Patent Grant
11364474
The present invention relates to an ultrafine bubble generating method and an ultrafine bubble generating apparatus for generating ultrafine bubbles smaller than 1.0 μm in diameter.
Recently, there have been developed techniques for applying the features of fine bubbles such as microbubbles of micrometer-size in diameter and nanobubbles of nanometer-size in diameter. Especially, the utility of ultrafine bubbles (hereinafter also referred to as “UFBs”) smaller than 1.0 μm in diameter have been confirmed in various fields.
Japanese Patent Laid-Open No. 2014-104441 discloses a fine air bubble generating apparatus that generates fine bubbles by applying pressure continuously to a liquid in which a gas is pressurized and dissolved and squirting the pressurized liquid from a depressurizing nozzle. International Publication No. WO2009/088085 discloses an apparatus that generates fine bubbles by repeating separating and converging of flows of a gas-mixed liquid with a mixing unit.
The UFB generating apparatuses of Japanese Patent Laid-Open No. 2014-104441 and International Publication No. WO2009/088085 have a problem that both require continuous pressurizing of a liquid at a predetermined pressure to generate the UFBs, and also the sizes of the apparatuses are large to accommodate the complex flow passages, which increases the power consumption.
Additionally, in a case of generating the UFBs of nanometer-size in diameter, the conventional UFB generating apparatuses generate large air bubbles such as the milli-bubbles of millimeter-size in diameter and the microbubbles of micrometer-size in diameter as by-products, and it requires time to generate the UFBs due to the low generation efficiency. Moreover, a large container is required to take out the UFBs from the various sizes of bubbles, and this makes it difficult to downsize the apparatus.
The present invention is made in view of solving the above-described problems, and the present invention provides an ultrafine bubble generating method and an ultrafine bubble generating apparatus capable of efficiently generating a UFB-containing liquid with high purity with a simple configuration.
Thus, a method of generating ultrafine bubbles in the present invention is characterized in that the method includes: a liquid supplying step where a liquid is supplied to a flow passage that allows a liquid to flow; a flow passage inner volume varying step where an inner volume of the flow passage to which the liquid is supplied is varied by varying a part of the flow passage; a pressurizing step where, due to the operation of the flow passage inner volume varying step, the liquid that has an amplified flow rate and is pressurized is caused to pass through a narrow portion, which narrows a part of the flow passage such that a flow passage area that is an area of a plane crossing a direction of the flow of the liquid in the flow passage is gradually reduced from upstream to downstream of the flow passage; and a depressurizing step where the liquid that is pressurized in the pressurizing step is depressurized.
According to the present invention, it is possible to provide an ultrafine bubble generating method and an ultrafine bubble generating apparatus capable of efficiently generating a UFB-containing liquid with high purity with a simple configuration.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
When a certain amount of the liquid W is reserved in the degassing container 101 and then the depressurizing pump 103 is activated with all the valves closed, already-gasified gas components are discharged, and gasification and discharge of gas components dissolved in the liquid W are also prompted. In this process, the internal pressure of the degassing container 101 may be depressurized to around several hundreds to thousands of Pa (1.0 Torr to 10.0 Torr) while checking a manometer 108. The gases to be removed by the pre-processing unit 100 includes nitrogen, oxygen, argon, carbon dioxide, and so on, for example.
The above-described degassing processing can be repeatedly performed on the same liquid W by utilizing the liquid circulation passage 105. Specifically, the shower head 102 is operated with the valve 109 of the liquid introduction passage 104 and a valve 110 of the liquid discharge passage 106 closed and a valve 107 of the liquid circulation passage 105 opened. This allows the liquid W reserved in the degassing container 101 and degassed once to be resprayed in the degassing container 101 from the shower head 102. In addition, with the depressurizing pump 103 operated, the gasification processing by the shower head 102 and the degassing processing by the depressurizing pump 103 are repeatedly performed on the same liquid W. Every time the above processing utilizing the liquid circulation passage 105 is performed repeatedly, it is possible to decrease the gas components contained in the liquid W in stages. Once the liquid W degassed to a desired purity is obtained, the liquid W is transferred to the dissolving unit 200 through the liquid discharge passage 106 with the valve 110 opened.
The liquid W supplied from the pre-processing unit 100 is supplied and reserved into the dissolving container 201 through the liquid introduction passage 204. Meanwhile, a gas G is supplied to the dissolving container 201 through the gas introduction passage 205.
Once predetermined amounts of the liquid W and the gas G are reserved in the dissolving container 201, the pressurizing pump 207 is activated to increase the internal pressure of the dissolving container 201 to about 0.5 MPa. A safety valve 208 is arranged between the pressurizing pump 207 and the dissolving container 201. With the rotation plate 202 in the liquid rotated via the rotation shaft 203, the gas G supplied to the dissolving container 201 is transformed into air bubbles, and the contact area between the gas G and the liquid W is increased to prompt the dissolution into the liquid W. This operation is continued until the solubility of the gas G reaches almost the maximum saturation solubility. In this case, a unit for decreasing the temperature of the liquid may be provided to dissolve the gas as much as possible. When the gas is with low solubility, it is also possible to increase the internal pressure of the dissolving container 201 to 0.5 MPa or higher. In this case, the material and the like of the container need to be the optimum for safety sake.
Once the liquid W in which the components of the gas G are dissolved at a desired concentration is obtained, the liquid W is discharged through the liquid discharge passage 206 and supplied to the UFB generating unit 300. In this process, a back-pressure valve 209 adjusts the flow pressure of the liquid W to prevent excessive increase of the pressure during the supplying.
The gas-dissolved liquid 3 in the drawings means “a region of the liquid W in which the dissolution concentration of the gas G mixed therein is relatively high.” In the gas components actually dissolved in the liquid W, the concentration of the gas components in the gas-dissolved liquid 3 is the highest at a portion surrounding the air bubble 2. In a case where the gas-dissolved liquid 3 is separated from the air bubble 2 the concentration of the gas components of the gas-dissolved liquid 3 is the highest at the center of the region, and the concentration is continuously decreased as away from the center. That is, although the region of the gas-dissolved liquid 3 is surrounded by a broken line in
The UFB generation unit 600 mainly includes a chamber 301, a liquid introduction path 302, and a liquid discharge passage 303, and a flow from the liquid introduction passage 302 through the chamber 301 to the liquid discharge passage 303 is formed by a not-illustrated flow pump. As the flow pump, various pumps including a diaphragm pump, a gear pump, and a screw pump may be employed as the flow pump. The gas-dissolved liquid 3 of the gas G put by the dissolving unit 200 is mixed in the liquid W introduced from the liquid introduction passage 302.
An element substrate 12 provided with a heating element 10 is arranged on a bottom section of the chamber 301. With a predetermined voltage pulse applied to the heating element 10, a bubble 13 generated by the film boiling (hereinafter, also referred to as a film boiling bubble 13) is generated in a region in contact with the heating element 10. Then, an ultrafine bubble (T-UFB) 11 containing the gas G is generated caused by expansion and shrinkage of the film boiling bubble 13. As a result, a UFB-containing liquid W containing many T-UFBs 11 is discharged from the liquid discharge passage 303.
As illustrated in
A cavitation-resistant film 310 for protecting the protective layer 309 from chemical and physical impacts due to the heat evolved by the resistive layer 307 is formed on a portion and around the portion on the surface of the protective layer 309, the portion corresponding to a heat-acting portion 311 that eventually becomes the heating element 10. A region on the surface of the resistive layer 307 in which the wiring 308 is not formed is the heat-acting portion 311 in which the resistive layer 307 evolves heat. The heating portion of the resistive layer 307 on which the wiring 308 is not formed functions as the heating element (heater) 10. As described above, the layers in the element substrate 12 are sequentially formed on the surface of the silicon substrate 304 by a semiconductor production technique, and the heat-acting portion 311 is thus provided on the silicon substrate 304.
The configuration illustrated in the drawings is an example, and various other configurations are applicable. For example, a configuration in which the laminating order of the resistive layer 307 and the wiring 308 is opposite, and a configuration in which an electrode is connected to a lower surface of the resistive layer 307 (so-called a plug electrode configuration) are applicable. In other words, as described later, any configuration may be applied as long as the configuration allows the heat-acting portion 311 to heat the liquid for generating the film boiling in the liquid.
The P-MOS 320 includes a source region 325 and a drain region 326 formed by partial introduction of N-type or P-type impurities in a top layer of the N-type well region 322, a gate wiring 335, and so on. The gate wiring 335 is deposited on a part of a top surface of the N-type well region 322 excluding the source region 325 and the drain region 326, with a gate insulation film 328 of several hundreds of Å in thickness interposed between the gate wiring 335 and the top surface of the N-type well region 322.
The N-MOS 321 includes the source region 325 and the drain region 326 formed by partial introduction of N-type or P-type impurities in a top layer of the P-type well region 323, the gate wiring 335, and so on. The gate wiring 335 is deposited on a part of a top surface of the P-type well region 323 excluding the source region 325 and the drain region 326, with the gate insulation film 328 of several hundreds of Å in thickness interposed between the gate wiring 335 and the top surface of the P-type well region 323. The gate wiring 335 is made of polysilicon of 3000 Å to 5000 Å in thickness deposited by the CVD method. A C-MOS logic is constructed with the P-MOS 320 and the N-MOS 321.
In the P-type well region 323, an N-MOS transistor 330 for driving an electrothermal conversion element (heating resistance element) is formed on a portion different from the portion including the N-MOS 321. The N-MOS transistor 330 includes a source region 332 and a drain region 331 partially provided in the top layer of the P-type well region 323 by the steps of introduction and diffusion of impurities, a gate wiring 333, and so on. The gate wiring 333 is deposited on a part of the top surface of the P-type well region 323 excluding the source region 332 and the drain region 331, with the gate insulation film 328 interposed between the gate wiring 333 and the top surface of the P-type well region 323.
In this example, the N-MOS transistor 330 is used as the transistor for driving the electrothermal conversion element. However, the transistor for driving is not limited to the N-MOS transistor 330, and any transistor may be used as long as the transistor has a capability of driving multiple electrothermal conversion elements individually and can implement the above-described fine configuration. Although the electrothermal conversion element and the transistor for driving the electrothermal conversion element are formed on the same substrate in this example, those may be formed on different substrates separately.
An oxide film separation region 324 is formed by field oxidation of 5000 Å to 10000 Å in thickness between the elements, such as between the P-MOS 320 and the N-MOS 321 and between the N-MOS 321 and the N-MOS transistor 330. The oxide film separation region 324 separates the elements. A portion of the oxide film separation region 324 corresponding to the heat-acting portion 311 functions as a heat-accumulating layer 334, which is the first layer on the silicon substrate 304.
An interlayer insulation film 336 including a PSG film, a BPSG film, or the like of about 7000 Å in thickness is formed by the CVD method on each surface of the elements such as the P-MOS 320, the N-MOS 321, and the N-MOS transistor 330. After the interlayer insulation film 336 is made flat by heat treatment, an Al electrode 337 as a first wiring layer is formed in a contact hole penetrating through the interlayer insulation film 336 and the gate insulation film 328. On surfaces of the interlayer insulation film 336 and the Al electrode 337, an interlayer insulation film 338 including an SiO2 film of 10000 Å to 15000 Å in thickness is formed by a plasma CVD method. On the surface of the interlayer insulation film 338, a resistive layer 307 including a TaSiN film of about 500 Å in thickness is formed by a co-sputter method on portions corresponding to the heat-acting portion 311 and the N-MOS transistor 330. The resistive layer 307 is electrically connected with the Al electrode 337 near the drain region 331 via a through-hole formed in the interlayer insulation film 338. On the surface of the resistive layer 307, the wiring 308 of Al as a second wiring layer for a wiring to each electrothermal conversion element is formed. The protective layer 309 on the surfaces of the wiring 308, the resistive layer 307, and the interlayer insulation film 338 includes an SiN film of 3000 Å in thickness formed by the plasma CVD method. The cavitation-resistant film 310 deposited on the surface of the protective layer 309 includes a thin film of about 2000 Å in thickness, which is at least one metal selected from the group consisting of Ta, Fe, Ni, Cr, Ge, Ru, Zr, Ir, and the like. Various materials other than the above-described TaSiN such as TaN, CrSiN, TaAl, WSiN, and the like can be applied as long as the material can generate the film boiling in the liquid.
Before a voltage is applied to the heating element 10, the atmospheric pressure is substantially maintained in the chamber 301. Once a voltage is applied to the heating element 10, the film boiling is generated in the liquid in contact with the heating element 10, and a thus-generated air bubble (hereinafter, referred to as the film boiling bubble 13) is expanded by a high pressure acting from inside (timing 1). A bubbling pressure in this process is expected to be around 8 to 10 MPa, which is a value close to a saturation vapor pressure of water.
The time for applying a voltage (pulse width) is around 0.5 μsec to 10.0 μsec, and the film boiling bubble 13 is expanded by the inertia of the pressure obtained in timing 1 even after the voltage application. However, a negative pressure generated with the expansion is gradually increased inside the film boiling bubble 13, and the negative pressure acts in a direction to shrink the film boiling bubble 13. After a while, the volume of the film boiling bubble 13 becomes the maximum in timing 2 when the inertial force and the negative pressure are balanced, and thereafter the film boiling bubble 13 shrinks rapidly by the negative pressure.
In the disappearance of the film boiling bubble 13, the film boiling bubble 13 disappears not in the entire surface of the heating element 10 but in one or more extremely small regions. For this reason, on the heating element 10, further greater force than that in the bubbling in timing 1 is generated in the extremely small region in which the film boiling bubble 13 disappears (timing 3).
The generation, expansion, shrinkage, and disappearance of the film boiling bubble 13 as described above are repeated every time a voltage pulse is applied to the heating element 10, and new T-UFBs 11 are generated each time.
The cation exchange resins 412 are synthetic resins in which a functional group (ion exchange group) is introduced in a high polymer matrix having a three-dimensional network, and the appearance of the synthetic resins is spherical particles of around 0.4 to 0.7 mm. A general high polymer matrix is the styrene-divinylbenzene copolymer, and the functional group may be that of methacrylic acid series and acrylic acid series, for example. Note that, the above materials are examples. As long as desired inorganic ions can be removed effectively, the above materials can be changed to various materials. The UFB-containing liquid W absorbed in the cation exchange resins 412 to remove the inorganic ions is collected by the collecting pipe 414 and transferred to the next step through the liquid discharge passage 415.
The impurities removed by the filtration filter 422 include organic materials that may be mixed at a tube or each unit, such as organic compounds including silicon, siloxane, and epoxy, for example. A filter film usable for the filtration filter 422 includes a filter of a sub-μm-mesh that can remove bacteria, and a filter of a nm-mesh that can remove virus.
After a certain amount of the UFB-containing liquid W is reserved in the storage container 421, the vacuum pump 423 is stopped and the valve 424 is opened to transfer the UFB-containing liquid in the storage container 421 to the next step through the liquid discharge passage 426. Although the vacuum filtration method is employed as the method of removing the organic impurities herein, a gravity filtration method and a pressurized filtration can also be employed as the filtration method using a filter, for example.
First, a predetermined amount of the UFB-containing liquid W is reserved into the precipitation container 431 through the liquid introduction passage 432 with the valve 433 closed, and leaving it for a while. Meanwhile, the solid substances in the UFB-containing liquid W are precipitated onto the bottom of the precipitation container 431 by gravity. Among the bubbles in the UFB-containing liquid, relatively large bubbles such as microbubbles are raised to the liquid surface by the buoyancy and also removed from the UFB-containing liquid. After a lapse of sufficient time, the valve 433 is opened, and the UFB-containing liquid W from which the solid substances and large bubbles are removed is transferred to the collecting unit 500 through the liquid discharge passage 434. The example of applying the three post-processing mechanisms in sequence is shown in this embodiment; however, the configuration is not limited thereto, and a needed post-processing mechanism may be employed if necessary.
Reference to
The collecting unit 500 collects and preserves the UFB-containing liquid W transferred from the post-processing unit 400. The UFB-containing liquid collected by the collecting unit 500 is a UFB-containing liquid with high purity from which various impurities are removed.
In the collecting unit 500, the UFB-containing liquid W may be classified by the sizes of the UFBs by performing some stages of filtration processing. Since it is expected that the temperature of the UFB-containing liquid W obtained by the UFB method is higher than the normal temperature, the collecting unit 500 may be provided with a cooling unit. The cooling unit may be provided in a part of the post-processing unit 400.
The overview of the UFB generating apparatus 1 is given above; however, it is needless to say that the illustrated multiple units can be changed, and not all of them need to be prepared. Depending on the types of the liquid W and the gas G to be used and the intended use of the UFB-containing liquid to be generated, some of the above-described units may be omitted, or another unit other than the above-described units may be added.
For example, in a case where the gas to be contained in the UFBs is the atmospheric air, the pre-processing unit 100 and the dissolving unit 200 can be omitted. On the other hand, in a case where multiple types of gases are desired to be contained in the UFBs, an additional dissolving unit 200 may be added.
The units for removing the impurities as described in
The UFB generating device 800 generates T-UFBs through the film boiling generated with the gas G being dissolved in the liquid W and the liquid W in which the gas G is dissolved being heated. Additionally, while generating the T-UFBs, the UFB generating device 800 uses the growth of the bubbles generated by the film boiling to move the liquid, further increases the flow rate of the moving liquid by a liquid flow rate amplifying element 805, and generates UFBs 807 by rapid depressurizing by the Venturi effect in a depressurizing area (depressurizing chamber) 806. Thus, the UFBs 807 that are generated by the further increase in the flow rate by the liquid flow rate amplifying element 805 and the rapid depressurizing by the Venturi effect in the depressurizing area 806 are referred to as Venturi-ultrafine bubbles (V-UFBs) herein.
As described above, there are also bubbles larger than 1 micrometer in the Venturi bubbles generated by the above-described method. However, in a case where the Venturi bubbles are generated by generating a pressure by the operation of the film boiling, the time required for the generation and the disappearance of the vacuum bubbles 815 corresponds to the film boiling 804, and thus the time is short such as 100 microseconds or less. Thus, in a case where the vacuum bubbles 815 are generated in short time, the ratio of the V-UFBs smaller than 1 micrometer is higher and the generation efficiency of the V-UFBs is higher than that of the Venturi bubbles generated by the normal steady flow Venturi.
In the state of
As described above, the generation processes of the T-UFBs 11 and the V-UFBs 807 are different from each other. The generation process of the T-UFBs 11 includes thermal histories, while the generation process of the V-UFBs 807 includes histories with relatively few thermal histories. In a case where the thermal histories are few like the V-UFBs, the thermal effect on the gas components contained in the V-UFBs 807 is small. Therefore, in the case of the V-UFBs 807, it is possible to generate the UFBs without transforming the properties of even the gas components that are likely to be affected by heat.
In this embodiment, with the film boiling generated by the heating element to vary the inner volume of the flow passage in the UFB generating liquid flow passage, the liquid W is pressurized such that the liquid passes through the narrow portion at high speed, and thus the UFBs are generated. However, the configuration is not limited thereto, and in order to pressurize the liquid, a flow passage inner volume varying element that varies the inner volume of the flow passage in the UFB generating liquid flow passage may be used.
Additionally, in this embodiment, the gas-dissolved water is generated by supplying the gas to the UFB generating liquid flow passage. However, the configuration is not limited thereto, and gas-dissolved water may be supplied to the UFB generating liquid flow passage.
As described above, the flow passage inner volume varying element is used to vary the flow passage inner volume, and the liquid is pressurized such that the liquid passes through the narrow portion at high speed and flows into the depressurizing area. Therefore, it is possible to provide an ultrafine bubble generating method and an ultrafine bubble generating apparatus capable of efficiently generating a UFB-containing liquid with high purity.
Hereinafter, a second embodiment of the present invention is described with reference to the drawings. Since the basic configuration of this embodiment is similar to that of the first embodiment, only a characteristic configuration is described below.
With the first gas G1 being supplied to the UFB generating liquid flow passage 906, becoming first gas bubbles 910, and being dissolved into the liquid W, the first gas G1 becomes first gas-dissolved water 912. With the second gas G2 being supplied to the UFB generating liquid flow passage 906, becoming second gas bubbles 911, and being dissolved into the liquid W, the second gas G2 becomes the second gas-dissolved water 913. There is also mixed dissolved water of the first gas G1 and the second gas G2 in a high pressure area 908.
Although the second gas supply passage 905 is provided near the first gas supply passage 904 and the heating element 10 in
Thus, the second gas-dissolved water 913 and the mixed dissolved water of the first gas G1 and the second gas G2 are not heated by the heating element 10, and the gas components contained in T-UFBs 914 are the first gas G1 while no components of the second gas G2 are contained in the T-UFBs 914.
In the high pressure area 908, there are the first gas-dissolved water 912, the second gas-dissolved water 913, and the mixed dissolved water of the first gas G1 and the second gas G2. Thus, the gas components contained in V-UFBs 915 are the first gas G1 components, the second gas G2 components, and mixed components of the first gas G1 and the second gas G2, and three types of V-UFBs 915 are generated.
That is, the UFB generating device 900 generates four types of UFBs, which are the T-UFBs 914 containing the first gas components, the V-UFBs 915 containing the first gas components, the V-UFBs 915 containing the second gas components, and the V-UFBs 915 containing the mixed components of the first gas G1 and the second gas G2.
The UFBs are generated in the UFB generating device 900, and the liquid W containing the UFBs is ejected from a liquid ejection passage 917 to be stored in a UFB liquid tank 918.
Since the thermal effect on the UFBs is small in the generation of the V-UFBs as described above, in a case of using a gas likely to be affected by heat, it is preferable to use the gas as the second gas G2.
Hereinafter, a third embodiment of the present invention is described with reference to the drawings. Since the basic configuration of this embodiment is similar to that of the first embodiment, only a characteristic configuration is described below.
The UFB generating device 1000 includes the piezo element 1004 and is capable of changing the inner volume of a UFB generating liquid flow passage 1007 by applying a voltage to the piezo element 1004, and is capable of decreasing and increasing the inner volume by changing the polarity of the voltage. With a voltage being applied to the piezo element 1004 to decrease the inner volume of the UFB generating liquid flow passage 1007, it is possible to increase the pressure on the liquid W in a high pressure area 1009.
The piezo element 1004 is intended for changing the inner volume of the UFB generating liquid flow passage 1007, and the piezo element itself does not generate the UFBs like the heating element generating the T-UFBs.
Since the pressure near the narrow portion 1013 of a depressurizing area 1010 is reduced by the Venturi effect, vacuum bubbles 1011, insides of which are in a vacuum, are generated while exceeding the viscous coupling of the liquid W and being teared apart. As the vacuum bubbles 1011 are generated, the gas G that is dissolved in the liquid W by the depressurizing near the vacuum bubbles 1011 become the Venturi bubbles while exceeding the dissolution and saturation limit and precipitating. The Venturi bubbles contain bubbles of smaller than 1 μm, and those small bubbles become V-UFBs 1012. The Venturi bubbles also contain bubbles larger than 1 μm; however, since the time required for the generation of the vacuum bubbles 1011 is considerably short such as 1 millisecond or less, which corresponds to the time required for the displacement of the piezo element, the ratio of the V-UFBs 1012 smaller than 1 μm is higher and the generation efficiency of the V-UFBs is higher than that of the normal steady flow Venturi.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2020-021502 filed Feb. 12, 2020, which is hereby incorporated by reference wherein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2020-021502 | Feb 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4428757 | Hall | Jan 1984 | A |
| 8740450 | Mogami et al. | Jun 2014 | B2 |
| 10022682 | Hata | Jul 2018 | B2 |
| 20200276803 | Arimizu et al. | Sep 2020 | A1 |
| Number | Date | Country |
|---|---|---|
| 2014-104441 | Jun 2014 | JP |
| 2009088085 | Jul 2009 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20210245116 A1 | Aug 2021 | US |
