JP7729556B2 - Microbubble generating device and microbubble generating method - Google Patents

Description

This disclosure relates to a microbubble generating device and a method for generating microbubbles.

In recent years, attention has been focused on the usefulness of technology using microscopic bubbles called fine bubbles, which are less than 100 μm in diameter. Fine bubbles include, for example, ultrafine bubbles with diameters of less than 1 μm and microbubbles with diameters of 1 μm or more. Reducing the size of bubbles can be expected to promote gas-liquid reactions in chemical reaction applications such as organic synthesis, and to increase the efficiency of oxygen supply in culturing applications such as microorganisms and animal cells. Other applications of technology using fine bubbles are being considered, including cleaning technology using liquids containing fine bubbles, water sterilization and deodorization, ozone water generation, health and medical equipment, water purification in lakes and aquaculture farms, various wastewater treatment applications from factories and livestock farms, and functional water production. Accordingly, the market for devices that generate microbubbles and ultrafine bubbles has also expanded in recent years.

The micro-bubble generator disclosed in Patent Document 1 has a gas swirling shear device including a fluid swirling chamber defined by a tubular member having a cylindrical inner 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 hole for introducing a gas-liquid mixture into the fluid swirling chamber, and a fluid outlet hole for discharging the gas-liquid mixture from the fluid swirling chamber. In this gas swirling shear device, the fluid inlet hole is located closer to the second end wall member than the axial center of the tubular member. The fluid outlet hole penetrates the second end wall member along the central axis of the inner surface of the tubular member. The gas-liquid mixture introduced into the fluid swirling chamber forms a swirling flow and proceeds toward the first end wall member, which does not have a discharge port. The first end wall then redirects the flow toward the radial center of the fluid swirling chamber, further increasing the swirling speed, and the flow moves toward the second end wall member before being discharged to the outside through the fluid discharge port. The document states that this increases the shear force on the gas contained in the liquid, facilitating atomization.

The ultrafine bubble generator disclosed in Patent Document 2 comprises a cylindrical casing having a liquid inlet at one end and a liquid outlet at the other end. The casing includes a flow rate acceleration section that accelerates the flow rate of the liquid introduced from the inlet toward the outlet; a gas suction section that draws gas from the outside into the casing, where the pressure is reduced by the liquid flow accelerated by the flow rate acceleration section; and an ultrafine bubble-containing liquid production section that shears the gas drawn in by the gas suction section with the accelerated liquid flow to produce a liquid containing ultrafine bubbles. The gas suction section of this ultrafine bubble generator is equipped with a pulsation suppressor that suppresses pulsation of the drawn gas. The document states that the installation of the pulsation suppressor reduces gas pulsation, enabling the stable generation of ultrafine bubbles and reducing vibration and noise.

The bubble generating device disclosed in Patent Document 3 comprises 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, thereby ejecting 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 the processes of depressurizing and pressurizing the gas flow path, a stirring force can be applied to the bubbles generated in the gas flow path, thereby efficiently reducing the size of the bubbles.

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, becoming tiny bubbles that are then introduced into the liquid. The vibration source then vibrates the surface of the porous member, causing the tiny bubbles to quickly drop off from the surface of the porous member. This document states that this configuration enables the efficient generation of tiny bubbles in a liquid.

Japanese Patent Application Laid-Open No. 2008-272719 JP 2014-028340 A Japanese Patent Application Laid-Open No. 2017-023996 Japanese Patent Application Laid-Open No. 2003-265939

However, in devices configured to generate bubbles in a liquid by passing a gas through a porous material (e.g., Patent Document 4), the bubbles generated tend to be larger in diameter than in devices with other configurations (e.g., Patent Documents 1 to 3).

This disclosure was made in consideration of the above-mentioned issues, and aims to provide a technology that uses a porous body to generate microbubbles more efficiently.

The microbubble generator disclosed herein is a device for generating microbubbles in a liquid. This device comprises 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 to release the gas supplied to the porous body into the liquid through the plurality of pores while the liquid is agitated by the liquid agitation mechanism.

In a microbubble generator configured as described above, while the liquid is oscillating along the first surface of the porous body, shear forces can be generated on the first surface due to the oscillating liquid. This allows for more efficient generation of microbubbles.

In one 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 makes it possible to better achieve the effects of the technology disclosed herein.

In another preferred embodiment of this device, the gas supply mechanism has a cylindrical gas supply pipe with both ends open, with the porous body disposed inside. 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 prevent liquid from leaking from the inside to the outside of the porous body.

In another preferred embodiment of this device, the porous body is configured in a cylindrical shape 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 makes it possible to better achieve the effects of the technology disclosed herein.

In another preferred aspect of this 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. This configuration increases the efficiency of generating microbubbles and enables the size of the microbubbles to be made smaller.

In another preferred embodiment of this device, the gas supply mechanism includes a gas supply source, piping that serves as a gas flow path from the supply source to the porous body, and a valve installed on the piping. The gas supply mechanism is configured to start and stop the supply of 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.

In another preferred aspect of this device, the liquid agitation mechanism is configured to agitate 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.

In another preferred aspect of this device, the liquid agitation mechanism includes a container for storing the liquid, a pressure reduction device, a pressurization 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 device and the pressurization device. The connection between the air storage chamber and the pressure reduction device and the connection between the air storage chamber and the pressurization device are switchable by the valve. The liquid agitation 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 reduction 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 pressurization device, alternately repeating this suction and discharge, thereby agitating the liquid. This configuration allows for smooth suction and discharge of liquid at the end, ultimately enabling more efficient generation of microbubbles.

In another preferred aspect of this device, the liquid oscillating mechanism includes a container for containing the liquid, a pressure reduction device, a pressurization 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 reduction device and the pressurization device, and the connection between the air storage chamber and the pressure reduction device and the connection between the air storage chamber and the pressurization device are switchable by the valve. The liquid oscillating mechanism is configured to oscillate the liquid by drawing the liquid from the container into the air storage chamber when the pressure inside the air storage chamber is reduced, and discharging the liquid from the air storage chamber into the container when the pressure inside the air storage chamber is increased, alternately repeating this suction and discharge. This configuration can suppress the coalescence of bubbles within the flow path, enabling more efficient generation of fine bubbles.

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 positioned above the porous body. With this configuration, gravity can be used to supply liquid to the porous body. This allows for the realization of the effect of simplifying the device in addition to the effect of the technology disclosed herein.

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 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 arranged 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 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. The liquid oscillating mechanism oscillates the liquid by alternately repeating this suction and discharge. This configuration not only achieves the benefits of the technology disclosed herein, but also simplifies the device configuration.

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 8000 or less. This configuration allows for more efficient generation of microbubbles.

In another preferred embodiment of this device, the average pore diameter of the porous body is less than 10 μm. This configuration allows for more efficient generation of fine bubbles.

A method for generating microbubbles in a liquid using the microbubble generator is also provided. This method can further reduce the size of the microbubbles.

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

Embodiments of the technology disclosed herein are described below. 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 content disclosed in this specification and the technical common sense in the relevant field. Note that the notation "A to B" indicating a numerical range in this specification means "greater than A and less than B," "greater than A and less than B," and also means "greater than A and less than B," "greater than A and less than B," and "greater than A and less than B." The U arrow in each figure indicates an upward direction in the direction of gravity. The D arrow in each figure indicates a downward direction in the direction of gravity.

In this specification, "fine bubbles" may include fine bubbles. Fine bubbles are defined by the International Organization for Standardization (ISO) standard (ISO 20480-1:2017) as bubbles with a diameter of less than 100 μm. 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.

As used herein, "fine bubbles" refers to bubbles having 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, "average bubble diameter" refers to the cumulative bubble diameter (D 50 ) of 50% from the smallest bubble diameter, calculated 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 analyzing the images using "ImageJ," a free image analysis software developed by the National Institutes of Health.

With regard 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. While not particularly limited, the mode diameter is generally 5 μm or more, and may be 10 μm or more. In this specification, "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 captured using a commercially available digital imaging device (e.g., a high-speed camera) and analyzing the images using the image analysis software "ImageJ."

With regard to "fine bubbles" in this specification, 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, "Sauter diameter" refers to a value obtained by randomly selecting 100 to 500 (e.g., 200 to 300) bubbles from an image captured 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.

First Embodiment
FIG. 1 is a schematic diagram of a micro-bubble generating device 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 generating device 100 (hereinafter also 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 further reduced. Furthermore, the bubble diameter distribution of the generated fine bubbles can be made narrower.

The oscillation of liquid LQ refers to, for example, the movement of liquid LQ alternating continuously between flowing from any point P on the first surface of porous body 110 toward any other point Q and flowing from point Q toward point P. The period during which liquid LQ is oscillating refers, for example, to the period during which liquid LQ is flowing from point P toward point Q and the period during which liquid LQ is flowing from point Q toward point P. The flow velocity of liquid LQ becomes zero at the point when the flow switches between flowing from point P toward point Q and flowing from point Q toward point P, and at the point when the flow switches between flowing from point Q toward point P and flowing from point P toward point Q. For this reason, these two points in time are excluded from "the period during which liquid LQ is oscillating."

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 microbubbles 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 gas G from the outer surface side 112 of the porous body 110. The gas supply mechanism 120 will be described further below. Note that 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.

As shown in FIG. 2, the porous body 110 is equipped with O-rings 91 and 92. The O-ring 91 is made of, for example, resin and is attached to one end 11A of the porous body 110. The O-ring 92 is attached to the other end 11B of the porous body 110. In this embodiment, the O-rings 91 and 92 are sandwiched between the piping 139 (here, the third piping 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 piping 139 (here, the third piping 13Z), and the gas supply pipe 126. This allows gas G to be supplied to the outer surface 112 of the porous body 110, and liquid LQ to flow through the inner cavity of the porous body 110.

The average pore diameter of the porous body 110 is set appropriately 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.

The average pore diameter can be measured by mercury intrusion porosimetry using a mercury porosimeter. Any commercially available, conventionally known mercury porosimeter can be used, such as the AutoPore IV 9500 manufactured by Micrometrics. The nominal value provided by the manufacturer or other sources may be used as the average pore diameter.

The porous body 110 may be made of, for example, ceramic. Examples of ceramics constituting the porous body 110 include oxide ceramics such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), magnesia (MgO), silica (SiO ₂ ), titania (TiO ₂ ), zircon (ZrSiO ₄ ), and mullite (Al ₆ O ₁₃ Si ₂ ); and non-oxide ceramics such as silicon nitride (Si ₃ N ₄ ), boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC), and boron carbonitride (BCN). The ceramic may be one of the above ceramics alone, or a composite material containing two or more of them. Alumina, boehmite, silica, and titania are preferred ceramics because they have stable quality, are inexpensive, and are easily available. The chemical formula in parentheses next to the name of each ceramic indicates a typical composition of the ceramic, and is not intended to limit the composition of the ceramic to that chemical formula. Furthermore, as described above, ceramic is given as an example of the material of the porous body 110, but the material is not limited to this. The porous body 110 may be made of, for example, metal or resin.

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 can be selected appropriately depending on the type of microbubbles desired. Gas G can be, for example, air, oxygen gas, ozone, hydrogen gas, nitrogen gas, carbon dioxide gas, etc., and is air in this example.

In this embodiment, the gas supply mechanism 120 is configured to switch between starting and stopping the supply of gas G depending on the state of oscillation of the liquid LQ. As described below, the operation of the gas supply mechanism 120 and the operation of the liquid oscillation mechanism 130 are controlled by a control unit. Therefore, 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 allows the start and stop of the supply of gas G to be switched 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 a period in which the direction in which the generated microbubbles are discharged to the outside of the porous body 110 coincides with the direction in which the liquid LQ flows, microbubbles can be generated more efficiently.

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, the start and stop of the supply of gas G to the porous body 110. In this embodiment, the valve 125 switches the start and stop of the supply of gas G to the gas supply pipe 126. Valve 125 is preferably an electrically controllable valve, such as a solenoid valve. As shown in FIG. 1, supply source 121, regulator 122, flow meter 123, pressure gauge 124, valve 125, and gas supply pipe 126 are interconnected via piping 127. piping 127 serves as a flow path for gas G from supply source 121 to porous body 110.

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 depending on the state of oscillation of the liquid LQ. For example, a program that opens and closes the valve 125 depending on the operation of the liquid oscillation mechanism 130 and switches between starting and stopping the supply of gas G can be pre-defined 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. It also makes it possible to further improve the efficiency of generating fine bubbles.

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 it. 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 a supply hole 12P and an exhaust hole 12Q in its wall. The supply hole 12P and the exhaust hole 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). Gas G is supplied to the gas supply pipe 126 via the pipe 127 and the supply hole 12P. A sealing plug 128, for example, 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 if 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 gas G to the porous body 110. Furthermore, even if the supply of gas G is stopped, gas G can 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.

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 third pipe 13Z and the connecting members 93 and 94 are connected by the locking portions Z1 and Z2 abutting against the periphery of the through holes in the connecting members 93 and 94.

As shown in FIG. 2, the gas supply pipe 126 has a holding portion 1261 on the end 12A side and a holding portion 1262 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. Liquid LQ is configured to flow through the inner cavity of the porous body 110 via this connection.

The liquid oscillation mechanism 130 is, for example, a mechanism that oscillates the liquid LQ in contact with the first surface (here, the inner surface 111) in a direction along the first surface. The type of liquid LQ is not particularly limited. In this case, the liquid LQ may be water.

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 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 a direction K1 from end 11A to end 11B, and in a direction K2 from end 11B to end 11A. As shown in FIG. 2, end 11A and end 11B are open ends. Therefore, by oscillating the liquid LQ between end 11A and end 11B, microbubbles generated from either end 11A or end 11B (here, end 11A) can be efficiently discharged to the outside of the porous body 110.

As shown in FIG. 1, the liquid agitation mechanism 130 includes a container 131, a pressure reduction device 132, a pressurization 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 pressurization 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 "pressurization line" below. The pressure reduction device 132 and the valve 137 are connected via the second pipe 13Y. This connection is also referred to as the "pressure reduction 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 storage 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 storage 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.

The container 131 contains, for example, liquid LQ. The container 131 is, for example, a supply source of liquid LQ to the porous body 110. The container 131 can also serve as a recovery unit that recovers gas G (fine bubbles FB) released from the porous body 110. The pressure reduction device 132 is a device that reduces the pressure inside the air storage 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 pressurization device 133 is a device that pressurizes the air storage 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 air supplied from the pressurization 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 between the first pipe 13X, the second pipe 13Y, and the third pipe 13Z. The valve 137 is configured to be able to switch between the connection between the air storage chamber 138 and the pressure reduction equipment 132 and the connection between the air storage chamber 138 and the pressure reduction equipment 133. The valve 137 is preferably an electrically controllable valve, such as a solenoid valve.

Here, the gas storage chamber 138 is a cylindrical (hollow cylindrical) tube with both ends open (end 13A and the other end in FIG. 2). The gas storage chamber 138 is configured to allow for the intake and discharge of liquid LQ contained in the container 131. In this embodiment, the gas storage chamber 138 has 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). 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 the third pipe 13Z. Through this connection, liquid LQ flows through the inner cavity of the porous body 110, allowing the liquid LQ to be drawn into and discharged from the air storage chamber 138.

In this embodiment, the liquid oscillation mechanism 130 draws 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 storage chamber 138 and the pressure reduction equipment 132. Furthermore, the liquid oscillation mechanism 130 discharges 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 storage chamber 138 and the pressure reduction equipment 133. The liquid oscillation mechanism 130 is configured to alternately repeat this 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. This allows for smooth suction and discharge of liquid LQ at the end 11A, ultimately enabling more efficient generation of microbubbles.

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 be equal to or less than 8000. 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 (kg/cm ³ ) of the liquid LQ, and when the liquid LQ is water, ρ=998.2 (kg/cm ³ ). 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 level 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 level in the air accumulation chamber 138) by that period (s). By setting the average Reynolds number Re in the above range, fine bubbles can be generated more efficiently.

The average Reynolds number Re of the liquid LQ can be set appropriately depending on the desired microbubble diameter, microbubble diameter distribution, amount of microbubbles generated, and the like. While not particularly limited, the average Reynolds number Re may be, for example, 1000 or greater. The average Reynolds number Re may also be, for example, 2300 or less, or less than 2300. The average Reynolds number Re can be set appropriately by, for example, changing the degree 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 greater but less than 4000 is defined as a "transition region," and a flow region where the average Reynolds number Re is 4000 or greater is defined as a "turbulent flow region."

Although not shown in the figures, the 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. The functions of the control unit can be processed by, for example, the hardware, such as the arithmetic units (also called processors, CPUs (Central Processing Units), or MPUs (Micro-processing units)) and storage units (memory, hard disks, etc.) of each computer constituting the control unit, working together with software. The configuration of the control unit does not characterize the technology disclosed herein, so a description of it will be omitted here.

Figure 3 is a flow diagram illustrating the operation of the micro-bubble generator 100. Before executing the control flow shown in Figure 3, the porous body 110, the gas supply mechanism 120, and the liquid agitation mechanism 130 are connected. For example, the porous body 110 and the liquid agitation mechanism 130 are first connected. For example, the porous body 110 is housed inside the gas supply pipe 126, and the gas storage 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 contained in the container 131. Next, the third pipe 13Z attached to the end of the gas storage chamber 138 (the end on the valve 137 side in Figure 1) is connected to the valve 137. It is recommended that the valve 137 be connected in advance to the pressurization equipment 133, regulator 134, flow meter 135, and pressure gauge 136 via the first piping 13X to establish a pressurization line. It is also recommended that the valve 137 be connected in advance to the depressurization equipment 132 via the second piping 13Y to establish a depressurization line.

Next, the porous body 110 is connected to the gas supply mechanism 120. 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, pipe 127 is connected to the supply hole 12P of the gas supply pipe 126. It is recommended that the supply source 121, regulator 122, flow meter 123, pressure gauge 124, and valve 125 be connected to pipe 127 in advance.

Once the various parts of the device 100 are connected, the control flow shown in FIG. 3 is executed. In this control flow, first, the porous body 110 is connected to the 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, the pressure inside the air storage chamber 138 and the inner cavity of the porous body 110 can be reduced. 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). The liquid LQ is then sucked into the air storage chamber 138. As a result, the liquid level of the liquid LQ inside the air storage chamber 138 rises.

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 storage chamber 138 has reached height H1. If there is a liquid level of the liquid LQ in the air storage chamber 138, it can be confirmed that at least the inner cavity of the porous body 110 is filled with liquid LQ. By using the fact that the liquid level of the liquid LQ has reached height H1 in the air storage 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 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.

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 pressurization equipment 133 is switched on to pressurize the air storage chamber 138 (step S6). At this time, air supplied from the pressurization equipment 133 into the air storage chamber 138 lowers the liquid level of the liquid LQ, and the liquid is discharged from the air storage 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.

Next, the valve 125 of the gas supply mechanism 120 is opened (step S8). By opening the valve 125, gas G adjusted to a predetermined supply pressure can be supplied to the porous body 110. When gas G is supplied to the porous body 110, as described above, 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 liquid LQ. By supplying gas G at a predetermined supply pressure at this timing, gas G enters the inner cavity of the porous body 110 through the pores MP. This allows microbubbles to be generated (step S9).

The timing for opening valve 125 in step S8 is not particularly limited and can be set appropriately depending on the operating conditions of device 100. This timing can be set, for example, to coincide with the pressurization of the air storage chamber 138 in step S6. By opening valve 125 simultaneously with the pressurization of the air storage chamber 138, the period during which fine bubbles are generated can be extended, thereby improving the efficiency of fine bubble generation.

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 storage chamber 138 has reached height H2. Height H2 can be set closer to the container 131 than the height H1. By using the fact that the liquid level of the liquid LQ has reached height H2 in the air storage chamber 138 as the criterion for determination in step S4, it is possible, for example, to prevent gas in the air storage chamber 138 from being discharged into the container 131 through the cylinder (inner cavity) of the porous body 110.

If it is determined in step S10 that the liquid level of liquid LQ has reached a predetermined height (here, height H2) (Yes), valve 125 is closed (step S11). Closing valve 125 stops the supply of gas G to gas supply pipe 126, and microbubbles will eventually 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 liquid LQ has reached a predetermined height (here, height H2) (No), the process returns to step S7, as shown in FIG. 3.

The technology disclosed herein provides a method for generating microscopic bubbles in liquid LQ using device 100. This method allows for more efficient generation of microscopic bubbles.

The first embodiment of the micro-bubble generator disclosed herein has been described above with reference to Figures 1 to 3. However, the micro-bubble generator disclosed herein is not limited to this and may include other variations. For example, in the device 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, this is not limiting. 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 in the first embodiment. Micro-bubbles can also be generated more efficiently by changing the supply pressure of gas G depending on the state of oscillation of the liquid LQ. The supply pressure P1 is not particularly limited as long as it is large enough to generate microbubbles, and can be set appropriately depending on the average pore diameter of the porous body 110, the desired size of the microbubbles, the desired amount of microbubbles, 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 microbubbles.

Furthermore, in the operation of the apparatus 100 configured as described above, the switching to the decompression line side and the switching to the pressurization 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, liquid LQ may have infiltrated the pores MP of the porous body 110. Even if the valve 125 is opened to supply gas G in this state, the liquid LQ that has infiltrated the pores MP must first be discharged, and microbubbles cannot be generated for the period required for such discharge of the liquid LQ. In this case, since the timing of discharging the liquid LQ from the lumen of the porous body 110 and the timing of generating the microbubbles cannot be synchronized, it may be difficult to control the bubble diameter. In such a case, the timing of switching the valve 137 to the pressurization line side and the timing of opening the valve 125 to supply gas G may be set to different times. For example, the valve 137 may be switched to the pressurization line side first, and after the discharge of the liquid LQ begins, the valve 125 may be opened to supply gas G to the porous body.

Next, we will explain a test example related to the first embodiment of the technology disclosed herein. Note that the test example shown below is not intended to limit the technology disclosed herein.

<Test 1>
In Test 1, fine bubbles were generated using the fine bubble generating device 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 Figure 2.

--Example 1 (Example 1A to Example 1D)--
The porous body 110 used was a porous body primarily composed of alumina with an average pore diameter of 0.5 μm and a porosity of 36%. First, a third pipe 13Z was connected to the inside of the cylindrical porous body 110 so that 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 enable switching 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 liquid LQ.

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 through the pores MP (through holes). A regulator 122, flow meter 123, pressure gauge 124, and valve 125 (solenoid valve) were connected to the middle of the pipe 127 so that the timing of the supply of gas G could be controlled.

To accelerate the vertical movement of the liquid LQ in the cavity of the porous body 110, the air in the air storage chamber 138 was first sucked out by the pressure reduction device 132 until the entire cavity 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 device 133 side to send air into the air storage chamber 138, 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 cavity of the porous body 110. By repeatedly depressurizing and pressurizing the air storage chamber 138 in this manner, the liquid LQ in the cavity of the porous body 110 was accelerated to move up and down. Valve 125 was opened at the timing when the liquid LQ in the cavity of the porous body 110 was being pushed down, and gas G was supplied. The time for which the valve 125 was open was set to be the same as the time for discharging the liquid LQ from the porous body 110. Additionally, the timing for opening valve 125 and the timing for switching valve 137 to the pressurized line side were set to be simultaneous.

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. Then, using the image analysis software "ImageJ," 300 bubbles were randomly selected from the acquired image, and the Sauter diameter (μm), number-average diameter (μm), _D10 (μm), _D50 (μm), and _D90 (μm) of the bubbles were calculated. 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 bubble diameters of the bubbles analyzed. _D10 (μm) is the bubble diameter at which the cumulative diameter of the bubbles analyzed, starting from the smallest, is 10%. _D50 (μm) is the bubble diameter at which the cumulative diameter from the smallest bubble of the analyzed bubbles is 50%, and _D90 (μm) is the bubble diameter at which the cumulative diameter from the smallest bubble of the analyzed bubbles is 90%.

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 in 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 in 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 the flow rate (L/min), average Reynolds number Re, fluid field, pressure (MPa), solenoid valve opening (%), and cycle (Hz); and the gas conditions for 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.

In Table 1 for liquid conditions, the "solenoid valve opening degree (%)" refers to the percentage of the period during which valve 137 was connected to the pressurized line, assuming one oscillation cycle as 100%. In Table 1 for gas G supply, the "solenoid valve opening degree (%)" refers to the percentage of the period during which valve 125 was open, assuming one oscillation cycle 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 the oscillation cycle (half the 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 the oscillation cycle. Also, here, one cycle of the oscillation of the liquid LQ is defined as the period from when the liquid level of the liquid LQ in the air storage chamber 138 drops from height H1 to height H2, and then rises from height H2 to height H1.

--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.

--Example 3 (Examples 3A to 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.

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

--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.

<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, the porous body 21 and a liquid feed pump 22b were connected via a pipe 22a so that the liquid LQ circulated inside the cylindrical porous body 21. The tip of the pipe 22a on the liquid feed pump 22b side was immersed in the liquid LQ in the container 23 so that the liquid LQ circulated at a constant speed inside the porous body 21. A voltage regulator 22c, which 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. The porous body 21 was housed in a gas supply pipe 25a, and a pipe 25b was connected to the gas supply pipe 25a so that gas G could be supplied from the outer surface of the porous body 21. A gas G supply source 25c, a regulator 25d, a flow meter 25e, and a pressure meter 25f were connected to the pipe 25b. With this configuration, gas G was supplied from the outer surface of the porous body 21 through the pores to the inner surface, and bubbles were generated.

--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 adjusted to a desired value by adjusting the voltage of the liquid supply pump 22b and the opening of the pipe 22a via 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.

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. Thereafter, using the same method as in Test 1 above, the Sauter diameter (μm), number average diameter (μm), coefficient of variation of the number average diameter (CV value) (%), _D10 (μm), _D50 (μm), and _D90 (μm) of the bubbles were calculated. The results are shown in the corresponding columns in Table 2.

Table 2 also lists the porous body conditions, liquid conditions, and gas conditions for each example.

--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.

- Comparative Example 3 (Comparative Example 3A to Comparative Example 3E) -
A porous body having an average pore diameter 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.

--Comparative Example 4 (Comparative Example 4A to Comparative Example 4D)--
A porous body having an average pore diameter 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 those used in Comparative Example 1. The data and conditions are shown in the corresponding columns in Table 2. Furthermore, in Comparative Example 4A, the bubbles that were generated coalesced, making it impossible to obtain data. The "-" in the "Bubble Characteristics" column for Comparative Example 4A in Table 2 indicates that data could not be obtained.

<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. Thereafter, 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.

--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.

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. Thereafter, using the same method as in Test 1 above, the Sauter diameter (μm), number average diameter (μm), coefficient of variation of the number average diameter (CV value) (%), _D10 (μm), _D50 (μm), and _D90 (μm) of the bubbles were calculated. The results are shown in the corresponding columns in Table 3.

--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.

--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.

From the results shown in Tables 1 to 3, it was found that fine bubbles can be generated by using a fine-bubble generating device 100 that includes a porous body 110, a gas supply mechanism 120, and a liquid oscillation mechanism 130, and is configured to release gas G supplied to the porous body 110 into the liquid LQ through multiple pores MP while the liquid LQ is oscillating. In particular, it was found that in the laminar flow region where the average Reynolds number Re is less than 2300, when device 100 is used, finer bubbles can be generated than when device 2 or device 3 is used. This shows that device 100 can generate fine bubbles more efficiently.

Second Embodiment
Fig. 6 is a schematic diagram of a micro-bubble generator according to a 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, descriptions 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.

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 microbubbles 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 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 enables microbubbles to be generated more efficiently.

The porous body 210 includes, for example, a support member 290. The support member 290 is attached, for example, to the end 21B of the porous body 210. As shown in FIG. 6, the support member 290 is connected to the piping 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 (lumen) of the porous body 210 by attaching the piping 227 to the through-hole.

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 interconnected 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.

In this embodiment, the liquid oscillation mechanism 230 is configured to oscillate 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 storage chamber 238. Therefore, it is preferable to oscillate the liquid LQ in a direction L1 from the first connection hole 23R to the second connection hole 23S (a direction from end 23A to end 23B) and in a direction L2 from the second connection hole 23S of the air storage chamber 238 to the first connection hole 23R (a direction from end 23B to end 23A).

As shown in FIG. 6, the liquid oscillation mechanism 230 includes a container 231, a pressure reduction device 232, a pressurization device 233, a regulator 234, a flow meter 235, a pressure gauge 236, a valve 237, an air storage chamber 238, and piping 239. The piping 239 includes a first piping 23X, a second piping 23Y, and a third piping 23Z. As shown in FIG. 6, the liquid oscillation mechanism 230 includes a pressurization line via the first piping 23X and a depressurization line via the second piping 23Y. The third piping 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 piping 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 storage 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. Also, as shown in FIG. 6, the container 231 is arranged below the end 21A of the porous body 210.

In this embodiment, the liquid agitation mechanism 230 draws liquid LQ from the container 231 into the gas storage chamber 238 when the pressure inside the gas storage chamber 238 is reduced. Furthermore, the liquid agitation mechanism 130 discharges liquid LQ from the gas storage chamber 238 into the container 231 when the pressure inside the gas storage chamber 238 is increased. 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 contained within 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 operation at higher supply gas flow rates 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.

The operation of the device 200 will be described below with reference to Figure 3. Before executing the control flow shown in Figure 3, the porous body 210, gas supply mechanism 220, and liquid agitation mechanism 230 are connected. For example, first, the porous body 210 and the liquid agitation mechanism 230 are connected. For example, the porous body 210 is housed inside the gas storage chamber 238, and the gas storage chamber 238 is connected to the container 231 and the gas storage 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 housed in the container 231. Next, the first pipe 23X and the second pipe 23Y are connected to the valve 237, establishing a pressurized line and a depressurized line.

Next, the porous body 210 and the gas supply mechanism 220 are connected. 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.

Once the various parts of the device 200 are connected, the control flow shown in FIG. 3 is executed. In this control flow, first, the air storage chamber 238 is connected to the decompression line (step S1). Next, the pressure inside the third pipe 23Z is reduced (step S2). For example, the pressure inside the air storage chamber 238 can be reduced by turning on the switch of the decompression equipment 233 and sucking the air inside the air storage chamber 238 through the third pipe 23Z. This causes the liquid LQ inside the container 231 to be sucked through the third pipe 23Z and flow into the air storage chamber 238 (step S3). As a result, the liquid level of the liquid LQ inside the air storage chamber 238 rises.

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 storage chamber 238 has reached height H3. In this embodiment, height H3 can be set closer to end 23B of the air storage chamber 238 than end 21B of the porous body 210.

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 air storage chamber 238 (step S6). At this time, air supplied from the pressurizing equipment 233 into the air storage chamber 238 lowers the liquid level of the liquid LQ, and the liquid is discharged from the air storage 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.

Next, the valve 225 of the gas supply mechanism 220 is opened (step S8). By opening the valve 225, gas G can be supplied to the porous body 210. When gas G is supplied to the porous body 210, as described above, liquid LQ is discharged from the gas storage chamber 238 toward the container 231. 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 liquid LQ. At this timing, gas G is supplied to the inner surface 211 of the porous body 210 at a predetermined supply pressure, whereby gas G is released outside the porous body 210 through the pores MP, generating microbubbles (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 device 200.

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 gas in the air storage chamber 238 from being discharged into the container 131 through the cylinder (inner cavity) of the porous body 110.

If it is determined in step S10 that the liquid level of liquid LQ has reached a predetermined height (here, height H4) (Yes), valve 225 is closed (step S11). Closing valve 225 stops the supply of gas G to the air storage chamber 238, and fine bubbles gradually 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 liquid LQ has reached a predetermined height (here, height H4) (No), the process returns to step S7.

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, descriptions 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.

As shown in Figure 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 piping 339 (here, the third piping 33Z). Furthermore, the end 31B is connected to the air storage chamber 338 via piping 339 (here, the third piping 33Z).

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 storage 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 is connected to the first connection hole 33R of the gas storage chamber 338 via the third pipe 33Z. In the embodiment shown in FIG. 7, the flow path for the liquid LQ runs from the container 331 through the inner cavity of the porous body 310 to the gas storage chamber 338 via the third pipe 33Z.

In this embodiment, the supply state of liquid LQ from the container 331 to the porous body 310 is configured to be switched by a first valve 3371 (e.g., a ball valve). The first valve 3371 is disposed, for example, on the third pipe 33Z. 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 storage chamber 338. Furthermore, for example, by closing the first valve 3371, the supply of liquid LQ to the porous body 310 can be stopped, and ultimately, operation of the device 300 can be stopped.

In this embodiment, the air storage chamber 338 is further connected to the pressurizing equipment 333 via the first pipe 33X. For example, in the liquid oscillation mechanism 330, a pressurization 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 storage chamber 338.

In addition, in this embodiment, the connection and disconnection between the air storage chamber 338 and the pressurizing equipment 333 can be switched by a second valve 3372 (e.g., a solenoid valve). The second valve 3372 is disposed, for example, on the first pipe 33X. Here, by opening the second valve 3372, the air storage chamber 338 and the pressurizing equipment 333 are connected, and the air storage chamber 338 is pressurized. In addition, by closing the second valve 3372, the air storage chamber 338 and the pressurizing equipment 333 are disconnected.

In this embodiment, the liquid oscillation mechanism 330 draws liquid LQ into the porous body 310 from the end 31A when the air storage chamber 338 and the pressurizing equipment 333 are not connected. Furthermore, when the air storage chamber 338 and the pressurizing equipment 333 are connected and the porous body 310 is pressurized, the liquid oscillation mechanism 330 discharges liquid LQ from the end 31A to the outside of the porous body 310. The liquid oscillation mechanism 330 is configured to oscillate the liquid LQ by alternately repeating this suction and discharge. In this embodiment, as described above, the container 331 is positioned 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, eliminating the need for the pressure reduction equipment used in the embodiments of Figures 2 and 6. Therefore, the device 300 can achieve the effect of simplifying the device configuration in addition to the effect of the technology disclosed herein.

Next, we will explain a test example related to the third embodiment of the technology disclosed herein. Note that the test example shown below is not intended to limit the technology disclosed herein.

<Test 4>
In Test 4, fine bubbles were generated using the fine bubble generating device 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.

--Examples 31 to 33--
The porous body 310 was made of a porous body primarily 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) could flow inside the porous body 310. Next, an empty container 331 was provided in the upper section of the third pipe 33Z (the upper section of the porous body 310) on the end 31A side. 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.

Next, piping 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 the 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, flow meter 323, pressure gauge 324, and valve 325 (solenoid valve) were connected to the middle of the piping 327 so that the timing of the supply of gas G could be controlled.

Next, after confirming that the first valve 3371 was closed, liquid LQ was poured into the container 331. Next, valve 325 of the gas supply mechanism 320 and second valve 3372 of the liquid oscillation mechanism 330 were opened. Next, the first valve 3371 was gradually opened, allowing the liquid LQ in the container 331 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 pressure (MPa) applied by 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 for each example is shown in the corresponding column in Table 4. Note that, as shown in FIG. 7, height H5 in the air storage chamber 338 was set at a position higher than height H6 (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 percentage (%) of the period during which the second valve 3372 is connected to the pressurizing line, with one oscillation cycle being 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.

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 for 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 is 100%.

For Examples 31 and 33, the solenoid valve opening degree for the liquid condition is 20%, and the solenoid valve opening degree for the gas condition is 99%, meaning that the valve was connected to the pressurized line for 20% of one oscillation cycle, and that gas G was being supplied for the entire oscillation cycle. For Example 32, the solenoid valve opening degree for the liquid condition and the solenoid valve opening degree for the gas condition are both 20%, meaning that the valve was connected to the pressurized line for 20% of one oscillation cycle, and that gas G was being supplied.

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. Then, 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, _D10 (μm), _D50 (μm), and _D90 (μm) of the bubbles were calculated. The results are shown in the corresponding columns in Table 4.

The results shown in Table 4 demonstrate that fine bubbles FB can be generated by using the fine-bubble generating device 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 generating devices of the first and second embodiments. However, Test 4 demonstrates that even when using a device 300 equipped with a liquid shaking mechanism 330 that does not have a pressure-reducing equipment, the liquid LQ can be drawn into the porous body 310 by gravity by positioning the container 331 containing the liquid LQ above the porous body 310.

As described above, this embodiment includes a container 331. The container 331 contains liquid LQ and is a supply source of liquid LQ to the porous body 310. The container 331 is located above the porous body 310. In an apparatus 300 configured as described above, the container 331, which is the supply source of liquid LQ, is located above the porous body 310, which generates microbubbles FB, so that gravity can be used to supply liquid LQ to the porous body 310. Therefore, the effects of the technology disclosed herein can be achieved even when a liquid oscillation mechanism 330 without a pressure reduction device is used. Furthermore, the effect of simplifying the apparatus by omitting the pressure reduction device can be achieved.

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

The technology disclosed here includes the manufacturing methods described in items 1 to 14 below.

[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;
2. The micro-bubble generating device according to claim 1, wherein the gas supply mechanism is configured to supply the gas from the outer surface side of the porous body.
[Item 3]
3. The fine-bubble generator according to claim 2, 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.
[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 fine-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 claims 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]
6. The fine-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:
8. The fine-bubble generator according to any one of items 4 to 7, wherein the liquid is sucked 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.
[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 generator according to any one of items 1 to 7, wherein the container is disposed 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]
Item 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]
Item 13. The fine bubble generator according to any one of items 1 to 12, wherein the porous body has an average pore diameter of less than 10 μm.
[Item 14]
Item 14. A method for generating fine bubbles in a liquid using the fine bubble generator according to any one of Items 1 to 13.

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 its spirit.

100 Micro-bubble generator 110 Porous body 120 Gas supply mechanism 121 Supply source 122 Regulator 123 Flow meter 124 Pressure gauge 125 Valve 126 Gas supply pipe 127 Piping 128 Sealing plug 130 Liquid shaking mechanism 131 Container 132 Pressure reduction equipment 133 Pressurization equipment 134 Regulator 135 Flow meter 136 Pressure gauge 137 Valve 138 Air storage chamber 139 Piping 91, 92 O-ring 200 Micro-bubble generator 210 Porous body 220 Gas supply mechanism 230 Liquid shaking mechanism 290 Support member 300 Micro-bubble generator 310 Porous body 320 Gas supply mechanism 330 Liquid shaking mechanism

Claims (13)

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. 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. 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 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 claim 1 , 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. 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. 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. 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. 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. 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. 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. 4. The micro-bubble generator according to claim 1 , wherein the liquid agitation mechanism is configured to adjust the average Reynolds number of the liquid during the agitation to 8000 or less. 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. A method for generating fine bubbles in a liquid using the fine bubble generator according to any one of claims 1 to 3 .