JP2002113340A - Method and device for generating micro air bubble using ultrasonic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and stably generate micro air bubbles having a relatively uniform dimension by utilizing unstable state at gas-liquid interface. SOLUTION: The method of continuously generating micro air bubbles from the gas-liquid interface comprises adding ultrasonic wave to the gas-liquid interface of gas and liquid before the gas forms complete air bubbles, which gas is supplied into the liquid from a gas feeding port of a fine pipe, which feeding port is provided in the liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for generating microbubbles.

[0002]

2. Description of the Related Art Microbubbles are used in liquid phase chemical reactors, blood contrast agents, harmful substances in solutions, and the like, because of their large specific surface area to volume and long residence time in water.
Alternatively, it is used in various fields such as reduction of frictional resistance.

For example, in a liquid phase chemical reaction, the dissolution process of a reaction gas often becomes a rate-determining reaction, and the use of a microbubble having a diameter on the order of sub-millimeters for the dissolution acceleration technology suppresses the stirring power. It has great significance as an energy-saving technology. When comparing a single bubble with many microbubbles of the same volume, the large number of microbubbles has a larger gas-liquid contact area, and the resistance to water against buoyancy increases, the rise speed decreases, and the reaction time also increases. To increase. Therefore, finer microbubbles contribute to improving the reaction efficiency.

[0004] Conventional techniques for generating microbubbles include a method in which a gas is ejected from micropores and a method using a shearing force. For the former, there is a method of blowing gas from a minute nozzle or a method of blowing gas from a porous plate,
There is a problem that processing and maintenance of members are difficult. The latter includes a method of entraining the gas on the liquid surface with a jet or a method of blowing the gas into a high-speed liquid flow, but has a problem that it is difficult to control the bubble diameter.

On the other hand, Japanese Patent Application Laid-Open No. 8-230763 discloses
Discloses an apparatus for generating microbubbles provided with an ultrasonic vibration element. Specifically, the apparatus includes a fluid transfer pipe connected to the pressurized water supply means, a pressurized gas supply means arranged inside the fluid transfer pipe and connected to supply the pressurized gas, and a fluid transfer pipe. An ultrasonic vibration element disposed downstream of the connection point with the pressurized gas supply means to apply ultrasonic vibration to the bubble-water mixed fluid inside the fluid transfer pipe to form fine bubbles. That is, microbubbles are generated by further applying ultrasonic vibration to the bubbles generated by the conventional microbubble generation technique.

However, in order to break bubbles in water, it is necessary to provide a frequency for oscillating the volume of the bubbles. Therefore, only bubbles having a diameter matching the given frequency can be satisfactorily broken. When the size of bubbles generated on the upstream side varies, it is considered that the size of bubbles generated in the first stage varies in the above idea, and fine bubbles are efficiently and efficiently generated. It is considered impossible. In addition, destroying the bubble once generated is like crushing a balloon, and the bubble is hard to be destroyed. Therefore, more energy is required to generate microbubbles. Further, it is considered that giving vibration to bubbles flowing in the liquid is inefficient. Therefore, from the above, Japanese Patent Application Laid-Open
In the method disclosed in No. 230763, it is not possible to efficiently and stably supply microbubbles.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on a completely new idea, and a method of generating microbubbles which can solve the above-mentioned problem while using ultrasonic vibration. It is intended to provide.

[0008]

The technical means adopted by the present invention is that a gas supplied from a gas supply port of a fine tube having a gas supply port in a liquid to the liquid before the bubble is generated.
By applying ultrasonic waves to the gas-liquid interface between the gas and the liquid,
A plurality of microbubbles are continuously generated from the gas-liquid interface.

Before the gas supplied into the liquid from the gas supply port of the fine tube generates bubbles, one preferable state is to apply pressure to the gas in the fine tube so that the gas is supplied from the gas supply port. A state in which gas slightly swells into the liquid.
By continuously applying ultrasonic waves to the gas-liquid interface between the bubbles swelling into the liquid and the liquid from the gas supply port, a plurality of microbubbles are continuously generated from the interface.

[0010] In one preferred embodiment, the microtubules are microsyringes. The cross-sectional shape of the gas supply path of the fine tube is not limited, and may be a circular cross section or a rectangular cross section as long as it has a small area. The inner diameter of the fine tube is preferably 0.5 mm or less, more preferably about 0.1 mm to 0.2 mm. The means for applying ultrasonic waves to the gas-liquid interface is not particularly limited, and is appropriately selected from known ultrasonic vibration generating means. In addition, although the applied frequency is affected by the diameter of the fine tube, the gas injection speed, and the like, it has been found that fine bubbles can be generated at a relatively low frequency of about 20 kHz under the conditions described later. It has also been found that changing the frequency can control the size of the diameter of the generated bubbles.

[0011]

Embodiments of the present invention will be described. FIG. 1 shows an experimental apparatus according to the present invention. The experimental apparatus includes a 200 mm × 50 mm × 100 mm water tank 1, a micro syringe 2, and a micro syringe pump (Bioan pump).
aluminum-based BD-MD1001), ultrasonic vibrator 3, function generator (Iwatsu)
SG4111), amplifier (Mess-Tex)
M2617). In the experiment, water was used as the liquid in the water tank, but the liquid stored in the water tank is not limited to water. Ultrasonic vibrator 3, function generator 4,
The amplifier 5 constitutes an ultrasonic generator, and the frequency is controlled by the function generator 4.
The magnitude of the ultrasonic output is controlled by the ultrasonic transducer 3
This converts the electrical input into ultrasonic vibration.

A micro syringe needle is inserted from the bottom of the water tank, and air is injected by a micro syringe pump. The air injection speed can be adjusted by replacing the micro syringe main body or changing the operation speed of the pump. In an experiment described below, the flow rate of the gas when the fine bubbles are generated is 5 μl / min. The magnetostrictive vibrator is placed horizontally on the bottom surface of the water tank, and is arranged such that the tip of the needle is located on the center axis where vibration is strongest. In the experiment, a microsyringe extending upward from below was used, but the spatial arrangement and the extending direction of the microtubes are not limited to this, and the microtubes may extend downward or in a horizontal direction. May be extended. The arrangement of the ultrasonic vibrating element is not limited to the one shown in the drawing. In short, the ultrasonic vibrating element may be any as long as it can appropriately apply ultrasonic vibration to the gas-liquid interface at the tip of the fine tube.

It has been observed that a plurality of microbubbles are continuously generated from the gas-liquid interface by vibrating the surface at the interface between air and water injected from the microsyringe by ultrasonic waves generated by the magnetostrictive vibrator. Was. About behavior of bubble C
Observed using a CD camera.

FIG. 2 shows a case where no ultrasonic wave is applied to the gas-liquid interface, and FIGS. 3 (a), 3 (b) and 3 (c) show cases where ultrasonic waves are applied to the gas-liquid interface. is there. The frequency applied to the gas-liquid surface is 18.9 kHz, the vibrator input is 1.48 W, the inner diameter of the needle is 0.2 mm, the needle distance is 10 mm,
The image frame is 1.64 mm x 1.31 mm. While the diameter of the bubble in the normal state is about 2 mm,
When vibrated, the diameter of the microbubbles was 14 μm on average, and it was found that the microbubbles were reduced to about 1/140 in diameter.

The fine bubbles 14 generated by the present invention
The diameter of μm is extremely superior to conventional microbubble generating means. For example, the average bubble diameter is 2 mm in the case of blowing from a micro nozzle or a porous material (pore diameter 0.2 mm), and the bubble diameter is 50 mm in the entrainment of gas by a jet.
When the gas is blown into the high-speed liquid, the average bubble diameter is about 400 μm.

In the experiment, bubbles that were not shaken rise toward the surface of the water after being released.
Due to the small volume and small buoyancy of the vibrated bubbles, it was observed that they were trapped in the pressure field formed by the ultrasonic waves and continued to stay in a certain area while vibrating, or were completely dissolved in water.

The mechanism of generation of microbubbles according to the present invention was considered. An experiment was conducted on the surface vibration of bubbles when the input was suppressed. Frequency is 18.9 kHz
z, vibrator input is 0.61W, needle inner diameter is 0.2m
m, needle distance 10 mm, image frame 1.64
mm × 1.31 mm. Suppress input by ultrasonic,
FIG. 3 shows a photograph capturing the vibration of the interface between the bubbles. In FIG. 4, the reflected light on the bubble surface is violently disturbed as compared with FIG. 2, and it can be seen that the surface of the bubble is wavy by ultrasonic waves. This is presumably because the ultrasonic waves excite the low to high order vibration modes of the surface vibration. The wavelength of the low order mode (first order) surface wave measured from the image is also 17
7.79 μm, which is almost consistent with the theoretical value of 172.14 μm obtained by substituting the experimental conditions into the equation of the surface tension wave.
The following Kelvin equation was used to derive the theoretical value. By the way, as a result of the other frequencies, the frequency is 40
In the case of kHz, the measured value is 126.99 μm and the theoretical value is 133.76 μm. When the frequency is 75 kHz, the measured value is 90.70 μm and the theoretical value is 87.97 μm.
m was obtained.

(Equation 1)

From the above, it is highly probable that this miniaturization is caused by surface vibration. The gas sent into the microtube forms a gas-liquid interface at the tip of the microtube. When ultrasonic vibration is applied to the interface by the ultrasonic vibrator, the interface shifts to an unstable state. If the ultrasonic vibration is further strengthened to some extent, microbubbles far smaller than the diameter of the microtube are generated there. Further, the generated microbubbles are extremely small, and have an effect of suppressing recombination.

[0019]

According to the method for generating microbubbles according to the present invention, the following advantageous effects can be obtained. (1) By utilizing the unstable state of the gas-liquid interface, fine bubbles having relatively uniform dimensions can be efficiently and stably generated. (2) Since the device for generating microbubbles has a simple configuration, the range of application is wide, the cost is low, and maintenance is easy. (3) Fine bubbles of an extremely small order can be generated as compared with the conventional physical fine bubble generation method. (4) Since the generated microbubbles are very small, the dissolution of the gas into the liquid is performed very efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an experimental apparatus.

FIG. 2 is a diagram showing a case where a gas is released without applying ultrasonic waves to a gas-liquid interface.

FIG. 3 is a diagram showing generation of microbubbles in a case where ultrasonic waves are applied to a gas-liquid interface in all three upper and lower images.

FIGS. 4A and 4B are diagrams in which input by ultrasonic waves is suppressed and vibration at the interface between bubbles is captured, and FIG. 4B is a partially enlarged view of FIG.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Fumio Takemura Innovator, 3-4-4 Hatchobori, Chuo-ku, Tokyo 2nd floor of Ainosho Building (72) Inventor Toshinori Makita 1114-1-103, Matsudo, Matsudo-shi, Chiba (72) Invention Person Yoichiro Matsumoto 1-42-20-302 Hayamiya, Nerima-ku, Tokyo F-term (reference) 4C301 DD01 EE20 FF30 4G035 AA30 AB05

Claims (2)

[Claims] An ultrasonic wave is applied to the gas-liquid interface between the gas and the liquid before the gas supplied into the liquid from the gas supply port of the fine tube provided with the gas supply port in the liquid generates bubbles. A microbubble generation method using ultrasonic waves, wherein a plurality of microbubbles are continuously generated from the gas-liquid interface by applying. 2. A micro tube having a gas supply port provided in a liquid, and an ultrasonic vibration generating means, wherein the gas supplied from the gas supply port forms the liquid before the gas is generated. By applying ultrasonic waves to the gas-liquid interface by the ultrasonic vibration generating means, a plurality of microbubbles are continuously generated from the gas-liquid interface. Micro bubble generator.