JP7772207B2 - Bubble generating device and bubble generating system - Google Patents

Description

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

In recent years, microscopic bubbles have been used in a variety of fields, including water purification, wastewater treatment, and fish farming. To this end, bubble generators that generate microscopic bubbles have been developed (see JP 2016-209825 A (Patent Document 1) and JP 2014-150784 A (Patent Document 2)). Furthermore, development is underway to use bubble generators to generate microscopic bubbles in liquid fuel, disinfectants, cosmetics, and other liquids in addition to water. For example, it has been reported that fuel efficiency can be improved by installing a bubble generator in a fuel injection system and incorporating microscopic bubbles into the liquid fuel injected into the piston.

Japanese Patent Application Laid-Open No. 2016-209825 JP 2014-150784 A

The bubble generator described in JP 2016-209825 A (Patent Document 1) has a supply unit below the vibrating plate that supplies gas in order to generate fine bubbles in a liquid. This supply unit is connected to a raw material supply pipe that supplies raw material from outside the bubble generator. A raw material container is connected to the raw material supply pipe via a pressure regulator that adjusts the pressure. When using a gas as a raw material to generate bubbles in a bubble generator, it was necessary to use a gas cylinder or similar as the raw material container.

In the bubble generator described in JP 2014-150784 A (Patent Document 2), a specific gas required for microbial cultivation is supplied from a compressor to a culture tank through through-holes in a vibrating plate. At this time, the bubble generator generates fine bubbles in the liquid by applying a specific frequency vibration to the vibrating plate from a piezoelectric vibrating element to which a high-frequency voltage is applied from an oscillator.

Therefore, in order to generate fine bubbles in a liquid with any bubble generating device, it was necessary to forcibly supply gas from below the vibrating plate using a gas cylinder or compressor, which hindered the device from being made smaller and less expensive.

Therefore, the object of the present disclosure is to provide a bubble generating device and a bubble generating system that can be made smaller and less expensive.

A bubble generator according to one aspect of the present disclosure is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank. The bubble generator includes a vibration plate having a plurality of openings formed therein, the first surface of the vibration plate being in contact with the liquid in the liquid tank and the second surface of the vibration plate being in contact with the gas, a vibrating body supporting the vibration plate, and a piezoelectric element provided on the vibrating body for vibrating the vibration plate. Each of the plurality of openings formed in the vibration plate has a larger opening diameter on the first surface side than on the second surface side. The vibrating body includes a head portion supporting the vibration plate, a plate-shaped spring portion supporting the head portion, a cylindrical body supporting one end of the spring portion at a position outside the position supporting the head portion, and a weight portion provided at the end of the cylindrical body. The piezoelectric element is provided on the surface of the spring portion supported by the cylindrical body.

Another aspect of the present disclosure relates to a bubble generating system comprising the aforementioned bubble generating device and a liquid tank.

According to the present disclosure, in the bubble generating device, the shape of each of the multiple openings formed in the vibrating plate is such that the opening diameter on the first surface side is larger than the opening diameter on the second surface side, allowing for the generation of fine bubbles in the liquid by natural aspiration, and eliminating the need for a supply unit that forcibly supplies gas, thereby enabling the device to be made smaller and less expensive.

1 is a schematic diagram of a bubble generation system in which a bubble generation device according to an embodiment is used. FIG. 1 is a cross-sectional perspective view of an air bubble generation device according to an embodiment. FIG. 2 is a cross-sectional view of a head portion of the air bubble generation device according to the embodiment. 5A and 5B are schematic diagrams for explaining forces generated near an opening of the bubble generation device according to the embodiment. FIG. 10 is a cross-sectional view of a bubble generation device according to a first modified example. FIG. 10 is a cross-sectional view of a bubble generation device according to a second modified example. FIG. 2 is a schematic diagram of a bubble generation system for explaining the installation position of the bubble generation device. 10 is a schematic diagram of a bubble generation system illustrating another installation position of the bubble generation device. FIG.

(Embodiment)
Hereinafter, an air bubble generating device and an air bubble generating system according to an embodiment will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings will be given the same reference numerals and their description will not be repeated.

First, Figure 1 is a schematic diagram of a bubble generation system 100 in which a bubble generation device 1 according to an embodiment of the present invention is used. The bubble generation device 1 shown in Figure 1 is installed above a liquid tank 10 that stores liquid such as water, gasoline, or diesel, and is used in the bubble generation system 100 to generate fine bubbles 200 in the liquid in the liquid tank 10. The bubble generation system 100 can be applied to a variety of systems, such as water purification devices, wastewater treatment devices, fish farming tanks, and fuel injection devices.

The liquid introduced into the liquid tank 10 varies depending on the system to which it is applied; for example, in a water purification system, it is water, but in a fuel injection system, it is liquid fuel. Furthermore, the liquid tank 10 is only required to be able to temporarily store liquid, and includes a pipe through which the liquid is introduced and through which the liquid constantly flows.

The bubble generator 1 comprises a vibration plate 2, a vibrating body 3, and a piezoelectric element 4. The bubble generator 1 is inserted through a hole in a lid provided on top of a liquid tank 10, and the bubble generator 1 is fixed to the lid of the liquid tank 10 with a holding flange 5 at a position where a portion of the vibrating body 3 provided with the vibration plate 2 is immersed in the liquid. By vibrating the vibration plate 2 immersed in the liquid using the piezoelectric element 4, fine bubbles 200 are generated from multiple pores (openings) formed in the vibration plate 2. The vibration plate 2 is arranged so that one surface (first surface) contacts the liquid in the liquid tank 10 and the other surface (second surface) contacts the gas.

Figure 2 is a cross-sectional perspective view of a bubble generator 1 according to an embodiment. As shown in Figure 2, the bubble generator 1 is composed of a vibration plate 2, a head portion 31 that fixes the periphery of the vibration plate 2, and a cylindrical body 32 that is connected to the head portion 31. The cylindrical body 32 is a so-called Langevin type vibrator. The cylindrical body 32 has a structure in which two piezoelectric elements 4 are sandwiched between an upper metal ring 32a and a lower metal ring 32b and fixed with a tightening bolt 34.

The two piezoelectric elements 4 are configured by stacking a first piezoelectric element 41 and a second piezoelectric element 42 with a polarization direction opposite to that of the first piezoelectric element 41. Terminals 43, 44 that supply power to the first piezoelectric element 41 and the second piezoelectric element 42 are drawn out from between the upper metal ring 32a, the lower metal ring 32b and the first piezoelectric element 41, and the second piezoelectric element 42, and are electrically connected by wiring to the controller 20 shown in Figure 1.

By supplying power from the controller 20 to the first piezoelectric element 41 and the second piezoelectric element 42, the cylindrical body 32 is driven at a resonant frequency that depends on the longitudinal dimensions of the head portion 31 and the cylindrical body 32, resulting in a large displacement of the vibration plate 2. Because the cylindrical body 32 resonates in multiple higher-order vibration modes, it is possible to select one resonant frequency from multiple resonant frequencies. Furthermore, by narrowing the diameter of the portion connecting the upper metal ring 32a to the head portion 31 smaller than the other portions, the displacement of the vibration plate 2 can be further amplified.

2, through holes 35 are provided in the centers of the upper metal ring 32a, the lower metal ring 32b, and the fastening bolt 34, and these through holes 35 serve as inlet portions for introducing gas into the diaphragm 2. The upper metal ring 32a, the lower metal ring 32b, and the fastening bolt 34 are made of stainless steel, aluminum, or the like. The first piezoelectric element 41 and the second piezoelectric element 42 are made of ceramics such as PZT (lead zirconate titanate) and KNN ((K,Na) _NbO3 ), or piezoelectric crystals such as lithium tantalate and lithium niobate.

Specifically, the cylindrical body 32 is made of SUS304 material, with the upper metal ring 32a having a diameter of 16 mm and a height including the head portion of 46.5 mm, and the lower metal ring 32b having a diameter of 16 mm and a height of 10 mm. The first piezoelectric element 41 and the second piezoelectric element 42 each have a diameter of 16 mm and a thickness of 2.55 mm. The total length of the vibrating body 3 is approximately 63 mm. The resonant frequency of the cylindrical body 32 depends on the shape of the head portion 31, but is approximately 45 kHz in the case of a half-wavelength resonance.

The cylindrical body 32 is constructed by fastening the upper metal ring 32a and the lower metal ring 32b with the fastening bolts 34, which applies a compressive bias to the first piezoelectric element 41 and the second piezoelectric element 42. Therefore, piezoelectric ceramics with low resistance to tensile stress are used for the first piezoelectric element 41 and the second piezoelectric element 42, making them less susceptible to damage even when driven by a large amount of power. Furthermore, because the upper metal ring 32a and the lower metal ring 32b are at the same potential, an application electrode must be sandwiched between the two piezoelectric elements 4. This application electrode is electrically connected to the terminal 43.

If there is no need to supply a large amount of power to drive the first piezoelectric element 41 and the second piezoelectric element 42, the cylindrical body 32 may not be fastened with the fastening bolts 34, but may instead be structured so that one piezoelectric element 4 is sandwiched and bonded between an upper metal ring 32a and a lower metal ring 32b. Alternatively, the cylindrical body 32 may be structured so that it only has an upper metal ring 32a, with the piezoelectric element 4 bonded to the bottom surface of the upper metal ring 32a. Regardless of the structure adopted for the cylindrical body 32, manufacturing costs can be reduced.

Figure 3 is a cross-sectional view of the head portion 31 of the bubble generation device 1 according to the embodiment. The head portion 31 is provided on the upper part of the cylindrical body 32 and has a truncated cone shape. Note that the shape of the head portion 31 shown in Figure 3 is an example, and is not limited to a truncated cone shape, and may be other shapes such as a cylindrical shape. Furthermore, the head portion 31 may be formed separately from the cylindrical body 32 and connected thereto, or may be formed integrally therewith.

The head portion 31 has a diaphragm 2 fixed to the upper periphery of its truncated cone shape using adhesive or welding. The diaphragm 2 is formed, for example, from a resin plate, metal plate, Si or SOI (Silicon On Insulator) substrate, porous ceramic plate, or glass plate. Specifically, the outer diameter Rc of the diaphragm 2 is 9 mm, and the diaphragm 2 is thinner in the center than in the periphery; for example, the thickness of the periphery is 0.15 mm and the thickness of the center is 0.05 mm.

The diaphragm 2 has 185 openings 2a in its central area where the thickness is thinner. As shown in Figure 3, the cross-sectional shape of each opening 2a is tapered, with the opening diameter Ra on one side (liquid side) being larger than the opening diameter Rb on the other side (gas side) (Ra > Rb). Note that the cross-sectional shape of the openings 2a is not limited to a tapered shape and may be any shape, such as a stepped shape, as long as at least the opening diameter Ra on the liquid side is larger than the opening diameter Rb on the gas side. Specifically, the opening diameter Ra on the liquid side is approximately 70 μm, and the opening diameter Rb on the gas side is approximately 10 μm.

In the bubble generator 1, the vibration plate 2 is attached to the head portion 31 with the larger opening diameter Ra on the liquid side and the smaller opening diameter Rb on the gas side, and piston vibration is used to vibrate the vibration plate 2 up and down, thereby generating fine bubbles 200 in the liquid using natural aspiration. Conversely, if the vibration plate 2 is attached to the head portion 31 with the larger opening diameter Ra on the gas side and the smaller opening diameter Rb on the liquid side, it is not possible to generate fine bubbles 200 in the liquid unless an air pressure of 20 kPa to 40 kPa is applied. In other words, if the opposite were true, the bubble generator 1 would require a compressor.

In the bubble generator 1, when the vibration plate 2 is attached to the head portion 31 with the larger opening diameter Ra on the liquid side and the smaller opening diameter Rb on the gas side and the vibration plate 2 is driven by a piston, a pump effect is thought to occur, sending gas into the liquid by natural aspiration. This pump effect can be explained based on Bernoulli's law. Specifically, when the vibration plate 2 is attached to the head portion 31 with the larger opening diameter Ra on the liquid side and the smaller opening diameter Rb on the gas side and the vibration plate 2 is driven by a piston, the flow rate increases in the small opening diameter portion, creating a low-pressure area and creating a pump effect that draws gas up from the gas side. Furthermore, when the vibration plate 2 is displaced downward by piston vibration, the gas that enters through the smaller opening diameter 2a spreads along the cross-sectional shape of the opening 2a and is pushed up by the tapered portion due to the upward displacement of the vibration plate 2, creating a pump effect.

In the bubble generator 1, to generate a pumping effect, it is preferable to use piston vibration, vibrating the diaphragm 2 up and down, rather than bending it. With a diaphragm 2 that bends easily, vertical vibrations are absorbed in the liquid, functioning as a "soft spring" and reducing the pumping effect. For this reason, it is preferable to use piston vibration on a diaphragm 2 that is less likely to bend. The pumping effect generated in the bubble generator 1 can be understood as a phenomenon that causes gas to flow in one direction, from the gas side to the liquid side. The pumping effect generated in the bubble generator 1 can be optimized by changing parameters such as the resonant frequency (vibration mode), the height of the head portion 31, the outer diameter Rc of the diaphragm 2, and the inner diameter Rd that holds the diaphragm 2.

As shown in Figure 1, when the bubble generator 1 is installed on the top of the liquid tank 10, liquid leakage from the opening 2a is not a problem. However, when the bubble generator 1 is installed on the bottom of the liquid tank 10, liquid leakage from the opening 2a becomes a problem when the vibration plate 2 is attached to the head portion 31 with the larger opening diameter Ra on the liquid side and the smaller opening diameter Rb on the gas side.

Therefore, we will consider liquid leakage from the opening 2a. Figure 4 is a schematic diagram illustrating the forces generated near the opening 2a of the bubble generation device 1 according to the embodiment. Figure 4(a) is a schematic diagram illustrating the case where the amount of liquid dripping from the opening 2a is small, and Figure 4(b) is a schematic diagram illustrating the case where the amount of liquid dripping from the opening 2a is large.

First, let Rb (m) be the diameter of one opening 2a on the gas side of the diaphragm 2, h (m) be the depth of the liquid (assumed to be water in this case), θ (°) be the contact angle between the liquid at the gas-side opening 2a and the interface, and m (kg) be the weight of the liquid dripping from the opening 2a. The surface tension of the liquid (water) is γ = 0.728 N/m, so a force F1 is generated in the upward direction in the figure. This force F1 can be expressed by Equation 1.
F1=2π×(Rb/2)×γ×cosθ
=0.728π(Rb)cosθ(N)...(Formula 1)
The pressure of the liquid (water pressure) acting on the opening 2a is 0.1 atmospheres = 10130 N/ ^m2 for a liquid depth of 1 m, and the cross-sectional area of the opening 2a is π × (Rb/2) ² ( ^m2 ), so a force F2 is generated in the downward direction in the figure. This force F2 can be expressed by Equation 2.
F2=10130×h×π×(Rb/2) ² (N) (Formula 2)
If we consider the mass m of the dripping liquid to be a sphere with an opening diameter Rb at most, it will be 4×π×(Rb/2) ² /3 (kg), so gravity mg acts downward in the figure. This gravity mg can be expressed as Equation 3.
mg (max) = 9.8 x π x (Rb) ² /3 (N) ... (Formula 3)
4(a), as long as the relationship F1 > F2 + mg holds, the liquid will not leak from the opening 2a of the diaphragm 2. Specifically, assuming that the opening diameter of the opening 2a of the diaphragm 2 is fine bubbles (less than 100 μm) to ultra-fine bubbles (less than 1 μm), the opening diameter Rb of the opening 2a will be in the range of 1×10 ⁻⁷ to 1×10 ⁻⁵ (m). If the contact angle is assumed to be 20°, the force F1 will be in the range of 2.15×10 ⁻⁷ to 2.15×10 ⁻⁵ (N), and the force F2 will be in the range of 7.96×10 ⁻¹¹ to 7.96×10 ⁻⁷ (N), even if the liquid depth (h) is assumed to be 1 m. Since the maximum gravity mg is in the range of 1.02×10 ^-20 to 1.02×10 ^-14 (N), whether or not the liquid leaks from the opening 2a of the diaphragm 2 is determined largely by the relationship between forces F1 and F2. When the contact angle is 20°, mathematically, if the opening diameter of the opening 2a is up to 26 μm, the relationship F1 > F2 + mg is satisfied, and therefore the liquid will not leak from the opening 2a of the diaphragm 2. Note that the result assuming that the opening diameter of the opening 2a is up to 26 μm is when the liquid depth (h) is 1 m; if the liquid depth (h) is, for example, 0.1 m (10 cm), the liquid will not leak from the opening 2a of the diaphragm 2 even if the opening diameter of the opening 2a is 100 μm.

Here, when the contact angle is 0°, the relationship between the opening diameter Rb of the opening 2a, the depth h of the liquid, and the surface tension ratio γa of the liquid when the surface tension of water is 1 can be calculated using Equations 1 to 3, as shown in Equation 4.
Rb<28×10 ⁻⁶ ×(γa)/h (Formula 4)
If the depth h of the liquid is 1 m and the liquid is water (γa = 1), the opening diameter Rb of the opening 2a is determined to be less than 28 μm. In other words, if the opening diameter Rb of the opening 2a is less than 28 μm, the liquid will not leak from the opening 2a of the diaphragm 2, and fine bubbles 200 can be generated in the liquid without the need for a compressor to send air.

Furthermore, even if the contact angle is 80°, the relationship between the opening diameter Rb of the opening 2a, the depth h of the liquid, and the surface tension ratio γa of the liquid when the surface tension of water is 1 can be calculated using Equations 1 to 3, as shown in Equation 5.
Rb<5×10 ⁻⁶ ×(γa)/h (Formula 5)
If the depth h of the liquid is 1 m and the liquid is water (γa = 1), the opening diameter Rb of the opening 2a is determined to be less than 5 μm. In other words, if the opening diameter Rb of the opening 2a is less than 5 μm, the liquid will not leak from the opening 2a of the diaphragm 2, and fine bubbles 200 can be generated in the liquid without the need for a compressor to send air.

As mentioned above, a diaphragm 2 with a thick plate thickness and low bending resistance is more suitable. Furthermore, the opening diameter Rb of the openings 2a is related to the size of the microscopic bubbles 200 to be generated. To create microbubbles of 100 μm or less that remain in the liquid for a long time, an opening diameter of 20 μm or less is preferable. Meanwhile, the limits of miniaturization and processing of the openings 2a are related to the aspect ratio between the opening diameter Rb and the thickness of the diaphragm 2. Processing with an aspect ratio exceeding 10 dramatically increases manufacturing costs. Therefore, forming a fine opening diameter Rb restricts the thickness of the diaphragm 2. Furthermore, tapering the cross-sectional shape of the openings 2a alleviates the restriction on increasing the thickness of the diaphragm 2. However, tapering the cross-sectional shape of the openings 2a imposes a new manufacturing constraint on the pitch of the openings 2a, which is determined by the opening diameter Ra.

Considering manufacturing ease, diaphragm 2 is made of metal. However, because standard etching techniques can only create an opening diameter approximately equal to the plate thickness, special plating techniques are required. Even so, the aspect ratio of opening diameter Rb to the plate thickness of diaphragm 2 is limited to approximately 10. Therefore, if opening diameter Rb is 10 μm, the plate thickness of diaphragm 2 is limited to a maximum of 100 μm. By using MEMS (Micro Electro Mechanical Systems) technology, it is possible to process the opening 2a by not only tapering the cross-sectional shape, but also by forming holes with different opening diameters on the front and back. Furthermore, if ceramic or glass is used as the material for diaphragm 2, asymmetrical hole processing is possible using sandblasting or laser processing techniques. The opening diameter Rb of opening 2a is preferably approximately 1 μm to 20 μm.

In addition to the benefit of eliminating the need for a compressor or other device to send air by realizing the pumping effect of the vibration plate 2, the bubble generator 1 also has the benefit of being able to control the amount of gas in the fine bubbles 200 generated by the drive amount of the vibration plate 2. In particular, when a compressor is used, if the air pressure applied to the vibration plate 2 is high, the gas that enters through the opening 2a may not be separated and destroyed by the vibration plate 2, but may instead be output as large bubbles, absorbing other fine bubbles. The bubble generator 1 also has the benefit of eliminating the need for complex controls for a compressor or other device, because the pumping effect prevents excessive gas from being supplied to the liquid.

As described above, the bubble generator 1 according to the embodiment is attached to a liquid tank 10 and generates fine bubbles in the liquid in the liquid tank 10. The bubble generator 1 comprises a vibration plate 2 having a plurality of openings 2a formed therein, a first surface in contact with the liquid in the liquid tank 10, and a second surface in contact with the gas, a vibrating body 3 that supports the vibration plate 2, and a piezoelectric element 4 that is provided on the vibrating body 3 and vibrates the vibration plate 2. The shape of each of the plurality of openings 2a formed in the vibration plate 2 is such that the opening diameter Ra on the liquid side is larger than the opening diameter Rb on the gas side.

As a result, in the bubble generating device 1, the shape of each of the multiple openings 2a formed in the vibration plate 2 is such that the opening diameter Ra on the liquid side is larger than the opening diameter Rb on the gas side, so fine bubbles can be generated in the liquid by natural aspiration, and since there is no need for a compressor or the like to forcibly supply gas, the device can be made smaller and less expensive.

The bubble generation system 100 comprises a bubble generation device 1 and a liquid tank 10. This allows the bubble generation system to be made smaller and less expensive.

(Variation 1)
In the bubble generator 1 shown in Fig. 2, the vibrating body 3 is described as a Langevin vibrator, but the vibrating body is not limited to this and may have any structure as long as it is a vibrating body that performs piston vibration to vibrate the diaphragm 2 up and down. Fig. 5 is a cross-sectional view of a bubble generator 1A according to Modification 1. Note that, in the bubble generator 1A shown in Fig. 5, the same components as those in the bubble generator 1 shown in Fig. 2 are designated by the same reference numerals and detailed description thereof will not be repeated. Furthermore, the diaphragm 2 is not shown in the bubble generator 1A shown in Fig. 5.

In the bubble generating device 1A, the vibration plate 2 is vibrated by a piezoelectric element 4 via a vibrating body 3A. The vibrating body 3A shown in Figure 5 includes a head portion 31, a spring portion 32c, a cylindrical body 33a, and a flange portion 34a.

The spring portion 32c is supported by the tubular body 33a at a position outside the position where it supports the head portion 31. The tubular body 33a is cylindrical in shape. One end of the tubular body 33a supports the spring portion 32c. The end of the tubular body 33a opposite the spring portion 32c side is supported by the flange portion 34a. The flange portion 34a is a plate-shaped member that supports the bottom surface of the cylindrical tubular body 33a and extends outward from the position where it supports the tubular body 33a.

A hollow circular piezoelectric element 4 is provided on the underside of the flange 34a to match the shape of the flange 34a. The piezoelectric element 4 vibrates in the direction of penetration of the cylindrical body 33a (up and down in the figure). When the piezoelectric element 4 vibrates in the direction of penetration of the cylindrical body 33a, the spring portion 32c vibrates in the direction of penetration of the cylindrical body 33a, causing the head portion 31 to displace approximately uniformly in the up and down direction. The piezoelectric element 4 may also be provided on the upper surface of the flange 34a.

The inside of the cylindrical body 33a is connected to the through-hole 35 provided in the head portion 31, and the inside of the cylindrical body 33a and the through-hole 35 serve as the introduction portion for introducing gas into the vibration plate 2. A flange 36 is provided on the outside of the cylindrical body 33a, and this flange 36 secures the bubble generation device 1A to the liquid tank 10. The side of the cylindrical body 33a on which this flange 36 is formed serves as a vibration node, and the liquid side and gas side can be separated by a support member joined to the flange 36 without transmitting the vibration of the piezoelectric element 4 to the liquid tank 10.

(Variation 2)
Fig. 6 is a cross-sectional view of a bubble generation device 1B according to Modification 2. In the bubble generation device 1B shown in Fig. 6, the same components as those in the bubble generation device 1 shown in Fig. 2 are designated by the same reference numerals and detailed description thereof will not be repeated. In addition, in the bubble generation device 1B shown in Fig. 6, the diaphragm 2 is not shown.

In the bubble generating device 1B, the vibration plate 2 is vibrated by the piezoelectric element 4 via the vibrating body 3B. The vibrating body 3B shown in Figure 6 includes a head portion 31, a spring portion 32d, a cylindrical body 33b, and a weight portion 34b.

The spring portion 32d is supported by the tubular body 33b at a position outside the position that supports the head portion 31. The tubular body 33b is cylindrical in shape. The tubular body 33b supports the spring portion 32d at one end. The tubular body 33b has a weight portion 34b on the outside of the end opposite the spring portion 32d side. The tubular body 33b and the weight portion 34b are positioned so that the amount of displacement of the side surface of the tubular body 33b is within a predetermined range when the spring portion 32d is vibrated by the piezoelectric element 4.

A hollow circular piezoelectric element 4 is provided on the underside of the spring portion 32d to match the shape of the spring portion 32d. The piezoelectric element 4 vibrates in the direction of penetration of the through-hole 35 provided in the head portion 31 (up and down in the figure). When the piezoelectric element 4 vibrates in the direction of penetration of the through-hole 35, the spring portion 32d vibrates in the direction of penetration of the through-hole 35, causing the head portion 31 to be displaced in a substantially uniform vertical direction.

The inside of the cylindrical body 33b, the hole in the piezoelectric element 4, and the through-hole 35 in the head portion 31 are connected, forming an inlet portion that introduces gas from the inside of the cylindrical body 33b through the through-hole 35 to the vibration plate 2. A flange (not shown) is provided on the outside of the cylindrical body 33b, and this flange secures the bubble generator 1B to the liquid tank 10. The side of the cylindrical body 33b on which this flange is formed acts as a vibration node, and the liquid side and gas side can be separated by a support member joined to the flange without transmitting the vibration of the piezoelectric element 4 to the liquid tank 10.

We will now describe a bubble generation system in which a bubble generator 1B is fixed to a liquid tank 10. Figure 7 is a schematic diagram of the bubble generation system to explain the installation position of the bubble generator. Figure 8 is a schematic diagram of the bubble generation system to explain another installation position of the bubble generator. Note that, of the bubble generation systems shown in Figures 7 and 8, the same components as those in the bubble generation system 100 shown in Figure 1 are designated by the same reference numerals and will not be described in detail again.

In the bubble generation system 100A shown in Figure 7(a), the bubble generation device 1B is fixed to the bottom surface of the liquid tank 10 so that at least a portion of the vibrating body 3B supporting the vibrating plate 2 is immersed in the liquid in the liquid tank 10. In the bubble generation system 100B shown in Figure 7(b), the bubble generation device 1B is fixed to the side of the liquid tank 10 so that at least a portion of the vibrating body 3B supporting the vibrating plate 2 is immersed in the liquid in the liquid tank 10.

In the bubble generation system 100C shown in Figure 8, the bubble generation device 1B is attached above the liquid surface of the liquid tank 10, and is fixed toward the bottom of the liquid tank 10 so that at least a portion of the vibrating body 3B supporting the vibrating plate 2 is immersed in the liquid in the liquid tank 10.

The mounting position of bubble generator 1B relative to the liquid tank 10 has been explained in Figures 7 and 8, but bubble generator 1 and bubble generator 1A can also be mounted in a similar position relative to the liquid tank 10. Compared to bubble generator 1, which uses a Langevin-type vibrator vibrator 3, bubble generator 1A and bubble generator 1B have a smaller portion of the vibrating bodies 3A and 3B submerged in the liquid, making them easier to mount on the bottom of the liquid tank 10 and allowing them to be mounted on any surface of the liquid tank 10.

(Aspect)
(1) The bubble generating device of the present disclosure is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank. The bubble generating device comprises a vibration plate 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 supporting the vibration plate, and a piezoelectric element provided on the vibrating body to vibrate the vibration plate. The shape of each of the plurality of openings formed in the vibration plate is such that the opening diameter on the first surface side is larger than the opening diameter on the second surface side.

According to the bubble generating device disclosed herein, the shape of each of the multiple openings formed in the vibration plate is such that the opening diameter on the first surface side is larger than the opening diameter on the second surface side, allowing for the generation of fine bubbles in the liquid by natural aspiration, and eliminating the need for a supply unit that forcibly supplies gas, making it possible to reduce the size and cost of the device.

(2) In the bubble generator described in (1), the cross-sectional shape of each of the multiple openings is tapered. This makes it easier for the bubble generator to generate fine bubbles in the liquid by natural aspiration.

(3) The bubble generator according to (1) or (2), wherein the relationship Rb<28×10 −6 × ^(γa )/h is satisfied, where Rb is the opening diameter on the first surface side, h is the distance from the vibration plate to the liquid surface of the liquid tank, and γa is the surface tension ratio of the liquid when the surface tension of water is 1. As a result, the bubble generator does not allow the liquid to leak from the opening of the vibration plate.

(4) The bubble generator according to (1) or (2), wherein the relationship Rb<5×10 −6 × ^(γa )/h is satisfied, where Rb is the opening diameter on the first surface side, h is the distance from the vibration plate to the liquid surface of the liquid tank, and γa is the surface tension ratio of the liquid when the surface tension of water is 1. As a result, the bubble generator does not allow the liquid to leak from the opening of the vibration plate.

(5) In the bubble generator described in any one of (1) to (4), the vibrator is configured as a Langevin vibrator. This makes it easier for the bubble generator to generate piston vibrations that vibrate the diaphragm up and down.

(6) A bubble generator according to any one of (1) to (4), wherein the vibrator includes a head portion supporting the vibration plate, a plate-shaped spring portion supporting the head portion, a cylindrical body supporting one end of the spring portion at a position outside the position supporting the head portion, and a plate-shaped flange portion provided at the end of the cylindrical body and extending outward from the position of the cylindrical body, and the piezoelectric element is provided on a first surface of the flange portion facing the cylindrical body or on a second surface opposite the first surface. This makes it easier for the bubble generator to produce piston-like vibrations that vibrate the vibration plate up and down.

(7) A bubble generator according to any one of (1) to (4), wherein the vibrator includes a head portion supporting the vibration plate, a plate-shaped spring portion supporting the head portion, a cylindrical body supporting one end of the spring portion at a position outside the position supporting the head portion, and a weight portion provided at the end of the cylindrical body, and the piezoelectric element is provided on the surface of the spring portion supported by the cylindrical body. This makes it easier for the bubble generator to produce piston-like vibrations that vibrate the vibration plate up and down.

(8) The bubble generation system of the present disclosure comprises the bubble generation device described in any one of (1) to (7) and a liquid tank. This allows the bubble generation system to be made smaller and less expensive.

(9) In the bubble generation system described in (8), the bubble generator is fixed to the bottom or side of the liquid tank so that at least a portion of the vibrator supporting the vibration plate is immersed in the liquid in the liquid tank. This allows the bubble generation system to generate fine bubbles in the liquid from the bottom or side of the liquid tank.

(10) In the bubble generation system described in (8), the bubble generator is attached above the liquid surface of the liquid tank and is fixed toward the bottom of the liquid tank so that at least a portion of the vibrator supporting the vibration plate is immersed in the liquid in the liquid tank. This allows the bubble generation system to generate fine bubbles in the liquid from the top surface of the liquid tank.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present disclosure is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1, 1A, 1B Bubble generating device, 2 Vibration plate, 2a Opening, 3, 3A, 3B Vibrating body, 4, 41, 42 Piezoelectric element, 5 Holding flange, 10 Liquid tank, 20 Controller, 31 Head portion, 32, 33a, 33b Cylindrical body, 32a Upper metal ring, 32b Lower metal ring, 32c, 32d Spring portion, 34 Fastening bolt, 34a Collar portion, 34b Weight portion, 35 Through hole, 36 Flange, 43, 44 Terminal, 100, 100A to 100C Bubble generating system, 200 Bubbles.

Claims (5)

A bubble generating device attached to a liquid tank to generate fine bubbles in the liquid in the liquid tank,
a vibration plate having a plurality of openings formed therein, a first surface of which contacts the liquid in the liquid tank, and a second surface of which contacts the gas;
a vibrating body supporting the diaphragm;
a piezoelectric element provided on the vibrating body to vibrate the diaphragm,
The shape of each of the plurality of openings formed in the diaphragm is such that the opening diameter on the first surface side is larger than the opening diameter on the second surface side,
The vibrating body is
a head portion supporting the diaphragm;
a plate-shaped spring portion that supports the head portion;
a cylindrical body that supports one end of the spring portion at a position outside a position that supports the head portion;
a weight portion provided at an end of the cylindrical body,
The piezoelectric element is provided on a surface of the spring portion supported by the cylindrical body . The bubble generator of claim 1, wherein the cross-sectional shape of each of the multiple openings is tapered. The bubble generating device according to claim 1 or 2 ;
a liquid tank. The bubble generation system according to claim 3 , wherein the bubble generation device is fixed to the bottom or side of the liquid tank so that at least a portion of the vibrator supporting the vibrating plate is immersed in the liquid in the liquid tank. The bubble generation system described in claim 3, wherein the bubble generation device is attached above the liquid level of the liquid tank and fixed toward the bottom surface of the liquid tank so that at least a portion of the vibrating body supporting the vibrating plate is immersed in the liquid in the liquid tank.