Ultrasonic treatment apparatus and fine bubble supply method

Abstract

To realize excellent durability of an apparatus, realize a dissolved gas amount suitable for propagation of ultrasonic waves, and stably generate fine bubbles that further comply with a treatment using ultrasonic waves. An ultrasonic treatment apparatus (1) according to the present invention includes: a treatment part capable of accommodating a treatment liquid (3) and an object to be treated; an ultrasonic generator (20) that is provided in the treatment part and applies ultrasonic waves to the object to be treated; and a circulation path (30) for circulating the treatment liquid (3) in the treatment part, in which a fine bubble generator (40) which performs deaeration on an extracted treatment liquid (3) and generates fine bubbles in the treatment liquid (3), is provided to the circulation path (30), in series with a treatment liquid extraction pipe (33). The fine bubble generator (40) has two or more narrow portions (41) each having an opening flow path with a size narrower than an inside diameter of the treatment liquid extraction pipe (33), in which the opening flow paths of the narrow portions (41) adjacent to each other are configured to prevent the treatment liquid (3) from proceeding straight, and an opening cross-sectional area at each pressure reduction zone satisfies a predetermined relation.

Description

Ultrasonic treatment device and fine bubble supply method

[0001] The present invention relates to an ultrasonic processing device and a method for supplying fine bubbles.

[0002] In general, in the manufacturing process of various metal objects such as steel plates and steel pipes, a cleaning method is widely adopted in which the metal object is immersed in a cleaning tank containing chemicals, rinses, etc., to remove dirt, scale, etc. present on the surface of the metal object. Examples of cleaning treatment devices that perform such cleaning treatment methods include treatment devices that use high-pressure air jet nozzles and ultrasonic treatment devices that use ultrasound.

[0003] In ultrasonic processing devices using such ultrasound, various efforts have been made to enhance the cavitation effect in ultrasonic cleaning, such as degassing to improve ultrasonic propagation and introducing microbubbles that serve as the nuclei of cavitation. For example, degassing methods have been proposed, such as a vacuum pump degassing method, a hollow fiber membrane degassing method, and a throttle degassing method. Furthermore, methods for introducing microbubbles have been proposed, such as a high-speed swirling bubble atomization method and a high-pressure supersaturated dissolution of gas to generate microbubbles upon release. However, the above-mentioned degassing method and microbubble generation method each require a dedicated unit, and devices that combine these methods tend to be large and very expensive.

[0004] Therefore, in recent years, studies have been conducted on devices that combine stable generation of fine bubbles with adjustment of the amount of dissolved gas (i.e., degassing).

[0005] For example, Patent Document 1 below proposes an apparatus that generates bubbles using an obstacle installed in a flow path that introduces a cleaning liquid into a propeller-type circulation pump, then breaks the bubbles into fine particles using the propeller of the circulation pump, and degasses the cleaning liquid using a degassing device connected to the flow path.

[0006] Furthermore, Patent Document 2 listed below proposes a method in which a liquid is introduced into the suction line of a liquid feed pump, and a portion of the suction line is throttled to reduce the pressure between the throttle and the liquid feed pump, and to liberate dissolved gas in the liquid as bubbles.

[0007] Furthermore, Patent Document 3 listed below proposes an apparatus for degassing a treatment liquid and generating fine bubbles by providing two pumps in opposite directions to a circulation path for circulating the treatment liquid.

[0008] Furthermore, as a technique for generating fine bubbles, the following Patent Documents 4 and 5 propose a method in which baffles or the like are provided at intervals in a liquid flow path, and cavitation is generated when the liquid collides with the baffles or the like.

[0009] Japanese Patent Application Laid-Open No. 2008-296217 Japanese Patent Application Laid-Open No. 7-328316 Japanese Patent Application Laid-Open No. 2020-14989 Japanese Patent Application Laid-Open No. 2005-95877 Special Publication No. 2016-536139

[0010] However, while the technologies disclosed in Patent Documents 1 and 2 can generate fine bubbles, they do not consistently generate fine bubbles with a bubble size suitable for ultrasonic cleaning processes. Furthermore, the technology disclosed in Patent Document 1 generates fine bubbles by shearing the bubbles with the propeller of the circulation pump, which can cause the propeller to be damaged by erosion, resulting in insufficient durability of the device. Furthermore, the technology disclosed in Patent Document 2 is equipped with a gas-liquid separation tank for floating and separating the generated bubbles, but it generates coarse bubbles with the purpose of intentionally eliminating the bubbles, and is therefore not capable of generating fine bubbles.

[0011] Furthermore, even if the technologies disclosed in Patent Documents 3 to 5 above were used, there was still room for improvement in terms of stable generation of fine bubbles having a bubble diameter sufficiently suitable for ultrasonic cleaning processes.

[0012] In particular, Patent Document 4 discloses a technology for reducing the pressure from a pressurized state to produce fine bubbles caused by cavitation. The inventors' investigations revealed that gas dissolved in a liquid cannot be turned into bubbles unless the pressure after decompression can be reduced to 1 atmosphere or less. Therefore, Patent Document 4 makes it difficult to achieve both degassing and fine bubble generation.

[0013] Therefore, the present invention has been made in consideration of the above problems, and the object of the present invention is to provide an ultrasonic processing device and a method for supplying fine bubbles that have excellent durability, can achieve a dissolved gas amount suitable for the propagation of ultrasonic waves, and can stably generate fine bubbles suitable for processing using ultrasonic waves.

[0014] In order to solve the above problems, the inventors conducted extensive research and discovered that by appropriately providing multiple narrow sections that meet certain conditions in the piping that introduces the treatment liquid into the circulation pump, it is possible to stably generate fine bubbles that are suitable for ultrasonic treatment without affecting the durability of the mechanism, and this led to the completion of the present invention. The gist of the present invention, which was completed based on this discovery, is as follows.

[0015] [1] A treatment device capable of accommodating a treatment liquid and a workpiece, an ultrasonic generator provided in the treatment device for applying ultrasonic waves to the workpiece, and a circulation path for circulating the treatment liquid within the treatment device, the circulation path having a circulation pump for circulating the treatment liquid, a treatment liquid withdrawal pipe connecting the treatment liquid withdrawn from the treatment device to the circulation pump, and a treatment liquid discharge pipe for discharging the treatment liquid that has passed through the circulation pump into the treatment device, and a fine bubble generator is provided in series with the treatment liquid withdrawal pipe for degassing the withdrawn treatment liquid and generating fine bubbles in the treatment liquid, the fine bubble generator having two or more narrow sections whose opening flow path for the treatment liquid is narrower than the inner diameter of the treatment liquid withdrawal pipe, and the opening flow path of adjacent narrow sections is configured so that the treatment liquid does not proceed in a straight line, and each of the narrow sections has an opening cross-sectional area of ​​the inner diameter of the treatment liquid withdrawal pipe that is equal to or smaller than A. ０ and the opening cross-sectional area of ​​the inner diameter of the treated liquid withdrawal pipe at the i-th narrow portion (i is an integer of 1 or more) from the treatment portion side to the circulation pump side is A ｉ When expressed as ｉ / A ０ The opening cross-sectional area ratio R of the i-th narrow portion is expressed as ｉ satisfies the following formula (1), and the distance between the i-th narrow portion and the i+1-th narrow portion is L ｉ An ultrasonic treatment apparatus that satisfies the following formula (2) when expressed as: [2] The ultrasonic treatment apparatus according to [1], wherein the positions of the open flow paths of adjacent narrow portions do not overlap each other when the treatment liquid withdrawal pipe is viewed in the pipe axial direction. [3] The ultrasonic treatment apparatus according to [1] or [2], wherein the treatment section is provided with a treatment tank that holds the treatment liquid, and the ultrasonic generator applies ultrasonic waves indirectly to the workpiece via the treatment liquid. [4] The ultrasonic treatment apparatus according to [1] or [2], wherein the ultrasonic generator applies ultrasonic waves directly to the workpiece immersed in the treatment liquid in the treatment section. [5] When the number of the narrow portions is N, the opening area ratio R of the Nth narrow portion from the treatment section side to the circulation pump side is ＮThe ultrasonic processing apparatus according to any one of [1] to [4], which satisfies the following formulas (3) and (4) when expressed as follows. [6] The ultrasonic processing apparatus according to any one of [1] to [5], wherein the number N of the narrow portions is 2 to 10. [7] The ultrasonic processing apparatus according to any one of [1] to [6], which has one or more of the narrow portions formed by a protruding member protruding from the inner surface of the treatment liquid withdrawal pipe. [8] The ultrasonic processing apparatus according to [7], which has as the narrow portion a movable protruding member protruding from the inner surface of the treatment liquid withdrawal pipe. [9] The ultrasonic processing apparatus according to any one of [1] to [8], which has one or more of the narrow portions formed by an opening member having one or more through holes.

[10] The ultrasonic processing apparatus according to any one of [1] to [9], wherein the ultrasonic generator can select the frequency of the ultrasonic waves from a frequency band of 20 kHz to 200 kHz.

[11] The ultrasonic processing apparatus according to any one of [1] to

[10] , wherein the ultrasonic generator can apply ultrasonic waves to the processing liquid while sweeping the frequency of the ultrasonic waves in a range of ±0.1 kHz to ±10 kHz around the selected frequency of the ultrasonic waves.

[12] A method for supplying fine bubbles, which supplies a treatment liquid containing fine bubbles to a treatment section capable of accommodating the treatment liquid and a workpiece while applying ultrasonic waves to the workpiece to perform a predetermined process, the method comprising the steps of: providing the treatment section with an ultrasonic generator that is provided in the treatment section and applies ultrasonic waves to the workpiece; and providing a circulation path for circulating the treatment liquid in the treatment section, the circulation path including a circulation pump that circulates the treatment liquid; a treatment liquid withdrawal pipe that connects the treatment liquid withdrawn from the treatment section to the circulation pump; and a circulation pump that connects the treatment liquid withdrawn from the treatment section to the circulation pump. and a treatment liquid discharge pipe for discharging the treatment liquid that has passed through a pump to the treatment section, and a fine bubble generator is provided in series with the treatment liquid withdrawal pipe for degassing the withdrawn treatment liquid and generating fine bubbles in the treatment liquid, the fine bubble generator having two or more narrow sections in which the size of the opening flow path for the treatment liquid is narrower than the inner diameter of the treatment liquid withdrawal pipe, the opening flow paths of adjacent narrow sections are configured so that the treatment liquid does not proceed in a straight line, and each of the narrow sections has an opening cross-sectional area A of the inner diameter of the treatment liquid withdrawal pipe. ０ and the opening cross-sectional area of ​​the inner diameter of the treated liquid withdrawal pipe at the i-th narrow portion (i is an integer of 1 or more) from the treatment portion side to the circulation pump side is A ｉ When expressed as ｉ / A ０ The opening cross-sectional area ratio R of the i-th narrow portion is expressed as ｉ satisfies the following formula (1), and the distance between the i-th narrow portion and the i+1-th narrow portion is L ｉ

[13] The method for supplying fine bubbles according to

[12] , wherein the fine bubble generator generates the fine bubbles so that the amount of dissolved gas in the treatment liquid discharged to the treatment section is 50% or less of the saturated dissolved gas amount.

[14] The method for supplying fine bubbles according to

[12] , wherein the fine bubble generator generates the fine bubbles having an average bubble diameter of 1 μm to 100 μm in the treatment liquid discharged to the treatment section at a bubble density of 1×10 ３ pieces / mL ~ 1×10 １０

[15] The method for supplying fine bubbles according to any one of

[12] to

[14] , wherein the ultrasonic generator selects the ultrasonic frequency from a frequency band of 20 kHz to 200 kHz.

[16] The method for supplying fine bubbles according to any one of

[12] to

[15] , wherein the ultrasonic generator applies ultrasonic waves to the treatment liquid while sweeping the selected ultrasonic frequency in a range of ±0.1 kHz to ±10 kHz.

[0016] R ｉ =0.10~0.50...Formula (1) 1.0≦L ｉ / 2 (A ０ / π) ０．５ ≦5.0...Formula (2) R ｉ＋１ ≧R ｉ ...Formula (3) R Ｎ / R １ ≧1.10...Formula (4)

[0017] As described above, according to the present invention, it is possible to provide an ultrasonic processing device and a method for supplying fine bubbles that can achieve a dissolved gas amount suitable for the propagation of ultrasonic waves, and can stably generate fine bubbles that are more suitable for processing using ultrasonic waves, and that also have excellent durability.

[0018] FIG. 1 is an explanatory diagram schematically showing an example of the configuration of an ultrasonic processing device according to an embodiment of the present invention. FIG. 1 is an explanatory diagram schematically showing an example of the configuration of an ultrasonic processing device according to the same embodiment. FIG. 2 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 3 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 4 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 5 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 6 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 7 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 8 is an explanatory diagram for explaining a fine bubble generator provided in the ultrasonic processing device according to the same embodiment. FIG. 9 is a graph showing the state of pressure change inside the fine bubble generator. FIG. 10 is a graph showing the state of pressure change inside the fine bubble generator. FIG. 11 is a graph showing the state of pressure change inside the fine bubble generator. FIG. 12 is a graph showing the state of pressure change inside the fine bubble generator. FIG. 13 is a graph showing the state of pressure change inside the fine bubble generator. FIG. 1 is a graph showing the pressure distribution inside a fine bubble generator. FIG. 2 is a graph for explaining a fine bubble generator. FIG. 3 is a graph for explaining a fine bubble generator. FIG. 4 is a graph for explaining a fine bubble generator. FIG. 5 is a graph showing the relationship between the particle size of fine bubbles and the dissolved oxygen concentration. FIG. 6 is an explanatory diagram schematically showing the configuration of the device used in Experimental Example 1. FIG. 7 is an explanatory diagram schematically showing the configuration of the fine bubble generator used in Experimental Example 1. FIG. 8 is an explanatory diagram schematically showing the configuration of the ultrasonic processing device used in Experimental Example 2. FIG. 9 is an explanatory diagram schematically showing the configuration of the ultrasonic processing device used in Experimental Example 2.Fig. 1 is an explanatory diagram for explaining measurement positions of ultrasonic intensity. Fig. 2 is an explanatory diagram schematically showing the configuration of the ultrasonic processing device used in Experimental Example 3. Fig. 3 is an explanatory diagram schematically showing the configuration of the ultrasonic processing device used in Experimental Example 4.

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0020] (Overall Configuration of Ultrasonic Processing Apparatus) First, the overall configuration of an ultrasonic processing apparatus according to an embodiment of the present invention will be briefly described with reference to Figures 1A and 1B. Figures 1A and 1B are explanatory diagrams schematically illustrating an example of the overall configuration of an ultrasonic processing apparatus according to this embodiment.

[0021] The ultrasonic processing apparatus 1 according to the present embodiment is an apparatus that uses ultrasonic waves in addition to a processing solution for performing a predetermined treatment on the surface of the workpiece (the portion in contact with the processing solution). The ultrasonic processing apparatus 1 can be used to perform various treatments, such as cleaning, on various metal objects, such as steel, and various non-metal objects, such as plastic resin components. For example, by using the ultrasonic processing apparatus 1 according to the present embodiment for various metal objects, such as steel plates, steel pipes, and steel wires, pickling, degreasing, and even cleaning can be performed on these metal objects. The ultrasonic processing apparatus 1 according to the present embodiment can also be used to perform a water washing process after pickling.

[0022] Here, pickling refers to a process that uses an acidic solution to remove oxide scale formed on the surface of a metal body, and degreasing refers to a process that uses an organic solvent, an organic solvent emulsified with a surfactant, or an alkaline degreasing solution to remove oils, such as lubricants and processing oils, used in processing. These pickling and degreasing processes are pretreatments performed on metal bodies prior to surface finishing treatments (metal coating, chemical conversion coating, painting, etc.). Pickling can also dissolve part of the base metal. Pickling is also used to dissolve metal bodies by etching to improve surface finish quality. In some cases, degreasing is performed before pickling, and the degreasing performance of the degreasing process can affect the scale removal in the subsequent pickling process. Furthermore, degreasing is also used to improve wettability, which is an oil content control index for the finish quality of the final product.

[0023] Furthermore, the ultrasonic processing device 1 according to this embodiment, which will be described in detail below, can be used not only for the cleaning process in the manufacturing line as described above, but also for cleaning used pipes, tanks, and equipment that require regular or irregular removal of dirt.

[0024] In the following, we will provide a detailed explanation of an example of a processing unit in which a processing tank containing processing liquid is present, and the object to be processed is arranged inside the processing tank so that it is filled with processing liquid.

[0025] However, the ultrasonic treatment device 1 of this embodiment can be applied without providing a separate treatment tank when a component already installed in the device to be treated can be used as a treatment tank, such as when performing ultrasonic treatment on piping installed in a heat exchanger.

[0026] As shown in Fig. 1A, the ultrasonic treatment apparatus 1 according to this embodiment includes a treatment tank 10, an ultrasonic generator 20, and a treatment liquid circulation path 30. As shown in Fig. 1A, the treatment liquid circulation path 30 includes a circulation pump 31, a treatment liquid withdrawal pipe 33, and a treatment liquid discharge pipe 35, and a fine bubble generator 40 is provided in series with the treatment liquid withdrawal pipe 33. The fine bubble generator 40 generates fine bubbles in the treatment liquid 3 flowing through the circulation path 30, and the generated fine bubbles are supplied into the treatment tank 10 together with the treatment liquid 3. In addition to the above configuration, the ultrasonic treatment apparatus 1 according to this embodiment preferably further includes a curved member 50.

[0027] Here, fine bubbles are minute bubbles with a diameter of 100 μm or less. Fine bubbles improve the propagation efficiency of ultrasonic waves to the object to be treated and act as nuclei for ultrasonic cavitation to improve treatment performance.

[0028] 1B, the number and arrangement of the ultrasonic generators 20, circulation paths 30, fine bubble generators 40, and curved members 50 are not particularly limited, and the number and arrangement can be adjusted appropriately depending on the shape and size of the treatment tank 10. The size of each member in the figure is exaggerated as appropriate for ease of explanation, and does not represent the actual dimensions or ratios between the members.

[0029] Each component of the ultrasonic processing apparatus 1 according to this embodiment will be described in detail below.

[0030] <Regarding the processing tank 10> The processing tank 10, which is an example of a processing unit, contains a processing liquid 3 used to perform a predetermined process on the object to be processed, as well as the object to be processed itself. As a result, the object to be processed contained in the processing tank 10 is immersed in the processing liquid 3, and is thereby filled with the processing liquid 3. The type of processing liquid 3 held in the processing tank 10 is not particularly limited, and any known processing liquid can be used depending on the process to be performed on the object to be processed.

[0031] Here, the material used to form the treatment tank 10 according to this embodiment is not particularly limited, and may be various metal materials such as iron, steel, stainless steel plate, etc., various plastic resins such as fiber reinforced plastic (FRP) and polypropylene (PP), etc., or various bricks such as acid-resistant bricks, etc. In other words, as the treatment tank 10 constituting the ultrasonic treatment apparatus 1 according to this embodiment, it is possible to prepare a new treatment tank made of the above-mentioned material, or it is also possible to use an existing treatment tank in various production lines.

[0032] Furthermore, the size of the treatment tank 10 is not particularly limited, and even large treatment tanks of various shapes, such as a liquid surface depth of approximately 1 to 2 m and a total length of approximately 3 to 25 m, can be used as the treatment tank 10 of the ultrasonic treatment device 1 of this embodiment.

[0033] <About the Ultrasonic Generator 20> The ultrasonic generator 20 applies ultrasonic waves of a predetermined frequency to the treatment liquid 3 and the object to be treated contained in the treatment tank 10. The ultrasonic generator 20 is not particularly limited, and a known ultrasonic vibrator connected to an ultrasonic oscillator (not shown) can be used. Although FIGS. 1A and 1B illustrate the ultrasonic generator 20 mounted on the wall surface of the treatment tank 10, the installation position of the ultrasonic generator 20 on the treatment tank 10 is not particularly limited, and one or more ultrasonic vibrators may be appropriately installed on the wall surface or bottom surface of the treatment tank 10. If ultrasonic waves are uniformly propagated throughout the treatment tank 10, the oscillation loads of the individual ultrasonic vibrators are uniformly balanced, and therefore, even if there are multiple ultrasonic vibrators, interference between the generated ultrasonic waves does not occur.

[0034] The frequency of the ultrasonic waves output from the ultrasonic generator 20 is preferably, for example, 20 kHz to 200 kHz. If the frequency of the ultrasonic waves is less than 20 kHz, the propagation of the ultrasonic waves may be hindered by large bubbles generated from the surface of the workpiece, and the effect of the ultrasonic waves in improving the processing performance may be reduced. Furthermore, if the frequency of the ultrasonic waves exceeds 200 kHz, the ultrasonic waves may propagate too linearly when processing the workpiece, which may reduce the uniformity of the processing. The frequency of the ultrasonic waves output from the ultrasonic generator 20 is preferably 20 kHz to 150 kHz, and more preferably 25 kHz to 100 kHz.

[0035] The frequency of the ultrasonic waves to be applied is preferably selected to be an appropriate value within the above range depending on the object to be treated, and ultrasonic waves of two or more different frequencies may be applied depending on the type of object to be treated.

[0036] Furthermore, it is preferable that the ultrasonic generator 20 has a frequency sweep function that can apply ultrasonic waves while sweeping the frequency within a predetermined range centered on a selected ultrasonic frequency. Such a frequency sweep function makes it possible to achieve the following two additional effects.

[0037] When ultrasonic waves are applied to microbubbles, including fine bubbles, present in a liquid, a force called the Bjerknes force acts on the microbubbles, and the microbubbles have a resonant bubble radius R that depends on the frequency. ０ When the frequency of the ultrasonic wave is changed by the frequency sweep function of the ultrasonic wave application mechanism 20, the resonant bubble radius R, which depends on the frequency, is increased. ０ The frequency sweep function of the ultrasonic generator 20 further improves the processing efficiency of the ultrasonic processing device 1 according to this embodiment.

[0038] On the other hand, a general property of ultrasonic waves is that "ultrasonic waves penetrate an object when their wavelength is 1 / 4 of the wavelength corresponding to the thickness of the object." Therefore, by applying ultrasonic waves while sweeping the frequency within an appropriate range, for example, when the object to be treated has a hollow portion such as a tubular body, it is possible to increase the amount of ultrasonic waves that penetrate into the tubular body, thereby further improving the processing efficiency of the ultrasonic processing device 1 according to this embodiment.

[0039] When considering the transmission of ultrasonic waves through the surface of an irradiated object, ultrasonic waves propagate not only when incident perpendicularly to the irradiated object but also through repeated multiple reflections, making it difficult to form a consistent sound field. In particular, in order to create conditions for transmission through the wall surface of the irradiated object, it is preferable to achieve a frequency that satisfies the condition that "the wavelength of the ultrasonic waves is 1 / 4 of the wavelength corresponding to the thickness of the object to be treated," regardless of the location of the object to be treated. The inventors' investigation of such a frequency range revealed that the above-described transmission of ultrasonic waves can be achieved by applying ultrasonic waves while sweeping the frequency in the range of ±0.1 kHz to ±10 kHz centered on a selected ultrasonic frequency. For these reasons, it is preferable that the ultrasonic generator 20 has a frequency sweep function that can apply ultrasonic waves while sweeping the frequency in the range of ±0.1 kHz to ±10 kHz centered on a selected ultrasonic frequency.

[0040] <Regarding the Circulation Path 30 and the Fine Bubble Generator 40> The circulation path 30 is a path for circulating the treatment liquid 3 held in the treatment tank 10. As shown in Fig. 1A, the circulation path 30 has at least a circulation pump 31 for circulating the treatment liquid 3, a treatment liquid withdrawal pipe 33 that connects the treatment liquid 3 withdrawn from the treatment tank 10 to the circulation pump 31, and a treatment liquid discharge pipe 35 that discharges the treatment liquid 3 that has passed through the circulation pump 31 into the treatment tank 10. In addition, as shown in Fig. 1A, the fine bubble generator 40 is provided in series with the treatment liquid withdrawal pipe 33, and degasses the treatment liquid 3 withdrawn from the treatment tank 10 and generates fine bubbles in the treatment liquid 3.

[0041] Here, the circulation pump 31 is a general-purpose pump such as a centrifugal pump or a diaphragm pump, and a special pump such as a vacuum pump, a decompression pump, or a pressure pump is not used.

[0042] The fine bubble generator 40 is provided in the treatment liquid withdrawal pipe 33, which is in a negative pressure environment. The fine bubble generator 40 generates fine bubbles in the treatment liquid 3 withdrawn from the treatment tank 10. If the fine bubble generator 40 were provided in the treatment liquid discharge pipe 35, which is in a positive pressure environment, instead of the treatment liquid withdrawal pipe 33, it would be impossible to degas the treatment liquid 3, and as a result, it would be impossible to generate the desired fine bubbles.

[0043] The average bubble diameter of the fine bubbles generated in the treatment liquid 3 discharged by the fine bubble generator 40 into the treatment tank 10 is preferably 1 μm to 100 μm. The average bubble diameter is the diameter at which the number of samples is greatest in the fine bubble diameter distribution. If the average bubble diameter is less than 1 μm, the fine bubble generator 40 will be large, which may make it difficult to supply fine bubbles with a uniform bubble diameter. The average bubble diameter is more preferably 2 μm or more, and even more preferably 3 μm or more. This makes it possible to more reliably supply fine bubbles with a uniform bubble diameter. On the other hand, if the average bubble diameter exceeds 100 μm, the fine bubble floating speed increases, shortening the lifespan of the fine bubbles in the cleaning liquid and making practical cleaning impossible. Furthermore, if the bubble diameter is too large, the fine bubbles may inhibit the propagation of ultrasonic waves, reducing the cleaning power-enhancing effect of ultrasonic waves. The average bubble diameter is more preferably 90 μm or less, even more preferably 80 μm or less, and even more preferably 70 μm or less, which makes it possible to more reliably prevent a decrease in the cleaning power-enhancing effect of ultrasonic waves.

[0044] The bubble density of the fine bubbles in the treatment liquid 3 discharged into the treatment tank 10 by the fine bubble generator 40 is 1×10 ３ pieces / mL ~ 1×10１０ It is preferable that the fine bubble density is 10 ３ If the density is less than 1 × 10 / mL, the ultrasonic propagation improving effect of the fine bubbles may not be sufficiently obtained, and the number of ultrasonic cavitation nuclei required for treatment will be reduced, which is not preferable. ３ 5×10 ３ 1×10 ４ This allows the fine bubbles to more reliably exert their ultrasonic propagation improving effect. １０ If the density exceeds 1 × 10 / mL, the fine bubble generator 40 will need to be large or the number of fine bubble generators 40 will need to be increased, which may make it impractical to supply fine bubbles, and is therefore undesirable. ９ particles / mL or less, and more preferably 1 x 10 ８ particles / mL or less, and even more preferably 1 x 10 ７ It is less than 1 / mL.

[0045] When working with the ultrasonic processing device 1 according to this embodiment, it is preferable to control the density of the fine bubbles in the processing liquid held in the processing tank 10 so that it matches the density of the fine bubbles in the processing liquid 3 discharged into the processing tank 10, before carrying out the various processes described above.

[0046] Furthermore, the fine bubble generator 40 preferably generates fine bubbles in the treatment liquid 3 so that the proportion of fine bubbles having a bubble diameter equal to or smaller than the frequency resonance diameter, which is the diameter that resonates with the ultrasonic frequency, is 70% or more of the total number of fine bubbles present in the treatment liquid 3. The reason for this is explained below.

[0047] The natural frequency of various types of bubbles, including fine bubbles, is also called the Minnaert resonance frequency and is given by the following equation 101.

[0048]

[0049] Here, in the above formula 101, f ０ : Natural frequency of the bubble (Minnaert resonance frequency) R ０ : average bubble radius p ∞ : average pressure of the surrounding liquid γ: adiabatic ratio (γ of air = 1.4) ρ: liquid density

[0050] Now, if we assume that there is air inside the bubble of interest, the liquid around the bubble is water, and the pressure is atmospheric pressure, then the product f of the natural frequency of the bubble and the average radius of the bubble is ０ R ０ The value of is about 3 kHz mm according to the above formula 101. Therefore, if the frequency of the applied ultrasonic wave is 20 kHz, the radius R of the bubble that resonates with the ultrasonic wave is ０ is approximately 150 μm, the frequency resonance diameter 2R, which is the diameter of the bubble that resonates with the ultrasonic wave of 20 kHz. ０ Similarly, if the frequency of the applied ultrasonic waves is 100 kHz, the radius R of the bubbles that resonate with the ultrasonic waves is ０ is approximately 30 μm, so the frequency resonance diameter 2R, which is the diameter of the bubble that resonates with the ultrasonic wave of 100 kHz, ０ is about 60 μm.

[0051] At this time, the resonance radius R ０ When bubbles, including fine bubbles, resonate, they repeatedly expand and contract in a short period of time and eventually collapse. However, when the first sound wave passes through the bubbles, the size of the bubbles is equal to the frequency resonance diameter 2R. ０ On the other hand, if the size of the bubble is greater than the frequency resonant diameter 2R at the time the first sound wave passes through the bubble, ０ If the value is smaller than , the ultrasonic waves can pass through the bubbles without being diffused at the bubble surface.

[0052] From this viewpoint, in the treatment liquid 3, the frequency resonance diameter 2R ０It is preferable that the ratio of the number of fine bubbles having the following bubble diameter is 70% or more of the total number of fine bubbles present in the treatment liquid 3. ０ By making the ratio of the number of fine bubbles having the following bubble diameters 70% or more, it is possible to further improve the ultrasonic wave propagation efficiency. Also, by propagating the first sound wave to the wall / bottom of the treatment tank 10, the ultrasonic waves are repeatedly diffused and reflected throughout the treatment tank 10, making it possible to realize a uniform ultrasonic treatment tank. Also, by making the frequency resonance diameter 2R ０ Even bubbles that are smaller than this size will repeatedly expand and contract and collapse when a predetermined ultrasonic irradiation time is exceeded, and can contribute to processing using cavitation.

[0053] In addition, the frequency resonance diameter is 2R ０ The ratio of the number of fine bubbles having the following bubble diameter is preferably 98% or less, taking into consideration that there are quite a few bubbles that expand immediately after being generated. ０ The percentage of the number of fine bubbles having the following bubble diameters is more preferably 80% or more and 98% or less.

[0054] The average bubble diameter and bubble density of the fine bubbles can be measured using known instruments such as a liquid particle counter or a bubble diameter distribution measuring device.

[0055] Furthermore, in the ultrasonic processing apparatus 1 according to this embodiment, in order to achieve both more uniform ultrasonic propagation and high cleaning performance, it is preferable to control the amount of dissolved gas (more specifically, the amount of dissolved oxygen) in the treatment liquid 3 to an appropriate value using the fine bubble generator 40. The appropriate amount of dissolved gas in the treatment liquid 3 is preferably 1% to 50% of the saturation level of the solution in the treatment liquid 3. A dissolved gas amount less than 1% of the saturation level is undesirable because it is difficult to generate fine bubbles, ultrasonic cavitation does not occur, and the ultrasonic treatment performance improvement ability (surface treatment performance improvement ability) cannot be fully realized. On the other hand, a dissolved gas amount exceeding 50% of the saturation level of the solution is undesirable because the dissolved gas inhibits ultrasonic propagation and prevents uniform ultrasonic propagation throughout the treatment tank 10. The amount of dissolved gas (dissolved oxygen) in the treatment liquid 3 is preferably 5% to 40% of the saturation level of the solution in the treatment liquid 3.

[0056] Here, if the temperature of the treatment liquid 3 changes, the dissolved saturation amount of the treatment liquid 3 changes. Furthermore, differences in the molecular momentum (e.g., water molecular momentum) of the liquid constituting the treatment liquid 3, resulting from temperature changes in the treatment liquid 3, affect propagation. Specifically, if the temperature is low, the molecular momentum of the liquid constituting the treatment liquid 3 is low, making it easier for ultrasonic waves to propagate, and the dissolved saturation amount (dissolved oxygen amount) of the treatment liquid 3 also increases. Therefore, it is preferable to appropriately control the temperature of the treatment liquid 3 so as to achieve a desired dissolved gas amount (dissolved oxygen amount) within the above range. The temperature of the treatment liquid 3 depends on the specific treatment content to be performed using the treatment liquid 3, but is preferably, for example, about 20°C to 85°C.

[0057] Specifically, the amount of dissolved gas in the treatment liquid 3 is preferably, for example, 0.1 ppm to 11.6 ppm, and more preferably 1.0 ppm to 11.0 ppm. Therefore, the circulation path 30 and the fine bubble generator 40 according to this embodiment control the temperature of the treatment liquid 3 and the amount of dissolved gas in the treatment liquid 3 so that the amount of dissolved gas in the treatment liquid 3 held in the treatment tank 10 falls within the above-mentioned range.

[0058] The amount of dissolved gas in the treatment liquid 3 can be measured by known devices such as a diaphragm electrode method and an optical dissolved oxygen meter.

[0059] The dissolved gases in the aqueous solution are mainly oxygen, nitrogen, carbon dioxide, helium, and argon, and although they are affected by the temperature and components of the aqueous solution, oxygen and nitrogen account for the majority. Furthermore, the dissolved gas that can affect various ultrasonic treatments, as focused on in this embodiment, is mainly oxygen.

[0060] The above-described average bubble diameter and bubble density of the fine bubbles, as well as the amount of dissolved gas in the treatment liquid 3, can be achieved by appropriately setting the structure of the fine bubble generator 40 as described in detail below and by appropriately controlling the pressure reduction-release cycle of the treatment liquid 3.

[0061] The fine bubble generator 40 according to this embodiment and the treatment liquid withdrawal pipe 33 to which the fine bubble generator 40 is attached will be described in detail below with reference to Figures 2 to 14. Figures 2 to 8 are explanatory diagrams for explaining the fine bubble generator provided in the ultrasonic treatment device according to this embodiment. Figures 9A to 9E are graphs showing pressure changes inside the fine bubble generator. Figures 10A to 10D are graphs showing pressure distribution inside the fine bubble generator. Figures 11 to 13 are graphs for explaining the fine bubble generator. Figure 14 is a graph showing the relationship between fine bubble particle size and dissolved oxygen concentration.

[0062] As shown in Fig. 2, the fine bubble generator 40 according to this embodiment has two or more narrow sections 41 in which the size of the open flow path for the treatment liquid 3 (the path through which the treatment liquid 3 flows) is narrower than the inner diameter of the treatment liquid withdrawal pipe 33, and the open flow paths of adjacent narrow sections 41 are configured so that the treatment liquid 3 does not flow in a straight line. As described in detail below, the treatment liquid 3 is depressurized in the narrow sections 41, and the pressure of the treatment liquid 3 in the depressurized state is released in the portion corresponding to the space between the adjacent narrow sections 41 (including the area without obstacles following the narrow section closest to the circulation pump 31; hereinafter, this area will also be referred to as the "non-narrow section 43"). Therefore, the narrow section 41 can be considered a depressurized area where the treatment liquid 3 is depressurized, and the non-narrow section 43 can be considered a release area where the pressure of the treatment liquid 3 in the depressurized state is released. The narrow portion 41 and the non-narrow portion 43 form a pressure reduction / release cycle 45 for reducing and releasing the pressure of the processing liquid 3 .

[0063] In each narrow section 41, an obstacle for the processing liquid 3 is provided on the inner wall of the processing liquid withdrawal pipe 33 so that the flow path of the processing liquid 3 is narrowed, and in each non-narrow section 43, no such obstacle exists, and the entire opening cross section of the processing liquid withdrawal pipe 33 becomes a flow path for the processing liquid 3.

[0064] If there is only one narrow portion 41 as described above, the treatment liquid 3 cannot be sufficiently decompressed, and the diameter of the bubbles generated by cavitation becomes too large, making it impossible to stably generate fine bubbles suitable for ultrasonic treatment. The number N of narrow portions 41 in the fine bubble generator 40 is preferably 10 or less. A number N of more than 10 narrow portions 41 is undesirable because it causes pressure loss and reduces the effect on the diameter of the fine bubbles. The number N of narrow portions 41 in the fine bubble generator 40 is more preferably 2 to 8, even more preferably 2 to 6, and even more preferably 2 to 4.

[0065] The presence of such narrow sections 41 in the treatment liquid withdrawal pipe 33 provides a more efficient reduced pressure zone in a negative pressure environment, making it possible to turn dissolved gas in the treatment liquid 3 into bubbles, and the generated bubbles can be made finer by repeatedly providing narrow sections 41. The negative pressure environment in the treatment liquid withdrawal pipe 33 is preferably within the range of −0.05 MPa to −0.10 MPa.

[0066] In the fine bubble generator 40 according to this embodiment, the opening cross-sectional area of ​​the inner diameter of the treated liquid withdrawal pipe 33 is set to A ０ The cross-sectional area of ​​the opening of the inner diameter of the treated liquid withdrawal pipe 33 at the ith narrow portion 41 (i is an integer of 1 or more and corresponds to the number of narrow portions 41) from the treatment tank 10 side to the circulation pump 31 side is A ｉ When this is done, A ｉ / A ０ The opening cross-sectional area ratio R of the i-th narrow portion 41 is expressed as ｉ are mutually independent and satisfy 0.10≦(A ｉ / A ０ )≦0.50.

[0067] Here, the opening cross-sectional area A ｉ is the maximum value of the area of ​​the portion that becomes an open flow path in the i-th narrow portion 41 (more specifically, the maximum value of the area of ​​the portion that becomes an open flow path when the i-th narrow portion 41 is projected onto a plane perpendicular to the tube axis direction).

[0068] In FIG. 2, each narrow portion 41 has a desired opening cross-sectional area ratio (A ｉ / A ０ 2, the opening cross-sectional area A of the narrow portion 41 in the first decompression release cycle 45 is 1 / 2. １ is the opening cross-sectional area A of the non-narrow portion 43 ０ For 0.10≦(A １ / A ０ )≦0.50. Similarly, the opening cross-sectional area A of the narrow portion 41 in the second pressure reduction / release cycle 45 satisfies the relationship expressed by ２ is the opening cross-sectional area A of the release area 43 ０ For 0.10≦(A２ / A ０ )≦0.50.

[0069] Opening cross-sectional area ratio (A ｉ / A ０ If the ratio of the cross-sectional area of ​​the opening (A) in each narrow portion 41 is less than 0.10, the flow path of the processing liquid 3 in the narrow portion 41 becomes too narrow, and as a result, a sufficient flow path cannot be secured, which causes a problem in circulating the processing liquid, and a breakdown may occur due to the load on the pump. ｉ / A ０ ) are each independently preferably 0.15 or more, more preferably 0.20 or more. ｉ / A ０ If the ratio of the cross-sectional area of ​​the opening (A ) of each narrow portion 41 is larger than 0.50, the flow path of the treatment liquid 3 in the narrow portion 41 becomes too wide, and as a result, sufficient pressure reduction cannot be achieved, and fine bubbles with an appropriate bubble diameter cannot be generated. ｉ / A ０ ) are each independently preferably 0.45 or less, more preferably 0.40 or less.

[0070] Furthermore, the results of the simulations conducted by the present inventors, which are shown below, revealed that negative pressure is generated starting from the edge of the obstacle (in the example shown in FIG. 2, the edge surrounded by the dashed line located on the treatment tank 10 side of the protruding member 401). Therefore, the protruding member 401 may have an edge shape as shown in FIG. 3. In the case of the protruding member 401 having the edge shape as shown in FIG. 3, negative pressure is generated starting from the portion where the size of the open flow path is narrowest. By shaping the protruding member 401 as shown in FIG. 3, it is possible to generate negative pressure more reliably.

[0071] The narrow portion 41 is not a protruding member 41 as shown in FIG. 2 or FIG. 3, but is a member having a desired opening cross-sectional area ratio (A ｉ / A ０) may be realized by an opening member 403 having one or more through holes formed therein so as to realize a desired opening cross-sectional area ratio (A ｉ / A ０ ) can be realized.

[0072] Furthermore, in order to more reliably prevent the treatment liquid 3 from flowing in a straight line, it is more preferable that the positions of the opening flow paths of adjacent narrow sections 41 do not overlap with each other when the treatment liquid withdrawal pipe 33 is viewed in the axial direction of the pipe.

[0073] 5, the narrow portion 41 may be a combination of the protruding member 401 as disclosed in Fig. 2 and Fig. 3 and the opening member 403 as disclosed in Fig. 4. That is, at least one of the narrow portions 41 may be realized by the protruding member 401 or the opening member 403.

[0074] Furthermore, at least one of the narrow portions 41 has a predetermined opening cross-sectional area ratio (A ｉ / A ０ 6, one narrow portion 41 is realized by the opening member 403, but the other narrow portion 41 may be realized by the protruding member 401.

[0075] The inventors constructed various models of a fine bubble generator 40 having two pressure reduction / release cycles 45 arranged in series, an example of which is shown in Figure 7, and performed various simulations of the fine bubble generator 40 using COMSOL Multiphysics, a commercially available general-purpose physical simulation software.

[0076] Here, as shown in FIG. 7, each narrow portion of the fine bubble generator 40 is realized by a protruding member 401, and the opening cross-sectional area of ​​each narrow portion is defined as A １ , A ２ The cross-sectional area of ​​the opening in the non-narrow portion (the cross-sectional area of ​​the opening of the treatment liquid withdrawal pipe 33) is defined as A ０ The cross-sectional area of ​​the opening in the non-narrow portion A ０ The inner diameter D of the treatment liquid withdrawal pipe 33 ０ was set to 50 mm. The first narrow portion and the second narrow portion were adjacent to each other with a separation distance L of 100 mm. Here, the separation distance L was the distance between the centers of the adjacent narrow portions. The pressure of the processing liquid 3 in the first narrow portion and the first non-narrow portion was set to P １ , P １ ', and the pressure of the processing liquid 3 in the second narrow portion and the second non-narrow portion is P ２ , P ２ '

[0077] Here, five types of fine bubble generator 40 models constructed in this simulation are shown in Figure 8, and models No. 4 and No. 5 are models of fine bubble generators 40 that are outside the scope of the present invention. In each model, the opening cross-sectional area ratio (A １ / A ０ ), (A ２ / A ０ 8, the pressure on the inlet side of the fine bubble generator 40 was set to a common value of 0 MPa, and the flow velocity of the treatment liquid 3 on the outlet side was set to a common value of 0.15 m / sec. In the simulations below, the inlet pressure of the fine bubble generator 40 was set to 0 Pa, so that a negative pressure was not created. However, it was separately confirmed that even when a negative pressure was created, the relationship of the pressure difference (gap) at each position shown below was maintained.

[0078] The particle size (average bubble diameter) of fine bubbles (sometimes abbreviated as "FB") at the outlet side of the fine bubble generator 40 obtained by this simulation is also shown in Figure 8. Furthermore, the changes in pressure inside the fine bubble generator 40 for models No. 1, No. 2, No. 3, No. 4, and No. 5 are shown in Figures 9A to 9E. Furthermore, the pressure distribution inside the fine bubble generator 40 for models No. 1, No. 2, No. 3, and No. 5 is shown in Figures 10A to 10D.

[0079] First, let us refer to the results shown in Fig. 9A for the model shown in No. 1 in Fig. 8. The treatment liquid 3 flowing into the fine bubble generator 40 from the inlet side thereof is condensed into the first narrow part by the P １ After the pressure is reduced to about −180 Pa, in the first non-narrow portion, １ The pressure rises to about −80 Pa to −60 Pa, and in the second narrow portion, P ２ After the pressure is further reduced to about −240 Pa, in the second non-narrow portion, ２ It can be seen that the pressure rose to approximately -140 Pa to -80 Pa. Furthermore, from Figure 8, it can be seen that the particle size of the fine bubbles obtained at this time was 0.010 mm (=10 μm). Furthermore, when attention is paid to the pressure distribution shown in Figure 10A, it can be seen that the starting points of the isobars (line segments connecting positions showing the same pressure value) in Figure 10A are end points located on the upstream side of the protruding member 401, and as mentioned earlier, it can be seen that negative pressure is generated with the edge of the obstacle (the edge of the protruding member 401 located on the treatment tank 10 side) as the starting point.

[0080] For the model shown in No. 2 of Fig. 8, the results shown in Fig. 9B are referred to. The treatment liquid 3 flowing into the fine bubble generator 40 from the inlet side thereof is condensed into the first narrow part by the flow of P １ After the pressure is reduced to about P = -140 Pa, the pressure is released in the first non-narrowed portion, and the pressure is released in the second narrowed portion. ２It can be seen that after the pressure was further reduced to approximately -280 Pa, the pressure was released in the second non-narrow section. Furthermore, from Figure 8, it can be seen that the particle size of the fine bubbles obtained at this time was 0.050 mm (=50 μm). Furthermore, when focusing on the pressure distribution shown in Figure 10B, as with Model No. 1, the starting points of the isobars in Figure 10B (line segments connecting positions showing the same pressure value) for this model are end points located upstream of the protruding member 401, and as mentioned previously, it can be seen that negative pressure is generated with the edge of the obstacle (the edge of the protruding member 401 located on the treatment tank 10 side) as the starting point.

[0081] For the model shown in No. 3 of Fig. 8, the results shown in Fig. 9C are referred to. The treatment liquid 3 flowing into the fine bubble generator 40 from the inlet side thereof is condensed into the first narrow part by the flow of P １ After the pressure is reduced to about P = -260 Pa, the pressure is released in the first non-narrow portion, and the pressure is also released in the second narrow portion. ２ It can be seen that after the pressure was further reduced to approximately -260 Pa, the pressure was released in the second non-narrow section. Furthermore, from Figure 8, it can be seen that the particle size of the fine bubbles obtained at this time was 0.005 mm (=5 μm). Furthermore, focusing on the pressure distribution shown in Figure 10C, in this model as well, as in Model No. 1, the starting points of the isobars in Figure 10C (line segments connecting positions showing the same pressure value) are end points located upstream of the protruding member 401, and as mentioned previously, it can be seen that negative pressure is generated with the edge of the obstacle (the edge of the protruding member 401 located on the treatment tank 10 side) as the starting point.

[0082] On the other hand, for the model shown in No. 4 of Fig. 8, in which the protruding member 401 is provided so that the treatment liquid 3 moves in a straight line, the results shown in Fig. 9D are referred to. The treatment liquid 3 that flows into the fine bubble generator 40 from the inlet side thereof passes through the first narrow part. １ After the pressure is reduced to about −180 Pa, in the first non-narrow portion, １ The pressure rises to about −90 Pa to −70 Pa, and in the second narrow portion, P ２After the pressure is reduced to about −140 Pa, in the second non-narrow portion, ２ It can be seen that the pressure rose to about −120 Pa to −70 Pa. Furthermore, it can be seen from FIG. 8 that the particle size of the fine bubbles obtained at this time was 0.200 mm (=200 μm).

[0083] Also, for the model No. 5 in Fig. 8, which has a structure similar to that of a conventional Venturi tube, the results shown in Fig. 9E are referenced. In this case, the treatment liquid 3 flowing into the fine bubble generator 40 from the inlet side thereof is compressed into the first narrow part, １ After the pressure is reduced to about −65 Pa, in the first non-narrow portion, １ It can be seen that the pressure is released to approximately ' = -35 Pa. Furthermore, it can be seen from FIG. 8 that the particle size of the fine bubbles obtained at this time was 5.00 mm. Furthermore, when focusing on the pressure distribution shown in FIG. 10C, in this model as well, the starting point of the isobaric lines in FIG. 10D is the end point located upstream of the protruding member 401.

[0084] FIG. 11 also shows the simulation results for the pressure values ​​in each narrow portion and non-narrow portion and the particle size of the fine bubbles obtained for the five types of models shown in FIG. 8 .

[0085] As mentioned previously, the fine bubble generator 40 according to this embodiment preferably generates fine bubbles with a particle size (average bubble diameter) of 100 μm or less. On the other hand, while models No. 1, No. 2, and No. 3 are able to generate fine bubbles with an average bubble diameter of 100 μm or less, models No. 4 and No. 5 are unable to generate fine bubbles with an average bubble diameter of 100 μm or less.

[0086] Comparing these results, it can be seen that in the model with an average bubble diameter of 100 μm or less, the pressure value in the second narrow section is sufficiently smaller than the pressure value in the first narrow section, while in the model with an average bubble diameter of more than 100 μm, the pressure value in the second narrow section is greater than the pressure value in the first narrow section. It can also be seen that it is preferable for the pressure values ​​in both the first and second narrow sections to be sufficiently small in two or more decompression / release cycles. It can also be seen that this result can be achieved by reducing the opening cross-sectional area ratio on the inlet side of the fine bubble generator 40.

[0087] 8, the separation distance L was set to 100 mm, and the flow rate of the treatment liquid 3 was set to 0.15 m / sec., and the inner diameter D ０ The simulation results when the inner diameter D of the treated liquid withdrawal pipe 33 was changed to four types, 25 mm, 50 mm, 100 mm, and 200 mm, are shown in FIG. ０ is the opening cross-sectional area A of the inner diameter of the treated liquid withdrawal pipe 33 ０ Using 2 × (A ０ / π) ０．５ It can also be expressed as:

[0088] In FIG. 12, the distance L / inner diameter D of the drawn pipe ０ When the relationship between the particle size of fine bubbles (average bubble diameter) and the particle size of fine bubbles is plotted on the horizontal axis, 1.0≦L / D ０ It can be seen that the particle size of the fine bubbles becomes 100 μm or less within the range of ≦5.0. ２ L / D becomes smaller ０ It can be seen that the particle size of fine bubbles becomes smaller when L / D = 2.0. ０ If the L / D ratio is less than 1.0, a sufficient pressure difference is not generated in the decompression section, and fine bubbles cannot be generated. ０ By satisfying this relationship, it is possible to achieve a particle size of fine bubbles of 100 μm or less. ０ The value of L / D is preferably 1.5 or more or 2.0 or more. ０ Or 2.0≦L / D０ On the other hand, when 5.0<L / D ０ Even within this range, fine bubbles with a particle size of 100 μm or less can be generated, but the pressure difference tends to be small, and the longer the separation distance L, the longer the piping required, which is not preferable from the viewpoint of restrictions on device installation. ０ The value of is preferably 4.5 or less, more preferably 4.0 or less.

[0089] In the above simulation, the inner diameter D ０ Even if the inner diameter is doubled, the same results as described above can be obtained by doubling the separation distance L and quadrupling the flow rate, and the average bubble diameter and bubble density of the fine bubbles do not change compared to the original inner diameter.

[0090] In addition, when the number of narrow sections was set to two or more, a similar simulation was conducted. As a result, it was revealed that in two or more decompression release cycles, the pressure values ​​of the first narrow section located closest to the treatment tank 10 and the second narrow section located downstream of the first narrow section (located adjacent to the first narrow section) both become smaller, which is effective in further miniaturizing the fine bubbles.

[0091] In addition to the above, it is preferable that the ratio of the cross-sectional area of ​​the opening located closer to the circulation pump 31 to the cross-sectional area of ​​the opening on the inlet side of the fine bubble generator 40 is 1.10 or more.

[0092] That is, when the number of narrow portions is N, the opening area ratio R of the Nth narrow portion from the treatment tank 10 side toward the circulation pump 31 side is Ｎ It is preferable that the following formulas (151) and (153) are satisfied.

[0093] R ｉ＋１ ≧R ｉ ...Formula (151) R Ｎ / R １ ≧1.10...Formula (153)

[0094] By satisfying both the above formula (151) and formula (153), it is possible to further reduce the pressure value in the narrow portion, making degassing even easier and also making it possible to further reduce the particle size of the fine bubbles. Ｎ / R １ The value is more preferably 1.25 or more.

[0095] Next, the flow velocity V of the treatment liquid 3 in the treatment liquid withdrawal pipe 33 and the fine bubble generator 40 will be considered. Here, considering stable circulation of the treatment liquid 3, the flow velocity V is preferably at least 0.05 m / sec or more. On the other hand, if the flow velocity V is set to a value exceeding 5 m / sec, the circulation pump 31 will become larger and the flow velocity V will become too fast, which may result in damage to the fine bubble generator 40. Therefore, in this embodiment, the flow velocity V of the treatment liquid 3 in the treatment liquid withdrawal pipe 33 and the fine bubble generator 40 is preferably set to 0.050 m / sec or more and 5,000 m / sec or less.

[0096] Here, for the model shown in No. 1 of Fig. 8, simulation results when the flow velocity of the treatment liquid 3 was changed to 0.075 m / sec, 0.150 m / sec, and 0.300 m / sec are shown in Fig. 13. As can be seen from Fig. 13, the pressure value P ２ It can be seen that as the diameter of the fine bubbles generated decreases, the particle size (average bubble diameter) also decreases.

[0097] The bubble density of the fine bubbles in the treatment liquid 3 is determined by the volume of the treatment liquid [m ３ ] / circulation flow rate (=flow rate [m / min] x (piping inner diameter D ０ [m] / 2) ２ By appropriately controlling the value of (π) × number of circulation paths × time [min], it is possible to adjust the value to the desired range. By setting the above range within the range of 0.03 to 6.70, it is possible to more reliably achieve an appropriate fine bubble density. The above range is more preferably within the range of 0.05 to 6.00.

[0098] The above description focuses on the various conditions in the treatment liquid withdrawal pipe 33 and the fine bubble generator 40 in this embodiment, but the conditions in the treatment liquid 3 will be considered below.

[0099] Figure 14 shows the relationship between the dissolved gas concentration (%) in the treatment liquid 3 (e.g., water) and the particle size (average bubble diameter) of fine bubbles present in the treatment liquid 3. As is clear from Figure 14, the particle size of fine bubbles changes depending on the dissolved gas concentration in the treatment liquid 3 (in other words, the degassing state of the treatment liquid 3), and it is clear that the particle size of fine bubbles can be controlled to a desired state by controlling the dissolved gas concentration in the treatment liquid 3. As is clear from Figure 14, in order to keep the particle size of fine bubbles 100 μm or less, it is preferable to keep the dissolved gas concentration in the treatment liquid 3 50% or less.

[0100] Here, the dissolved gas concentration (i.e., the amount of dissolved gas) in the treatment liquid 3 can be changed by changing the flow velocity V of the treatment liquid 3 or by changing the opening cross-sectional area ratio (A ｉ / A ０ ) can be adjusted to a value within a desired range. For example, by increasing the output of the circulation pump 31 to increase the flow velocity V of the treatment liquid 3, the generated negative pressure can be increased and the dissolved gas concentration can be reduced. In addition, the opening cross-sectional area ratio (A ｉ / A ０ ), the generated negative pressure can be increased and the dissolved gas concentration can be reduced. In this case, the amount of dissolved gas can be measured downstream of the fine bubble generating mechanism 40 according to this embodiment using the known device described above, and the above-mentioned control conditions can be adjusted until the amount of dissolved gas falls within a desired range. Note that the flow velocity V of the treatment liquid 3 and the opening cross-sectional area ratio (A ｉ / A ０ ) should be adjusted first, and the control condition that is easier to adjust may be adjusted first. By adjusting the amount of dissolved gas in the treatment liquid 3 in the above-mentioned manner, the average bubble diameter and concentration (density) of the generated fine bubbles can be adjusted to values ​​within the desired range.

[0101] The circulation path 30 and the fine bubble generating mechanism 40 according to this embodiment have been described in detail above with reference to FIGS. 2 to 14.

[0102] 1A and 1B, the curved member 50 according to this embodiment will be briefly described. The curved member 50 is a member having a curved surface that is convex toward the vibration surface of the ultrasonic generator 20, and is a member that reflects ultrasonic waves that reach the curved member 50 in multiple directions. By providing such a curved member 50 on at least one of the wall surface and bottom surface of the treatment tank 10, it becomes possible to propagate ultrasonic waves generated from the vibration surface of the ultrasonic generator 20 throughout the treatment tank 10. Note that the curved member 50 may be provided as needed, and the curved member 50 may not be present in the ultrasonic treatment device 1 according to this embodiment.

[0103] More specifically, the curved member 50 according to this embodiment has at least a convexly curved portion having a spherical or aspherical surface shape, and the convexly curved portion has a convex curved surface that protrudes further toward the vibration surface of the ultrasound application mechanism 20 than the remaining portions. The curved member 50 according to this embodiment may also have a non-convexly curved portion that is not a convexly curved portion, or may be composed solely of a convexly curved surface. Furthermore, the curved member 50 according to this embodiment may be a solid columnar body or a hollow cylindrical body. When the curved member 50 is hollow, various gases such as air or various liquids such as the treatment liquid 3 held in the treatment tank 10 may be present in the voids of the curved member 50 when it is attached to the treatment tank 10.

[0104] By having the convex curved surface of the curved member 50 as described above, ultrasonic waves are reflected in multiple directions, achieving uniform ultrasonic propagation without bias and suppressing interference between ultrasonic waves. Here, if the curved member 50 includes a concave portion, the ultrasonic waves are reflected at the concave portion and focused, and the ultrasonic waves cannot be effectively reflected throughout the treatment tank 10. Furthermore, even if the curved member 50 includes a convex portion, if the convex portion is flat rather than curved, the ultrasonic waves can only be reflected in one direction, and the ultrasonic waves cannot be effectively reflected throughout the treatment tank 10.

[0105] The curved member 50 having the above-described shape is preferably formed using a material that reflects ultrasonic waves. Such a material may have an acoustic impedance (specific acoustic impedance) of 1×10 or less. ７ [kg m －２ ・sec －１ ] or more 2 x 10 ８ [kg m －２ ・sec －１ Examples of materials include those with an acoustic impedance of 1×10 ７ [kg m －２ ・sec －１ ] or more 2 x 10 ８ [kg m －２ ・sec －１ By using a material that has a coefficient of reflection of 0.1 or less, it is possible to efficiently reflect ultrasonic waves.

[0106] Acoustic impedance is 1 x 10 ７ [kg m －２ ・sec －１ ] or more 2 x 10 ８ [kg m －２ ・sec －１ ] or less, for example, various metals or metal oxides, and various ceramics including non-oxide ceramics, etc. Specific examples of such materials include steel (with a specific acoustic impedance [kg m －２ ・sec －１ ]: 4.70 x 10 ７ , hereinafter, the values ​​in parentheses similarly represent the values ​​of specific acoustic impedance.), iron (3.97 × 10 ７ ), stainless steel (SUS, 3.97 x 10 ７ ), titanium (2.73 x 10 ７ ), zinc (3.00 x 10 ７ ), Nickel (5.35 x 10 ７ ), aluminum (1.38 x 10 ７ ), tungsten (1.03 × 10 ８ ), glass (1.32 x 10 ７ ), quartz glass (1.27 × 10 ７ ), glass lining (1.67 x 10 ７), alumina (aluminum oxide, 3.84 x 10 ７ ), zirconia (zirconium oxide, 3.91 × 10 ７ ), silicon nitride (SiN, 3.15 × 10 ７ ), silicon carbide (SiC, 3.92 × 10 ７ ), tungsten carbide (WC, 9.18 × 10 ７ In the curved member 50 according to this embodiment, the material used to form the curved member 50 may be appropriately selected depending on the properties of the treatment liquid 3 held in the treatment tank 10, the strength required for the curved member 50, and the like, but it is preferable to use various metals or metal oxides having the above-mentioned acoustic impedance.

[0107] The curved member 50 according to this embodiment has been briefly described above.

[0108] The overall configuration of the ultrasonic processing device 1 according to this embodiment has been described in detail above with reference to FIGS. 1A to 14.

[0109] In the above explanation, an example was given in which an object to be treated immersed in a treatment liquid 3 is placed inside a treatment tank 10 provided as a treatment section, and ultrasonic waves are applied indirectly to the object to be treated via the treatment liquid 3 held in the treatment tank 10. However, the ultrasonic generator 20 may also apply ultrasonic waves directly to the object to be treated filled with a treatment liquid inside the treatment section.

[0110] For example, the object to be treated may be a hollow member itself that is filled with liquid, such as a pipe installed inside a heat exchanger or a connecting pipe that connects multiple pieces of equipment that use liquid. In such cases, fine bubbles are generated in the liquid held inside the hollow member, and then ultrasonic waves are applied to the hollow member itself.

[0111] Next, the ultrasonic processing device and ultrasonic processing method according to the present invention will be specifically described with reference to examples and comparative examples. Note that the examples shown below are merely examples of the ultrasonic processing device and ultrasonic processing method according to the present invention, and the ultrasonic processing device and ultrasonic processing method according to the present invention are not limited to the examples shown below.

[0112] (Experimental Example 1) Figure 15 is a diagram of an apparatus used to verify the relationship between various fine bubble generators and the amount of dissolved gas. In this experimental example, purified water was used as the treatment liquid 3. The treatment tank 10 had an outer wall made of SUS and a capacity of 0.1 m, with dimensions of 0.5 m wide x 0.5 m long x 0.4 m. ３ The treatment tank 10 was provided with a circulation path 30 including a circulation pump 31, a treatment liquid withdrawal pipe 33, and a treatment liquid discharge pipe 35. The circulation pump 31 was a general-purpose pump, manufactured by IWAKI, model MD-40RZ, MD-70RZ, or MD-100R. The inner diameter D of the treatment liquid withdrawal pipe 33 was ０ As a result, the negative pressure environment in the treatment liquid withdrawal pipe 33 was in the range of −0.05 MPa to −0.10 MPa.

[0113] Furthermore, fine bubble generators 40 having the structure shown in Figure 16 were prepared as jigs that could be attached to and detached from the treated liquid withdrawal pipe 33, and these jigs could be connected in series to the treated liquid withdrawal pipe 33. In structures a, b, and e in Figure 16, the open flow paths of the narrowed sections do not overlap in the axial direction as shown in Figure 2, and in structure d, the open flow paths do not overlap in the axial direction as shown in Figure 3. Furthermore, in structures c and g, the two cross sections have different shapes in the axial direction, but similarly the open flow paths of the narrowed sections do not overlap. In structure f, the open flow paths of some narrowed sections overlap as shown in Figure 4. In fine bubble generators 40 with multiple consecutive narrowed sections, the separation distance L was set to 10 mm, 20 mm, 50 mm, 100 mm, and 120 mm. Furthermore, a flow meter was attached to the treated liquid withdrawal pipe 33 to measure the flow rate of the treated liquid withdrawal pipe 33. The flow velocity (m / s) of the treatment liquid 3 was calculated by dividing the measured flow rate by the inner diameter cross-sectional area of ​​the pipe.

[0114] Furthermore, regarding the pressure change during the decompression / release cycle in each fine bubble generator 40, the pressure difference between the decompression zone and the release zone when the treatment liquid 3 flowed at a flow rate of 0.15 m / s was calculated using COMSOL Multiphysics, a commercially available fluid analysis software.

[0115] The average bubble diameter of the fine bubbles was determined by measuring the solution in the treatment tank 10 using a Beckman Coulter precision particle size distribution analyzer Multisizer 4 and a Malvern nanoparticle analyzer NanoSight LM10. The amount of dissolved gas was measured using a HORIBA dissolved oxygen meter LAQUA OM-51. The amount of dissolved oxygen (DO) was measured every minute as a value proportional to the amount of dissolved gas, and the amount of dissolved gas (%) relative to the dissolved saturation amount was estimated. More specifically, the amount of dissolved oxygen (DO) was measured every minute, and the difference ΔDO from the amount of dissolved oxygen measured previously was calculated. When the ΔDO value was less than 0.1 for each of the three consecutive minutes, it was determined that the amount of dissolved oxygen had reached the lower limit, and the amount of dissolved oxygen and the average bubble diameter at that time were compared.

[0116]

[0117] The results obtained are also shown in Table 1. In the column of "narrow portion opening cross-sectional area ratio" in Table 1, the narrow portion opening cross-sectional area ratio R Ｎ The value of is shown at the leftmost position in the column, and the narrow portion opening cross-sectional area ratio R ０ The value of is shown at the rightmost position in the column, and when there are multiple narrow sections with the same narrow section opening cross-sectional area ratio, the notation is simplified, for example, as "0.50 x 4". Furthermore, under the condition where there are multiple narrow sections, the value obtained from the combination that gives the maximum opening cross-sectional area ratio is used as R Ｎ / R １ It was decided.

[0118] First, looking at the comparative examples, in Comparative Example 1, where there was no decompression release cycle and the flow path was simply narrowed, it was possible to reduce the amount of dissolved gas, but the average bubble diameter remained large without forming fine bubbles. In Comparative Examples 2 and 3, where a decompression release cycle was provided and the flow path was straight, the average bubble diameter was large, almost the same as in Comparative Example 1. In addition, the separation distance ratio L / D ０In Comparative Example 4, where the ratio was less than 1.0, and Comparative Example 5, where the ratio was greater than 5.0, the average bubble diameter did not reach 100 μm or less, which is the level at which fine bubbles can be considered. Furthermore, in Comparative Examples 6 and 7, where the opening cross-sectional area ratio of the narrow portion was greater than 0.50, the pressure did not decrease and almost no bubbles were generated. In Comparative Examples 8 and 9, where the opening cross-sectional area ratio of the narrow portion was less than 0.10, almost no liquid was available for circulation, so no bubbles were generated, or the circulation pump ran idly, making it impossible to pump the liquid at all.

[0119] On the other hand, in Examples 1 to 7, in which two or more pressure reduction / release cycles were installed and the separation distance ratio of the narrowed portion, which was set so that the open flow path did not move in a straight line, was within a predetermined range, Examples 8 to 9, in which the number of pressure reduction / release cycles was increased, and Examples 10 to 14, in which the shape of the narrowed portion was changed, the average bubble diameter was 100 μm or less, which can be considered as fine bubbles. At the same time, it was observed that the amount of dissolved gas also decreased. In particular, by narrowing the narrowed portion on the side of the pressure reduction / release cycle near the pump, R １ / R Ｎ In Examples 15 to 18, which satisfied the relationship of ≧1.10, the pressure difference between the decompression and release periods increased, and a decrease in dissolved gas and fine bubbles were observed, with the bubbles becoming finer to several μm or less, resulting in an increase in bubble density.

[0120] 17A and 17B are explanatory diagrams showing a schematic diagram of a water-rinsing treatment of a steel plate using an ultrasonic treatment apparatus according to the present invention. Purified water was used as the rinse solution, which is the treatment liquid 3. The treatment tank 10 has an outer wall made of SUS and a capacity of 7 m, with dimensions of 2.0 m wide x 7 m long x 0.5 m. ３ The steel plate to be treated was held by the rolls.

[0121] 17B, ​​two circulation paths 30 each having a circulation pump 31, a treatment liquid withdrawal pipe 33, and a treatment liquid discharge pipe 35 were provided in the treatment tank 10. Two general-purpose pumps, MEP-0505-2P manufactured by Seiko Kakoki Co., Ltd., were used as the circulation pumps 31. The inner diameter D of the treatment liquid withdrawal pipe 33 was ０ As a result, the negative pressure environment in the treatment liquid withdrawal pipe 33 was in the range of −0.05 MPa to −0.10 MPa.

[0122] 16, fine bubble generators 40 having the structures shown in Table 2 below were prepared as jigs that could be attached to and detached from the treatment liquid withdrawal pipe 33, and these jigs were arranged to be connectable in series to the treatment liquid withdrawal pipe 33. In the fine bubble generators 40 having multiple consecutive narrow sections, the separation distances L were set to 20 mm, 40 mm, 100 mm, 200 mm, and 300 mm. Furthermore, a flow meter was attached to the treatment liquid withdrawal pipe 33 to measure the flow rate of the treatment liquid withdrawal pipe 33 and control the flow rate of the treatment liquid 3 so that it was within the preferred range mentioned earlier.

[0123] The ultrasonic oscillator of the ultrasonic generator 20 had an output of 1200 W and an ultrasonic frequency of 35 kHz. Five SUS immersion vibrators were arranged on one long side wall of the treatment tank 10 as shown in Fig. 17B, and ultrasonic waves were applied to the treatment liquid 3.

[0124] The average bubble diameter of the fine bubbles was determined by measuring the solution in the treatment tank 10 using a Beckman Coulter precision particle size distribution analyzer Multisizer 4 and a Malvern nanoparticle analyzer NanoSight LM10. The amount of dissolved gas was measured using a HORIBA dissolved oxygen meter LAQUA OM-51. The amount of dissolved oxygen (DO) was measured every minute as a value proportional to the amount of dissolved gas, and the amount of dissolved gas (%) relative to the dissolved saturation amount was estimated. More specifically, the amount of dissolved oxygen (DO) was measured every minute, and the difference ΔDO from the amount of dissolved oxygen measured previously was calculated. When the ΔDO value was less than 0.1 for each of the three consecutive minutes, it was determined that the amount of dissolved oxygen had reached the lower limit, and the amount of dissolved oxygen and the average bubble diameter at that time were compared.

[0125] In this experimental example, as shown schematically in Figure 18, an ultrasonic level monitor (Kaijo 19001D) was used to measure the ultrasonic intensity (mV) at a total of 26 locations at 0.5 m intervals, and the relative ultrasonic intensity (the relative intensity when the measurement result of Comparative Example 1, i.e., the measured ultrasonic intensity when the decompression release cycle was not performed, was taken as 1) and standard deviation (σ) were calculated to compare the ultrasonic propagation throughout the treatment tank 10.

[0126] In this experimental example, a steel plate on which an oxide scale film had been formed and which had been pickled was prepared as the object to be treated, and the steel plate on whose surface oxide fine particles had adhered was rinsed using the treatment tank 10 described above.

[0127] In this experimental example, the removal rate of oxide particles on the surface of the steel sheet was measured, and the measured removal rate of oxide particles was evaluated as cleaning performance. More specifically, the ratio of the amount of oxide particles removed under each condition to the total amount of oxide particles adhering to the surface of the steel sheet before and after water rinsing was calculated as follows, and this was taken as the removal rate of oxide particles.

[0128] That is, a steel plate sample (5 cm × 10 cm) on which an oxide scale film had been formed was attached to a steel plate held by a roll, and cleaning performance was evaluated. The steel plate sample was pickled, pre-washed with water, and dried. Then, using two pieces of general-purpose cellophane tape (15 mm wide × 5 cm long) whose mass had been measured in advance, oxide fine particles adhering to the steel plate surface were peeled from two locations, and the measured mass of the tape before rinsing was recorded. In addition, tape peeling was performed in the same manner after rinsing at a location different from the location where it was peeled before rinsing, and the mass of the peeled tape was measured.

[0129] The value obtained by subtracting the pre-measured tape mass from the tape measurement value before rinsing corresponds to the total amount of oxide fine particles, and the value obtained by subtracting the pre-measured tape mass from the tape measurement value after rinsing corresponds to the remaining amount of oxide fine particles. Therefore, the value obtained by subtracting the remaining amount of oxide fine particles from the total amount of oxide fine particles is the amount of oxide fine particles removed. The ratio of the amount of oxide fine particles removed under each condition to the total amount of oxide fine particles was defined as the oxide fine particle removal rate. The steel sheet sample was attached between rolls and then removed, and the removal rate was calculated at a sheet running speed of 100 mpm. The evaluation criteria for cleaning performance in Table 2 below are as follows:

[0130] Oxide particulate removal rate AA: 100% or less to 95% or more A: Less than 95% to 90% or more AB: Less than 90% to 85% or more B: Less than 85% to 80% or more C: Less than 80% to 60% or more D: Less than 60% to 40% or more E: Less than 40%

[0131] That is, the ratings "AA" and "A" indicate that the cleaning performance was very good, the ratings "AB" and "B" indicate that the cleaning performance was good, the rating "C" indicates that the cleaning performance was somewhat poor, and the ratings "D" and "E" indicate that the cleaning performance was poor.

[0132]

[0133] The results obtained are also shown in Table 2. The notation methods in the columns "narrow portion opening cross-sectional area ratio" and "opening cross-sectional area ratio" are the same as in Table 1.

[0134] First, referring to the comparative examples, under conditions where the water was simply circulated (Comparative Example 1), the amount of dissolved gas could not be reduced, and no bubbles were generated. Therefore, although the intensity near the ultrasonic oscillation was high, the ultrasonic waves did not propagate to other locations, and the standard deviation, which is an index of variation, exceeded 20 for an ultrasonic intensity of 33 mV, indicating that the ultrasonic waves were not propagated uniformly. Furthermore, in Comparative Examples 2 and 3, where the flow path was simply narrowed without a decompression / release cycle, the amount of dissolved gas could be reduced, but the bubble diameter did not become fine bubbles. The relative ultrasonic intensity at this time was almost the same as in Comparative Example 1, and the water washing performance was poor. In Comparative Examples 4 and 5, where a decompression / release cycle was provided and the flow path was in a straight line, the relative ultrasonic intensity increased by 1.3 times, but the standard deviation of the ultrasonic intensity was large. In these comparative examples, the water washing performance was also insufficient, resulting in uneven cleaning. Furthermore, the narrow portion spacing L / D ０In Comparative Examples 6 to 8, where the ratio was less than 1.0 or more than 5.0, fine bubbles were not generated, the standard deviation of the ultrasonic intensity increased, the water washing performance was insufficient, and uneven washing occurred. In Comparative Example 9, where the opening cross-sectional area ratio of the narrow portion was less than 0.10, there was almost no liquid that could be circulated, so no bubbles were generated, or the circulation pump ran idle, making it impossible to send liquid at all. In Comparative Example 10, where the opening cross-sectional area ratio was more than 0.50, almost no bubbles were generated. The relative ultrasonic intensity at this time was the same as in Comparative Example 1, and the water washing performance was also poor.

[0135] On the other hand, in Examples 1 to 6, in which two or more pressure reduction / release cycles were installed, there were narrowed sections that prevented the opening flow path from moving in a straight line, and the intervals between the narrowed sections were within a predetermined range, Examples 7 to 9, in which the number of pressure reduction / release cycles was increased, and Examples 10 to 14, in which the shape of the narrowed sections was changed, the average bubble diameter was 100 μm or less, which can be considered fine bubbles. Furthermore, a decrease in the amount of dissolved gas was observed, the ultrasonic intensity was more than three times higher, the standard deviation was also smaller, and the cleaning performance was good. Furthermore, by narrowing the narrowed section on the side closer to the pump in the pressure reduction / release cycle, R １ / R Ｎ In Examples 15 to 18, which satisfied the relationship of ≧1.10, the pressure difference between the decompression and release periods increased, and a decrease in dissolved gas and fine bubbles were observed, with the bubbles becoming finer to several μm or less, resulting in an increase in bubble density.

[0136] 19A and 19B are explanatory diagrams showing the degreasing treatment of a steel pipe using the ultrasonic treatment device according to the present invention. The treatment tank 10 has a steel outer wall, a PTFE lining on the surface, and a capacity of 9 m2, with dimensions of 1.0 m wide x 15.0 m long x 0.6 m. ３ A steel pipe having oil on its surface was immersed in the treatment tank 10 for a predetermined period of time. An alkaline degreasing solution was used as the treatment liquid 3, which was the degreasing solution. Buffer materials (more specifically, hollow buffer pipes made of SUS304) that functioned as curved members were provided at intervals of 1 m between the steel pipe, which was the object to be cleaned, and the treatment tank 10.

[0137] 19B, two circulation paths 30 each having a circulation pump 31, a processing liquid withdrawal pipe 33, and a processing liquid discharge pipe 35 were installed on the short side of the processing tank 10. Two general-purpose pumps, MEP-0505-2P manufactured by Seiko Kakoki Co., Ltd., were used as the circulation pumps 31. The inner diameter D of the processing liquid withdrawal pipe 33 was ０ As a result, the negative pressure environment in the treatment liquid withdrawal pipe 33 was in the range of −0.05 MPa to −0.10 MPa.

[0138] A plurality of movable protruding members were arranged so as to protrude facing each other within the pipe, and were installed in series with the treated liquid withdrawal pipe 33 with separation distances L of 40 mm, 100 mm, 200 mm, and 300 mm to form a fine bubble generator 40. That is, this fine bubble generator 40 had the structure indicated by notation a in Figure 16. Furthermore, a flow meter was attached to the treated liquid withdrawal pipe 33 to measure the flow rate of the treated liquid withdrawal pipe 33 and control the flow rate of the treated liquid 3 so that it was within the preferred range mentioned earlier.

[0139] The ultrasonic generator 20 used an ultrasonic oscillator with an output of 1200 W and a frequency sweep function, and ten SUS immersion vibrators were installed on the longitudinal wall surface of the treatment tank 10. The ultrasonic frequency was 25 to 192 kHz.

[0140] The average bubble diameter of the fine bubbles was determined by measuring the solution in the treatment tank 10 using a Beckman Coulter precision particle size distribution analyzer Multisizer 4 and a Malvern nanoparticle analyzer NanoSight LM10. The amount of dissolved gas was measured using a HORIBA dissolved oxygen meter LAQUA OM-51. The amount of dissolved oxygen (DO) was measured every minute as a value proportional to the amount of dissolved gas, and the amount of dissolved gas (%) relative to the dissolved saturation amount was estimated. More specifically, the amount of dissolved oxygen (DO) was measured every minute, and the difference ΔDO from the amount of dissolved oxygen measured previously was calculated. When the ΔDO value was less than 0.1 for each of the three consecutive minutes, it was determined that the amount of dissolved oxygen had reached the lower limit, and the amount of dissolved gas and the average bubble diameter at that time were compared.

[0141] In this experimental example, buffer materials were placed at regular intervals inside the treatment tank 10 as shown in Figures 19A and 19B to prevent scratches on the steel pipes, and 20 steel pipes with an inner diameter of 40 mm and a length of 10 m were immersed in the center of the treatment tank 10 to perform cleaning evaluation.

[0142] In this experimental example, the oil removal rate on the steel sheet surface was measured, and the measured oil removal rate was evaluated as degreasing performance. More specifically, the amount of oil removed was calculated from the change in mass before and after cleaning, and the ratio of the amount of oil removed under each cleaning condition to the total amount of oil adhering to the steel sheet surface was defined as the oil removal rate. The evaluation criteria for degreasing performance in Table 3 below are as follows:

[0143] Oil removal rate AA: 100% or less - 95% or more A: Less than 95% - 90% or more AB: Less than 90% - 85% or more B: Less than 85% - 80% or more C: Less than 80% - 60% or more D: Less than 60% - 40% or more E: Less than 40%

[0144] That is, the ratings "AA" and "A" indicate that the degreasing performance was very good, the ratings "AB" and "B" indicate that the degreasing performance was good, the rating "C" indicates that the degreasing performance was somewhat poor, and the ratings "D" and "E" indicate that the degreasing performance was poor.

[0145]

[0146] The results obtained are also shown in Table 3. The notation methods in the columns "narrow portion opening cross-sectional area ratio" and "opening cross-sectional area ratio" are the same as in Table 1.

[0147] First, referring to the comparative examples, Comparative Examples 1 to 3 do not have two or more decompression release cycles according to the present invention, and the narrow portion interval L / D ０ Comparative Example 4 in which the narrow portion spacing L / D is less than 1.0 ０In Comparative Example 5, where the opening cross-sectional area ratio was greater than 5.0, no fine bubbles were generated and there were few bubbles smaller than the resonance diameter. In Comparative Example 6, where the opening cross-sectional area ratio was greater than 0.5, and Comparative Example 7, where the opening cross-sectional area ratio was less than 0.1, almost no fine bubbles were generated and there were few bubbles smaller than the resonance diameter for the ultrasonic frequency. In addition, the amount of dissolved gas was not reduced, and as a result, the degreasing performance was poor or areas were insufficiently cleaned.

[0148] On the other hand, Examples 1 to 15, which had two or more pressure reduction / release cycles and a narrow portion opening cross-sectional area ratio of 0.5 or less, had good cleaning performance, and Examples 1 to 5, which had a narrow portion spacing satisfying 1.0≦L / D≦5.0, had even better cleaning performance. Furthermore, Examples 12 to 15, which performed ultrasonic frequency sweeping, enabled more effective cleaning.

[0149] (Experimental Example 4) A vertical heat exchanger was used, with its outer wall made of SS (general structural rolled steel) and pipes with an inner diameter of 45 mm, a length of 3.0 m, and a thickness of 9 mm connected continuously to the inside. The pipes of this vertical heat exchanger were used as the object to be treated. In this experimental example, the inside of the pipes was filled with water, and the deposits adhering to the inner surface of the pipes were circulated for a predetermined period of time. In other words, in this experimental example, the pipes themselves, which were the object to be treated, functioned as the treatment section.

[0150] FIG. 20 is an explanatory diagram schematically illustrating the implementation of a cleaning process for piping in a heat exchanger using an ultrasonic processing device according to the present invention. As shown in FIG. 20 , a treatment liquid withdrawal pipe 33 was connected to one end of a pipe 11 installed inside the heat exchanger, and the treatment liquid withdrawal pipe 33 was connected to a circulation pump 31. The circulation pump 31 used was a general-purpose pump, the MEP-0505-2P manufactured by Seiko Chemical Engineering. As a result, the negative pressure environment within the treatment liquid withdrawal pipe 33 was within the range of −0.05 MPa to −0.10 MPa. Furthermore, two movable protruding members were arranged in series with the treatment liquid withdrawal pipe 33, protruding from the pipe so as to face each other within the pipe, forming a fine bubble generator 40. In other words, the fine bubble generator 40 had the structure indicated by notation a in FIG. 16 . Furthermore, a treatment liquid discharge pipe 35 was provided on the positive pressure side of the circulation pump 31 and connected to the other end of the pipe 11. In the fine bubble generator 40, the separation distance L was set to 40 mm, 100 mm, 200 mm, and 300 mm.

[0151] 20, an air vent valve 60 and a water supply valve 70 were provided for the treatment liquid discharge pipe 35, and the insides of pipe 11, the treatment liquid withdrawal pipe 33, the fine bubble generator 40, and the treatment liquid discharge pipe 35 were filled with water (more specifically, clean supply water) as the treatment liquid 3. Furthermore, a drain valve 80 was provided for the treatment liquid withdrawal pipe 33, so that a portion of the treatment liquid 3 flowing through the circulation path 30 as shown in FIG. 20 could be collected. A flow meter was attached to the treatment liquid withdrawal pipe 33 to measure the flow rate of the treatment liquid withdrawal pipe 33 and control the flow rate of the treatment liquid 3 to be within the preferred range mentioned earlier.

[0152] The ultrasonic generator 20 had an ultrasonic oscillator with a frequency of 30 kHz and an output of 600 W, and clamp-type SUS ultrasonic vibrators were attached to the connection between the pipe 11 and the treatment liquid withdrawal pipe 33, and to the connection between the pipe 11 and the treatment liquid discharge pipe 35, respectively, as shown schematically in FIG. 20 .

[0153] The average bubble diameter of the fine bubbles was determined by measuring the solution collected from the drain valve 80 using a Beckman Coulter precision particle size distribution analyzer Multisizer 4 and a Malvern nanoparticle analyzer NanoSight LM10. The amount of dissolved gas was measured using a HORIBA dissolved oxygen meter LAQUA OM-51. The amount of dissolved oxygen (DO) was measured every minute as a value proportional to the amount of dissolved gas, and the amount of dissolved gas (%) relative to the dissolved saturation amount was estimated. More specifically, the amount of dissolved oxygen (DO) was measured every minute, and the difference ΔDO from the amount of dissolved oxygen measured previously was calculated. When the ΔDO value was less than 0.1 for each of the three consecutive minutes, it was determined that the amount of dissolved oxygen had reached the lower limit, and the amount of dissolved gas and the average bubble diameter at that time were compared.

[0154] In this experimental example, the cleanliness inside the piping was measured and evaluated as cleaning performance. More specifically, 1 L of the treatment liquid was recovered from the drain valve 80 after 1 minute of cleaning, and the turbidity was measured using a turbidity meter TC-3000 manufactured by Optex Co., Ltd., and this was used as the cleanliness of the treatment liquid 3. The evaluation criteria for cleaning performance in Table 4 below are as follows:

[0155] Cleanliness (Turbidity) A: 3000 or less to 1500 or more B: Less than 1500 to 800 or more C: Less than 800 to 500 or more D: Less than 500 to 300 or more E: Less than 300 to 100 or more F: Less than 100 to 1 or more

[0156] That is, ratings "A" and "B" mean that the turbidity increased due to the successful recovery of sediments, and that the cleaning performance was very good; rating "C" means that the cleaning performance was good; rating "D" means that the cleaning performance was somewhat poor; and ratings "E" and "F" mean that the cleaning performance was poor.

[0157]

[0158] The results obtained are also shown in Table 4. The notation methods in the columns "narrow portion opening cross-sectional area ratio" and "opening cross-sectional area ratio" are the same as in Table 1.

[0159] First, looking at the comparative examples, Comparative Examples 1 and 2, which do not have two or more decompression release cycles according to the present invention, and narrow portion interval L / D ０ Comparative Example 3 in which the narrow portion spacing L / D is less than 1 ０ In Comparative Example 4, where the opening cross-sectional area ratio was greater than 5, almost no fine bubbles were generated, resulting in poor cleaning performance. In Comparative Example 5, where the opening cross-sectional area ratio was greater than 0.5, and Comparative Example 6, where the opening cross-sectional area ratio was less than 0.1, almost no fine bubbles were generated. In addition, the amount of dissolved gas was not reduced, resulting in poor cleaning performance.

[0160] On the other hand, Examples 1 to 6, in which two or more decompression release cycles are installed and the opening cross-sectional area ratio is within 0.5, have good cleaning performance, and in particular, when the narrow part interval is 1.0≦L / D ０ Examples 1 to 4, which satisfied the condition of ≦5.0, had even better cleaning performance.

[0161] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0162] REFERENCE SIGNS LIST 1 ultrasonic treatment device 3 treatment liquid 10 treatment tank 20 ultrasonic generator 30 circulation path 31 circulation pump 33 treatment liquid extraction piping 35 treatment liquid discharge piping 40 fine bubble generator 41 narrow section 43 non-narrow section 45 pressure reduction release cycle 50 curved member

Claims

1. A processing unit capable of storing a processing liquid and an object to be processed, an ultrasonic generator provided in the processing unit for applying ultrasonic waves to the object to be processed, and a circulation path for circulating the processing liquid in the processing unit. The circulation path includes a circulation pump for circulating the processing liquid, a processing liquid extraction pipe connecting the processing liquid extracted from the processing unit to the circulation pump, and a processing liquid discharge pipe for discharging the processing liquid that has passed through the circulation pump to the processing unit. In series with the processing liquid extraction pipe, a fine bubble generator is provided for degassing the extracted processing liquid and generating fine bubbles in the processing liquid. The fine bubble generator has two or more constricted portions where the size of the opening flow path of the processing liquid is narrower than the inner diameter of the processing liquid extraction pipe, and the opening flow paths of adjacent constricted portions are configured such that the processing liquid does not flow straight. Each constricted portion has an opening cross-sectional area A of the inner diameter of the processing liquid extraction pipe ０ as A, and when the opening cross-sectional area of the inner diameter of the processing liquid extraction pipe at the i-th (i is an integer of 1 or more) constricted portion from the processing unit side toward the circulation pump side is represented as A ｉ , when represented as A ｉ / A ０ , the opening cross-sectional area ratio R ｉ of the i-th constricted portion is satisfied by the following formula (1), and when the distance between the i-th constricted portion and the (i + 1)-th constricted portion is represented as L ｉ , the ultrasonic processing apparatus that satisfies the following formula (2). R ｉ = 0.10 to 0.50... Formula (1) 1.0 ≤ L ｉ / 2(A ０ / π) ０．５ ≤ 5.0... Formula (2) 2. The ultrasonic processing apparatus according to claim 1, wherein when the processing liquid extraction pipe is viewed in the pipe axis direction, the positions of the opening channels of the adjacent narrow portions do not overlap with each other.

3. The ultrasonic processing apparatus according to claim 1 or 2, wherein a processing tank for holding the processing liquid is provided as the processing unit, and the ultrasonic generator indirectly applies ultrasonic waves to the object to be processed through the processing liquid.

4. The ultrasonic processing apparatus according to claim 1 or 2, wherein the ultrasonic generator directly applies ultrasonic waves to the object to be processed immersed in the processing liquid within the processing unit.

5. Let the number of the constricted portions be N, and the Nth opening area ratio R from the processing unit side toward the circulation pump side Ｎ When expressed as, the ultrasonic treatment apparatus according to any one of claims 1 to 4, which satisfies the following formulas (3) and (4). R ｉ＋１ ≧R ｉ ... Formula (3) R Ｎ / R １ ≧1.10... Formula (4) 6. The ultrasonic processing apparatus according to any one of claims 1 to 5, wherein the number N of the narrow portions is 2 to 10.

7. The ultrasonic processing apparatus according to any one of claims 1 to 6, having one or more of the narrow portions formed by a protruding member protruding from the inner surface of the processing liquid extraction pipe.

8. The ultrasonic processing apparatus according to claim 7, wherein the narrow portion has a movable protruding member protruding from the inner surface of the processing liquid extraction pipe.

9. The ultrasonic processing apparatus according to any one of claims 1 to 8, having one or more of the narrow portions formed by an opening member provided with one or more through holes.

10. The ultrasonic processing apparatus according to any one of claims 1 to 9, wherein the ultrasonic generator can select the frequency of the ultrasonic waves from a frequency band of 20 kHz to 200 kHz.

11. The ultrasonic processing apparatus according to any one of claims 1 to 10, wherein the ultrasonic generator applies ultrasonic waves to the processing liquid while sweeping in a range of ±0.1 kHz to ±10 kHz centered on the selected frequency of the ultrasonic waves.

12. A method for supplying fine bubbles, which supplies a treatment liquid containing fine bubbles to a treatment unit that can store a treatment liquid and an object to be treated, while applying ultrasonic waves to the object to be treated. The treatment unit is provided with an ultrasonic generator that applies ultrasonic waves to the object to be treated and a circulation path for circulating the treatment liquid in the treatment unit. The circulation path includes a circulation pump for circulating the treatment liquid, a treatment liquid extraction pipe that connects the treatment liquid extracted from the treatment unit to the circulation pump, and a treatment liquid discharge pipe that discharges the treatment liquid that has passed through the circulation pump to the treatment unit. In series with the treatment liquid extraction pipe, a fine bubble generator is provided that degasses the extracted treatment liquid and generates fine bubbles in the treatment liquid. The fine bubble generator has two or more constricted portions where the size of the opening flow path of the treatment liquid is narrower than the inner diameter of the treatment liquid extraction pipe, and the opening flow paths of adjacent constricted portions are configured such that the treatment liquid does not flow straight. Each constricted portion has an opening cross-sectional area A of the inner diameter of the treatment liquid extraction pipe ０ as A, and when the opening cross-sectional area of the inner diameter of the treatment liquid extraction pipe at the i-th (i is an integer of 1 or more) constricted portion from the treatment unit side toward the circulation pump side is represented as A ｉ the opening cross-sectional area ratio R ｉ of the i-th constricted portion represented as A ０ / A ｉ satisfies the following formula (1), and when the distance between the i-th constricted portion and the (i + 1)-th constricted portion is represented as L ｉ the method for supplying fine bubbles that satisfies the following formula (2). R ｉ = 0.10 to 0.50... Formula (1) 1.0 ≤ L ｉ / 2(A ０ / π) ０．５ ≤ 5.0... Formula (2) 13. The method for supplying fine bubbles according to claim 12, wherein the fine bubble generator generates the fine bubbles such that the amount of dissolved gas in the processing liquid discharged into the processing unit is 50% or less of the saturated dissolved gas amount.

14. The fine bubble generator generates the fine bubbles such that, in the processing liquid discharged to the processing unit, the fine bubbles having an average bubble diameter of 1 μm to 100 μm are present in a range of bubble density of 1 × 10 ３ pieces / mL to 1 × 10 １０ pieces / mL. The method for supplying fine bubbles according to claim 12 or 13.

15. The method for supplying fine bubbles according to any one of claims 12 to 14, wherein the ultrasonic generator selects the frequency of the ultrasonic waves from a frequency band of 20 kHz to 200 kHz.

16. The method for supplying fine bubbles according to any one of claims 12 to 15, wherein the ultrasonic generator applies ultrasonic waves to the processing liquid while sweeping in a range of ±0.1 kHz to ±10 kHz centered on the selected frequency of the ultrasonic waves.