Fine bubble generation device and method for manufacturing fine bubble generation device

Abstract

Provided is a fine bubble generation device that comprises a bubble generator for mixing a liquid continuously supplied from a liquid supply source with a gas supplied from a gas supply means, generating fine bubbles, and ejecting a gas-liquid mixed liquid, which is a mixture of the fine bubbles and the liquid. The bubble generator includes: a confluence pipe formed as an independent component and having a liquid introduction part for supplying a liquid to the inside, a gas introduction part for supplying a gas to the inside, and a discharge part for generating fine bubbles and discharging a gas-liquid mixed liquid containing the fine bubbles; and a tubular internal component assembled and accommodated inside the confluence pipe, and having therein a flow passage that allows the liquid supplied from the liquid introduction part to flow to the discharge part. The internal component includes a downstream inner pipe formed as an independent component and disposed on the downstream side in the direction in which the liquid flows, and an upstream inner pipe formed as an independent component and disposed on the upstream side. The upstream inner pipe has a through-hole bored for introducing the gas supplied from the gas introduction part into the flow passage. The downstream inner pipe is coupled to the upstream inner pipe inside the confluence pipe. The flow passage extends between the liquid introduction part and the discharge part, and allows communication between the upstream inner pipe and the downstream inner pipe in a substantially coaxial manner.

Description

Microbubble generating device and method for manufacturing the same

[0001] The present invention relates to a microbubble generator for generating microbubbles in a liquid and a method for manufacturing the microbubble generator.

[0002] Fine bubbles with a diameter of less than 50 μm are commonly called "microbubbles" or "nanobubbles," and have properties that differ from larger bubbles such as those found in typical carbonated water (with a diameter of 1 mm or more). These fine bubbles have the following characteristics: they dissolve a large amount of gas into the liquid, thereby increasing the concentration of dissolved gases such as dissolved oxygen; their surfaces are negatively charged; they dissolve a large amount of gas such as air or oxygen; and they have various physiologically active effects. For this reason, this type of fine bubble-related technology is used in a variety of fields.

[0003] For example, in the agricultural field, spraying water containing microbubbled air onto the medium in soil or hydroponic cultivation can provide an optimal supply of oxygen to roots, which tend to be oxygen-deficient. By converting air into microbubbles, the amount of dissolved gas increases, and the smaller the bubble diameter, the less likely the bubbles are to burst, allowing them to be stably retained in the water. As a result, plants can be provided with water with a high concentration of dissolved oxygen, which leads to rapid growth and the production of high-quality crops. It has also been reported that increased dissolved oxygen concentration in water has the effect of suppressing anaerobic bacteria and controlling pests.

[0004] Furthermore, in the fields of beauty and health, it is known that when water containing microbubbled air is used to wash hair, scalp, and other skin, the microbubbles selectively adsorb oil and dirt adhering to the hair, etc., resulting in a high cleansing effect. It is said that the smaller the diameter of the microbubbles, the more easily they can penetrate into gaps in hair roots and hair tissue, resulting in a higher cleansing effect. It has also been recognized that the microbubbles stimulate sensory nerves, increasing blood flow and promoting blood circulation.

[0005] As an apparatus for generating such microbubbles, a device for generating microbubbles inside a tubular body is disclosed in Patent Document 1. The microbubble generating apparatus described in Patent Document 1 is an innovative device that realizes a high concentration of microbubbles in a liquid and generates microbubbles with small bubble diameters of several tens of micrometers or less.

[0006] International Publication No. 2019 / 212028

[0007] The conventional micro-bubble generator described in Patent Document 1 (see FIG. 19 ) generates micro-bubbles by mixing a liquid L continuously supplied from a liquid supply source with a gas G supplied from a gas supply means, and discharges a gas-liquid mixture M of the micro-bubbles and the liquid. In order to introduce pressurized gas G into the continuously supplied liquid L in this manner, the tubular body 130, which serves as the liquid flow path 70, needs to be able to withstand high air pressure around the through-holes 56 through which the gas G flows, and also needs to be able to withstand high water pressure inside the tubular body 130.

[0008] To meet such demands, in Patent Document 1, the tubular body 130 is integrally formed so that the axis of the flow path 70 is linear, and is fixed in close contact with the casing 110 by tightening a nut 120 around the through hole 56. However, such a structure requires many parts, and the manufacturing process is complicated.

[0009] The present invention has been made from this perspective, and its object is to provide a micro-bubble generator and a method for manufacturing a micro-bubble generator that can be manufactured at low cost while increasing product strength.

[0010] As a result of extensive research, the inventors have achieved a reduction in manufacturing costs by combining separately formed tubular bodies. In Patent Document 1, pressure resistance is ensured by integrally forming the tubular bodies, but the inventors have found that with the configuration of the tubular body (internal part) and casing (junction pipe) of the present invention, sufficient pressure resistance can be ensured even if the tubular body is divided.

[0011] According to the present invention, there is provided a micro-bubble generating device having a bubble generator that mixes a liquid continuously supplied from a liquid supply source with a gas supplied from a gas supply means, generates micro-bubbles, and discharges a gas-liquid mixture containing the micro-bubbles and the liquid. The bubble generator includes a junction pipe formed as an independent component, which has a liquid inlet for supplying the liquid into the device, a gas inlet for supplying the gas into the device, and an outlet for generating micro-bubbles and discharging the gas-liquid mixture containing the micro-bubbles. The junction pipe also includes a tubular internal part assembled and housed within the junction pipe and having an internal flow path for directing the liquid supplied from the liquid inlet to the outlet. The internal part includes a downstream internal pipe formed as an independent component and located downstream in the direction of liquid flow, and an upstream internal pipe formed as an independent component, which is located upstream. The upstream internal pipe has a through-hole formed in it for introducing the gas supplied from the gas inlet into the flow path. The downstream inner pipe is connected to the upstream inner pipe inside the confluence pipe, and the flow path connects the upstream inner pipe and the downstream inner pipe approximately coaxially between the liquid inlet section and the outlet section.

[0012] According to the present invention, a gas can be mixed with a liquid flowing through a flow path inside a bubble generator, thereby effectively discharging a gas-liquid mixture containing fine bubbles with nano-order bubble diameters. This bubble generator is configured with a junction pipe formed as an independent component serving as a casing, and internal components disposed inside the junction pipe. The internal components are assembled so that an upstream inner pipe and a downstream inner pipe formed as independent components are housed and connected inside the junction pipe. The assembly process of introducing a long tubular member into another tubular member is very complicated, but the division of the internal components facilitates assembly. Furthermore, connecting the upstream inner pipe and the downstream inner pipe inside the junction pipe ensures pressure resistance. Furthermore, since the bubble generator is configured with the internal components housed inside the junction pipe, product strength is improved and connection to piping is easy. Therefore, the micro-bubble generator not only achieves low manufacturing costs but also low maintenance costs.

[0013] Preferably, the downstream inner pipe has a downstream connecting portion connecting to the upstream inner pipe, a downstream end portion connected to the inside of the outlet portion, and a downstream reduced diameter portion whose inner diameter is reduced from the downstream connecting portion toward the downstream end, and the upstream inner pipe has an upstream reduced diameter portion whose inner diameter is reduced toward the downstream side, an expanded diameter portion whose inner diameter is expanded from the upstream reduced diameter portion toward the downstream side, and an upstream connecting portion connecting to the downstream connecting portion, and the through hole is arranged in the expanded diameter portion.

[0014] With this configuration, the flow path through which liquid continuously supplied from the liquid supply source flows within the bubble generator contracts in diameter in the upstream inner tube, then expands, contracts again in the downstream inner tube, and expands again at the outlet. Because the small-diameter portion of the flow path is in a reduced-pressure state due to the Venturi effect, the pressure difference with the gas pressurized above atmospheric pressure increases, causing a large amount of gas to be drawn into the flow path through the through-holes. In this invention, the flow velocity of the gas introduced into the flow path is increased, and the gas forcefully introduced into the flow path through the through-holes generates a strong swirling flow between the expanded-diameter portion and the downstream reduced-diameter portion (gas-liquid mixing portion). Therefore, a large amount of gas is introduced into the flow path, and the gas and liquid are reliably mixed within the flow path, resulting in a gas-liquid mixture containing a large amount of bubbles. Furthermore, the high flow velocity of the gas introduced into the flow path through the through-holes accelerates the flow velocity of the liquid (gas-liquid mixture) flowing through the flow path. Furthermore, in the present invention, the gas-liquid mixture that has passed through the upstream small-diameter section and the gas-liquid mixing section subsequently passes through the downstream small-diameter section. At this time, the downstream small-diameter section is reduced in pressure due to the Venturi effect, causing the bubbles in the gas-liquid mixture to expand, but the outlet section has a large inner diameter, which reduces the flow rate and increases the pressure. As a result, the expanded bubbles collapse and shrink in the outlet section, resulting in finer bubbles with smaller diameters.

[0015] Preferably, the minimum inner diameter of the downstream inner pipe is smaller than the minimum inner diameter of the upstream inner pipe, and the outlet portion has at least a portion larger than the minimum inner diameter of the downstream inner pipe. This allows the bubble diameter to be made smaller, and a gas-liquid mixture containing fine bubbles with a nano-order bubble diameter can be obtained. In this specification, fine bubbles with a nano-order bubble diameter refer to fine bubbles with a bubble diameter of less than 1 μm.

[0016] Preferably, the downstream end is fitted and connected to the outlet portion. This configuration provides a strong connection between the outlet portion and the downstream inner pipe, thereby improving the pressure resistance of the bubble generator. Furthermore, fitting allows for positioning of internal components, making it easier to assemble the components.

[0017] Preferably, the central axis of the flow path at the downstream reduced diameter section is coaxial with the central axis of the flow path at the upstream reduced diameter section, thereby maintaining a high flow velocity of the gas-liquid mixture flowing through the flow path and allowing the gas-liquid mixture discharged through the outlet section to have an appropriate liquid pressure.

[0018] Preferably, the downstream connecting part is connected to the upstream connecting part so that the inner surface of the downstream connecting part is substantially flush with the inner surface of the upstream connecting part. High pressure is generated in the liquid flowing through the flow path in the downstream connecting part and the upstream connecting part, and by making these inner surfaces flush, the pressure resistance of the micro-bubble generator is improved.

[0019] Preferably, the downstream connecting portion and the upstream connecting portion are connected at an end surface that is substantially perpendicular to the central axis of the flow path at the upstream reduced diameter portion. This configuration facilitates assembly of the internal components and also provides excellent pressure resistance.

[0020] Preferably, the through-holes penetrate the pipe wall of the expanded diameter section at an angle with respect to the central axis of the flow path in the upstream reduced diameter section. This configuration allows the gas to be introduced into the gas-liquid mixing section through the through-holes with greater force, generating a strong swirling flow in the gas-liquid mixing section, thereby producing a gas-liquid mixture containing a large amount of bubbles. Therefore, the gas-liquid mixture discharged by the present invention can contain fine bubbles at a higher concentration.

[0021] Preferably, the through holes are plural and uniformly arranged in the circumferential direction of the expanded diameter portion, whereby the pressurized gas is introduced into the gas-liquid mixing portion with greater force to generate a strong swirling flow, thereby ensuring that the pressurized gas and the liquid are mixed in the flow path and producing a gas-liquid mixture containing a large amount of bubbles.

[0022] Preferably, gaps are formed between the outer surfaces of the upstream reduced diameter section and the upstream expanded diameter section and the inner surface of the junction pipe, and the through holes extend from the gaps to the flow paths. This configuration allows the pressurized gas to be introduced into the gas-liquid mixing section more efficiently.

[0023] Preferably, the liquid inlet, the gas inlet, and the outlet have threads formed thereon for threadably engaging other piping. This configuration allows the piping to be connected to the bubble generator more efficiently and more firmly, and further improves the pressure resistance of the bubble generator.

[0024] Furthermore, the present invention provides a method for manufacturing a micro-bubble generator that mixes a liquid continuously supplied from a liquid supply source with a gas supplied from a gas supply means, generates micro-bubbles, and discharges a gas-liquid mixture of the micro-bubbles and the liquid. This manufacturing method includes the steps of: forming, as an independent part, a junction pipe having a liquid inlet portion for supplying liquid into the interior, a gas inlet portion for supplying gas into the interior, and an outlet portion for generating microbubbles and discharging a gas-liquid mixture containing the microbubbles; forming, as an independent part, a downstream inner pipe that is located downstream in the direction of liquid flow; forming, as an independent part, an upstream inner pipe that is located upstream in the direction of liquid flow and has a through hole formed therein for introducing the gas supplied from the gas inlet portion; and assembling and accommodating the downstream inner pipe and the upstream inner pipe that communicates with the downstream inner pipe inside the formed junction pipe so that the formed upstream inner pipe and the formed downstream inner pipe are arranged coaxially and form a flow path for flowing the liquid supplied from the liquid inlet portion to the outlet portion.

[0025] According to the present invention, a gas can be mixed with a liquid flowing through a flow path inside a bubble generator, thereby effectively discharging a gas-liquid mixture containing fine bubbles with nano-order bubble diameters. This bubble generator is configured with a junction pipe formed as an independent component serving as a casing, and internal components disposed inside the junction pipe. The internal components are assembled so that an upstream inner pipe and a downstream inner pipe formed as independent components are housed and connected inside the junction pipe. The assembly process of introducing a long tubular member into another tubular member is very complicated, but the division of the internal components facilitates assembly. Furthermore, connecting the upstream inner pipe and the downstream inner pipe inside the junction pipe ensures pressure resistance. Furthermore, since the bubble generator is configured with the internal components housed inside the junction pipe, product strength is improved and connection to piping is easy. Therefore, the micro-bubble generator not only achieves low manufacturing costs but also low maintenance costs.

[0026] Preferably, the downstream inner pipe forming process includes a process of forming a downstream inner pipe having a downstream connecting portion that connects to the upstream inner pipe, a downstream end portion that connects to the inside of the outlet portion, and a downstream reduced diameter portion whose inner diameter is reduced from the downstream connecting portion toward the downstream end, and the upstream inner pipe forming process includes a process of forming an upstream inner pipe having an upstream reduced diameter portion whose inner diameter is reduced toward the downstream side, an expanded diameter portion whose inner diameter is expanded from the upstream reduced diameter portion toward the downstream side, and an upstream connecting portion that connects to the downstream connecting portion, and arranging a through hole in the expanded diameter portion.

[0027] Preferably, the downstream inner pipe forming step or the upstream inner pipe forming step includes a step of forming the downstream inner pipe so that the minimum inner diameter of the downstream inner pipe is smaller than the minimum inner diameter of the upstream inner pipe, and the junction pipe forming step includes a step of forming the outlet portion so that it has at least a portion larger than the minimum inner diameter of the downstream inner pipe.

[0028] Preferably, the assembling step includes a step of fitting and connecting the downstream end of the downstream inner pipe to the outlet portion of the junction pipe.

[0029] Preferably, the assembling step includes a step of arranging a central axis of a flow channel in the downstream reduced diameter portion of the downstream inner pipe coaxially with a central axis of a flow channel in the upstream reduced diameter portion of the upstream inner pipe.

[0030] Preferably, the assembling step includes the step of connecting the upstream connecting portion so that an inner surface of the downstream connecting portion of the downstream inner pipe is substantially flush with an inner surface of the upstream connecting portion of the upstream inner pipe.

[0031] Preferably, the assembly process includes a step of connecting the downstream connecting portion of the downstream inner pipe and the upstream connecting portion of the upstream inner pipe at end faces that are approximately perpendicular to the central axis of the flow path in the upstream reduced diameter portion of the upstream inner pipe.

[0032] Preferably, the upstream inner pipe forming step includes the step of forming the upstream inner pipe so that the through hole penetrates the pipe wall of the expanded diameter portion at an angle with respect to a central axis of the flow path in the upstream reduced diameter portion.

[0033] Preferably, the upstream inner pipe forming step includes a step of forming a plurality of through holes that are uniformly arranged in the circumferential direction of the expanded diameter portion.

[0034] Preferably, the assembly process includes an assembly step in which a gap is formed between the outer surfaces of the upstream reduced diameter section and the expanded diameter section of the upstream inner pipe and the inner surface of the merging pipe, and a plurality of through holes extend from the gap to the flow path.

[0035] Preferably, the junction pipe forming step includes the step of forming threads for threadably coupling other pipes to the liquid inlet, gas inlet and outlet portions, respectively.

[0036] According to the present invention, a micro-bubble generator and a method for manufacturing a micro-bubble generator can be provided that have the following excellent effects. That is, in the micro-bubble generator, the bubble generator accommodates an upstream inner pipe and a downstream inner pipe formed as independent components inside a junction pipe formed as independent components, and the upstream inner pipe and the downstream inner pipe are assembled so as to be connected inside the junction pipe, which makes assembly easy and has excellent pressure resistance. In addition, a gas-liquid mixture containing microbubbles with bubble diameters on the nano-order level can be efficiently discharged.

[0037] FIG. 1 is a diagram showing the configuration of a fine-bubble generating device according to one embodiment of the present invention. FIG. 2 is a perspective view showing an outline of a bubble generator constituting the fine-bubble generating device shown in FIG. 1. FIG. 3 is an exploded perspective view of the bubble generator shown in FIG. 2. FIG. 4 is a perspective view showing an outline of a portion of the junction pipe shown in FIG. 3. FIG. 5 is a front view showing the configuration of the junction pipe shown in FIG. 4. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 4. FIG. 8 is a perspective view showing an outline of a portion of the downstream inner pipe shown in FIG. 3. FIG. 9 is a front view showing the configuration of the downstream inner pipe shown in FIG. 8. FIG. 10 is a bottom view showing the configuration of the downstream inner pipe shown in FIG. 8. FIG. 11 is a perspective view showing an outline of a portion of the upstream inner pipe shown in FIG. 3. FIG. 12 is a front view showing the configuration of the upstream inner pipe shown in FIG. 11. FIG. 13 is a bottom view showing the configuration of the upstream inner pipe shown in FIG. 11. FIG. 14 is a front view showing the configuration of the bubble generator shown in FIG. 2. Figure 15 is a bottom view showing the configuration of the bubble generator shown in Figure 2. Figure 16 is a cross-sectional view taken along line XVI-XVI shown in Figure 2. Figure 17 is a cross-sectional view taken along line XVII-XVII shown in Figure 2. Figure 18 is a partially enlarged cross-sectional view showing the operation of the fine-bubble generator shown in Figure 1. Figure 19 is a partially enlarged cross-sectional view showing an outline of a conventional fine-bubble generator.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although the description will be made with reference to the drawings as necessary, the contents shown in the drawings are merely shown schematically and exemplarily to facilitate understanding of the present invention, and the appearance and dimensional ratios may differ from the actual product. Furthermore, the present invention will be described in detail below with reference to the embodiments, but is not limited to these embodiments.

[0039] (Overall Configuration of the Micro-Bubble Generator) First, the overall configuration of the micro-bubble generator of this embodiment will be described. FIG. 1 is a diagram showing the state of use of a micro-bubble generator 1 according to one embodiment of the present invention, which is used in a beauty salon or the like. As shown in FIG. 1, the micro-bubble generator 1 has a bubble generator 2 that generates micro-bubbles and delivers a gas-liquid mixture M containing micro-bubbles. The bubble generator 2 mixes a liquid L and a gas G to generate micro-bubbles therein. As shown in FIG. 1, the bubble generator 2 is connected via piping 4 to a water faucet 7, such as a water supply, as an example of a liquid supply source, so that the liquid L is continuously supplied. The bubble generator 2 is also connected via piping 5 to a compressor 8, as an example of a gas supply means, so that pressurized gas G is supplied. The bubble generator 2 is also connected via piping 6 to a discharger, such as a shower head 3, so that the gas-liquid mixture M containing micro-bubbles can be continuously discharged from the shower head 3.

[0040] 18 is a partially enlarged cross-sectional view showing the operation of the micro-bubble generator 1 of this embodiment. As shown in FIG. 18 , the bubble generator 2 is assembled such that a downstream inner pipe 30 and an upstream inner pipe 50, each formed as an independent component, are housed inside a cylindrical junction pipe 10 formed as an independent component, and these inner pipes form a flow path 70 through which a liquid L or a gas G flows. One upstream end of the junction pipe 10 is provided with a liquid inlet 20, which is provided with a liquid supply port 21 connected to a water faucet via a pipe 4. On the other hand, one downstream end of the junction pipe 10 is provided with an outlet 26, which is provided with an outlet 27 for discharging the gas-liquid mixture M generated inside the bubble generator 2. The main body 12 connecting the liquid inlet 20 and the outlet 26 is provided with a gas inlet 14 having a gas supply port 15. The gas L is supplied from the gas supply port 15, which is connected to a compressor 8 via a pipe 5, into the junction pipe 10.

[0041] As shown in FIG. 18 , the space inside the internal components (the downstream inner tube 30 and the upstream inner tube 50) constitutes a flow path 70. The flow path 70 is connected from the upstream side of the upstream inner tube 50 to the downstream side of the downstream inner tube 30, with the axis Cz along the Z-axis as its central axis. That is, the center of a cross section of the flow path 70 perpendicular to the Z-axis is configured to be a substantially straight line. This prevents backflow or a decrease in flow velocity of the liquid L or gas-liquid mixture M flowing through the flow path 70 in the flow direction F, thereby maintaining a smooth flow of the liquid L or the like within the flow path 70. The flow path 70 includes a first flow path portion 71 that increases the flow velocity and a second flow path portion 72 (gas-liquid mixing section) located downstream thereof that mixes the liquid G and the gas G. In this specification, downstream refers to the direction in which the liquid L and the gas-liquid mixture M flow, and in the bubble generator 2, refers to the side where the outlet 27 in the Z-axis direction is located. Further, the upstream side refers to the source from which the liquid L and the gas-liquid mixture liquid M flow, and in the bubble generator 2, refers to the side where the liquid supply port 21 in the Z-axis direction is located.

[0042] As shown in FIG. 18 , the first flow path portion 71 narrows downstream and connects to the second flow path portion 72. Therefore, the liquid L flowing through the first flow path portion 71 is continuously supplied to the second flow path portion while increasing its flow velocity. The second flow path portion 72 also expands in diameter downstream from the minimum diameter φ7 portion of the first flow path portion 71. A through-hole 56 is provided downstream near the minimum inner diameter φ7 portion of the first flow path portion 71 and connects to the second flow path portion 72 from the outside of the upstream inner pipe 50. Gas G supplied from the gas introduction portion 14 passes through the through-hole 56 and is supplied from the outside of the upstream inner pipe 50 to the second flow path portion 72. Due to the Venturi effect, the liquid L is in a reduced pressure state near the minimum inner diameter φ7 portion. This allows the gas G to be forcefully introduced from the through-hole 56 into the second flow path portion 72, subsequently generating a strong swirling flow in the first gas-liquid mixing section 24. Therefore, the gas G and the liquid L are reliably mixed in the second flow path portion 72, and a gas-liquid mixture M containing a large amount of bubbles is obtained.

[0043] The second flow path portion 72 narrows further downstream, and the gas-liquid mixture M is reduced in pressure due to the Venturi effect. The most downstream portion of the second flow path portion 72 has a minimum inner diameter φ5 and is connected to the generation portion 29. The minimum diameter φ5 of the second flow path portion 72 is not particularly limited, but is preferably smaller than the minimum diameter φ7 of the first flow path portion 71. This configuration allows the gas-liquid mixture M to be supplied to the generation portion 29 with force. Furthermore, the inner diameter φ2 of the generation portion 29 is rapidly increased compared to the minimum diameter φ5 of the second flow path portion 72. This increases the pressure difference between the second flow path portion 72 and the generation portion 29, accelerating the collapse and contraction of bubbles in the gas-liquid mixture M in the generation portion 29 and generating fine bubbles.

[0044] (Overall Configuration of the Bubble Generator) Next, the configuration of the bubble generator 2 will be described in detail. FIG. 2 is a perspective view schematically illustrating the configuration of the bubble generator 2. As shown in FIG. 2, the bubble generator 2 has a liquid introduction section 20 that supplies liquid to the interior and an outlet section 26 that outlets the gas-liquid mixture to the outside. The bubble generator 2 also has a main body 12 that extends along the Z-axis direction and connects the liquid introduction section 20 to the introduction section 20. The bubble generator 2 has a cylindrical structure in which the liquid introduction section 20 has a liquid supply port 21 and the outlet section 26 has a discharge port 27, and these are connected to each other with an axis Cz along the Z-axis direction as the central axis. The bubble generator 2 also has a gas introduction section 14 that supplies gas to the interior. The gas introduction section 14 has a gas supply port 15 that is connected to the interior with an axis Cy along the Y-axis direction as the central axis, on a first surface 11b1 of the outer surface 11b of the main body 12. In the drawings, the X-axis, Y-axis, and Z-axis are perpendicular to one another.

[0045] 3 is an exploded perspective view showing the configuration of the bubble generator 2. As shown in FIG. 3, the bubble generator 2 includes a junction pipe 10 having a cylindrical main body 12, and a downstream inner pipe 30 and an upstream inner pipe 50 housed inside the main body 12 with an axis Cz as the central axis. The downstream inner pipe 30 has a downstream end 35 fitted into the outlet portion 26 inside the main body 12 for connection. The upstream inner pipe 50 is disposed upstream of the downstream inner pipe 30 inside the main body 12, and a connection end face 58 of the upstream connecting portion 57 is connected to the connection end face 33 of the downstream connecting portion 32 of the downstream inner pipe 30. In this embodiment, the junction pipe 10 functions as a casing that completely houses the downstream inner pipe 30 and the upstream inner pipe 50 therein.

[0046] The materials for the junction pipe 10, the downstream inner pipe 30, and the upstream inner pipe 50 are not particularly limited, but are preferably materials that are resistant to corrosion by tap water. Furthermore, the junction pipe 10, the downstream inner pipe 30, and the upstream inner pipe 50 are preferably formed from a material that is strong enough to withstand the introduction of pressurized gas into the liquid flowing therethrough. Examples of materials for the junction pipe 10, the downstream inner pipe 30, and the upstream inner pipe 50 include rigid PVC (polyvinyl chloride resin), aluminum, and stainless steel (SUS), with stainless steel being particularly preferred. The junction pipe 10, the downstream inner pipe 30, and the upstream inner pipe 50 are preferably integrally molded.

[0047] Figure 4 is a perspective view showing the configuration of the junction pipe 10. The junction pipe 10 has a liquid inlet 20 with a liquid supply port 21 and an outlet 26 with an outlet 27. The junction pipe 10 also has a main body 12 that connects the liquid inlet 20 and the inlet 26. The junction pipe 10 is tubular, with an inner surface 11a, and is connected from the liquid supply port 21 to the outlet 27. In the main body 12, a gas supply port 15 of a gas inlet 14 that supplies gas to the interior penetrates a pipe wall 10b (see Figure 7).

[0048] 4, the outer surface 11b of the main body 12 and the liquid introduction portion 20 of the junction pipe 10 has a first surface 11b1, a second surface 11b2, a third surface 11b3, a fourth surface 11b4, a fifth surface 11b5, and a sixth surface 11b6, and has an outer shape of a substantially regular hexagonal prism that is long in the Z-axis direction from the first end surface 11b1 to the second end surface 11b2 (see FIG. 7). Therefore, the junction pipe 10 can be easily held with a wrench, hexagonal wrench, or the like.

[0049] As shown in FIG. 4 , a thread 22 is formed on the inner peripheral surface of the liquid introduction portion 20, allowing it to be threadedly engaged with the pipe 4 shown in FIG. 1 . The outlet portion 26 of the junction pipe 10 has a thread 28 on its outer peripheral surface, protruding from the second end face 11 b 2 of the regular hexagonal column-shaped portion to the tip face 11 c 3 , allowing it to be threadedly engaged with the pipe 6 shown in FIG. 1 . A thread 16 is formed on the inner peripheral surface of the gas introduction portion 12, allowing it to be threadedly engaged with the pipe 5 shown in FIG. 1 . This facilitates the connection work with the pipes 4, 5, 6, etc. shown in FIG. 1 . In this embodiment, the end in the Z-axis direction is chamfered to make it easier to hold with a hexagonal wrench (see FIG. 5 ).

[0050] The junction pipe 10 has a depth D0 in the Y-axis direction (see FIG. 7), a width W0 in the X-axis direction (see FIG. 5), and a length H0 in the Z-axis direction (see FIG. 5). The depth D0, width W0, and length H0 are not particularly limited. For example, the depth D0 may be 20 mm to 50 mm, and is preferably 22 mm to 30 mm from the viewpoints of reducing manufacturing costs, compactness, and product strength. The depth D0 preferably corresponds to an existing wrench size. The width W0 preferably corresponds to the depth D0 so that the external shape in a plan view is a regular hexagon, and may be 23 mm to 58 mm. The length H0 may be 40 mm to 170 mm, and is preferably 45 mm to 65 mm from the viewpoints of reducing manufacturing costs, compactness, and product strength. Furthermore, when the pressure of the liquid and pressurized gas supplied to the interior is high, the depth D0, width W0, and length H0 may be further increased depending on the pressure.

[0051] The length H1 of the liquid introduction portion 20 from the first end surface 11b1 to the stopper surface 11a0 shown in Figures 5 and 6 is not particularly limited and may be 7 mm to 25 mm. From the viewpoints of reducing manufacturing costs, making the product compact, and ensuring product strength, the length H1 is preferably 8 mm to 12 mm. Furthermore, the length H2 of the main body portion 12 from the stopper surface 11a0 to the second end surface 11b2 is not particularly limited and may be 20 mm to 120 mm. From the viewpoints of reducing manufacturing costs, making the product compact, and ensuring product strength, the length H2 is preferably 30 mm to 40 mm.

[0052] As shown in FIG. 5 , in this embodiment, the tip surface 11c3 of the outlet portion 26 protrudes a length H3 in the Z-axis direction from the second end surface 11c2 of the substantially hexagonal columnar portion. The protruding length H3 of the outlet portion 26 is not particularly limited and may be 7 mm to 25 mm. From the viewpoints of reducing manufacturing costs, making the product more compact, improving product strength, and effectively generating fine bubbles, the length H3 is preferably 8 mm to 12 mm. Note that, when the pressure of the liquid and the pressure of the pressurized gas supplied to the interior are high, the lengths H1, H2, and H3 may be further increased according to the depth D0, width W0, and length H0.

[0053] As shown in FIG. 6 , the junction pipe 10 has a main body portion inner surface 11a1 and an outlet portion inner surface 11a3 that form a cylindrical interior 10a extending along the Z-axis (see FIG. 7 ). As shown in FIGS. 6 and 7 , in this embodiment, the inner diameter φ2 of the outlet portion 26 is smaller than the inner diameter φ1 of the interior 10a of the main body portion 12, but the inner diameters φ1 and φ2 are not particularly limited. However, the inner diameter φ1 of the main body portion 12 is preferably large enough to accommodate internal components (the downstream inner pipe 30 and the upstream inner pipe 50) in the interior 10a of the junction pipe 10 and to allow the downstream inner pipe 30 and the upstream inner pipe 50 to fit within the interior 10a of the junction pipe 10. For example, the inner diameter φ1 may be 10 mm to 25 mm, and is preferably 15 mm to 20 mm. The inner diameter φ2 of the outlet portion 26 is preferably large enough to allow the downstream end 35 of the downstream inner pipe 30 to fit within the interior 10a of the junction pipe 10. For example, the inner diameter φ2 may be 8 mm to 20 mm, and preferably 12 mm to 18 mm. Furthermore, the wall thickness D1 of the pipe wall 10b of the junction pipe 10 shown in FIG. 7 is not particularly limited. For example, the wall thickness D1 of the pipe wall 10b may be 2 mm to 12 mm. From the viewpoints of reducing manufacturing costs, making the product more compact, and increasing product strength, the wall thickness D1 of the pipe wall 10b is preferably 3 mm or greater. Note that, in cases where the pressure of the liquid and the pressure of the pressurized gas supplied to the interior are high, the inner diameters φ1 and φ2 and the wall thickness D1 may be further increased according to the depth D0, width W0, and length H0.

[0054] As shown in Figure 6, the main body inner surface 11a1 is connected to a stopper surface 11a0 that is approximately perpendicular to the main body inner surface 11a1. The main body inner surface 11a1 and the outlet inner surface 11a3 are connected to each other by a positioning surface 11a2 that is perpendicular to the main body inner surface 11a1 and the outlet inner surface 11a3. The stopper surface 11a0 determines the downstream position at which the above-mentioned piping 4 can be inserted. A step surface 38 (see Figure 9) of the downstream inner pipe 30, which will be described later, abuts against the positioning surface 11a2, enabling the downstream inner pipe 30 to be positioned.

[0055] As shown in Fig. 8, the downstream inner pipe 30 has a pipe wall 31 with an outer surface 31b and an inner surface 31a extending generally along the Z axis, and has a generally circular tubular outer shape with the axis Cz as its central axis. Also, as shown in Fig. 9, the downstream inner pipe 30 generally has a downstream end portion 35 located downstream, a downstream connecting portion 32 located upstream, and a downstream reduced diameter portion 34 located between the downstream end portion 35 and the downstream connecting portion 32.

[0056] As shown in Figure 9, the first portion 31a1, which is the inner surface 31a at the downstream connecting portion 32, extends a length H4 in the Z-axis direction. The third portion 31a3, which is the inner surface 31a at the downstream end 35, extends a length H6 in the Z-axis direction. The inner diameter φ5 at the downstream end 35 of the downstream inner pipe 30 is smaller than the inner diameter φ6 at the downstream connecting portion 32 of the downstream inner pipe 30. The downstream reduced diameter portion 34 has a length H5 in the Z-axis direction, and the second portion 31a2, which is the inner surface 31a at the downstream reduced diameter portion 34, is continuously connected in an arc from the first portion 31a to the third portion 31a3. The inner diameter of the downstream reduced diameter portion 34 of the downstream inner pipe 30 decreases from the downstream connecting portion 32 toward the downstream end 35.

[0057] Although there are no particular limitations on the thickness D2 of the pipe wall 31 at the downstream connecting portion 32 shown in Fig. 9, it is preferably 2 mm or more from the viewpoints of ease of assembly and product strength. The diameter φ3 of the downstream inner pipe 30 shown in Figs. 9 and 10 is preferably designed to be the same diameter as or smaller than the inner diameter φ1 of the interior 10a of the junction pipe 10 so that the downstream inner pipe 30 fits into the junction pipe 10 (see Fig. 7).

[0058] As shown in FIG. 9 , the downstream inner pipe 30 has a connecting end surface 33 of the downstream connecting portion 32 that is perpendicular to the Z-axis direction, and a tip portion 36 of the downstream end portion 35 that is positioned inside the outlet portion 26 (see FIG. 6 ) and protrudes to connect to it. The tip portion 36 has a tip outer surface 37 that is formed along the outlet portion inner surface 11 a 3 and an end surface 39 that is perpendicular to the tip outer surface 37. The outer surface 31 b and the tip outer surface 37 are connected by a step surface 38 that is perpendicular to each other. The step surface 38 of the downstream end portion 35 abuts against the positioning surface 11 a 2 of the junction pipe 10. Furthermore, to facilitate insertion of the downstream inner pipe 30 into the interior 10 a of the junction pipe 10 through the liquid supply port 21, the corner where the step surface 38 intersects with the outer surface 31 b is preferably chamfered.

[0059] 9 and 10 , the diameter φ4 of the tip portion 36 is preferably designed to be equal to or smaller than the inner diameter φ2 of the interior 10a of the outlet portion 26 (see FIG. 4 ) so that the tip portion 36 of the downstream end portion 35 can fit into the outlet portion 26. The protruding length H12 of the tip portion 36 is not particularly limited, but is preferably 0.5 mm or greater from the viewpoint of fitting and fixing the tip portion 36 into the outlet portion 26. Furthermore, the tip portion 36 of the downstream end portion 35 preferably has a chamfered corner where the tip outer surface 37 and the end face 39 intersect to facilitate fitting into the outlet portion 26.

[0060] The inner diameter φ6 of the downstream connecting portion 32 shown in FIG. 9 , the inner diameter φ5 of the downstream end portion 35 of the downstream inner tube 30, and the radius of the arc described by the second portion 31a2 of the inner surface 31a are not particularly limited. From the viewpoints of ease of manufacturing, compactness of the product, and satisfactory mixing of the gas with the liquid, the inner diameter φ6 is preferably, for example, 8 mm to 20 mm, and more preferably 10 mm to 15 mm. From the viewpoints of ease of manufacturing, compactness of the product, and satisfactory mixing of the gas with the liquid, the inner diameter φ5 is preferably, for example, 3 mm to 15 mm, and more preferably 5 mm to 8 mm. The radius of the arc described by the second portion 31a2 shown in FIG. 9 may be 15 mm to 20 mm, and preferably 16 mm to 18 mm, from the viewpoints of ease of manufacturing, compactness of the product, and satisfactory mixing of the gas with the liquid. The second portion 31a2 of the inner surface 31a may be connected linearly from the first portion 31a to the third portion 31a3 without forming an arc. Furthermore, if the pressure of the liquid supplied to the interior and the pressure of the pressurized gas are high, the radius of the arc described by the inner diameters φ6, φ5 and the second portion 31a2 may also be made larger according to the depth D0, width W0 and length H0.

[0061] The length H4 of the downstream connecting portion 32, the length H5 of the downstream reduced diameter portion 34, and the length H6 of the downstream end portion 35 shown in FIG. 9 are not particularly limited. However, if the entire downstream inner pipe 30 is too long in the Z-axis direction, it becomes difficult to insert the downstream inner pipe 30 into the junction pipe 10 and assemble it. Furthermore, if the entire downstream inner pipe 30 is too short, the gas-liquid mixing section (second flow path portion 72) where gas-liquid mixing occurs will not be sufficiently secured. Therefore, the lengths H4, H5, and H6 can be appropriately designed taking these points into consideration. For example, the length H4 may be 1 mm to 15 mm, the length H5 may be 7 mm to 20 mm, and the length H6 may be 2 mm to 15 mm. Preferably, the length H4 is 1 mm to 5 mm, the length H5 is 5 mm to 12 mm, and the length H6 is 2 mm to 5 mm. If the pressure of the liquid and the pressure of the pressurized gas supplied to the interior are high, the lengths H4, H5, H6, H12, and D2 may also be increased according to the depth D0, width W0, and length H0.

[0062] As shown in Fig. 11 , the upstream inner pipe 50 has a generally circular tubular shape with the axis Cz as its central axis. As shown in Fig. 12 , the upstream inner pipe 50 has a generally constant thickness D3 from the outer surface 51b to the inner surface 51a of the pipe wall 51, and the inner diameter φ7 at the constricted portion 60 is smaller than the inner diameter φ8 at both ends in the Z-axis direction, resulting in a constricted outer shape that is the smallest inner diameter of the upstream inner pipe 50. The thickness D3 of the pipe wall 51 is not particularly limited, but is preferably equal to the thickness D2 of the pipe wall 31 at the downstream connecting portion 32 of the downstream inner pipe 30 (see Fig. 9 ). The diameters of the upstream inner pipe 50 at both ends in the Z-axis direction are preferably equal to the diameter φ3 of the downstream inner pipe 30, and are preferably designed to be equal to or smaller than the inner diameter φ1 of the inner portion 10a of the confluence pipe 10 (see Fig. 7 ) so that the upstream inner pipe 50 fits into the confluence pipe 10. The upstream inner pipe 50 generally has an upstream end portion 52 , an upstream reduced diameter portion 54 , an expanded diameter portion 55 , and an upstream connecting portion 57 .

[0063] As shown in Figure 12, the first portion 51a1, which is the inner surface 51a at the upstream end 52, extends along the Z-axis for a length H7. The fourth portion 51a4, which is the inner surface 51a at the upstream connecting portion 57, extends in the Z-axis direction for a length H10. The upstream reduced diameter portion 54 has a length H8 in the Z-axis direction, and the second portion 51a2, which is the inner surface 51a at the upstream reduced diameter portion 54, continues from the first portion 51a1 toward the constricted portion 60, which has a minimum inner diameter of φ7. The inner diameter of the upstream reduced diameter portion 54 of the upstream inner pipe 50 decreases from the upstream end 52 toward the constricted portion 60. The expanded diameter portion 55 has a length H9 in the Z-axis direction, and the third portion 51a3, which is the inner surface 51a at the expanded diameter portion 55, continues from the constricted portion 60 toward the upstream connecting portion 57. The inner diameter of the expanded diameter portion 55 of the upstream inner pipe 50 increases from the constricted portion 60 toward the upstream connecting portion 57 .

[0064] As shown in FIG. 13 , multiple through holes 56 are drilled in the upstream inner pipe 50. Each through hole 56 is rotationally symmetric about the axis Cz, and is evenly spaced in the expanded diameter section 55, rotated by 90°. As shown in FIG. 12 , each through hole 56 penetrates the pipe wall 51 from the outer surface 51b of the expanded diameter section 55 toward the third portion 51a3 of the inner surface, with its central axis Cg inclined at an angle θ1 with respect to the axis Cz. Each through hole 56 is formed so that its center O1 on the outer surface 51b is located downstream of a position C0 on the Z axis of the constricted portion 60 by a distance H11 in the Z-axis direction. The length H11 may be, for example, 5 mm or less. The inner diameter φ9 of each through hole 56 is not particularly limited, but is preferably smaller than the minimum inner diameter φ7 of the upstream inner pipe 50, and may be, for example, 2 mm to 7 mm. The angle θ1 is not particularly limited, but is preferably 20° to 50°.

[0065] 12 , in the upstream inner pipe 50, the connecting end face 58 of the upstream connecting portion 57 and the end face 53 of the upstream end portion 52 are perpendicular to the Z-axis direction. The connecting end face 58 of the upstream connecting portion 57 abuts the connecting end face 33 of the downstream connecting portion 32. The end face 53 of the upstream end portion 52 and the outer surface 51 b intersect approximately perpendicularly. On the other hand, to make it easier to insert the upstream inner pipe 50 into the interior 10 a from the liquid supply port 21 of the junction pipe 10, it is preferable that the corner where the connecting end face 58 of the upstream connecting portion 57 and the outer surface 51 b intersect is chamfered.

[0066] The inner diameter φ8 of the upstream connecting portion 57 of the upstream inner pipe 50 and the inner diameter φ8 of the upstream end portion 52 of the upstream inner pipe 50 shown in FIG. 12 are not particularly limited. The inner diameter φ8 of the upstream end portion 52 can be designed to be the same value as the inner diameter φ6 of the downstream connecting portion 32, but is preferably equal to the inner diameter φ6 of the downstream connecting portion 32 (see FIG. 9 ). With this configuration, when the upstream connecting portion 57 is connected to the downstream connecting portion 32 inside the merging pipe 10, the fourth portion 51a4, which is the inner surface of the upstream connecting portion 57, and the first portion 31a1, which is the inner surface of the downstream connecting portion 32, are approximately flush with each other. The term "approximately flush" refers to a surface that is smooth enough not to reduce the flow rate of the liquid flowing through the internal components, and may include some unevenness. In this specification, the term "approximately flush" also includes a case where the fourth portion 51a4, which is the inner surface of the upstream connecting portion 57, and the first portion 31a1, which is the inner surface of the downstream connecting portion 32, have a difference of 0.5 mm or less.

[0067] 12 is preferably larger than the inner diameter φ5 (see FIG. 9) at the downstream end 35 of the downstream inner tube 30. For example, from the viewpoints of ease of manufacture, product miniaturization, and satisfactory mixing of gas with liquid, the inner diameter φ7 is preferably 5 mm to 20 mm, and more preferably 6 mm to 10 mm.

[0068] The length H7 of the upstream end 52, the length H8 of the upstream reduced diameter portion 54, the length H9 of the expanded diameter portion 55, and the length H10 of the upstream end 37 shown in FIG. 12 are not particularly limited. However, if the entire upstream inner pipe 50 is too long in the Z-axis direction, it becomes difficult to insert the upstream inner pipe 50 into the junction pipe 10 and assemble it. Furthermore, if the upstream inner pipe 50 is too long compared to the outer diameter of the constricted portion 60, the strength of the periphery of the constricted portion 60 decreases. From these perspectives, the lengths H7, H8, H9, and H10 can be designed appropriately. For example, the length H7 may be 1 mm to 15 mm, the length H8 may be 4 mm to 20 mm, the length H9 may be 4 mm to 20 mm, and the length H10 may be 1 mm to 15 mm. Preferably, the length H7 is 1 mm to 5 mm, the length H8 is 7 mm to 12 mm, the length H9 is 7 mm to 12 mm, and the length H10 is 1 mm to 5 mm. In addition, if the pressure of the liquid and the pressure of the pressurized gas supplied to the interior are high, the lengths H7, H8, H9, H10, H11, and D3 may also be further increased according to the depth D0, width W0, and length H0.

[0069] Fig. 14 is a front view showing the configuration of the bubble generator 2 in a state in which the junction pipe 10 and the internal components (the downstream inner pipe 30 and the upstream inner pipe 50) are assembled. As shown in Fig. 14, the minimum inner diameter φ0 of the liquid introduction section 20 is larger than the diameter φ3 of the internal components. Therefore, the internal components can be inserted through the liquid supply port 21 of the liquid introduction section 20. When assembling the bubble generator 2, first, the downstream inner pipe 30 is inserted through the liquid supply port 21, and then the upstream inner pipe 50 is inserted, thereby assembling the bubble generator 2 in which the downstream inner pipe 30 and the upstream inner pipe 50 are housed inside the junction pipe 10.

[0070] 17 is a cross-sectional view of the bubble generator 2 in a state where the junction pipe 10 and internal components (the downstream inner pipe 30 and the upstream inner pipe 50) are assembled. The liquid inlet 20, the gas inlet 14, and the outlet 26 are threaded, and the fine-bubble generator 1 can be assembled simply by connecting the liquid inlet 20 and the faucet 7 with a pipe 4, connecting the gas inlet 14 and the compressor 8 with a pipe 5, and connecting the outlet 26 to the shower head 7. Such a fine-bubble generator 1 not only has low manufacturing costs, but also enables reduced maintenance costs.

[0071] As shown in FIG. 17 , the inner diameter φ2 at the outlet portion 26 is larger than the minimum inner diameter φ5 at the downstream inner tube 30. Furthermore, the end face 39 of the tip portion 36 is perpendicular to the axis Cz of the flow path 70. That is, the diameter φ5 at the downstream side of the flow path 70 suddenly widens to a diameter φ2 at the generation portion 29. Furthermore, the location of the minimum inner diameter φ5 at the downstream inner tube 30 is the most downstream tip portion 36, and the minimum inner diameter φ5 is smaller than the minimum inner diameter φ7 of the upstream inner tube 50. Therefore, the gas-liquid mixture has the highest flow velocity and is in a reduced pressure state when passing through the tip portion 36 of the downstream inner tube 30 in the flow path 70. Therefore, the gas-liquid mixture continuously flowing through the flow path 70 is suddenly pressurized at the generation portion 29 of the outlet portion 26, which effectively crushes the bubbles contained in the liquid, thereby producing a gas-liquid mixture containing fine bubbles with diameters on the nano-order level (less than 1 μm).

[0072] 17 , the internal part has an upstream-side reduced diameter section 54, and a first flow path portion 71 at the most upstream side of the flow path 70, which has a diameter of φ8, is reduced to a minimum diameter of φ7. The internal part also has an expanded diameter section 55, and a second flow path portion 72 of the flow path 70 is expanded to a diameter of φ6. Therefore, in the flow path 70 around the constricted portion 60, the liquid accelerates and enters a reduced pressure state, making it possible to efficiently introduce gas into the second flow path portion 72 of the liquid flow path 70.

[0073] As shown in FIG. 14 , the downstream inner pipe 30 and the upstream inner pipe 50 are arranged side by side in the Z-axis direction, with the same central axis Cz, inside the junction pipe 10. As shown in FIG. 15 , a flow path 70 in the internal component passes through the outlet 27 of the outlet portion 26, with the same central axis Cz. This maintains a high flow rate of the gas-liquid mixture flowing through the flow path 70, and ensures that the gas-liquid mixture discharged through the outlet portion 26 has an appropriate liquid pressure. As shown in FIG. 17 , the junction pipe 10 and the internal component are preferably designed so that the constricted portion 60 of the upstream inner pipe 50 is positioned in the XY plane having the central axis Cy of the gas supply port 15. This configuration enables the gas to be efficiently introduced into the liquid flow path.

[0074] FIG. 16 is a cross-sectional view of the gas supply port 15 taken along the XY plane having the central axis Cy. As shown in FIG. 16 , a gap 80 is formed between the outer surface 51b of the upstream inner pipe 50 at the constricted portion 60 and the inner surface 11a1 of the main body of the junction pipe 10, surrounding the outer surface 51b in the circumferential direction. Furthermore, all of the through holes 56 extend from the gap 80 to the flow path 70. Therefore, gas supplied from the gas supply port 15 to the inside of the junction pipe 10 is supplied to all of the through holes 56 through the gap 80 and then to the flow path 70 via all of the through holes 56. The through holes 56 are evenly spaced, and the central axes Cg of the through holes 56 are inclined relative to the central axis Cz of the flow path, penetrating the pipe wall 51 of the expanded diameter portion 55 (see FIG. 12 ). This configuration allows the gas introduced into the flow path 70 to be introduced more forcefully through the through holes 56. By supplying gas from all of the through-holes 56 in this manner, a strong swirling flow is effectively generated in the second flow path portion 72, thereby obtaining a gas-liquid mixture containing a large amount of bubbles. Therefore, in this embodiment, the gas-liquid mixture discharged by the micro-bubble generator can contain a higher concentration of micro-bubbles.

[0075] 17, the downstream inner pipe 30 is arranged so that the stepped surface 38 abuts against the positioning surface 11a2 of the junction pipe 10. The upstream inner pipe 50 is arranged so that the end surface 53 of the upstream end 52 is flush with the stopper surface 11a0 of the junction pipe 10. With this configuration, the internal parts (the upstream inner pipe 50 and the downstream inner pipe 30) are completely housed in the junction pipe 10, which serves as a casing. Therefore, when the bubble generator 2 is connected to the pipes 4, 5, and 6, the internal parts are no longer exposed to the outside of the junction pipe 10, and the product strength of the bubble generator 2 is significantly improved (see FIG. 18).

[0076] Furthermore, as shown in Fig. 17 , the end face 53 of the upstream end 52 is substantially flush with the stopper surface 11a0 of the junction pipe 10, which makes it difficult for liquid to enter between the junction pipe 10 and the upstream end 52, improving product strength. As shown in Fig. 18 , if the piping 4 and the junction pipe 10 are threaded together so that the end of the piping 4 abuts against the end face 53 and the stopper surface 11a0, respectively, the strong connection achieved by threading the piping 4 and the junction pipe 10 can further securely house the internal components in the junction pipe 10. Furthermore, as shown in Fig. 17 , the connecting end face 58 of the upstream inner pipe 50 is connected to the connecting end face 33 of the downstream inner pipe 30 at an internal position downstream of the gas supply port 15 of the junction pipe 10. Connecting the upstream inner pipe 50 and the downstream inner pipe 30 at this position facilitates assembly and ensures product strength. The upstream inner pipe 50 and the downstream inner pipe 30 do not need to be connected directly to each other at their connecting end faces, as long as they are connected without creating gaps that would allow the gas-liquid mixture to leak from the flow path. For example, they may be connected via an adhesive or packing to improve airtightness. Alternatively, the upstream inner pipe 50 and the downstream inner pipe 30 may be indirectly connected by disposing another tubular member between them.

[0077] FIG. 17 is a cross-sectional view of the flow path 70 taken along the YZ plane having the central axis Cz. As shown in FIG. 17 , the downstream inner pipe 30 is connected by fitting the tip end 36 of the downstream end 35 to the outlet portion 26 of the junction pipe 10. This configuration firmly connects the outlet portion 26 and the downstream inner pipe 30, improving the pressure resistance of the bubble generator 2. Furthermore, the fitting allows the internal components to be positioned, facilitating assembly. The tip outer surface 37 of the tip end 36 abuts the outlet portion inner surface 11a3. The stepped surface 38 of the downstream inner pipe 30 abuts the positioning surface 11a2. Furthermore, the outer surface 31b of the downstream inner pipe 30 abuts the main body portion inner surface 11a1. Therefore, the downstream inner pipe 30 is fitted into the junction pipe 10 with virtually no gap except for the chamfered portion, providing a strong connection between the junction pipe 10 and the downstream inner pipe 30 and improving product strength.

[0078] As shown in FIG. 17 , the connecting end surface 33 of the downstream connecting portion 32 and the connecting end surface 58 of the upstream connecting portion 57 are substantially perpendicular to the axis Cz of the flow path 70. This configuration facilitates assembly of the internal components and allows the connecting end surfaces to be connected with virtually no gaps except for the chamfered portion, resulting in excellent pressure resistance. Furthermore, the downstream connecting portion 32 is connected to the upstream connecting portion so that the first portion 31a1 of its inner surface is substantially flush with the fourth portion 51a4 of the inner surface of the upstream connecting portion 57, thereby improving the pressure resistance of the micro-bubble generator. Furthermore, the outer surface 51b of the upstream connecting portion 57 and the outer surface 51b of the upstream end portion 52 of the upstream inner pipe 50 abut against the main body inner surface 11a1. Therefore, the downstream inner pipe 50 is fitted into the junction pipe 10 with virtually no gaps except for the chamfered portion and the gap 80, strengthening the connection between the junction pipe 10 and the upstream inner pipe 50 and improving product strength.

[0079] In this embodiment, the junction pipe 10 and the internal components (the downstream inner pipe 30 and the upstream inner pipe 50) are connected by fitting together, but they may also be fixed together using an adhesive, etc. However, from the viewpoint of eliminating the possibility of fragments of the adhesive or the like being mixed into the gas-liquid mixture, it is preferable to design the internal components to have an appropriate size that allows them to fit into the junction pipe 10 and obtain sufficient fixing strength without using an adhesive, etc.

[0080] As described above, the micro-bubble generator 1 mixes pressurized gas with the liquid flowing through the flow path 70 inside the bubble generator 2, and can effectively discharge a gas-liquid mixture containing microbubbles with nano-order bubble diameters. That is, the gas-liquid mixture flowing from the flow path 70 generates microbubbles in the generating section 29. The flow path 70 can be easily formed by inserting the downstream inner tube 30 and the upstream inner tube 50 through the liquid supply port 21 into the junction pipe 10 as a casing. Therefore, the bubble generator 2 is easy to assemble. Furthermore, the downstream inner tube 30 and the upstream inner tube 50 can be firmly connected inside the junction pipe 10, which not only provides resistance to external impacts but also provides excellent pressure resistance to the fluid flowing through the flow paths.

[0081] The present invention is not limited to the above-described embodiments, and its technical scope also includes various modified designs within the scope that does not deviate from the gist of the invention described in the claims.

[0082] The size of the micro-bubble generator and the number of through-holes are appropriately changed depending on the flow rate of the liquid, the diameter of the flow path, the pressure of the gas to be mixed, etc. For example, when the micro-bubble generator is used in agricultural fields where it is necessary to release a gas-liquid mixture containing a large amount of micro-bubbles, the bubble generator may have a length H0 of 30 cm and a width W0 of more than 15 cm. Note that, if sufficient product strength can be ensured, the length H0 may be made longer than the width W0 to ensure a longer gas-liquid mixing section 72.

[0083] Furthermore, in the above-described embodiment, the internal part is divided into two parts, an upstream inner pipe and a downstream inner pipe, but it may be divided into three or more parts and housed inside the merging pipe.

[0084] Next, a method for manufacturing the micro-bubble generating device 1 according to the embodiment of the present invention will be described.

[0085] In this manufacturing method, the junction pipe 10, the downstream inner pipe 30, and the upstream inner pipe 50 are each formed separately as independent parts, and then, in an assembly process, the downstream inner pipe 30 and the upstream inner pipe 50 are housed within the junction pipe 10 and assembled. That is, this manufacturing method includes the steps of: forming, as an independent component, a junction pipe 10 having a liquid inlet 20 for supplying a liquid therein, a gas inlet 14 for supplying a gas therein, and an outlet 26 for generating microbubbles and discharging a gas-liquid mixture containing the microbubbles; forming, as an independent component, a downstream inner pipe 30 that is disposed downstream in the direction of liquid flow; forming, as an independent component, an upstream inner pipe 50 that is disposed upstream in the direction of liquid flow and has a through hole 56 formed therein for introducing the gas supplied from the gas inlet 14; and assembling and accommodating, inside the formed junction pipe 10, the downstream inner pipe 30 and the upstream inner pipe 50 that communicates with the downstream inner pipe 30, so that the formed upstream inner pipe 50 and the formed downstream inner pipe 30 are coaxially arranged and form a flow path for flowing the liquid supplied from the liquid inlet 20 to the outlet 26.

[0086] The micro-bubble generator 1 manufactured by this manufacturing method can mix gas with a liquid flowing through a flow path inside the bubble generator 2 and effectively discharge a gas-liquid mixture containing micro-bubbles with nano-order bubble diameters. The bubble generator 2 is configured with a junction pipe 10 formed as an independent component serving as a casing, and internal components disposed inside the junction pipe 10. The internal components are assembled so that an upstream inner pipe 50 and a downstream inner pipe 30, both formed as independent components, are housed and connected inside the junction pipe 10. The assembly process of introducing a long tubular member into another tubular member is very complicated, but the separation of the internal components facilitates assembly. Furthermore, connecting the upstream inner pipe 50 and the downstream inner pipe 30 inside the junction pipe 10 ensures pressure resistance. Furthermore, since the internal components of the bubble generator 2 are housed inside the junction pipe 10, the product strength is improved and connection to piping is easy. Therefore, the micro-bubble generator 1 not only has low manufacturing costs, but also reduces maintenance costs.

[0087] The downstream inner pipe forming process includes a process of forming the downstream inner pipe 30 having a downstream connecting portion 32 that connects to the upstream inner pipe 50, a downstream end portion 35 that connects to the inside of the outlet portion 26, and a downstream reduced diameter portion 34 whose inner diameter decreases from the downstream connecting portion 32 toward the downstream end 35, and it is desirable that the upstream inner pipe forming process includes a process of forming the upstream inner pipe 50 having an upstream reduced diameter portion 54 whose inner diameter decreases toward the downstream side, an expanded diameter portion 55 whose inner diameter increases from the upstream reduced diameter portion 54 toward the downstream side, and an upstream connecting portion 57 that connects to the downstream connecting portion 32, and arranging a through hole 56 in the expanded diameter portion 55.

[0088] The downstream inner pipe forming process or the upstream inner pipe forming process preferably includes a process of forming the downstream inner pipe 30 so that its minimum inner diameter is smaller than the minimum inner diameter of the upstream inner pipe 50, and the confluence pipe forming process preferably includes a process of forming the outlet portion 26 so that it has at least a portion that is larger than the minimum inner diameter of the downstream inner pipe 30.

[0089] The assembly process preferably includes a step of fitting and connecting the downstream end 35 of the downstream inner pipe 30 to the outlet portion 26 of the junction pipe 10 .

[0090] The assembly process desirably includes a step of aligning the central axis of the flow path 70 in the downstream reduced diameter section 34 of the downstream inner pipe 30 coaxially with the central axis of the flow path 70 in the upstream reduced diameter section 54 of the upstream inner pipe 50.

[0091] The assembly process preferably includes a step of connecting the upstream connecting portion 57 so that the inner surface of the downstream connecting portion 32 of the downstream inner pipe 30 is approximately flush with the inner surface of the upstream connecting portion 57 of the upstream inner pipe 50.

[0092] The assembly process desirably includes a step of connecting the downstream connecting portion 32 of the downstream inner pipe 30 and the upstream connecting portion 57 of the upstream inner pipe 50 at the end faces 33 and 53 that are approximately perpendicular to the central axis of the flow path 70 in the upstream reduced diameter portion 54 of the upstream inner pipe 50.

[0093] The upstream inner pipe forming process desirably includes a step of forming the upstream inner pipe 50 so that the through hole 56 penetrates the pipe wall of the expanded diameter section 55 at an angle relative to the central axis of the flow path 70 in the upstream reduced diameter section 54.

[0094] The upstream inner pipe forming step preferably includes a step of forming a plurality of through holes 56 that are evenly spaced in the circumferential direction of the expanded diameter portion 55 .

[0095] The assembly process desirably includes an assembly step in which a gap 80 is formed between the outer surfaces of the upstream reduced diameter section 54 and the expanded diameter section 55 of the upstream inner pipe 50 and the inner surface of the junction pipe 10, and a plurality of through holes 56 extend from the gap to the flow path 70.

[0096] The confluence pipe forming step preferably includes the step of forming threads 22, 16 and 28 for screwing other piping into the liquid inlet 20, the gas inlet 14 and the outlet 26, respectively.

[0097] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0098] [Example] 1. Measurement of particle size, etc. of fine bubbles contained in gas-liquid mixture (1) A gas-liquid mixture M was generated using the fine-bubble generator 1 according to the present invention, and the particle size distribution of the fine bubbles contained in the gas-liquid mixture M was measured. Note that a nanoparticle analysis system (model number: NanoSight NS300, Malvern, UK) was used to measure the particle size distribution of the fine bubbles. The device according to the embodiment shown in Figure 1 was used as the fine-bubble generator 1, and measurements were performed by connecting the bubble generator 2 to a compressor 8 and a shower head 3 as gas supply means.

[0099] Specifically, the junction pipe 10, downstream inner pipe 30, and upstream inner pipe 50 shown in Fig. 2 were assembled and used as the bubble generator 2. The junction pipe 10 of the bubble generator 2 had the external shape of a substantially hexagonal prism shown in Figs. 4 to 7 , and was made of stainless steel, with a length H0 (total length) of 55 mm, a depth D0 of 25 mm, a length H1 of the liquid inlet 20 of 10 mm, a length H2 of the main body 12 of 35 mm, a protruding length H3 of the outlet 26 of 10 mm, an inner diameter φ1 of the interior 10 a of the main body 12 of 18 mm, an inner diameter φ2 of the interior 10 a of the outlet 26 of 14 mm, the thread 22 of the liquid inlet 20 being a G1 / 2 (JIS) female thread, and the thread 28 of the outlet 26 being a G1 / 2 (JIS) male thread. The confluence pipe 10 was formed by forming a gas inlet 14 having a female screw thread 16 of Rc1 / 8 (JIS standard) on the main body 12 of this stainless steel pipe.

[0100] The downstream inner pipe 30 used was a stainless steel pipe having a circular tubular outer shape as shown in Figures 8 to 10, with a diameter φ3 of 18 mm, a length H4 of the downstream connecting portion 32 of 2 mm, a length H5 of the downstream reduced diameter portion 34 of 10 mm, a length H6 of the downstream end portion 35 of 3 mm, a diameter φ4 at the tip portion 36 of 14 mm, an inner diameter φ6 at the downstream connecting portion 32 of 13 mm, an inner diameter φ5 at the downstream end portion 35 of 6.5 mm, and a radius of the arc described by the second portion 31a of the inner surface 31a of 17.01 mm.

[0101] The upstream inner pipe 50 was made of stainless steel and had a circular tubular outer shape as shown in Figures 11 to 13, a diameter φ3 of 18 mm, and a wall thickness D3 of 2.5 mm. It was machined so that the length H7 of the upstream end 52 was 2 mm, the length H8 of the upstream reduced diameter section 54 was 8 mm, the length H9 of the expanded diameter section 55 was 8 mm, the length H10 of the upstream connecting section 57 was 2 mm, the inner diameter φ8 of the upstream end 52 and the upstream connecting section 57 was 13 mm, the minimum inner diameter φ7 was 8 mm, the inner diameter φ9 of each of the four through holes 56 was 3 mm, the inclination angle θ1 of each through hole 56 was 30°, and the distance H11 between the center O1 of the outer surface 51 b of the through hole 56 and the position C0 of the minimum inner diameter φ7 was 2 mm.

[0102] An air compressor SR-045 (manufactured by Fujiwara Sangyo Co., Ltd., model number: SRL04SPT-01) was used as the compressor 8, and was connected to the bubble generator 2 via piping 5. A tap for a water supply was used as the water faucet 7, and a hose was directly connected to the tap and connected to the bubble generator 2 via piping 4. A shower head 3 was used (manufactured by Aramik Co., Ltd., product name: Pro Shower Clear ProC-48N) with a small diameter of 0.3 mm in the water discharge hole of the spray plate.

[0103] The experimental conditions were as follows: the pressurized gas G was air, the pressurized gas pressure by the compressor was 0.19 MPa, the water pressure of the liquid L, i.e., water, supplied from the water faucet 6 to the bubble generator 2 was 0.15 MPa, and the flow rate of the water was 20 L / min.

[0104] [Comparative Example] 2. Measurement of particle size, etc. of fine bubbles contained in gas-liquid mixture (2) As a comparative example, a gas-liquid mixture M was generated under the same experimental conditions as in the example using the fine-bubble generator described in Patent Document 1, which is a conventional technique, and the particle size distribution of the fine bubbles contained in the gas-liquid mixture M was measured. In the comparative example, a fine-bubble generator 101 shown in Figure 19 was used as the fine-bubble generator described in Patent Document 1, which is a conventional technique.

[0105] Specifically, the bubble generator 102 of the fine-bubble generator 101 was formed by using a first tubular body 130 made of a rigid PVC pipe having a diameter φ103 of 18 mm, an inner diameter φ108 of 13 mm, and a wall thickness of 2.5 mm, and a second tubular body 150 made of a rigid PVC pipe having an outer diameter of 24 mm, an inner diameter φ102 of 18 mm, and a wall thickness of 3 mm. The total length H100 of the bubble generator 102 was 20.6 cm. The first tubular body 130 was formed by drawing the outer periphery of the tapered upstream portion until the minimum inner diameter φ107 of the downstream PVC pipe was 8 mm, and then cutting the downstream PVC pipe so that an end portion having a minimum inner diameter φ105 of 6.4 mm was exposed. Four through-holes 156, each 2.5 mm in diameter, were formed at approximately 90-degree intervals in the circumferential direction of the outer wall of the first tubular body 130. The first tubular body 130 was inserted into a cylindrical casing 110, and both ends of the cylinder were tightened with nuts 120 and spacers, thereby airtightly fixing the first tubular body 130 to the casing 110. The pipe 4 connected to the faucet was connected to the first tubular body 130 via a liquid introduction section 20, which is an adapter. The pipe 5 connected to the compressor 8 was connected to a gas introduction section formed in the casing 110. The pipe 6 connected to the showerhead was connected to the second tubular body 150.

[0106] In the examples and comparative examples, measurements were carried out five times for each gas-liquid mixed water. The results are shown in Table 1.

[0107]

[0108] As shown in Table 1, it was found that gas-liquid mixed water containing many nano-order level fine bubbles (bubble diameter less than 1 μm) can be obtained by using the fine bubble generator 1 according to the example. Specifically, in the gas-liquid mixed water obtained by the fine bubble generator 1 of the example, the average bubble diameter was 114.2 nm, the standard deviation (SD) of the bubble diameter in the measurement was 39.0, and these fine bubbles were present in an average of 7.14 × 10 per mL. ７In the example, 90% of the bubbles contained in the gas-liquid mixed water were 167.0 nm or less. In contrast, in the gas-liquid mixed water obtained in the comparative example, the average bubble diameter was 120.9 nm, the standard deviation (SD) of the bubble particle diameter in the measurement was 39.0, and these fine bubbles were present at an average density of 3.22 × 10 per mL. ７ In the comparative example, 90% of the bubbles contained in the gas-liquid mixed water were 185.1 nm or less.

[0109] From this, it was found that the fine bubbles contained in the gas-liquid mixture obtained with the fine-bubble generator 1 of the Example were finer and of a higher concentration than those of the Comparative Example. Furthermore, while the fine-bubble generator 101 of the Comparative Example had a total length H100 of 20.6 cm, the fine-bubble generator 1 of the Example had a total length H0 of 55 mm, which was 30% smaller than the conventional device, and it was confirmed that the fine-bubble generator 1 of the Example could withstand the pressure of air G and water M under similar conditions. It was also confirmed that the fine-bubble generator 1 of the Example had fewer parts and required fewer manufacturing steps than the fine-bubble generator 101 of the Comparative Example.

[0110] The fine-bubble generating device according to the present invention is used to produce a gas-liquid mixture containing fine bubbles, and can be suitably used in the fields of beauty and health, agriculture, etc.

[0111] REFERENCE SIGNS LIST 1 Micro-bubble generator 2 Bubble generator 10 Confluence pipe 10a Interior 10b Pipe wall 11a Inner surface 11a0 Stopper surface 11a1 Main body inner surface 11a2 Positioning surface 11a3 Outlet inner surface 11b Outer surface 11b1 First surface 11b2 Second surface 11b3 Third surface 11b4 Fourth surface 11b5 Fifth surface 11b6 Sixth surface 11c1 First end surface 11c2 Second end surface 11c3 Tip surface 12 Main body 14 Gas inlet 15 Gas supply port 16 Thread 20 Liquid inlet 21 Liquid supply port 22 Thread 26 Outlet 27 Discharge port 28 Thread 29 Generation section 30 Downstream inner pipe 31 Pipe wall 31a Inner surface 31a1 First portion 31a2 Second portion 31a3 Third portion 31b Outer surface 32 Downstream connecting portion 33 End surface 34 Downstream reduced diameter portion 35 Downstream end portion 36 Tip portion 37 Tip outer surface 38 Step surface 39 End surface 50 Upstream inner pipe 51 Pipe wall 51a Inner surface 51a1 First portion 51a2 Second portion 51a3 Third portion 51a4 Fourth portion 51b Outer surface 52 Upstream end portion 53 End surface 54 Upstream reduced diameter portion 55 Expanded diameter portion 56 Through hole 57 Upstream connecting portion 58 End surface 60 Constricted portion 70 Flow path 71 First flow path portion 72 Second flow path portion (gas-liquid mixing portion) 80 Gap 3 Shower head 4, 5, 6 Piping 7 Liquid supply source 8 Gas supply means L Liquid G Pressurized gas M Gas-liquid mixture 101 Fine bubble generator 102 Bubble generator 110 Casing 120 Nut 130 First tubular body 150 Second tubular body

Claims

1. A microbubble generating apparatus having a bubble generator that mixes a liquid continuously supplied from a liquid supply source with a gas supplied from a gas supply means to generate microbubbles and discharges a gas-liquid mixture in which the microbubbles and the liquid are mixed, The bubble generator is, A confluence pipe having a liquid inlet for supplying the liquid inside, a gas inlet for supplying the gas inside, and an outlet for generating the fine bubbles and discharging the gas-liquid mixture containing the fine bubbles, formed as an independent component, It has a tubular internal component that is assembled and housed inside the confluence pipe and has a flow path inside for the liquid supplied from the liquid introduction section to flow to the outlet section, The aforementioned internal components are It consists of a downstream inner tube, which is located downstream in the direction in which the liquid flows and is formed as an independent component, and an upstream inner tube, which is located upstream and is formed as an independent component. The upstream inner pipe is provided with a through-hole for introducing the gas supplied from the gas introduction section into the flow path. The downstream inner pipe is connected to the upstream inner pipe inside the confluence pipe. The flow path connects the upstream inner pipe and the downstream inner pipe coaxially from the liquid inlet to the outlet, The downstream inner pipe has a downstream connecting portion that connects to the upstream inner pipe, a downstream end that connects to the inside of the outlet portion, and a downstream reduced diameter portion in which the inner diameter is reduced from the downstream connecting portion toward the downstream end. The upstream inner pipe has an upstream reduced-diameter section in which the inner diameter is reduced toward the downstream side, an enlarged-diameter section in which the inner diameter is increased toward the downstream side from the upstream reduced-diameter section, and an upstream connecting section that connects to the downstream connecting section. The microbubble generating device is characterized in that the through-hole is located in the enlarged diameter portion.

2. (delete)

3. The minimum inner diameter of the downstream inner pipe is smaller than the minimum inner diameter of the upstream inner pipe. The microbubble generating apparatus according to claim 1, characterized in that the outlet portion has at least a portion that is larger than the minimum inner diameter of the downstream inner tube.

4. The microbubble generating apparatus according to claim 1, characterized in that the downstream end is fitted and connected to the outlet portion.

5. The microbubble generating apparatus according to claim 1, characterized in that the central axis of the flow path in the downstream diameter-reduced section is arranged coaxially with the central axis of the flow path in the upstream diameter-reduced section.

6. The microbubble generating apparatus according to claim 1, characterized in that the downstream connecting portion is connected to the upstream connecting portion such that its inner surface is substantially flush with the inner surface of the upstream connecting portion.

7. The microbubble generating apparatus according to claim 1, characterized in that the downstream connecting portion and the upstream connecting portion are connected by an end face substantially perpendicular to the central axis of the flow path in the upstream diameter-reduced portion.

8. The microbubble generating device according to claim 1, characterized in that the through-hole penetrates the pipe wall of the enlarged diameter section, inclined with respect to the central axis of the flow path in the upstream reduced diameter section.

9. The microbubble generating device according to claim 1, characterized in that the through holes are arranged evenly in the circumferential direction of the enlarged diameter portion.

10. A gap is formed between the outer surfaces of the upstream reduced diameter portion and the enlarged diameter portion and the inner surface of the confluence pipe. The microbubble generating apparatus according to claim 1, characterized in that each of the aforementioned through holes extends from the gap to the flow path.

11. The microbubble generating apparatus according to claim 1, characterized in that the liquid introduction section, the gas introduction section, and the outlet section each have screw threads formed therein for screwing in other pipes.

12. A method for manufacturing a microbubble generator, which mixes a liquid continuously supplied from a liquid supply source with a gas supplied from a gas supply means, generates microbubbles, and discharges a gas-liquid mixture in which the microbubbles and the liquid are mixed, A confluence pipe forming step, in which a confluence pipe having a liquid introduction section for supplying the liquid inside, a gas introduction section for supplying the gas inside, and an outlet section for generating the fine bubbles and discharged the gas-liquid mixture containing the fine bubbles is formed as an independent component, A downstream inner tube forming step, which involves forming a downstream inner tube, which is located downstream in the direction in which the liquid flows, as an independent component, An upstream inner tube forming step is to form an upstream inner tube as an independent component, which is located upstream in the direction in which the liquid flows and has a through hole drilled for introducing the gas supplied from the gas introduction section. The assembly process includes assembling and housing the downstream inner pipe and the upstream inner pipe communicating with the downstream inner pipe inside the formed confluence pipe so that the formed upstream inner pipe and the formed downstream inner pipe are arranged coaxially and a flow path is formed for the liquid supplied from the liquid introduction section to flow to the discharge section, The downstream inner pipe forming step includes forming a downstream inner pipe having a downstream connecting portion that connects to the upstream inner pipe, a downstream end that connects to the inside of the outlet portion, and a downstream reduced diameter portion in which the inner diameter is reduced from the downstream connecting portion toward the downstream end. The method for manufacturing a microbubble generator is characterized in that the upstream inner tube forming step includes forming an upstream inner tube having an upstream reduced diameter portion in which the inner diameter is reduced toward the downstream side, an enlarged diameter portion in which the inner diameter is increased toward the downstream side from the upstream reduced diameter portion, and an upstream connecting portion that connects to the downstream connecting portion, and also includes a step of arranging the through hole in the enlarged diameter portion.

13. (delete)

14. The downstream inner pipe forming step or the upstream inner pipe forming step includes a step of forming the downstream inner pipe such that the minimum inner diameter is smaller than the minimum inner diameter of the upstream inner pipe. The method for manufacturing a microbubble generator according to claim 12, characterized in that the confluence pipe formation step includes a step of forming the outlet portion such that it has at least a portion that is larger than the minimum inner diameter of the downstream inner pipe.

15. The method for manufacturing a microbubble generating device according to claim 12, characterized in that the assembly step includes a step of fitting and connecting the downstream end of the downstream inner pipe with the outlet portion of the confluence pipe.

16. The method for manufacturing a microbubble generator according to claim 12, characterized in that the assembly step includes a step of arranging the central axis of the flow path in the downstream diameter-reduced portion of the downstream inner tube to be coaxial with the central axis of the flow path in the upstream diameter-reduced portion of the upstream inner tube.

17. The method for manufacturing a microbubble generator according to claim 12, characterized in that the assembly step includes a step of connecting the upstream connecting portion such that the inner surface of the downstream connecting portion of the downstream inner pipe is substantially flush with the inner surface of the upstream connecting portion of the upstream inner pipe.

18. The method for manufacturing a microbubble generator according to claim 12, characterized in that the assembly step includes a step of connecting the downstream connecting portion of the downstream inner pipe and the upstream connecting portion of the upstream inner pipe with end faces that are substantially perpendicular to the central axis of the flow path in the upstream diameter-reduced portion of the upstream inner pipe.

19. The method for manufacturing a microbubble generator according to claim 12, characterized in that the upstream inner tube forming step includes a step of forming the upstream inner tube such that the through hole penetrates the tube wall of the enlarged diameter portion at an inclination with respect to the central axis of the flow path in the upstream reduced diameter portion.

20. The method for manufacturing a microbubble generator according to claim 12, characterized in that the upstream inner tube forming step includes a step of forming a plurality of through holes evenly arranged in the circumferential direction of the enlarged diameter portion.

21. The method for manufacturing a microbubble generator according to claim 12, characterized in that the assembly step includes a step of assembling the device such that a gap is formed between the outer surfaces of the upstream reduced diameter portion and the expanded diameter portion of the upstream inner pipe and the inner surface of the confluence pipe, and the plurality of through holes extend from the gap to the flow path.

22. The method for manufacturing a microbubble generator according to claim 12, characterized in that the confluence pipe formation step includes a step of forming screw threads for screwing other pipes into the liquid introduction section, the gas introduction section, and the outlet section.