Microbubble generator

Abstract

[Problem] To provide a microbubble generator capable of stably generating a large number of microbubbles and suppressing clogging of a gas introduction hole and a flow passage caused by, for example, the precipitation of a solute in a fluid within a microbubble generation device. [Solution] A microbubble generator including: a case body having a main passage that connects an inlet opening for liquid provided to one end side with an outlet opening provided to the other end side; a throttle part disposed in the main passage; and a gas mixing means formed in the vicinity of the throttle part, wherein the gas mixing means is provided with at least an upstream-side first introduction part and a downstream-side second introduction part, both of which penetrate the case body in the thickness direction and release gas into the main passage.

Description

Microbubble Generator

[0001] The present invention relates to a microbubble generator that generates microbubbles of micrometer size, nanometer size, etc. in a liquid.

[0002] Microscopic bubbles of micrometer order size or the like that are generated in a liquid have a small bubble volume, so they rise slower than normal-sized bubbles with a diameter of, for example, about 1 millimeter, and remain in the liquid for a longer period of time.

[0003] Furthermore, bubbles have the property that the smaller their size, the higher the internal pressure of the bubbles due to the effect of the liquid's surface tension, causing the gas to dissolve in the water. These bubbles are known to have many uses, including improving the yield of plants and cultivated products through their physiological activity, purifying water, cleaning machinery and equipment, and removing surfactants from wastewater.

[0004] A requirement for good performance of such a device for generating fine bubbles in a liquid is that it can generate a large amount of fine bubbles uniformly and reliably in the liquid.

[0005] Incidentally, a microbubble generator has already been disclosed in Patent Document 1.

[0006] Japanese Patent Application Laid-Open No. 2007-21343

[0007] The microbubble generator of Patent Document 1 has a double-cylindrical arrangement of a flow straightening cylinder 6 inside a cylindrical casing 4, a first propeller-type blade row 7 installed in the gap between the casing and the flow straightening cylinder 6, and a second propeller-type blade row 8 installed inside the flow straightening cylinder 6, and gas is introduced into the casing 4 through small holes 18 communicating with a gas inlet port 17, causing the gas-liquid mixture to swirl in a counter-inward and counter-outward direction, thereby promoting the generation of microbubbles.

[0008] However, the microbubble generator described in Patent Document 1 has a structure in which blades (propeller-shaped blade rows 7, 8) that guide the fluid in a spiral shape are installed between the casing 4 and the straightening cylinder 6, and within the straightening cylinder 6. This makes manufacturing difficult and increases costs. In addition, the gas introduction port 17 is formed in only one location, the small hole 18, which limits the amount of microbubbles generated and prevents sufficient effectiveness from being achieved.

[0009] Furthermore, if the fluid flowing through the flow straightening cylinder 6 contains a large amount of solutes, the solutes will precipitate on the walls of the flow straightening cylinder 6, causing a serious problem of blocking the gas introduction port 17 and the liquid flow path itself.

[0010] Therefore, an object of the present invention is to provide a micro-bubble generator that can stably generate a large amount of micro-bubbles by suppressing clogging of the gas inlet hole and flow path due to precipitation of solutes in the fluid inside the micro-bubble generator, etc.

[0011] In order to solve the above problems, the present invention has the following configurations. [1] A fine-bubble generator having a case body having a liquid inlet opening at one end and a liquid outlet opening at the other end communicating with each other through a main passage, a throttle section disposed in the main passage, and a gas mixing means formed near the throttle section, wherein the gas mixing means includes at least a first upstream introduction section and a second downstream introduction section that penetrate the case body in the thickness direction and release gas into the main passage. [2] The fine-bubble generator according to [1], wherein the first introduction section and the second introduction section are formed as slits or holes in the case body. [3] The fine-bubble generator according to [2], wherein the slit in the first introduction section or the second introduction section has a width of 1 mm to 3 mm. [4] The fine-bubble generator according to [2] or [3], wherein the hole in the first introduction section or the second introduction section has a diameter of 1 mm to 3 mm. [5] The fine-bubble generator according to any one of [2] to [4], wherein the number of holes in the first introduction section or the second introduction section is 8 or 16. [6] The fine-bubble generator according to any one of [2] to [5], wherein the first introduction section is formed as a slit and the second introduction section is formed as a hole. [7] The fine-bubble generator according to any one of [1] to [6], wherein the second introduction section is disposed at a position where the distance d5 from the maximum throttle position of the throttle section in the axial direction of the case body is 3 mm to 30 mm. [8] The fine-bubble generator according to any one of [1] to [7], wherein the first introduction section is disposed downstream of the maximum throttle position of the throttle section in the axial direction of the case body. [9] The fine-bubble generator according to [1], further comprising an introduction section downstream of the second introduction section that penetrates the case body in the thickness direction and releases gas into the main passage.

[0012] The micro-bubble generator of the present invention comprises a case body having a liquid inlet opening at one end and a liquid outlet opening at the other end connected by a main passage, a throttle section disposed in the main passage, and a gas mixing means formed near the throttle section. The gas mixing means has a first upstream inlet and a second downstream inlet that penetrate the case body in the thickness direction and release gas into the main passage. When the micro-bubble generator is operated, gas is introduced from the first and second inlet sections toward the liquid flowing through the main passage. The second inlet is positioned at a distance d5 from the maximum throttle position of the throttle section in the axial direction of the case body of 3 mm to 30 mm, and is located downstream of the first inlet in the liquid flow. Therefore, the first inlet has a greater gas suction force than the second inlet. By adjusting the slit width and hole diameter of the first and second inlet sections, an optimal master-slave relationship can be established. This allows the gas to be introduced into the liquid while being broken down by a smooth flow into the main passage, so that a large number of fine bubbles of uniform size can be reliably generated.

[0013] In addition, the main passage is a Venturi tube that starts at the maximum throttle position of the throttle section and expands in diameter toward the inlet opening and outlet opening, and further, the first introduction section is arranged downstream of the maximum throttle position, so that gas can be introduced where the flow rate of the liquid is accelerating, and the introduced gas can be efficiently converted into fine bubbles.

[0014] The gas mixing means also includes a plurality of introduction ports, such as a first introduction port and a second introduction port, near the throttle portion. The first introduction port and the second introduction port may have a slit shape. By providing a plurality of gas introduction ports and forming each introduction port large, even if a large amount of solute dissolved in the liquid precipitates in the introduction port, problems such as reduced efficiency in generating fine bubbles due to clogging can be eliminated. In this case, in addition to the first introduction port and the second introduction port, it is also possible to add additional introduction ports, such as a third introduction port and a fourth introduction port.

[0015] As described above, the micro-bubble generator of the present invention has a relatively simple configuration and can be manufactured at low cost. In addition, it can effectively suppress adverse effects such as clogging caused by the precipitation of solutes in the fluid moving within the case body.

[0016] Fig. 1 is a front view showing the configuration of a fine-bubble generator according to one embodiment of the present invention. Fig. 2 is an end view showing the internal structure of a fine-bubble generator according to one embodiment of the present invention. Fig. 3 is a cross-sectional view showing the configuration of a fan-shaped slit of a fine-bubble generator according to one embodiment of the present invention. Fig. 4 is a cross-sectional view showing the configuration of a circular hole of a fine-bubble generator according to one embodiment of the present invention. Fig. 5 is a front view showing a state in which a third introduction section and a fourth introduction section are provided in a fine-bubble generator according to one embodiment of the present invention. Fig. 6 is a schematic explanatory view showing an example installation configuration of a fine-bubble generator according to one embodiment of the present invention. Fig. 7 is a schematic cross-sectional view showing the internal structure of a fine-bubble generator according to one embodiment of the present invention in an installed state.

[0017] Next, an embodiment of the fine-bubble generator of the present invention will be described with reference to the drawings. Fig. 2 is an end view of the fine-bubble generator A shown in Fig. 1 cut in half in the depth direction, Fig. 2(a) is the entire view, and Fig. 2(b) is a partially enlarged view showing the maximum throttling position 3a. Fig. 3 is a cross-sectional view of the fine-bubble generator A cut longitudinally at the position of the fan-shaped slit 41 and viewed from the inlet opening 2a side. Fig. 4 is a cross-sectional view of the fine-bubble generator A cut longitudinally at the position of the circular hole 42 and viewed from the inlet opening 2a side. Fig. 7 is a cross-sectional view of the fine-bubble generator A shown in Fig. 6 cut in the same manner as in Fig. 2. Note that Figs. 1, 2, 5, 6, and 7 are illustrated as if liquid were to flow in from the left side and flow from left to right, so the left end of the case body 1 is the inlet opening 2a and the right end is the outlet opening 2b.

[0018] The micro-bubble generator A of the present invention is a device or apparatus that pumps a liquid through a main passage 2 in a case body 1 and simultaneously introduces gas into the flow of the liquid to generate micro-bubbles.

[0019] Specifically, a gas-liquid mixture is generated by crushing and introducing gas from the outside while pumping liquid into the main passage 2. The fine bubbles generated at this time have diameters of about several tens of microns, and form a large amount of uniformly distributed gas-liquid mixture.

[0020] Here, the term "microbubbles" refers to bubbles smaller than 100 μm in size, including bubbles smaller than 1 μm.

[0021] 1 to 4 show the configuration of a fine-bubble generator A according to one embodiment of the present invention. In each figure, the fine-bubble generator A comprises a case body 1 having a main passage 2 whose cylindrical interior serves as a liquid flow path, a throttle section 3 formed midway through the main passage 2, and a gas mixing means 4 disposed near the throttle section 3.

[0022] A substantially cylindrical case body 1 defines a main passage 2 that passes through the interior along its axis. An inlet opening 2a for liquid is provided at one end of the main passage 2, and an outlet opening 2b for liquid is provided at the other end of the main passage 2. In other words, the inlet opening 2a and the outlet opening 2b are connected by the main passage 2.

[0023] As shown in FIG. 1, the case body 1 is composed of a first case portion 11 that forms the inlet opening 2a side and a second case portion 12 that forms the outlet opening 2b side, with the maximum throttle position 3a (described later) as the boundary.

[0024] As shown in Fig. 2, the inside of the first case portion 11 constituting the main passage 2 has a first tapered portion 21 whose diameter gradually decreases toward the downstream side in the direction of liquid flow. Similarly, the inside of the second case portion 12 constituting the main passage 2 has a second tapered portion 22 whose diameter gradually increases toward the downstream side in the direction of liquid flow. The first case portion 11 and the second case portion 12 are connected in series to constitute the case body 1 and the internal main passage 2. Note that the first case portion 11 and the second case portion 12 may also be formed integrally.

[0025] The first case portion 11 is a cylindrical body that is shorter in length than the second case portion 12 , and the second case portion 12 is a cylindrical body that is longer in length than the first case portion 11 .

[0026] The case body 1 is made of a material that has the strength and rigidity to withstand the pressure of pumping liquid, such as metal, plastic, glass, or ceramic. In this embodiment, plastic is used because it is easy to mold and has low manufacturing costs. The product can be molded by cutting from bulk material, casting, extrusion molding, or other methods.

[0027] The main passage 2 has a throttle section 3 formed by a first tapered section 21 and a second tapered section 22. This throttle section 3 has a maximum throttle position 3a where the main passage 2 is narrowest, i.e., where the hole diameter is smallest, at the connecting portion between the first tapered section 21 and the second tapered section 22. In the embodiment shown in Figures 1 and 2, the maximum throttle position 3a is provided at a position where the entire length is internally divided at a ratio of, for example, slightly more than 1:2 from the inlet opening 2a side.

[0028] Therefore, the main passage 2 is formed as a so-called Venturi tube, gradually expanding in diameter from the maximum throttle position 3a toward the front and rear of the liquid flow (the inlet opening 2a and the outlet opening 2b). When the diameter of the inlet opening 2a is d1, the diameter at the maximum throttle position 3a is d2, and the diameter of the outlet opening 2b is d3, the relationship in size is d1 > d2 < d3. It is preferable that the relationship in size between the diameter d1 of the inlet opening 2a and the diameter d3 of the outlet opening 2b be d1 ≦ d3.

[0029] At the maximum throttling position 3a, the width (hole diameter) of the main passage 2 through which the liquid flows is reduced to throttle the flow, thereby increasing the flow rate and causing the pressure downstream of the maximum throttling position 3a to drop more rapidly than at the first tapered section 21. In other words, the pressure in the main passage 2 (second tapered section 22) after the maximum throttling position 3a becomes significantly negative, which causes the introduced gas to be crushed by the accelerated liquid, generating fine bubbles.

[0030] The inclination angle α of the second tapered portion 22 with respect to the center line of the main passage 2 (the line shown by the dashed line in FIG. 2 dividing the case body 1 into upper and lower halves) is set to 3 to 13 degrees. Furthermore, the length of the second tapered portion 22, i.e., the distance d6 from the maximum throttling position 3a to the outflow opening 2b, is set to a range of (d3 - d2) to 20(d3 - d2), and more preferably a range of 3(d3 - d2) to 15(d3 - d2), in terms of the relationship between the diameter d2 at the maximum throttling position 3a and the diameter d3 of the outflow opening 2b.

[0031] The gas mixer 4 is provided near the throttle section 3 having the maximum throttle position 3a. The gas mixer 4 comprises a pair of fan-shaped slits 41 (see FIG. 3) as first introduction sections arranged at opposing positions, and eight circular holes 42 (see FIG. 4) as second introduction sections arranged at approximately equal intervals along the circumferential direction of the case body 1.

[0032] 1 to 4, in the present embodiment, a cutout portion 1a is formed in the outer surface of the second case portion 12 in the case main body 1 near the throttle portion 3 of the second case portion 12, and a fan-shaped slit 41 is provided that penetrates from this cutout portion 1a in the thickness direction of the case main body 1 and communicates with the main passage 2. Similarly, a circular hole 42 is provided downstream of the cutout portion 1a that penetrates in the thickness direction and communicates with the main passage 2.

[0033] The fan-shaped slit 41 (first inlet) and the circular hole 42 (second inlet) are guide passages that introduce, for example, air and all other gases from the outside into the main passage 2 of the case body 1, and are preferably grooves or passages that extend linearly in the thickness direction. The gas introduced into the main passage 2 may be pressurized by a blower or the like, or may be naturally sucked in on the main passage 2 side.

[0034] In order to efficiently generate fine bubbles, the gas mixing means 4 preferably has the width of the fan-shaped slits 41 and the diameter of the circular holes 42 both in the range of 1 mm to 3 mm. More specifically, when the liquid flow rate is less than 30 cubic meters per hour, the width is less than 2 mm. When the liquid flow rate is 30 cubic meters per hour, the width is preferably about 3 mm because the introduction section may become narrow due to accumulated biofilm. This allows the gas to flow forcefully into the main passage 2, even when a relatively large amount of solute is dissolved in the liquid introduced into the main passage 2, and effectively prevents the solute from precipitating in the introduction section or the main passage 2.

[0035] The sectorial slit 41, which is the first introduction part, is provided downstream of the maximum throttle position 3a in the liquid flow (toward the outlet opening 2b). Specifically, it is preferable that the distance d4 from the maximum throttle position 3a to the edge of the sectorial slit 41 (first introduction part) on the inlet opening 2a side be set in the range of 0.1 mm to 5 mm.

[0036] Furthermore, the distance d5 from the maximum throttle position 3a to the edge of the circular hole 42 (second introduction part) on the inlet opening 2a side is set within 3 mm to 30 mm, and particularly preferably 5 mm to 15 mm.

[0037] It is desirable that all of the introduction parts provided in the vicinity of the throttling section 3, including the first introduction part (fan-shaped slit 41) and the second introduction part (circular hole 42), be arranged within a range of 0.1 mm to 15 mm downstream of the maximum throttling position 3a.

[0038] In terms of the distance relationship between the maximum throttling position 3a and the sectorial slit 41 (first introduction portion) and the distance relationship between the maximum throttling position 3a and the circular hole 42 (second introduction portion), the sectorial slit 41 is provided closer to the maximum throttling position 3a. Therefore, due to the difference in negative pressure generated inside the main passage 2 formed as a Venturi tube, the sectorial slit 41 preferentially introduces gas, that is, a master-slave relationship is established between the sectorial slit 41 and the circular hole 42.

[0039] Furthermore, the master-slave relationship between the fan-shaped slits 41 and the circular holes 42 can be appropriately and precisely set by finely adjusting the speed and amount of gas introduced from the first introduction part and the speed and amount of gas introduced from the second introduction part by appropriately changing the width of the fan-shaped slits 41 and the circular holes 42. This allows the gas to be introduced into the main passage 2 with a smooth flow and to be broken up by the flowing liquid, reliably generating a large number of uniformly sized fine bubbles.

[0040] In this embodiment, the first introduction portion and the second introduction portion are respectively the fan-shaped slit 41 and the circular hole 42, but there are no particular limitations on their shapes as long as they function as guide passages for introducing gas into the main passage 2. In this embodiment, the fan-shaped slits 41 are configured as a pair, i.e., two, provided near the throttle portion 3, but the number is not limited to this. Also, it is preferable to provide 8 to 16 circular holes 42, but the number is not limited thereto either.

[0041] Furthermore, the number of gas introduction ports in the gas mixer 4 is not limited to two, and may be three or more. For example, as shown in Fig. 5, a fan-shaped slit 41 may be provided as a third introduction port downstream of the second introduction port, and a circular hole 42 as a fourth introduction port further downstream thereof. Of course, it is also possible to provide only the third introduction port without providing the fourth introduction port, or to provide fifth and subsequent introduction ports as well, and the shapes of the third and subsequent introduction ports themselves are not limited to a fixed shape.

[0042] Therefore, in this embodiment, the fan-shaped slit 41 is disposed on the inlet opening 2a side of the circular hole 42, but conversely, the fan-shaped slit 41 may be disposed on the outlet opening 2b side of the circular hole 42. That is, it is also possible to form the first introduction part as a circular hole 42 and the second introduction part as a fan-shaped slit 41. Of course, both the first introduction part and the second introduction part can be formed as fan-shaped slits 41, or they can also be formed as circular holes 42.

[0043] Next, the action and mechanism of the fine-bubble generator A of this embodiment will be described. The fine-bubble generator A of this embodiment is used, for example, for water quality improvement, and can be applied to a known device or system in which the fine-bubble generator A, connected to a pressure pump 51 via a pressure pipe 52, is disposed in a water source W to be treated, one end of a gas supply hose 53 that can introduce gas into a first introduction part and a second introduction part is connected to the fine-bubble generator A, and the other end of the gas supply hose 53 is placed in an atmosphere-open state or connected to a compressor, and the liquid in the water source W is returned to the suction side of the pressure pump 51 via a return pipe 54.

[0044] More specifically, as shown in Fig. 6, a fine-bubble generator A connected to a pressure pump 51 via a pressure pipe 52 is placed in the water of a water source W to be treated. At this time, the water pressure of the liquid pressure-fed from the pressure pump 51 and flowing into the fine-bubble generator A through the inlet opening 2a is preferably 0.1 MPa to 5 MPa.

[0045] The fine-bubble generator A may be connected directly to the pressure pipe 52, but in this embodiment, as shown in Figure 7, it is connected to the pressure pipe 52 while being housed in a cylindrical pipe 55 made of resin or the like. The pipe 55 is also formed with a hose connection part 551 that connects the space S formed between the pipe 55 and the cutout part 1a of the fine-bubble generator A housed therein to the outside of the pipe 55.

[0046] One end of a gas supply hose 53 for sending gas to the fine-bubble generator A is connected to the hose connecting part 551. The other end of the gas supply hose 53 is open to the atmosphere. Therefore, the main passage 2 of the fine-bubble generator A and the atmosphere are in communication with each other via the introduction part (the fan-shaped slit 41 and the circular hole 42), the hose connecting part 551, and the gas supply hose 53 through the space S.

[0047] In the micro-bubble generator A, liquid sent from a pressure pump 51 via a pressure pipe 52 flows from the inlet opening 2a into the main passage 2. The liquid that has flowed into the main passage 2 flows through the interior of the main passage 2 and is discharged from the outlet opening 2b.

[0048] 7, the main passage 2 is formed as a Venturi tube, and therefore the speed of the liquid flowing through the main passage 2 is maximum at the maximum throttle position 3a. Specifically, the liquid that flows in from the inlet opening 2a has its passage abruptly narrowed at the first tapered section 21, and its flow speed increases, until it reaches its maximum speed at the maximum throttle position 3a.

[0049] Another feature of the Venturi tube is that the pressure inside the passage drops suddenly when passing through the throttle portion. Therefore, a large negative pressure state occurs in the second tapered portion 22 near the throttle portion 3, through which the liquid flows after passing through the maximum throttle position 3a.

[0050] At this time, the fan-shaped slit 41 and the circular hole 42, which are gas inlet sections arranged downstream of the liquid flow at the maximum throttling position 3a (on the outflow opening 2b side), are affected by the negative pressure and forcefully introduce gas into the main passage 2 via the gas supply hose 53, which is open to the atmosphere.

[0051] The gas introduced into the main passage 2 with great force collides at high speed with the liquid accelerated at the maximum throttle position 3a, where it is broken up into fine bubbles. Then, in the process of passing through the second tapered section 22, the generated fine bubbles dissolve uniformly in the liquid and become part of a gas-liquid mixture fluid containing fine bubbles of high quality.

[0052] By circulating the water source W through the above-mentioned mechanism, the physical properties of the water can be significantly changed. The effects and changes in water caused by the microbubbles include surfactant action on the bubble surface, generation of free radicals, and an increase in the dissolved oxygen concentration in the circulating water. These actions can have effects such as improving biological functions, increasing the yield of plants and cultivated products, and purifying the water.

[0053] This allows for the generation of fine air bubbles in the liquid, whether seawater, water, or freshwater, thereby purifying the water and promoting the growth of aquatic organisms. The liquid is not particularly limited, and tap water, seawater, lake water, chemicals, cleaning solutions, etc., can be used. When using highly corrosive liquids, it is advisable to construct the case body 1 using a highly corrosion-resistant material.

[0054] The gas introduced from the introduction portion (the sectorial slit 41 and the circular hole 42 in this embodiment) is not particularly limited, and gases such as air, oxygen, nitrogen, carbon dioxide, ozone, etc. The slits may be provided with a control valve or the like for controlling the amount of gas introduced, so that the gas flow rate can be controlled.

[0055] The micro-bubble generator A can be installed in an environment containing liquid and used for purposes such as water purification. If a bubbling-treated liquid is used, the generator A can also be used for various other applications such as cleaning, sterilization, and in the agricultural and fishing fields.

[0056] Furthermore, the fine-bubble generator A according to the present invention is provided with a plurality of introduction sections, such as the first introduction section and the second introduction section, and by forming these introduction sections in the form of slits, such as the fan-shaped slit 41, it is possible to minimize the risk of clogging even if solute precipitates in the gas introduction section. Therefore, it is possible to prevent as much as possible a decrease in the efficiency of fine-bubble generation due to clogging. Note that this action and mechanism was discovered as a result of extensive trial and error by the inventors of the present application.

[0057] Although several embodiments of the micro-bubble generator according to the present invention have been described above, it goes without saying that these are not intended to limit the technical scope of the present invention. These novel embodiments may be realized in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the present invention. These embodiments and modifications are included within the scope and spirit of the present invention, as well as within the scope of the inventions set forth in the claims and their equivalents.

[0058] A Fine bubble generator 1 Case body 1a Notch portion 11 First case portion 12 Second case portion 2 Main passage 2a Inlet opening 2b Outlet opening 21 First tapered portion 22 Second tapered portion 3 Throttle portion 3a Maximum throttle position 4 Gas mixing means 41 Fan-shaped slit 42 Circular hole W Water source 51 Pressure pump 52 Pressure pipe 53 Gas supply hose 54 Return pipe 55 Pipe 551 Hose connection portion S Space

Claims

1. A fine-bubble generator having a case body with a liquid inlet opening at one end and an outlet opening at the other end connected by a main passage, a throttle section disposed in the main passage, and a gas mixing means formed in the vicinity of the throttle section, wherein the gas mixing means has at least a first upstream introduction section and a second downstream introduction section that penetrate the case body in the thickness direction and release gas into the main passage.

2. A fine-bubble generator according to claim 1, wherein the first introduction section and the second introduction section are formed as slits or holes in the case body.

3. A fine-bubble generator according to claim 2, wherein the slit in the first introduction section or the second introduction section has a width of 1 mm to 3 mm.

4. A fine-bubble generator according to claim 2 or 3, wherein the holes in the first introduction section or the second introduction section have a diameter of 1 mm to 3 mm.

5. A fine-bubble generator according to any one of claims 2 to 4, wherein the number of holes in the first introduction section or the second introduction section is 8 or 16.

6. A micro-bubble generator according to any one of claims 2 to 5, wherein the first introduction section is formed as a slit and the second introduction section is formed as a hole.

7. A fine-bubble generator as described in any one of claims 1 to 6, wherein the second introduction section is arranged at a position in the axial direction of the case body at a distance d5 from the maximum throttling position of the throttling section of 3 mm to 30 mm.

8. A fine-bubble generator according to any one of claims 1 to 7, wherein the first introduction section is disposed downstream of the maximum throttle position of the throttle section in the axial direction of the case body.

9. A fine-bubble generator as claimed in claim 1, further comprising an introduction section downstream of said second introduction section, which penetrates said case body in the thickness direction and releases gas into said main passage.

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