Bubble generation device and bubble generation system

Abstract

The present disclosure provides a bubble generation device and a bubble generation system that are capable of selectively generating microbubbles or ultra-fine bubbles, using a single device. A bubble generation device (1) is attached to a liquid tank (10) and generates fine bubbles in a liquid within the liquid tank (10). The bubble generation device (1) is provided with a vibration plate (2), a vibration body (3), and a piezoelectric element (4). The vibration body (3) has, as a vibration mode to vibrate the vibration plate (2): a first vibration mode in which a ventilation pressure or a ventilation amount of a gas which passes through the vibration plate (2) is set to a first value, and when the vibration plate is vibrated at a first resonance frequency, the displacement direction of the vibration plate (2) and the displacement direction of the vibration body (3) have the same phase; and a second vibration mode in which the ventilation pressure or the ventilation amount of the gas which passes through the vibration plate (2) is set to a second value, and when the vibration plate (2) is vibrated at a second resonance frequency, the displacement direction of the vibration plate (2) and the displacement direction of the vibration body (3) have opposite phases.

Description

Bubble generating device and bubble generating system

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

[0002] Fine bubbles are used in a variety of fields, including water purification, wastewater treatment, and fish farming. Fine bubbles are generally classified into microbubbles (MB) and ultrafine bubbles (UFB) based on their diameter. Specifically, fine bubbles with a diameter of 1 μm to 100 μm are classified as microbubbles, while fine bubbles with a diameter of several tens of nanometers to less than 1 μm are classified as ultrafine bubbles. For example, a bubble generator using a ceramic porous material to generate fine bubbles has been developed (see JP 2016-140801 A (Patent Document 1)). A bubble generator capable of generating both microbubbles and ultrafine bubbles has also been developed (see JP 2021-183052 A (Patent Document 2)).

[0003] JP 2016-140801 A JP 2021-183052 A

[0004] The bubble generator described in JP 2016-140801 A (Patent Document 1) uses a porous member made of a porous ceramic layer to generate fine bubbles, so microbubbles and ultrafine bubbles are generated simultaneously, making it impossible to selectively generate microbubbles or ultrafine bubbles. Furthermore, the bubble generator described in JP 2021-183052 A (Patent Document 2) requires the preparation of multiple devices with different configurations, each of which has a device for generating microbubbles and a device for generating ultrafine bubbles.

[0005] Therefore, an object of the present disclosure is to provide a bubble generating device and a bubble generating system that can selectively generate microbubbles or ultrafine bubbles with a single device.

[0006] A bubble generator according to one aspect of the present disclosure is a bubble generator that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank by vibration. The bubble generator includes a diaphragm having a plurality of openings, 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 and vibrates the diaphragm, and a piezoelectric element provided on the vibrating body. The vibrating body has a first resonant frequency and a second resonant frequency higher than the first resonant frequency as resonant frequencies at which the diaphragm vibrates. The vibrator has two vibration modes for vibrating the diaphragm: a first vibration mode in which the displacement direction of the diaphragm and the displacement direction of the vibrator are in phase when the ventilation pressure or ventilation volume of the gas passing through the diaphragm is adjusted to a first value and the diaphragm is vibrated at a first resonance frequency; and a second vibration mode in which the displacement direction of the diaphragm and the displacement direction of the vibrator are in opposite phase when the ventilation pressure or ventilation volume of the gas passing through the diaphragm is adjusted to a second value smaller than the first value and the diaphragm is vibrated at a second resonance frequency.

[0007] A bubble generation system according to another embodiment of the present disclosure includes the bubble generation device described above, a liquid tank, and a gas adjustment device that adjusts the ventilation pressure or ventilation volume of the gas passing through the vibration plate.

[0008] According to the present disclosure, in the bubble generating device, the vibration plate can be vibrated in a first vibration mode and a second vibration mode, so that microbubbles or ultrafine bubbles can be selectively generated with a single device.

[0009] FIG. 1 is a schematic diagram of a bubble generation system in which a bubble generation device according to embodiment 1 is used. FIG. 2 is a half sectional view of the bubble generation device according to embodiment 1. FIG. 3 is a schematic diagram for explaining the displacement of the bubble generation device according to embodiment 1. FIG. 4 is a graph for explaining the relationship between the vibration mode and the resonance frequency of the diaphragm. FIG. 5 is a graph for explaining the displacement of the diaphragm. FIG. 6 is a diagram showing the number of bubbles generated when the diaphragm is vibrated in an in-phase mode. FIG. 7 is a graph for explaining the bubble generation state when the diaphragm is vibrated in an in-phase mode. FIG. 8 is a graph for explaining the bubble generation state when the diaphragm is vibrated in an anti-phase mode. FIG. 9 is a sectional perspective view of a bubble generation device according to embodiment 2. FIG. 10 is a graph for explaining the relationship between the vibration mode of the bubble generation device according to embodiment 2 and the resonance frequency of the diaphragm.

[0010] 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.

[0011] (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 generation device 1 shown in Fig. 1 is provided below 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.

[0012] 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 constantly flows.

[0013] Furthermore, in the bubble generator 1, the compressor 30 (gas adjusting device) adjusts the ventilation pressure or volume of the gas passing through the diaphragm 2, thereby changing the resonance frequency of the diaphragm 2, thereby switching the vibration mode in which the diaphragm 2 vibrates. The switchable vibration modes include a first vibration mode in which microbubbles (MB) are predominantly generated, and a second vibration mode in which ultrafine bubbles (UFB) are predominantly generated. In other words, the bubble generator 1 can selectively generate microbubbles or ultrafine bubbles with a single device. The vibration modes of the bubble generator 1 will be described in detail later.

[0014] First, the bubble generator 1 includes a vibration plate 2, a vibrating body 3, and a piezoelectric element 4. The bubble generator 1 is fixed to the liquid tank 10 by joining the outer surface of the vibrating body 3 to a holding flange 5 provided in a hole opened in the bottom surface of the liquid tank 10. When the bubble generator 1 is fixed to the liquid tank 10, a portion of the vibrating body 3 provided with the vibration plate 2 is immersed in the liquid. In this state, the vibration plate 2 immersed in the liquid is vibrated by the piezoelectric element 4, thereby generating fine bubbles 200 from a plurality of pores (openings) formed in the vibration plate 2. The vibration plate 2 is provided so that one surface (first surface) contacts the liquid in the liquid tank 10 and the other surface (second surface) contacts the gas.

[0015] The diaphragm 2 is formed of a metal plate, such as stainless steel. Specifically, the diameter of the diaphragm 2 is 9 mm, and the thickness of the diaphragm 2 is, for example, 0.15 mm, preferably 0.1 mm to 0.3 mm, and more preferably 0.1 mm to 0.2 mm. The diaphragm 2 is, for example, a perforated plate with 121 openings in the center.

[0016] FIG. 2 is a half-sectional view of the bubble generator 1 according to the first embodiment. The X and Z directions in the figure indicate the horizontal and vertical directions of the bubble generator 1, respectively. The dashed-dotted line in FIG. 2 indicates the portion passing through the central axis of the bubble generator 1. In the bubble generator 1, the vibration of the piezoelectric element 4 is transmitted to the vibration plate 2 via the vibrating body 3, causing the vibration plate 2 to vibrate. The vibrating body 3 shown in FIG. 2 includes a head portion 31 (first cylindrical body), a spring portion 32, a cylindrical body 33 (second cylindrical body), and a flange 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 flange portion 34 are integrally formed, or may be formed separately and joined together.

[0017] The spring portion 32 is supported by the tubular body 33 at a position outside the position where the head portion 31 is supported. The tubular body 33 has a cylindrical shape. The tubular body 33 supports the spring portion 32 at one end. The end of the tubular body 33 opposite the spring portion 32 side extends outward to form a weight 33A. The flange portion 34 is provided on the side surface of the tubular body 33 and is joined to the holding flange 5 of the liquid vat 10.

[0018] A hollow circular piezoelectric element 4 is provided on the underside of the spring portion 32 to match the shape of the spring portion 32. The piezoelectric element 4 is electrically connected to the controller 20 shown in FIG. 1 via wiring. When power is supplied from the controller 20 to the piezoelectric element 4, the piezoelectric element 4 vibrates in the penetration direction (Z direction) of the vibrating body 3. When the piezoelectric element 4 vibrates in the penetration direction of the vibrating body 3, the spring portion 32 is vibrated in the penetration direction of the vibrating body 3, and the head portion 31 can be displaced approximately uniformly in the Z direction (up and down direction). The piezoelectric element 4 may also be provided in the cylindrical body 33.

[0019] The inside of the cylindrical body 33 is connected to a through-hole 35 provided in the head portion 31, and the inside of the cylindrical body 33 and the through-hole 35 serve as an introduction portion for introducing gas into the diaphragm 2. Gas is supplied from the compressor 30 to the diaphragm 2 through the through-hole 35, and the gas is introduced into the liquid in the liquid tank 10 through the opening in the diaphragm 2. The compressor 30 is electrically connected to the controller 20 by wiring. Therefore, the controller 20 can control the compressor 30 to adjust the ventilation pressure or ventilation volume of the gas passing through the diaphragm 2. Note that the device that introduces gas into the opening in the diaphragm 2 is not limited to the compressor 30, and any gas adjustment device that adjusts the ventilation pressure or ventilation volume of the gas passing through the diaphragm 2 may be used.

[0020] Next, the vibration modes of the bubble generation device 1 and the displacement of the diaphragm 2 and the vibrating body 3 in these vibration modes will be described. Fig. 3 is a schematic diagram for explaining the displacements that occur in the bubble generation device 1 according to embodiment 1. The X and Z directions in the figure indicate the horizontal and vertical directions of the bubble generation device 1, respectively. The dashed dotted line in Fig. 3 indicates the portion that passes through the central axis of the bubble generation device 1.

[0021] The bubble generator 1 is structured so that the natural vibration of the vibrating body 3, which is independent of the other, resonates with the natural vibration of the vibrating plate 2, which is a porous plate, and this structure increases the vibration amplitude of the vibrating plate 2. As a result, the bubble generator 1 can maintain a large displacement of the vibrating plate 2 even when gas is not introduced into the vibrating plate 2 in liquid by the compressor 30. By increasing the displacement of the vibrating plate 2, the bubble generator 1 can generate strong cavitation and efficiently generate fine bubbles (for example, ultra-fine bubbles).

[0022] The bubble generator 1, which satisfies the state in which the natural vibration of the vibrating body 3 and the natural vibration of the vibrating plate 2 resonate with each other, has two vibration modes. Specifically, as shown in Fig. 3(a), the bubble generator 1 has an in-phase mode in which the displacement direction A of the vibrating plate 2 and the displacement direction B of the vibrating body 3 are in phase, and an anti-phase mode in which the displacement direction C of the vibrating plate 2 and the displacement direction D of the vibrating body 3 are in anti-phase, as shown in Fig. 3(b). In Fig. 3, the magnitude of the displacement is indicated by the shade of the hatching.

[0023] FIG. 4 is a graph illustrating the relationship between the vibration mode and the resonant frequency of the diaphragm 2. In the graph shown in FIG. 4, the vertical axis represents impedance (Ω) and the horizontal axis represents frequency (kHz). When the bubble generator 1 is driven in air (not immersed in the liquid tank 10), the impedance characteristics shown in graph E are obtained. The bubble generator 1 can be driven in in-phase mode by vibrating the diaphragm 2 at a resonant frequency of approximately 30.5 kHz. When the bubble generator 1 is driven in liquid (immersed in the liquid tank 10) without introducing gas into the diaphragm 2 using the compressor 30, the impedance characteristics shown in graph F are obtained. The bubble generator 1 can be driven in out-of-phase mode by vibrating the diaphragm 2 at a resonant frequency of approximately 31.8 kHz. Note that, with the impedance characteristics shown in graph F, when driving the bubble generator 1 in in-phase mode, the diaphragm 2 needs to be vibrated at a resonant frequency of approximately 23.0 kHz, which is significantly off the 30 kHz mark.

[0024] Furthermore, when the bubble generator 1 is driven in liquid (immersed in the liquid tank 10) with gas introduced into the diaphragm 2 by the compressor 30, the impedance characteristics are as shown in graph G, and the bubble generator 1 can be driven in in-phase mode by vibrating the diaphragm 2 at a resonance frequency of approximately 30.0 kHz. Note that with the impedance characteristics of graph G, when driving the bubble generator 1 in out-of-phase mode, it is necessary to vibrate the diaphragm 2 at a resonance frequency of approximately 36.0 kHz, which is significantly different from the vicinity of 30 kHz.

[0025] As described above, the bubble generator 1 has two resonance modes, an anti-phase mode and an in-phase mode, in the vicinity of 30 kHz (in the range of 25 to 35 kHz), and can switch between these two resonance modes. It has been experimentally observed that in the bubble generator 1, microbubbles (MB) are predominantly generated when the diaphragm 2 is vibrated in the in-phase mode (first vibration mode) with gas introduced into the diaphragm 2. When the bubble generator 1 is vibrated in the first vibration mode, the microbubbles (MB) reflect and absorb sound waves, weakening the cavitation that contributes to the generation of ultrafine bubbles (UFB).

[0026] On the other hand, it has been experimentally observed that the bubble generator 1 predominantly generates ultrafine bubbles (UFB) when the diaphragm 2 is vibrated in the reverse phase mode (second vibration mode) without introducing gas into the diaphragm 2. When the bubble generator 1 is vibrated in the second vibration mode, almost no microbubbles (MB) are generated and ultrafine bubbles (UFB) are mainly generated, and cavitation, which contributes to the generation of ultrafine bubbles (UFB), is strengthened.

[0027] 4, the bubble generator 1 has a resonance resistance equivalent to that in air, whether the diaphragm 2 is vibrated in the in-phase mode with gas introduced into the diaphragm 2 (first vibration mode) or in the out-of-phase mode with no gas introduced into the diaphragm 2 (second vibration mode). In other words, it can be seen that the bubble generator 1 has small damping even in the liquid in which it is actually used.

[0028] In particular, when the bubble generator 1 vibrates the diaphragm 2 in the reverse phase mode without introducing gas into the diaphragm 2 (second vibration mode), damping is smaller and the diaphragm displacement is larger than that of the conventional bubble generator. FIG. 5 is a graph for explaining the displacement of the diaphragm 2. In the graph shown in FIG. 5, the vertical axis represents the diaphragm displacement (μm) and the horizontal axis represents the drive voltage (V) applied to the piezoelectric element 4. In FIG. 5, graph G shows the diaphragm displacement in the conventional bubble generator, and graphs I and H show the diaphragm displacement in the bubble generator 1 when the diaphragm 2 is vibrated in the reverse phase mode without introducing gas into the diaphragm 2. It can be seen that graphs I and H achieve approximately twice the displacement of the diaphragm 2 compared to graph G.

[0029] Next, the results of vibration in the first vibration mode are shown, showing that the bubble generator 1 predominantly generates microbubbles (MB). Fig. 6 is a diagram showing the number of bubbles generated when the diaphragm 2 is vibrated in the in-phase mode. Fig. 6 shows the number and average size of microbubbles (MB) measured by a measuring device when the drive voltage applied to the piezoelectric element 4 is changed to 20 V, 50 V, and 100 V.

[0030] The measuring device is a known measuring device capable of measuring the number and average size of microbubbles (MB), with the lower limit of measurement being 1000 / mL, and measurement is not possible if the number of generated microbubbles (MB) is less than 1000 / mL.

[0031] When the bubble generator 1 vibrates the diaphragm 2 in the in-phase mode with gas introduced into the diaphragm 2, the number of microbubbles (MB) is 3,000 / mL and the average size is 78 μm when the drive voltage is 20 V. Similarly, the number of microbubbles (MB) is 12,000 / mL and the average size is 35 μm when the drive voltage is 50 V, and the number of microbubbles (MB) is 20,000 / mL and the average size is 28 μm when the drive voltage is 100 V.

[0032] When the diaphragm 2 is vibrated in the reverse phase mode without introducing gas into the diaphragm 2, the bubble generator 1 generates almost no microbubbles (MB) and mainly ultrafine bubbles (UFB). Therefore, as shown in Figure 6, the values ​​are below the lower limit of measurement at all drive voltages.

[0033] Furthermore, the figures show the results of measurements of the frequency of bubble generation and the cumulative number of bubbles for each bubble size when the bubble generator 1 vibrates the diaphragm 2 in the first vibration mode and the second vibration mode. Fig. 7 is a graph illustrating the bubble generation state when the diaphragm 2 is vibrated in the in-phase mode. Fig. 8 is a graph illustrating the bubble generation state when the diaphragm 2 is vibrated in the out-of-phase mode. In the graphs shown in Figs. 7 and 8, the left vertical axis represents the generation frequency (bubbles / mL), the right vertical axis represents the cumulative number (bubbles / mL), and the horizontal axis represents the bubble size (μm). The measuring device used in Figs. 7 and 8 is a known measuring device capable of measuring the number and size of microbubbles (MB) and ultrafine bubbles (UFB).

[0034] First, when the bubble generator 1 vibrated the diaphragm 2 in the first vibration mode, the measurement results shown in Fig. 7 were obtained. In the measurements shown in Fig. 7, the diaphragm 2 was vibrated at 30.1 kHz, and gas was introduced into the diaphragm 2 at a ventilation pressure of 25 to 40 kPa and an aeration rate of 10 mL / min to 20 mL / min. The diaphragm 2 was made of stainless steel and had a thickness of 0.2 mm, and had 121 openings with a diameter of 10 μm.

[0035] 7, graph J1 shows the frequency of bubbles generated by each bubble size when the diaphragm 2 is vibrated in the same phase mode at a drive voltage of 20 V, and graph J2 shows the cumulative number of bubbles generated by each bubble size in the same case. Graph J1 shows that bubbles of approximately 78 μm are generated most frequently, and graph J2 shows that the cumulative number is 3,000 bubbles / mL.

[0036] 7, graph K1 shows the frequency of bubbles generated by each bubble size when the diaphragm 2 is vibrated in the same phase mode at a drive voltage of 50 V, and graph K2 shows the cumulative number of bubbles generated by each bubble size in the same case. Graph K1 shows that bubbles of approximately 35 μm are generated with a high frequency, and graph K2 shows that the cumulative number is 12,000 bubbles / mL.

[0037] 7, graph L1 shows the frequency of bubbles generated by each bubble size when the diaphragm 2 is vibrated in the same phase mode at a drive voltage of 100 V, and graph L2 shows the cumulative number of bubbles generated by each bubble size in the same case. Graph L1 shows that the frequency of bubbles of approximately 28 μm is high, and graph L2 shows that the cumulative number is 20,000 bubbles / mL.

[0038] Next, Fig. 8 shows a comparison result between the case where the bubble generator 1 vibrated the diaphragm 2 in the first vibration mode and the case where the diaphragm 2 was vibrated in the second vibration mode. In the measurements shown in Fig. 8, in the first vibration mode, the diaphragm 2 was vibrated at 30.1 kHz, and gas was introduced into the diaphragm 2 at a ventilation pressure of 25 to 40 kPa and an airflow rate of 10 to 20 mL / min. In the second vibration mode, the diaphragm 2 was vibrated at 31.5 kHz, and gas was not introduced into the diaphragm 2 at a ventilation pressure of 10 to 20 kPa and an airflow rate of 0 mL / min. The diaphragm 2 was made of stainless steel with a thickness of 0.1 mm and had 121 openings with a diameter of 10 µm.

[0039] 8, graph M1 shows the frequency of bubbles generated for each bubble size when vibrating plate 2 is vibrated in the first vibration mode, and graph M2 shows the cumulative number of bubbles generated for each bubble size in the same case. Graph M2 shows that the cumulative number is 30 million bubbles / mL.

[0040] 8, graph N1 shows the frequency of bubbles generated by each size when diaphragm 2 is vibrated in the second vibration mode, and graph N2 shows the cumulative number of bubbles generated by each size when the vibration mode is the same. Graph N1 shows that bubbles of approximately 0.13 μm are generated frequently, and graph N2 shows that the cumulative number is 330 million bubbles / mL.

[0041] 6 and 7, the bubble generator 1 can predominantly generate microbubbles (MB) by vibrating the diaphragm 2 in the in-phase mode (first vibration mode) with gas introduced into the diaphragm 2. Note that in the first vibration mode, the bubble generator 1 may generate not only microbubbles (MB) but also ultrafine bubbles (UFB) at the same time, but it is believed that microbubbles (MB) are predominantly generated in terms of volume ratio.

[0042] As can be seen from the results shown in Figures 6 and 8, by vibrating the vibration plate 2 in the reverse phase mode (second vibration mode) without introducing gas into the vibration plate 2, the bubble generator 1 can predominantly generate ultrafine bubbles (UFB).

[0043] Therefore, the bubble generator 1 can switch between a first vibration mode in which microbubbles (MB) are predominantly generated and a second vibration mode in which ultrafine bubbles (UFB) are predominantly generated by adjusting the ventilation pressure or ventilation rate of the gas passing through the diaphragm 2 and changing the resonance frequency of the diaphragm 2. This allows the bubble generator 1 to selectively generate microbubbles or ultrafine bubbles with a single device.

[0044] 2, the vibrating body 3 has been described as having a structure in which the head portion 31 is supported by the spring portion 32, the cylindrical body 33, and the flange portion 34. However, the present invention is not limited to this, and any structure may be used as long as the vibrating body performs piston vibrations that vibrate the diaphragm 2 up and down. In the second embodiment, a case will be described in which a Langevin vibrator is used as the vibrating body.

[0045] Fig. 9 is a cross-sectional perspective view of a bubble generator 1A according to embodiment 2. The same components of the bubble generator 1A shown in Fig. 9 as those of the bubble generator 1 shown in Fig. 2 are designated by the same reference numerals, and detailed description thereof will not be repeated. As shown in Fig. 9, the bubble generator 1A includes a diaphragm 2, a vibrating body 3A, and a piezoelectric element 4. The vibrating body 3A is composed of a head portion 31 that fixes the peripheral portion of the diaphragm 2, and a cylindrical body 33a that is connected 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.

[0046] The head portion 31 is provided on the upper part of the cylindrical body 33a and has a truncated cone shape. In the vibrating body 3A, the taper angle θ is the angle between the head portion 31 and the cylindrical body 33a and the joint surface between the head portion 31 and the cylindrical body 33a. The head portion 31 may be formed separately from the cylindrical body 33a and joined thereto, or may be formed integrally with the cylindrical body 33a.

[0047] The two piezoelectric elements 4 are configured by stacking a piezoelectric element 41 and a piezoelectric element 42 that has a polarization direction opposite to that of the piezoelectric element 41. Terminals 43, 44 that supply power to the piezoelectric elements 41 and 42 are drawn out from between the upper metal ring 33a1, the lower metal ring 33a2 and the piezoelectric elements 41, 42, and are electrically connected by wiring to the controller 20 shown in FIG.

[0048] 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 longitudinal dimensions of the head portion 31 and the cylindrical body 33a, resulting in a large displacement of the vibration plate 2. Because the cylindrical body 33a resonates in multiple higher-order vibration modes, it is possible to select one resonant frequency from multiple resonant frequencies. Furthermore, by forming the head portion 31 into a truncated cone shape, the diameter of the portion connecting the upper metal ring 33a1 to the head portion 31 is narrower than the other portions, further amplifying the displacement of the vibration plate 2. Furthermore, because the diameter of the cylindrical body 33a itself is reduced, the inner diameter of the piezoelectric element 4 used for excitation can also be reduced.

[0049] As shown in FIG. 9, through-holes 35 are provided in the centers of the upper metal ring 33a1, the lower metal ring 33a2, and the fastening bolts 34a, and these through-holes 35 serve as inlet portions for introducing gas into the diaphragm 2. Although not shown in FIG. 9, a compressor for adjusting the ventilation pressure or volume of the gas passing through the diaphragm 2 is provided at the end of the through-hole 35 (the end where the fastening bolts 34a are provided). The upper metal ring 33a1, the lower metal ring 33a2, and the fastening bolts 34a are made of stainless steel, aluminum, or the like. The piezoelectric elements 41 and 42 are made of materials such as PZT (lead zirconate titanate) or KNN ((K,Na)NbO ３ Ceramic materials such as tantalum oxide, lithium niobate, and other piezoelectric crystals are used.

[0050] Specifically, the cylindrical body 33a is made of SUS304 material, with the upper metal ring 33a1 having a diameter of 16 mm and a height including the head portion of 46.5 mm, and the lower metal ring 33a2 having a diameter of 16 mm and a height of 10 mm. 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.

[0051] The cylindrical body 33a is configured such that the upper metal ring 33a1 and the lower metal ring 33a2 are fastened together by the fastening bolts 34a, which applies a compressive bias to the piezoelectric elements 41, 42. For this reason, piezoelectric ceramics with low resistance to tensile stress are used for the piezoelectric elements 41, 42, making the piezoelectric elements 41, 42 less likely to break even when driven by a large amount of power. As a result, the upper metal ring 33a1 and the lower metal ring 33a2 are at the same potential, so it is necessary to sandwich an application electrode between the two piezoelectric elements 41, 42. The application electrode is electrically connected to the terminal 43.

[0052] If it is not necessary to supply a large amount of power to drive the piezoelectric elements 41, 42, the cylindrical body 33a may have a structure in which one piezoelectric element 4 is sandwiched and bonded between an upper metal ring 33a1 and a lower metal ring 33a2, rather than being fastened with the fastening bolts 34a. Alternatively, the cylindrical body 33a may have a structure in which only the upper metal ring 33a1 is formed, and the piezoelectric element 4 is bonded to the bottom surface of the upper metal ring 33a1. Whichever structure is adopted for the cylindrical body 33a, the manufacturing cost can be reduced.

[0053] FIG. 10 is a graph illustrating the relationship between the vibration mode and the resonant frequency of the diaphragm of the bubble generator 1A according to embodiment 2. In the graph shown in FIG. 10, the vertical axis represents impedance (Ω) and the horizontal axis represents frequency (kHz). When the bubble generator 1A is driven in air (not immersed in the liquid tank 10), the impedance characteristics shown in graph Ea are obtained. The bubble generator 1A can be driven in the in-phase mode by vibrating the diaphragm 2 at a resonant frequency of approximately 44.8 kHz. When the bubble generator 1A is driven in liquid (immersed in the liquid tank 10) without introducing gas into the diaphragm 2 using the compressor 30, the impedance characteristics shown in graph Fa are obtained. The bubble generator 1A can be driven in the out-of-phase mode by vibrating the diaphragm 2 at a resonant frequency of approximately 45.8 kHz. In the impedance characteristics of graph Fa, when the bubble generation device 1A is driven in the in-phase mode, the diaphragm 2 needs to be vibrated at a resonance frequency of about 42.8 kHz, which is far from the vicinity of 44 kHz.

[0054] Furthermore, when the bubble generator 1A is driven in liquid (immersed in the liquid tank 10) with gas introduced into the diaphragm 2 by the compressor 30, the impedance characteristics are as shown in graph Ga, and the bubble generator 1A can be driven in in-phase mode by vibrating the diaphragm 2 at a resonance frequency of approximately 44.8 kHz. With the impedance characteristics of graph Ga, when driving the bubble generator 1A in out-of-phase mode, it is necessary to vibrate the diaphragm 2 at a resonance frequency of approximately 49.0 kHz, which is significantly different from the vicinity of 44 kHz.

[0055] As described above, the bubble generator 1A has two resonance modes, an anti-phase mode and an in-phase mode, in the vicinity of 44 kHz (in the range of 40 to 50 kHz), and can switch between the two resonance modes in the same way as the bubble generator 1 according to embodiment 1. Therefore, the bubble generator 1A can switch between a first vibration mode in which microbubbles (MB) are predominantly generated and a second vibration mode in which ultrafine bubbles (UFB) are predominantly generated by adjusting the ventilation pressure or ventilation rate of the gas passing through the diaphragm 2 to change the resonance frequency of the diaphragm 2. This allows the bubble generator 1A to selectively generate microbubbles or ultrafine bubbles using a single device.

[0056] (Other Modifications) In the above-described embodiment, the head portion 31 is described as being made of a truncated cone-shaped solid material with a cylindrical through-hole 35 formed therein. However, the head portion 31 is not limited to being made of a truncated cone-shaped solid material, and may be made of a plate member with a truncated cone shape. When the truncated cone-shaped head portion 31 is made of a plate member, the hollow portion of the head portion 31 functions as the through-hole 35.

[0057] Furthermore, in the above-described embodiment, it has been explained that the first vibration mode vibrates the diaphragm 2 in an in-phase mode with gas introduced into the diaphragm 2, and the second vibration mode vibrates the diaphragm 2 in an out-of-phase mode with no gas introduced into the diaphragm 2. However, the second vibration mode is not limited to a state in which no gas is introduced into the diaphragm 2. In the first vibration mode, if the ventilation pressure or ventilation volume of the gas passing through the diaphragm 2 is set to a first value, then in the second vibration mode, the ventilation pressure or ventilation volume of the gas passing through the diaphragm 2 may be adjusted to a second value that is at least smaller than the first value.

[0058] (Aspects) (1) A bubble generator according to the present disclosure is a bubble generator that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank by vibration, the bubble generator comprising: 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 gas; a vibrator that supports the vibration plate and vibrates the vibration plate; and a piezoelectric element provided on the vibrator, wherein the vibrator has a first resonance frequency and a second resonance frequency higher than the first resonance frequency set as resonance frequencies for vibrating the vibration plate; and a first vibration mode in which the air flow pressure or airflow rate of the gas passing through the vibration plate is adjusted to a first value and, when the vibration plate is vibrated at the first resonance frequency, the displacement direction of the vibration plate and the displacement direction of the vibrator are in phase; When the ventilation pressure or ventilation volume of the gas passing through the vibration plate is adjusted to a second value smaller than the first value and the vibration plate is vibrated at a second resonant frequency, a second vibration mode is generated in which the displacement direction of the vibration plate and the displacement direction of the vibrating body are in opposite phase.

[0059] According to the bubble generating device of the present disclosure, the vibration plate can be vibrated in the first vibration mode and the second vibration mode, so that microbubbles or ultrafine bubbles can be selectively generated with a single device.

[0060] (2) The bubble generating device according to (1), further comprising a control unit that controls a vibration mode for vibrating the vibration plate, and the control unit switches between the first vibration mode and the second vibration mode.

[0061] (3) A bubble generating device according to (1) or (2), wherein the bubbles generated in the liquid in the liquid tank when the vibrating plate is vibrated in the first vibration mode generate more microbubbles and less ultrafine bubbles than the bubbles generated in the liquid in the liquid tank when the vibrating plate is vibrated in the second vibration mode.

[0062] (4) A bubble generating device according to any one of (1) to (3), wherein the vibrating body includes a first cylindrical body supporting a vibrating plate at one end, a spring portion supporting the other end of the first cylindrical body, and a second cylindrical body supporting the spring portion at one end, and a piezoelectric element is provided at the other end of the spring portion or the second cylindrical body.

[0063] (5) In the bubble generating device according to any one of (1) to (3), the vibrating body is configured as a Langevin vibrator.

[0064] (6) The bubble generating device according to (4), wherein the vibration frequency of the vibrator is within the range of 25 to 35 kHz.

[0065] (7) The bubble generating device according to (5), wherein the vibration frequency of the vibrator is within the range of 40 to 50 kHz.

[0066] (8) In the bubble generation device according to any one of (1) to (7), the vibration plate is a metal plate having a plurality of openings formed therein.

[0067] (9) The bubble generating device and the metal plate described in (8) are stainless steel plates with a thickness of 0.1 mm to 0.3 mm.

[0068] (10) The bubble generation system of the present disclosure comprises: a bubble generation device described in any one of (1) to (9); a liquid tank in which the bubble generation device is mounted; and a gas adjustment device that adjusts the ventilation pressure or ventilation volume of the gas passing through the vibration plate.

[0069] 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.

[0070] 1, 1A Bubble generating device, 2 Vibration plate, 3, 3A Vibrating body, 4, 41, 42 Piezoelectric element, 5 Holding flange, 10 Liquid tank, 20 Controller, 30 Compressor, 31, 31a Head portion, 32 Spring portion, 33, 33a Cylindrical body, 33A Weight, 33a1 Upper metal ring, 33a2 Lower metal ring, 34 Flange portion, 34a Fastening bolt, 35 Through hole, 43, 44 Terminal, 100 Bubble generating system, 200 Bubbles.

Claims

1. A bubble generating device that is attached to a liquid tank and generates fine bubbles in the liquid in the liquid tank by vibration, comprising: 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 gas; a vibrator that supports the vibration plate and vibrates the vibration plate; and a piezoelectric element provided on the vibrator, wherein the vibrator has a first resonance frequency and a second resonance frequency higher than the first resonance frequency set as resonance frequencies for vibrating the vibration plate; a first vibration mode in which the air pressure or amount of gas passing through the vibration plate is adjusted to a first value and the displacement direction of the vibration plate and the displacement direction of the vibrator are in phase when the vibration plate is vibrated at the first resonance frequency; A bubble generating device having a second vibration mode in which, when the air pressure or air volume of the gas passing through the vibration plate is adjusted to a second value smaller than the first value and the vibration plate is vibrated at the second resonant frequency, the displacement direction of the vibration plate and the displacement direction of the vibrating body are in opposite phase.

2. The bubble generating device of claim 1, further comprising a control unit that controls the vibration mode in which the vibration plate vibrates, the control unit switching between the first vibration mode and the second vibration mode.

3. A bubble generating device as described in claim 1 or claim 2, wherein the bubbles generated in the liquid in the liquid tank when the vibration plate is vibrated in the first vibration mode generate a greater amount of microbubbles and a smaller amount of ultrafine bubbles than the bubbles generated in the liquid in the liquid tank when the vibration plate is vibrated in the second vibration mode.

4. A bubble generating device as described in any one of claims 1 to 3, wherein the vibrating body includes a first cylindrical body supporting the vibrating plate at one end, a spring portion supporting the other end of the first cylindrical body, and a second cylindrical body supporting the spring portion at one end, and the piezoelectric element is provided on the other end of the spring portion or the second cylindrical body.

5. A bubble generating device as described in any one of claims 1 to 3, wherein the vibrating body is composed of a Langevin type vibrator.

6. The bubble generating device according to claim 4, wherein the vibration frequency of the vibrator is within the range of 25 to 35 kHz.

7. The bubble generating device according to claim 5, wherein the vibration frequency of the vibrator is within the range of 40 to 50 kHz.

8. A bubble generating device as described in any one of claims 1 to 7, wherein the vibration plate is a metal plate having a plurality of openings formed therein.

9. The bubble generating device according to claim 8, wherein the metal plate is stainless steel having a thickness of 0.1 mm to 0.3 mm.

10. A bubble generating system comprising: the bubble generating device according to any one of claims 1 to 9; a liquid tank in which the bubble generating device is mounted; and a gas adjusting device for adjusting the ventilation pressure or volume of gas passing through the vibration plate.

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