WO2023233701A1 - Bubble generation device and bubble generation system - Google Patents

Abstract

The present disclosure provides: a bubble generation device that achieves a reduction in device size and a reduction in cost; and a bubble generation system. A bubble generation device (1) according to the present disclosure is attached to a liquid tank (10) and produces fine bubbles in a liquid within the liquid tank (10). The bubble generation device (1) comprises: a vibration plate (2) which has multiple openings formed therein and in which a first surface is in contact with the liquid in the liquid tank (10) and a second surface is in contact with a gas; a vibration body (3) which supports the vibration plate (2); and a piezoelectric element (4) which is provided to the vibration body (3) and causes the vibration plate (2) to vibrate. The vibration body (3) includes: a head part (31), one end of which supports the vibration plate (2); and a cylindrical body (33) which supports the other end of the head part (31). In the head part (31), the diameter of the side for supporting the vibration plate (2) is larger than that of the side supported by the cylindrical body (33).

Description

Air bubble generator and air bubble generation system

The present disclosure relates to a bubble generation device and a bubble generation system.

In recent years, microscopic air bubbles have been used for water purification, wastewater treatment, fish farming, etc., and microscopic air bubbles are being used in a variety of fields. Therefore, bubble generators that generate fine bubbles have been developed (Japanese Patent Laid-Open No. 2016-209825 (Patent Document 1), International Publication No. 2021/245995 (Patent Document 2)). In addition, the use of bubble generators to generate fine bubbles in liquid fuels, disinfectants, cosmetics, etc. in addition to water is being developed. For example, it has been reported that improved fuel efficiency can be achieved by providing a fuel injection device with a bubble generator to include fine bubbles in the liquid fuel injected into the piston.

JP2016-209825A International Publication No. 2021/245995

The bubble generator described in International Publication No. 2021/245995 (Patent Document 2) includes a diaphragm, a cylindrical body, and a piezoelectric element, and vibrates the diaphragm with the piezoelectric element through the cylindrical body. Microscopic air bubbles are generated from multiple openings formed in the diaphragm. In order to efficiently generate fine air bubbles from the opening, it is necessary to vibrate the entire diaphragm in the vertical direction to vibrate the piston, so the cylindrical body is connected to the first cylindrical body, the spring part, and the second cylindrical body. It has a structure including a cylindrical body and a flange.

However, in this bubble generator, when the size of the diaphragm is determined by the amount of bubbles to be generated, the diameter of the first cylindrical body is determined, and the circumference of the second cylindrical body, which has a larger diameter than the first cylindrical body, is determined. Since the structure includes a circular flange, it has been difficult to downsize. Further, since a hollow circular piezoelectric element is provided on the lower surface of the flange, it is difficult to reduce the area of the piezoelectric element and reduce manufacturing costs.

Therefore, an object of the present disclosure is to provide a bubble generation device and a bubble generation system that can reduce the size and cost of the device.

A bubble generating device according to an embodiment of the present disclosure is a bubble generating device that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank, in which a plurality of openings are formed and a first surface is The device includes a diaphragm that is in contact with the liquid in the liquid tank and whose second surface is in contact with the gas, a vibrating body that supports the diaphragm, and a piezoelectric element that is provided on the vibrating body and vibrates the diaphragm. The vibrating body includes a first cylindrical body that supports a diaphragm at one end, and a second cylindrical body that supports the other end of the first cylindrical body. The diameter of the first cylindrical body on the side supporting the diaphragm is larger than the diameter on the side supported by the second cylindrical body.

A bubble generation system according to another embodiment of the present disclosure includes the above-described bubble generation device and a liquid tank.

According to the present disclosure, in the bubble generator, the diameter of the first cylindrical body on the side supporting the diaphragm is larger than the diameter of the side supported by the second cylindrical body, so that the second cylindrical body vibrates. The device can be made smaller and lower in cost without being restricted by the size of the plate.

1 is a schematic diagram of a bubble generation system in which the bubble generation device according to Embodiment 1 is used. 1 is a cross-sectional perspective view of the bubble generator according to Embodiment 1. FIG. FIG. 3 is a schematic diagram for explaining displacement of the bubble generator according to the first embodiment. FIG. 3 is a schematic diagram for explaining the structure and displacement of a vibrating body. FIG. 3 is a diagram showing the structure of a vibrating body and numerical values of displacement. FIG. 3 is a diagram showing numerical values of displacement of the bubble generator according to the first embodiment. It is a schematic diagram for explaining displacement of a head part. It is a schematic diagram of a bubble generation system for explaining the attachment position of a bubble generation device. FIG. 2 is a cross-sectional perspective view of a bubble generator according to a second embodiment. 7 is a graph showing vibration modes of the bubble generator according to Embodiment 2. FIG. It is a graph showing displacement distribution of each vibration mode. It is a schematic diagram for explaining the shape of a head part. 7 is a graph showing a displacement distribution of a lower plane position of a ring portion that is joined to a diaphragm of a vibrating body head portion. It is a figure which shows the numerical value of the displacement of a head part of different shapes. It is a graph showing impedance characteristics in water when the head section is vibrated in the first vibration mode. It is a graph which shows the impedance characteristic in water when a head part is vibrated in a 2nd vibration mode. FIG. 3 is a cross-sectional perspective view of a bubble generator according to a third embodiment. FIG. 3 is a schematic diagram of a bubble generation system in which a bubble generation device according to a third embodiment is used. FIG. 7 is a schematic diagram for explaining displacement of the bubble generator according to Embodiment 3. FIG. FIG. 7 is a schematic diagram for explaining a fastening mechanism of a bubble generator according to a third embodiment.

Below, a bubble generation device and a bubble generation system according to an embodiment will be described in detail with reference to the drawings. Note that the same or corresponding parts in the figures are designated by the same reference numerals, and the description thereof will not be repeated.

(Embodiment 1)
First, FIG. 1 is a schematic diagram of a bubble generation system 100 in which a bubble generation device 1 according to Embodiment 1 is used. The bubble generator 1 shown in FIG. 1 is installed at the bottom of a liquid tank 10 that stores liquid such as water, gasoline, or light oil, and is used as a bubble generator system 100 that generates fine bubbles 200 in the liquid in the liquid tank 10. used. Note that the bubble generation system 100 can be applied to various systems such as, for example, a water purification device, a wastewater treatment device, a fish culture tank, and a fuel injection device.

Further, the liquid introduced into the liquid tank 10 differs depending on the system to which it is applied, and if it is a water purification device, it will be water, but if it is a fuel injection device, it will be liquid fuel. Further, the liquid tank 10 only needs to be able to temporarily store liquid, and includes a pipe into which the liquid is introduced, in which the liquid always flows.

The bubble generator 1 includes a diaphragm 2, a vibrating body 3, and a piezoelectric element 4. The bubble generator 1 is attached to the liquid tank 10 by joining the holding flange 5 provided in a hole made in the bottom of the liquid tank 10 and the flange 36 (see FIG. 2) provided on the outside of the cylindrical body 33 of the vibrating body 3. Fixed. Note that instead of a structure in which the holding flange 5 and the flange 36 are separated, a structure in which the holding flange 5 and the flange 36 are integrally molded and provided on the liquid tank 10 side or the vibrating body 3 side may be used. When the bubble generator 1 is fixed to the liquid tank 10, a part of the vibrating body 3 provided with the vibrating plate 2 is immersed in the liquid. By vibrating the diaphragm 2 immersed in the liquid in this state using the piezoelectric element 4, fine bubbles 200 are generated from a plurality of pores (openings) formed in the diaphragm 2. Note that the diaphragm 2 is provided so that one surface (first surface) is in contact with the liquid in the liquid tank 10 and the other surface (second surface) is in contact with the gas.

The diaphragm 2 is formed of, for example, a resin plate, a metal plate, a Si or SOI (Silicon On Insulator) substrate, a porous ceramic plate, a glass plate, or the like. Specifically, the diameter of the diaphragm 2 is 9 mm, and the thickness of the diaphragm 2 is thinner at the center than at the periphery.For example, the thickness at the periphery is 0.15 mm, and the thickness at the center is 0.15 mm. The thickness is 0.05 mm. The diaphragm 2 has 185 openings in its thinner central portion.

FIG. 2 is a cross-sectional perspective view of the bubble generator 1 according to the first embodiment. In addition, in the bubble generator 1 shown in FIG. 2, illustration of the diaphragm 2 is omitted. In the bubble generator 1, a diaphragm 2 is vibrated by a piezoelectric element 4 via a vibrating body 3. The vibrating body 3 shown in FIG. 1 includes a head portion 31, a spring portion 32, a cylindrical body 33, and a collar portion 34. The vibrating body 3 may have a structure in which the head portion 31, the spring portion 32, the cylindrical body 33, and the collar portion 34 are integrally formed, or may have a structure in which they are formed separately and joined.

The spring portion 32 is supported by a cylindrical body 33 at a position outside the position where the head portion 31 is supported. The cylindrical body 33 has a cylindrical shape. The cylindrical body 33 supports the spring portion 32 at one end. The end of the cylindrical body 33 on the opposite side to the spring portion 32 is supported by the collar portion 34 . The flange portion 34 is a plate-shaped member that supports the bottom surface of the cylindrical body 33 and extends outward from the position where the cylindrical body 33 is supported.

A hollow circular piezoelectric element 4 is provided on the lower surface of the flange 34 to match the shape of the flange 34. The piezoelectric element 4 is electrically connected to the controller 20 shown in FIG. 1 by wiring. By supplying electric power from the controller 20 to the piezoelectric element 4, the piezoelectric element 4 vibrates in the penetrating direction of the cylindrical body 33 (vertical direction in the figure). The piezoelectric element 4 vibrates in the penetrating direction of the cylindrical body 33, thereby causing the spring portion 32 to vibrate in the penetrating direction of the cylindrical body 33, thereby displacing the head portion 31 substantially uniformly in the vertical direction. Note that the piezoelectric element 4 may be provided on the upper surface of the collar portion 34.

The inside of the cylindrical body 33 and the through hole 35 provided in the head part 31 are connected, and the inside of the cylindrical body 33 and the through hole 35 serve as an introduction part for introducing gas into the diaphragm 2. The head portion 31 has a disk-shaped depression 310 on the surface (second surface) that supports the diaphragm 2, and the depression 310 communicates with a through hole 35 provided on the central axis of the truncated cone. . Therefore, gas is introduced from the through hole 35 into the depression 310, and from the depression 310, the gas is introduced into the liquid through the opening of the diaphragm 2. Note that the gas may be introduced into the through hole 35 by using a compressor or the like, or by natural intake. Further, even if the head portion 31 is formed with the depression 310 and the through hole 35 in a solid material in the shape of a truncated cone, the depression 310 can be formed by joining the ring member to the solid material in the shape of a truncated cone in which the through hole 35 is formed. may be formed.

A flange 36 is provided on the outside of the cylindrical body 33, and the bubble generator 1 is fixed to the liquid tank 10 by joining the flange 36 and the holding flange 5. The side surface of the cylindrical body 33 on which the flange 36 is formed serves as a vibration node, and is used to hold the liquid side and the gas side together with the flange 36 without transmitting the vibrations of the piezoelectric element 4 to the liquid tank 10. They can be separated by a flange 5.

FIG. 3 is a schematic diagram for explaining the displacement that occurs in the bubble generator 1 according to the first embodiment. Note that the X and Z directions in the figure indicate the lateral direction and height direction of the bubble generator 1, respectively. The one-dot chain line shown in FIG. 3 is a portion passing through the central axis of the bubble generator 1. As can be seen from FIG. 3, in the vibrating body 3, when the piezoelectric element 4 vibrates in the Z direction of the cylindrical body 33, the spring part 32 that supports the head part 31 is elastically deformed, and the vibration plate 2 is moved in the Z direction. It is being displaced. In addition, in FIG. 3, the magnitude of displacement is indicated by the shade of hatching.

In order to realize miniaturization and cost reduction of the bubble generator 1 without being restricted by the size of the diaphragm 2, the head portion 31 has a truncated conical shape and has a surface supported by a spring portion 32 The diaphragm 2 is supported on the wider surface (second surface) than the first surface. By making the shape of the head portion 31 into a truncated conical shape, the cylindrical body 33 and the flange portion 34 can be made smaller, and the piezoelectric element 4 provided on the flange portion 34 can also be made smaller, thereby reducing manufacturing costs. Further, by forming the head portion 31 into a truncated conical shape, it is possible to increase the electromechanical coupling coefficient and suppress damping of the vibrator performance in the liquid. In particular, the vibrator performance can be improved by optimizing the angle θ (taper angle) formed between the head portion 31 and the spring portion 32.

Therefore, the improvement of the vibrator performance of the vibrating body 3 by making the shape of the head portion 31 into a truncated cone shape will be explained in more detail. FIG. 4 is a schematic diagram for explaining the structure and displacement of the vibrating body. The vibrator performance of the vibrating body 3a shown in FIG. 4 has a head portion 31z having a T-shaped cross section as a preliminary step to examining the head portion 31 having a truncated conical shape. FIG. 4(a) is a diagram showing the displacement of the vibrating body 3a, and FIG. 4(b) is a diagram explaining the structure of the vibrating body 3a.

The factors that determine the resonance frequency of the vibrating body 3a are the stroke of the spring portion 32 and the thickness of the spring portion 32. Note that the stroke of the spring portion 32 is determined by the holding position B1 of the head portion 31 in the spring portion 32 and the diameter Rb of the cylindrical body 33 shown in FIG. 4(b). Here, if the head part 31z has a cylindrical shape, the holding position B1 of the head part 31z will be the same as the diameter Ra of the diaphragm 2, but if the head part 31z has a T-shaped cross section, the diaphragm 2 The holding position B1 of the head portion 31z can be changed without being restricted by the diameter Ra.

However, since the head portion 31z needs to have a through hole for introducing gas into the diaphragm 2, the holding position B1 of the head portion 31 cannot be made smaller than the through hole. For example, when the diameter Rc of the through hole is set to the holding position B1 of the head section 31, if the stroke and thickness of the spring section 32 are set to achieve the same resonance frequency, then when the shape of the head section 31z is cylindrical, The diameters of the cylindrical body 33 and the flange portion 34 are smaller than those shown in FIG. That is, the inner diameter of the piezoelectric element 4 for excitation can be reduced.

When the head portion 31z having a T-shaped cross section is vibrated, as shown in FIG. A displacement A3 due to piston vibration of 32 occurs. The relationship between these displacements A1 to A3, the holding position B1 of the head portion 31, and the thickness B2 of the portion supporting the diaphragm 2 will be explained.

FIG. 5 is a diagram showing the structure of the vibrating body and numerical values of displacement. FIG. 5(a) shows displacements A1 to A3, resonance frequency Fr, electromechanical coupling coefficient k, and The ratio (A2/A3) between displacement A2 and displacement A3 is shown. FIG. 5(b) shows displacements A1 to A3, resonance frequency Fr, electromechanical coupling coefficient k, and The ratio (A2/A3) between displacement A2 and displacement A3 is shown. Note that the ratio (A2/A3) between the displacement A2 and the displacement A3 is an index indicating that the diaphragm 2 is vibrating uniformly.

The results shown in FIG. 5 are based on a porous alumina diaphragm 2 with a diameter Ra of 9 mm and a thickness of 1 mm, a head portion 31z with a thickness of 0.5 mm and a height of 3 mm, and the length from the hole to the end ( This is the result of a simulation in which a spring portion 32 with a maximum stroke of 5 mm and a thickness of 2.5 mm is combined. However, the cylindrical body 33 has an inner diameter of 12 mm and a thickness of 1.5 mm, and the collar portion 34 has an outer diameter of 24.4 mm and a thickness of 2.5 mm. The head portion 31z, the spring portion 32, the cylindrical body 33, and the collar portion 34 are made of SUS metal.

The piezoelectric element 4 has an outer diameter of 21 mm, an inner diameter of 11 mm, and a thickness of 1 mm. As the material of the piezoelectric element 4, ceramics such as PZT (lead zirconate titanate) and KNN ((K,Na)NbO ₃ ), and piezoelectric crystals such as lithium tantalate and lithium niobate are used.

As shown in FIG. 5(a), when the holding position B1 of the head part 31 is changed from 2 mm to 5 mm, when the holding position B1=2 mm (the holding position of the head part 31 is on the side of the hole provided in the spring part 32) Displacements A1 to A3 are maximum at the tip end). The displacement A2 at the end of the diaphragm 2 increases in synchronization with the displacement A3 caused by the piston vibration of the spring portion 32, and as a result, the displacement A1 at the center of the diaphragm 2 becomes maximum. In other words, it can be seen that the vibrator performance of the vibrating body 3a in air becomes higher as the holding position B1 of the head portion 31 becomes smaller.

In FIG. 5(b), the thickness B2 of the portion supporting the diaphragm 2 is varied from 0.5 mm to 2.5 mm. As the thickness B2 increases from 0.5 mm to 2.5 mm, the displacement A3 of the spring portion 32 due to piston vibration increases, but the electromechanical coupling coefficient k reaches a peak when the thickness B2 is 1.5 mm, and then decreases. ing.

When the displacement of the vibrating body 3a is measured in water as shown in FIG. 1, if the electromechanical coupling coefficient k is approximately the same, the quality of the vibrating body performance is determined by the displacement A3 due to the piston vibration of the spring portion 32. Further, as shown in the results in FIG. 5(b), it is understood that even if the thickness B2 is greater than 1.5 mm, the electromechanical coupling coefficient k decreases, and therefore sufficient vibrating body performance cannot be obtained underwater.

From the above results, in order to improve the performance of the vibrating body in water, the bubble generator should adopt a head shape that has a large electromechanical coupling coefficient k and a large displacement A3 due to piston vibration of the spring part 32. It is. Therefore, in this embodiment, by adopting a truncated conical shape as the shape of the head part, the bubble generator 1 is realized which has a large electromechanical coupling coefficient k and a large displacement A3 due to piston vibration of the spring part 32. . FIG. 6 is a diagram showing numerical values of displacement of the bubble generator 1 according to the first embodiment.

In FIG. 6, the displacements A1 to A3, the resonance frequency Fr, the electromechanical coupling coefficient k, the taper angle θ, and the displacements A2 and A3 when the height H of the truncated cone of the head portion 31 shown in FIG. 3 is changed are shown. The ratio (A2/A3) is shown. As can be seen from the results shown in FIG. 6, when the truncated cone height H is in the range of 2.5 mm to 5 mm, the displacement A3 of the spring portion 32 due to piston vibration exceeds 400 nm/V, as shown in FIG. 5(b). It also exceeds the peak value of the electromechanical coupling coefficient k of 20.98.

In FIG. 6, the electromechanical coupling coefficient k is large in the range where the taper angle θ formed by the head portion 31 and the spring portion 32 is low, and the displacement A3 of the spring portion 32 due to piston vibration is also sufficiently large. On the other hand, in a range where the taper angle θ formed by the head portion 31 and the spring portion 32 is high, the electromechanical coupling coefficient k becomes small, but the displacement A3 of the spring portion 32 due to piston vibration becomes large.

FIG. 7 is a schematic diagram for explaining the displacement of the head section. FIG. 7(a) is a schematic diagram for explaining the displacement of the head portion 31z having a T-shaped cross section, and FIG. 7(b) is a schematic diagram for explaining the displacement of the head portion 31 having a truncated cone shape. It is a diagram. As shown in FIG. 7(a), the head part 31z has a large difference between the displacement A3 due to the piston vibration of the spring part 32 and the displacement A2 at the end of the diaphragm 2, so when it is vibrated underwater, Plate 2 will act as a soft spring. Therefore, in the head portion 31z, even if the displacement A1 at the center of the diaphragm 2 is large in air, it is considered that it is hardly reflected in the liquid. Note that even if the bubble generating device 1 employs the head portion 31z having a T-shaped cross section, the device can be made smaller and lower in cost.

On the other hand, in the truncated conical head part 31, if the taper angle θ is 40 degrees or more, the displacement A3 due to the piston vibration of the spring part 32 and the end part of the diaphragm 2 will change as shown in FIG. 7(b). Since the difference from the displacement A2 is small, the diaphragm 2 vibrates uniformly, and it is considered that the displacement A1 at the center of the diaphragm 2 is large in liquid as well as in air. In the head portion 31, the taper angle θ is preferably in the range of 40 degrees to 70 degrees, and more preferably the taper angle θ is in the range of 45 degrees to 65 degrees. In addition, although the resonant frequency of the bubble generator 1 which employ|adopted the truncated cone-shaped head part 31 was demonstrated as an example in the range of 40 kHz to 50 kHz, it is not limited to this.

Next, the mounting position of the bubble generator 1 in the liquid tank 10 will be explained. In the bubble generation system 100 shown in FIG. 1, it has been explained that the bubble generation device 1 is fixed to a hole formed in the bottom surface of the liquid tank 10 with the holding flange 5. The mounting position of the bubble generator 1 in the liquid tank 10 is not limited to this. FIG. 8 is a schematic diagram of the bubble generation system for explaining the mounting position of the bubble generation device 1. In addition, among the bubble generation systems shown in FIG. 8, the same components as the bubble generation system 100 shown in FIG.

In the bubble generation system 100A shown in FIG. 8(a), the bubble generation device 1 is fixed to the side surface of the liquid tank 10 so that at least a part of the vibrating body 3 supporting the diaphragm 2 is immersed in the liquid in the liquid tank 10. ing.

In the bubble generation system 100B shown in FIG. 8(b), the bubble generation device 1 is installed at a position above the liquid level of the liquid tank 10, and the bubble generation device 1 has at least a part of the vibrating body 3 supporting the diaphragm 2. It is fixed toward the bottom of the liquid tank 10 so as to be immersed in the liquid in the liquid tank 10.

Although the mounting position of the bubble generator 1 with respect to the liquid tank 10 has been described with reference to FIGS. 1 and 8, other bubble generators can also be mounted in the same position with respect to the liquid tank 10.

As described above, the bubble generator 1 according to the first embodiment is attached to the liquid tank 10 and generates fine bubbles in the liquid in the liquid tank 10. The bubble generator 1 includes a diaphragm 2 in which a plurality of openings are formed, a first surface is in contact with liquid in a liquid tank 10, and a second surface is in contact with gas, and a diaphragm 3 that supports the diaphragm 2. , a piezoelectric element 4 provided on the vibrating body 3 and vibrating the diaphragm 2. The vibrating body 3 includes a head portion 31 (first cylindrical body) that supports the diaphragm 2 at one end, and a cylindrical body 33 (second cylindrical body) that supports the other end of the head portion 31. including. In the head portion 31, the diameter Ra on the side supporting the diaphragm 2 is larger than the diameter on the side supported by the cylindrical body 33 (holding position B1 of the head portion 31).

As a result, in the bubble generator 1, the diameter Ra of the head part 31 on the side supporting the diaphragm 2 is larger than the diameter of the side supported by the cylindrical body 33 (holding position B1 of the head part 31), The shaped body 33 is not limited by the size of the diaphragm 2, and the device can be made smaller and lower in cost.

The bubble generation system 100 includes a bubble generation device 1 and a liquid tank 10. Thereby, the bubble generation system can be made smaller and lower in cost.

(Embodiment 2)
In the bubble generator 1 shown in FIG. 2, it has been explained that the vibrating body 3 has a structure in which the head part 31 is supported by the spring part 32, the cylindrical body 33, and the collar part 34, but the structure is not limited to this. Any structure may be used as long as it is a vibrating body that vibrates a piston that vibrates up and down. In Embodiment 2, a case will be described in which a Langevin type vibrator is employed as the vibrating body.

FIG. 9 is a cross-sectional perspective view of the bubble generator 1A according to the second embodiment. In addition, among the bubble generators 1A shown in FIG. 9, the same components as those of the bubble generator 1 shown in FIG. 2 are given the same reference numerals, and detailed description thereof will not be repeated. The bubble generator 1A includes a diaphragm 2, a vibrating body 3A, and a piezoelectric element 4, as shown in FIG. The vibrating body 3A includes a head portion 31 that fixes the periphery of the vibrating plate 2, and a cylindrical body 33a continuous to the head portion 31. The cylindrical body 33a is a so-called Langevin type vibrator. The cylindrical body 33a has a structure in which two piezoelectric elements 4 are sandwiched between an upper metal ring 33a1 and a lower metal ring 33a2 and fixed with tightening bolts 34a.

The head portion 31 is provided at the top of the cylindrical body 33a and has a truncated cone shape. In the vibrating body 3A, the taper angle θ is the angle formed by the head portion 31 and the joint surface between the head portion 31 and the cylindrical body 33a. Note that the head portion 31 may be formed separately from the cylindrical body 33a and joined together, or may be formed integrally with the cylindrical body 33a.

The two piezoelectric elements 4 have a structure in which a piezoelectric element 41 and a piezoelectric element 42 whose polarization direction is opposite to that of the piezoelectric element 41 are stacked on top of each other. Terminals 43 and 44 for supplying power to the piezoelectric element 41 and the piezoelectric element 42 are pulled out from between the upper metal ring 33a1 and the lower metal ring 33a2 and the piezoelectric elements 41 and 42, and are connected to the controller 20 shown in FIG. electrically connected by wiring.

By supplying power from the controller 20 to the piezoelectric elements 41 and 42, the cylindrical body 33a is driven at a resonant frequency that depends on the lengthwise dimension including the head portion 31 and the cylindrical body 33a, and the vibration plate 2, a large displacement is obtained. Since a plurality of high-order vibration modes exist in the resonance of the cylindrical body 33a, it is possible to select one resonance frequency from among the plurality of resonance frequencies. Moreover, by making the shape of the head part 31 into a truncated cone shape, the diameter of the part connecting from the upper metal ring 33a1 to the head part 31 becomes smaller than other parts, and the displacement of the diaphragm 2 can be further amplified. I can do it. Furthermore, since the diameter of the cylindrical body 33a itself is reduced, the inner diameter of the piezoelectric element 4 for exciting can also be reduced.

As shown in FIG. 9, a through hole 35 is provided in the center of the upper metal ring 33a1, the lower metal ring 33a2, and the tightening bolt 34a, and the through hole 35 introduces gas into the diaphragm 2. This is an introductory part. Stainless steel, aluminum, or the like is used for the upper metal ring 33a1, the lower metal ring 33a2, and the tightening bolt 34a. For the piezoelectric elements 41 and 42, ceramics such as PZT (lead zirconate titanate) and KNN ((K,Na)NbO ₃ ), piezoelectric crystals such as lithium tantalate and lithium niobate are used.

Specifically, the cylindrical body 33a is made of SUSU304 material, the diameter of the upper metal ring 33a1 is 16 mm, the height including the head portion is 46.5 mm, and the diameter of the lower metal ring 33a2 is 16 mm, and the height is 10 mm. It is. The piezoelectric elements 41 and 42 each have a diameter of 16 mm and a thickness of 2.55 mm. The total length of the vibrating body 3A is approximately 63 mm.

Since the cylindrical body 33a has a structure in which the upper metal ring 33a1 and the lower metal ring 33a2 are tightened with tightening bolts 34a, a compression bias is applied to the piezoelectric elements 41 and 42. Therefore, piezoelectric ceramics having low resistance to tensile stress are used for the piezoelectric elements 41 and 42, and the structure is such that the piezoelectric elements 41 and 42 are difficult to break even when a large amount of power is supplied to the piezoelectric elements 41 and 42 to drive them. . As a result, the upper metal ring 33a1 and the lower metal ring 33a2 have the same potential, so it is necessary to sandwich the application electrode between the two piezoelectric elements 4. The application electrode and the terminal 43 are electrically connected.

Note that, unless it is necessary to drive the piezoelectric elements 41 and 42 by supplying a large amount of power, the cylindrical body 33a does not have a structure in which the piezoelectric elements 4 are tightened with the tightening bolts 34a, and one piezoelectric element 4 is connected to the upper metal ring 33a1. A structure in which it is sandwiched and bonded to the lower metal ring 33a2 may also be used. Further, the cylindrical body 33a may have a structure including only the upper metal ring 33a1, and the piezoelectric element 4 may be bonded to the bottom surface of the upper metal ring 33a1. No matter which structure is adopted for the cylindrical body 33a, manufacturing costs can be reduced.

FIG. 10 is a graph showing the vibration mode of the bubble generator 1A according to the second embodiment. In the graph shown in FIG. 10, the vertical axis represents impedance (Ω), and the horizontal axis represents frequency (kHz). The bubble generator 1A employs a Langevin type vibrator vibrator 3A, with a first vibration mode at 1/2 of the resonant frequency (1/2λ resonance), a second vibration mode at the resonant frequency (λ resonance), and a resonant frequency. A third vibration mode appears at 3/2 (3/2λ resonance).

When the total length of the vibrating body 3A of the Langevin type vibrator is 63 mm, there is a first vibration mode (1/2λ resonance) near 45 kHz as shown in FIG. It will be close to. In FIG. 10, there is a second vibration mode (λ resonance) near 63 kHz, and a third vibration mode (3/2λ resonance) near 95 kHz.

FIG. 11 is a graph showing the displacement distribution of each vibration mode. In the graph shown in FIG. 11, the vertical axis is displacement (m/V), and the horizontal axis is distance (mm) from one end of the diaphragm 2. FIG. 11 shows the displacement of the lower plane position of the ring portion of the vibrating body head portion that connects with the diaphragm when the diaphragm 2 is vibrated in the first vibration mode (1/2λ resonance), and the second vibration mode (λ Displacement of the lower plane position of the ring part of the vibrator head that connects with the diaphragm when the diaphragm 2 is vibrated in the 3rd vibration mode (3/2λ resonance), when the diaphragm 2 is vibrated in the 3rd vibration mode (3/2λ resonance) The displacement of the lower plane position of the ring part that joins with the diaphragm of the vibrating body head part is shown. Note that when the diaphragm 2 is vibrated in the third vibration mode (3/2λ resonance), the lower plane position of the ring part that connects with the diaphragm of the vibrating body head part vibrates more uniformly than in other vibration modes. I haven't been able to do that.

Next, the vibration of the diaphragm 2 when the height of the truncated cone of the head portion 31 is changed will be compared. FIG. 12 is a schematic diagram for explaining the shape of the head section. The head portion 31a shown in FIG. 12(a) has an outer diameter of 9 mm at a portion that supports the diaphragm 2, and a truncated cone height of 3 mm. The head portion 31b shown in FIG. 12(b) has an outer diameter of 9 mm at a portion that supports the diaphragm 2, and a truncated cone height of 6 mm.

The displacement of the diaphragm 2 vibrated by the head portion 31a and the displacement of the diaphragm 2 vibrated by the head portion 31b are compared. FIG. 13 is a graph showing the displacement distribution of the lower plane position of the ring portion that joins with the diaphragm of the vibrating body head portion. FIG. 13(a) shows the displacement of the lower plane position of the ring portion of the vibrating body head portion that connects with the diaphragm when the diaphragm 2 is vibrated in the first vibration mode (1/2λ resonance). (b) shows the displacement of the lower plane position of the ring portion of the vibrating head portion that is joined to the diaphragm when the diaphragm 2 is vibrated in the second vibration mode (λ resonance). In the graphs shown in FIGS. 13(a) and 13(b), the vertical axis is the displacement (m/V), and the horizontal axis is the distance (mm) from one end of the diaphragm 2.

In the first vibration mode (1/2λ resonance), as shown in FIG. 13(a), even if the head portion 31a has a low truncated cone height or the head portion 31b has a high truncated cone height, In both cases, there is no difference in the magnitude of displacement between the center and the periphery of the diaphragm 2. However, in the second vibration mode (λ resonance), as shown in FIG. 13(b), in the head portion 31a where the height of the truncated cone is low, there is a difference in the magnitude of displacement between the center part and the peripheral part of the diaphragm 2. is occurring.

The difference in displacement between the central part and the peripheral part of the diaphragm 2 corresponds to the ratio (A2/A3) between the displacement A2 and the displacement A3 explained in FIG. 6. FIG. 14 is a diagram showing numerical values of displacement of head portions of different shapes. In FIG. 14, wavelength, resonance frequency Fr, electromechanical coupling coefficient k, displacement A2, and displacement are shown for each of the head portion 31a with a low truncated cone height (3 mm) and the head portion 31b with a high truncated cone height (6 mm). The ratio with A3 (A2/A3) is shown.

In the head portion 31a with a low truncated cone height, as shown in FIG. 14, A2/A3=1.01 in the first vibration mode (1/2λ resonance), but A2/A3=1.01 in the second vibration mode (λ resonance). A2/A3=1.21. That is, in the head portion 31a having a low truncated cone height, the value of A2/A3 increases as the resonant frequency Fr of the vibrating body 3A increases.

The impedance characteristics when the head portion 31a and the head portion 31b are vibrated in water are shown. FIG. 15 is a graph showing the impedance characteristics in water when the head section is vibrated in the first vibration mode. FIG. 16 is a graph showing the impedance characteristics in water when the head section is vibrated in the second vibration mode. 15(a) and 16(a) show impedance characteristics in water when the head portion 31a having a low truncated cone height is vibrated. FIGS. 15(b) and 16(b) show impedance characteristics in water when the head portion 31b having a high truncated cone height is vibrated.

In the graphs shown in FIGS. 15 and 16, the vertical axis represents impedance (Ω), and the horizontal axis represents frequency (kHz). In addition, the graphs shown in FIGS. 15 and 16 show the impedance characteristics when the head portions 31a and 31b are vibrated in the air, and when the head portions 31a and 31b are immersed in 1 mm of liquid and vibrated. The impedance characteristics when the head portion 31a and the head portion 31b are immersed in 3 mm of liquid and vibrated are shown.

As can be seen from the graphs in FIGS. 15(a) and 15(b), when the head parts 31a and 31b are vibrated in the first vibration mode, there is almost no change in the impedance characteristics. Even when 31a and 31b are vibrated in the first vibration mode, almost no damping occurs in the vibrations. However, as can be seen from the graph in FIG. 16(a), when the head section 31a is vibrated in the second vibration mode, the impedance characteristics change significantly. When it vibrates, damping occurs in the vibration.

In other words, as shown in FIG. 13(b), in the head portion 31a where there is a difference in the magnitude of displacement between the center and peripheral portions of the diaphragm 2, damping occurs in the vibration when vibrating underwater. The value of A2/A3 when the head portion 31a is vibrated in the second vibration mode is 1.21 as shown in FIG. From this, it is preferable to vibrate the head parts 31a and 31b so that the resonance frequency Fr of the vibrating body 3A is any frequency and the value of A2/A3 is 1.2 or less. In other words, when a truncated cone-shaped head part is employed in the bubble generator, the taper angle is preferably 45 degrees or more as shown in FIG. 6, taking into account damping of vibrations in water.

As described above, in the bubble generator 1A according to the second embodiment, the vibrating body 3A is composed of a Langevin type vibrator. Thereby, the bubble generator 1A easily causes piston vibration that vibrates the diaphragm 2 up and down.

(Embodiment 3)
The bubble generator 1 shown in FIG. 2 has been described as having a structure in which the vibrating body 3 supports the head portion 31 with the spring portion 32, the cylindrical body 33, and the collar portion 34. In Embodiment 3, the vibrating body has a structure including a head portion, a spring portion, a cylindrical body, and a weight portion. FIG. 17 is a cross-sectional view of a bubble generator 1B according to the third embodiment. In addition, among the bubble generation apparatus 1B shown in FIG. 17, the same components as the bubble generation apparatus 1 shown in FIG. 2 are given the same reference numerals, and detailed description thereof will not be repeated. Moreover, in the bubble generator 1B shown in FIG. 17, illustration of the diaphragm 2 is omitted.

In the bubble generator 1B, the diaphragm 2 is vibrated by the piezoelectric element 4 via the vibrating body 3B. The vibrating body 3B shown in FIG. 17 includes a head portion 31, a spring portion 32b, a cylindrical body 33b, and a weight portion 34b.

The spring portion 32b is supported by the cylindrical body 33b at a position outside the position where the head portion 31 is supported. The cylindrical body 33b has a cylindrical shape. The cylindrical body 33b supports the spring portion 32b at one end. The cylindrical body 33b has a weight portion 34b on the outside of the end opposite to the spring portion 32b. The cylindrical body 33b and the weight portion 34b are provided at positions such that when the piezoelectric element 4 vibrates the spring portion 32b, the amount of displacement of the side surface of the cylindrical body 33b falls within a predetermined range.

A hollow circular piezoelectric element 4 is provided on the lower surface of the spring portion 32b to match the shape of the spring portion 32b. The piezoelectric element 4 vibrates in the penetrating direction of the through hole 35 provided in the head portion 31 (vertical direction in the figure). The piezoelectric element 4 vibrates in the direction of penetration of the through hole 35, thereby causing the spring portion 32b to vibrate in the direction of penetration of the through hole 35, thereby displacing the head portion 31 substantially uniformly in the vertical direction.

The inside of the cylindrical body 33b, the hole provided in the piezoelectric element 4, and the through hole 35 provided in the head portion 31 are connected, and gas is introduced into the diaphragm 2 from the inside of the cylindrical body 33b through the through hole 35. This is the introductory part.

When attaching the bubble generator 1B to the liquid tank 10, a flange is provided on the outside of the cylindrical body 33b, and the flange is joined to a holding flange as shown in FIG. 1 to fix the bubble generator 1B to the liquid tank 10. There may be cases where this is the case. However, it is necessary to prepare a holding flange separately from the cylindrical body 33b, and it is necessary to join the cylindrical body 33b and the holding flange and fix them to the liquid tank 10.

Therefore, the bubble generator 1B adopts a structure in which the cylindrical body 33b and the holding flange are integrated. FIG. 18 is a schematic diagram of a bubble generation system 100C in which a bubble generation device 1B according to the third embodiment is used. In addition, among the bubble generation system 100C shown in FIG. 18, the same components as the bubble generation system 100 shown in FIG.

In the bubble generation system 100C, a holding flange 50 is integrally formed on the cylindrical body 33b of the bubble generation device 1B. The holding flange 50 is a plate-shaped member provided around the cylindrical body 33b, and extends outward from the side surface of the cylindrical body 33b. Further, the holding flange 50 is provided with a step at a portion to be fixed to the liquid tank 10, and a screw hole is provided at the portion. Therefore, as shown in FIG. 18, the bubble generator 1B can be fixed to the liquid tank 10 by passing the screws 51 through the screw holes provided in the holding flange 50. The holding flange 50 is made thinner (for example, 0.5 mm) than other parts, but the part where the screw holes are provided is made thicker.

In the bubble generator 1B, a holding flange 50 for separating the liquid side and the gas side is integrally formed on the side surface of the cylindrical body 33b, which serves as a vibration node. Therefore, no gap is created between the cylindrical body 33b and the holding flange 50, and there is no possibility of liquid leaking from the gap to the gas side. Further, the holding flange 50 is provided with a step relative to the portion fixed to the liquid tank 10 (the portion provided with the screw hole), and is connected to the side surface of the cylindrical body 33b at the lowered portion. By forming the holding flange 50 in the shape shown in FIG. 18, vibrations leaking from the cylindrical body 33b through the holding flange 50 into the liquid tank 10 can be reduced by about 90%, and the vibration caused by the piezoelectric element 4 can be reduced by about 90%. The driving force of 3B can be efficiently transmitted to the diaphragm 2.

FIG. 19 is a schematic diagram for explaining the displacement of the bubble generator 1B according to the third embodiment. As can be seen from FIG. 19, when the piezoelectric element 4 vibrates, the spring portion 32b supporting the head portion 31 is elastically deformed and the diaphragm 2 is displaced. However, the holding flange 50 provided on the side surface of the cylindrical body 33b is hardly displaced. In addition, in FIG. 19, the magnitude of displacement is shown by the shade of hatching, where darkly hatched areas indicate large displacement areas, and light hatched areas indicate small displacement areas.

Next, FIG. 20 is a schematic diagram for explaining the fastening mechanism of the bubble generator 1B according to the third embodiment. FIG. 20 is a plan view of the bubble generator 1B viewed from above the diaphragm 2. In FIG. As shown in FIG. 20, screw holes 51a are provided at four locations on the holding flange 50. This screw hole 51a is a fastening mechanism for fixing the bubble generator 1B to the liquid tank 10. Note that the fastening mechanism of the screw hole 51a is just one example, and any mechanism may be used as long as it is a mechanism for fixing the bubble generator 1B to the liquid tank 10. Further, the configuration of the holding flange 50 can be similarly applied to the cylindrical body 33 shown in FIG. 2 and the cylindrical body 33a shown in FIG. 9.

As described above, in the bubble generator 1B according to the second embodiment, the vibrating body 3B is connected to the spring portion 32b provided between the head portion 31 and the cylindrical body 33b and the end portion of the cylindrical body 33b. It further includes a weight portion 34b provided. The piezoelectric element 4 is provided on the surface of the spring portion 32b supported by the cylindrical body 33b. Thereby, the bubble generator 1B easily causes piston vibration that vibrates the diaphragm 2 up and down.

(Other variations)
In the above-described embodiment, the head portion 31 is a solid member having a truncated cone shape, and has a structure in which a cylindrical through hole 35 is formed. However, the head portion 31 is not limited to a solid material having a truncated cone shape, but may have a structure in which a truncated cone shape is formed using a plate member. When the truncated cone-shaped head portion 31 is formed of a plate member, the hollow portion of the head portion 31 functions as the through hole 35 .

(mode)
(1) The bubble generating device of the present disclosure is a bubble generating device that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank, in which a plurality of openings are formed and a first surface faces the liquid. A vibrating plate that is in contact with the liquid in the tank and whose second surface is in contact with the gas, a vibrating body that supports the vibrating plate, and a piezoelectric element that is provided on the vibrating body and vibrates the vibrating plate. a first cylindrical body supporting the diaphragm by one end thereof, and a second cylindrical body supporting the other end of the first cylindrical body, the first cylindrical body having a side supporting the diaphragm. is larger than the diameter of the side supported by the second cylindrical body.

According to the bubble generator of the present disclosure, the diameter of the first cylindrical body on the side supporting the diaphragm is larger than the diameter of the side supported by the second cylindrical body, so that the second cylindrical body serves as the diaphragm. The device can be made smaller and lower in cost without being limited by the size of the device.

(2) In the bubble generator described in (1), the first cylindrical body has a truncated cone shape and supports the diaphragm on the second surface side, which is wider than the first surface. Thereby, the bubble generator can be made smaller and lower in cost.

(3) The bubble generator according to (2), wherein the first cylindrical body has a disc-shaped depression on the second surface supporting the diaphragm, and is provided on the central axis of the truncated cone. The through hole and the depression communicate with each other. Thereby, the bubble generator can introduce gas into the diaphragm through the through hole.

(4) In the bubble generating device described in (3), the first cylindrical body has a hollow and a through hole formed in a solid material having a truncated conical shape. Thereby, the cost of the bubble generator can be reduced.

(5) In the bubble generator according to any one of (2) to (4), the first cylindrical body has a truncated conical shape with a taper angle of 40 degrees or more. Thereby, the bubble generator can obtain sufficient vibrator performance in liquid.

(6) The bubble generator according to any one of (1) to (5), in which the vibrating body is composed of a Langevin type vibrator. Thereby, the bubble generator easily causes piston vibration that vibrates the diaphragm up and down.

(7) The bubble generator according to any one of (1) to (5), wherein the vibrating body is a spring portion provided between the first cylindrical body and the second cylindrical body; , further including a plate-shaped collar provided at the end of the second cylindrical body and extending outward from the position of the second cylindrical body, and the spring part supports the first cylindrical body at one end. The piezoelectric element is supported by the second cylindrical body at the other end located outside the position supporting the first cylindrical body, and the piezoelectric element is attached to the first surface of the flange portion on the second cylindrical body side or It is provided on the second surface on the opposite side of the surface. Thereby, the bubble generator easily causes piston vibration that vibrates the diaphragm up and down.

(8) The bubble generator according to any one of (1) to (5), wherein the vibrating body is a spring portion provided between the first cylindrical body and the second cylindrical body. , a weight part provided at the end of the second cylindrical body, and the piezoelectric element is provided on the surface of the spring part supported by the second cylindrical body. Thereby, the bubble generator easily causes piston vibration that vibrates the diaphragm up and down.

(9) A bubble generation system of the present disclosure includes the bubble generation device according to any one of (1) to (8) and a liquid tank. Thereby, the bubble generation system can be made smaller and lower in cost.

(10) The bubble generation system according to (9), wherein the bubble generator is fixed to the bottom or side surface of the liquid tank so that at least a part of the vibrating body supporting the diaphragm is immersed in the liquid in the liquid tank. ing. Thereby, the bubble generation system can generate fine bubbles in the liquid from the bottom or side of the liquid tank.

(11) In the bubble generation system according to (9), the bubble generation device is installed at a position above the liquid level of the liquid tank, and at least a part of the vibrating body supporting the diaphragm is exposed to the liquid in the liquid tank. It is fixed toward the bottom of the liquid tank so that it can be submerged. Thereby, the bubble generation system can generate fine bubbles in the liquid from the top surface of the liquid tank.

The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

1, 1A, 1B bubble generator, 2 diaphragm, 3, 3A, 3B, 3a vibrator, 4, 41, 42 piezoelectric element, 5, 50 holding flange, 10 liquid tank, 20 controller, 31, 31a, 31b head part, 32, 32b spring part, 33, 33a, 33b cylindrical body, 33a1 upper metal ring, 33b1 lower metal ring, 34 collar part, 34a tightening bolt, 34b weight part, 35 through hole, 36 flange, 43, 44 terminal, 51 screw, 51a screw hole, 100, 100A to 100C bubble generation system, 200 bubble.

Claims (11)

1. A bubble generator that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank,
   a diaphragm having a plurality of openings formed therein, a first surface in contact with the liquid in the liquid tank, and a second surface in contact with the gas;
   a vibrating body that supports the diaphragm;
   a piezoelectric element provided on the vibrating body and vibrating the vibrating plate,
   The vibrating body is
   a first cylindrical body supporting the diaphragm with one end;
   a second cylindrical body supporting the other end of the first cylindrical body,
   The first cylindrical body is a bubble generating device in which a diameter on a side supporting the diaphragm is larger than a diameter on a side supported by the second cylindrical body.
2. The bubble generator according to claim 1, wherein the first cylindrical body has a truncated cone shape and supports the diaphragm on a second surface side that is wider than the first surface.
3. 2. The first cylindrical body has a disk-shaped depression on the second surface that supports the diaphragm, and the depression communicates with a through hole provided in a central axis of a truncated cone. The bubble generator described in .
4. The bubble generating device according to claim 3, wherein the first cylindrical body has the depression and the through hole formed in a solid material having a truncated cone shape.
5. The bubble generator according to any one of claims 2 to 4, wherein the first cylindrical body has a truncated cone shape with a taper angle of 40 degrees or more.
6. The bubble generating device according to any one of claims 1 to 5, wherein the vibrating body is composed of a Langevin type vibrator.
7. The vibrating body is
   a spring portion provided between the first cylindrical body and the second cylindrical body;
   further comprising a plate-shaped collar provided at an end of the second cylindrical body and extending outward from the position of the second cylindrical body,
   The spring portion supports the first cylindrical body at one end, and is supported by the second cylindrical body at the other end located at a position outside the position supporting the first cylindrical body,
   According to any one of claims 1 to 5, the piezoelectric element is provided on a first surface of the collar portion on the second cylindrical body side or a second surface on the opposite side of the first surface. The bubble generator described.
8. The vibrating body is
   a spring portion provided between the first cylindrical body and the second cylindrical body;
   further comprising a weight provided at an end of the second cylindrical body,
   The bubble generating device according to any one of claims 1 to 5, wherein the piezoelectric element is provided on a surface of the spring portion supported by the second cylindrical body.
9. The bubble generator according to any one of claims 1 to 8;
   A bubble generation system comprising: the liquid tank.
10. The bubble generator according to claim 9, wherein the bubble generator is fixed to the bottom or side surface of the liquid tank so that at least a part of the vibrating body that supports the diaphragm is immersed in the liquid in the liquid tank. system.
11. The bubble generator is installed above the liquid level of the liquid tank, and is mounted toward the bottom of the liquid tank so that at least a part of the vibrating body that supports the diaphragm is immersed in the liquid in the liquid tank. 10. The bubble generation system of claim 9, which is fixed.

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