adjust the average Reynolds number of the liquid during the agitation to 8000 or less. [Item 13] 13. The fine-bubble generator according to any one of items 1 to 12, wherein the porous body has an average pore size of less than 10 μm. [Item 14] 14. A method for generating fine bubbles in a liquid using the fine bubble generator according to any one of items 1 to 13.

[0130] The technology disclosed herein has been described above, but these are merely examples and do not limit the scope of the claims. Various modifications can be made to the technology disclosed herein without departing from the spirit of the technology. [Explanation of symbols]

[0131] 100 Microbubble generator 110 Porous materials 120 Gas supply mechanism 121 Source 122 Regulator 123 Flow meter 124 Pressure Gauge 125 valve 126 Gas supply pipe 127 Piping 128 Sealing plug 130 Liquid Oscillation Mechanism 131 Container 132 Pressure reducing equipment 133 Pressurized Equipment 134 Regulator 135 Flow meter 136 Pressure Gauge 137 Valve 138 Air storage chamber 139 Piping 91,92 O-ring 200 Microbubble generator 210 Porous Materials 220 Gas supply mechanism 230 Liquid Oscillation Mechanism 290 Support member 300 Microbubble Generator 310 Porous Materials 320 Gas supply mechanism 330 Liquid Oscillation Mechanism

Claims

1. A microbubble generator that generates microbubbles in a liquid, a porous body having a first surface that contacts the liquid and has a plurality of pores that generate the microbubbles; a gas supply mechanism for supplying a gas to the porous body; a liquid oscillation mechanism that oscillates the liquid in contact with the first surface in a direction along the first surface; It is equipped with the gas supplied to the porous body is released into the liquid through the plurality of pores while the liquid is being agitated by the liquid agitation mechanism, the porous body is configured in a cylindrical shape with both ends open, and the inner surface of the porous body is the first surface having the plurality of pores which are a plurality of through holes; The gas supply mechanism is configured to supply the gas from the outer surface side of the porous body.

2. 2. The micro-bubble generating device according to claim 1, wherein the gas supply mechanism has a cylindrical gas supply pipe with both ends open, with the porous body disposed inside, and is configured to supply the gas between the inner wall surface of the gas supply pipe and the outer surface of the porous body.

3. A microbubble generator for generating microbubbles in a liquid, comprising: a porous body having a first surface that contacts the liquid and has a plurality of pores that generate the microbubbles; a gas supply mechanism for supplying a gas to the porous body; a liquid oscillation mechanism that oscillates the liquid in contact with the first surface in a direction along the first surface; It is equipped with the gas supplied to the porous body is released into the liquid through the plurality of pores while the liquid is being agitated by the liquid agitation mechanism, the porous body is configured in a cylindrical shape with one end closed and the other end open, and the outer surface of the porous body is the first surface having the plurality of pores which are a plurality of through holes; The gas supply mechanism is configured to supply the gas from the inner surface side of the porous body.

4. The micro-bubble generating device according to any one of claims 1 to 3, wherein the gas supply mechanism is configured to be able to switch between starting and stopping the supply of the gas depending on the state of the oscillation.

5. The fine-bubble generating device according to claim 4, wherein the gas supply mechanism includes a gas supply source, a pipe that serves as a gas flow path from the gas supply source to the porous body, and a valve provided on the pipe, and is configured to start and stop supplying the gas to the porous body by opening and closing the valve depending on the state of the oscillation.

6. The micro-bubble generator according to any one of claims 1 to 3, wherein the liquid oscillating mechanism is configured to oscillate the liquid in a direction from one end of the cylindrical porous body to the other end, and in a direction from the other end to the one end.

7. the liquid agitation mechanism includes a container for storing the liquid, a pressure reducing device, a pressure increasing device, an air storage chamber, a valve, and piping; one end of the porous body is connected to the container via the piping, and the other end of the porous body is connected to the air storage chamber; the air storage chamber is connected to the pressure reduction equipment and the pressurization equipment, and the connection between the air storage chamber and the pressure reduction equipment and the connection between the air storage chamber and the pressurization equipment are switchable by the valve; The liquid shaking mechanism includes:

3. The fine-bubble generating device according to claim 1 or 2, wherein the device is configured to suck the liquid into the porous body from the one end when the inside of the porous body is depressurized via the connection between the air storage chamber and the depressurization equipment, and to discharge the liquid from the one end to the outside of the porous body when the inside of the porous body is pressurized via the connection between the air storage chamber and the pressurization equipment, by alternately repeating the suction and discharge, thereby causing the liquid to oscillate.

8. the liquid agitation mechanism includes a container for storing the liquid, a pressure reducing device, a pressure increasing device, an air storage chamber, and a valve; The container is connected to the air storage chamber, The porous body is disposed in the air storage chamber, the air storage chamber is connected to the pressure reduction equipment and the pressurization equipment, and the connection between the air storage chamber and the pressure reduction equipment and the connection between the air storage chamber and the pressurization equipment are switchable by the valve; The liquid shaking mechanism includes:

4. The fine bubble generator according to claim 3, wherein the liquid is suctioned from the container into the air storage chamber when the pressure inside the air storage chamber is reduced, and the liquid is discharged from the air storage chamber into the container when the pressure inside the air storage chamber is increased, and the suction and discharge are alternately repeated to cause the liquid to oscillate.

9. the liquid agitation mechanism includes a container that contains the liquid and is a supply source of the liquid to the porous body, and that collects the gas released from the porous body; The fine-bubble generating device according to any one of claims 1 to 3, wherein the container is disposed above the porous body.

10. the liquid agitation mechanism includes a container for storing the liquid, a pressurizing device, an air storage chamber, a valve, and piping; the porous body is arranged so that one end is on the upper side and the other end is on the lower side, the container is disposed above the one end of the porous body and is connected to the one end via the piping; the air storage chamber is connected to the other end of the porous body via the piping and is also connected to the pressurizing equipment; The connection and disconnection between the air storage chamber and the pressurizing equipment can be switched by the valve, The liquid shaking mechanism includes:

3. The fine-bubble generating device according to claim 1 or 2, wherein the device is configured to suck the liquid into the porous body from the one end when the air storage chamber and the pressurizing equipment are not connected, and to discharge the liquid from the one end to the outside of the porous body when the air storage chamber and the pressurizing equipment are connected and the inside of the porous body is pressurized, by alternately repeating the suction and discharge, thereby causing the liquid to oscillate.

11. 4. The micro-bubble generating device according to claim 1, wherein the liquid agitating mechanism is configured to adjust the average Reynolds number of the liquid during the agitation to 8000 or less.

12. The micro-bubble generator according to any one of claims 1 to 3, wherein the porous body has an average pore size of less than 10 µm.

13. A method for generating fine bubbles in a liquid using the fine bubble generator according to any one of claims 1 to 3.

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