JP6651094B1 - Microbubble generating member and underwater aeration and stirring device using the same - Google Patents

Abstract

What is claimed is: 1. A microbubble generating member provided in a cavity of a hub of an impeller of an underwater aeration and stirring device, wherein the microbubble generating member has a cross section in which four short sides and four long sides are alternately arranged. A hub having a different octagonal shape, the upper surface being closed and the lower surface being open, and the four short sides being formed with slits extending between the upper surface and the lower surface, respectively, Are provided so that their axes coincide with each other, and are rotated together with the impeller.

Description

  The present invention relates to the field of an underwater aeration / agitator installed in a water tank such as a wastewater treatment facility and configured to aerate and agitate wastewater in a water tank, and particularly to a microbubble generating member and an underwater aeration / agitator using the same.

  2. Description of the Related Art In order to improve the quality of drainage in a water tank of a wastewater treatment facility or the like or river water, an underwater aeration / agitator that forcibly generates convection with surface water while supplying oxygen to low-rise water is used. The underwater aeration and stirring device is required to have a performance capable of stirring water over a wide range while minimizing attenuation of a water flow. In response, the applicant of the present application has proposed an ingenious device for discharging water (see Patent Document 1).

  The underwater aeration and stirring device disclosed in Patent Document 1 employs a short cylindrical discharge casing provided with a plurality of discharge ports for radially discharging water at appropriate intervals in a circumferential direction, and the discharge ports are , Each of which is circumferentially divided by a partition member having a pair of partition portions extending substantially in the radial direction. A guide groove extending in the radial direction is formed in the discharge casing by opening between the partition portions of the partition members upward and outward.

  In the above-described underwater aeration and stirring apparatus, since the discharge casing is divided into a plurality of discharge ports by the partition member, water is discharged from each discharge port as a bundle of water flow. Thereby, attenuation of the water flow discharged from each discharge port is suppressed. As a result, each stream can agitate the water over a wide range. In addition, due to the water flow discharged from each discharge port, a wake that flows through the guide groove is generated in each water flow. Thereby, the attenuation of the water flow from each discharge port due to the Karman vortex is eliminated, and the stirring power is further improved.

  By the way, recently, in addition to excellent stirring power, higher aeration performance tends to be required for the underwater aeration and stirring device. In order to respond to such a request, it is necessary to take measures for minimizing bubbles mixed in the discharged water flow as much as possible.

Here, the microbubbles, so-called microbubbles, are a general term for microbubbles, micronanobubbles, and nanobubbles. Microbubbles generally refer to fine bubbles having a diameter of 10 μm to several tens μm or less. Micro-nano bubbles refer to bubbles having a diameter of several hundred nm to 10 μm. Nanobubbles are bubbles having a diameter of several hundred nm or less. The microbubbles are said to become micro-nanobubbles with the passage of time. At this size, the shrinkage speed increases and the size rapidly decreases. Many nanobubbles are generated during this process. Microbubbles increase the oxygen concentration in water, thereby activating aerobic microorganisms in the water, thereby promoting water purification.

  As means for generating the above-mentioned fine bubbles, conventionally, a pressurized depressurization method in which a gas is pressurized and dissolved in water in a large amount and then rebubble by decompression (for example, see Patent Document 2), A gas-liquid shearing method in which gas is sheared and generated by rotating the fan several hundred seconds per second in the liquid (for example, see Patent Document 3), or by passing high-pressure air through a film having micropores A fine pore pressurizing method for generating fine bubbles (for example, see Patent Document 4) and the like are known.

Japanese Patent No. 3203336 JP 2014-69160 A JP 2012-228644 A JP 2009-119400 A

  However, all of the above-mentioned conventional means for generating microbubbles require a large-scale apparatus, and therefore, it is hardly expected to incorporate them into the underwater aeration and stirring apparatus described in Patent Document 1. Therefore, a separate microbubble generator must be installed before the underwater aeration and stirring device. Then, two types of devices are required for aeration and agitation of water, so that the installation and maintenance of the devices are complicated, and the equipment and maintenance costs for water treatment are increased. .

  The present invention has been made in order to solve such a problem, and has a very simple configuration, and easily imparts both excellent agitation power and high aeration performance to a conventional underwater aeration and agitation device equipped with an impeller. It is intended to provide a microbubble generating member that can perform the above-mentioned steps. Further, it is an object of the present invention to provide a submersible aeration / stirring apparatus which can meet the demands of both excellent stirring power and high aeration performance with a single unit, and is also excellent in economic efficiency.

  In order to solve the above problems, the present invention provides an impeller provided with blades on a peripheral surface of a hollow hub having an air discharge port on an upper peripheral surface and an air intake on a lower surface, and a motor for rotating the impeller. An air supply pipe for supplying air into the hub of the impeller through the air intake port, and a gas-liquid mixture flow in which air discharged from the air discharge port of the hub is mixed with a water flow generated by rotation of the impeller. And a discharge port for discharging the radiating liquid in the radial direction. In addition, it is an invention specific matter that a microbubble generating member provided in the cavity of the hub is provided. That is, the micro-bubble generating member has a cross section of a different octagonal shape in which four short sides and four long sides are alternately arranged, and a cylindrical shape in which the upper surface is closed while the lower surface is open. And slits extending between the upper surface and the lower surface are formed in the four short sides, respectively, and provided in the cavity of the hub so that their axes coincide with each other, and are rotated together with the impeller. It is characterized by that.

In order to solve the above problems, the present invention provides an impeller provided with blades on a peripheral surface of a hollow hub having an air discharge port on an upper peripheral surface and an air intake on a lower surface, and a motor for rotating the impeller. An air supply pipe for supplying air into the hub of the impeller through the air intake port, and a gas-liquid mixture flow in which air discharged from the air discharge port of the hub is mixed with a water flow generated by rotation of the impeller. And a discharge port for discharging the radiating liquid in the radial direction. In addition, it is an invention specific matter that a microbubble generating member provided in the cavity of the hub is provided. That is, the micro-bubble generating member has a cross section having a different octagonal shape in which four short sides and four long sides are alternately arranged, and a cylindrical shape in which the upper surface is closed while the lower surface is open. And slits extending between the upper surface and the lower surface are formed in the four short sides, respectively, so that the axis of the hub and the axis of the microbubble generating member coincide in the cavity of the hub. And rotated with the impeller.

  As shown in FIG. 5, the fine bubble generation member 70 has a cross section having a different octagonal shape in which four short sides A and four long sides B are alternately arranged, and the upper surface U is closed. Since the lower surface L is formed in a tubular shape with an open surface, and the slits S extending between the upper surface U and the lower surface L are formed on the four short sides A, the microbubble generating member 70 thus formed Is rotated together with the impeller, a pressure difference is generated due to the difference in the lengths of the two types of sides A and B, and the pressure difference causes the fluid to expand, whereby bubbles in the fluid are miniaturized. Hereinafter, this point will be described in detail.

Since the micro-bubble generating member 70 has the above-mentioned heterooctagon, as shown in FIG. 6, a radius r _A from the center O of the micro-bubble generating member 70 to the center A _{O in} the width direction of the short side A, The radius r _B from the center O to the center B _{O in} the width direction of the long side B is different, and r _A > r _B. When the speed of the point A _{O on} the short side A is v _A , the speed of the point B _{O on} the long side B is v _B, and the pressures at the points A _O and B _O are P _A and P _B , respectively, the speed v Since (m / s) = r × ω and ω is constant at both points A _O and B _O , v _A > v _B. The sum of the energies of the points A _O and B _O is Z _A + v _A ² / 2g + P _A / γ = Z _B + v _B ² / 2g + P _B / γ. Since both potential energies are equal, (v ^{_{a 2 -v B 2) / 2g}} = a _{(P B -P a) / γ} . Its velocity difference _v ^{A 2} _-v ^B 2 causes a differential pressure _P B -P _A inside the fine bubble generation member 70. When a mixture of air and water flowing into the inside of the microbubble generating member 70 is considered as a kind of ideal gas, the pressure and volume of the fluid are represented by PV = RT. P _B -P _a is decreased after exiting the slit S of the short side a, the volume only the decrement expands. As a result of the impact of the expanding fluid on the air (bubbles) in the water, the bubbles are miniaturized.

  The fluid containing fine bubbles generated by the fine bubble generating member as described above is discharged from the air discharge port provided on the upper peripheral surface of the hub, mixed with the water flow generated by the rotation of the impeller, and radiated from the discharge port. Discharged in the direction.

  Here, the slit S may be a rectangle whose long side is along the axis of the microbubble generating member 70, but it is preferable that both end edges of the slit S have a semicircular shape having a diameter equal to the width dimension of the slit S. desirable. Hereinafter, this point will be described in detail.

By supplying air from the lower surface opening of the fine bubble generating member 70, the mixed fluid of water and air passes through the slit S having a width d as shown in FIG. Of the air is promoted outside. At this time, if the both end edges of the slit S are not rectangular, but are semicircular having a diameter equal to the width d of the slit S (R = １ ／ d when the width is d), the fineness of air will be described for the following reason. Is promoted.
(1) Increasing the discharge pressure by reducing the flow rate through the slit The potential energy Z, velocity energy v ² / 2g, and pressure energy P / γ act on the fluid surrounding the microbubble generating member 70 in principle. Always satisfies the relationship of Z + v ² / 2g + P / γ = constant.

Here, in order to promote the miniaturization of the air, it is necessary to make the shape in which the pressure generated in the slit S of the microbubble generating member 70 does not easily decrease.
(2) Prevention of entanglement of residue When using the fine bubble generation member 70 in sewage, there is a concern that the residue may be entangled at both ends of the slit S, and the entire slit may be closed depending on the shape of the slit. Therefore, when the edges of the slit S are semicircular (arc-shaped), the residue is more likely to be separated from the slit S when the residue is entangled with the slit S than in the case of a rectangular shape, and the pressure generated in the slit S is reduced. Since it is difficult, it becomes easy to push the residue in the discharge direction (from inside the fine bubble generation member 70 to outside).
(3) Conclusion When the shape of the both edges of the slit S of the microbubble generating member 70 is not a rectangle (the whole slit S is rectangular) but an arc as described above, the flow velocity in the slit S is reduced, so The decrease in pressure from the inlet to the outlet (slit S) of the bubble generation member 70 can be reduced. As a result, not only the promotion of air micronization, but also the pushing of the residue with a high pressure from the inside of the microbubble generating member 70 to the outside can prevent the clogging of the slit S by the residue. Therefore, both end edges of the slit S are formed in a semicircular shape whose diameter is the width d of the slit S. Hereinafter, the principle of the pressure difference between the case where the shape of the both ends of the slit S is rectangular and the case where the shape is semicircular will be described in detail.

-About the pressure difference between the case where the shape of both ends of the slit S is rectangular and the case where the shape is semicircular-
The flow velocity with respect to the shape in the flow direction is defined by the following equation using Manning's equation.

    Here, when n and I are constant, the flow velocity v is left to the diameter R (m).

  When R is small, v also becomes small and a high pressure tends to be maintained (however, the potential energy Z is fixed: see the following equation). In addition, please refer to FIG.

Therefore, the difference between the case where the shape of the both ends of the slit S is semicircular and the case where the shape of the both ends of the slit S is rectangular will be calculated. Is small and proves to be hydraulically advantageous as described above.
(1) When the shape of both ends of the slit is semicircular As shown in FIG. 9, when the shape of both ends of the slit S is semicircular and R = Ｒd, And the angle θ with respect to the center of the circle forming the circle is defined by the following equation. However, the range of θ is 0 ° <θ ≦ 180 °.

Here, sin2α = 2 sinαcosα (α is an arbitrary angle)
sinαcosα = 1/2 · sin2α
When this is substituted, the following equation (1) is obtained.

  Next, the wet side length P of running water is given by the following equation (2).

  When the diameter R is calculated from the above equations (1) and (2), the result is as follows.

Therefore, when the shape of both edges of the slit S is semicircular and R = 1 / 2d, the radial depth R can be expressed by the above equation (3).
(2) When the shape of both ends of the slit is rectangular When the shape of both ends of the slit S is rectangular, the relationship between the cross-sectional area A of the flowing water and the angle of the center forming the same is defined as follows. Is done. However, the range of θ is set to 90 ° <θ ≦ 180 °.

  The cross-sectional area A of the flowing water having the central angle θ can be represented by a square abcd as shown in FIG.

  Therefore, it is as follows.

  Next, the wet side length P of running water is as follows.

  Calculating the depth R 'from Equations 4 and 5 gives the following.

(3) Comparative study The radial depth R in the case where the shape of both end edges of the slit S is semicircular is R <d / 4 in the range of 0 ° <θ ≦ 180 ° according to the equation (3).

  On the other hand, when the shape of both edges of the slit S is rectangular, the depth R ′ is always R ′ ≧ d / 4 in the range of 90 ° <θ ≦ 180 ° according to the equation (6).

  In other words, the radial depth is smaller than the rectangular shape when the shape of both edges of the slit S is semicircular, and the relationship of R′−R> 0 is always satisfied when the center angle θ is the same.

  Therefore, the flow velocity with respect to the shape in the flow direction is given by Manning's equation as follows:

The smaller the diameter R is, the smaller the flow velocity is, so that a high pressure can be maintained when the fluid passes through the slit S.

  The flow velocity difference between the case where the shape of the both ends of the slit S is rectangular and the case where the shape is semicircular is

When the shape of both edges of the slit S is semicircular, a higher pressure can be obtained than the speed difference and the pressure of the slit S when the shape of both edges is rectangular.

  From the above, it is preferable that the shape of the slit S of the microbubble generating member 70 according to the present invention be a semicircle (R = １ ／ d) whose both end edges have a diameter of the width d of the slit S.

  Supplementing with reference to FIG. 11, the velocity difference between the flow velocity v when the shape of the both ends of the slit S is rectangular and the flow velocity v ′ when the shape is semicircular is:

Then, a difference occurs in the pressure generated in each case by the speed difference.

  The above PP ′ becomes a difference for supplying a high pressure to the fine bubble generating member 70, and is an advantageous element for promoting the finer air and preventing the entanglement of the residue.

  By the way, the microbubble generating member according to the present invention may be detachable from the hub of the impeller.

  According to the present invention, the microbubble generating member can be attached to the impeller of the existing underwater aeration / stirring apparatus, so that the existing underwater aeration / stirring apparatus can be used.

  Since the underwater aeration and stirring apparatus according to the present invention includes the above-described fine bubble generation member, it has a very simple configuration, but can respond to the demands of both excellent stirring power and high aeration performance with one unit. be able to.

  As described above, according to the present invention, while having a very simple configuration, it is possible to meet the demands of both excellent stirring power and high aeration performance with a single unit, and it is also excellent in economic efficiency. An underwater aeration / stirring apparatus can be provided.

FIG. 1 is a perspective view showing an underwater aeration and stirring device. FIG. 2 is a partially cutaway front view of the underwater aeration and stirring device. FIG. 3 is a partially broken perspective view of the underwater aeration and stirring device. FIG. 4 is a cross-sectional view of the impeller showing a mounted state of the fine bubble generation member. FIG. 5 is a perspective view of the fine bubble generation member. FIG. 6 is a view for explaining the principle of making bubbles fine by the fine bubble generating member. FIG. 7 is a diagram illustrating the shape of both end edges of the slit of the microbubble generating member. FIG. 8 is a diagram illustrating the shape of both end edges of the slit of the fine bubble generation member. FIG. 9 is a view for explaining a case where the shape of both end edges of the slit of the microbubble generating member is semicircular. FIG. 10 is a diagram illustrating a case where the shape of both end edges of the slit of the microbubble generating member is rectangular. FIG. 11 is a diagram for explaining a difference in shape of both end edges of the slit of the microbubble generating member. FIG. 12 is a graph showing the performance difference between the underwater aeration and stirring device A provided with the fine bubble generation member and the underwater aeration and stirring device not provided with the fine bubble generation member. FIG. 13 is a graph showing the performance difference between the underwater aeration and stirring device B having the fine bubble generating member and the underwater aeration and stirring device not having the fine bubble generating member.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Hereinafter, the underwater aeration and stirring device will be described first, and then the microbubble generating member will be described.

  FIG. 1 is a perspective view showing an underwater aeration and stirring device 1 according to an embodiment of the present invention, FIG. 2 is a partially cutaway front view of the underwater aeration and stirring device 1, and FIG. FIG. 4 is a cutaway perspective view, FIG. 4 is a cross-sectional view of an impeller showing a mounted state of the fine bubble generating member, and FIG. 5 is a perspective view of the fine bubble generating member.

  As shown in FIG. 1 and FIG. 2, the underwater aeration and stirring device 1 has a rotating power mechanism 10 disposed at an upper part with a vertical axis, and a rotating power mechanism 10 below the rotating power mechanism 10 to be rotated by the rotating power mechanism 10. And an impeller 20 attached to the side. The impeller 20 is arranged in a pump casing 30 formed in a cylindrical shape, and a discharge casing 40 provided with a plurality of discharge ports 411 extending in a radial direction is mounted on the upper side of the pump casing 30. Hereinafter, each of the above components will be described in detail from the rotary power mechanism 10.

-Rotary drive mechanism-
As shown in FIG. 2, the rotary power mechanism 10 includes a motor 11 whose axis is in a vertical state, and a speed reducer 12 attached to an output shaft extending below the motor 11.

  The motor 11 is disposed above the discharge casing 40. Above the motor 11, a cabtire cable 13 for supplying electric power to the rotary power mechanism 10 is connected.

  The speed reducer 12 is disposed in the discharge casing 40 so as to be supported by the discharge casing 40. The output shaft of the reduction gear 12 penetrates the center of the discharge casing 40 and reaches the inside of the pump casing 30. An impeller 20 is attached to an output shaft of the speed reducer 12 located in the pump casing 30.

-Impeller-
The impeller 20 is surrounded by a pump casing 30 and has a cylindrical hub 21 attached so that the output shaft of the speed reducer 12 is inserted upward, and a plurality of blades arranged at equal intervals in the circumferential direction of the hub 21. 22. Power from the drive of the motor 11 is transmitted to the hub 21 via the output shaft of the motor 11, the reduction gear 12, and the output shaft of the reduction gear 12, whereby the impeller 20 rotates. The impeller 20 has a role of sucking water from below the pump casing 30 and sending it into the discharge casing 40 by its rotation operation.

  The hub 21 and the blades 22 are both made of austenitic stainless steel, but are not limited thereto as long as they have excellent durability.

  The hub 21 has an opening 23 at the bottom, and the tip of an air supply pipe 50 that supplies air into the underwater aeration and stirring device 1 is inserted into the opening 23. On the upper peripheral surface of the hub 21, a plurality of air discharge ports 21a are arranged at equal intervals in the circumferential direction. The air supplied from the air supply pipe 50 into the hub 21 is discharged into the pump casing 30 through each air discharge port 21a.

  Each of the blades 22 is formed to extend radially from the peripheral surface of the hub 21 at a large pitch angle so as to generate a strong upward water flow by rotation of the impeller 20.

-Pump casing-
The pump casing 30 has a cylindrical pump casing main body 31 whose diameter gradually increases toward the lower side, and a plurality of legs 32 formed to extend below the pump casing main body 31.

  The pump casing body 31 is formed such that the upper and lower surfaces are open. The outer peripheral surface of the pump casing body 31 is reinforced by a plurality of vertically extending reinforcing ribs 31a arranged at equal intervals in the circumferential direction. The pump casing body 31 is made of a cast iron material having excellent workability, but is not limited to this.

  The legs 32 are arranged at equal intervals in the circumferential direction. The underwater aeration and stirring device 1 is supported by the legs 32 so as to stand upright in the water tank. For example, the underwater aeration and stirring device 1 is supported by three legs 32, but the number of legs 32 is not limited thereto. The length of the leg 32 is set such that a sufficient clearance for piping the air supply pipe 50 can be secured from below the pump casing main body 31 to the bottom surface where the underwater aeration / agitating device 1 is installed. .

-Discharge casing-
The discharge casing 40 is attached to the upper side of the pump casing 30 and has a plurality of discharge ports 411 extending in the radial direction. It has a plurality of cooling nozzles 42 arranged at the base end, a flange 43 fastened to the pump casing 30, and a hook member 44 to which the hanging tool 60 is locked.

  The discharge casing body 41 is formed so that the upper and lower surfaces are open. The discharge casing main body 41 is made of a cast iron material having excellent workability, like the pump casing main body 31, but is not limited to this.

  Each discharge port 411 is provided for discharging the water sent from the impeller 20 into the discharge casing 40, and is provided with an annular lower guide plate 413 and an appropriate upper part with respect to the lower guide plate 413. An opening formed by an annular upper guide plate 412 arranged at intervals and a plurality of partitions 414 connecting the upper guide plate 412 and the lower guide plate 413.

  The lower guide plate 413 has an opening at the axial center thereof, and is formed so as to be sequentially inclined downward at an angle of about 5 to 40 degrees toward the outside.

  The upper guide plate 412 has a through hole in the center, and is arranged above the lower guide plate 413 at a predetermined interval and substantially in parallel. The inner peripheral side portion of the upper guide plate 412 is gently curved in an arc shape so as to go downward, and the inner peripheral edge thereof is located concentrically in the opening of the lower guide plate 413.

  As shown in FIG. 3, the upper guide plate 412 is divided into six equal parts by six pairs of partition walls 414 extending in the radial direction at six equally divided positions in the circumferential direction. The number of divisions may be changed as appropriate according to the model or the like.

  Each partition 414 is formed integrally with the upper guide plate 412 by being bent downward, and is formed such that the lower edge thereof is brought into contact with the upper surface of the lower guide plate 413. A connecting portion 415 for connecting the inner peripheral portions of the partition walls 414 is provided on the inner peripheral side portion of the partition wall 414. The connecting portion 415 is formed to be curved in an arc shape with a relatively large curvature so as to protrude toward the inner peripheral side, and to be inclined at about 30 to 60 degrees so as to be located upward as approaching the inner peripheral side. You.

  Between the partition walls 414, there are formed guide grooves 416 which are open upward and radially and extend in the radial direction.

  A lower end edge of a truncated cone-shaped stay 417 is supported by a curved portion on the inner peripheral side of the upper guide plate 412. The stay 417 is formed concentrically with the through hole of the upper guide plate 412, and is formed so that its peripheral surface is inclined at about 45 degrees so as to be continuous with the connecting portion 415 of the partition wall 414. The upper and lower surfaces of the stay 417 are opened, and the speed reducer 12 is built in between the inner peripheral portion of the upper guide plate 412 and the stay 417.

  A flange 43 is provided on the inner peripheral edge of the lower opening portion of the discharge casing body 41 over the entire circumference. The flange 43 is placed on the entire upper surface of the pump casing main body 31 and is fixed to the upper surface of the pump casing main body 31 with bolts or the like.

  The hook members 44 are attached to the upper surfaces of the upper guide plates 412 located on one side of every other guide groove 416 in all the guide grooves 416. As shown in FIGS. 1 and 2, the lower end of the hanging tool 60 is locked to each hook member 44. A wire rope or the like is locked to the hanging tool 60, and the entire underwater aeration and stirring device is lowered into the inside of the water treatment reaction tank or the like, and is installed on the bottom surface thereof.

-Microbubble generating member-
In the cavity 21b of the hub 21, a microbubble generating member 70 having a smaller volume than the cavity 21b is provided. The microbubble generating member 70 generates bubbles in the mixed fluid based on the above-described principle with respect to a mixed fluid of water sucked into the cavity 21b by the rotation of the impeller 20 and air supplied from the air supply pipe 50. It turns into fine bubbles.

  As shown in FIG. 5, the fine bubble generation member 70 has a cross section having a different octagonal shape in which four short sides A and four long sides B are alternately arranged, and the upper surface U is closed. The lower surface L is formed in a tubular shape with an open top. On each of the four short sides A, a slit S extending between the upper surface U and the lower surface L is formed. Although the upper and lower ends of the slit S are arc-shaped, the overall shape is not limited to this and may be a simple rectangle. A flange 71 is provided on an outer peripheral edge of the lower surface L, and is detachably attached to the hub 21 of the impeller 20 via the flange 71 by a bolt (not shown). More specifically, as shown in FIG. 4, an inner flange 21d is provided on the inner peripheral edge of the air intake 21c provided on the lower surface of the hub 21, and four screw holes 21e are formed in the inner flange 21d by 90 degrees. It is provided at intervals. On the other hand, four bolt insertion holes 72 are provided in the flange 71 of the fine bubble generation member 70 in correspondence with the screw holes 21e. The microbubble generating member 70 is attached by inserting the head of the microbubble generating member 70 into the cavity 21b of the hub 21 via the air inlet 21c, and connecting the lower surface of the inner flange 21d of the hub 21 to the microbubble generating member 70. The upper surface of the flange 71 is brought into contact with the screw hole 21e such that the screw hole 21e and the bolt insertion hole 72 match, and a bolt is screwed into the screw hole 21e from the lower surface side of the flange 71 through the bolt insertion hole 72. The flanges 21d and 71 are fastened to each other. As a result, the microbubble generating member 70 is detachably mounted in the cavity 21b of the hub 21 so that the axes of the microbubble generating members 70 coincide with each other.

  Here, the volume of the microbubble generating member 70 is set smaller than that of the cavity 21 b of the hub 21. That is, as shown in FIG. 4, in the cavity 21b, around the microbubble generating member 70, the fluid in the microbubble generating member 70 expands after passing through the slit S on the short side A, and the expanding force is generated. Thus, a space is provided to the extent that the air (bubbles) in the water is hit and the air bubbles are finely reduced. A space is provided above the upper surface U of the microbubble generating member 70 such that the gas-liquid mixed water flow in which the microbubbles are generated in the space smoothly flows to the air discharge port 21 a of the hub 21. The size of the space around and above the microbubble generating member 70 is appropriately determined according to the size of the impeller 21. In addition, the difference between the widths of the short side A and the long side B and the width and length of the slit S are appropriately determined in accordance with the size of the impeller 21 as in the above-described space.

-Example-
Hereinafter, examples of the present invention will be described.

  Using two types of underwater aeration / stirring devices A and B having different air supply performances, the oxygen transfer speed in the water tank was measured when the microbubble generating member was installed, and the oxygen transfer speed was measured when the microbubble generating member was not mounted. It was compared with the moving speed.

<Underwater aeration and stirring device A>
Motor output: 5.5kW
Air supply range: minimum: Q = 2.1 m ³ / min
Maximum: Q = 9.7 m ³ / min
Dimensions of each part of the microbubble generating member attached to the underwater aeration and stirring device A Total height: 178 mm
Width of short side: 45.1mm (outside dimension), 41.7mm (inside dimension)
Dimensions between long sides: 145mm (outside dimension), 137mm (inside dimension)
Slit width: 26mm
Slit length: 146mm
Radius of each semicircular portion on the upper and lower ends of the slit: 13 mm
<Underwater aeration and stirring device B>
Motor output: 7.5 kW
Air supply range: minimum: Q = 3.2 m ³ / min
Maximum: Q = 12.9 m ³ / min
Dimensions of each part of the microbubble generating member attached to the underwater aeration and stirring device B Overall height: 207 mm
Short side width dimension: 57.4 mm (outside dimension), 54.1 mm (inside dimension)
Dimensions between long sides: 182mm (outside dimension), 174mm (inside dimension)
Slit width: 34mm
Slit length dimension: 169mm
Radius of each semicircular part on the upper and lower ends of the slit: 17 mm
<Test conditions>
Air supply amount of the underwater aeration and stirring device A: 6.0 m ³ / min
The air supply amount of the underwater aeration and stirring device B: 8.0 m ³ / min
Water tank capacity: 180m ³ (length 6m, depth 6m, water depth 5m)
Water in the water tank: clear water Installation position of the underwater aeration and stirring device: bottom center of the water tank <Evaluation of oxygen transfer performance>
In evaluating the oxygen transfer performance, the reference aeration performance (oxygen transfer performance) of the underwater aeration and stirring device per unit volume is expressed by the following equation (1-) under the condition that the water temperature with respect to fresh water is 20 ° C. and dissolved oxygen = 0. Is done.

N (20) = KLa (20) · Cs (20) · V (1-1)
here,
N (20): oxygen transfer rate at a water temperature of 20 ° C. (kg · O ₂ / h)
V: Reaction tank (water tank) volume (m ³ )
KLa (20): Overall oxygen transfer capacity coefficient at 20 ° C. (l / h)
Cs (20): Saturated dissolved oxygen concentration (mg / l) in the liquid at the set water depth and water temperature of 20 ° C
The oxygen transfer rate N (t) per unit volume at the water temperature t ° C. is represented by the following equation (1-2).
N (t) = KLa (t) · (Cst−C) · V (1-2)
here,
N: oxygen transfer rate at t ° C (kg · O ₂ / h)
V: Reaction tank (water tank) volume (m ³ )
KLa (t): Overall oxygen transfer capacity coefficient at t ° C (l / h)
Cst: The saturated dissolved oxygen concentration of fresh water at t ° C and under atmospheric pressure (mg / l)
C: dissolved oxygen concentration in the liquid (mg / l)
Equation (1-3) is obtained by integrating and arranging equation (1-2).

Here, C1: dissolved oxygen concentration after T1 hour (mg / l)
C2: dissolved oxygen concentration after T2 hours (mg / l)
When the time change of the DO concentration is plotted on a logarithmic graph according to the equation (1-3), KLa (t) is obtained from the linear gradient (unsteady state test). Further, KLa (t) measured at t ° C. is converted into 20 ° C. using the following equation to be a reference value.

KLa (20) = KLa (t) · θ ^(20−t) Equation (1-4)
Here, KLa (20): overall oxygen transfer capacity coefficient at 20 ° C. (l / h)
θ: temperature coefficient (1.024)
The set dissolved water depth and the saturated dissolved oxygen concentration Cs (20) in the liquid at 20 ° C. are calculated by correcting the water depth according to the following equation.

Here, Cs (20) ′: saturated dissolved oxygen concentration of fresh water at 20 ° C. under atmospheric pressure (= 8.84 mg / l)
H: Water depth (m)
Using these above equations, in order to compare with the performance of the underwater aeration and stirring apparatus without the fine bubble generating member, N (20) under each experimental condition: the oxygen transfer rate at a water temperature of 20 ° C. (kg · O ₂ / h) was calculated, and the performance of the microbubble generating member was verified.
<Test method>
In the test, a performance confirmation test was performed in accordance with “Sewage test method Chapter 2 Reaction tank characteristic test Section 1 Overall oxygen transfer coefficient”.
(1) Deoxygenation The deoxygenation test was carried out by using cobalt chloride hydrate (CoCl ₂ ) as a catalyst for the deoxygenation reaction of 98% industrial grade sodium sulfite (Na ₂ SO ₃ ), which is a reducing substance of dissolved oxygen, and sodium sulfite. 6H ₂ O) for deoxygenation. Here, since all the dissolved oxygen existing in the water is removed, the concentration of sodium sulfite = 100 mg / l, and the cobalt hydrate = 0.5 mg / l. Each deoxygenated solution was individually adjusted and added in advance, and in the test, the reaction was performed by completely mixing in the tank using the stirring function of the underwater aeration device to perform deoxygenation.
(2) Measurement of dissolved oxygen concentration The dissolved oxygen concentration (DO) was measured by a first sensor installed at a depth of 0.5 m at a distance of 1 m from the center of one side of the water tank and 1 m from the center of the other side of the water tank. The measurement was performed by using a second sensor installed at a distance of 2.5 m away from the water. The sensor used was YSI58 (Yellow Springs Instrument, USA).
(3) Measurement of Ventilation Volume From the test measurement values, the blower ventilation volume (reading by a flow meter), the ventilation pressure, and the ventilation temperature, the actual ventilation volume was calculated from the formula (1-6) using an air flow meter.

Here, Q: actual air flow rate (m ³ / min 20 ° C., 101.3 kPa, 65% RH)
Q0: Air flow (flow meter reading) (m ³ / min 0 ° C., 101.3 kPa, 0% RH)
P1: Measurement pressure (kPa)
P0: Flow meter set pressure (kPa)
T1: Measurement temperature (° C)
T0: Flowmeter set temperature (° C)
<Experimental results>
Table 1 shows the experimental results. The oxygen transfer speed N (20) is 27.7 (kg · O ₂ / h) on average in the underwater aeration and stirring device A, and 35.2 (kg · O ₂ / h) on the average in the underwater aeration and stirring device B. It can be seen that, compared to the case where the bubble generating member is not mounted, the water aeration and stirring device A is improved by 19% and the water aeration and stirring device B is improved by 17%.

FIG. 12 is a graph showing an oxygen transfer rate curve of the above-described experiment for the underwater aeration and stirring apparatus A, and FIG. 13 is a graph showing an oxygen transfer rate curve of the above-described experiment for the underwater aeration and stirring apparatus B. In each graph, the upper curve shows the case where the microbubble generating member is mounted, and the lower curve shows the case where the microbubble generating member is not mounted. From this, it can be seen that when the microbubble generating member is mounted, the oxygen transfer rate is improved, that is, the dissolved oxygen amount is increased.
It should be noted that the above-described embodiments and examples are exemplifications in all respects, and are not grounds for restrictive interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Further, all changes within the meaning and scope equivalent to the claims are included.

INDUSTRIAL APPLICABILITY The present invention can be suitably used for improving the quality of water in a water tank such as a wastewater treatment facility or in a river.

DESCRIPTION OF SYMBOLS 1 Underwater aeration stirring device 11 Motor 20 Impeller 21 Hub 21a Air discharge port 21b Cavity 21c Air intake 22 Blade 23 Opening 30 Pump casing 40 Discharge casing 411 Discharge port 50 Air supply pipe 70 Fine bubble generation member A Long side B Short side L Lower surface S Slit U Upper surface

Claims (4)

An impeller provided with blades on the peripheral surface of a hollow hub having an air discharge port on the upper peripheral surface and having an air intake on the lower surface,
A motor for rotating the impeller,
An air supply pipe for supplying air through the air inlet into the hub of the impeller;
A discharge port for radially discharging a gas-liquid mixed water flow in which air discharged from the air discharge port of the hub is mixed with a water flow generated by rotation of the impeller,
A microbubble generating member provided in the cavity of the hub of the underwater aeration and stirring device provided with:
The micro-bubble generating member has a cross section having a different octagonal shape in which four short sides and four long sides are alternately arranged, and a cylindrical shape in which the upper surface is closed while the lower surface is open. And a slit extending between the upper surface and the lower surface is formed on each of the four short sides, and the axis of the hub and the axis of the microbubble generating member coincide in the cavity of the hub. Characterized in that it is provided and rotated with the impeller. The microbubble generating member according to claim 1,
The micro-bubble generating member, wherein the slit has a semicircular shape having a diameter equal to a width dimension of the slit. The microbubble generating member according to claim 1 or 2,
A microbubble generating member, which is detachable from a hub of the impeller. An impeller provided with blades on the peripheral surface of a hollow hub having an air discharge port on the upper peripheral surface and having an air intake on the lower surface,
A motor for rotating the impeller,
An air supply pipe for supplying air through the air inlet into the hub of the impeller;
A discharge port for radially discharging a gas-liquid mixed water flow in which air discharged from the air discharge port of the hub is mixed with a water flow generated by rotation of the impeller,
An underwater aeration and stirring device provided with:
3. An underwater aeration and stirring device, further comprising the microbubble generating member according to claim 1 or 2 in the cavity of the hub.

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