Tubular member, bubble generation device, and bubble generation method

Abstract

A tubular member (100) is formed in a tubular shape that defines a flow path (200) for a gas-liquid mixed fluid containing a liquid and a gas component mixed with the liquid. The gas-liquid mixed fluid is introduced under pressure from one end of the tubular member (100) and flows out from the other end of the tubular member (100). The tubular member (100) has a first throttle part (110), a second throttle part (120) closer to the other end than the first throttle part (110), an intermediate part (130), and an outside air introduction part (140). A first narrow flow path part (210) is a portion of the flow path (200) that is narrowed in the first throttle part (110). A second narrow flow path part (220) is a portion of the flow path (200) that is narrowed in the second throttle part (120). The outside air introduction part (140) guides outside air to the first narrow flow path part (210). The cross-sectional area of the second narrow flow path part (220) is larger than the cross-sectional area of the first narrow flow path part (210).

Description

Tubular member, bubble generation device, and bubble generation method

[0001] The present invention relates to a tubular member, a bubble generation device, and a bubble generation method.

[0002] As disclosed in Patent Document 1, there is known a bubble generation device including a pump that pumps a fluid (hereinafter referred to as a gas-liquid mixed fluid) containing a liquid and a gas component mixed in the liquid, and a tubular member into which the gas-liquid mixed fluid pumped by the pump flows.

[0003] In this bubble generation device, the tubular member has a first throttle portion and a second throttle portion arranged in series at intervals in the length direction of the tubular member. In each of the first throttle portion and the second throttle portion, the gas component contained in the gas-liquid mixed fluid is dissolved in the liquid by pressurization, and the dissolved gas component is precipitated as bubbles by depressurization.

[0004] International Publication No. 2018 / 021182

[0005] According to the above bubble generation device, fine bubbles with a high number density can be generated in a liquid. However, since the gas component dissolved in the liquid precipitates as bubbles, the concentration (hereinafter referred to as the dissolved concentration) of the gas component dissolved at the molecular level in the liquid decreases in the liquid. Therefore, there has been a limit to improving the dissolved concentration of the gas component in the liquid.

[0006] However, not only the gas component present in the form of bubbles in the liquid but also the gas component dissolved at the molecular level in the liquid can contribute to various reactions and the like. Therefore, depending on the use of the gas-liquid mixed fluid obtained by the bubble generation device, it may be desirable to achieve both an improvement in the number density of bubbles and an improvement in the dissolved concentration of the gas component.

[0007] An object of the present invention is to provide a technique capable of generating fine bubbles with a sufficient number density in a liquid and sufficiently dissolving a gas component in the liquid.

[0008] The tubular member according to the present invention is formed in a tubular shape that defines a flow path for a gas-liquid mixed fluid containing a liquid and a gaseous component mixed with the liquid, and the gas-liquid mixed fluid is injected into the tubular member from one end and the injected gas-liquid mixed fluid flows out from the other end, and comprises: a first throttling portion that restricts the flow of the gas-liquid mixed fluid by locally narrowing the area of ​​the cross-sectional surface of the flow path perpendicular to the length direction of the tubular member; a second throttling portion that is adjacent to the first throttling portion at a position closer to the other end than the first throttling portion and restricts the flow of the gas-liquid mixed fluid that has passed through the first throttling portion by locally narrowing the area of ​​the cross-sectional surface of the flow path; an intermediate portion that defines an intermediate flow path portion between the first narrowed flow path portion, which is the portion of the flow path that is narrowed in the first throttling portion, and the second narrowed flow path portion, which is the portion that is narrowed in the second throttling portion; and an outside air introduction portion that guides outside air into the first narrowed flow path portion. The area of ​​the cross-section of the second narrow channel is larger than the area of ​​the cross-section of the first narrow channel.

[0009] The first narrow cross section, which is the cross-section of the first narrow channel, has a shape in which the longitudinal direction is in the U1 axis direction parallel to the first narrow cross section, and the second narrow cross section, which is the cross-section of the second narrow channel, has a shape in which the longitudinal direction is in the V1 axis direction parallel to the second narrow cross section, the dimension of the first narrow cross section in the U1 axis direction and the dimension of the second narrow cross section in the V1 axis direction are equal, and the dimension of the second narrow cross section in the V2 axis direction, which is parallel to the second narrow cross section and perpendicular to the V1 axis direction, may be larger than the dimension of the first narrow cross section in the U2 axis direction, which is parallel to the first narrow cross section and perpendicular to the U1 axis direction.

[0010] When the dimension of the first narrow cross-section in the U2 axial direction is LA, and the dimension of the second narrow cross-section in the V2 axial direction is LB, the relationship 1.5 × LA ≤ LB ≤ 6.5 × LA may be satisfied.

[0011] When the equivalent diameter of the intermediate flow channel is denoted as LC, the relationship 8 × LA ≤ LC ≤ 32 × LA may be satisfied.

[0012] The following relationships may also be satisfied: 0.8 [mm] ≤ LA < 3 [mm], LA + 2 [mm] ≤ LB, and 3 [mm] ≤ LB ≤ 5 [mm].

[0013] The distance in the longitudinal direction between the first narrow channel and the second narrow channel may be shorter than the interval at which the longitudinal flow velocity of the gas-liquid mixed fluid that passes through the first constriction and flows through the intermediate channel returns to the longitudinal flow velocity of the gas-liquid mixed fluid when it is pressed into the tubular member from one end.

[0014] When the distance in the longitudinal direction between the first narrow channel section and the second narrow channel section is LZ, and the equivalent diameter of the intermediate channel section is LC, the relationship 1.5 × LC ≤ LZ ≤ 3 × LC may be satisfied.

[0015] The direction of the V1 axis may be parallel to the direction of the U1 axis.

[0016] The V1 axis direction may be the direction in which the U1 axis direction is rotated around a virtual central axis parallel to the longitudinal direction.

[0017] The bubble generating apparatus according to the present invention comprises the tubular member according to the present invention described above, and a pump that pressurizes the gas-liquid mixed fluid into the tubular member.

[0018] The bubble generating apparatus according to the present invention further comprises: a liquid tank in which the gas-liquid mixed fluid is stored; a return pipe connecting the inside of the liquid tank to the other end of the tubular member; and a supply pipe connecting the inside of the liquid tank to the pump, wherein the pump draws the gas-liquid mixed fluid from the inside of the liquid tank through the supply pipe, and pumps the drawn-in gas-liquid mixed fluid together with the gas to the tubular member, and the gas-liquid mixed fluid that flows out from the other end of the tubular member returns to the inside of the liquid tank through the return pipe.

[0019] A bubble generation method according to the present invention uses a tubular member formed in the shape of a tube that defines a flow path for a gas-liquid mixed fluid containing a liquid and a gaseous component mixed with the liquid, into which the gas-liquid mixed fluid is injected under pressure from one end and out of the other end, wherein the tubular member has: a first throttling portion that restricts the flow of the gas-liquid mixed fluid by locally narrowing the area of ​​the cross-sectional surface of the flow path perpendicular to the length direction of the tubular member; a second throttling portion that is adjacent to the first throttling portion at a position closer to the other end than the first throttling portion and restricts the flow of the gas-liquid mixed fluid that has passed through the first throttling portion by locally narrowing the area of ​​the cross-sectional surface of the flow path; and an intermediate portion that defines an intermediate flow path portion, which is the portion of the flow path between a first narrowed flow path portion, which is the portion narrowed in the first throttling portion, and a second narrowed flow path portion, which is the portion narrowed in the second throttling portion. The apparatus includes: an outside air introduction section that guides outside air into the first narrow channel section, wherein the area of ​​the cross-section of the second narrow channel section is larger than the area of ​​the cross-section of the first narrow channel section, and precipitate bubbles are generated as the gaseous components dissolved in the liquid precipitate in the first narrow channel section; an outside air-derived bubble generation step in which outside air-derived bubbles, which are bubbles originating from the outside air, are generated as the outside air is guided into the first narrow channel section through the outside air introduction section by the negative pressure generated in the first narrow channel section; and a stirring step in which the outside air-derived bubbles and the precipitate bubbles are stirred in the intermediate channel section by the turbulence generated in the intermediate channel section.

[0020] According to the tubular member of the present invention, dissolved gaseous components precipitate in the first narrow channel, generating precipitated bubbles. Furthermore, the negative pressure generated in the first narrow channel leads outside air into the first narrow channel through the outside air introduction section, generating outside air-derived bubbles. In addition, the turbulence generated in the intermediate channel stirs the outside air-derived bubbles and precipitated bubbles in the intermediate channel.

[0021] In this way, by generating precipitated bubbles and bubbles derived from the outside air, and by stirring in the intermediate channel between the generated precipitated bubbles and the bubbles derived from the outside air, it is possible to generate fine bubbles with a sufficient number density in the liquid.

[0022] Furthermore, even though the gaseous components dissolved in the liquid precipitate as precipitated bubbles, stirring in the intermediate channel promotes the dissolution of bubbles originating from the outside air into the liquid. Therefore, it is possible to sufficiently dissolve the gaseous components in the liquid.

[0023] A conceptual diagram showing the configuration of the bubble generating device according to the first embodiment. A cross-sectional view showing a cross-section parallel to the longitudinal direction of the tubular member according to the first embodiment. A schematic perspective view showing the three-dimensional shape of the inner surface of the tubular member according to the first embodiment. A side view of the tubular member according to the first embodiment, viewed in the longitudinal direction. A flowchart of the bubble generating method according to the first embodiment. A side view of the tubular member according to the second embodiment, viewed in the longitudinal direction. A graph showing the mode diameter of the red tide control agent crushed using the bubble generating device according to the example and comparative example. A graph showing the distribution of the number density with respect to the bubble diameter of bubbles generated using the bubble generating device according to the example.

[0024] The bubble generating apparatus according to an embodiment will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[0025] [First Embodiment] As shown in Figure 1, the bubble generating apparatus 700 according to this embodiment includes a liquid tank 500. A gas-liquid mixed fluid 600 is stored inside the liquid tank 500.

[0026] The gas-liquid mixed fluid 600 refers to a fluid containing a liquid 610 and a gaseous component mixed in the liquid 610. In this specification, "a gaseous component is mixed" means not only that the gaseous component exists in the liquid 610 in the form of bubbles 620, but also that it exists in a form dissolved in the liquid 610 at the molecular level without forming bubbles 620.

[0027] Furthermore, the bubble generating device 700 includes a pump 300 for pumping the gas-liquid mixed fluid 600 stored in the liquid tank 500, a tubular member 100 into which the gas-liquid mixed fluid 600 pumped by the pump 300 is injected, and piping 400.

[0028] The piping 400 defines the flow path of the gas-liquid mixed fluid 600 from inside the liquid tank 500 through the pump 300 to the tubular member 100. Specifically, the piping 400 has a supply pipe 410 connecting the inside of the liquid tank 500 to the pump 300, and an intermediate pipe 420 connecting the pump 300 to the tubular member 100.

[0029] The pump 300 includes a liquid pump 310 and a first outside air inlet 320. The liquid pump 310 draws in the gas-liquid mixed fluid 600 stored in the liquid tank 500 through the supply pipe 410 and sends the drawn-in gas-liquid mixed fluid 600 to the tubular member 100 through the intermediate pipe 420.

[0030] The first outside air inlet 320 is provided in the supply piping 410. The first outside air inlet 320 connects the inside of the supply piping 410 to the outside in order to introduce outside air into the supply piping 410. That is, the action of the liquid pump 310 in drawing in the gas-liquid mixed fluid 600 creates a negative pressure inside the supply piping 410 that is lower than the external atmospheric pressure (typically atmospheric pressure). Due to this negative pressure, outside air naturally flows into the supply piping 410 through the first outside air inlet 320.

[0031] In this way, the gas-liquid mixed fluid 600, which is drawn out from the liquid tank 500 by the liquid pump 310, is sent to the tubular member 100 through the intermediate piping 420 together with the outside air taken in through the first outside air introduction section 320.

[0032] The tubular member 100 is formed in a tubular shape that defines the flow path for the gas-liquid mixed fluid 600. The gas-liquid mixed fluid 600, which is pumped by the pumper 300, flows in from one end (hereinafter referred to as the inlet end) 101 of the tubular member 100, and the flowing gas-liquid mixed fluid 600 flows out from the other end (hereinafter referred to as the outlet end) 102 of the tubular member 100.

[0033] The tubular member 100, like the pressure pump 300, has the function of taking in outside air into the gas-liquid mixed fluid 600. Specifically, the tubular member 100 has a second outside air inlet 140. Due to the negative pressure generated inside the tubular member 100, outside air naturally flows into the tubular member 100 through the second outside air inlet 140. The second outside air inlet 140 is an example of an outside air inlet according to the present invention.

[0034] The tubular member 100 primarily plays the roles of increasing the number density of bubbles 620 in the liquid 610 of the gas-liquid mixed fluid 600, refining the bubbles 620, and increasing the dissolved concentration of gaseous components dissolved at the molecular level in the liquid 610.

[0035] Furthermore, the piping 400 according to this embodiment also includes a return pipe 430 that connects the outlet end 102 of the tubular member 100 to the inside of the liquid tank 500. That is, the gas-liquid mixed fluid 600 that flows out from the outlet end 102 of the tubular member 100 returns to the inside of the liquid tank 500 through the return pipe 430.

[0036] Therefore, the gas-liquid mixed fluid 600, which was sucked out of the liquid tank 500 by the liquid pump 310 and then returned to the liquid tank 500 via the tubular member 100, is then sucked out of the liquid tank 500 again by the liquid pump 310.

[0037] In this way, the gas-liquid mixed fluid 600 circulates through a closed circuit comprising the piping 400 and the liquid tank 500. Each time the circulation of the gas-liquid mixed fluid 600 is repeated, the number density of bubbles 620 in the tubular member 100 is increased, the bubbles 620 become finer, and the dissolved concentration of gaseous components in the liquid 610 is increased.

[0038] Before starting the liquid pump 310, the liquid tank 500 may contain a liquid 610 with a gaseous content that is negligible. At the first outside air inlet 320, outside air is introduced into the liquid 610. Thus, in the pump 300 having the first outside air inlet 320, a gas-liquid mixed fluid 600 is formed to be injected into the tubular member 100.

[0039] The bubble generator 700 according to this embodiment has the greatest feature in the configuration of the tubular member 100. Therefore, the configuration of the tubular member 100 will be specifically described below.

[0040] As shown in FIG. 2, the tubular member 100 is formed in a straight tubular shape. The tubular member 100 defines a flow path 200 inside that extends from an inflow end 101 to an outflow end 102. The gas-liquid mixed fluid 600 pressurized by the pressure pump 300 shown in FIG. 1 flows through the flow path 200.

[0041] Hereinafter, the side closer to the outflow end 102 in the length direction of the tubular member 100 will be referred to as "rear". The tubular member 100 has a configuration in which a first throttle portion 110, an intermediate portion 130, and a second throttle portion 120 are arranged in this order toward the rear between the inflow end 101 and the outflow end 102.

[0042] The first throttle portion 110 locally narrows the area of the cross section (hereinafter also simply referred to as the cross-sectional area) of the flow path 200 that is perpendicular to the length direction of the tubular member 100. As a result, the flow of the gas-liquid mixed fluid 600 press-fitted from the inflow end 101 is throttled at the first throttle portion 110.

[0043] Specifically, the first throttle portion 110 includes a narrowing taper portion 111 that gradually decreases the cross-sectional area of the flow path 200 toward the rear, an expanding taper portion 113 that gradually increases the cross-sectional area of the flow path 200 toward the rear, and a throat portion 112 located between the narrowing taper portion 111 and the expanding taper portion 1​​​​​​

[0046] Specifically, the second throttle portion 120 includes a narrowing taper portion 121 that gradually decreases the cross-sectional area of the flow path 200 toward the rear, an expanding taper portion 123 that gradually increases the cross-sectional area of the flow path 200 toward the rear, and a throat portion 122 located between the narrowing taper portion 121 and the expanding taper portion 123.

[0047] In the second throttle portion 120, the cross-sectional area of the flow path 200 at the position of the throat portion 122 is the smallest. Hereinafter, the portion of the flow path 200 that is narrowed at the throat portion 122 of the second throttle portion 120 is referred to as the "second narrow flow path portion 220".

[0048] The intermediate portion 130 is located between the first throttle portion 110 and the second throttle portion 120. The intermediate portion 130 defines an intermediate flow path portion 230 that is the portion of the flow path 200 between the first throttle portion 110 and the second throttle portion 120. The cross-sectional area of the intermediate flow path portion 230 is constant in the longitudinal direction of the tubular member 100.

[0049] Hereinafter, the portion of the flow path 200 between the inflow end 101 and the first throttle portion 110 is referred to as the "inflow end flow path portion 240". Also, the portion of the flow path 200 between the second throttle portion 120 and the outflow end 102 is referred to as the "outflow end flow path portion 250".

[0050] The cross-sectional area of each of the inflow end flow path portion 240 and the outflow end flow path portion 250 is constant in the longitudinal direction of the tubular member 100. The cross-sectional area of the inflow end flow path portion 240 is equal to the cross-sectional area of the outflow end flow path portion 250. Also, the cross-sectional area of the intermediate flow path portion 230 is equal to the cross-sectional area of the inflow end flow path portion 240.

[0051] Also, hereinafter, the distance in the longitudinal direction of the tubular member 100 between the first narrow flow path portion 210 and the second narrow flow path portion 220 (hereinafter simply referred to as the distance) is denoted as LZ. Specifically, the distance LZ refers to the distance in the longitudinal direction of the tubular member 100 between the intermediate position in the longitudinal direction of the tubular member 100 of the throat portion 112 of the first throttle portion 110 and the intermediate position in the longitudinal direction of the tubular member 100 of the throat portion 122 of the second throttle portion 120.

[0052] Furthermore, in the following, the value obtained by averaging the component of the gas-liquid mixed fluid 600's flow velocity in the longitudinal direction of the tubular member 100 within the above cross-sectional area will simply be referred to as the "longitudinal flow velocity" of the gas-liquid mixed fluid 600. The longitudinal flow velocity of the gas-liquid mixed fluid 600 can be expressed as a function of the longitudinal position of the tubular member 100.

[0053] Due to the flow resistance in the first throttling section 110, the longitudinal flow velocity of the gas-liquid mixed fluid 600 may decrease in the first throttling section 110. However, depending on the length of the gap LZ, the longitudinal flow velocity of the gas-liquid mixed fluid 600 flowing through the intermediate flow channel section 230 may return to the longitudinal flow velocity of the gas-liquid mixed fluid 600 when it was injected into the tubular member 100 from the inlet end 101 (hereinafter referred to as the initial flow velocity). Here, the initial flow velocity specifically refers to the longitudinal flow velocity of the gas-liquid mixed fluid 600 at the position of the inlet end 101.

[0054] However, in this embodiment, the interval LZ is designed to be shorter than the interval at which the longitudinal flow velocity of the gas-liquid mixed fluid 600 flowing through the intermediate flow channel 230 returns to the initial flow velocity. In other words, in this embodiment, the longitudinal flow velocity of the gas-liquid mixed fluid 600 at the location of the intermediate flow channel 230 is smaller than the initial flow velocity. As a result, turbulence occurs in the portion of the flow channel 200 that includes the intermediate flow channel 230, from the first narrow flow channel 210 to the second narrow flow channel 220.

[0055] Furthermore, as previously described, the tubular member 100 is equipped with a second outside air introduction section 140, as shown in Figure 1. The second outside air introduction section 140 guides outside air to the first narrow flow channel section 210. Specifically, the second outside air introduction section 140 defines a ventilation passage 141 that connects the first narrow flow channel section 210 to the outside of the tubular member 100. The ventilation passage 141 extends perpendicular to the length direction of the tubular member 100.

[0056] To facilitate the following explanation, we define an XYZ Cartesian coordinate system in which the longitudinal direction of the tubular member 100 is the Z-axis direction, the extending direction of the ventilation passage 141 defined by the second outside air introduction section 140 is the Y-axis direction, and the direction perpendicular to the Z-axis and Y-axis directions is the X-axis direction.

[0057] Figure 3 is a schematic perspective view showing only the inner surface of the tubular member 100 in order to represent the three-dimensional shape of the flow path 200 defined by the tubular member 100. As shown in Figure 3, multiple ventilation passages 141 are arranged in the X-axis direction. Each ventilation passage 141 connects the first narrow flow path section 210 to the outside of the tubular member 100.

[0058] When the diameter of each ventilation passage 141 is P, the distance between adjacent ventilation passages 141 in the X-axis direction is P or greater. This prevents bubbles 620 discharged from one ventilation passage 141 into the first narrow channel section 210 from contacting or merging with bubbles 620 discharged from an adjacent ventilation passage 141 into the first narrow channel section 210 in the channel 200 beyond the first narrow channel section 210.

[0059] Next, the shape of the first narrow channel section 210 will be described. Hereafter, the cross-section of the first narrow channel section 210 will be referred to as the "first narrow cross-section".

[0060] The first narrow section has a shape where the longitudinal direction is in one direction parallel to the first narrow section (hereinafter referred to as the U1 axis direction) and the short direction is in a direction parallel to the first narrow section and perpendicular to the U1 axis direction (hereinafter referred to as the U2 axis direction), specifically forming a rectangle. In other words, the dimension of the first narrow section in the U2 axis direction is smaller than the dimension of the first narrow section in the U1 axis direction.

[0061] Next, the shape of the second narrow channel section 220 will be described. In the following, the cross-section of the second narrow channel section 220 will be referred to as the "second narrow cross-section".

[0062] The second narrow section, like the first narrow section, has a shape where the longitudinal direction is in one direction parallel to the second narrow section (hereinafter referred to as the V1 axis direction) and the short direction is in a direction parallel to the second narrow section and perpendicular to the V1 axis direction (hereinafter referred to as the V2 axis direction), specifically forming a rectangle. In other words, the dimension of the second narrow section in the V2 axis direction is smaller than the dimension of the second narrow section in the V1 axis direction.

[0063] As shown in Figure 4, in this embodiment, the V1 axis direction, which is the longitudinal direction of the second narrow section, is parallel to the U1 axis direction, which is the longitudinal direction of the first narrow section. Furthermore, the U1 axis direction and the V1 axis direction are parallel to the X axis direction. Consequently, the U2 axis direction, which is the short direction of the first narrow section, and the V2 axis direction, which is the short direction of the second narrow section, are parallel to the Y axis direction.

[0064] Furthermore, the Y-axis positions of the first narrow channel section 210 and the second narrow channel section 220 are the same. That is, the Y-axis center position of the first narrow section and the Y-axis center position of the second narrow section are the same. The longitudinal dimension, i.e., the X-axis dimension, of the first narrow section is equal to the longitudinal dimension, i.e., the X-axis dimension, of the second narrow section. Let LC be the X-axis dimension of the first narrow channel section 210 and the second narrow channel section 220.

[0065] However, when LB is the dimension of the second narrow cross-section in the direction of its shorter side, the V2 axis direction, i.e., the Y axis direction, and LA is the dimension of the first narrow cross-section in the direction of its shorter side, the U2 axis direction, i.e., the Y axis direction, then LB > LA. For this reason, the cross-sectional area of ​​the second narrow channel section 220 is larger than the cross-sectional area of ​​the first narrow channel section 210.

[0066] As shown in Figure 4, the tubular member 100 according to this embodiment is formed in a circular shape when viewed in the Z-axis direction. In Figure 2, the cross-sections of the intermediate flow channel 230, the inlet end flow channel 240, and the outlet end flow channel 250 are circular. The longitudinal dimension LC of the first narrow flow channel 210 and the second narrow flow channel 220 shown in Figure 4 is equal to the diameter LC of the cross-section of the intermediate flow channel 230, the inlet end flow channel 240, and the outlet end flow channel 250 shown in Figure 2.

[0067] Referring to Figures 5 and 2, the manner in which bubbles 620 are generated in the tubular member 100 will be described below.

[0068] As previously described, the gas-liquid mixed fluid 600 flows into the tubular member 100 from the inlet end 101. The water pressure of the incoming gas-liquid mixed fluid 600 gradually increases towards the rear as the cross-sectional area of ​​the flow path 200 decreases in the narrowing tapered section 111. As a result, during the process of the gas-liquid mixed fluid 600 passing through the narrowing tapered section 111, the gas bubbles 620 contained in the gas-liquid mixed fluid 600 dissolve into the liquid 610 due to the pressurization.

[0069] On the other hand, the flow velocity of the gas-liquid mixed fluid 600 gradually increases towards the throat portion 112. The flow velocity of the gas-liquid mixed fluid 600 is maximized in the first narrow channel portion 210 defined by the throat portion 112. As the dynamic pressure of the gas-liquid mixed fluid 600 increases in this way, the static pressure of the gas-liquid mixed fluid 600 becomes minimum in the first narrow channel portion 210, and a negative pressure lower than atmospheric pressure is generated in the first narrow channel portion 210.

[0070] As a result, the gaseous components dissolved in the liquid 610 of the gas-liquid mixed fluid 600 precipitate in the first narrow channel section 210. In this specification, "precipitation" refers to the appearance of gaseous components dissolved in the liquid 610 as bubbles 620. That is, in the first narrow channel section 210, precipitated bubbles 621 are generated by the precipitation of gaseous components dissolved in the liquid 610 (precipitated bubble generation step S1). The precipitation of precipitated bubbles 621 also occurs in the intermediate channel section 230.

[0071] Furthermore, the negative pressure generated in the first narrow channel section 210 causes outside air to be guided into the first narrow channel section 210 through the second outside air introduction section 140. As a result, outside air-derived bubbles 622, which are bubbles 620 originating from the outside air introduced through the second outside air introduction section 140, are generated separately from the precipitated bubbles 621 (outside air-derived bubble generation step S2). Note that the precipitated bubble generation step S1 and the outside air-derived bubble generation step S2 can be carried out in parallel.

[0072] As previously described, the distance LZ between the first narrow channel section 210 and the second narrow channel section 220 is shorter than the interval at which the longitudinal flow velocity of the gas-liquid mixed fluid 600 that has passed through the first throttling section 110 returns to its initial flow velocity. As a result, turbulence is generated throughout the entire intermediate channel section 230. This turbulence in the intermediate channel section 230 then agitates the precipitated bubbles 621 and the bubbles 622 originating from the outside air (agitation step S3).

[0073] This stirring causes the precipitated bubbles 621 and the bubbles derived from the outside air 622 to be broken up or crushed in the intermediate flow channel 230. After the stirring step S3, the flow of the bubble generation method returns to the precipitated bubble generation step S1 and the bubbles derived from the outside air generation step S2 described above (RETURN). Here, "RETURN" means that the gas-liquid mixed fluid 600 circulates through a closed circuit consisting of the piping 400 and the liquid tank 500 shown in Figure 1, so that the precipitated bubble generation step S1 and the bubbles derived from the outside air generation step S2 and the stirring step S3 are continuously repeated. The flow of the bubble generation method shown in Figure 5 ends when the operation of the liquid pump 310 shown in Figure 1 is stopped.

[0074] As described above, by repeatedly generating precipitated bubbles 621 and bubbles derived from outside air 622, and stirring the generated precipitated bubbles 621 and bubbles derived from outside air 622 in the intermediate channel 230, bubbles 620 with a sufficient number density can be generated in the liquid 610.

[0075] Furthermore, even though the gaseous components dissolved in the liquid 610 precipitate as precipitated bubbles 621, stirring in the intermediate channel 230 promotes the dissolution of air-derived bubbles 622 into the liquid. Therefore, it is possible to sufficiently dissolve the gaseous components in the liquid 610.

[0076] Furthermore, stirring of the precipitated bubbles 621 and the bubbles 622 originating from the outside air in the intermediate channel section 230 also contributes to the refinement of the bubbles 620. According to this embodiment, it is possible to generate bubbles 620 with a diameter of 300 [μm] or less, more specifically, bubbles 620 with a diameter of 100 [μm] or less, which are called so-called fine bubbles, and even bubbles 620 with a diameter of 1 [μm] or less, which are called so-called ultrafine bubbles. The "diameter" referred to here may be the mode diameter or the median diameter in the frequency distribution with respect to bubble diameter.

[0077] Furthermore, as previously described, the cross-sectional area of ​​the second narrow channel section 220 is larger than the cross-sectional area of ​​the first narrow channel section 210. This mainly contributes to ensuring sufficient turbulence in the intermediate channel section 230 by moderately suppressing the resistance experienced by the flow of the gas-liquid mixed fluid 600 in the second throttling section 120.

[0078] Furthermore, the more intense the turbulence generated in the intermediate flow channel 230, the greater the number density of the bubbles 620, the greater the dissolved concentration of gaseous components in the liquid 610, and the finer the bubbles 620 become.

[0079] Furthermore, the configuration in which the cross-sectional area of ​​the second narrow channel section 220 is larger than that of the first narrow channel section 210 contributes to promoting the precipitation of precipitated bubbles 621 in the intermediate channel section 230 by appropriately suppressing the pressure in the intermediate channel section 230.

[0080] Furthermore, if the cross-sectional area of ​​the second narrow channel section 220 is less than or equal to the cross-sectional area of ​​the first narrow channel section 210, the pressure loss in the second throttling section 120 becomes too large, making it impossible to form sufficiently violent turbulence in the intermediate channel section 230. Also, because the pressure in the intermediate channel section 230 becomes too high, it becomes difficult for precipitated bubbles 621 to precipitate sufficiently in the intermediate channel section 230.

[0081] Furthermore, according to this embodiment, since the pressure loss in the second throttling section 120 can be moderately suppressed, a strong turbulent flow can be formed in the intermediate flow path section 230 without setting the pressure of the gas-liquid mixed fluid 600 at the discharge position of the liquid pump 310 shown in Figure 1, i.e., the discharge pressure of the liquid pump 310, to a very high level.

[0082] As an example, the discharge pressure of the liquid pump 310 can be kept to 1.0 [MPa] or less, preferably 0.4 [MPa] or less. However, the discharge pressure of the liquid pump 310 is not particularly limited, and a higher discharge pressure may create more intense turbulence in the intermediate flow path section 230.

[0083] The following describes particularly preferred dimensional conditions for the tubular member 100.

[0084] Refer to Figure 2 again. As previously described, the dimension of the first narrow section in the short direction (U2 axis direction) is LA, and the dimension of the second narrow section in the short direction (V2 axis direction) is LB. It is preferable that the tubular member 100 satisfies the relationship 1.5 × LA ≤ LB ≤ 6.5 × LA.

[0085] By setting the dimension LB to 1.5 × LA or greater, the water pressure in the intermediate channel section 230 can be appropriately suppressed. As a result, precipitated bubbles 621 with a higher number density can be generated not only in the first narrow channel section 210 but also in the intermediate channel section 230.

[0086] By setting the dimension LB to 6.5 × LA or less, more intense turbulence can be formed in the intermediate channel section 230, allowing the precipitated bubbles 621 and the bubbles 622 originating from the outside air to be vigorously stirred at high speed in the intermediate channel section 230. In particular, the vigorous stirring of the bubbles 622 originating from the outside air at high speed further promotes their dissolution into the liquid 610, leading to a further improvement in the dissolved concentration of gaseous components in the liquid 610.

[0087] In one specific example, the value of dimension LA satisfies the relationship 0.8 [mm] ≤ LA < 3 [mm]. By setting dimension LA to 0.8 [mm] or more, a sufficient amount of outside air can be drawn into the first narrow channel section 210 through the ventilation passage 141. Furthermore, by setting dimension LA to 3 [mm] or less, precipitated bubbles 621 with a higher number density can be made to appear in the first narrow channel section 210.

[0088] Furthermore, when determining the specific value of dimension LA in this manner, it is preferable that, in addition to the above relationship, the following relationships are also satisfied: LA + 2 [mm] ≤ LB and 3 [mm] ≤ LB ≤ 5 [mm].

[0089] Furthermore, it is preferable that the diameter LC of the intermediate flow channel 230 satisfies the relationship 8 × LA ≤ LC ≤ 32 × LA.

[0090] By setting the diameter LC of the intermediate channel section 230 to 8 × LA or more, more intense turbulence can be formed in the intermediate channel section 230, and sufficient space can be secured for stirring the precipitated bubbles 621 and bubbles 622 originating from the outside air. Alternatively, by setting the diameter LC of the intermediate channel section 230 to 32 × LA or less, the occurrence of flow stagnation can be suppressed, and more intense turbulence can be formed throughout the entire intermediate channel section 230.

[0091] In this embodiment, a configuration in which the cross-section of the intermediate channel section 230 is circular is illustrated. However, the influence of the "shape" of the cross-section of the intermediate channel section 230 on the characteristics of bubble 620 generation is considered to be almost negligible. That is, the shape of the cross-section of the intermediate channel section 230 is not limited to a circle, but may be non-circular, such as an ellipse, triangle, or polygon with four or more sides. The same applies to the shape of the cross-sections of the inlet end channel section 240 and the outlet end channel section 250.

[0092] Therefore, the above-mentioned "diameter LC" can be generalized to "equivalent diameter LC" to include not only cases where the cross-section of the intermediate flow channel 230 is circular, but also cases where it is not circular. In this specification, "equivalent diameter of the flow channel" refers to a value defined as D = 4 × A / W, where A is the area of ​​the cross-section of the flow channel and W is the circumference of the cross-section. When the cross-section of the flow channel is circular, the equivalent diameter is equal to the diameter of the circle formed by the cross-section of the flow channel.

[0093] Furthermore, as previously described, the distance LZ between the first narrow channel section 210 and the second narrow channel section 220 is shorter than the interval at which the longitudinal flow velocity of the gas-liquid mixed fluid 600 in the intermediate channel section 230 returns to its initial flow velocity. To satisfy this requirement, it is preferable that the distance LZ satisfies the relationship 1.5 × LC ≤ LZ ≤ 3 × LC. Here, as described above, LC represents the equivalent diameter of the intermediate channel section 230.

[0094] [Second Embodiment] Figure 4 illustrates a configuration in which the V1 axis direction, which is the longitudinal direction of the second narrow cross-section, is parallel to the U1 axis direction, which is the longitudinal direction of the first narrow cross-section. The V1 axis direction and the U1 axis direction do not have to be parallel to each other. Specific examples are described below.

[0095] As shown in Figure 6, a virtual central axis CL is defined parallel to the longitudinal direction of the tubular member 100, i.e., the Z-axis direction. The virtual central axis CL passes through the centroid of the cross-section of the tubular member 100.

[0096] In this embodiment, the V1 axis direction, which is the longitudinal direction of the second narrow section, is rotated by an angle θ around the virtual central axis CL with respect to the U1 axis direction, which is the longitudinal direction of the first narrow section. Figure 6 illustrates the case where angle θ = 90°. However, angle θ may be any value greater than 0° and less than or equal to 90°.

[0097] The fact that the longitudinal direction of the first narrow cross-section, the U1 axis direction, coincides with the X axis direction is the same as in the first embodiment. Therefore, when the angle θ = 90°, the longitudinal direction of the second narrow cross-section, the V1 axis direction, coincides with the Y axis direction. In addition, the other configurations, including the spacing LZ shown in Figures 2 and 3, are the same as in the first embodiment. According to this embodiment, more intense turbulence can be formed in the intermediate flow channel 230.

[0098] [Third Embodiment] Hereinafter, the structure that restricts the flow of the gas-liquid mixed fluid 600 will be generally referred to as a "restriction section," and the narrowest part of the flow path of the gas-liquid mixed fluid 600 defined by the restriction section will be referred to as a "narrow flow path section." The concept of a restriction section includes the first restriction section 110 and the second restriction section 120 described above. The concept of a narrow flow path section also includes the first narrow flow path section 210 and the second narrow flow path section 220 described above.

[0099] In the first and second embodiments, a tubular member 100 having two diaphragm sections, a first diaphragm section 110 and a second diaphragm section 120, was described. The tubular member 100 may have further diaphragm sections (hereinafter referred to as additional diaphragm sections), as long as it has the first diaphragm section 110 and the second diaphragm section 120 which defines an intermediate flow path section 230 between the first diaphragm section 110 and the second diaphragm section 120.

[0100] Therefore, the tubular member 100 according to this embodiment further comprises an additional throttling portion. The additional throttling portion may be located behind the second throttling portion 120 or in front of the first throttling portion 110. Here, "rear" refers to the side closer to the outlet end 102 with respect to the Z-axis direction, as previously described. "Front" refers to the side closer to the inlet end 101 with respect to the Z-axis direction.

[0101] Furthermore, multiple additional aperture sections may be arranged in series behind the second aperture section 120 or in front of the first aperture section 110, or one or more additional aperture sections may be arranged both behind the second aperture section 120 and in front of the first aperture section 110. The area of ​​the cross-section of the narrow flow path defined by the additional aperture section is not particularly limited.

[0102] [Example A] To explore an example of a preferred arrangement of the diaphragm, experiments were conducted by changing the arrangement of the diaphragm in various ways. In all cases, the cross-sectional shape of the narrow channel defined by the diaphragm was rectangular. The conditions for this experiment are shown in Table 1 below.

[0103]

[0104] In Table 1, “A [mm] - B [mm]” represents a configuration in which two aperture sections are arranged in series, with the width of the narrow channel defined by the front aperture section being A [mm] (hereinafter also referred to as the width of the aperture section), and the width of the rear aperture section being B [mm]. Similarly, “A [mm] - B [mm] - C [mm]” represents a configuration in which three aperture sections are arranged in series, with the width of the foremost aperture section being A [mm], the width of the rearmost aperture section being C [mm], and the width of the central aperture section being B [mm]. Furthermore, “A [mm]” represents a configuration in which only one aperture section is arranged, and the width of that aperture section is A [mm].

[0105] In all of the experimental examples A1-A14, a circular pipe with an inner diameter of 25 mm was used as the object to which the constriction section was provided. A tubular member is a circular pipe to which a constriction section has been provided. That is, in the tubular member relating to any of the experimental examples A1-A14, the inner diameter of the portion between the constriction section adjacent to the inlet end and the inlet end, and the inner diameter of the portion between the constriction section adjacent to the outlet end and the outlet end, are 25 mm.

[0106] Furthermore, in experimental examples A1-A5, A7, A9, A11, A13, and A14, where multiple aperture sections are arranged in series, the inner diameter of the tubular member between adjacent aperture sections in the Z-axis direction is also 25 mm. In addition, the distance in the Z-axis direction between adjacent aperture sections was set to 50 mm.

[0107] In the tubular member according to experimental example A1, the 4 mm wide constricted portion corresponds to the second constricted portion 120 described above, and the 1 mm wide constricted portion corresponds to the first constricted portion 110 described above. Therefore, the tubular member according to experimental example A1 corresponds to the embodiment in terms of the arrangement of the constricted portions.

[0108] In the tubular members of experimental examples A2-A5, the 4 mm wide constricted portion corresponds to the second constricted portion 120 described above, and the 1 mm wide constricted portion located in front of that constricted portion corresponds to the first constricted portion 110 described above. Therefore, the tubular members of experimental examples A2-A5 also correspond to the embodiment in terms of the arrangement of the constricted portions.

[0109] In addition, in the tubular members of experimental examples A2 and A3, the 1 mm wide diaphragm located behind the second diaphragm 120 corresponds to the additional diaphragm described above. Furthermore, in the tubular members of experimental examples A4 and A5, the 1 mm wide diaphragm located in front of the first diaphragm 110 corresponds to the additional diaphragm described above.

[0110] The tubular members in experimental examples A6, A8, A10, and A12 are comparative examples in terms of the arrangement of the constricted portion, as they have only one constricted portion.

[0111] The tubular members in experimental examples A7, A9, A11, and A13 have two constricted sections, but in terms of the arrangement of the constricted sections, the cross-sectional areas of the narrow flow channels defined by these constricted sections are equal to each other.

[0112] Although the tubular member in experimental example A14 has two constricted sections, the cross-sectional area of ​​the narrow channel defined by the front constricted section is larger than the cross-sectional area of ​​the narrow channel defined by the rear constricted section, and therefore it falls under the comparative example in terms of the arrangement of the constricted sections.

[0113] Furthermore, in Table 1, "gas" refers to the type of gaseous component to be included in the gas-liquid mixed fluid. In all of the experimental examples A1-A14, the outside air introduction section for introducing outside air into the tubular member, i.e., the second outside air introduction section 140 shown in Figure 2, was omitted, and the "gas" listed in Table 1 were introduced only from the first outside air introduction section 320 upstream of the liquid pump 310 shown in Figure 1.

[0114] Then, in order to evaluate each of the tubular members related to experimental examples A1-A14, the red tide control agent was added to seawater, which was the liquid 610 in the liquid tank 500, and the liquid pump 310 was operated to pulverize the red tide control agent through the stirring action caused by the turbulence generated in the tubular members. The discharge pressure of the liquid pump 310 was adjusted to 0.35 [MPa] or less.

[0115] The red tide control agent used was primarily composed of clay containing montmorillonite. Aluminum ions leached from the clay into seawater destroy plankton cells. The bubbles 620 generated in the tubular member enhance the red tide control function by dispersing the red tide control agent.

[0116] Figure 7 shows the measurement results of the mode diameter of the red tide control agent crushed using the tubular member according to experimental examples A1-A14, as described above. The smaller the mode diameter of the red tide control agent, the more vigorously the gas-liquid mixed fluid 600 containing the red tide control agent was stirred in the tubular member. Therefore, the smaller the mode diameter of the red tide control agent, the more preferable the arrangement of the constriction portion in the tubular member used to crush the red tide control agent is.

[0117] As shown in Figure 7, experimental examples A1-A5, which correspond to the examples, yielded experimental results showing that the mode diameter of the red tide control agent was smaller compared to experimental examples A6-A14, which correspond to the comparative examples. In other words, experimental examples A1-A5, which correspond to the examples, were able to sufficiently dissolve viscous aggregated particles, which are ultrafine powders with a particle size of about 10 [μm] or less, without using a dispersant.

[0118] The results of this experiment showed that a configuration having at least two adjacent diaphragm sections, where the cross-sectional area of ​​the narrow channel defined by the rear diaphragm section is larger than the cross-sectional area of ​​the narrow channel defined by the front diaphragm section, is preferable.

[0119] In the tubular members of experimental examples A6, A8, A10, and A12, there is only one constricted section, so the red tide control agent cannot be sufficiently crushed.

[0120] Although the tubular member in experimental example A14 has two constricted sections, the cross-sectional area of ​​the narrow channel defined by the front constricted section is larger than the cross-sectional area of ​​the narrow channel defined by the rear constricted section. As a result, the flow resistance in the rear constricted section is too great, and it is not possible to form high-speed, sufficiently violent turbulence in the intermediate channel between the two constricted sections, resulting in insufficient pulverization of the red tide control agent.

[0121] Although the tubular members in experimental examples A7, A9, A11, and A13 also have two constricted sections, the cross-sectional areas of the narrow channel sections defined by these constricted sections are equal. Even if the cross-sectional areas of the two narrow channel sections are equal, the intensity of the turbulence generated in the intermediate channel section is not sufficient, and the red tide control agent cannot be sufficiently crushed.

[0122] [Example B] An experiment was conducted with various modifications to the method of introducing gas into liquid 610 and the resulting gas-liquid mixed fluid 600, with the aim of investigating the relationship between the method of introducing gas and other factors. Air was used as the gas. The conditions for this experiment are shown in Table 2 below.

[0123]

[0124] In Table 2, experimental examples B1-B5 correspond to the embodiments in terms of the method of introducing the gas and the arrangement of the throttling section. In experimental examples B1-B5, the configuration shown in Figure 1 is adopted, and outside air is introduced into the gas-liquid mixed fluid 600 from the first outside air introduction section 320 and the second outside air introduction section 140, respectively.

[0125] The "two-stage cross" configuration of the tubular member 100 in experimental examples B1 and B2 refers to a configuration in which, as shown in Figure 6, the longitudinal direction of the second narrow channel section 220 crosses the longitudinal direction of the first narrow channel section 210 when viewed in the Z-axis direction, specifically, a configuration in which the angle θ shown in Figure 6 is 90°.

[0126] Furthermore, the term "two-stage parallel" used to describe the configuration of the tubular member 100 in experimental examples B3-B5 means a configuration in which the longitudinal direction of the second narrow channel section 220 is parallel to the longitudinal direction of the first narrow channel section 210, as shown in Figure 4.

[0127] In experimental examples B1-B5, as in experimental example A1 described above, the shapes of both the first and second narrow cross-sections were rectangular, the dimension of the first narrow channel section 210 in the short direction was 1 mm, the dimension of the second narrow channel section 220 in the short direction was 4 mm, and the distance between the first narrow channel section 210 and the second narrow channel section 220 in the Z-axis direction was 50 mm. Furthermore, a circular pipe with an inner diameter of 25 mm was used as the object on which the first and second constriction sections 110 and 120 were provided.

[0128] In Table 2, experimental examples B6-B9 correspond to comparative examples with respect to the gas introduction method and the arrangement of the throttling section. The term "single stage" used to describe the configuration of the tubular member in experimental examples B6-B9 means that there is only one throttling section. The dimension in the short direction of the narrow flow path defined by this single throttling section was set to 1 [mm].

[0129] The term "pressure-dissolving type" used to describe the configuration of the tubular member in Experimental Example B6 means that the only point where outside air is drawn in by negative pressure is the first outside air inlet 320 located upstream of the liquid pump 310 shown in Figure 1. In Experimental Example B6, the second outside air inlet 140 and the second throttling section 120 shown in Figure 2 are omitted. The other configurations are the same as those in Experimental Examples B1-B5.

[0130] The term "ejector type," which describes the configuration of the tubular member in experimental examples B7-B9, means that the only point where outside air is drawn in by negative pressure is the second outside air inlet 140 shown in Figure 2. In experimental examples B7-B9, the first outside air inlet 320 shown in Figure 1 and the second throttling section 120 shown in Figure 2 are omitted. The other configurations are the same as those in experimental examples B1-B5.

[0131] In Table 2, "gas flow rate" refers to the flow rate of air introduced into the gas-liquid mixed fluid 600 by negative pressure. Specifically, in experimental example B6, which is a comparative example, "gas flow rate" refers to the flow rate of air introduced from the first outside air inlet 320. In experimental examples B7-B9, which are comparative examples, "gas flow rate" refers to the flow rate of air introduced from the second outside air inlet 140.

[0132] Furthermore, in experimental examples B1-B5, which are examples, "gas flow rate" refers to the sum of the flow rate of air introduced from the first outside air inlet 320 and the flow rate of air introduced from the second outside air inlet 140. In all of experimental examples B1-B5, the flow rate of air introduced from the first outside air inlet 320 was 0.1 [L / min], and the flow rate of air introduced from the second outside air inlet 140 was 0.3 [L / min].

[0133] Furthermore, in Table 2, "liquid pump discharge pressure" refers to the pressure of the gas-liquid mixed fluid 600 at the position where the liquid pump 310 shown in Figure 1 discharges. Also, in Table 2, "gas-liquid mixed fluid flow rate" refers to the flow rate of the gas-liquid mixed fluid 600 flowing through the tubular member.

[0134] Furthermore, in Table 2, the "overall mass transfer capacity coefficient" is an index that quantitatively evaluates the performance of dissolving gaseous components. A larger overall mass transfer capacity coefficient indicates that gaseous components can be dissolved efficiently in liquid 610, and that a larger amount of gaseous components are dissolved relative to liquid 610.

[0135] As shown in Table 2, experimental results obtained in experimental examples B1-B5, which correspond to the examples, showed a dramatic increase in the overall mass transfer capacity coefficient compared to experimental examples B6-B9, which correspond to the comparative examples. In other words, experimental examples B1-B5, which correspond to the examples, allow for the dissolution of a large amount of gaseous components in liquid 610.

[0136] The results of this experiment showed that, in the tubular member 100 into which a gas-liquid mixed fluid 600 containing liquid 610 and gaseous components is injected under pressure, a configuration in which outside air is further introduced from a second outside air introduction section 140 provided in the first constriction section 110 is preferable. With such a configuration, the dissolved concentration of gaseous components in liquid 610 can be dramatically increased.

[0137] In the configuration of Experimental Example B6, which corresponds to a comparative example, the same effect as in the example is obtained in which the gaseous component dissolved in the liquid 610 precipitates as bubbles 620 in the constricted portion inside the tubular member. However, because the precipitation of the gaseous component as bubbles 620 reduces the dissolved concentration of the gaseous component in the liquid 610, there is a limit to how much the overall mass transfer capacity coefficient can be increased.

[0138] In contrast, in the configurations of experimental examples B1-B5, which correspond to the embodiments, outside air is introduced not only in the preparation stage of preparing the gas-liquid mixed fluid 600 to be injected into the tubular member 100, but also in the second outside air introduction section 140 inside the tubular member 100.

[0139] Therefore, even though the gaseous components dissolved in the liquid 610 precipitate as precipitated bubbles 621 inside the tubular member 100, the outside air-derived bubbles 622 introduced from the second outside air introduction section 140 can be dissolved in the liquid 610 by stirring in the intermediate flow channel section 230. As a result, the gaseous components can be sufficiently dissolved in the liquid 610.

[0140] In the configurations of experimental examples B7-B9, which are comparative examples, outside air is introduced from the second outside air introduction section 140 inside the tubular member 100, but since there is only one constriction section, an intermediate flow path section 230 is not formed inside the tubular member. As a result, the outside air introduced from the second outside air introduction section 140 is not sufficiently agitated inside the tubular member. Consequently, the outside air cannot be sufficiently dissolved in the liquid 610, and there is a limit to how much the overall mass transfer capacity coefficient can be increased.

[0141] Figure 8 shows the number density distribution against diameter, i.e., bubble diameter, of bubbles 620 generated using the bubble generating apparatus according to Experimental Example B4, which corresponds to the embodiment. In the vertical axis of Figure 8, "E8" means 10 to the power of 8. That is, for example, "2.0E8" means 2.0 × 10⁸ [bubbles / mL]. In addition, in Figure 8, the bubble diameter at the position of the maximum point is noted near the maximum point of the curve representing the average of the number density measurement results.

[0142] As shown in Figure 8, the diameter of the bubbles 620 in the gas-liquid mixed fluid 600 is 500 nm or less. That is, it was confirmed that ultrafine bubbles with a diameter of 1 μm or less could be formed. The mode diameter of the bubbles 620 in the gas-liquid mixed fluid 600 was 115.6 nm, and the number density at that mode diameter was 3.3 × 10⁸ bubbles / mL. Here, the mode diameter refers to the diameter of the bubble with the highest frequency.

[0143] The embodiments and experimental examples have been described above. The following modifications are also possible.

[0144] Figures 3, 4, and 6 illustrate rectangles as the shape of the first narrow cross section, which is the cross-section of the first narrow channel section 210, and the shape of the second narrow cross section, which is the cross-section of the second narrow channel section 220. The first and second narrow cross sections are preferably shaped such that the longitudinal direction is perpendicular to the Z-axis (hereinafter referred to as the elongated shape), but the elongated shape is not particularly limited to a rectangle. The elongated shape may be an ellipse with the above-mentioned direction as the direction of the major axis, or it may be a rectangle with its four corners rounded with the above-mentioned direction as the longitudinal direction.

[0145] Furthermore, the shapes of the first and second narrow cross-sections do not necessarily have to be elongated. In short, it is sufficient that the area of ​​the second narrow cross-section is designed to be larger than the area of ​​the first narrow cross-section. This allows the flow resistance in the second constriction section 120 to be moderately suppressed, and allows for the formation of intense turbulence in the intermediate flow channel section 230.

[0146] Figure 1 shows a return pipe 430, but the return pipe 430 may be omitted. If the return pipe 430 is omitted, the gas-liquid mixed fluid 600 flowing out from the outlet end 102 of the tubular member 100 will be supplied to a liquid-tight container or other destination not shown. Also, the liquid tank 500 shown in Figure 1 is not essential. In short, any configuration in which the gas-liquid mixed fluid 600, containing liquid 610 and gaseous components, is injected into the tubular member 100 under pressure is sufficient.

[0147] Figure 1 illustrates a first outside air inlet 320 for preparing a gas-liquid mixed fluid 600 to be injected into the tubular member 100, but the configuration for preparing the gas-liquid mixed fluid 600 to be injected into the tubular member 100 is arbitrary. The gas-liquid mixed fluid 600 containing gaseous components may be prepared by a known method that does not use the first outside air inlet 320, and the gas-liquid mixed fluid 600 may be pumped into the tubular member 100 by a liquid pump 310 or other pressurizing means.

[0148] Figure 3 shows an example of four ventilation passages 141, but the number of ventilation passages 141 is not particularly limited. Only one ventilation passage 141 may be provided.

[0149] In the above embodiments and experimental examples, air was used as an example of the gaseous component contained in the gas-liquid mixed fluid 600, but the gaseous component is arbitrary. In addition to air, carbon dioxide, oxygen, ozone, nitrogen, etc. may be used as the gaseous component.

[0150] In the configuration shown in Figure 1, the outside air introduced from the first outside air introduction section 320 and the outside air introduced from the second outside air introduction section 140 may be the same or different. In this specification, "outside air" means gas present outside the tubular member 100 and is not limited to gas constituting the atmosphere surrounding the bubble generating device 700 (hereinafter referred to as atmosphere-constituting gas).

[0151] A gas different from the atmospheric gas may be prepared in a cylinder, gas bag, or other airtight container, and the gas in that airtight container may be introduced through the first outside air inlet 320 and the second outside air inlet 140 by negative pressure. Here, negative pressure means a pressure lower than the atmospheric pressure inside the airtight container.

[0152] In the above embodiments and experimental examples, water was used as an example of the liquid 610 constituting the gas-liquid mixed fluid 600. In this specification, the concept of "water" includes tap water, ion-exchanged water, distilled water and other tap water, industrial water and other reclaimed water, sewage, seawater, lake water, river water, groundwater, etc. Furthermore, liquid 610 is not limited to water. Examples of liquid 610 at room temperature and atmospheric pressure include water, ethanol, organic solvents, etc.

[0153] The present invention can be modified in various ways without departing from the broad spirit and scope of the invention. The above embodiments and experimental examples are for illustrative purposes only and do not limit the scope of the invention. The scope of the invention is indicated by the claims, not by the embodiments and experimental examples. Various modifications made within the scope of the claims and equivalent inventive meaning are considered to be within the scope of the invention.

[0154] This application is based on Japanese Patent Application No. 2024-160882, filed on 18 September 2024. The entire specification, claims, and drawings of Japanese Patent Application No. 2024-160882 are incorporated herein by reference.

[0155] 100...Tubular member, 101...Inlet end (one end), 102...Outlet end (other end), 110...First constriction section, 111...Narrowing tapered section, 112...Throat section, 113...Expanding tapered section, 120...Second constriction section, 121...Narrowing tapered section, 122...Throat section, 123...Expanding tapered section, 130...Intermediate section, 140...Second outside air inlet section (outside air inlet section), 141...Ventilation passage, 200...Flow path, 210...First narrowed flow path section, 220...Second narrowed flow path section, 230...Intermediate flow path section, 240...Inlet end flow path section, 250...Outlet end flow path section, 300...Pressure pump, 310...Liquid pump, 320...First outside air inlet section, 400...Piping, 410... Supply piping, 420... Intermediate piping, 430... Return piping, 500... Liquid tank, 600... Gas-liquid mixed fluid, 610... Liquid, 620... Bubbles, 621... Precipitated bubbles, 622... Bubbles originating from outside air, 700... Bubble generation device, CL... Virtual central axis.

Claims

1. A tubular member formed in the shape of a tube that defines a flow path for a gas-liquid mixed fluid containing a liquid and a gaseous component mixed with the liquid, into which the gas-liquid mixed fluid is injected under pressure from one end and out of the other end, comprising: a first throttling portion that restricts the flow of the gas-liquid mixed fluid by locally narrowing the area of ​​the cross-section of the flow path perpendicular to the length direction of the tubular member; a second throttling portion located closer to the other end than the first throttling portion and adjacent to the first throttling portion, which restricts the flow of the gas-liquid mixed fluid that has passed through the first throttling portion by locally narrowing the area of ​​the cross-section of the flow path; an intermediate portion that defines an intermediate flow path portion between the first narrowed flow path portion, which is the portion of the flow path narrowed in the first throttling portion, and the second narrowed flow path portion, which is the portion of the flow path narrowed in the second throttling portion; and an outside air introduction portion that guides outside air into the first narrowed flow path portion. A tubular member wherein the area of ​​the cross-section of the second narrow channel portion is larger than the area of ​​the cross-section of the first narrow channel portion.

2. The tubular member according to claim 1, wherein the first narrow cross section, which is the cross-section of the first narrow channel, has a shape in which the longitudinal direction is in the U1 axis direction parallel to the first narrow cross section, and the second narrow cross section, which is the cross-section of the second narrow channel, has a shape in which the longitudinal direction is in the V1 axis direction parallel to the second narrow cross section, the dimension of the first narrow cross section in the U1 axis direction is equal to the dimension of the second narrow cross section in the V1 axis direction, and the dimension of the second narrow cross section in the V2 axis direction, which is parallel to the second narrow cross section and perpendicular to the V1 axis direction, is greater than the dimension of the first narrow cross section in the U2 axis direction, which is parallel to the first narrow cross section and perpendicular to the U1 axis direction.

3. The tubular member according to claim 2, wherein when the dimension of the first narrow cross section in the U2 axial direction is LA and the dimension of the second narrow cross section in the V2 axial direction is LB, the relationship 1.5 × LA ≤ LB ≤ 6.5 × LA is satisfied.

4. The tubular member according to claim 3, wherein when the equivalent diameter of the intermediate flow channel is LC, the relationship 8 × LA ≤ LC ≤ 32 × LA is satisfied.

5. The tubular member according to claim 3, further satisfying the following relationships: 0.8 [mm] ≤ LA < 3 [mm], LA + 2 [mm] ≤ LB, and 3 [mm] ≤ LB ≤ 5 [mm].

6. The tubular member according to claim 1, wherein the distance in the longitudinal direction between the first narrow channel and the second narrow channel is shorter than the interval at which the longitudinal flow velocity of the gas-liquid mixed fluid that passes through the first constriction and flows through the intermediate channel returns to the longitudinal flow velocity of the gas-liquid mixed fluid when it is pressed into the tubular member from one end.

7. The tubular member according to claim 1, wherein when the distance in the longitudinal direction between the first narrow channel portion and the second narrow channel portion is LZ, and the equivalent diameter of the intermediate channel portion is LC, the relationship 1.5 × LC ≤ LZ ≤ 3 × LC is satisfied.

8. The tubular member according to claim 2, wherein the direction of the V1 axis is parallel to the direction of the U1 axis.

9. The tubular member according to claim 2, wherein the V1 axis direction is the direction obtained by rotating the U1 axis direction around a virtual central axis parallel to the longitudinal direction.

10. A bubble generating apparatus comprising a tubular member according to any one of claims 1 to 9, and a pump for pressurizing the gas-liquid mixed fluid into the tubular member.

11. The bubble generating apparatus according to claim 10, further comprising: a liquid tank in which the gas-liquid mixed fluid is stored; a return pipe connecting the interior of the liquid tank to the other end of the tubular member; and a supply pipe connecting the interior of the liquid tank to a pump, wherein the pump draws the gas-liquid mixed fluid from the interior of the liquid tank through the supply pipe, pumps the drawn-in gas-liquid mixed fluid together with the gas to the tubular member, and the gas-liquid mixed fluid that flows out from the other end of the tubular member returns to the interior of the liquid tank through the return pipe.

12. A bubble generation method using a tubular member formed in the shape of a tube that defines a flow path for a gas-liquid mixed fluid containing a liquid and a gaseous component mixed with the liquid, the gas-liquid mixed fluid being injected from one end and the injected gas-liquid mixed fluid being injected out from the other end, wherein the tubular member comprises: a first throttling portion that restricts the flow of the gas-liquid mixed fluid by locally narrowing the area of ​​the cross-sectional surface of the flow path perpendicular to the length direction of the tubular member; a second throttling portion located closer to the other end than the first throttling portion and adjacent to the first throttling portion, which restricts the flow of the gas-liquid mixed fluid that has passed through the first throttling portion by locally narrowing the area of ​​the cross-sectional surface of the flow path; an intermediate portion that defines an intermediate flow path portion of the flow path, which is the portion between the first narrowed flow path portion, which is the portion narrowed in the first throttling portion, and the second narrowed flow path portion, which is the portion narrowed in the second throttling portion; and an outside air introduction portion that guides outside air into the first narrowed flow path portion. A bubble generation method comprising: a precipitate bubble generation step in which precipitate bubbles are generated by the precipitation of the gaseous component dissolved in the liquid in the first narrow channel, wherein the area of ​​the cross-section of the second narrow channel is larger than the area of ​​the cross-section of the first narrow channel; an outside air derived bubble generation step in which outside air is introduced into the first narrow channel through the outside air introduction section by the negative pressure generated in the first narrow channel, thereby generating outside air derived bubbles which are bubbles originating from the outside air; and a stirring step in which the outside air derived bubbles and the precipitate bubbles are stirred in the intermediate channel by the turbulence generated in the intermediate channel.

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