Bubble generating device and bubble generating system

Abstract

The present invention provides: a bubble generator capable of being reduced in size and cost; and a bubble generation system. This bubble generator (1) is attached to a liquid tank (10) and generates fine bubbles in the liquid inside the liquid tank (10). The bubble generator (1) comprises: a vibration plate (2) having a plurality of openings and having a first surface, which comes into contact with the liquid inside the liquid tank (10), and a second surface, which comes into contact with a gas; a vibrator (3) supporting the vibration plate (2); and a piezoelectric element (4) provided to the vibrator (3) and vibrating the vibration plate (2). The openings formed in the vibration plate (2) each have such a shape that the liquid-side opening diameter is larger than the gas-side opening diameter.

Description

[Technical Field]

[0001] The present disclosure relates to a bubble generating device and a bubble generating system. [Background technology]

[0002] In recent years, fine bubbles have been used in a variety of fields, including water purification, wastewater treatment, and fish farming. For this reason, bubble generators that generate fine bubbles have been developed (see JP 2016-209825 A (Patent Document 1) and JP 2014-150784 A (Patent Document 2)). Furthermore, development of applications for bubble generators to generate fine bubbles in liquid fuel, disinfectants, cosmetics, and other liquids in addition to water has been progressing. For example, it has been reported that fuel efficiency can be improved by providing a bubble generator in a fuel injection system and incorporating fine bubbles into the liquid fuel injected into the piston. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-209825 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-150784 Summary of the Invention [Problem to be solved by the invention]

[0004] In the bubble generator described in JP 2016-209825 A (Patent Document 1), a supply unit for supplying gas is provided below a vibrating plate 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 has been necessary to use a gas cylinder or the like as the raw material container.

[0005] 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.

[0006] Therefore, in any bubble generating device, in order to generate fine bubbles in a liquid, it is necessary to forcibly supply gas from below the vibrating plate using a gas cylinder or compressor, which has hindered the miniaturization and cost reduction of the device.

[0007] Therefore, an 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. [Means for solving the problem]

[0008] A bubble generator according to one aspect of the present disclosure is attached to a liquid tank to generate fine bubbles in the liquid in the liquid tank, and includes 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 supporting the diaphragm, and a piezoelectric element provided on the vibrating body to vibrate the diaphragm. Each of the plurality of openings formed in the diaphragm has a larger opening diameter on the first surface side than on the second surface side. The vibrating body includes a head portion supporting a 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.

[0009] A bubble generation system according to another embodiment of the present disclosure includes the bubble generation device described above and a liquid tank. [Effects of the Invention]

[0010] 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, so that fine bubbles can be generated in the liquid by natural aspiration, and since a supply section that forcibly supplies gas is not required, the device can be made smaller and less expensive. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a bubble generation system in which a bubble generation device according to an embodiment is used. [Figure 2] FIG. 1 is a cross-sectional perspective view of an air bubble generation device according to an embodiment. [Figure 3] FIG. 2 is a cross-sectional view of a head portion of the air bubble generation device according to the embodiment. [Figure 4] 5A and 5B are schematic diagrams for explaining forces generated near an opening of the bubble generation device according to the embodiment. [Figure 5] FIG. 10 is a cross-sectional view of a bubble generation device according to a first modified example. [Figure 6] FIG. 10 is a cross-sectional view of a bubble generation device according to a second modification. [Figure 7] FIG. 2 is a schematic diagram of a bubble generation system for explaining the installation position of the bubble generation device. [Figure 8] 10 is a schematic diagram of a bubble generation system illustrating another installation position of the bubble generation device. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment) Hereinafter, a bubble generating device and a 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.

[0013] First, Fig. 1 is a schematic diagram of a bubble generation system 100 in which a bubble generation device 1 according to an embodiment is used. The bubble generation device 1 shown in Fig. 1 is provided above a liquid tank 10 that stores a 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 various systems, such as water purification devices, wastewater treatment devices, fish farming tanks, and fuel injection devices.

[0014] The liquid introduced into the liquid tank 10 varies depending on the system to which it is applied, for example, water for a water purification system, liquid fuel for a fuel injection system, etc. Furthermore, the liquid tank 10 only needs to be able to temporarily store the liquid, and includes a pipe through which the liquid is introduced and through which the liquid always flows.

[0015] 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. The vibration plate 2 immersed in the liquid is vibrated by the piezoelectric element 4, thereby generating fine bubbles 200 from multiple pores (openings) formed in the vibration plate 2. The vibration plate 2 is provided so that one surface (first surface) comes into contact with the liquid in the liquid tank 10 and the other surface (second surface) comes into contact with the gas.

[0016] Fig. 2 is a cross-sectional perspective view of a bubble generation device 1 according to an embodiment. As shown in Fig. 2, the bubble generation device 1 is composed of a diaphragm 2, a head portion 31 that fixes the peripheral portion of the diaphragm 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.

[0017] The two piezoelectric elements 4 are configured by stacking a first piezoelectric element 41 and a second piezoelectric element 42 having 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 to the controller 20 shown in FIG.

[0018] 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 resonance 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 resonance frequency from multiple resonance frequencies. In addition, by narrowing the diameter of the portion connecting the upper metal ring 32a to the head portion 31 smaller than the diameter of the other portions, the displacement of the vibration plate 2 can be further amplified.

[0019] 2, through holes 35 are provided in the centers of upper metal ring 32a, lower metal ring 32b, and fastening bolt 34, and these through holes 35 serve as inlet portions for introducing gas into diaphragm 2. Upper metal ring 32a, lower metal ring 32b, and fastening bolt 34 are made of stainless steel, aluminum, or the like. First piezoelectric element 41 and 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.

[0020] Specifically, the cylindrical body 32 is made of SUSU304 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.

[0021] The cylindrical body 32 has a structure in which the upper metal ring 32a and the lower metal ring 32b are fastened together with fastening bolts 34, so that a compressive bias is applied to the first piezoelectric element 41 and the second piezoelectric element 42. For this reason, piezoelectric ceramics with low resistance to tensile stress are used for the first piezoelectric element 41 and the second piezoelectric element 42, making the first piezoelectric element 41 and the second piezoelectric element 42 less likely to break even when a large amount of power is supplied to drive them. Note that the upper metal ring 32a and the lower metal ring 32b are at the same potential, so an application electrode must be sandwiched between the two piezoelectric elements 4. The application electrode is electrically connected to a terminal 43.

[0022] If it is not necessary 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 have a structure in which one piezoelectric element 4 is sandwiched and bonded between an upper metal ring 32a and a lower metal ring 32b, rather than being fastened with the fastening bolts 34. Alternatively, the cylindrical body 32 may have a structure in which only the upper metal ring 32a is formed, and the piezoelectric element 4 is bonded to the bottom surface of the upper metal ring 32a. Whichever structure is adopted for the cylindrical body 32, the manufacturing cost can be reduced.

[0023] Fig. 3 is a cross-sectional view of the head portion 31 of the air 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. The shape of the head portion 31 shown in Fig. 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.

[0024] The head portion 31 has the diaphragm 2 fixed to the upper peripheral portion of the truncated cone shape by adhesive, welding, etc. 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, or a glass plate. Specifically, the outer diameter Rc of the diaphragm 2 is 9 mm, and the thickness of the central portion of the diaphragm 2 is thinner than that of the peripheral portion, for example, the thickness of the peripheral portion is 0.15 mm and the thickness of the central portion is 0.05 mm.

[0025] The diaphragm 2 has 185 openings 2a in its central area where the thickness is thinner. As shown in FIG. 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.

[0026] 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 performed to vibrate the vibration plate 2 up and down, thereby generating fine bubbles 200 in the liquid by natural aspiration. Conversely, when 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 to be done, the bubble generator 1 would require a compressor.

[0027] 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, in which gas is sent 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.

[0028] In the bubble generator 1, to generate a pumping effect, it is preferable to use piston vibration, vibrating the diaphragm 2 up and down without bending it. With a diaphragm 2 that is easily bent, the longitudinal vibration is absorbed in the liquid, functioning as a "soft spring" and reducing the pumping effect. For this reason, it is preferable to use piston vibration for the diaphragm 2, which is difficult to bend. The pumping effect generated in the bubble generator 1 can be understood as a phenomenon that generates a unidirectional gas flow 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 unit 31, the outer diameter Rc of the diaphragm 2, and the inner diameter Rd of the diaphragm 2.

[0029] 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 does not become 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 part 31 with the larger opening diameter Ra on the liquid side and the smaller opening diameter Rb on the gas side.

[0030] Therefore, we will consider liquid leakage from the opening 2a. Figure 4 is a schematic diagram for explaining the force generated near the opening 2a of the bubble generation device 1 according to the embodiment. Figure 4(a) is a schematic diagram when the amount of liquid dripping from the opening 2a is small, and Figure 4(b) is a schematic diagram when the amount of liquid dripping from the opening 2a is large.

[0031] First, let Rb (m) be the diameter of one opening 2a on the gas side of 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 opening 2a on the gas side and the interface, and m (kg) be the weight of the liquid dripping from 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 (water pressure) of the liquid acting on the opening 2a is 0.1 atmospheres for a depth of 1 m of liquid = 10130 N / m 2 and the cross-sectional area of ​​the opening 2a is π×(Rb / 2) 2 (m 2 ) so a force F2 is generated in the downward direction in the figure. This force F2 can be expressed as 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 of Rb at most, then it is 4×π×(Rb / 2) 2 / 3 (kg), so gravity mg acts downward in the diagram. This gravity mg can be expressed as equation 3. mg(max)=9.8×π×(Rb) 2 / 3(N)...(Formula 3) Therefore, as shown in Figure 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, when considering fine bubbles (less than 100 μm) to ultra-fine bubbles (less than 1 μm), the opening diameter Rb of the opening 2a is 1 × 10 -7 ~1×10 -5(m). If the contact angle is assumed to be 20°, the force F1 is 2.15 × 10 -7 ~2.15×10 -5 (N), and the force F2 is 7.96 x 10 -11 ~7.96×10 -7 (N). The maximum gravity mg is 1.02×10 -20 ~1.02×10 -14 Since the contact angle is in the range of (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 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.

[0032] 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 (Equation 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.

[0033] 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 (Equation 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.

[0034] 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 with a size 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 restriction on the pitch of the openings 2a, which is determined by the opening diameter Ra.

[0035] From a manufacturing perspective, using a metal diaphragm 2 is easy. However, because conventional etching techniques can only form an opening diameter approximately equal to the plate thickness, a special plating technique is required. Even so, the aspect ratio of the opening diameter Rb to the plate thickness of the diaphragm 2 is limited to approximately 10. Therefore, if the opening diameter Rb is 10 μm, the plate thickness of the diaphragm 2 is limited to a maximum of 100 μm. Using MEMS (Micro Electro Mechanical Systems) technology, it is possible to process the opening 2a by not only forming a tapered cross-sectional shape, but also by forming holes with different opening diameters on the front and back. Additionally, if ceramic or glass is used as the material for the diaphragm 2, sandblasting or laser processing techniques can be used to process asymmetric holes. The opening diameter Rb of the opening 2a is preferably approximately 1 μm to 20 μm.

[0036] The bubble generator 1 has the advantage of not requiring a compressor or the like to send air by realizing the pumping effect of the vibrating plate 2, and also has the advantage of being able to control the amount of gas in the fine bubbles 200 to be generated by the amount of drive of the vibrating plate 2. In particular, when a compressor is used, if the air pressure applied to the vibrating plate 2 is high, the gas that enters through the opening 2a may not be separated and destroyed by the vibrating plate 2 and may be output as large bubbles, which may absorb other fine bubbles. The bubble generator 1 has the advantage of not requiring complex control of a compressor or the like, because the pumping effect does not cause excessive gas to be supplied to the liquid.

[0037] As described above, the bubble generator 1 according to the 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 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.

[0038] 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 that 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.

[0039] The bubble generation system 100 includes a bubble generation device 1 and a liquid tank 10. This allows the bubble generation system to be made smaller and at lower cost.

[0040] (Variation 1) In the bubble generator 1 shown in Fig. 2, the vibrating body 3 has been 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 will not be repeated. Furthermore, the diaphragm 2 is not shown in the bubble generator 1A shown in Fig. 5.

[0041] In the air bubble generation device 1A, a vibration plate 2 is vibrated by a piezoelectric element 4 via a vibrating body 3A. The vibrating body 3A shown in Fig. 5 includes a head portion 31, a spring portion 32c, a cylindrical body 33a, and a flange portion 34a.

[0042] The spring portion 32c is supported by the tubular body 33a at a position outside the position where the head portion 31 is supported. The tubular body 33a has a cylindrical shape. The tubular body 33a supports the spring portion 32c at one end. The end of the tubular body 33a opposite the spring portion 32c side is supported by a 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 the tubular body 33a is supported.

[0043] 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 penetration direction of the cylindrical body 33a (the up-and-down direction in the figure). When the piezoelectric element 4 vibrates in the penetration direction of the cylindrical body 33a, the spring portion 32c vibrates in the penetration direction 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.

[0044] The inside of the cylindrical body 33a is connected to a through-hole 35 provided in the head portion 31, and the inside of the cylindrical body 33a and the through-hole 35 serve as an introduction portion for introducing gas into the vibration plate 2. A flange 36 is provided on the outside of the cylindrical body 33a, and the bubble generation device 1A is fixed to the liquid tank 10 by this flange 36. The side of the cylindrical body 33a on which the flange 36 is formed serves as a vibration node, and the liquid side and the 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.

[0045] (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. Furthermore, in the bubble generation device 1B shown in Fig. 6, the diaphragm 2 is not shown.

[0046] In the air bubble generation device 1B, a vibration plate 2 is vibrated by a piezoelectric element 4 via a vibrating body 3B. The vibrating body 3B shown in Fig. 6 includes a head portion 31, a spring portion 32d, a cylindrical body 33b, and a weight portion 34b.

[0047] The spring portion 32d is supported by the tubular body 33b at a position outside the position where the head portion 31 is supported. The tubular body 33b has a cylindrical 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 located at a position where the displacement of the side surface of the tubular body 33b falls within a predetermined range when the spring portion 32d is vibrated by the piezoelectric element 4.

[0048] 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 penetration direction (vertical direction in the figure) of a through-hole 35 provided in the head portion 31. When the piezoelectric element 4 vibrates in the penetration direction of the through-hole 35, the spring portion 32d is vibrated in the penetration direction of the through-hole 35, causing the head portion 31 to be displaced approximately uniformly in the vertical direction.

[0049] 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 form an introduction 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 serves as a vibration node, and the liquid side and the 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.

[0050] A bubble generation system in which a bubble generation device 1B is fixed to a liquid tank 10 will be described. Fig. 7 is a schematic diagram of the bubble generation system for explaining the installation position of the bubble generation device. Fig. 8 is a schematic diagram of the bubble generation system for explaining another installation position of the bubble generation device. In the bubble generation systems shown in Figs. 7 and 8, the same components as those in the bubble generation system 100 shown in Fig. 1 are designated by the same reference numerals and detailed explanations will not be repeated.

[0051] In a bubble generation system 100A shown in Figure 7(a), a bubble generation device 1B is fixed to the bottom surface of a liquid tank 10 so that at least a portion of a vibrating body 3B supporting a vibrating plate 2 is immersed in the liquid in the liquid tank 10. In a bubble generation system 100B shown in Figure 7(b), a bubble generation device 1B is fixed to the side surface of a liquid tank 10 so that at least a portion of a vibrating body 3B supporting a vibrating plate 2 is immersed in the liquid in the liquid tank 10.

[0052] 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.

[0053] The mounting position of the bubble generator 1B relative to the liquid tank 10 has been explained with reference to Figures 7 and 8, but the bubble generator 1 and the bubble generator 1A can also be mounted in a similar position relative to the liquid tank 10. Compared to the bubble generator 1 that uses the vibrating body 3 of a Langevin vibrator, the bubble generator 1A and the bubble generator 1B have a smaller portion of the vibrating bodies 3A and 3B that are submerged in the liquid, making them easier to mount on the bottom surface of the liquid tank 10 and allowing them to be mounted on any surface of the liquid tank 10.

[0054] (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.

[0055] 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, so that fine bubbles can be generated in the liquid by natural aspiration, and since a supply section that forcibly supplies gas is not required, the device can be made smaller and less expensive.

[0056] (2) In the air bubble generation device according to (1), the cross-sectional shape of each of the plurality of openings is tapered. This makes it easier for the air bubble generation device to generate fine bubbles in the liquid by natural aspiration.

[0057] (3) In the bubble generating device according to (1) or (2), when the diameter of the opening on the first surface side is Rb, the distance from the vibration plate to the liquid surface of the liquid tank is h, and the surface tension ratio of the liquid to the surface tension of water is 1, Rb<28×10 -6 × (γa) / h. This prevents the liquid from leaking from the opening of the vibration plate in the bubble generator.

[0058] (4) In the bubble generating device according to (1) or (2), when the diameter of the opening on the first surface side is Rb, the distance from the vibration plate to the liquid surface of the liquid tank is h, and the surface tension ratio of the liquid to the surface tension of water is 1, Rb<5×10 -6 × (γa) / h. This prevents the liquid from leaking from the opening of the vibration plate in the bubble generator.

[0059] (5) In the air bubble generator according to any one of (1) to (4), the vibrator is a Langevin vibrator, which makes it easy for the air bubble generator to generate piston vibrations that vibrate the diaphragm up and down.

[0060] (6) In the bubble generator according to any one of (1) to (4), 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 to the first surface. This makes it easy for the bubble generator to produce piston-like vibration that vibrates the vibration plate up and down.

[0061] (7) In the bubble generation device according to any one of (1) to (4), 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 easy for the bubble generation device to generate piston-like vibrations that vibrate the vibration plate up and down.

[0062] (8) A bubble generation system according to the present disclosure includes the bubble generation device according to any one of (1) to (7) and a liquid tank, thereby enabling the bubble generation system to be miniaturized and reduced in cost.

[0063] (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 part 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.

[0064] (10) In the bubble generation system described in (8), the bubble generator is fixed to the bottom of the liquid tank so that the mounting position is above the liquid surface of the liquid tank and at least a portion of the vibrator supporting the vibrating 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.

[0065] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0066] 1, 1A, 1B bubble generator, 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 tightening bolt, 34a flange portion, 34b weight portion, 35 through hole, 36 flange, 43, 44 terminal, 100, 100A to 100C bubble generation system, 200 bubbles.

Claims

1. 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.

2. The bubble generation device according to claim 1 , wherein each of the plurality of openings has a tapered cross-sectional shape.

3. The bubble generating device according to claim 1 or 2; a liquid tank.

4. 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.

5. 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.

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