Fine air bubble generator

Abstract

To provide a fine air bubble generator which can generate fine air bubble efficiently.SOLUTION: A fine air bubble generator (1) includes: a first passage part (11) including an inlet (20) at an upstream end, and a discharge port (23) which has a diameter smaller than the inlet at a downstream end; and a second passage part (12) communicating with the first passage part through the discharge port and provided with an expanding part (31) having a passage width larger than a diameter of the discharge port. The expanding part has an annular pocket (35) which is recessed in a half doughnut-shape toward the inlet side relative to a position of the discharge port and continuous in a circumferential direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fine bubble generator that generates fine bubbles in a liquid.

Background Art

[0002] In recent years, technologies for purifying water quality by using fine bubbles, such as sterilization effects, have been increasing. There are various methods for generating fine bubbles, and one of them is the cavitation method in which the gas phase is pulverized by a sudden contraction and expansion of a flow path.

[0003] In Japanese Unexamined Patent Application Publication No. 2021-20153 (Patent Document 1), there is disclosed a fine bubble generator including an inlet portion located on the inlet side of a cylindrical housing, having an inner diameter that gradually narrows, an orifice (small-diameter portion) connected to the inlet portion, and a diameter-expanding portion located on the outlet side of the cylindrical housing, connected to the orifice, and having an inner diameter that gradually expands, in which a small recess is formed in the outlet peripheral wall of the orifice.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, a plurality of recesses are evenly arranged in the circumferential direction on the outlet peripheral wall of the orifice. In such a configuration, since the swirling flow of the liquid discharged from the orifice is inhibited by the recesses, it is considered that large vortices with high speed cannot be generated over a wide range.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide a fine bubble generator capable of efficiently generating fine bubbles.

Means for Solving the Problem

[0007] A microbubble generator according to an aspect of the present invention includes a first flow path portion having an inlet at an upstream end and a discharge port having a smaller diameter than the inlet at a downstream end, and a second flow path portion communicating with the first flow path portion via the discharge port and provided with an enlarged portion having a flow path width larger than that of the discharge port. The enlarged portion is recessed in a semi-donut shape toward the inlet side from the position of the discharge port and has an annular pocket continuous in the circumferential direction.

[0008] Preferably, the radial cross-sectional line of the wall surface of the annular pocket is substantially C-shaped or substantially U-shaped.

[0009] More preferably, the radial cross-sectional line of the wall surface of the annular pocket is a substantially arc-shaped curve.

[0010] The wall surface of the annular pocket may be constituted by a plurality of bowl-shaped curved surfaces continuous along the circumferential direction.

[0011] Alternatively, a plurality of rib portions or groove portions extending in the axial direction or the radial direction may be provided on the wall surface of the annular pocket.

[0012] Preferably, the wall surface of the annular pocket and the peripheral wall surface of the enlarged portion are continuously connected.

[0013] Preferably, the first flow path portion is provided between the inlet and the discharge port and includes a tapered portion that gradually decreases in diameter toward the downstream side, and the tip opening of the tapered portion constitutes the discharge port. In this case, it is desirable that the annular pocket is provided so as to surround the tip portion of the tapered portion.

[0014] Preferably, the second flow path portion includes a tapered portion that gradually decreases in diameter toward the downstream side and a reverse tapered portion that gradually increases in diameter toward the downstream side in this order, and the enlarged portion is constituted by at least a part of the tapered portion.

Advantages of the Invention

[0015] According to the present invention, microbubbles can be efficiently generated.

Brief Description of the Drawings

[0016]

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Embodiments for Carrying Out the Invention

[0017] Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0018] <Regarding the configuration> (Schematic configuration) With reference to FIGS. 1 and 2, the schematic configuration of the fine bubble generator 1 according to the present embodiment will be described. FIG. 1 is a perspective view showing the appearance of the fine bubble generator 1. FIG. 2 is a cross-sectional view showing the internal structure of the fine bubble generator 1.

[0019] As shown in FIGS. 1 and 2, the fine bubble generator 1 is a cylindrical member having openings 10a and 10b at both ends, and is coaxially arranged between the upstream pipe 91 and the downstream pipe 92 in the use state. In FIGS. 1 and the like, the central axis X of the fine bubble generator 1 is indicated by a one-dot chain line. Also, the flow direction of the liquid from the upstream pipe 91 to the downstream pipe 92 is indicated by an arrow A. In the following description, the direction along the central axis X is referred to as the "axial direction", and the direction orthogonal to the central axis X is referred to as the "radial direction" or "radius direction".

[0020] The fine bubble generator 1 generates fine bubbles by reducing the pressure of the liquid flowing in from the upstream pipe 91 to below the saturated vapor pressure by the cavitation method, and causes the liquid containing the fine bubbles to flow out to the downstream pipe 92. Note that the "fine bubbles" are so-called Fine Bubble (registered trademark), and represent bubbles having a particle diameter in the microscale or nanoscale.

[0021] As shown in FIG. 2, the fine bubble generator 1 mainly includes a first flow path portion 11 and a second flow path portion 12 in this order. The first flow path portion 11 has an inlet 20 at its upstream end, and is a flow path provided with a "constriction portion 22" for increasing the velocity of the liquid flowing in from the inlet 20. The first flow path portion 11 has a discharge port 23 with a smaller diameter than the inlet 20 at its downstream end. The second flow path portion 12 communicates with the first flow path portion 11 via the discharge port 23, and is a flow path provided with an "expansion portion 31" having a flow path width larger than that of the discharge port 23. The second flow path portion 12 has an outlet 34 at its downstream end. The fine bubble generator 1 according to the present embodiment features mainly that an annular pocket 35 is formed in the expansion portion of the second flow path portion 12, as will be described later.

[0022] Specific examples of the first flow path portion 11 and the second flow path portion 12 will be described in detail below. In the present embodiment, an example is shown in which the inlet 20 of the first flow path portion 11 constitutes an opening 10a connected to the upstream pipe 91, and the outlet 34 of the second flow path portion 12 constitutes an opening 10b connected to the downstream pipe 92, but the present invention is not limited to such an example. That is, the fine bubble generator 1 may further include a flow path portion located upstream of the first flow path portion 11 or a flow path portion located downstream of the second flow path portion 12.

[0023] (First Flow Path Portion) As shown in FIG. 2, the first flow path portion 11 in the present embodiment includes an entrance portion 21 extending in the axial direction with a constant flow path width, and a constriction portion 22 having a smaller diameter than the entrance portion 21 to increase the flow velocity of the liquid, in this order.

[0024] The inlet portion 21 is a flow path defined by a straight cylindrical peripheral wall surface 210 that extends straight in the axial direction. The upstream end of the peripheral wall surface 210 constitutes the inlet 20. The constriction portion 22 is composed of only a tapered portion 201 that gradually reduces in diameter toward the downstream side. That is, the constriction portion 22 is a flow path defined by a conical frustum-shaped (tapered) peripheral wall surface 220. In the present embodiment, the tip opening of the tapered portion 201 (the downstream end of the peripheral wall surface 220) constitutes the discharge port 23. The radius φ2 of the discharge port 23 is desirably, for example, 2 / 3 or less, and preferably 1 / 2 or less of the radius φ1 of the inlet 20.

[0025] In FIG. 2, the axial position of the discharge port 23 of the first flow path portion 11 (hereinafter referred to as the "reference position") is indicated by a dashed-dotted line B.

[0026] (Second flow path portion) As shown in FIG. 2, the second flow path portion 12 includes an enlarged portion 31 provided continuously with the discharge port 23. The enlarged portion 31 in the present embodiment is constituted by the upstream end portion (at least a part) or the whole of a tapered portion 301 that gradually reduces in diameter toward the downstream side from the reference position B. That is, the enlarged portion 31 is defined by a conical frustum-shaped peripheral wall surface 311. The tapered portion 301 of the second flow path portion 12 is provided coaxially and continuously with the tapered portion 201 of the first flow path portion 11.

[0027] In the present embodiment, on the downstream side of the tapered portion 301, an inverse tapered portion 302 that gradually increases in diameter toward the downstream side is continuously provided. A throttle portion 32 is formed by the downstream end portion of the tapered portion 301 and the upstream end portion of the inverse tapered portion 302. An outlet portion 33 is formed by the downstream end portion (at least a part) of the inverse tapered portion 302. Thus, the second flow path portion 12 includes the enlarged portion 31, the throttle portion 32, and the outlet portion 33 in this order. Note that a short and long straight cylindrical portion may be interposed between the tapered portion 301 and the inverse tapered portion 302.

[0028] The maximum radius φ3 of the enlarged portion 31 is, for example, at least twice the radius φ2 of the discharge port 23, and desirably at least three times. Also, the maximum radius φ3 of the enlarged portion 31 is desirably larger than the radius φ5 of the outlet 34. The minimum radius φ4 of the throttle portion 32 is, as an example, larger than the radius φ2 of the discharge port 23 and smaller than the radius φ1 of the inlet 20. Although the upper limit of the maximum radius φ3 of the enlarged portion 31 is not particularly limited, about five times the radius φ2 of the discharge port 23 is assumed. The radius φ1 of the inlet 20 and the radius φ5 of the outlet 34 are substantially equal.

[0029] In the present embodiment, the inclination angle θ2 of the tapered portion 301 (the circumferential wall surface 310 in the shape of a truncated cone) and the inclination angle θ3 of the reverse tapered portion 302 (the circumferential wall surface 320 in the shape of an inverted truncated cone) can both be defined in the range of 10 degrees to 45 degrees. The angle θ3 of the reverse tapered portion 302 may be smaller than the angle θ2 of the tapered portion 301. In the illustrated example, the inclination angle θ1 of the tapered portion 201 of the first flow path portion 11 is substantially equal to the inclination angle θ2 of the tapered portion 301 of the second flow path portion 12.

[0030] Here, the details of the enlarged portion 31 will be further described with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view showing an enlarged connection portion between the first flow path portion 11 and the second flow path portion 12. FIG. 4 is a cross-sectional view showing the shape of the annular pocket 35 of the enlarged portion 31, corresponding to the cross-section along line IV-IV in FIG. 3.

[0031] As shown in FIG. 3, the enlarged portion 31 is recessed in a semi-donut shape toward the inlet 20 side (in the direction opposite to the liquid flow direction) from the reference position B and has an annular pocket 35 that is continuous in the circumferential direction. As shown in FIG. 4, the annular pocket 35 is provided so as to surround the tip (downstream end) of the tapered portion 201 of the first flow path portion 11 when viewed in the axial direction. In other words, the tip of the tapered portion 201 of the first flow path portion 11 is inserted into the space surrounded by the annular pocket 35.

[0032] The wall surface 30 of the annular pocket 35 and the peripheral wall surface 310 of the enlarged portion 31 are continuously connected. As shown in FIG. 3, the radial cross-sectional line of the wall surface 30 of the annular pocket 35 is preferably substantially C-shaped and is preferably a substantially arc-shaped curve (substantially a semi-circle). There is no step between the outer peripheral edge 352 of the wall surface 30 of the annular pocket 35 and the peripheral wall surface 310 of the enlarged portion 31, and the wall surface 30 and the peripheral wall surface 310 are smoothly connected. The axial position of the outer peripheral edge 352 of the wall surface 30 of the annular pocket 35 coincides with the reference position B.

[0033] It is desirable that the radial inlet width L1 of the annular pocket 35 is larger than the radius φ2 (FIG. 2) of the discharge port 23. The depth L2 of the annular pocket 35 is typically equal to or less than the inlet width L1 and is equal to or more than 1 / 3 of the inlet width L1.

[0034] From the viewpoint of manufacturing constraints and the like, a slight peripheral wall portion 36 orthogonal to the axial direction may be interposed between the inner peripheral edge 351 of the wall surface 30 of the annular pocket 35 and the discharge port 23. Alternatively, as shown in FIG. 9, it is also possible to form the annular pocket 35 so that there is no peripheral wall portion 36 orthogonal to the axial direction between the inner peripheral edge 351 of the wall surface 30 of the annular pocket 35 and the discharge port 23.

[0035] As shown in FIG. 4, the wall surface 30 of the annular pocket 35 has no unevenness in the circumferential direction and there is nothing to block the flow of the liquid in both the radial direction and the circumferential direction. Thereby, the swirling flow described later can be efficiently retained in the annular pocket 35.

[0036] It is desirable that there are no partial recesses or protrusions on the peripheral wall surfaces of the first flow path portion 11 and the second flow path portion 12 that block the flow of the liquid.

[0037] <Method for generating fine bubbles> With reference to FIGS. 4 and 5, a method for generating fine bubbles by the fine bubble generator 1 will be described. FIG. 5 is a diagram schematically showing the flow of the liquid inside the fine bubble generator 1.

[0038] The liquid flowing from the upstream pipe 91 into the inlet portion 21 of the first flow path portion 11 increases in flow velocity and decreases in pressure in the tapered portion 201 which is the constriction portion 22. As a result, cavitation occurs at the position P2 near the discharge port 23. The bubbles generated by cavitation collapse and are refined due to the rapid pressure rise in the enlarged portion 31. The liquid flowing out from the discharge port 23 into the enlarged portion 31 of the second flow path portion 12 flows downstream together with the bubbles. At this time, the liquid in the space (the large space including the annular pocket 35) P3 defined by the peripheral wall surface 310 of the tapered portion 301 and the wall surface 30 of the annular pocket 35 is also pulled downstream. Then, in order to compensate for the shortage of the liquid pulled downstream from the space P3, a flow of liquid upstream (a flow toward the annular pocket 35) occurs. As a result, in the space P3, the liquid containing bubbles rotates greatly and at high speed.

[0039] The shape of the wall surface 30 of the annular pocket 35 is substantially arc-shaped, and since the wall surface 30 is provided without a step with respect to the peripheral wall surface 310 of the tapered portion 301, there is nothing that serves as a barrier to the fluid in the space P3. Therefore, the liquid can be rotated greatly and at high speed in the space P3. Further, due to the centrifugal force of the swirling flow of this liquid, a wide range of the enlarged portion 31 becomes a negative pressure, and cavitation can be promoted.

[0040] Further, since the space P3 includes the large annular pocket 35, the bubbles swirling in the annular pocket 35 can be retained for a long time. As a result, the bubbles repeatedly collapse in the space P3, so that the bubble size can be efficiently reduced (nanosized).

[0041] In addition, in the present embodiment, since the throttle portion 32 is provided on the downstream side of the enlarged portion 31, a pressure drop also occurs at the position P4 near the throttle portion 32. Therefore, the liquid flowing out from the discharge port 23 is pulled toward both the annular pocket 35 side (upstream side) and the throttle portion 32 side (downstream side). As a result, the above-described high-speed swirling flow continuously occurs over a wide range. The flow velocity once increases and the pressure decreases at the position P4 near the throttle portion 32. However, since the flow path width of the outlet portion 33 expands toward the outlet 34, the pressure of the liquid flowing out from the outlet 34 can be set to an allowable value. As an example, when a simulation is performed with the pressure at the position P1 of the inlet portion 21 being 0.3 MPa and the water temperature being 20 degrees, the pressure at the position P5 of the outlet portion 33 was about 0.1 to 0.2 MPa.

[0042] <Modification Example> (Annular Pocket) In the present embodiment, an example is shown in which the wall surface 30 of the annular pocket 35 has no irregularities in the circumferential direction and is formed in a typical semi-donut shape. However, the present invention is not limited to such an example. Each of the examples shown below is also regarded as an example of a semi-donut shape.

[0043] As shown in FIG. 6, in the axial direction view, a plurality of rib portions 41 may be provided on the wall surface 30 of the annular pocket 35, for example, radially. Thereby, it is possible to suppress the liquid swirling in the annular pocket 35 from being dispersed in the circumferential direction, and thus it is possible to improve the swirling speed of the liquid in the annular pocket 35.

[0044] Note that the wall surface 30 of the annular pocket 35 may have a plurality of groove portions instead of the plurality of rib portions 41 (not shown). That is, the annular pocket 35 may be provided with rib portions 41 or groove portions extending in the axial direction or the radial direction.

[0045] In addition, in FIG. 6, an example in which each rib portion 41 is formed linearly is shown. However, the shape of the rib portion 41 does not have to be linear.

[0046] Also, as shown in FIG. 7, a semi-donut-shaped annular pocket 35A may be formed by connecting a plurality of substantially hemispherical recesses 350 in the circumferential direction. That is, the wall surface 30 of the annular pocket 35A may be constituted by a plurality of bowl-shaped (substantially C-shaped) curved surfaces 300 that are continuous along the circumferential direction. The plurality of bowl-shaped curved surfaces 300 are provided at a constant pitch along the circumferential direction.

[0047] As shown in FIG. 7, although it is desirable that the substantially hemispherical recess 350 is provided so as to be inscribed in the above-described outer peripheral edge 352 when viewed in the axial direction, the recess 350 may be provided radially inward of the outer peripheral edge 352. That is, there may be a slight step between the peripheral wall surface 310 of the enlarged portion 31 shown in FIG. 3 and the bowl-shaped curved surface 300.

[0048] FIG. 8 is a developed cross-sectional view schematically showing the shape of the wall surface 30 of the annular pocket 35A along the circumferential direction. FIG. 8 shows a cross-sectional line of the wall surface 30 cut by a virtual circle (shown by a one-dot chain line in FIG. 7) passing through the central position in the radial direction of the annular pocket 35A. As shown in FIG. 8, the wall surface 30 is formed in a wavy shape as a whole along the circumferential direction.

[0049] As shown in FIG. 8, the boundary portion 300a between two adjacent bowl-shaped curved surfaces 300 in the circumferential direction is located upstream of the reference position B (the axial position of the discharge port 23 and the outer peripheral edge 352). Thereby, an annular pocket 35A that is continuously wavy in the circumferential direction is formed.

[0050] Also, in any of the present embodiment and each modification, although it is desirable that the cross-sectional line in the radial direction of the wall surface 30 of the annular pocket 35 is substantially arc-shaped, it may be substantially C-shaped. For example, the cross-section of the wall surface 30 may be dish-shaped, or may be a shape cut from a polygon having five or more sides. Alternatively, as shown in FIG. 10, the cross-sectional line in the radial direction of the wall surface 30 of the annular pocket 35 may be substantially U-shaped (U-shaped).

[0051] (Enlarged portion) In this embodiment, an example is shown in which the enlarged portion 31 is constituted by the upstream end portion (at least a part) or the whole of the tapered portion 301, but the example is not limited to this. As shown in FIG. 11, a part of the enlarged portion 31 may be constituted by a straight cylindrical portion 303 extending in the axial direction with a constant channel width. In the example of FIG. 11, the straight cylindrical portion 303 is disposed upstream of the tapered portion 301, and the wall surface 30 of the annular pocket 35 is provided continuously (without a step) on the peripheral wall surface of the straight cylindrical portion 303.

[0052] (First flow path portion) In this embodiment, an example is shown in which the constricted portion 22 of the first flow path portion 11 is formed only by the tapered portion 201. However, as shown in FIGS. 12 and 13, the tapered portion 201 and a small-diameter straight cylindrical portion 202 connected to the tapered portion 201 are included, and the discharge port 23 of the first flow path portion 11 may be constituted by the downstream end of the straight cylindrical portion 202. In this case, the annular pocket 35 of the second flow path portion 12 is disposed so as to surround the straight cylindrical portion 202. Also in this modification, a peripheral wall portion 36 may be interposed between the wall surface 30 of the annular pocket 35 and the discharge port 23 (FIG. 12), or the peripheral wall portion 36 may not be interposed (FIG. 13).

[0053] Further, as shown in FIG. 14, the constricted portion 22A of the first flow path portion 11 may be constituted only by a relatively long straight cylindrical portion 202 without including the tapered portion 201.

[0054] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of reference numerals

[0055] 1 Microbubble generator, 11 First flow path section, 12 Second flow path section, 20 Inlet, 21 Inlet section, 22, 22A Narrow section, 23 Outlet, 30 Wall surface, 31 Enlarged section, 32 Throttle section, 33 Outlet section, 34 Flow outlet, 35, 35A Annular pocket, 36 Peripheral wall section, 41, 42 Rib sections, 201, 301 Taper sections, 202, 303 Straight tube sections, 210, 220, 310, 311, 320 Peripheral wall surfaces, 350 Bowl-shaped curved surface, 302 Reverse taper section.

Claims

1. A first flow path portion having an inlet at an upstream end and a discharge port with a smaller diameter than the inlet at a downstream end; A second flow path portion communicating with the first flow path portion through the discharge port and provided with an enlarged portion having a flow path width larger than that of the discharge port; The enlarged portion is recessed in a semi-donut shape toward the inlet side from the position of the discharge port and has an annular pocket continuous in the circumferential direction, a fine bubble generator.

2. The fine bubble generator according to claim 1, wherein a radial cross-sectional line of a wall surface of the annular pocket is substantially C-shaped or substantially U-shaped.

3. The fine bubble generator according to claim 2, wherein a radial cross-sectional line of a wall surface of the annular pocket is a substantially arc-shaped curve.

4. The fine bubble generator according to claim 1, wherein a wall surface of the annular pocket is constituted by a plurality of bowl-shaped curved surfaces continuous along the circumferential direction.

5. The fine bubble generator according to claim 1, wherein a plurality of rib portions or groove portions extending in the axial direction or the radial direction are provided on a wall surface of the annular pocket.

6. The fine bubble generator according to claim 1, wherein a wall surface of the annular pocket and a peripheral wall surface of the enlarged portion are continuously connected.

7. The first flow path portion is provided between the inlet and the discharge port and includes a tapered portion that gradually reduces in diameter toward the downstream side, an opening at a tip of the tapered portion constitutes the discharge port, The fine bubble generator according to claim 1, wherein the annular pocket is provided so as to surround a tip portion of the tapered portion.

8. The second flow path portion includes, in this order, a tapered portion that gradually reduces in diameter toward the downstream side and a reverse tapered portion that gradually increases in diameter toward the downstream side, The microbubble generator according to claim 1, wherein the enlarged portion is constituted by at least a part of the tapered portion.

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