JP4893365B2 - Microbubble generator and microbubble generator system - Google Patents

Description

  The present invention relates to a microbubble generator for supplying fine bubbles into a liquid and a microbubble generator system having the microbubble generator.

  Bubbles with a diameter of several hundreds of micrometers or less that exist in water are called microbubbles. The smaller the diameter, the more useful characteristics are exhibited, and application research focusing on them has been actively conducted in various fields. ing.

The first characteristic of microbubbles is that the bubble diameter is small, so the pressure inside the bubbles is high due to the balance with the surface tension of water, and the size increases in inverse proportion to the diameter. When the pressure increases, the solubility of the gas in the bubbles in water increases according to Henry's law. Furthermore, as the cell diameter is small, the gas-liquid interfacial area is increased, 1 if the l 10cc of air in water and aerated, interfacial area 0.03 m ² in bubble diameter 1 mm, 10 [mu] m in 3m ^2, further 30m in 1μm ^{Also 2} At the same time, the rising speed of the bubbles is slower as the bubble diameter is smaller, and the microbubbles stay in the water for a long time. Due to these characteristics, the gas dissolution efficiency of microbubbles is high, and various gases (for example, oxygen) can be efficiently dissolved in water.

  Secondly, the phenomenon at the gas-liquid interface becomes prominent, and the repulsive force is generated between the bubbles due to the negative charge of the interface due to the water molecule being an electric dipole (however, the water temperature is about 0 to 40 ° C.). It has the feature that it acts and microbubbles can exist without being united. Further, there is a feature that a positively charged object can be attracted by this negative charging. Furthermore, there is a feature that a hydrophobic group of a molecule such as an organic substance or a surfactant is adsorbed on a gas-liquid interface by air bubbles and floats and separates from water.

  In addition to these characteristics, there are various characteristics that are being verified, such as physiological activation phenomenon and free radical generation, and it is expected to be applicable in a wide range of fields.

  The generation of microbubbles is roughly divided into the following six methods (for example, Non-Patent Document 1). (A) Channel expansion method using a venturi tube or the like (see Non-patent Document 2 and Patent Document 1), (b) Supersaturated precipitation method of pressurized dissolved gas (pressurized dissolution method), (c) Swirl flow bubble A shearing method (swirl flow method), (d) a high-pressure opening method using an orifice or the like, (e) a gas discharge method from a fine hole, and (f) a bubble breaking method using ultrasonic waves or a machine are known.

Both methods devise various methods for generating bubbles and destroying generated bubbles. In particular, the methods (a) to (d) are based on pressure fluctuations and water flow, the method (e) is by reducing the diameter of the gas discharge hole, and the method (f) is a power other than water flow (medium This is due to vibration or mechanical shearing.
Hirofumi Taisei, “Basics of Microbubbles”, Foam Engineering, 2005, pp. 423-429 Reiko Fujiwara, “Microbubble generation method using Venturi tube”, Eco-Industry, 2006, Vol. 11, no. 3, 27-30 JP2003-230824

  The microbubble generation method other than the method (a) has the following problems.

  The method (b) requires a large pump power for pressurizing water and a compressor for supplying gas.

  In the method (c), when the void ratio (volume ratio occupied by the gas) is greater than about 1%, the bubble diameter increases.

  The method (d) requires a large pump power for generating a high pressure.

  In the method (e), the generated bubbles become large. In order to make these bubbles fine, a high-pressure compressor for gas pressure feeding by making the holes fine is necessary.

  The ultrasonic method of (f) is not suitable for steady use. Extra power is required to generate ultrasonic waves and drive the machine.

  On the other hand, the flow path enlargement method (a) has a feature that it is difficult to collect impurities because a water passage can be secured wider than the methods (b) to (f).

  The principle of microbubble generation of a flow channel expansion type (hereinafter referred to as a single nozzle method) using a single venturi tube will be described with reference to FIG.

  The venturi tube 5 shown in FIG. 6 has a throttle part 52, a throat part 53, a taper part 54, and a discharge part 55 formed in this order on the downstream side of the cylindrical part 51. An air introduction pipe 56 is connected to the cylindrical portion 51. Air is introduced from the air introduction pipe 56 into the water flow formed in the cylindrical portion 51. When the water flow passes through the throttle portion 52, the flow velocity is increased to the throat portion 53 and the pressure is reduced. In the taper part 54, the flow velocity of the water flow decreases as the discharge part 55 is approached, and the pressure recovers to the external water pressure. As the pressure recovers, the bubbles 57 in the tapered portion 54 are compressed. At the same time, in the process in which the liquid phase in the taper 54 is discharged from the discharge portion 55, the flow velocity near the throat 53 exceeds the sound velocity due to the phenomenon of sound velocity drop in the gas-liquid two-phase flow, and a shock wave is generated. . Bubbles 57 are destroyed and refined by this shock wave.

  However, the single nozzle method has the following problems. The pump power needs to be increased to achieve a high void rate. The generated bubble concentration is as thin as 100 to 200 / ml. The generated bubble distribution peak value is as large as about 100 μm. Since the nozzle has a single flow path, the pressure loss of the throttle portion is large and a large pump power is required. Since the pressure in the pipe becomes high, an air supply compressor is required. A surfactant is required to make the bubble diameter about several tens of μm.

Therefore, the microbubble generator of the present invention includes a flow passage to which a gas-liquid mixed phase flow is supplied, a pressure receiving portion that receives the gas-liquid mixed phase flow on one end side of the flow passage, and a flow passage side surface in the vicinity of the pressure receiving portion. A plurality of discharge passages for introducing the gas-liquid mixed phase flow to generate microbubbles, the inner surface of the pressure receiving portion is formed in a curved concave surface, and the inner surface of each discharge passage has a large outlet diameter. The opening angle of each discharge passage is set so that the differential pressure between the inlet and the outlet of the discharge passage is maximized .

The microbubble generation system includes a tank in which a microbubble generator is installed, a pipe for circulatingly supplying a liquid phase in the tank, a pump installed in the pipe, and the pipe by the pump. An air intake device that supplies gas to the liquid phase that circulates in the interior, and the microbubble generator is configured to supply a gas-liquid mixed phase flow that is generated by supplying the gas to the liquid phase that circulates in the pipe. A pressure receiving portion that receives the gas-liquid mixed phase flow at one end of the flow passage, and a plurality of discharge passages that introduce the gas-liquid mixed phase flow from the side surface of the flow passage near the pressure receiving portion to generate microbubbles. And the inner surface of each pressure receiving portion is formed in a curved concave surface, the inner surface of each discharge passage is formed in a taper shape with a large outlet diameter, and the opening angle of each discharge passage is Maximum pressure difference between inlet and outlet It is sea urchin set.

  According to the above invention, the nozzle pressure loss can be reduced to a single nozzle system with the same pump power, the pump discharge amount can be increased accordingly, and more gas can be introduced as a gas-liquid mixed phase flow even with relatively small pump power And the void ratio increases. Further, the concentration of microbubbles obtained by the above invention is higher than that obtained by the single nozzle method, and more gas can be efficiently dissolved in the liquid. Furthermore, according to the said invention, the microbubble which has a fine bubble diameter distribution (bubble diameter peak value 50 micrometers or less) compared with a single nozzle system is generable. Therefore, auxiliary means such as a surfactant are not necessary.

  Moreover, since the said invention can self-suck gas, a compressor becomes unnecessary. Therefore, the amount of energy used is reduced, the system configuration is simplified, and the cost is reduced.

In order to generate microbubbles in the single nozzle system, it is necessary to reduce the sectional area of the inlet of the nozzle and to secure a large water flow rate (flow velocity). On the other hand, according to the invention, the pressure loss can be adjusted by the number of discharge passages and the sectional area of the inlet, and by optimizing the opening angle of the discharge passage, the pressure loss seen from the pump is reduced and the microbubbles are efficient. Is generated. This reduces pump power, increases energy efficiency, and reduces costs. In particular, in the present invention, since the opening angle of the discharge passage (as a example 9 ° to 11 °) the pressure difference between the inlet and outlet of the discharge passage is such that the maximum has been set, the microbubbles efficiency Can be refined.

  Further, in the microbubble generator, the plurality of discharge paths may be connected radially about the axis of the flow path. Since the microbubbles are ejected radially around the axis of the flow path, the microbubbles can be supplied in an isotropic and wide range.

  The plurality of discharge paths may be arranged to discharge microbubbles in the axial direction of the flow path. It is possible to supply microbubbles in a single direction.

In the present invention, since the pressure receiving surface that receives the gas-liquid mixed flow is formed into a curved concave surface, the gas-liquid mixed phase flow in the flow passage diffuses in the inner circumferential direction of the flow passage. It becomes easy to be provided to each discharge path equally.

  In the microbubble generation system, the intake device may be installed on the secondary side of the pump. Gas accumulation is less likely to occur inside the pump, and the gas-liquid mixed phase flow is stabilized.

  The intake device may include a gas flow rate control valve. Since the amount of intake air that is self-priming becomes variable, the peak diameter of the bubble diameter distribution can be changed to some extent.

  Examples of the gas include air, oxygen, ozone, and carbon dioxide. Microbubbles can be generated for various applications.

  Therefore, according to the above invention, energy-efficient and finer microbubbles can be generated.

  FIG. 1A is a plan sectional view of a microbubble generator 1 according to a first embodiment of the invention. FIG. 1B is a cross-sectional view of the microbubble generator 1.

  The microbubble generator 1 includes a discharge unit 10 and a piping unit 11. A flow passage 101, a pressure receiving portion 12, and a discharge passage 13 are formed inside the discharge portion 10. The flow passage 101 communicates with the flow passage 111 of the piping part 11. The inner diameter of the flow passage 101 is the same as the inner diameter of the flow passage 111. A gas-liquid mixed phase flow is supplied to the flow passage 101 via the flow passage 111.

The pressure receiving unit 12 receives the gas-liquid mixed phase flow. The pressure receiving portion 12 is formed at one end of the flow passage 101. The pressure receiving portion 12 has a maximum inner diameter that is the same as that of the flow passage 111. Further, the surface 121 that directly receives the gas-liquid mixed phase in the pressure receiving portion 12 is formed as a concave surface that is curved as shown in FIG.

  The discharge path 13 discharges a liquid phase containing microbubbles. As shown in FIGS. 1A and 1B, the discharge passage 13 is connected to the side surface of the flow passage 101 near the surface 121. The individual discharge passages 13 are radially connected around the axis of the flow passage 101. Further, the inner surface of the discharge passage 13 is formed in a tapered shape so that the outlet diameter of the discharge passage 13 is large.

  The gas-liquid mixed phase flow in the flow passage 101 collides violently by the pressure receiving portion 12 and is diffused in the inner peripheral direction of the flow passage 101 and is provided to the individual discharge passages 13 equally. The gas-liquid mixed phase flow introduced into the individual discharge passages 13 causes a drop in water pressure due to the high-speed flow near the entrance of the discharge passages 13 and enlarges bubbles contained in the mixed phase flow. Further, when the flow velocity exceeds a predetermined flow rate, bubbles of dissolved gas are generated by the generation of cavitation. These bubbles are destroyed by water pressure that rapidly recovers as they move to the outlet portion of the discharge passage 13 and are discharged as microbubbles. At the same time, in this discharge process, the flow velocity near the inlet of the discharge passage 13 exceeds the sound velocity due to the phenomenon of a decrease in the sound velocity in the gas-liquid two-phase flow, thereby generating a shock wave. Bubbles are destroyed and refined by this shock wave. Moreover, since the microbubble generator 1 can discharge a water flow in the radial direction around the axis of the flow passage 101, it is suitable for applications that require isotropic supply of microbubbles over a wide range.

  An example of the microbubble generator according to the second embodiment of the invention is the microbubble generator 2 shown in FIG. FIG. 2A is a perspective view of the microbubble generator 2. FIG. 2B is a cross-sectional view of the microbubble generator 2 taken along the line AA. FIG. 2C is a cross-sectional view of the microbubble generator 2 taken along the line BB.

  The microbubble generator 2 has the same configuration as the microbubble generator 1 except that the microbubbles are discharged in the axial direction of the piping part 21. That is, the microbubble generator 2 includes a discharge unit 20 and a piping unit 21 as shown in FIG.

  As shown in FIG. 2C, a flow passage 201, a pressure receiving portion 22, and a discharge passage 23 are formed inside the discharge portion 20. The flow path 201 is in communication with the flow path 211 of the piping part 21. The inner diameter of the flow passage 201 is the same as the inner diameter of the flow passage 211. A gas-liquid mixed phase flow is supplied to the flow passage 201 via the flow passage 211.

  The pressure receiving unit 22 receives a gas-liquid mixed phase flow introduced through the flow passage 201. The maximum inner diameter of the pressure receiving unit 22 is set to the same diameter as the flow passage 211. Further, the surface 221 that directly receives the gas-liquid mixed phase flow in the pressure receiving unit 22 is curved similarly to the pressure receiving unit 12 of the microbubble generator 1.

  The discharge path 23 discharges a liquid phase containing microbubbles. A plurality of discharge passages 23 are connected to the side surface of the flow passage 201 near the surface 221. As shown in FIG. 2B, the individual discharge passages 23 are installed in the same direction as the flow passage 211 and are arranged in an arc shape around the axis of the flow passage 211. As shown in FIG. 2C, the inner surface of the discharge path 23 is formed in a taper shape so that the outlet diameter of the discharge path 23 is large.

  The gas-liquid mixed phase flow in the pipe portion 21 collides violently by the pressure receiving portion 22 and diffuses in the inner peripheral direction of the flow passage 201 and is evenly distributed to the individual discharge passages 23. The distributed gas-liquid mixed phase flow generates microbubbles by the same operating principle as the microbubble generator 1 described above with reference to FIG. The microbubble generator 2 is suitable for applications that require the supply of microbubbles in a single direction.

  The opening angle θ of the discharge paths 13 and 23 of the microbubble generators 1 and 2 is set to about 8 ° to 12 °. In the expanding flow path, the resistance coefficient increases at an angle of 6 ° or less and 12 ° or more, and the flow rate that can be supplied with the same pump power decreases. From this viewpoint, the angle with the largest flow rate is about 6 to 12 °. Further, it is necessary to increase the pressure difference between the inlets and outlets of the discharge passages 13 and 23 in order to make the bubbles finer. According to the relationship between the pressure difference (pressure loss) and the opening angle in consideration of the resistance coefficient shown in FIG. 5 (in the case of a single nozzle system having an inlet diameter of 3 mm and a total length of 30 mm), the angle at which the largest pressure difference can be secured is 9 °. It is ˜11 °. Therefore, the opening angle of the discharge passages 13 and 23 for generating microbubbles is preferably set to about 9 ° to 11 °.

  As the opening angle of the discharge passages 13 and 23 is set larger, the position where the bubbles become finer approaches the inlets of the discharge passages 13 and 23. For example, when the inlet diameter of the discharge passages 13 and 23 is 3 mm and the flow rate is about 8 L / min, the opening angle is about 20 mm at 6 °, about 15 mm at 9 °, and about 5 mm at 15 °. Becomes shorter. Therefore, in order to reduce the size of the discharge passages 13 and 23, the opening angle of the discharge passages 13 and 23 may be increased. However, the relationship between the pressure difference (pressure loss) and the opening angle described with reference to FIG. It is necessary to select the opening angle in consideration.

  The shape of the discharge passages 13 and 23 is a tapered or conical expansion tube as described above. As for the shapes of the inlet portions of the discharge passages 13 and 23, if the acute angle portion is cut and rounded, the fluid resistance is reduced and the pressure loss is further reduced, so that the pump power is reduced.

In addition, the void ratio of the microbubble generators 1 and 2 is experimentally confirmed to be about 5% under the conditions of pump power of 0.56 kW-2P, water flow rate of about 30 L / min, and discharge path pressure loss of about 0.2 MPa. It was done. At this time, the inlet cross-sectional area of the discharge passages 13 and 23 (8 provided) is about 25 mm ² , and the inlet dimension of the discharge passages 13 and 23 is set to about 2 mm in diameter. As a comparative example, bubbles obtained by a conventional single-nozzle microbubble generator set to an inlet cross-sectional area of 25 mm ² become coarse bubbles of 1 mm or more, and discharge channels 13 and 23 having the same inlet cross-sectional area are formed. Microbubbles (bubble diameter peak value of 50 μm or less) as generated by the microbubble generators 1 and 2 possessed were not obtained.

  Therefore, compared to the single-nozzle microbubble generator, the microbubble generators 1 and 2 generate finer and higher-concentration microbubbles with less pump power without using auxiliary means such as a surfactant. be able to.

  As described above, according to the microbubble generators 1 and 2, by having a plurality of discharge passages 13, the nozzle pressure loss is reduced as compared with the single-nozzle microbubble generator, and the pump discharge flow rate is increased accordingly. . As the flow rate increases, the flow velocity of the gas-liquid mixed phase flow in the flow passages 111 and 211 increases, so that the amount of self-supplied air intake increases and a high void ratio is achieved. Then, fine bubbles are generated at a high void ratio, and high concentration microbubbles are obtained. Therefore, it can be applied to various uses such as factory wastewater treatment, washing, oil separation, flotation separation of sewage and the like, as well as supply of microbubble-containing water in water purification, agriculture and aquaculture.

  Examples of the microbubble generation system to which the microbubble generators 1 and 2 are applied include the microbubble generation system 3 shown in FIG. 3 and the microbubble generation system 4 shown in FIG. 4.

  The microbubble generating system 3 includes a tank 31 in which the microbubble generating device 1 (or the microbubble generating apparatus 2) is installed, a pipe 32 for circulatingly supplying the liquid phase in the tank 31, and the pipe 32. And a suction device 34 installed on the secondary side of the pump 33. The microbubble generator 1 (or microbubble generator 2) is immersed in the liquid phase staying in the tank 31. The pump 33 may be a known vortex pump. The intake device 34 includes an intake pipe 35 for introducing gas. The intake device 34 may employ a known ejector or the like. In addition, if the gas flow rate adjusting valve is provided in the intake pipe 35, the peak diameter of the bubble diameter distribution can be changed by changing the amount of intake air that is sucked. When the intake amount is decreased, the generated bubble diameter is reduced, and when the intake amount is increased, the generated bubble diameter is increased.

  Examples of the gas introduced by the intake device 34 include air, oxygen, ozone, carbon dioxide, and the like, which are appropriately selected according to the purpose of use and combined with the forms of the microbubble generators 1 and 2 described so far. It is possible to generate various microbubbles and dissolve gas with high efficiency.

  On the other hand, the microbubble generation system 3 has the same system configuration as the microbubble generation system 2 except that the intake device 34 is installed on the primary side of the pump 33.

  Since the microbubble generation systems 3 and 4 can self-suck the gas via the intake device 34, a compressor is unnecessary, and only the power of the pump 33 that generates a water flow in the pipe 32 is required. A part of the liquid phase in the tank 31 sucked by the pump 33 circulates in the pipe 32 and returns to the tank 31 through the intake device 34. In the pipe 32, microbubbles generated in the process in which the flow that has become a gas-liquid mixed phase flow is discharged from the microbubble generator 1 (or the microbubble generator 2) are supplied to the liquid phase of the tank 31.

(A) The cross-sectional view of the microbubble generator which concerns on 1st embodiment of invention, (b) Sectional drawing of the said microbubble generator. (A) The perspective view of the microbubble generator which concerns on 2nd embodiment of invention, (b) AA sectional drawing of the said microbubble generator, (c) BB sectional drawing of the said microbubble generator. The block diagram of the microbubble generation system to which the microbubble generator which concerns on invention is applied. The block diagram of the microbubble generation system to which the microbubble generator which concerns on invention is applied. The characteristic view which showed the relationship between the opening angle of a discharge path, and differential pressure | voltage. Sectional drawing of the conventional microbubble generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Micro bubble generator 3, 4 ... Micro bubble generation system 10, 20 ... Discharge part, 11, 21 ... Piping part, 12, 22 ... Pressure receiving part, 13, 23 ... Discharge path 31 ... Tank, 32 ... Piping , 33 ... pump, 34 ... intake device, 35 ... intake pipe 101, 111, 201, 211 ... flow passage

Claims (7)

A flow path through which a gas-liquid mixed phase flow is supplied;
A pressure receiving portion that receives the gas-liquid mixed phase flow at one end of the flow path;
A plurality of discharge passages for generating microbubbles by introducing the gas-liquid mixed phase flow from the flow passage side surface in the vicinity of the pressure receiving portion;
The inner surface of the pressure receiving portion is formed as a curved concave surface ,
The inner surface of each discharge passage is formed in a taper shape so that the outlet diameter is large, and the opening angle of each discharge passage is set so that the differential pressure between the inlet and outlet of the discharge passage is maximized. <br/> Microbubble generator characterized by the above. 2. The microbubble generator according to claim 1, wherein the plurality of discharge passages are radially connected around an axis of the flow passage. The microbubble generator according to claim 2, wherein the plurality of discharge paths are arranged to discharge microbubbles in an axial direction of the flow path. A tank in which a microbubble generator is installed;
Piping for cyclically supplying the liquid phase in the tank;
A pump installed in this pipe,
An intake device for supplying gas to the liquid phase flowing through the pipe by the pump;
The microbubble generator is
A flow path through which a gas-liquid mixed phase flow generated by supplying the gas to the liquid phase flowing through the pipe is supplied;
A pressure receiving portion that receives the gas-liquid mixed phase flow at one end of the flow path;
A plurality of discharge passages for generating microbubbles by introducing the gas-liquid mixed phase flow from the flow passage side surface in the vicinity of the pressure receiving portion;
The inner surface of the pressure receiving portion is formed as a curved concave surface ,
The inner surface of each discharge passage is formed in a taper shape so that the outlet diameter is large, and the opening angle of each discharge passage is set so that the differential pressure between the inlet and outlet of the discharge passage is maximized. <br/> Microbubble generation system characterized by The microbubble generation system according to claim 4 , wherein the intake device is installed on a secondary side of the pump. The microbubble generation system according to claim 4 , wherein the intake device includes a gas flow rate control valve. The microbubble generating system according to claim 4 , wherein the gas is air, oxygen, ozone, or carbon dioxide.

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