Microbubble generator

Abstract

To provide a microbubble generator which reduces the air supply amount to a low level and can generate microbubbles efficiently.SOLUTION: A microbubble generator 10 which is provided on a pipe where a liquid circulates for generating microbubbles in the liquid includes: a device body 20; and a flow passage 50 which extends inside the device body 20 and where the liquid circulates. The flow passage 50 includes: a spiral flow passage 38b with a step whose circumferential position around a central axis O varies gradually toward a downstream side in an axial direction along the central axis O of the device body 20; and an air supply flow passage 36 which is arranged on an upstream side in an axial direction of the spiral flow passage 38b with a step, extends in the axial direction, and communicates the spiral flow passage 38b with a step. The device body 20 has an air supplying part 14 for supplying air to the air supply flow passage 36, and the air supplying part 14 has an air spraying slit 46 which extends annularly along an inner peripheral surface of the air supply flow passage 36 and opens toward a downstream side in the axial direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a microbubble generator. [Background technology]

[0002] A microbubble generator, for example, as described in Patent Document 1, is known. The microbubble generator is installed in a part of a pipe and generates microbubbles in a liquid flowing through the pipe. The microbubbles in the liquid have functions such as removing deposits attached to the inner wall of the pipe and suppressing the attachment of new deposits. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-142185 Summary of the Invention [Problem to be solved by the invention]

[0004] This type of microbubble generator is required to efficiently generate microbubbles by keeping the amount of air supplied to the liquid to a minimum.

[0005] An object of the present invention is to provide a microbubble generator that can efficiently generate microbubbles while keeping the amount of air supply low. [Means for solving the problem]

[0006] One aspect of the present invention is a microbubble generator that is provided in a pipe through which a liquid flows and generates microbubbles in the liquid, the microbubble generator comprising: a device main body; and a flow path that extends inside the device main body and through which the liquid flows, the flow path having a stepped spiral flow path whose circumferential position around the central axis changes in stages as it extends along the central axis of the device main body toward the downstream side in the axial direction, and an air supply flow path that is disposed upstream in the axial direction of the stepped spiral flow path, extends in the axial direction, and communicates with the stepped spiral flow path, the device main body having an air supply unit that supplies air to the air supply flow path, the air supply unit having an air injection slit that extends annularly along the inner circumferential surface of the air supply flow path and opens toward the downstream side in the axial direction, the air injection slit being a cylindrical gap that extends in the axial direction. The downstream end of the air injection slit in the axial direction is open toward the downstream side in the axial direction. .

[0007] In the microbubble generator of the present invention, fine air (bubbles) are injected into the liquid in a circular pattern from the air injection slits of the air supply unit, and the liquid containing this air flows through the stepped spiral flow path downstream in the axial direction. This causes the fine bubbles to become even smaller, generating microbubbles. That is, when the liquid containing air flows through the stepped spiral flow path, the unevenness of the inner surface of the stepped spiral flow path causes a cavitation effect, and centrifugal force acts on the liquid, generating microbubbles in the liquid. The microbubbles in the liquid have the function of removing deposits that have adhered to the inner walls of pipes, etc., and the function of suppressing the adhesion of new deposits, etc. Therefore, a cleaning effect can be obtained throughout the entire liquid distribution system, including the pipes through which the liquid flows.

[0008] According to the present invention, a thin, high-speed air curtain, known as an air knife, is supplied from the air injection slit into the liquid. The injected air and air-containing liquid flow along the inner circumferential surface of the flow path due to the Coanda effect, and then enter the stepped spiral flow path downstream. Because the liquid containing tiny air flows along the unevenness of the inner surface of the stepped spiral flow path, the air bubbles can be efficiently converted into microbubbles. Furthermore, the Coanda effect increases the flow rate of the liquid being pumped downstream, enabling microbubbles to stably reach parts of the pipe far from the microbubble generator, further enhancing the cleaning effect of the distribution system.

[0009] Furthermore, the air injection slit injects fine air in a circular pattern along the inner circumferential surface of the air supply flow path, i.e., over the entire 360° circumference, so that the above-mentioned effects can be obtained over a wide circumferential range within the stepped spiral flow path. Furthermore, because the air injection slits inject air in the direction of the liquid flow, i.e., downstream, backflow of liquid into the air injection slits is suppressed, which prevents deposits from adhering to the air injection slits and maintains the various functions of the air injection slits described above.

[0010] After passing through the stepped spiral flow path, the liquid turns into a swirling flow and flows downstream of the microbubble generator. This swirling flow also makes it easier for microbubbles to be distributed stably even in parts of the pipe far from the microbubble generator, thereby improving the cleaning effect throughout the entire liquid distribution system.

[0011] As described above, according to the present invention, air is injected into the liquid from the air injection slit at a high flow rate but at a low flow rate, thereby efficiently generating microbubbles while keeping the amount of air supplied to the liquid low. Specifically, compared with the air supply amount of conventional microbubble generators, the microbubble generator of the present invention can reduce the air supply amount to about one-third while still ensuring sufficient cleaning effect. In addition, it is easy to configure the air injection slit compactly, making it easy to miniaturize the microbubble generator. Furthermore, the microbubble generator of the present invention can be easily applied to existing piping equipment, etc., making it highly versatile.

[0012] In the above microbubble generator, it is preferable that the slit width dimension of the air injection slit is 0.1 mm or less.

[0013] When the slit width of the air injection slit is 0.1 mm or less, the function as an air knife is stably ensured. That is, fine air (air bubbles) can be stably injected into the liquid at high speed from the air injection slit, and a larger number of microbubbles can be generated. In addition, the amount of air supplied can be more suitably reduced. Furthermore, by making the slit width sufficiently small, it is possible to prevent the liquid from flowing back from the flow path into the air supply unit through the air injection slit. Therefore, the function of the air supply unit is maintained well. Preferably, the slit width of the air injection slit is 0.05 mm or less, and more preferably 0.03 mm or less. From the viewpoint of facilitating manufacturing and ensuring a predetermined amount of air supply, the slit width is preferably, for example, 0.01 mm or more.

[0014] In the above microbubble generator, it is preferable that a plurality of the stepped spiral flow channels are provided and aligned in a circumferential direction around the central axis.

[0015] In this case, the multiple stepped spiral flow paths can generate more microbubbles.

[0016] In the microbubble generator, the air injection slit may be annular about the central axis.

[0017] In this case, microbubbles can be generated uniformly in the circumferential direction around the central axis of the device body.

[0018] In the above-described microbubble generator, the air injection slit may be annular and concentric with a flow path center of a flow path portion connected to an upstream end of the stepped spiral flow path in the axial direction.

[0019] In this case, the liquid containing fine air particles can be supplied to the entire inner circumferential surface of the stepped spiral flow path, thereby generating microbubbles more efficiently. [Effects of the Invention]

[0020] According to the microbubble generator of one aspect of the present invention, the amount of air supplied can be kept small and microbubbles can be generated efficiently. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a side view schematically showing a liquid circulation system including a microbubble generator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a front view of the microbubble generator according to the first embodiment of the present invention as seen from the axial direction. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III of FIG. [Figure 4] FIG. 4 is a diagram illustrating the arrangement of the flow holes of the plurality of plate members. [Figure 5] FIG. 5 is an enlarged cross-sectional view of part V in FIG. [Figure 6] FIG. 6 is a front view of a microbubble generator according to a second embodiment of the present invention, as viewed from the axial direction. [Figure 7] FIG. 7 is a cross-sectional view showing a cross section taken along line VII-VII in FIG. [Figure 8] 8(a) is an enlarged cross-sectional view of part VIIIa in FIG. 7, and FIG. 8(b) is a rear view taken along the arrow VIIIb in FIG. 8(a). DETAILED DESCRIPTION OF THE INVENTION

[0022] First Embodiment A microbubble generator 10 according to a first embodiment of the present invention will be described with reference to FIGS. As shown in Fig. 1, a microbubble generator 10 of this embodiment is provided in a pipe 100 through which a liquid flows, and generates microbubbles in the liquid flowing through the pipe 100. Specifically, the microbubble generator 10 is provided midway through a pipe (piping) 100 through which service water flows, for example, in a can manufacturing factory, and forms part of the pipe 100. The liquid flowing through the pipe 100 is, for example, an alkaline slaked lime solution. That is, the solute of the liquid is slaked lime or the like, and the solvent is water or the like.

[0023] Liquid is pumped by pump 102 from tank 101, which stores slaked lime solution, and flows through pipe 100, before being sent to each treatment tank (not shown) through multiple branch pipes 100a of pipe 100. Excess liquid that does not flow into branch pipe 100a is returned to tank 101 through pipe 100. For example, acidic wastewater used in can manufacturing processes flows into multiple treatment tanks (not shown), and slaked lime solution is supplied to this wastewater through branch pipe 100a, thereby adjusting the pH of the wastewater in the treatment tank. The pH-adjusted wastewater is sent to a thickener or the like (not shown).

[0024] As shown in FIGS. 2 and 3, the microbubble generator 10 includes a device main body 20 and a flow path 50 that extends inside the device main body 20 and through which a liquid flows. The device body 20 has a columnar shape centered on a central axis O, and in this embodiment has a substantially cylindrical shape. The device body 20 includes a main body tube 11, an air supply unit 14, a plurality of plate members 13, spacer members 12, and a fixing unit 15. The liquid flows through the inside of the flow channel 50 from one end to the other end in the direction along the central axis O of the device body 20.

[0025] In this embodiment, the direction in which the central axis O of the device body 20 extends is referred to as the axial direction. The axial direction corresponds to the Z-axis direction shown in each figure. Within the axial direction, the direction in which the liquid flows is referred to as the downstream axial side (+Z side) or simply the downstream side. The downstream axial side is the direction from one axial end of the device body 20 to the other axial end. Within the axial direction, the direction opposite to the direction in which the liquid flows is referred to as the upstream axial side (-Z side) or simply the upstream side. The upstream axial side is the direction from the other axial end of the device body 20 to one axial end. 1, in this embodiment, the microbubble generator 10 is installed in the pipe 100 with the downstream side in the axial direction facing upward in the vertical direction. This makes it easier for microbubbles to flow downstream of the microbubble generator 10 together with air (air bubbles).

[0026] 2 and 3, the direction perpendicular to the central axis O is called the radial direction. Within the radial direction, the direction approaching the central axis O is called the radially inner direction, and the direction away from the central axis O is called the radially outer direction. The direction circumferentially around the central axis O is called the circumferential direction. As shown in Fig. 2, when viewing the device body 20 from the upstream side in the axial direction, a predetermined direction within the circumferential direction is called one circumferential side θ1, and the direction opposite to the predetermined direction is called the other circumferential side θ2. In this embodiment, the one circumferential side θ1 is the counterclockwise direction around the central axis O in Fig. 2, and the other circumferential side θ2 is the clockwise direction around the central axis O in Fig. 2.

[0027] The main body tube 11 has a substantially cylindrical shape extending in the axial direction around a central axis O. As shown in Fig. 3, the main body tube 11 has an outflow tubular section 17 located at the downstream end of the main body tube 11 in the axial direction, and an intermediate tubular section 18 located upstream of the outflow tubular section 17 in the axial direction.

[0028] The outflow tube portion 17 has a downstream side flow tube 17a and a downstream side flange 17b. The downstream side flow tube 17a has a cylindrical shape extending in the axial direction and includes a downstream side seal groove 17c and a downstream side seal member 17d.

[0029] The downstream seal groove 17c is recessed radially inward from the outer circumferential surface of the downstream flow tube 17a and has an annular shape extending in the circumferential direction. In this embodiment, a plurality of downstream seal grooves 17c are provided at intervals in the axial direction. The downstream seal member 17d is an annular elastic member extending in the circumferential direction, such as an O-ring. In this embodiment, a plurality of downstream seal members 17d are provided at intervals in the axial direction. Each downstream seal member 17d is disposed in a corresponding downstream seal groove 17c.

[0030] The inner diameter of the inner peripheral surface 17e of the downstream side flow tube 17a decreases from the upstream end of the downstream side flow tube 17a in the axial direction toward the downstream side. The inner peripheral surface 17e of the downstream side flow tube 17a has a tapered surface shape in which the diameter gradually decreases toward the downstream side in the axial direction.

[0031] The downstream flange 17b has a flange shape that expands radially outward from the downstream portion of the outer circumferential surface of the downstream flow tube 17a. The downstream flange 17b is fixed to the downstream end of the intermediate tube portion 18 in the axial direction by a plurality of bolt members 19b. Although not particularly shown, the downstream flange 17b is fixed to the portion of the tube 100 axially adjacent to the microbubble generator 10, i.e., the connection end of the tube 100 adjacent to the downstream side of the microbubble generator 10 in the axial direction, by bolt members or the like.

[0032] The intermediate tubular portion 18 has a cylindrical shape extending in the axial direction. The end face of the intermediate tubular portion 18 facing the downstream side in the axial direction contacts the end face of the downstream flange 17b facing the upstream side in the axial direction. The downstream end of the intermediate tubular portion 18 in the axial direction is fitted into the outer peripheral surface of the downstream flow tube 17a. The downstream seal member 17d contacts the downstream end of the inner peripheral surface of the intermediate tubular portion 18 in the axial direction over the entire circumferential direction.

[0033] 2 and 3, the air supply unit 14 supplies air to a portion of the flow path 50 located upstream of the plurality of plate members 13 in the axial direction (an air supply flow path 36, which will be described later). The air supply section 14 has an inlet tube section 16, an air supply tube section 43, an air introduction hole 44, an air supply path 45, an air injection slit 46, a check valve (non-return valve) 29, and an air supply source (not shown).

[0034] The inlet tube portion 16 has an upstream flow tube 16a and an upstream flange 16b. The upstream flow tube 16a has a cylindrical shape extending in the axial direction and includes an upstream seal groove 16c and an upstream seal member 16d.

[0035] The upstream seal groove 16c is recessed radially inward from the outer circumferential surface of the upstream flow tube 16a and has an annular shape extending circumferentially. In this embodiment, a plurality of upstream seal grooves 16c are provided at intervals in the axial direction. The upstream seal member 16d is an annular elastic member extending in the circumferential direction, such as an O-ring. In this embodiment, a plurality of upstream seal members 16d are provided at intervals in the axial direction. Each upstream seal member 16d is disposed in a corresponding upstream seal groove 16c.

[0036] As shown in FIG. 5, the upstream flow tube 16a has, on its inner peripheral surface, a large-diameter inner peripheral portion 16e, a medium-diameter inner peripheral portion 16f, a small-diameter inner peripheral portion 16g, and a tapered portion 16h. The large-diameter inner peripheral portion 16e is disposed at the upstream end of the inner peripheral surface of the upstream-side flow tube 16a. The large-diameter inner peripheral portion 16e faces radially inward and extends along the axial direction. The medium-diameter inner peripheral portion 16f is disposed downstream of the large-diameter inner peripheral portion 16e. The medium-diameter inner peripheral portion 16f has a smaller inner diameter than the large-diameter inner peripheral portion 16e. The medium-diameter inner peripheral portion 16f faces radially inward and extends along the axial direction.

[0037] The small-diameter inner peripheral portion 16g is disposed downstream of the medium-diameter inner peripheral portion 16f. The small-diameter inner peripheral portion 16g has the smallest inner diameter among the inner peripheral surfaces of the upstream flow tube 16a. The small-diameter inner peripheral portion 16g faces radially inward and extends along the axial direction. A downstream portion (part) of the small-diameter inner peripheral portion 16g guides the air injected from the air injection slits 46 toward the downstream side in the axial direction by the Coanda effect. For this reason, the small-diameter inner peripheral portion 16g may also be referred to as the axial air guide portion 16g. Furthermore, an upstream portion of the small-diameter inner circumferential portion 16g (a part different from the part mentioned above) constitutes one of a pair of slit inner walls that define the air injection slit 46 and face each other with a gap in the radial direction.

[0038] The small-diameter inner circumferential portion 16g has a portion that is located downstream of the downstream end of the air supply tube portion 43. In the illustrated example, more than half of the small-diameter inner circumferential portion 16g in the axial direction, including the downstream end, protrudes and extends downstream in the axial direction beyond the air supply tube portion 43.

[0039] The tapered portion 16h is disposed downstream of the small-diameter inner circumferential portion 16g. The tapered portion 16h is connected to the downstream end of the small-diameter inner circumferential portion 16g and is positioned radially outward from this connection toward the downstream side. The tapered portion 16h has a tapered surface shape that gradually widens in diameter toward the downstream side in the axial direction. The tapered portion 16h guides the air injected from the air injection slits 46 radially outward as it approaches the downstream side in the axial direction due to the Coanda effect. For this reason, the tapered portion 16h may also be referred to as an expanding-diameter air guide portion 16h.

[0040] 3, the upstream flange 16b has a flange shape that expands radially outward from an upstream portion in the axial direction on the outer circumferential surface of the upstream flow tube 16a. The upstream flange 16b is fixed to an upstream end portion in the axial direction of the intermediate tube portion 18 by a plurality of bolt members 19a. Although not particularly shown, the upstream flange 16b is fixed to a portion of the tube 100 axially adjacent to the microbubble generator 10, i.e., a connection end portion of the tube 100 adjacent to the upstream side in the axial direction of the microbubble generator 10, by bolt members or the like.

[0041] The upstream end face of the intermediate tubular portion 18 contacts the downstream end face of the upstream flange 16b. The upstream end of the intermediate tubular portion 18 fits into the outer peripheral surface of the upstream flow tube 16a. The upstream seal member 16d contacts the upstream end of the inner peripheral surface of the intermediate tubular portion 18 over the entire circumferential direction.

[0042] The air supply tube 43 has a cylindrical shape extending in the axial direction. The air supply tube 43 fits into the upstream flow tube 16a. As shown in Fig. 5, the air supply tube 43 has a large-diameter outer peripheral portion 43a, a medium-diameter outer peripheral portion 43b, a small-diameter outer peripheral portion 43c, and an annular groove 43d on its outer circumferential surface. The large-diameter outer peripheral portion 43a is disposed at the upstream end of the outer peripheral surface of the air supply tube portion 43. The large-diameter outer peripheral portion 43a faces radially outward and extends along the axial direction. The large-diameter outer peripheral portion 43a contacts the large-diameter inner peripheral portion 16e.

[0043] The medium-diameter outer peripheral portion 43b is disposed downstream of the large-diameter outer peripheral portion 43a. The medium-diameter outer peripheral portion 43b has a smaller outer diameter than the large-diameter outer peripheral portion 43a. The medium-diameter outer peripheral portion 43b faces radially outward and extends along the axial direction. The medium-diameter outer peripheral portion 43b contacts the medium-diameter inner peripheral portion 16f. The end face located between the large diameter outer peripheral portion 43a and the medium diameter outer peripheral portion 43b and facing downstream in the axial direction comes into contact with the end face located between the large diameter inner peripheral portion 16e and the medium diameter inner peripheral portion 16f and facing upstream in the axial direction.

[0044] The small-diameter outer peripheral portion 43c is disposed downstream of the medium-diameter outer peripheral portion 43b. The small-diameter outer peripheral portion 43c has a smaller outer diameter than the medium-diameter outer peripheral portion 43b. The small-diameter outer peripheral portion 43c is disposed at the downstream end of the outer peripheral surface of the air supply tube portion 43. The small-diameter outer peripheral portion 43c faces radially outward and extends along the axial direction. The small-diameter outer peripheral portion 43c faces the small-diameter inner peripheral portion 16g over the entire circumferential direction with a radial gap therebetween. The small-diameter outer peripheral portion 43c constitutes the other of a pair of slit inner walls that face each other with a radial gap therebetween and define the air injection slit 46.

[0045] The annular groove 43d is disposed between the medium-diameter outer peripheral portion 43b and the small-diameter outer peripheral portion 43c in the axial direction. The annular groove 43d is recessed radially inward from the small-diameter outer peripheral portion 43c and extends circumferentially. The annular groove 43d is a circular ring-shaped groove centered on the central axis O. The annular groove 43d is disposed so as to overlap with the medium-diameter inner peripheral portion 16f when viewed radially.

[0046] The air supply tube 43 has an inclined portion 43e on its inner circumferential surface. The inclined portion 43e is located at least on the downstream end of the inner circumferential surface of the air supply tube 43. The inclined portion 43e has a tapered surface that is positioned radially outward as it approaches the downstream side in the axial direction. The inclined portion 43e guides air so that it draws in liquid when air is ejected downstream from the air ejection slit 46. For this reason, the inclined portion 43e may also be referred to as a liquid drawing guide portion 43e. In the illustrated example, the portion of the inner circumferential surface of the air supply tube 43 that is located upstream of the inclined portion 43e extends along the axial direction.

[0047] As shown in Fig. 3, the air introduction hole 44 penetrates the inlet tube portion 16 in the radial direction. The radially outer end of the air introduction hole 44 opens to the outer peripheral surface of the upstream flange 16b. The radially inner end of the air introduction hole 44 opens to the inner peripheral surface of the upstream flow tube 16a. Specifically, as shown in Fig. 5, the radially inner end of the air introduction hole 44 opens to the medium-diameter inner peripheral portion 16f.

[0048] The air supply passage 45 is disposed between the upstream flow tube 16a and the air supply tube portion 43 in the radial direction. The air supply passage 45 is an annular air flow path centered on the central axis O. The air supply passage 45 is connected to the radially inner end of the air introduction hole 44 and communicates with the air introduction hole 44. The air supply passage 45 is disposed between the medium-diameter inner circumferential portion 16f and the small-diameter inner circumferential portion 16g, and is an annular chamber (space) defined by an end face facing upstream in the axial direction, the medium-diameter inner circumferential portion 16f, and the annular groove 43d.

[0049] As shown in FIGS. 3 and 5, the air injection slit 46 is disposed radially between the upstream flow tube 16a and the air supply tube portion 43. The air injection slit 46 is an annular air flow path centered on the central axis O. Specifically, the air injection slit 46 is a cylindrical air flow path extending in the axial direction. More specifically, the air injection slit 46 is a cylindrical gap (space) defined radially between the small-diameter inner peripheral portion 16g and the small-diameter outer peripheral portion 43c. The air injection slit 46 is disposed downstream in the axial direction of the air supply path 45. The upstream end of the air injection slit 46 in the axial direction is connected to the air supply path 45. The downstream end of the air injection slit 46 in the axial direction opens toward the downstream side in the axial direction within the inlet tube portion 16. The air injection slit 46 opens toward the downstream side in the axial direction over a full 360° circumference around the central axis O.

[0050] 5, the radial dimension of the air injection slit 46, i.e., the slit width dimension S, is 0.1 mm or less. Preferably, the slit width dimension S of the air injection slit 46 is 0.05 mm or less, and more preferably, 0.03 mm or less. Furthermore, it is preferable that the slit width dimension S is, for example, 0.01 mm or more.

[0051] 3, in this embodiment, a check valve 29 is provided in the inlet cylindrical portion 16. The check valve 29 is fixed to the air introduction hole 44 by screwing or the like. The check valve 29 allows the flow of air from an air supply source (not shown) toward the air introduction hole 44, and blocks the flow of air and liquid from the air introduction hole 44 toward the air supply source.

[0052] Although not shown, the air supply source is connected to the check valve 29 via piping, tubing, etc. The air supply source is, for example, an air compressor, etc. The air supply source supplies compressed air to the check valve 29.

[0053] The plurality of plate members 13 are disposed inside the intermediate cylindrical portion 18 and overlap one another in the axial direction. Each of the plurality of plate members 13 is plate-shaped, with each plate surface facing the axial direction. The plate surfaces of plate members 13 adjacent to each other in the axial direction are in contact with each other. In this embodiment, as shown in FIG. 4, the plate members 13 are disk-shaped. The thickness of the plate members 13 in the axial direction is, for example, 3 to 5 mm. The plate members 13 are made of resin, for example, plastic. The plate member 13 has a communication hole 21 and a fixing hole 22 .

[0054] The through holes 21 penetrate the plate member 13 in the axial direction and constitute a part of the flow path 50. The through holes 21 are arranged at positions in the plate member 13 that are radially shifted from the central axis O. In this embodiment, the through holes 21 are circular holes. The through holes 21 of the multiple plate members 13 aligned in the axial direction are connected to each other, and the multiple connected through holes 21 form part of the flow path 50 (a stepped spiral flow path 38b described later).

[0055] As shown in FIGS. 2 to 4, the flow holes 21 of the plurality of plate members 13 are arranged in a spiral pattern with their circumferential positions around the central axis O shifted as they move downstream in the axial direction. Between axially adjacent plate members 13, the flow holes 21 that communicate with each other are arranged with a circumferential shift, thereby forming a step portion 23. The step portion 23 is arranged in a portion of the plate surface of the plate member 13 adjacent to the flow hole 21. By arranging the plurality of plate members 13 in the axial direction, a plurality of step portions 23 are provided at intervals from each other in the axial direction.

[0056] 4 is a front view showing five plate members 13g, 13h, 13i, 13h, and 13g arranged near the center in the axial direction out of the multiple plate members 13 arranged in the axial direction, and is a diagram illustrating the arrangement of the communication holes 21 of each plate member 13. In FIG. 4, the plate members 13 located to the right in the figure are located more upstream in the axial direction, and the plate members 13 located to the left in the figure are located more downstream in the axial direction.

[0057] In this embodiment, the interconnected flow holes 21 of the plurality of plate members 13 are arranged in a spiral pattern toward one circumferential side θ1 as they extend downstream in the axial direction. That is, in this embodiment, a plurality of types of plate members 13 having different arrangements of the flow holes 21 are provided. Specifically, as shown in FIG. 3 , ten types of plate members 13a, 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, and 13j are arranged in the axial direction, for a total of 18 plate members. More specifically, the plurality of plate members 13 are arranged in the following order from upstream to downstream in the axial direction: 13a, 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, 13h, 13g, 13f, 13e, 13d, 13c, 13b, 13a, and 13j.

[0058] 2, when viewed from the axial direction, the central angle β between the hole centers C of each of the through holes 21 of a pair of axially adjacent plate members 13, centered on the central axis O, is 1° or more and 5° or less, and is, for example, 2.5° in this embodiment. Specifically, among the multiple plate members 13 shown in FIGS. 3 and 4, the through holes 21 of each plate member 13 are arranged in the order of plate members 13b, 13c, 13d, 13e, 13f, 13g, 13h, 13i, 13h, 13g, 13f, 13e, 13d, 13c, 13b, 13a, and 13j, from plate member 13a located at the upstream end in the axial direction toward the downstream side in the axial direction, with a circumferential shift θ1, for example, every 2.5°.

[0059] 3, among the plurality of plate members 13, plate members 13a to 13h located axially upstream of plate member 13i located at the center in the axial direction, and plate members 13a to 13h located axially downstream of plate member 13i are arranged in an axially inverted position relative to each other. That is, among plate members 13a to 13h, a pair of plate members 13 with the same reference numerals located axially upstream and downstream of plate member 13i are identical parts. In other words, the plurality of plate members 13 include pairs of plate members 13 made of identical parts that are arranged in an axially inverted position relative to each other, and a plurality of such pairs are provided in this embodiment.

[0060] 2, the central angle α between the center C of the through hole 21 of the plate member 13a located at the upstream end in the axial direction and the center C of the through hole 21 of the plate member 13j located at the downstream end in the axial direction, with the central axis O as the center, is 40° or more and 90° or less. In this embodiment, the central angle α is, for example, 45°.

[0061] 4, a plurality of communication holes 21 are provided at intervals in the circumferential direction of the plate member 13. In this embodiment, eight communication holes 21 are provided in the plate member 13 at equal intervals in the circumferential direction.

[0062] The fixing hole 22 penetrates the plate member 13 in the axial direction. The fixing hole 22 is located on the central axis O of the plate member 13. The fixing hole 22 is arranged coaxially with the central axis O. In this embodiment, the fixing hole 22 has a substantially circular hole shape. The fixing hole 22 has a key fitting portion 22a. The key fitting portion 22a is concave and recessed radially outward from the inner circumferential surface of the fixing hole 22.

[0063] As shown in FIG. 3 , the spacer member 12 is disposed inside the intermediate cylindrical portion 18. The spacer member 12 is plate-shaped with a pair of plate surfaces facing the axial direction, or columnar with a pair of end surfaces facing the axial direction. In this embodiment, the spacer member 12 is disk-shaped or columnar with a central axis O. The spacer member 12 fits into the intermediate cylindrical portion 18 and is located upstream in the axial direction of the multiple plate members 13. The spacer member 12 is disposed adjacent to the upstream side of the plate member 13a, which is located at the upstream end of the multiple plate members 13 in the axial direction. In other words, the spacer member 12 and the plate member 13a contact each other in the axial direction. The spacer member 12 is also disposed adjacent to the downstream side of the upstream flow tube 16a in the axial direction. In other words, the spacer member 12 and the inlet cylindrical portion 16 contact each other in the axial direction.

[0064] The spacer member 12 has an insertion hole 24 a, an intermediate seal groove 24 b, an intermediate seal member 28 , and a through hole 25 . The insertion hole 24a penetrates the spacer member 12 in the axial direction. The insertion hole 24a is located on the central axis O of the spacer member 12. The insertion hole 24a is arranged coaxially with the central axis O. In this embodiment, the insertion hole 24a is a substantially circular hole. The insertion hole 24a has a key fitting groove 24c. The key fitting groove 24c is recessed radially outward from the inner circumferential surface of the insertion hole 24a and is groove-shaped extending in the axial direction. When viewed in the axial direction, the key fitting groove 24c is arranged to overlap with each of the key fitting portions 22a of the multiple plate members 13.

[0065] The intermediate seal groove 24b is a groove that extends in the circumferential direction and is recessed radially inward from the outer circumferential surface of the spacer member 12. The intermediate seal groove 24b is an annular groove that is centered on the central axis O. The intermediate seal member 28 is an annular elastic member extending in the circumferential direction, such as an O-ring. The intermediate seal member 28 is disposed in the intermediate seal groove 24b. The intermediate seal member 28 contacts the inner circumferential surface of the intermediate cylindrical portion 18 over the entire circumferential direction.

[0066] The through hole 25 penetrates the spacer member 12 in the axial direction and constitutes part of the flow path 50 (a linear flow path 38a described later). The through hole 25 is disposed in the spacer member 12 at a position radially shifted from the central axis O. In this embodiment, the through hole 25 is a circular hole. The through hole 25 is located upstream of the flow hole 21 in the axial direction and communicates with the flow hole 21. A plurality of through holes 25 are provided in the spacer member 12 at intervals in the circumferential direction. In this embodiment, eight through holes 25 are provided in the spacer member 12 at equal intervals in the circumferential direction. The radial positions of each through hole 25 in the spacer member 12 are the same as the radial positions of each communication hole 21 in the plate member 13. The inner diameter of the through holes 25 is equal to or greater than the inner diameter of the communication hole 21.

[0067] As shown in FIGS. 2 and 3, the fixing portion 15 has a shaft 31, a key 32, an inflow guide 33, and an outflow guide . The shaft 31 extends in the axial direction. In this embodiment, the shaft 31 is cylindrical. The shaft 31 is inserted into the insertion hole 24a of the spacer member 12 and each of the fixing holes 22 of the plurality of plate members 13. The shaft 31 has a key groove. The key groove is recessed radially inward from the outer circumferential surface of the shaft 31 and extends in the axial direction.

[0068] The key 32 extends in the axial direction. The key 32 is disposed in a key groove of the shaft 31 and protrudes radially outward from the outer circumferential surface of the shaft 31. The key 32 is inserted into the key fitting groove 24c of the spacer member 12 and into each of the key fitting portions 22a of the multiple plate members 13. This restricts relative movement of the shaft 31, spacer member 12, and multiple plate members 13 in the circumferential direction.

[0069] The inflow guide 33 is disposed on the upstream side of the shaft 31 in the axial direction. In this embodiment, the inflow guide 33 is formed integrally with the shaft 31. The inflow guide 33 has a pyramidal shape extending in the axial direction about the central axis O, and in this embodiment, is conical. The outer diameter of the inflow guide 33 is larger than the outer diameter of the shaft 31. The outer diameter of the inflow guide 33 increases from the upstream side to the downstream side in the axial direction. In other words, the outer peripheral surface of the inflow guide 33 has a tapered surface shape that increases in diameter toward the downstream side in the axial direction.

[0070] The leading end surface of the inflow guide 33 facing the upstream side in the axial direction is curved and convex toward the upstream side, and in this embodiment is a convex spherical surface. The rear end surface of the inflow guide 33 facing the downstream side in the axial direction is flat and extends in a direction perpendicular to the central axis O. The rear end surface of the inflow guide 33 comes into contact with a portion of the plate surface (end face) of the spacer member 12 facing the upstream side in the axial direction, which is located radially inside the through hole 25.

[0071] As shown in FIG. 3 , the outflow guide 34 is disposed downstream in the axial direction of the shaft 31. In this embodiment, the outflow guide 34 is fixed to the shaft 31 by a bolt member 35. The outflow guide 34 has a bolt hole extending in the axial direction, and the bolt member 35 is inserted into this bolt hole and screwed to the shaft 31. The outflow guide 34 has a cone shape extending in the axial direction about a central axis O, and in this embodiment, is conical. The outer diameter of the outflow guide 34 is larger than the outer diameter of the shaft 31. The outer diameter of the outflow guide 34 decreases from the upstream side to the downstream side in the axial direction. In other words, the outer peripheral surface of the outflow guide 34 has a tapered surface shape that decreases in diameter toward the downstream side in the axial direction.

[0072] A bolt hole opens in the rear end surface of the outflow guide 34 facing the downstream side in the axial direction. The tip surface of the outflow guide 34 facing the upstream side in the axial direction is flat and extends in a direction perpendicular to the central axis O. The tip surface of the outflow guide 34 comes into contact with a portion of the plate surface facing the downstream side in the axial direction of the plate member 13j located at the downstream end in the axial direction, which portion is located radially inside the flow hole 21.

[0073] The flow path 50 is provided so as to penetrate the device main body 20 in the axial direction. A liquid flows through the inside of the flow path 50. The flow path 50 has an upstream flow path section (air supply flow path) 36, a downstream flow path section 37, and an intermediate flow path section 38. The air supply section 14 of this embodiment supplies air to the upstream flow path section 36. That is, in this embodiment, the upstream flow path section 36 corresponds to the air supply flow path. For this reason, the upstream flow path section 36 may also be referred to as the air supply flow path 36.

[0074] The upstream flow path section 36 is located at the upstream end of the flow path 50 in the axial direction. The upstream flow path section 36 is disposed at least at the upstream end of the device main body 20 in the axial direction. The upstream flow path section 36 is a portion of the flow path 50 formed between the inner circumferential surfaces of the upstream flow tube 16a and the air supply tube section 43 and the outer surface of the inflow guide 33. The diameter of the upstream flow path section 36 increases toward the downstream side in the axial direction.

[0075] The upstream flow path section 36, i.e., the air supply flow path 36, is located axially upstream of a stepped spiral flow path 38b (described later) of the intermediate flow path section 38, extends in the axial direction, and communicates with the stepped spiral flow path 38b. The air injection slit 46 of the air supply section 14 extends annularly along the inner circumferential surface of the air supply flow path 36 and opens downstream within the air supply flow path 36.

[0076] The downstream flow path section 37 is located at the downstream end of the flow path 50 in the axial direction. The downstream flow path section 37 is disposed at least at the downstream end of the device main body 20 in the axial direction. The downstream flow path section 37 is a portion of the flow path 50 formed between the inner circumferential surface 17e of the downstream flow tube 17a and the outer surface of the outflow guide 34. The diameter of the downstream flow path section 37 decreases toward the downstream side in the axial direction.

[0077] The intermediate flow path section 38 is located between the upstream end and downstream end of the flow path 50 in the axial direction. The intermediate flow path section 38 is disposed in an intermediate portion between the upstream end and downstream end of the device main body 20 in the axial direction. The intermediate flow path section 38 communicates with the upstream flow path section 36 and the downstream flow path section 37. The upstream end of the intermediate flow path section 38 in the axial direction is connected to the downstream end of the upstream flow path section 36 in the axial direction. The downstream end of the intermediate flow path section 38 in the axial direction is connected to the upstream end of the downstream flow path section 37 in the axial direction.

[0078] The intermediate flow path section 38 has a straight flow path 38a and a stepped spiral flow path 38b. The straight flow passage 38a is located at the upstream end of the intermediate flow passage section 38 in the axial direction. The straight flow passage 38a extends linearly along the axial direction. The straight flow passage 38a is a part of the flow passage 50 formed by the inner circumferential surface of the through hole 25 of the spacer member 12. A plurality of straight flow passages 38a are provided at intervals in the circumferential direction. In this embodiment, eight straight flow passages 38a are provided at equal intervals in the circumferential direction.

[0079] The stepped spiral flow path 38b is located in a portion of the intermediate flow path section 38 other than the upstream end in the axial direction. The stepped spiral flow path 38b is located downstream in the axial direction of the straight flow path 38a. The stepped spiral flow path 38b is connected to the straight flow path 38a. The stepped spiral flow path 38b extends in the circumferential direction toward the downstream side in the axial direction. In this embodiment, the stepped spiral flow path 38b extends spirally toward one circumferential side θ1 from the upstream side to the downstream side in the axial direction. The circumferential position of the stepped spiral flow path 38b around the central axis O changes in stages toward the downstream side in the axial direction. The stepped spiral flow path 38b is a portion of the flow path 50 formed by the inner circumferential surfaces of the flow holes 21 of the multiple plate members 13 and the multiple step portions 23. A plurality of stepped spiral flow paths 38b are provided at intervals from each other in the circumferential direction. That is, a plurality of stepped spiral flow channels 38b are provided lined up in the circumferential direction. In this embodiment, eight stepped spiral flow channels 38b are provided at equal intervals in the circumferential direction.

[0080] In this embodiment, the flow path 50 in the device main body 20 branches from one upstream flow path section 36 to multiple intermediate flow path sections 38 from the upstream to downstream axial direction, and then the multiple intermediate flow path sections 38 are combined into one downstream flow path section 37.

[0081] In the microbubble generator 10 of this embodiment described above, fine air (air bubbles) are injected into the liquid in a circular pattern from the air injection slit 46 of the air supply unit 14, and the liquid containing this air flows through the stepped spiral flow path 38b on the downstream side in the axial direction. This causes the fine air bubbles to become even smaller, generating microbubbles. That is, when the liquid containing air flows through the stepped spiral flow path 38b, the unevenness of the inner surface of the stepped spiral flow path 38b causes a cavitation effect and centrifugal force acts on the liquid, generating microbubbles in the liquid. The microbubbles in the liquid have the function of removing deposits adhering to the inner wall of the pipe 100 and the function of suppressing the adhesion of new deposits, etc. Therefore, a cleaning effect can be obtained over the entire liquid flow system, including the pipe 100 through which the liquid flows.

[0082] According to this embodiment, air is supplied from the air injection slit 46 into the liquid in the form of a thin, high-speed air curtain, known as an air knife or the like. The air and the liquid containing the air thus injected flow along the inner circumferential surface of the flow path 50 due to the Coanda effect, and then flow into the stepped spiral flow path 38b on the downstream side. The liquid containing fine air flows along the unevenness of the inner surface of the stepped spiral flow path 38b, so the air bubbles can be efficiently converted into microbubbles. In addition, the Coanda effect can increase the flow rate of the liquid sent downstream, so that microbubbles can stably reach parts of the pipe 100 far from the microbubble generator 10, further improving the cleaning effect of the distribution system.

[0083] Furthermore, the air injection slits 46 inject fine air in a circular pattern along the inner circumferential surface of the air supply flow path 36, i.e., over the entire 360° circumference, so that the above-mentioned effects can be obtained over a wide circumferential range within the stepped spiral flow path 38b. Furthermore, the air injection slits 46 inject air in the direction of the liquid flow, i.e., downstream, thereby preventing the liquid from flowing back into the air injection slits 46. This prevents deposits from adhering to the inside of the air injection slits 46, and the various functions of the air injection slits 46 described above are maintained in good condition.

[0084] After passing through the stepped spiral flow path 38b, the liquid turns into a swirling flow and flows downstream of the microbubble generator 10. This swirling flow also makes it easier for microbubbles to spread stably even to parts of the pipe 100 that are far away from the microbubble generator 10, thereby improving the cleaning effect throughout the entire liquid distribution system.

[0085] As described above, according to this embodiment, air is injected into the liquid from the air injection slit 46 at a high flow rate but at a low flow rate, thereby efficiently generating microbubbles while keeping the amount of air supplied to the liquid low. Specifically, compared with the amount of air supplied by conventional microbubble generators, the microbubble generator 10 of this embodiment can reduce the amount of air supplied to about one-third while still ensuring a sufficient cleaning effect. In addition, it is easy to configure the air injection slit 46 compactly, making it easy to miniaturize the microbubble generator 10. Furthermore, the microbubble generator 10 of this embodiment can be easily applied to existing piping equipment, etc., making it highly versatile.

[0086] In this embodiment, the slit width dimension S of the air injection slit 46 is 0.1 mm or less. When the slit width dimension S of the air injection slit 46 is 0.1 mm or less, the function as an air knife is stably ensured. That is, fine air (air bubbles) can be stably injected into the liquid at high speed from the air injection slit 46, and a larger number of microbubbles can be generated. In addition, the amount of air supplied can be more suitably reduced. Furthermore, by making the slit width dimension S sufficiently small, it is possible to prevent the liquid from flowing back from the flow path 50 to the air supply path 45 through the air injection slit 46. Therefore, the function of the air supply unit 14 is maintained satisfactorily. Preferably, the slit width dimension S of the air injection slit 46 is 0.05 mm or less, and more preferably 0.03 mm or less. From the standpoint of facilitating manufacturing and ensuring a predetermined or greater amount of air supply, the slit width dimension S is preferably, for example, 0.01 mm or more.

[0087] In this embodiment, a plurality of stepped spiral flow paths 38b are provided lined up in the circumferential direction around the central axis O. In this case, the multiple stepped spiral flow paths 38b can generate more microbubbles.

[0088] In this embodiment, the air injection slit 46 is annular with the central axis O as its center. In this case, microbubbles can be generated uniformly in the circumferential direction around the central axis O of the device body 20.

[0089] Furthermore, in this embodiment, the plurality of plate members 13 includes a pair of plate members 13 made of identical parts that are arranged in an axially inverted position, and thus the use of common parts reduces the number of types of the plurality of plate members 13. In particular, in this embodiment, since a plurality of such pairs are provided, the number of types of plate members 13 can be further reduced.

[0090] In addition, in this embodiment, when viewed from the axial direction, the central angle α between the hole center C of the flow hole 21 of the plate member 13a located at the upstream end in the axial direction among the multiple plate members 13 and the hole center C of the flow hole 21 of the plate member 13j located at the downstream end in the axial direction, centered on the central axis O, is greater than or equal to 40° and less than 90°. When the central angle α of the spiral staircase-like flow path portion (stepped spiral flow path 38b) formed by each of the through holes 21 of the multiple plate members 13 is 40° or more, a swirling flow can be stably generated in the liquid flowing through the stepped spiral flow path 38b, further enhancing the cleaning effect of this embodiment. In addition, since the surface area of ​​the stepped portion 23 is large, microbubbles can be more stably generated by the cavitation effect. Furthermore, if the central angle α is 90° or less, the total length in the axial direction of the spiral staircase-shaped flow path portion can be prevented from becoming too long, allowing the device to be configured compactly.

[0091] In this embodiment, the central angle β between the hole centers C of the respective flow holes 21 of a pair of axially adjacent plate members 13 about the central axis O is 1° or more and 5° or less when viewed from the axial direction. When the central angle β is 1° or more, the function of the step portion 23 formed in the stepped spiral flow path 38b is stably obtained, and microbubbles are efficiently generated. Furthermore, when the central angle β is 5° or less, the pressure loss of the liquid flowing through the stepped spiral flow path 38b is prevented from becoming too large, and the flow state of the liquid flowing through the flow path 50 can be stabilized.

[0092] Second Embodiment Next, a microbubble generator 40 according to a second embodiment of the present invention will be described with reference to Fig. 6 to Fig. 8. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof may be omitted.

[0093] The microbubble generator 40 of this embodiment differs from the microbubble generator 10 described in the previous embodiment in the configuration of the air supply unit 27, etc. Accordingly, the air supply flow path 38a that supplies air from the air supply unit 27 is also different. In the above-described embodiment, the air supply unit 14 is provided at the upstream end of the device body 20 and includes the inlet tube portion 16 and the air supply tube portion 43, whereas in this embodiment, the air supply unit 27 is provided in the intermediate portion between the upstream end and downstream end of the device body 20 and includes the intermediate tube portion 18, the spacer member 12, and the air supply tube portion 41. Also in this embodiment, the main body tube 11 includes the inlet tube portion 16.

[0094] As shown in Figures 6 and 7, in detail, in this embodiment, the air supply section 27 has an intermediate cylindrical section 18, a spacer member 12, an air supply cylindrical section 41, an air introduction hole 51, an air supply path 52, a communication hole 42, an air injection slit 53, a check valve (non-return valve) 29, and an air supply source (not shown).

[0095] 7, in this embodiment, the spacer member 12 has a plurality of sets of intermediate seal grooves 24b and intermediate seal members 28. The plurality of sets are arranged at intervals from one another in the axial direction. The spacer member 12 also has a supply groove 26. The supply groove 26 is recessed radially inward from the outer peripheral surface of the spacer member 12 and has a groove shape that extends in the circumferential direction. The supply groove 26 is annular and centered on the central axis O. In this embodiment, the supply groove 26 is disposed between a pair of axially adjacent intermediate seal grooves 24b.

[0096] The through-hole 25 of the spacer member 12 has a hole center A, which is its central axis, extending parallel to the central axis O of the device body 20. Therefore, the direction in which the hole center A extends corresponds to the axial direction of the central axis O. In this embodiment, the direction perpendicular to the hole center A is called the hole diameter direction. Of the hole diameter directions, the direction approaching the hole center A is called the inner hole diameter direction, and the direction away from the hole center A is called the outer hole diameter direction. The direction going around the hole center A is called the hole circumferential direction.

[0097] The inner peripheral surface of the through hole 25 faces inward in the hole diameter direction and extends along the axial direction. The downstream portion (part) of the through hole 25 guides the air injected from the air injection slit 53 toward the downstream side in the axial direction by the Coanda effect. For this reason, the through hole 25 may also be referred to as the axial air guide portion 25. As shown in Figure 8(a), a part of the intermediate part of the through hole 25 located between the upstream end and the downstream end in the axial direction (a part different from the part mentioned above) constitutes one of a pair of opposing slit inner walls separated by a gap in the hole diameter direction that define the air injection slit 53.

[0098] The through-hole 25 has a portion located downstream of the downstream end of the air supply cylindrical portion 41. In the illustrated example, the downstream portion of the through-hole 25, which includes at least the downstream end, protrudes and extends downstream in the axial direction beyond the end face 41d of the air supply cylindrical portion 41 facing the downstream side.

[0099] In this embodiment, the spacer member 12 has a step portion 24d. The step portion 24d is disposed on the axial upstream side of the through hole 25. The step portion 24d is annular and extends in the circumferential direction of the hole, centered on the hole center A. The inner diameter of the step portion 24d is larger than the inner diameter of the through hole 25.

[0100] The air supply tube portion 41 is tubular and centered on the hole center A, and extends in the axial direction. In this embodiment, the air supply tube portion 41 is substantially cylindrical. The air supply tube portion 41 fits into the through hole 25. As shown in FIG. 6 , a plurality of air supply tube portions 41 are provided at intervals from one another around the central axis O. In this embodiment, eight air supply tube portions 41 are provided at equal intervals in the circumferential direction on the spacer member 12. One air supply tube portion 41 is disposed in each through hole 25. 7 and 8(a), the axial length of the air supply tube portion 41 is smaller than the axial length of the through-hole 25. The air supply tube portion 41 is located inside the through-hole 25 in a portion other than the downstream portion.

[0101] As shown in FIGS. 8(a) and 8(b), the air supply cylinder 41 has a cylinder main body 41a and a cylinder flange 41b. The cylindrical body 41a is cylindrical and has its center at the hole center A, and extends in the axial direction. The cylindrical body 41a has a cylindrical air groove 41c and a cylindrical small-diameter outer peripheral portion 41e. The outer peripheral surface of the cylindrical body 41a contacts the inner peripheral surface of the through-hole 25 except for the cylindrical air groove 41c and the cylindrical small-diameter outer peripheral portion 41e.

[0102] The cylindrical air groove 41c is recessed inward in the hole diameter direction from the outer peripheral surface of the cylindrical body 41a and extends in the hole circumferential direction. The cylindrical air groove 41c is an annular groove centered on the hole center A. The cylindrical air groove 41c is located in the downstream portion of the cylindrical body 41a.

[0103] The small-diameter outer peripheral portion 41e is located downstream of the cylinder air groove 41c. The small-diameter outer peripheral portion 41e has a smaller outer diameter than the portions of the cylinder main body 41a other than the cylinder air groove 41c and the small-diameter outer peripheral portion 41e. The small-diameter outer peripheral portion 41e is located at the downstream end of the outer peripheral surface of the cylinder main body 41a. The small-diameter outer peripheral portion 41e faces outward in the hole diameter direction and extends along the axial direction. The small-diameter outer peripheral portion 41e faces the inner peripheral surface of the through hole 25 over the entire circumference in the hole diameter direction, with a gap in the hole diameter direction. The small-diameter outer peripheral portion 41e constitutes the other of a pair of opposing slit inner walls that define the air injection slit 53 and are spaced apart in the hole diameter direction.

[0104] The cylinder flange 41b is annular and has a plate shape centered on the hole center A. The cylinder flange 41b extends outward in the hole diameter direction from the upstream end of the cylinder body 41a in the axial direction. The outer diameter of the cylinder flange 41b is larger than the inner diameter of the through hole 25. The cylinder flange 41b is disposed on the step portion 24d. The plate surface of the cylinder flange 41b facing the downstream side in the axial direction contacts the bottom surface of the step portion 24d facing the upstream side in the axial direction.

[0105] 7, the air introduction hole 51 penetrates the intermediate cylindrical portion 18 in the radial direction. The radially outer end of the air introduction hole 51 opens to the outer peripheral surface of the intermediate cylindrical portion 18. The radially inner end of the air introduction hole 51 opens to the inner peripheral surface of the intermediate cylindrical portion 18. As shown in FIG. 6, in this embodiment, a plurality of (two) air introduction holes 51 are provided at equal intervals in the circumferential direction.

[0106] 7, the air supply passage 52 is disposed between the intermediate cylindrical portion 18 and the spacer member 12 in the radial direction. The air supply passage 52 is an annular air flow path centered on the central axis O. The air supply passage 52 is connected to each of the radial inner ends of the multiple air introduction holes 51 and communicates with each of the air introduction holes 51. The air supply passage 52 is an annular chamber (space) defined by the supply groove 26 and the inner circumferential surface of the intermediate cylindrical portion 18.

[0107] The communication holes 42 open to the supply groove 26 and to a portion of the through-hole 25 facing the cylindrical air groove 41c. The communication holes 42 extend radially between the supply groove 26 and the cylindrical air groove 41c. As shown in FIG. 6 , a plurality of communication holes 42 are provided at intervals in the circumferential direction. In this embodiment, eight communication holes 42 are provided at equal intervals in the circumferential direction in the spacer member 12. That is, the number of communication holes 42 and the number of air supply tube portions 41 are the same, and each communication hole 42 communicates with the cylindrical air groove 41c of each air supply tube portion 41. Furthermore, each communication hole 42 communicates with each air introduction hole 51 via the supply groove 26.

[0108] As shown in Figures 7, 8(a), and 8(b), the air injection slit 53 is disposed between the spacer member 12 and the air supply tube portion 41 in the hole diameter direction. The air injection slit 53 is an annular air flow path centered on the hole center A. That is, the air injection slit 53 is annular and concentric with the flow path center (hole center A) of the flow path portion (straight flow path 38a) connected to the axially upstream end of the stepped spiral flow path 38b. Specifically, the air injection slit 53 is a cylindrical air flow path extending in the axial direction. More specifically, the air injection slit 53 is a cylindrical gap (space) defined in the hole diameter direction between the inner circumferential surface of the through hole 25 and the tube small diameter outer circumferential portion 41e.

[0109] The air injection slit 53 is disposed downstream in the axial direction of the cylindrical air groove 41c. The upstream end of the air injection slit 53 in the axial direction is connected to the cylindrical air groove 41c. The downstream end of the air injection slit 53 in the axial direction opens toward the downstream side in the axial direction within the through hole 25. The air injection slit 53 opens toward the downstream side in the axial direction over the entire 360° circumference around the hole center A.

[0110] The dimension of the air injection slit 53 in the hole diameter direction, that is, the slit width dimension S, is the same as the slit width dimension S of the air injection slit 46 described in the previous embodiment. A plurality of air injection slits 53 are provided lined up in the circumferential direction around the central axis O. One air injection slit 53 is disposed in each through hole 25. In this embodiment, eight air injection slits 53 are provided at equal intervals in the circumferential direction.

[0111] As shown in Fig. 7, in this embodiment, a check valve 29 is provided in the intermediate cylindrical portion 18. As shown in Fig. 6, in this embodiment, a plurality of (two) check valves 29 are provided at equal intervals from each other in the circumferential direction. Each check valve 29 is fixed to each air introduction hole 51 by screwing or the like. The check valve 29 allows the flow of air from an air supply source (not shown) toward the air introduction hole 51, and blocks the flow of air and liquid from the air introduction hole 51 toward the air supply source.

[0112] As shown in FIGS. 7, 8(a), and 8(b), in this embodiment, the straight flow path 38a of the flow path 50 is formed by the inner circumferential surface of the air supply tube portion 41 and the downstream portion of the inner circumferential surface of the through-hole 25. The straight flow path 38a is disposed axially upstream of the stepped spiral flow path 38b, extends axially, and communicates with the stepped spiral flow path 38b. In this embodiment, the air supply unit 27 supplies air to the straight flow path 38a. That is, in this embodiment, the straight flow path 38a corresponds to the air supply flow path. For this reason, the straight flow path 38a may also be referred to as the air supply flow path 38a. The air injection slit 53 of the air supply unit 27 extends annularly along the inner circumferential surface of the air supply flow path 38a and opens downstream within the air supply flow path 38a.

[0113] According to the microbubble generator 40 of this embodiment described above, the same effects as those of the above-described embodiment can be obtained.

[0114] In this embodiment, the air injection slit 53 is annular and concentric with the flow path center (hole center A) of the straight flow path 38a connected to the stepped spiral flow path 38b. In this case, the liquid containing fine air particles can be supplied to the entire inner circumferential surface of the stepped spiral flow path 38b, thereby generating microbubbles more efficiently.

[0115] In this embodiment, a plurality of air injection slits 53 are provided, one for each of the plurality of straight flow paths 38a, and each air injection slit 53 supplies air to each stepped spiral flow path 38b through each straight flow path 38a. In this case, a large amount of microbubbles can be generated in the liquid more efficiently.

[0116] The present invention is not limited to the above-described embodiment, and the configuration can be changed within the scope of the present invention, as will be described below.

[0117] 2 and 6, the embodiment described above exemplifies the case where, when viewed from the upstream side in the axial direction of the device body 20, one circumferential side θ1 is a counterclockwise direction about the central axis O, and the other circumferential side θ2 is a clockwise direction about the central axis O. However, this is not limiting. That is, when viewed from the upstream side in the axial direction of the device body 20, one circumferential side θ1 may be a clockwise direction about the central axis O, and the other circumferential side θ2 may be a counterclockwise direction about the central axis O. In this case, the twist direction of the stepped spiral flow path 38b about the central axis O is opposite to that in the embodiment described above.

[0118] In addition, the various configurations described in the above embodiments and modifications may be combined, and additions, omissions, substitutions, and other modifications of the configurations are possible, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above embodiments, but is limited only by the claims. [Industrial Applicability]

[0119] The microbubble generator of the present invention can efficiently generate microbubbles while keeping the amount of air supply low, and therefore has industrial applicability. [Explanation of symbols]

[0120] 10, 40... Microbubble generator, 14, 27... Air supply unit, 20... Device body, 36... Upstream flow path section (air supply flow path), 38a... Straight flow path (air supply flow path), 38b... Stepped spiral flow path, 46, 53... Air injection slit, 50... Flow path, 100... Pipe, O... Central axis, S... Slit width dimension

Claims

1. A microbubble generator that is provided in a pipe through which a liquid flows and generates microbubbles in the liquid, A device body, a flow path extending inside the device body and through which a liquid flows; The flow path is a stepped spiral flow path whose circumferential position around the central axis changes stepwise along the central axis of the device body toward the downstream side in the axial direction; an air supply flow path that is disposed upstream of the stepped spiral flow path in the axial direction, extends in the axial direction, and communicates with the stepped spiral flow path; the device body has an air supply unit that supplies air to the air supply channel, the air supply portion has an air injection slit that extends annularly along an inner circumferential surface of the air supply flow path and opens toward a downstream side in the axial direction, The air injection slit is a cylindrical gap extending in the axial direction, an end portion of the air injection slit on the downstream side in the axial direction opens toward the downstream side in the axial direction; Microbubble generator.

2. The slit width dimension of the air injection slit is 0.1 mm or less. The microbubble generator according to claim 1.

3. The stepped spiral flow path is provided in plurality and arranged in a circumferential direction around the central axis. The microbubble generator according to claim 1 or 2.

4. The air injection slit is annular about the central axis. The microbubble generator according to any one of claims 1 to 3.

5. the air injection slit is annular and concentric with the center of the flow path of the flow path portion connected to the upstream end of the stepped spiral flow path in the axial direction. The microbubble generator according to any one of claims 1 to 3.

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