Gas dissolution device and gas dissolution method

Abstract

To provide a gas dissolution device and a gas dissolution method that realize high gas dissolution capacity and considerably improve persistence of a containing gas concentration of an obtained liquid.SOLUTION: A liquid is fed at a flow rate which obtains a value of an effective valley point flow rate density α of 1.0 pieces or parts / L to 3.5 pieces or parts / L, to a gas ejection nozzle 1, and the liquid collides against a cavitation screw member 10 positioned within a throttle part 9. In addition, gas is fed to a gas introduction hole 6 of a nozzle body 2, and while the gas from the gas introduction hole 6 is sucked into the liquid, the gas is mixed into a turbulent flow generated within a gas dissolution diameter expansion part 13 and dissolved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas dissolving device and a gas dissolving method. [Background technology]

[0002] Venturi ejectors (Patent Documents 1 and 2) are known as gas ejection nozzles for gas-liquid mixing. These gas ejection nozzles have a throttle section in the middle of the flow path, and a gas inlet hole at or directly below the throttle section. The gas supplied is entrained and mixed with the liquid flow, which accelerates at the throttle section. These gas ejection nozzles have the advantage of being free of obstacles within the throttle section and relatively low pressure loss, making it easy for gas to self-suck due to the decompression effect generated by the throttle. Meanwhile, Patent Document 3 discloses a gas ejection nozzle in which a screw member is installed upright at the throttle section of a Venturi-shaped nozzle body, and the gas is entrained and mixed in the cavitation turbulence generated downstream of the screw member. Because the cavitation turbulence produces a significant gas-liquid mixing effect, this gas ejection nozzle has the advantage of being able to demonstrate high liquid dissolving ability even when a relatively low liquid supply pressure is used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-085237 [Patent Document 2] Japanese Patent Publication No. 2023-066081 [Patent Document 3] WO2016 / 195116 publication [Patent Document 4] WO2016 / 199930 publication [Non-patent literature]

[0004] [Non-Patent Document 1] NanotechJapan Bulletin Vol. 8, No. 4, 2015 Special feature "Collabo Nanotechnology" <4th> pp. 1-6 Summary of the Invention [Problem to be solved by the invention]

[0005] The Venturi ejectors disclosed in Patent Documents 1 and 2 have a drawback in gas dissolving capacity, and there is a problem in that the gas dissolving efficiency per flow pass cannot be sufficiently ensured.

[0006] Furthermore, the gas ejection nozzle disclosed in Patent Document 3 has a gas inlet opening upstream of a screw member for forming a cavitation point. In this structure, not only liquid but also gas is supplied from the upstream side of the screw member. Therefore, the liquid passes through the screw member in a mixed phase with coarse bubbles, and the thread roots that come into contact with the coarse bubbles are unable to function as cavitation points. As a result, compared to when only liquid is circulated, cavitation turbulence is less likely to occur, and sufficient gas dissolution efficiency per flow path cannot be ensured.

[0007] For example, in the carbon dioxide dissolution test disclosed in Patent Document 3, it is stated that "carbon dioxide is supplied so that the flow rate of the carbon dioxide is 70% of the water flow rate," but the carbon dioxide is forcibly injected at a pressure (0.2 MPa) that is twice the liquid supply pressure (0.1 MPa). Therefore, referring to the gas supply form disclosed in Figure 31 of Patent Document 3, the carbon dioxide flow rate is supplied at 140% of the water flow rate converted to normal pressure, and it is presumed that the carbon dioxide dissolution efficiencies disclosed in Tables 1 to 6 are all less than 50%.

[0008] On the other hand, Tables 1 to 6 of Patent Document 3 do not directly disclose the sustainability of the contained gas concentration when water obtained by passing various gases through the water is left in the atmosphere, and no specific means for improving this are mentioned. The sustainability of the contained gas concentration may be related to the amount of fine bubbles generated when water is passed through a nozzle without supplying gas, but Tables 1 to 6 of Patent Document 3 only disclose the number average diameter of fine bubbles measured with a laser scattering particle sizer when tap water is passed through the nozzle used in the test without supplying gas, but do not disclose anything about the number density of the fine bubbles.

[0009] Similarly, Patent Document 4 discloses a hydrogen dissolution method using a similar gas ejection nozzle, and also provides detailed disclosure of the sustainability of the hydrogen concentration when the water is left in the atmosphere after gas introduction. However, like Patent Document 3, the gas inlet hole is opened upstream of the screw member, and the sustainability of the hydrogen concentration is only achieved when the water is circulated three to five times while hydrogen gas is continuously introduced. In this case, the hydrogen gas dissolution efficiency is also estimated to be less than 50%, and the gas dissolution efficiency per circulation pass is not sufficiently ensured. Furthermore, there is no disclosure of the number density of fine bubbles required to achieve a sustainable hydrogen concentration.

[0010] An object of the present invention is to provide a gas dissolution device and a gas dissolution method that can achieve high gas dissolution capacity by using a gas ejection nozzle that uses a cavitation screw member, and that can significantly improve the sustainability of the gas concentration contained in the resulting liquid. [Means for solving the problem]

[0011] In order to solve the above problems, the gas dissolution device of the present invention comprises a nozzle body having a single liquid flow path formed therein with a liquid inlet at one end and a liquid outlet at the other end, and a throttle section formed midway through the liquid flow path so that the diameter of the liquid flow path is smaller than that of the liquid inlet; a cavitation screw member disposed within the throttle section and having a thread section formed on its outer surface with a thread pitch of 0.20 mm to 0.40 mm, a thread root depth of 0.20 mm to 0.40 mm, and a nominal diameter of 1.0 mm to 2.0 mm; and a gas dissolution expansion section that forms part of the liquid flow path and is connected to the downstream side of the throttle section, and whose axial cross-sectional area expands continuously or stepwise toward the liquid outlet. The nozzle body comprises a gas introduction hole that communicates with the throttle section or the gas dissolution expansion section downstream of all of the cavitation screw members located within the throttle section and that is formed to connect the outside of the nozzle body to the liquid flow path. The axial cross-sectional diameter of the throttle section is 2.0 mm to 8.0 mm, and the flow cross-sectional area of ​​the throttle section is 2.0 mm to 8.0 mm. 2 Over 42mm 2 Hereinafter, the number of thread valleys of a cavitation screw member that exists within 70% of the radius from the center in the axial cross section of the throttled portion is defined as the 70% valley number, and the value of the 70% valley number divided by the flow cross-sectional area, which is the 70% valley point area density, is 1.00 pieces / mm 2 More than 3.50 pieces / mm 2A gas ejection nozzle defined within the following range, a gas supply unit that supplies gas to the gas inlet of the nozzle body, and a gas ejection nozzle in which the flow velocity distribution in the radial direction of the cross section immediately before the liquid collides with the cavitation screw member is parabolic, with a maximum at the center of the cross section and zero at the inner wall surface of the flow path, and further the radius of the axial cross section is R, the outlet side of the gas ejection nozzle is open, and water is passed through the gas ejection nozzle under standard conditions where the dynamic water pressure supplied to the gas ejection nozzle is 0.1 MPa. The critical flow velocity is defined as the flow velocity at a position 0.71R from the center of the axial cross section, and the total number of valley points of the thread valleys of the cavitation screw member that are equal to or greater than the critical flow velocity when projected onto the axial cross section is defined as the effective valley number N, the liquid supply flow rate is ρ, and the effective valley point flow rate density α = N / ρ.The nozzle is characterized by comprising a liquid delivery unit that delivers liquid to the liquid inlet of the nozzle body at a flow rate such that the average flow velocity within the axial cross section of the flow path in which the screw member is arranged is 9 m / s or more and the value of the effective valley point flow rate density α is between 1.0 particles·min / L and 3.5 particles·min / L.

[0012] The gas dissolving method of the present invention also provides a nozzle body having a single liquid flow path formed therein with a liquid inlet at one end and a liquid outlet at the other end, and a throttle portion formed midway through the liquid flow path so that the diameter of the liquid flow path is smaller than that of the liquid inlet; a cavitation screw member disposed within the throttle portion, and having a thread portion formed on its outer surface with a thread pitch of 0.20 mm or more and 0.40 mm or less, a thread root depth of 0.20 mm or more and 0.40 mm or less, and a nominal diameter of 1.0 mm or more and 2.0 mm or less; and a gas dissolving expansion portion that forms part of the liquid flow path and is connected to the downstream side of the throttle portion, and whose axial cross-sectional area expands continuously or stepwise toward the liquid outlet. The nozzle body also has a gas inlet that communicates with the throttle portion or the gas dissolving expansion portion downstream of all of the cavitation screw members located within the throttle portion, and that is formed to connect the outside of the nozzle body to the liquid flow path. The axial cross-sectional diameter of the throttle portion is 2.0 mm or more and 8.0 mm or less, and the flow cross-sectional area of ​​the throttle portion is 2.0 mm or more and 2.0 mm or less. 2 Over 42mm 2Hereinafter, the number of thread valleys of a cavitation screw member that exists within 70% of the radius from the center in the axial cross section of the throttled portion is defined as the 70% valley number, and the value of the 70% valley number divided by the flow cross-sectional area, which is the 70% valley point area density, is 1.00 pieces / mm 2 More than 3.50 pieces / mm 2 A gas ejection nozzle defined within the following range, a gas supply unit that supplies gas to the gas inlet hole of the nozzle body, and a gas ejection nozzle in which the flow velocity distribution in the radial direction of the cross section immediately before the liquid collides with the cavitation screw member is parabolic, with the flow velocity distribution being maximum at the center of the cross section and zero at the inner wall surface of the flow passage, and furthermore, the radius of the axial cross section is defined as R, the outlet side of the gas ejection nozzle is open, and water is passed through the gas ejection nozzle under standard conditions where the dynamic water pressure supplied to the gas ejection nozzle is 0.1 MPa. The flow velocity at a position 0.71R from the center of the axial cross section is defined as the critical flow velocity, and the critical flow velocity is defined as the flow velocity at a position 0.71R from the center of the axial cross section when projected onto the axial cross section. and a liquid delivery unit that delivers liquid to a liquid inlet of a nozzle body at a flow rate such that the average flow velocity in the axial cross section of a flow path in which the screw member is arranged is 9 m / s or more and the value of the effective valley point flow density α is between 1.0 particles·min / L and 3.5 particles·min / L, where N is the effective valley point number, ρ is the liquid supply flow rate, and α = N / ρ is the effective valley point flow density. The gas dissolution device is characterized in that gas is supplied to a gas introduction hole in the nozzle body of the gas ejection nozzle, and the gas from the gas introduction hole is sucked into the liquid, while being entrained in the turbulence generated in the gas dissolution expansion section and dissolved. [Effects of the Invention]

[0013] The gas dissolution device of the present invention employs a gas ejection nozzle using a cavitation screw member, supplies gas downstream of the cavitation screw member, and supplies liquid at a flow rate such that the effective valley point flow density α is between 1.0 particles·min / L and 3.5 particles·min / L, inclusive. This significantly improves the gas dissolution efficiency per flow path and significantly improves the sustainability of the gas concentration of the resulting liquid when it is left in the air. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view showing one embodiment of a gas ejection nozzle used in the present invention. [Figure 2] 2 is an axial cross-sectional view of the throttle portion of the gas ejection nozzle of FIG. 1 at a position including the cavitation screw member. [Figure 3] FIG. 2 is a structural explanatory diagram showing a flow system according to a first example of the gas dissolving device of the present invention. [Figure 4] FIG. 10 is a structural explanatory diagram showing a flow system according to a second example of a gas dissolving device of the present invention. [Figure 5] FIG. 10 is an axial cross-sectional view showing a first modified example of the arrangement of the cavitation screw member in the throttle portion. [Figure 6] FIG. 10 is an axial cross-sectional view showing a second modified example of the arrangement of the cavitation screw member in the throttle portion. [Figure 7] FIG. 10 is an axial cross-sectional view showing a third modified example of the arrangement of the cavitation screw members in the throttle portion. [Figure 8] FIG. 2 is a cross-sectional view showing a first example of a gas ejection nozzle in which a gas-dissolving expanded diameter portion is formed into a cylindrical surface. [Figure 9] FIG. 10 is a cross-sectional view showing a second example of a gas ejection nozzle in which the gas-dissolving expanded diameter portion is formed into a cylindrical surface shape. [Figure 10] 10 is a graph showing the relationship between the flow cross-sectional area of ​​the throttle portion of the gas ejection nozzle in Table 7 and the average flow velocity at the position of the cavitation screw member when water is passed through at a hydrodynamic pressure of 0.1 MPa. [Figure 11] FIG. 1 is a diagram illustrating the concept of effective valley point flow density. [Figure 12] Schematic diagram illustrating how a bubble nucleus grows to become a bubble. [Figure 13] 10 is a graph showing an example of test results investigating the relationship between the effective valley point flow density and the number density of generated ultra-fine bubbles when water is circulated without supplying gas to the gas ejection nozzle. [Figure 14] 1 is a histogram showing the measurement results of the bubble volume density distribution for each test water of test number 5 and test number 16 in Table 2. [Figure 15] A histogram showing Figure 14 converted into a bubble number density distribution. [Figure 16] This graph shows the results of a test to examine the sustainability of the carbon dioxide concentration when water obtained by passing carbon dioxide gas through the gas ejection nozzle No. 5 in Table 1 once at various water flow rates and gas-liquid ratios was left in the atmosphere, in comparison with water in a comparative example in which carbon dioxide was dissolved using a gas exchange membrane. [Figure 17] 17 is a graph showing an example of exponential regression performed on the test results of FIG. 16 to calculate half-life. [Figure 18] Graph showing the relationship between the number density measurement results of UFBs generated when water is circulated without gas supply to the gas ejection nozzle and the half-life of carbon dioxide gas concentration when water obtained by supplying carbon dioxide gas is left standing. [Figure 19] 1 is a graph showing an example of test results investigating the relationship between the number density of UFBs generated when water is circulated without supplying gas to the gas ejection nozzle and the dissolution efficiency when carbon dioxide gas is supplied. [Figure 20] 1 is a graph showing an example of test results for investigating the relationship between the gas-liquid ratio and carbon dioxide dissolution efficiency when carbon dioxide gas was passed through gas ejection nozzles numbered 1, 2, and 3 in Table 1 at a water flow rate of 10 L / min. [Figure 21] 10 is a graph showing the change in negative suction pressure generated in the gas introduction hole when water is passed through the throttle portions of the gas ejection nozzles Nos. 502 and 520 in Table 7 at various dynamic water pressures. [Figure 22] 10 is a graph showing characteristic curves of negative suction pressure generated in the gas introduction hole when water is passed through the throttle portions of the gas ejection nozzles numbered 502 and 520 in Table 7 at various flow rates. [Figure 23] 10 is a graph showing the change in negative suction pressure generated in the gas introduction hole when water is passed through the throttle portions of the gas ejection nozzles Nos. 503 and 521 in Table 7 at various dynamic water pressures. [Figure 24] 10 is a graph showing characteristic curves of negative suction pressure generated in the gas introduction hole when water is passed through the throttle portions of the gas ejection nozzles numbered 503 and 521 in Table 7 at various throttle portion flow rates. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described. 1 is a cross-sectional view of a gas ejection nozzle 1 constituting one embodiment of the present invention. The gas ejection nozzle 1 comprises a nozzle body 2 and a cavitation screw member 10. The nozzle body 2 is formed with a single liquid flow path 11 having a liquid inlet 3 at one end and a liquid outlet 4 at the other end. In addition, a throttle portion 9 having a smaller diameter than the liquid inlet 3 is formed midway along the liquid flow path 11. The nozzle body 2 is made of a resin such as PTFE, ABS, acrylic, or polyacetal, but metals such as stainless steel, brass, or aluminum alloys may also be used.

[0016] Joints 3F, 4F for connecting a liquid supply pipe and a liquid take-out pipe are formed in the portions of the nozzle body 2 that form the liquid inlet 3 and liquid outlet 4. In this embodiment, the joints 3F, 4F are formed with female threads (for example, tapered pipe threads such as R1 / 2), but these can be changed to other types of joints as appropriate depending on the size and joint shape of the pipe to be connected.

[0017] The cavitation screw member 10 (hereinafter simply referred to as the "screw member 10") is disposed within the constricted portion 9. As shown in FIG. 2, the leg portion of the cavitation screw member 10 has a threaded portion formed on the outer surface thereof. The threaded portion has a thread 31 with a pitch of 0.20 mm to 0.40 mm, a thread root 32 with a depth of 0.20 mm to 0.40 mm, and a nominal diameter M of 1.0 mm to 2.0 mm. In this embodiment, the screw member 10 is a JIS No. 0, Class 1 pan head machine screw (coarse pitch) made of metal, for example. However, the screw member 10 may also be made of inorganic materials such as alumina, zirconia, or glass. Stainless steel, titanium, or the like can be used as the specific material for the screw member 10 to ensure corrosion resistance. When used to dissolve corrosive gases such as ozone, the screw member 10 is preferably made of titanium or a titanium alloy. Furthermore, a screw member made of quartz can also be used for applications where even trace amounts of metal contamination are a problem, such as semiconductor applications.

[0018] In this embodiment, as shown in FIG. 2, the screw member 10 is screwed into the threaded hole 8 formed in the nozzle body 2 so that the tip protrudes from the outer peripheral surface of the wall into the constricted portion 9, but it may also be configured to be integrated with the nozzle body 2 by insert molding or the like.

[0019] The throttle section 9 has an axial cross-sectional diameter of 2.0 mm or more and 8.0 mm or less, and a flow cross-sectional area of ​​2 mm 2 Over 42mm 2 The number of thread valley points of the threaded member 10 present within 70% of the radius from the center in the axial cross section of the reduced portion 9 is defined as the 70% valley point number, and the value of the 70% valley point area density, which is the value obtained by dividing the 70% valley point number by the flow cross-sectional area, is 1.00 pieces / mm 2 More than 3.50 pieces / mm 2 When the screw member 10 is arranged as shown in FIG. 2, the inner diameter of the throttle portion 9 is d, the nominal diameter of the screw member 10 is M, the pitch of the thread is p, and the depth of the thread root is W, then the flow cross-sectional area S is given by S=(d / 2) 2 π-(MW) d (1) It can be calculated as follows.

[0020] Returning to FIG. 1 , a gas-dissolving expanded diameter section 13, whose axial cross-sectional area expands continuously (or stepwise: the configuration shown in FIG. 8 or FIG. 9 , described below) toward the liquid outlet 4, is connected to the nozzle body 2 downstream of the throttle section 9, forming part of the liquid flow path 11. A gas inlet hole 6 is formed in the nozzle body 2 downstream of all of the screw members 10 located within the throttle section 9, so as to communicate with the throttle section 9 (or the gas-dissolving expanded diameter section 13, described below) and to connect the outside of the nozzle body 2 with the liquid flow path 11. A female threaded hole 7, for attaching a gas inlet joint, is formed in the outer peripheral surface of the nozzle body 2, so as to communicate with the gas inlet hole 6. The inner diameter of the gas inlet hole 6 is, for example, 0.3 mm or more and 2 mm or less.

[0021] In this embodiment, the constriction section 9 has a cylindrical inner surface shape, and at its upstream end is formed an inlet taper section 5 that narrows in diameter from the liquid inlet 3 toward the constriction section 9 at a steeper angle than the gas dissolution expansion section 13.

[0022] 3 is a structural explanatory diagram showing the flow system of an example of a gas dissolution apparatus using the gas ejection nozzle 1 of FIG. 1. The gas dissolution apparatus 100 has a storage tank 50 and a main liquid pipe 101, on which a pump 55 constituting a liquid delivery section and the aforementioned gas ejection nozzle 1 are provided. One end of the main liquid delivery pipe 101 is connected to the storage tank 50, and the pump 55 pressure-feeds the liquid L in the storage tank 50 to the liquid inlet 3 (FIG. 1) of the gas ejection nozzle 1. On the main liquid delivery pipe 101, upstream of the gas ejection nozzle 1, a pressure gauge 110 for measuring the flow dynamic pressure of the liquid L relative to the gas ejection nozzle 1 and a flow meter 111 for measuring the flow rate of the liquid L are provided.

[0023] The liquid L may be, for example, water or water-based liquids (soft drinks such as juice, tea, coffee, lactic acid bacteria drinks, fruit juice, seawater, and other aqueous solutions), as well as alcoholic beverages, other alcoholic drinks, fossil fuels, organic solvents, and edible oils, but is not limited to these.

[0024] A gas supply main pipe 121 is connected to a gas introduction joint 15 attached to the female threaded hole 7 (FIG. 1) of the gas ejection nozzle 1, and the gas to be used for dissolution is supplied from a gas supply source 123 provided at the end of the gas supply main pipe 121. The gas supply source 123 can be selected, for example, as follows, depending on the type of gas to be used. (1) Oxygen: Pressure Swing Adsorption (PSA) oxygen generators, oxygen cylinders, etc. (2) Hydrogen: Electrolytic hydrogen generators, chemical hydrogen generators, hydrogen cylinders, etc. (3) Nitrogen: PSA nitrogen generator, nitrogen cylinder, etc. (4) Nitrogen-hydrogen mixed gas: A device that mixes the hydrogen and nitrogen generated in (2) and (3) through piping, a cylinder filled with the mixed gas, etc. (5) Ozone-containing gas (e.g., oxygen-ozone mixed gas, air-ozone mixed gas): Ozonizer (oxygen source is PSA oxygen gas generator, oxygen cylinder, air, etc.) (6) Carbon dioxide: fossil fuel combustion equipment, carbon dioxide cylinders, etc. (7) Ammonia: ammonia generators, ammonia cylinders, etc. (8) Air: air cylinder, air compressor. When the gas ejection nozzle 1 is self-sucking atmospheric air using its negative pressure suction capability, the gas inlet 6 functions as a gas supply unit.

[0025] A flow rate adjustment valve 124 for adjusting the gas supply flow rate to the gas ejection nozzle 1 and a flow rate / pressure measurement device 125 for monitoring the gas flow rate and gas supply pressure are provided on the main gas supply pipe 121. A measurement pipe 126 branches off from the main gas supply pipe 121 via a switching valve 122, and a negative pressure meter 127 is connected to the end of the measurement pipe. If measurement of the suction negative pressure is not required, the switching valve 122, the measurement pipe 126, and the negative pressure meter 127 can be omitted.

[0026] A relief pipe 104 branches off from the main liquid pipe 101 on the discharge side of the pump 55, and the liquid passing through the relief pipe 104 is returned to the storage tank 50. A flow control valve 116 is provided on the relief pipe 104, and adjusting the opening of the flow control valve 116 makes it possible to change the dynamic water pressure and flow rate applied to the gas ejection nozzle 1. By changing the opening of the flow control valve 116 while referring to the reading of the flow meter 111, the flow rate of the relief pipe 104 can be adjusted, and ultimately the distribution flow rate of the liquid applied to the gas ejection nozzle 1 can be set to a desired value.

[0027] In the gas dissolving apparatus 200 shown in Fig. 4, a water supply pipe 1005 is connected to a main liquid pipe 101 via a water supply valve 1010. The dynamic water pressure and the flow rate of tap water applied to the gas ejection nozzle 1 can be changed by adjusting the opening of the water supply valve 1010. In this case, the water supply valve 1010 constitutes the liquid delivery section, and the storage tank 50 and pump 55 in the configuration of Fig. 3 are omitted.

[0028] Returning to FIG. 3, downstream of the liquid outlet 4 (FIG. 1) of the gas ejection nozzle 1, the main liquid pipe 101 branches into a liquid extraction pipe 103 and a circulation pipe 105, which can be switched by a switching valve 117. The end of the circulation pipe 105 is connected to a storage tank 50. When the switching valve 117 is tilted to the liquid extraction pipe 103 side, the liquid L is circulated through the gas ejection nozzle 1, in a single pass, and when the switching valve 117 is tilted to the circulation pipe 105 side, the liquid L is circulated through the gas ejection nozzle 1. When only one of the single-pass circulation and the circulation circulation is adopted, it is possible to leave only one of the liquid extraction pipe 103 and the circulation pipe 105, and omit the other together with the switching valve 117.

[0029] Next, the concept of effective valley point flow density for the gas ejection nozzle 1 is explained using Figure 11. In the axial cross section (top of Figure 11) where the threaded member 10 of the gas ejection nozzle 1 is located, the flow velocity distribution in the radial direction of the axial cross section of the flow path immediately before impacting with the threaded member 10 is defined as a parabola that reaches a maximum at the center O of the cross section and reaches zero at the flow path inner wall surface 9A of the throttle section 9. Furthermore, the radius of the axial cross section is defined as R, and under standard conditions where the outlet side of the gas ejection nozzle 1 is open and the dynamic water pressure supplied to the gas ejection nozzle 1 is 0.1 MPa, the flow velocity at the thread valley point located at a position 0.71R (R70) from the center of the axial cross section is defined as the critical flow velocity. The radius R of the axial cross section is determined so that the average flow velocity in the axial cross section of the flow path where the threaded member is located is 9 m / s or greater when water is passed through it under standard conditions. The average flow velocity in the throttle section 9 is calculated by dividing the measured liquid flow rate ρ by the cross-sectional flow area S obtained by subtracting the area of ​​the projected region of the screw member 10 from the total cross-sectional area of ​​the throttle section 9, as shown in Figure 2.

[0030] It is well known in hydraulics that the flow velocity distribution in a circular pipe is parabolic, and it is considered technically reasonable to assume that the flow velocity distribution in the axial cross section of the gas ejection nozzle 1 immediately before impact with the threaded member 10 is parabolic as described above. Furthermore, the standard operating conditions are defined as those in which the outlet side of the gas ejection nozzle 1 is open and the hydrodynamic pressure supplied to the gas ejection nozzle 1 is 0.1 MPa. If the flow velocity under standard conditions at the center O of the axial cross section of the gas ejection nozzle 1 where the threaded member 10 is located is defined as ν (hereinafter referred to as the "standard central flow velocity"), then position R70, where the flow velocity in the thread root is 0.5ν, is located 0.71R ((√2 / 2)R) from the center of the axial cross section, assuming a parabolic flow velocity distribution. Under standard conditions, thread roots located radially outward from this point (shown as black circles in Figure 2 ) are excluded as they have poor bubble nucleation ability (cavitation treatment ability). Furthermore, the flow velocity at the thread root corresponding to 0.5ν represents the critical value for determining whether or not the thread root contributes to the cavitation treatment effect, and is therefore referred to as the "critical flow velocity" as described above.

[0031] When a liquid flows through the gas ejection nozzle 1 under standard conditions, only the valley points (white circles in Figure 2) located within the region of the circle C70 where the flow velocity is 0.5ν or greater, i.e., the critical flow velocity, assuming a parabolic flow velocity distribution, can be considered to be effective valley points that contribute to bubble nucleation, i.e., "effective valley points" that contribute to the cavitation treatment effect. When the liquid delivery pressure from the pump 55 (liquid delivery section) decreases and the flow rate of the gas ejection nozzle 1 decreases below the standard condition, the flow velocity at the center of the axial cross section at that time decreases below the standard central flow velocity ν. As a result, the axial cross section radius of the region where the flow velocity is greater than the critical flow velocity decreases compared to the standard condition, and the number of valley points located within the circle C70eq with the axial cross section radius R70eq (hereinafter referred to as the "critical flow velocity circle"), i.e., the number of effective valley points, decreases compared to the standard condition. On the other hand, when the liquid delivery pressure increases and the flow rate of the gas ejection nozzle 1 increases above the standard condition, the flow velocity at the center of the axial cross section becomes greater than the standard center flow velocity v. As a result, the radial position of the axial cross section where the critical flow velocity is obtained expands compared to the standard condition, and the number of valleys inside the critical flow velocity circle, i.e., the number of effective valleys, increases compared to the standard condition.

[0032] When the number of effective valley points changes due to changes in the dynamic pressure of the gas ejection nozzle 1, the density of bubble nuclei generated in the liquid being treated is thought to increase as the value obtained by dividing the effective valley points by the flow rate of the supplied liquid increases. Therefore, when the number of effective valley points N is the number of valley points in the threaded member 10 that are equal to or greater than the critical flow velocity within the axial cross section of the gas ejection nozzle 1 at a given dynamic pressure, and the supply flow rate is ρ, the effective valley point flow rate density α is defined as α = N / ρ. The effective valley point number N can be determined by first identifying the positions of all valley points of the threaded member 10 that appear on the axial cross section projection of the flow path of the gas ejection nozzle 1, as shown in the top of Figure 11, calculating the radius R70eq (hereinafter referred to as the "standard equivalent radius") of the critical flow velocity circle C70eq of the gas ejection nozzle 1 at a given dynamic pressure, and then counting the valley points of the threaded portion that appear within the circle C70eq when the critical flow velocity circle C70eq is projected onto the axial cross section with the standard equivalent radius R70eq. According to Bernoulli's theorem, if we consider that the average flow velocity in the axial cross section changes in proportion to the square root of the dynamic hydraulic pressure, then with the flow rate under standard conditions being ρ0 and the flow rate at a given dynamic hydraulic pressure being ρ, the standard equivalent radius R70eq is calculated as the ratio to the axial cross-sectional radius R of the gas ejection nozzle 1, as follows: R70eq=(1-0.5 / (ρ / ρ0))0.5×100 (%) ···(2) It can be calculated as:

[0033] The pump 55 (liquid delivery unit) in FIG. 3 delivers liquid to the liquid inlet 3 of the nozzle body 2 of the gas ejection nozzle 1 in FIG. 1 at a flow rate such that the average flow velocity in the axial cross section of the flow path in which the screw member is disposed is 9 m / s or more and the effective valley point flow density α is between 1.0 particles·min / L and 3.5 particles·min / L, where ρ is the liquid supply flow rate and α=N / ρ is the effective valley point flow density. Specifically, the head and output of the pump 55 are set to obtain a flow rate such that the effective valley point flow density α falls within the above range. Note that if no special flow rate adjustment is required (e.g., if the type of gas ejection nozzle 1 used is fixed and a pump 55 with a head and output appropriate for the required flow rate can be used), the flow rate adjustment valve 116 and relief pipe 104 can be omitted.

[0034] The operation of the gas dissolving device 100 will now be described. The storage tank 50 is filled with the liquid L, and in the case of one-path circulation, the switching valve 117 is switched to the liquid outlet pipe 103 side and the pump 55 is operated. As a result, the liquid L in the storage tank 50 flows through the gas ejection nozzle 1 and then flows out from the end of the liquid outlet pipe 103. At this time, if the switching valve 122 is switched to the measurement pipe 126 side, the negative suction pressure generated in the gas inlet hole 6 of the gas ejection nozzle 1 can be measured by the negative pressure gauge 127. Next, the switching valve 122 is switched to the gas supply main pipe 121 side, and the opening of the flow rate adjustment valve 124 is adjusted while referring to the pressure and flow rate indication values ​​of the flow rate / pressure measurement device 125 to set the gas flow rate to a desired value.

[0035] When liquid is supplied to the gas ejection nozzle 1, the liquid flow is first rapidly throttled toward the throttle section 9 at the inlet tapered section 5. As shown in Figure 2, the liquid passes through the main flow region 21 formed between the cavitating screw member 10 and the inner circumferential surface of the throttle section 9, colliding with the cavitating screw member 10. As the liquid passes through the outer circumferential surface of the screw member 10, the flow forms a high-speed region in the thread roots 32 and a low-speed region in the threads 31. The high-speed region in the thread roots 32 becomes a negative pressure region according to Bernoulli's theorem, and bubbles FB are generated by cavitation, i.e., decompression deposition of dissolved air. Because the thread roots 32 are formed in multiple turns around the outer periphery of the screw member 10, this decompression deposition occurs simultaneously and violently in multiple thread roots 32 within the throttle section 9. Furthermore, as the liquid flow detours downstream of the screw member 10, numerous microvortices are generated, forming a strongly stirred region containing a high density of microvortices derived from Karman vortices around and immediately downstream of the screw member 10.

[0036] For example, in the nozzle of Patent Document 3, not only liquid but also gas is supplied from the upstream side of the screw member. As a result, when liquid containing floating coarse bubbles passes through the screw member, the thread roots in contact with the bubbles cannot function as cavitation points. On the other hand, in the gas ejection nozzle 1 of the present invention, only liquid is supplied from the upstream side of the screw member 10, so that when the liquid passes through the screw member 10, the coarse bubbles immediately after supply do not come into contact with the thread roots 32 ( FIG. 2 ). As a result, all of the thread roots 32 formed in the screw member 10 can function well as cavitation points.

[0037] The thread roots 32 are aligned in the thread leg thrust direction within the axial cross section of the throttle section 9, and are less susceptible to interference from large bubbles of the supply gas immediately downstream of the screw member. This is thought to result in the tendency of the high-speed localized flux generated in each thread root 32 to converge toward the center of the axial cross section. It is also possible that the micro-vortices generated in large numbers downstream of the screw member 10 reduce wall friction loss against the flow. From these facts, it is speculated that a region where the flow is even faster (central flow velocity boost region) is formed steeply in the central region of the axial cross section downstream of the screw member 10 than when the screw member 10 is not provided in the throttle section 9, and that the gas dissolution effect becomes more pronounced.

[0038] Here, the reduced pressure region where bubble nuclei precipitate in the thread valley 32 is limited to the vicinity of the valley bottom, and the liquid flow passes through this region instantaneously and then returns to normal pressure, so it is thought that most of the generated bubble nuclei stop growing in the nucleus state. The exact size of the bubble nuclei is unknown, but for example, Non-Patent Document 1 describes how, in an image obtained by flash-freezing water treated with a swirling flow type ultra-fine bubble (UFB: defined as bubbles with a diameter of 1 μm or less) generator and observing it with an ultra-high voltage electron microscope, minute spots with an average diameter of 10 nm or less are present, for example, at a number density of 8.1 × 10 17 It has been reported that approximately 1 / cc of bubbles are observed. Although not discussed in the literature, the inventors believe that the spots seen in the electron microscope photograph are quite likely to represent bubble nuclei, judging from their size and number density. However, the density of bubble nuclei of this size cannot be measured using general UFB measuring devices (e.g., laser diffraction particle size analyzers or nanotrunking measuring devices).

[0039] According to the gas dissolution device 100 of the present invention, contact between the liquid and the cavitation screw member 10 generates bubble nuclei (which do not grow into bubbles) at a sufficient density. In other words, it can be considered that a pretreatment aimed at generating bubble nuclei is performed before the gas is introduced through the gas inlet 6 in the gas ejection nozzle 1 shown in FIG. 1 . Meanwhile, a turbulent flow region is formed directly below the cavitation screw member 10, as described above. A high proportion of the gas introduced through the gas inlet 6 is entrained in the turbulent flow and dissolved, resulting in dissolved gas. Meanwhile, a large number of bubble nuclei are present in the liquid L. When the outer flow with a high dissolved gas concentration is entrained by the swirling flow into the high-speed central flow, the dissolved gas grows into larger, persistent bubbles GB suspended in the liquid L, using the bubble nuclei BN as seeds, as shown in FIG. 12 . These persistent bubbles GB are believed to be a factor in improving the sustainability of the gas concentration in the resulting liquid.

[0040] It is believed that some of these persistent bubbles GB grow to a size that can be measured using, for example, a laser scattering or nanotracking fine bubble measuring device. However, when the inventors conducted a dissolution test using carbon dioxide gas, they found that the total volume of all the measured bubbles was less than several percent of the total carbon dioxide volume estimated from the carbon dioxide concentration indicated by the concentration meter. Therefore, it is believed that the majority of persistent bubbles GB exist in the liquid at a size (e.g., 10 to 50 nm) that cannot be measured using a typical fine bubble measuring device.

[0041] Although Patent Document 3 does not directly disclose the sustainability of the gas concentration in water obtained through various gases when left in the atmosphere, it does show a tendency for the nozzle with a larger 70% valley point area density, calculated by dividing the number of 70% valley points in the screw member by the total flow cross-sectional area, to have a higher carbon dioxide concentration in the water obtained. Therefore, it appears that the total volume of persistent bubbles GB retained in liquid L increases as the density of bubble nuclei BN increases.

[0042] However, as mentioned above, in the gas dissolution device of Patent Document 3, because gas is supplied from the upstream side of the screw member, a considerable number of thread grooves do not function as cavitation points, the relationship between the number density of cavitation points and the sustainability of the contained gas concentration cannot be understood, and the gas dissolution efficiency per circulation pass is also low. The same situation applies to the hydrogen dissolution method disclosed in Patent Document 4, which, although a detailed disclosure is made about the sustainability of the contained hydrogen concentration, the sustainability of the contained hydrogen concentration is only achieved when water is circulated through multiple passes while continuously introducing hydrogen gas, and it is not possible to understand the sustainability of the contained hydrogen concentration of the water after one circulation pass, or the relationship between this sustainability and the number density of cavitation points.

[0043] The inventors discovered that by modifying the configuration of a gas dissolution device using a cavitation-type gas ejection nozzle (1) so that gas is supplied from the downstream side of the cavitation screw member (10), and by feeding the liquid to the gas ejection nozzle (1) at a flow rate such that the average flow velocity in the axial cross section of the flow path in which the cavitation screw member (10) is disposed is 9 m / s or greater and the effective valley point flow density α is between 1.0 particles·min / L and 3.5 particles·min / L, where ρ is the liquid supply flow rate and the effective valley point flow density α is N / ρ, the gas dissolution efficiency per flow path is dramatically improved and the sustainability of the contained gas concentration is also significantly improved, leading to the completion of the present invention. Note that, in this specification, the gas dissolution efficiency is defined as the ratio of the total amount of gas ultimately contained in the liquid to the total amount of gas introduced, and does not refer to the ratio of only the dissolved gas.

[0044] The improvement in the sustainability of the contained gas concentration is presumably due to the increase in the number density of the minute persistent bubbles GB in the liquid, which are based on the dissolved gas, as explained using Figure 12. As mentioned above, it is considered difficult to measure the absolute quantity of these persistent bubbles GB using existing fine bubble measuring devices. On the other hand, persistent bubbles GB are generated from bubble nuclei BN, and it is thought that bubble nuclei BN are generated at a higher density under flow conditions with a higher value of the effective valley point flow density α.

[0045] Under liquid flow conditions where the effective valley point flow density α is less than 1.0 particles·min / L, the gas dissolution efficiency deteriorates and the resulting gas-containing water has insufficient sustained gas concentration. This is believed to be due to a lack of bubble nuclei BN generated in the liquid, resulting in an insufficient amount of persistent bubbles GB. Here, under liquid flow conditions where the average flow velocity within the axial cross section of the flow path in which the screw member 10 is disposed is less than 9 m / s, the standard equivalent radius R70eq of the critical flow velocity circle C70eq is extremely reduced, making it impossible to ensure the effective valley point flow density α is equal to or greater than the lower limit. Even if it is possible to ensure the effective valley point flow density α, only effective valley points with relatively low flow velocities are obtained even near the center of the cross section, resulting in insufficient sustained gas concentration. Therefore, the average flow velocity is set to 9 m / s or greater.

[0046] On the other hand, what is more important in the present invention is that when the effective valley point flow density α exceeds the upper limit, not only does the gas dissolution efficiency decrease, but the persistence of the contained gas concentration also decreases. This can be understood as the result of the excessive density of bubble nuclei BN, and when the bubble nuclei BN grow due to the introduced gas, adjacent bubbles coalesce and escape to the outside of the liquid, which in turn reduces the amount of persistent bubbles GB.

[0047] Therefore, in the gas dissolution device and method of the present invention, the liquid delivery conditions during gas mixing for the gas ejection nozzle 1 using the cavitation screw member 10 are set so that the effective valley point flow rate density α is 3.5 particles·min / L or less. This adjusts the flow rate of the liquid in contact with the cavitation screw member 10 to a level that does not result in excessive bubble nucleation density, suppressing bubble coalescence and floating. As a result, the gas dissolution efficiency per flow path and the sustainability of the contained gas concentration can be significantly improved. It is more desirable for the liquid delivery conditions during gas mixing to be such that the effective valley point flow rate density α is 1.2 particles·min / L or more and 3.0 particles·min / L or less.

[0048] The 70% valley area density of gas ejection nozzle 1 was 1.00 pieces / mm 2 More than 3.50 pieces / mm2 The value is determined within the following range: 70% valley point area density is 1.00 pieces / mm 2 If the average flow velocity is less than 9 m / s, it becomes difficult to ensure that the effective valley point flow density α is 1.0 particles / min / L or more. 2 If the effective valley point flow density α exceeds 3.5 particles / min / L, it becomes difficult to keep the effective valley point flow density α at 3.5 particles / min / L or less unless the liquid supply flow rate to the gas ejection nozzle 1 is significantly increased. The 70% valley point area density of the gas ejection nozzle 1 is more preferably 1.20 particles / mm 2 More than 3.00 pieces / mm 2 It is preferable that the range be set within the following range.

[0049] Returning to Figure 3, when the selector valve 117 is flipped to the circulation pipe 105 side and the pump 55 is activated, the liquid L in the storage tank 50 flows through the gas ejection nozzle 1 and then returns to the storage tank 50 via the circulation pipe 105. As the liquid L circulates through the gas ejection nozzle 1, the gas introduced through the gas inlet 6 is repeatedly mixed and stirred, resulting in a liquid containing a higher concentration of gas than in a single-pass flow. However, some of the dissolved gas introduced into the liquid through the gas ejection nozzle 1 forms bubbles again, precipitates under reduced pressure, and coalesces and floats to the surface, resulting in loss. As a result, the increase in the gas concentration in the liquid during the second and subsequent passes is smaller than the increase during the first pass, and the gas concentration in the liquid often reaches an equilibrium value within approximately three to five passes. Therefore, when performing two or more passes of circulation while continuing to introduce gas, the final total gas dissolution efficiency is lower than in a single-pass flow.

[0050] The gas dissolving device 100 of the present invention will be described in further detail below. When water is supplied to the liquid inlet 3 of the nozzle body 2 with the liquid outlet 4 open and at a dynamic water pressure of 0.1 MPa, which is equivalent to the pressure of a typical tap water supply, the inner diameter of the axial cross section of the throttle portion 9 is preferably set within the range of 2.0 mm to 8.0 mm to ensure that the average flow velocity at the position where the cavitation screw member is located is 9 m / s or more at a flow rate of 1 L / min to 35 L / min. Furthermore, to achieve an average flow velocity within the above range at the throttle portion 9 at a relatively large flow rate, for example, 4 L / min to 25 L / min, it is more desirable to set the inner diameter of the axial cross section of the throttle portion within the range of 3.5 mm to 8.0 mm. There is no upper limit to the average flow velocity at the position where the cavitation screw member is located at the throttle portion 9. However, because pressure loss increases as the inner diameter of the throttle portion 9 decreases, the limit to the average flow velocity due to the decrease in inner diameter is thought to be approximately 13 to 14 m / s.

[0051] The reasons for setting the numerical ranges of the thread pitch and thread root depth of the cavitation screw member 10 as described above are as follows. First, if the thread root depth is less than 0.2 mm, the cavitation effect (the bubble precipitation effect due to reduced pressure of dissolved gas) necessary for forming a strong stirring region for gas dissolution becomes insignificant. Furthermore, if the thread root depth is insufficient, the local flow velocity at the thread root position cannot be sufficiently ensured, and the cavitation effect also becomes insignificant.

[0052] On the other hand, if the thread root depth is 0.40 mm or greater, the improvement in the cavitation effect plateaus. If the thread pitch is increased to 0.40 mm or greater, the number of thread roots per unit length of the thread stem decreases, and the number of thread roots within the cross section of the constricted portion may not be sufficient. Therefore, in the present invention, the thread pitch and thread root depth are set to 0.20 mm or greater and 0.40 mm or less. Furthermore, to ensure the strength of the threaded member, to prevent the constricted portion from being excessively occupied by the threaded member, and to ensure sufficient liquid flow even with normal fluid supply pressures similar to tap water pressure, the nominal diameter of the threaded member is set to 1.0 mm or greater and 2.0 mm or less. This range of nominal diameter values ​​roughly corresponds to the range of nominal thread diameters for JIS coarse pitch threads, which covers the above-mentioned thread pitch and thread root depth. It is even more preferable that the threaded portion of the cavitation threaded member 10 has a thread pitch of 0.28 mm or greater and 0.32 mm or less, and a thread root depth of 0.28 mm or greater and 0.32 mm or less.

[0053] Next, in the configuration shown in FIG. 2, the cavitation screw member 10 is arranged in the diametric direction of the axial cross section of the throttle portion 9. This is because the flow velocity distribution within the throttle portion 9 increases toward the center of the cross section, which has the advantage of making it easier to form thread grooves 32 through which liquid is supplied at a higher flow velocity. In this case, it is more preferable to arrange the cavitation screw member 10 along a predetermined diameter of the axial cross section of the throttle portion 9 so that the length of the leg of the screw member 10 located within the throttle portion 9 is greater than the radius of the throttle portion 9. This ensures that the thread grooves 32 are located near the center of the axial cross section of the throttle portion 9, where the flow velocity is highest, contributing to an improvement in the density of bubble nuclei. From the perspective of enhancing this effect, as shown in FIG. 2, it is desirable that the cavitation screw member 10 does not have any voids formed along the diametric direction and that the leg located within the throttle portion 9 is structurally arranged so that it spans the entire diameter of the axial cross section of the throttle portion 9.

[0054] Although the gas dissolution efficiency per flow path may be somewhat impaired, it is also possible to employ a configuration in which two screw members 10 are used to form a gap 215 near the center of the cross section in the diameter direction, as shown in Fig. 5, or a configuration in which a gap 215 is formed between the tip of the leg of the screw member 10 and the inner circumferential surface of the throttle section 9, as shown in Fig. 6. Also, as shown in Fig. 7, it is possible to employ a configuration in which four screw members 10 are arranged in a cross shape along two diameters that are perpendicular to each other, to form a square-shaped gap 215 near the center of the cross section.

[0055] Returning to FIG. 1 , the gas-dissolving expansion section 13 is formed as a tapered surface whose axial cross-sectional area continuously increases with increasing distance downstream from the throttle section 9. The gas inlet hole 6 communicates with the liquid flow path 11 within section B, which extends from the downstream edge of the outer circumferential surface of the cavitation screw member 10 located within the throttle section 9 to a position on the inner circumferential surface of the gas-dissolving expansion section 13 where the cross-sectional diameter is 1.5 times (1.5d) the inner diameter d of the throttle section 9. By forming the gas-dissolving expansion section 13 as a tapered surface, a swirling flow is easily generated in the liquid that passes through the cavitation screw member 10 and flows into the gas-dissolving expansion section 13 along the inner circumferential surface of the tapered surface. The formation of this swirling flow enables the gas ejection nozzle 1 to generate a significant gas self-suction capability (negative pressure suction capability) in the gas inlet hole 6, which communicates with the throttle section 9 or the gas-dissolving expansion section 13 downstream of the screw member 10. As a result, not only can gas be smoothly supplied to the gas inlet hole 6 at a relatively low supply pressure, but the gas-liquid mixing action in the downstream area of ​​the screw member 10 is effectively enhanced, and the gas dissolution efficiency per flow path can be further significantly improved.

[0056] In the above configuration, the negative pressure suction effect may not be sufficiently achieved downstream of the position where the gas introduction hole 6 is 1.5 times the inner diameter d of the constricted section 9 (downstream of section B in FIG. 1). In FIG. 1, the gas introduction hole 6 opens into the constricted section 9, but as shown by the dashed line in the figure, the gas introduction hole 6 may open into the gas dissolution expansion section 13 as long as it is within section B.

[0057] When the gradient angle of the inner peripheral surface of the gas dissolution expansion section 13 relative to the center line of the constricted section 9 is θ, the gas self-suction ability of the gas inlet hole 6 is further dramatically improved by making the gas dissolution expansion section 13 an expansion tapered surface in which the gradient section with tan θ of 0.04 to 0.14 accounts for 90% or more of the section length of the gas dissolution expansion section 13. This is thought to be because the formation of a swirling flow for gas dissolution becomes extremely pronounced when the gradient angle θ of the inner peripheral surface of the gas dissolution expansion section 13 is set gradual within the above range.

[0058] In the above configuration, if tan θ is 0.14 or more, the pressure loss due to expansion increases, and a significant improvement in gas self-priming capacity may not be expected. The reason why the gradient section with a small tan θ is set to 90% or more of the length of the gas-dissolving expansion section 13 is because applying a section with a small tan θ to only a small portion of the gas-dissolving expansion section 13 and using a tapered surface or stepped surface with a steeper gradient for the remaining expansion area does not improve gas self-priming capacity. In the configuration of Figure 1, tan θ is set constant in the range of 0.04 to 0.14 throughout the entire gas-dissolving expansion section 13. However, an expansion section with a tan θ outside the above range may be added to the end of the expansion side of the gas-dissolving expansion section 13 as long as it is less than 10% of the length of the gas-dissolving expansion section 13.

[0059] The inner peripheral surface of the gas-dissolving expansion section 13 may be a cylindrical surface 13' without a taper (i.e., tan θ = 0), as shown in FIG. 8 . That is, the gas-dissolving expansion section 13 may be formed as an expansion-diameter cylindrical surface that expands discontinuously (i.e., in stages) from the throttle section 9, and the gas inlet 6 may be configured to communicate with the liquid flow path 11 within the throttle section 9 or at the boundary between the throttle section 9 and the gas-dissolving expansion section 13. In this case, the connection between the throttle section 9 and the gas-dissolving expansion section 13 forms an orifice-like stepped surface. In the configuration shown in FIG. 8 , the gas inlet 6 is opened at the connection between the throttle section 9 and the gas-dissolving expansion section 13, but it is also possible to open the gas inlet 6 to the throttle section 9, as shown in FIG. 9 . [Example]

[0060] Various tests were carried out below to confirm the effects of the present invention. Example 1 Various test gas ejection nozzles (hereinafter referred to as "test nozzles") were fabricated with the shapes shown in FIGS. 1 and 8. A nozzle disclosed in Patent Document 4, Table 9, No. 110, was also prepared (No. 14 in Table 1 of this specification: Outside the scope of the invention (gas introduction hole formed upstream of the cavitation screw member)). The nozzle body 2 was made of PTFE resin and machined into a cylindrical shape with an outer diameter of 30 mm and a length of 76 mm. The inlet tapered section 5 had an axial length of 2 mm, and the opening inner diameter of the liquid inlet 3 was 20 mm. The gas-dissolving expanded diameter section 13 had an axial length L of 24 mm, and the opening inner diameter on the liquid outlet 4 side was 20 mm. The length of the constricted section 9 was 10 mm, and the inner diameter d was set to various values ​​between 2.6 mm and 10.0 mm, as shown in Table 1.

[0061] The shape of the gas-dissolving expansion portion 13 for the test nozzle numbered 1 in Table 1 was a cylindrical surface without a taper, and the slope angle θ of the inner peripheral surface relative to the center line of the constricted portion 9 was zero (i.e., tan θ = 0). The connection between the constricted portion 9 and the gas-dissolving expansion portion 13 was an orifice-shaped stepped surface. On the other hand, for the test nozzles numbered 2 to 13, the inner surface of the gas-dissolving expansion portion 13 was the expansion tapered surface shown in Figure 1, and the aforementioned slope angle θ of the expansion tapered surface was set so that tan θ was various values ​​between 0.08 and 0.13.

[0062] The cavitation screw member 10 is a No. 0, Class 1 pan head machine screw with a metric coarse pitch as specified in JIS:B0205 (1997) and is made of stainless steel (SUS304). The cavitation screw members 10 used have nominal thread diameters of M1.0 (thread pitch: 0.25 mm, screw head outer diameter: 1.8 mm), M1.2 (thread pitch: 0.25 mm, screw head outer diameter: 1.8 mm), M1.4 (thread pitch: 0.30 mm, screw head outer diameter: 2.0 mm), and M1.6 (thread pitch: 0.35 mm, screw head outer diameter: 2.4 mm). For the test nozzles numbered 2 to 7, 9 to 11, and 13 in Table 1, only one cavitation screw member 10 was placed across the entire diameter of the axial cross section, as shown in Figure 2. On the other hand, for test nozzle No. 8, four M1.4 threaded members were arranged in a cross shape in the diametrically orthogonal directions in the layout shown in Figure 7. The spacing of the gaps 215 was 1.4 mm. For test nozzle No. 12, two M1.4 threaded members were arranged in a diametrical direction in the layout shown in Figure 5. The spacing of the gaps 215 was 1.4 mm.

[0063] The gas inlet 6 has an inner diameter of 1.0 mm and is opened at the connection position of the throttle section 9 and the gas-dissolving expanded diameter section 13 so that its central axis is parallel to that of the cavitation screw member 10. The opening position of the gas inlet 6 is 2 mm downstream of the cavitation screw member 10 in terms of the distance between the central axes. Note that the test nozzle numbered 1 is a comparative example in which the cavitation screw member 10 is omitted.

[0064] In addition, the number of 70% valley points N inside the reference circle was counted on a projected image showing the layout of the screw member 10 inside the constriction section 9, and the value of the 70% valley point area density β was calculated for each test nozzle by dividing this by the flow cross-sectional area S of the constriction section 9. The values ​​of the inner diameter d of the constriction section, the flow cross-sectional area S, the 70% valley point number N, and the 70% valley point area density β of each test nozzle are summarized in Table 1.

[0065] [Table 1]

[0066] Each test nozzle was installed in the gas dissolution apparatus 100 shown in Figure 3, and the storage tank 50 (volume: 20 L) was filled with tap water at 20°C. The selector valve 117 was then shifted to the circulation pipe 105 side, and the pump 55 (Tohshin Technical vane pump: TVP-MS1803-A) was operated. While checking the reading on the pressure gauge 110, the opening of the flow control valve 116 was adjusted appropriately to set the dynamic water pressure applied to the test nozzle at various values ​​between 0.08 and 0.60 MPa. The flow rate of tap water flowing through the test nozzle was measured with the flowmeter 111. Based on the measured flow rate and the cross-sectional area of ​​each test nozzle, the average flow velocity at the position of the threaded member in the throttle section 9 was calculated. Furthermore, for the water flow conditions of each test number, the standard equivalent radius R70eq was calculated using Equation (2). The effective valley point number N for the gas ejection nozzle used was calculated, and the effective valley point flow density α was calculated using the formula α = N / ρ, where ρ is the supply flow rate.

[0067] In addition, the treated water was filled into a quartz batch cell, and the bubble density in the UFB region (bubble diameter: 1 μm or less) was measured using a laser diffraction high-sensitivity fine bubble measurement system (Shimadzu Corporation: SALD-7500 × 10).

[0068] Next, a carbon dioxide gas cylinder was connected to the gas dissolution apparatus 100 as the gas supply source 123. The gas supply switching valve 122 was turned to the main gas supply pipe 121, and while monitoring the flow rate of tap water flowing through the test nozzle with the flow meter 111, the opening of the flow control valve 124 was appropriately changed to adjust the flow rate of carbon dioxide gas so that the gas-liquid mixture ratio (gas flow rate / water flow rate under standard conditions) was various values ​​between 0.60 and 0.76. The carbon dioxide gas flow rate under standard conditions was calculated from the pressure and flow rate indication values ​​of the flow / pressure measuring device 125. Note that for test nozzles Nos. 1 to 13, a negative suction pressure was generated in the gas inlet hole 6, so the carbon dioxide gas supply pressure was set to 0.1 MPa. On the other hand, for test nozzle No. 14, carbon dioxide gas could not be supplied at a supply pressure of 0.1 MPa, so carbon dioxide gas was supplied at 0.2 MPa, as in Patent Document 3.

[0069] After adjusting the gas-liquid ratio, the selector valve 117 was quickly switched to the liquid outlet pipe 103 side, and water was passed through the gas ejection nozzle 1 once while introducing carbon dioxide, and the resulting dissolved water was collected. The carbon dioxide concentration of the dissolved water was measured using a commercially available carbon dioxide concentration meter (DKK-TOA Corporation: CGP-31 (diaphragm electrode type)). For each condition, the theoretical carbon dioxide concentration Ct was calculated assuming that all of the supplied carbon dioxide dissolved, and the carbon dioxide dissolution efficiency was calculated by dividing the measured carbon dioxide concentration C by Ct. Furthermore, 5 L of the dissolved water was collected in a resin beaker with an 18 cm opening diameter, and the change in carbon dioxide concentration over time was measured while exposed to the atmosphere at 20°C. The obtained measurement points were curve-fitted with an exponential function to obtain a regression curve, and the half-life was calculated as the time until the carbon dioxide concentration on the regression curve became half of its initial value. The results are summarized in Table 2.

[0070] [Table 2]

[0071] Table 3 shows the results of similar tests conducted by adjusting the gas-liquid mixture ratio to a value of 0.1 or 0.3, and Table 4 shows the results of similar tests conducted by adjusting the gas-liquid mixture ratio to various values ​​between 1.00 and 1.53.

[0072] [Table 3]

[0073] [Table 4]

[0074] Figure 13 is a graph showing the relationship between the effective valley point flow density and the UFB number density measurement results when water was passed through the nuclear gas ejection nozzle without gas supply under conditions where the cross-sectional average flow velocity exceeded 9 m / s, as shown in Table 2. As is clear from the results, the UFB number density was particularly high when the effective valley point flow density α was between 1.0 and 3.5 particles·min / L, especially between 1.2 and 3.0 particles·min / L. Figure 14 shows histograms of the bubble volume density distribution obtained by measuring the test waters obtained in Test Nos. 5 and 16 in Table 2 using the fine bubble measurement system. Figure 15 shows a histogram of the bubble number density distribution obtained by converting Figure 14 into a bubble number density distribution.

[0075] FIG. 16 is a graph showing the results of a test to examine the sustainability of the carbon dioxide concentration when carbonated water (specifically, test numbers 104, 202, and 203 in Tables 3 and 4) obtained by passing carbon dioxide gas through a single pass using the gas ejection nozzle No. 5 in Table 1 at various water flow rates and gas-liquid ratios was left in the atmosphere, compared with water in which carbon dioxide was dissolved using a gas exchange membrane (comparison example). It can be seen that the sustainability of the carbon dioxide concentration of the carbonated water of the present invention was significantly improved compared to the carbonated water of the comparison example, despite the single-pass flow. Note that test number 202 exhibited a unique phenomenon in which the carbon dioxide concentration initially increased and then decreased. This is presumably due to the difference in detection sensitivity between dissolved carbon dioxide and sustained-bubble carbon dioxide in the carbon dioxide concentration meter used, resulting in the carbon dioxide in the sustained-bubble state changing to dissolved carbon dioxide during storage.

[0076] In such cases, the carbon dioxide concentration meter reading when the concentration is maximized after standing is considered to be closer to the true value of the carbon dioxide concentration immediately after collection. However, it is difficult to determine the ratio of dissolved carbon dioxide and carbon dioxide in a sustained bubble state from the carbon dioxide concentration meter reading alone, and considering the possibility that the detection sensitivity for carbon dioxide in both states may differ, it is assumed that the carbon dioxide concentration indicated by the carbon dioxide concentration meter reading also contains a certain amount of error. Therefore, as shown in Figure 17, the measurement points of the change in carbon dioxide concentration over time are curve-fitted with an exponential function to obtain a regression curve, and the standing time on this regression curve until the carbon dioxide concentration becomes half of its initial value is calculated as the half-life, and the sustainability of the carbon dioxide concentration is evaluated based on this half-life. According to the test results shown in Figure 17 (see also Tables 2 to 4), the half-life of the carbonated water in the comparative example was just over one hour, whereas the half-lives of the carbonated water in test numbers 104, 202, and 203, which are examples of the present invention, exceeded 15 hours, demonstrating that the durability was extremely good despite the carbon dioxide gas dissolution being carried out in a single-pass flow.

[0077] Figure 18 is a graph plotting the half-life of the carbon dioxide concentration when water is left standing after carbon dioxide gas is supplied to the gas ejection nozzle against the UFB number density measured when water is circulated without gas supply. It is clear that the greater the UFB number density when water is circulated without gas supply, the longer the half-life of the carbon dioxide concentration in the resulting water, and the better the sustainability. Also referring to Figure 13, it can be seen that the sustainability of the carbon dioxide concentration is not improved by the flow conditions with a higher effective valley point flow density α, but is particularly improved when the effective valley point flow density α is adjusted within an appropriate range (specifically, from 1.0 particles·min / L to 3.5 particles·min / L, and particularly from 1.2 particles·min / L to 3.0 particles·min / L).

[0078] 19 is a graph plotting the dissolution efficiency when carbon dioxide gas is supplied against the UFB number density measured when water is circulated without gas being supplied to the gas ejection nozzle. It can be seen that in a single-pass flow, the higher the UFB number density when water is circulated without gas supply, the more the carbon dioxide dissolution efficiency improves.

[0079] FIG. 20 is a graph showing the relationship between the gas-liquid ratio and the carbon dioxide dissolution efficiency when carbon dioxide gas is passed through the gas ejection nozzles Nos. 1, 2, and 3 in Table 1 at a water flow rate of 10 L / min. For all nozzles, the carbon dioxide dissolution efficiency improves as the gas-liquid ratio increases. For example, when comparing the critical gas-liquid ratio at which the carbon dioxide dissolution efficiency reaches 50%, the critical gas-liquid ratio is approximately 0.6 when No. 1, which does not use a cavitation screw element, is used. However, when Nos. 2 and 3, which use a cavitation screw element, are used, the critical gas-liquid ratio for No. 2 is approximately 0.3, and the critical gas-liquid ratio for No. 3 is approximately 0.05, which is significantly below 0.1. In other words, the use of a gas ejection nozzle that has a cavitation screw element and supplies gas downstream of the cavitation screw element enables more efficient gas dissolution even at low gas-liquid ratios than the use of an ejection nozzle without a cavitation screw element.

[0080] Example 2 Nozzle No. 3 in Table 1 and nozzle No. 14 for comparison were installed in the gas dissolution apparatus 100 shown in Fig. 3 in the same manner as in Example 1, and the storage tank 50 (volume: 20 L) was filled with tap water at 20°C, and a hydrogen gas cylinder was connected as the gas supply source 123. In this state, first, the switching valve 117 was switched to the circulation pipe 105 side to operate the pump 55, and the opening of the flow rate control valve 116 was appropriately changed while checking the reading displayed on the pressure gauge 110, so that the dynamic water pressure applied to the test nozzle was set to 0.08 MPa for nozzle No. 3 and 0.3 MPa for nozzle No. 14.

[0081] Next, the gas supply switching valve 122 was switched to the main gas supply pipe 121, and while monitoring the flow rate of tap water flowing through the test nozzle with the flow meter 111, the opening of the flow control valve 124 was appropriately changed to adjust the hydrogen gas flow rate so that the gas-liquid mixture ratio (gas flow rate / water flow rate under standard conditions) was 0.1 or 0.2. The hydrogen gas flow rate under standard conditions was calculated from the pressure and flow rate readings of the flow / pressure measuring device 125. After adjustment, the switching valve 117 was quickly switched to the liquid extraction pipe 103 side, and the resulting water was collected. The hydrogen concentration was measured using a commercially available diaphragm polarographic electrode-type dissolved hydrogen meter (Kyoei Electronics Laboratory: KM2100DH). For each condition, the theoretical hydrogen concentration Ct, which would be obtained assuming that all the supplied hydrogen gas had dissolved, was calculated, and the hydrogen gas dissolution efficiency was calculated by dividing the measured hydrogen concentration C by Ct. Furthermore, 5 L of the dissolved water was collected in a resin beaker with an opening diameter of 18 cm, and the change in hydrogen concentration over time was measured while the beaker was exposed to the atmosphere at 20°C. The measurement points obtained were curve-fitted with an exponential function to obtain a regression curve, and the time it took for the hydrogen concentration on the regression curve to become half of its initial value was calculated as the half-life. The above results are summarized in Table 5.

[0082] [Table 5]

[0083] It can be seen that the use of a gas ejection nozzle (number 3) that has a cavitation screw member and supplies gas downstream of the cavitation screw member results in a better gas dissolution efficiency per flow pass than the use of a gas ejection nozzle (number 14: outside the scope of the invention) that supplies gas upstream of the cavitation screw member. Furthermore, the half-life of the hydrogen-containing water obtained using the gas ejection nozzle number 3 is longer than that using the gas ejection nozzle number 14. It can be seen that the values ​​are more than twice as good as when the

[0084] Example 3 The nozzle numbered 3 in Table 1 was incorporated into the gas dissolution apparatus 100 shown in Figure 3, as in Example 1, and the storage tank 50 (capacity: 100 L) was filled with tap water at 20°C, and a commercially available ozone generator was connected as the gas supply source 123. The ozone generator receives a supply of pure oxygen from an oxygen cylinder and generates an ozone-containing gas by silent discharge at normal pressure. The concentration of the resulting ozone-containing gas was 90 g / m 3 In this state, first, the switching valve 117 was switched to the circulation pipe 105 side to operate the pump 55, and the opening of the flow rate control valve 116 was appropriately changed while checking the reading displayed on the pressure gauge 110, so that the dynamic water pressure applied to the test nozzle was set to 0.08 MPa.

[0085] Next, the gas supply switching valve 122 was closed to the main gas supply pipe 121. While monitoring the flow rate of tap water flowing through the test nozzle with the flow meter 111, the flow rate of the ozone-containing gas was adjusted by appropriately adjusting the opening of the flow control valve 124 so that the gas-liquid mixture ratio (gas flow rate / water flow rate under standard conditions) was 0.10. The standard flow rate of the ozone-containing gas was calculated from the pressure and flow rate readings of the flow / pressure measuring device 125. After adjustment, 5 L of water was collected from the storage tank 50 after one and two circulations into a resin beaker with an 18 cm opening, and the ozone concentration was measured using a commercially available dissolved ozone monitor (HZ-960, manufactured by HORIBA Advanced Techno Co., Ltd.). For each condition, the theoretical ozone concentration Ct, which is obtained assuming that all the supplied ozone was dissolved, was calculated, and the ozone dissolution efficiency was calculated by dividing the measured ozone concentration C by Ct. Furthermore, the water in the container was exposed to the air at 20°C while the change in ozone concentration over time was measured, and the obtained measurement points were curve-fitted with an exponential function to obtain a regression curve. The time it took for the ozone concentration on the regression curve to become half of its initial value was calculated as the half-life.

[0086] For comparison, ozone water was prepared by bubbling ozone-containing gas from an ozone generator through a 2 mm inner diameter tube at 1 NL / min into 5 L of tap water at 20°C in a plastic beaker until the dissolved ozone concentration reached 4 ppm. The results are summarized in Table 6.

[0087] [Table 6]

[0088] It can be seen that by using a gas ejection nozzle (number 3) that has a cavitation screw element and supplies gas downstream of the cavitation screw element, ozone can be dissolved with an efficiency of over 80%. Furthermore, it can be seen that the ozone water obtained shows good durability, about three times longer, compared to ozone water obtained by bubbling dissolution.

[0089] Example 4 Various test nozzles with the shapes shown in Figures 1 and 8 were created for evaluating self-priming performance. The nozzle body 2 was made of PTFE resin and was machined into a cylindrical shape with an outer diameter of 30 mm and a length of 76 mm. The inlet tapered section 5 had an axial length of 2 mm, and the opening inner diameter of the liquid inlet 3 was 20 mm. The gas-dissolving expanded diameter section 13 had an axial length L of 24 mm, and the opening inner diameter on the liquid outlet 4 side was 20 mm. The length of the constricted section 9 was 10 mm, and the inner diameter d was variously set between 2.2 mm and 8.0 mm, as shown in Table 7.

[0090] For the test nozzles numbered 501, 520, and 521 in Table 7, the shape of the gas-dissolving expansion portion 13 is a cylindrical surface without a taper as shown in Figure 8, and the slope angle θ of the inner peripheral surface relative to the center line of the constricted portion 9 is zero (i.e., tan θ = 0). The connection between the constricted portion 9 and the gas-dissolving expansion portion 13 is an orifice-shaped stepped surface. For the test nozzles numbered 502 to 519 and 522 and 523, the inner surface of the gas-dissolving expansion portion 13 is the expansion tapered surface shown in Figure 1, and the aforementioned slope angle θ of the expansion tapered surface is set to various values ​​of tan θ between 0.042 and 0.197.

[0091] The cavitation screw elements 10 used had nominal thread diameters of M1.0 (thread pitch: 0.25 mm, screw head outer diameter: 1.8 mm), M1.4 (thread pitch: 0.30 mm, screw head outer diameter: 2.0 mm), and M1.6 (thread pitch: 0.35 mm, screw head outer diameter: 2.4 mm). For test nozzles numbered 501 to 516 and 519 in Table 7, only one cavitation screw element 10 was arranged across the entire diameter of the axial cross section, as shown in Figure 2. For test nozzle numbered 517, four M1.4 screw elements were arranged in a cross shape in the diametrically perpendicular directions, as shown in Figure 7. The spacing between the gaps 215 was 1.4 mm. For test nozzle numbered 518, two M1.4 screw elements were arranged in one diametrical direction, as shown in Figure 5. The gap 215 is 1.4 mm in width.

[0092] The gas inlet 6 has an inner diameter of 1.0 mm and is opened at the connection position of the throttle section 9 and the gas-dissolving expanded section 13 so that its central axis is parallel to that of the cavitation screw member 10. The opening position of the gas inlet 6 is 2 mm downstream of the cavitation screw member 10 in terms of the distance between the central axes. Note that the test nozzles numbered 520 and 521 and the test nozzles numbered 522 and 523 are comparative examples in which the cavitation screw member 10 is omitted.

[0093] In addition, the number of 70% valley points N inside the reference circle was counted on a projected image showing the layout of the screw member 10 inside the constriction section 9, and the value of the 70% valley point area density β was calculated for each test nozzle by dividing this by the flow cross-sectional area S of the constriction section 9. The values ​​of the inner diameter d of the constriction section, the flow cross-sectional area S, the 70% valley point number N, and the 70% valley point area density β of each test nozzle are summarized in Table 7.

[0094] Each test nozzle was installed in the gas dissolution device 100 shown in Figure 3, and the storage tank 50 (volume: 20 L) was filled with tap water at 20°C. The selector valve 117 was then shifted to the circulation pipe 105 side to operate the pump 55 (Tohshin Technical vane pump: TVP-MS1803-A). While checking the reading on the pressure gauge 110, the opening of the flow control valve 116 was adjusted appropriately to set the dynamic water pressure applied to the test nozzle to 0.1 MPa. The selector valve 122 was then shifted to the measurement pipe 126 side, and the negative suction pressure generated in the gas inlet hole 6 of the test nozzle was measured with the negative pressure gauge 127 without gas being supplied. The flow rate of tap water flowing through the test nozzle was measured with the flow meter 111, and the average flow velocity at the position of the screw member in the throttle section 9 was calculated based on the measured value and the cross-sectional area of ​​each test nozzle. The results are summarized in Table 7.

[0095] [Table 7]

[0096] It can be seen that the test nozzles numbered 501 to 519 all generated higher negative suction pressure values ​​than the comparative test nozzles numbered 520 to 523, which did not use a cavitation screw member. In these test nozzles, the throttle section 9 had a flow rate of 1 L / min to 35 L / min and an average flow velocity of 9 m / sec to 13.5 m / sec when water was supplied to the liquid inlet 3 of the nozzle body 2 at a supply dynamic pressure of 0.1 MPa. The inner diameter of the axial cross section of the throttle section 9 was φ2.0 mm to φ8.0 mm, and all test nozzles achieved a good negative suction pressure value of -0.06 MPa or less.

[0097] In order to ensure a good suction negative pressure, it is desirable that the average flow velocity at the cavitation screw position be larger at the same liquid supply dynamic pressure. Figure 10 is a graph showing the relationship between the flow cross-sectional area of ​​the throttle section of the test nozzle in Table 7 and the average flow velocity at the cavitation screw position when water is passed through at a dynamic pressure of 0.1 MPa. 2In the region where the above is ensured, the average flow velocity at the position where the screw member 10 is disposed is almost constant at around 12.5 m / sec. However, in the region where the flow cross-sectional area S of the throttle portion is smaller than this, the average flow velocity starts to decrease due to an increase in flow pressure loss, and especially when the flow cross-sectional area S of the throttle portion is 3 mm 2 The average flow velocity decreases significantly in the region where the flow cross-sectional area S of the constricted section is less than 3 mm 2 Above 8mm, preferably 2 Above 11mm, preferably 11mm 2 It is advisable that the above is secured.

[0098] Of the nozzles in which the inner surface of the gas-dissolving expansion section 13 is an expansion-diameter tapered surface, the test nozzles numbered 502 to 506 and 511, 512, and 519 have M1.4 cavitation screw members 10 arranged relative to the throttling section 9 in the layout shown in Figure 2. The test results in Table 7 for these test nozzles reveal the following.

[0099] The test nozzles numbered 502 to 506 have a tan θ value of the expanding tapered surface forming the gas-dissolving expanding portion 13 set within a range of 0.04 to 0.14, whereas the test nozzles numbered 509 to 506 have a tan θ value of the expanding tapered surface that exceeds this range. The test nozzles numbered 502 to 506 have a higher suction negative pressure value than the test nozzles numbered 509 to 516. Furthermore, the test nozzle numbered 502 and the test nozzle numbered 519 have the same flow cross-sectional area in the throttling portion 9, but the tan θ value of the expanding tapered surface is 0.160 for the test nozzle numbered 519, whereas the tan θ value for the test nozzle numbered 502 is set to a smaller value of 0.125. The suction negative pressure value for the test nozzle numbered 502 is higher than the test nozzles numbered 509 to 516. It is clear that setting the angle θ of the expanding tapered surface to a small value, in particular setting the value of tan θ to be within the range of 0.04 or more and 0.14 or less, is advantageous in improving the value of the suction negative pressure.

[0100] Test nozzles Nos. 502 to 506 have the same thread layout as in Figure 2, but the inner diameter d of the constricted portion is changed, and the 70% valley point area density value gradually decreases from No. 502 to No. 506. Of these, the value of the 70% valley point area density is 1.00 count / mm 2 The test nozzles No. 502 to No. 505, which are above the above, have a 70% valley area density of 1.00 pieces / mm 2 The negative suction pressure is greater than that of test nozzle No. 506, which is less than 1.20 / mm. 2 More than 2.25 / mm 2 The test nozzles numbered 502 to 504 below achieved very good results, with negative suction pressure values ​​of -0.09 MPa or less under water flow conditions of a dynamic water pressure of 0.1 MPa.

[0101] The test nozzles Nos. 507 and 508 have approximately the same cross-sectional flow area S of the throttling portion 9, but the nominal diameter of the cavitation screw element 10 used is changed to M1.2 or M1.6, which is different from the test nozzle No. 502. The measured suction negative pressure values ​​for these test nozzles are also relatively good, but slightly inferior to the test nozzle No. 2, which uses M1.4. These differences are thought to be caused by the difference in the depth of the thread roots of the screw elements used.

[0102] The test nozzles 502, 517, and 518 use the same M1.4 screw member as the cavitation screw member 10, and the cross-sectional flow area S of the throttle section 9 is set to a similar value, but the number and layout of the screw members are different. Specifically, the test nozzle 502 has one screw member 10 arranged across the entire area of ​​a predetermined diameter of the axial cross section of the throttle section 9 (i.e., so that the leg length of the screw member 10 located within the throttle section 9 is longer than the radius of the throttle section 9), while the test nozzle 517 has four screw members arranged along two diameters and forms a gap 215 in the center of the cross section (see Figure 7). The test nozzle 518 has two screw members arranged in the direction of one diameter and forms a gap 215 in the center of the cross section (see Figure 5). Comparing the results for these test nozzles, test nozzle number 502 generates a higher negative suction pressure value than test nozzles number 517 and number 518.

[0103] The test nozzles numbered 501 and 502 have the same screw arrangement and the same inner diameter of the constricted portion, but the test nozzle numbered 501 has a cylindrical inner surface of the gas-dissolving expansion portion 13 as shown in Figure 8, whereas the test nozzle numbered 502 has a more gradual tapered inner surface of the gas-dissolving expansion portion 13 as shown in Figure 1. The test nozzle numbered 502 has a higher suction negative pressure.

[0104] Figure 21 shows the measurement results of the negative pressure dynamic water pressure characteristic curve, which shows the relationship between the dynamic water pressure value and the suction negative pressure generated in the gas introduction hole 6 when water is passed through the nozzle main body 2 with the nozzle outlet side open, comparing the test nozzle number 502 and the test nozzle number 520. The flow cross-sectional area at the constriction part of the test nozzle number 2 was 8.2 mm 2 , No. 520 test nozzle is 7.1 mm 2 There is not much difference in the average flow velocity values ​​at a dynamic water pressure of 0.10 MPa shown in Table 1, but the shapes of the negative pressure dynamic water pressure characteristic curves are clearly different.

[0105] Specifically, for test nozzle 520 (an orifice-type nozzle with a cylindrical gas-dissolving expansion section 13), the change in negative suction pressure with increasing water dynamic pressure was gradual, and the negative suction pressure at a water dynamic pressure of 0.10 MPa was found to be approximately -0.055 MPa. Furthermore, the critical water dynamic pressure for the negative suction pressure to be -0.07 MPa or less was 0.16 MPa, and the critical water dynamic pressure for the negative suction pressure to be -0.09 MPa or less was 0.27 MPa.

[0106] On the other hand, the test nozzle numbered 502 clearly shows a much steeper change in negative suction pressure with increasing water dynamic pressure by forming the inner surface of the gas dissolution expansion section 13 into a gradually expanding tapered surface and locating a cavitation screw member downstream of the gas inlet hole 6. The negative suction pressure at a water dynamic pressure of 0.10 MPa was -0.093 MPa, the critical water dynamic pressure for the negative suction pressure to be -0.07 MPa or less was 0.06 MPa (i.e., 0.07 MPa or less), and the critical water dynamic pressure for the negative suction pressure to be -0.09 MPa or less was 0.082 MPa (i.e., 0.09 MPa or less), indicating that sufficient negative suction pressure was obtained even at low flow rates (i.e., low water dynamic pressures).

[0107] Figure 22 shows a comparison of the negative pressure flow velocity characteristic curves, obtained by converting the horizontal axis of Figure 21 into the average flow velocity value at the choke section, for test nozzle No. 502 and test nozzle No. 520. Test nozzle No. 520 had a high critical flow velocity of 17.1 m / s for the suction negative pressure to be −0.07 MPa or less, and a high critical flow velocity of 21.0 m / s for the suction negative pressure to be −0.09 MPa or less. On the other hand, test nozzle No. 502 had a critical flow velocity of 12.3 m / s (i.e., 13 m / s or less) for the suction negative pressure to be −0.07 MPa or less, and a high critical flow velocity of 13.8 m / s (i.e., 14 m / s or less) for the suction negative pressure to be −0.09 MPa or less, both of which were significantly lower than those of test nozzle No. 520.

[0108] Figure 23 shows the measurement results of the negative pressure dynamic water pressure characteristic curves for the test nozzle No. 503 (Example) and the test nozzle No. 521 (Comparative Example) in comparison. The cross-sectional flow area at the throttle section of the test nozzle No. 502 was 14.1 mm2 , No. 521 test nozzle is 12.6 mm 2 According to Table 1, the difference in the average flow velocity at a hydrodynamic pressure of 0.10 MPa is within a few percent. However, in the above-mentioned region of the cross-sectional flow area where the pressure loss in the throttle section 9 is reduced, the difference in the shape of the negative pressure hydrodynamic characteristic curve between the example test nozzle and the comparative example test nozzle becomes even more pronounced.

[0109] Specifically, for test nozzle No. 521, the negative suction pressure was approximately -0.057 MPa at a hydrodynamic pressure of 0.10 MPa. The critical hydrodynamic pressure for a negative suction pressure of -0.07 MPa or less was 0.14 MPa, and the critical hydrodynamic pressure for a negative suction pressure of -0.09 MPa or less was 0.27 MPa. Compared to test nozzle No. 520, the performance in the low hydrodynamic pressure range was slightly improved, but a large hydrodynamic pressure was still required to achieve a negative suction pressure of -0.09 MPa or less.

[0110] On the other hand, as is clear from a comparison with Figure 21, the change in negative suction pressure with increasing water dynamic pressure for test nozzle No. 503 is even steeper than for test nozzle No. 502. The critical water dynamic pressure for negative suction pressure to be -0.07 MPa or less is 0.040 MPa, and the critical water dynamic pressure for negative suction pressure to be -0.09 MPa or less is 0.051 MPa. It can be seen that in the range of water dynamic pressures above 0.10 MPa, a nearly flat negative suction pressure close to the physical maximum value is obtained.

[0111] Figure 24 shows a comparison of the negative pressure flow velocity characteristic curves, obtained by converting the horizontal axis of Figure 23 into the average flow velocity value at the choke section, for test nozzle No. 503 and test nozzle No. 521. For test nozzle No. 521, the critical flow velocity value for the suction negative pressure to be -0.07 MPa or less is 17.1 m / s, and the critical flow velocity value for the suction negative pressure to be -0.09 MPa or less is 21.3 m / s. On the other hand, for test nozzle No. 503, the critical flow velocity value for the suction negative pressure to be -0.07 MPa or less is 11.3 m / s, and the critical flow velocity value for the suction negative pressure to be -0.09 MPa or less is 12.4 m / s. [Explanation of symbols]

[0112] 1 Gas ejection nozzle 2 Nozzle body 3 liquid inlet 5. Inlet tapered section 6 Gas inlet 9. Constriction section 10 Cavitation screw element 11 Liquid flow path 13 Gas dissolving expansion section 31 threads 32 Neji Valley

Claims

1. a nozzle body having a single liquid flow path formed therein with a liquid inlet at one end and a liquid outlet at the other end, and a throttled section formed midway through the liquid flow path so as to have a diameter smaller than that of the liquid inlet; a cavitation screw member disposed within the throttled section, and having a threaded section formed on its outer surface with a thread pitch of 0.20 mm or more and 0.40 mm or less, a thread root depth of 0.20 mm or more and 0.40 mm or less, and a nominal diameter of 1.0 mm or more and 2.0 mm or less; and a gas dissolution expansion section connected to the downstream side of the throttled section in a manner forming a part of the liquid flow path, and having an axial cross-sectional area that expands continuously or stepwise toward the liquid outlet; and a gas introduction hole formed downstream of all of the cavitation screw members located within the throttled section, and connecting the outside of the nozzle body to the liquid flow path, the gas introduction hole communicating with the throttled section or the gas dissolution expansion section, and ２ Over 42mm ２ Hereinafter, the number of thread valley points of the cavitation screw member that exist within 70% of the radius from the center in the axial cross section of the throttled portion is defined as the 70% valley point number, and the value of the 70% valley point area density, which is the value obtained by dividing the 70% valley point number by the flow cross-sectional area, is 1.00 points / mm ２ 3.50 pieces / mm or more ２ a gas ejection nozzle defined within the following ranges; a gas supply unit that supplies gas to the gas introduction hole of the nozzle body; In the gas ejection nozzle, the flow velocity distribution in the radial direction of the cross section immediately before the liquid collides with the cavitation screw member is parabolic, being maximum at the center of the cross section and zero at the inner wall surface of the flow path, and further, the radius of the axial cross section is R, and the outlet side of the gas ejection nozzle is open, and water is passed through the gas ejection nozzle under standard conditions where the dynamic water pressure supplied to the gas ejection nozzle is 0.1 MPa. The flow velocity at a position 0.71R from the center of the axial cross section is a liquid delivery unit that delivers liquid to the liquid inlet of the nozzle body at a flow rate such that an average flow velocity in the axial cross section of the flow path in which the screw member is disposed is 9 m / s or more and the value of the effective valley point flow density α is 1.0 particles min / L or more and 3.5 particles min / L or less, where N is an effective valley point number N and ρ is the total number of valley points of the thread valleys of the cavitation screw member that are equal to or higher than the critical flow velocity when projected onto the axial cross section, ρ is the supply flow rate of the liquid, and α is an effective valley point flow density α = N / ρ; A gas dissolving device comprising:

2. 2. The gas dissolution device according to claim 1, wherein the cavitation screw member of the gas ejection nozzle is arranged so that the length of the leg of the screw member located within the constricted portion is greater than the radius of the constricted portion along a predetermined diameter of the axial cross section of the constricted portion.

3. 3. The gas dissolving device according to claim 2, wherein the cavitation screw member of the gas ejection nozzle is arranged so that the leg portion located within the throttle portion spans the entire diameter of the axial cross section of the throttle portion.

4. 2. The gas dissolution device according to claim 1, wherein the gas ejection nozzle has a gas-dissolving expansion section formed as a tapered surface whose axial cross-sectional area continuously increases with increasing distance from the throttle section downstream, and the gas introduction hole communicates with the liquid flow path within a section from the downstream edge of the outer peripheral surface of the cavitation screw member located within the throttle section to a position on the inner peripheral surface of the gas-dissolving expansion section where the cross-sectional diameter is 1.5 times the inner diameter of the throttle section.

5. 2. The gas dissolution device according to claim 1, wherein the gas-dissolving expansion portion of the gas ejection nozzle has an expansion tapered surface, and when the gradient angle of the inner peripheral surface with respect to the center line of the constricted portion is θ, a gradient section in which tan θ is 0.04 or more and 0.14 or less accounts for 90% or more of the section length of the gas-dissolving expansion portion.

6. 6. The gas dissolving device according to claim 5, wherein in a negative pressure hydrodynamic characteristic curve showing the relationship between the hydrodynamic pressure value and the suction negative pressure generated in the gas introduction hole when water is passed through the nozzle main body with the nozzle outlet side in an open state, the critical hydrodynamic pressure value for the suction negative pressure value to be −0.07 MPa or less is 0.07 MPa or less.

7. 6. The gas dissolving device according to claim 5, wherein in a negative pressure flow velocity characteristic curve showing the relationship between the average flow velocity value of the throttle section and the negative suction pressure generated in the gas introduction hole when water is passed through the nozzle main body with the nozzle outlet side in an open state, the critical flow velocity value for the negative suction pressure value to be −0.07 MPa or less is 13 m / s or less.

8. 6. The gas dissolving device according to claim 5, wherein in a negative pressure dynamic water pressure characteristic curve showing the relationship between the dynamic water pressure value when water is passed through the nozzle body and the negative suction pressure generated in the gas introduction hole, a critical dynamic water pressure value for the negative suction pressure value to be −0.09 MPa or less is 0.09 MPa or less.

9. 6. The gas dissolving device according to claim 5, wherein in a negative pressure flow velocity characteristic curve showing the relationship between the average flow velocity value of the throttle section when water is passed through the nozzle body and the suction negative pressure generated in the gas introduction hole, the critical flow velocity value for the suction negative pressure value to be −0.09 MPa or less is 14 m / s or less.

10. 2. The gas dissolution device according to claim 1, wherein the gas dissolution expansion section is formed as an expansion cylindrical surface that discontinuously expands in diameter from the constriction section, and the gas introduction hole communicates with the liquid flow path within the constriction section or at the boundary between the constriction section and the gas dissolution expansion section.

11. a nozzle body having a single liquid flow path formed therein with a liquid inlet at one end and a liquid outlet at the other end, and a throttled section formed midway through the liquid flow path so as to have a diameter smaller than that of the liquid inlet; a cavitation screw member disposed within the throttled section, and having a threaded section formed on its outer surface with a thread pitch of 0.20 mm or more and 0.40 mm or less, a thread root depth of 0.20 mm or more and 0.40 mm or less, and a nominal diameter of 1.0 mm or more and 2.0 mm or less; and a gas dissolution expansion section connected to the downstream side of the throttled section in a manner forming a part of the liquid flow path, and having an axial cross-sectional area that expands continuously or stepwise toward the liquid outlet; and a gas introduction hole formed downstream of all of the cavitation screw members located within the throttled section, and connecting the outside of the nozzle body to the liquid flow path, the gas introduction hole communicating with the throttled section or the gas dissolution expansion section, and ２ Over 42mm ２ Hereinafter, the number of thread valley points of the cavitation screw member that exist within 70% of the radius from the center in the axial cross section of the throttled portion is defined as the 70% valley point number, and the value of the 70% valley point area density, which is the value obtained by dividing the 70% valley point number by the flow cross-sectional area, is 1.00 points / mm ２ 3.50 pieces / mm or more ２ a gas ejection nozzle defined within the following range; a gas supply unit that supplies gas to the gas inlet hole of the nozzle body; and a gas ejection nozzle in which the flow velocity distribution in the radial direction of a cross section immediately before the liquid collides with the cavitation screw member is parabolic, maximizing at the center of the cross section and becoming zero at the inner wall surface of the flow passage; further, the radius of the axial cross section is defined as R, the outlet side of the gas ejection nozzle is open, and when water is passed through the gas ejection nozzle under standard conditions where the dynamic water pressure supplied to the gas ejection nozzle is 0.1 MPa, the flow velocity at a position 0.71R from the center of the axial cross section is defined as a critical flow velocity; and and a liquid delivery unit that delivers liquid to the liquid inlet of the nozzle body at a flow rate such that an average flow velocity in an axial cross section of the flow path in which the screw member is disposed is 9 m / s or more and a value of the effective valley point flow density α is 1.0 particles min / L or more and 3.5 particles min / L or less, where N is an effective valley point number, ρ is the supply flow rate of the liquid, and α is an effective valley point flow density = N / ρ. In this gas dissolution device, a gas is supplied to the gas introduction hole of the nozzle body of the gas ejection nozzle, and the gas from the gas introduction hole is sucked into the liquid while being entrained in turbulence generated in the gas dissolution expansion section and dissolved.

12. the liquid is water, 12. The method for dissolving a gas according to claim 11, wherein the gas comprises one or more gases selected from the group consisting of carbon dioxide gas, ozone-containing gas, oxygen, nitrogen, air, ammonia, and hydrogen.

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