JP2001280924A - Device and method for observing cavitation foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow easy observation, at a low cost, free from restriction of the number of picked-up images and a limit of resolution as to a time and to clearly grasp foam and behavior thereof even when the cavitation foam moves. SOLUTION: This device 1 of the present invention is a device for observing the behavior of the cavitation foam generated in a liquid by an ultrasonic wave and is provided with an ultrasonic cell 2 for putting the liquid in and comprising a transparent wall, an oscillator 3 mounted thereon with the ultrasonic cell 2 and for vibrating the cell 2, a stroboscope light source 4 arranged in one side of the cell 2, an image pick-up means 5 arranged in the other side of the cell 2 and having an optical system with the optical axis same to those of the light source 4 and the cell 2, and a signal generating means 6 for generating a signal S1 for vibrating the oscillator 3 by a frequency f1, and a signal S2 for illuminating the light source 4 by a frequency f2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cavitation bubble observation apparatus and method for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves.

[0002]

2. Description of the Related Art The cavitation phenomenon has been known for a long time, and a phenomenon such as corrosion of a ship screw is famous. Cavitation is a phenomenon in which, when ultrasonic waves propagate in a liquid medium as longitudinal waves, the density of the medium changes with the period of the ultrasonic waves, so that the dissolved gas appears as bubbles, and the bubbles are When the pressure is low, it expands, and when the pressure increases, it contracts or collapses.

When a cavitation bubble collapses, its volume instantaneously becomes zero, so that an extremely high-temperature and high-pressure extreme environment field is generated at the center of the bubble for a very short time. As is clear from this phenomenon that the screw corrodes, a strong force acts in the cavitation sound field.
It is said that if an cavitation phenomenon caused by ultrasonic waves is used, an extreme environmental field can be generated on a desk, so that synthesis of chemicals, decomposition of dioxin, and the like are possible.
At present, research is actively being conducted to control light emission (sonoluminescence) and chemical action (sonochemistry) by arbitrarily controlling a sound field to freely generate cavitation.

In carrying out these studies, the behavior of cavitation bubbles (eg, size (maximum diameter, minimum diameter), rebound (re-expansion / shrinkage due to recoil after shrinkage), change in position) is observed and understood. It is necessary. If the cavitation bubble is a bubble generated in a sound field by, for example, an ultrasonic wave of 20 kHz, it repeats expansion and contraction 20,000 times per second. There are several methods for observing such bubbles, including one using a high-speed camera and one using a light-emitting diode with a short light-emitting time.

[0005]

The above-mentioned high-speed cameras include a system using a film and a system using a CCD (solid-state electronic image sensor). The method using a film enables high-speed photographing (for example, 20 million images / second), but the number of captured images is limited (about 10), and it is impossible to record changes over a long period of time. In addition, in the method using the CCD, a sufficient amount of captured images can be provided by adding a semiconductor memory and a relatively long-time shooting can be performed. However, the shooting speed is about 10,000 images / second at the maximum. 2 per second
Even if an image of a cavitation bubble that repeats expansion and contraction 0000 times is taken, the temporal resolution is limited. In any case, a camera for high-speed photography is very expensive.

On the other hand, as an example using the above light emitting diode, there is a cavitation bubble observation performed by Tian et al. (J. Acoustic. Soc. Am. 100).
(6), December 1996 pp3976-
3978). Tian et al. Irradiate cavitation bubbles (single bubbles) in single-bubble sonoluminescence, which repeatedly expand and contract at the same position in a standing wave sound field, with pulsed light from a light-emitting diode in synchronization with the period of ultrasonic waves. Images by multiple flashes are superimposed and multiple-exposed,
Behavior observation using a CD camera.

However, in this method, it is possible to take a picture if the cavitation bubbles are stationary at the same place in the standing wave sound field, but if the sound field is unstable, the position of the cavitation bubbles changes, In such a case, the camera performs multiple exposure on the trajectory of the cavitation bubble during the exposure time, and the cavitation bubble overlaps and is imaged. Therefore, the cavitation bubble and its behavior cannot be clearly captured.

Further, the light-emitting diode has various problems such as a small light-emitting area, a need to perform optical axis alignment with high accuracy, and complexity.

[0009] The present invention has been proposed in view of the above,
Cavitation that can be easily observed at low cost without being limited by the number of captured images or the limit of temporal resolution, and even when cavitation bubbles move, they can be captured clearly. An object of the present invention is to provide a bubble observation device and a cavitation bubble observation method.

[0010]

According to one aspect of the present invention, there is provided a cavitation bubble observation apparatus for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves. ,
An ultrasonic cell composed of a transparent wall, a vibrator on which the ultrasonic cell is mounted and which vibrates the ultrasonic cell, a strobe light source arranged on one side of the ultrasonic cell, and the other side of the ultrasonic cell And an imaging unit having an optical system having the same optical axis as the strobe light source and the ultrasonic cell; a first signal for vibrating the vibrator at a first frequency; A signal generating means for generating a second signal to emit light in the step (a), and taking one screen image of cavitation bubbles generated in the liquid of the ultrasonic cell by the vibration of the vibrator at each light emission timing of the strobe light source; It is characterized by:

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the first frequency of the first signal is changed to the second frequency of the second signal. Is set to an integral multiple of.

According to a third aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the first frequency of the first signal is changed to the second frequency of the second signal. Is set to a value slightly different from an integral multiple of.

Further, according to a fifth aspect of the present invention, there is provided a cavitation bubble observation method for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves. It is characterized in that one screen is imaged at each light emission timing of a strobe light source that emits cavitation bubbles generated therein at a predetermined frequency.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a view showing the entire configuration of a cavitation bubble observation apparatus according to the present invention. In the figure, a cavitation bubble observation device 1 of the present invention is a device for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves, and includes an ultrasonic cell 2 formed of a transparent wall and containing a liquid, and an ultrasonic cell. A vibrator 3 on which the ultrasonic cell 2 is mounted and fixed and vibrates the ultrasonic cell 2, a strobe light source 4 arranged on one side of the ultrasonic cell 2, and a strobe light source 4 arranged on the other side of the ultrasonic cell 2, An imaging unit 5 having an optical system having the same optical axis as the ultrasonic cell 2 and a vibrator 3 having a frequency f
1 and the frequency f of the strobe light source 4
Signal generating means 6 for generating a signal S2 for causing light emission at 2
And

The ultrasonic cell 2 is a rectangular parallelepiped glass square pipe into which deaerated pure water as a medium is injected.
The pure water has an upper surface in contact with the atmosphere and a lower surface in contact with the vibrator 3 via the bottom wall of the cell 2.

The image pickup means 5 has a magnification of 0.75 to 0.75.
NTSC C with 4.5x zoom lens 51 and 2x auxiliary lens (maximum magnification of optical system is 9x)
It has a CD camera 52, this zoom lens 51 and CC
The optical system in the D camera 52 is disposed so as to have the same optical axis as the strobe light source 4 and the ultrasonic cell 2 as described above. The image from the CCD camera 52 is recorded on the VTR 13 while being checked on the monitor 14. Note that C
Since the CCD element of the CD camera 52 is a 1/3 inch element (4.8 × 3.6 mm), the field of view at the maximum magnification (9 ×) is 0.53 mm × 0.4 mm.

The signal generating means 6 is, for example, a function generator, and has two systems (two channels (c
h)), the first channel generates a signal S1 having a frequency f1 for generating ultrasonic waves. This signal S1 is supplied to the amplifier 11
And applied to the vibrator 3 at a voltage of about 10 to 30 Vpp (positive / negative amplitude voltage). This amplified signal S1
Is measured and monitored by the oscilloscope 12.

On the other hand, the second channel generates a trigger signal S2 for causing the strobe light source 4 to emit light at the frequency f2. The flash time of the strobe light source 4 is 75 nanoseconds (ns).

In the cavitation bubble observation apparatus 1 having the above configuration, when a voltage is applied from the signal generating means 6 to the vibrator 3, a standing wave sound field is generated between the vibrator 3 and the water surface in the ultrasonic cell 2. You. When cavitation bubbles are generated and trapped at the antinode of the sound pressure in the standing wave sound field, the cavitation bubbles repeat expansion and contraction at the frequency f1 of the signal S1 in synchronization with the frequency of the vibrator 3. Then, the behavior of the cavitation bubble is photographed as a shadow picture by the CCD camera 52 arranged facing the strobe light source 4.
The strobe light source 4 has a high luminance and can secure a sufficient amount of light. By adjusting the sensitivity, the magnification of the lens, and the brightness on the side of the imaging means 5, one picture is taken at each light emission timing of the strobe light source 4. be able to. In addition, the reason why the photographing is performed with the so-called backlight illumination is to secure a sufficient light amount when photographing the microscopic region up to about 9 times at the maximum.

As described above, the cavitation bubbles repeatedly expand and contract at high speed at the frequency f1 of the signal S1,
When the frequency f1 of the signal S1 is set to an integral multiple of the frequency f2 of the signal S2, that is, an integral multiple of the emission frequency of the strobe light source 4, the strobe light is applied to bubbles under any of the phases of maximum expansion to maximum contraction. Always illuminates bubbles in the same phase, and the CCD camera 52 photographs the bubbles in the same phase.

On the other hand, the frequency f1 of the signal S1 is
If the value is set to a value slightly different from the integral multiple of the frequency f2 of the strobe light source 4, that is, a value slightly different from the integral multiple of the emission frequency of the strobe light source 4, the strobe light is emitted to the bubbles under any of the phases of maximum expansion to maximum contraction. Will illuminate the bubbles with slightly different phases, and the CCD camera 52
The bubbles that gradually change in phase are photographed.

FIG. 2 is a diagram showing the relationship between the phase of the cavitation bubble and the emission timing of the strobe light. Here, the description will be made on the assumption that the frequency f1 of the signal S1 is 24.48 kHz and the frequency f2 of the signal S2 is 30 Hz. 24.4
8 kHz is equivalent to an integral multiple (816 times) of 30 Hz.

In the figure, (a), (c) and (e) correspond to 24.
The phase change of the ultrasonic wave oscillating by the signal S1 of 48 kHz, that is, the phase change of the cavitation bubble is shown, (b)
Shows the emission timing of the strobe light emitted by the signal S2 of 30 Hz, and (d) shows the emission timing of the strobe light emitted by the signal whose frequency changes little by little from 30 Hz and sequentially increases. The number given to each wave of the sound wave shown in (a) is a number indicating the order of the wave.

The sound wave No. of FIG. At 0, if the strobe light source 4 emits light when the bubble diameter is at its maximum, then the strobe light source 4 emits light after 816 cycles, that is, when the sound wave No. At 816, the bubble diameter is maximum (see (b) and (c)). Thereafter, when the strobe light source 4 emits light, the bubble always has the maximum diameter, and is actually 2 bubbles per second.
Although the bubble is repeatedly expanded and contracted 4480 times, only the state of the maximum diameter (at the time of maximum expansion) is continuously observed.

Next, consider the case where the light emission timing (phase) is sequentially changed and increased. As shown in (d), when the light emission timing is changed, (d) and (e)
As can be seen from the relationship, the strobe light illuminates the bubbles having slightly different phases with respect to the bubbles under any of the phases of the maximum expansion to the maximum contraction. It becomes possible to observe.

By the way, the timing (phase) of the light emission of the strobe light source 4 is sequentially changed, and the signal S
Setting the frequency f1 of 1 to a value slightly different from an integral multiple of the emission frequency f2 of the strobe light source 4 is equivalent. For example, the frequency f1 of the signal S1 is set to 24.48 kHz.
And 1 Hz is added to the frequency of 24.48 kHz, and the frequency f
If 1 is set to 24.481 kHz, 1 per second
Since the phase changes continuously at the rate of the cycle, the expansion and contraction of the cavitation bubble can be observed as a slow motion of 1 Hz.

In the following, the frequency f1 is set to 24.4805 kHz.
An experimental result when observed as z will be described. From an integral multiple of 30 Hz (816 times) of strobe light to 0.5
Hz, there is a slow motion in which expansion and contraction are repeated once in 2 seconds. The CCD camera 52 includes:
To capture 30 images per second and record them on the VTR 13,
One cycle of change was obtained as a series of 60 images.

FIG. 3 is a view showing images of cavitation bubbles obtained by the above observation every five images. The voltage applied to the vibrator 3 was set to 29.2 Vpp. The standing wave sound field generated in the pure water in the ultrasonic cell 2 is in a favorable state, and the position of the cavitation bubble indicated by the arrow is not much changed as shown in the figure. FIG. 4 is a graph showing the result of performing image processing on the obtained image using a computer and automatically measuring the radius of the cavitation bubble. Parts (a) to-indicated by arrows in the graph of FIG.
(I) corresponds to the images (a) to (i) in FIG.

It can be seen that the state in which the cavitation bubbles expand and contract can be clearly photographed as an image, and the change in the size can be automatically measured. Although FIGS. 3 and 4 show only one cycle, the expansion of bubbles and
The phenomenon of contraction is repeated many times.

Looking at the continuous photograph of FIG. 3, it can be seen that the position of the cavitation bubble slightly fluctuates left and right. This is because the cavitation bubbles actually oscillate right and left, and in the conventional method of multiple exposure using light emitting diodes, all of them are photographed overlapping and photographed in a state where they are spread left and right,
Cavitation bubbles and their behavior could not be clearly seen.

On the other hand, in the present invention, the strobe light source 4
, The photographing is performed by one light emission, so that the behavior at that moment can be clearly grasped regardless of how the cavitation bubble moves up, down, left and right.

A typical serial photograph of this is shown in FIG. The experiment of FIG. 3 shows that the frequency f1 is 24.4805 kHz.
But the applied voltage to the vibrator 3 is 22.0 Vp
p was set low. For this reason, the standing wave sound field generated in the pure water in the ultrasonic cell 2 becomes unstable, and the cavitation bubbles can swing up, down, left, and right over a wide area. In FIG. 5, the situation is clearly captured, and while the cavitation bubbles move around the screen violently,
The manner in which the size changes can be clearly observed. If the cavitation bubbles change this way,
In the conventional method using multiple light-emitting diodes,
It was almost unobservable.

As described above, in the embodiment according to the present invention, the cavitation bubbles generated in the pure water of the ultrasonic cell 2 by the vibration of the vibrator 3 are used to reduce the brightness of the strobe light source 4.
Since the image is picked up with a single light emission, it is possible to secure a sufficient amount of light in one image pickup, so that multiple exposure is not required, and a small cavitation bubble of about 0.1 mm at the maximum diameter can be clearly photographed. it can. Further, even if the cavitation bubbles move violently in the ultrasonic sound field, the bubbles and the behavior can be clearly photographed.

Therefore, it is possible to measure the change in the size of the bubble, and it is possible to estimate the sound pressure. In addition, it is possible to accurately know the fluctuation of the bubble position and the shape of the bubble, and it is possible to know the degree of stability of the sound field from the information. Information on such a sound field can be applied to multi-valve sonoluminescence, which is a sound field in which a large number of cavitation bubbles are present, greatly accelerating chemical reactions,
It can be used for rapid synthesis of pharmaceuticals, development of new materials such as amorphous metals and diamonds, and decomposition of harmful substances such as dioxins and chlorofluorocarbons.

Further, in the embodiment according to the present invention, since it is not necessary to use a high-speed camera, observation can be performed at a low cost without being limited by the number of captured images or being limited by temporal resolution.

Further, since a strobe light is used as a light source, a light emitting area can be enlarged, and high-precision alignment of an optical system is not required, so that observation can be performed easily.

In the above description, the strobe light source 4 is configured to emit light at the frequency f2. However, as the strobe light source, a light source that is always lit and a shielding plate having a hole are combined to form a shielding light source. The light may be turned on and off at the frequency f2 by rotating the plate.

Further, the pure water is stored in the ultrasonic cell 2, but another liquid medium may be stored instead of the pure water.

[0040]

Since the present invention has the above-described configuration,
The following effects can be obtained.

According to the first and fifth aspects of the present invention, the cavitation bubbles generated in the liquid medium of the ultrasonic cell by the vibration of the vibrator are imaged at each light emission timing of the strobe light source. A sufficient amount of light can be secured in each imaging, so that multiple exposure is not required,
Small cavitation bubbles of about 0.1 mm can be clearly photographed even at the maximum diameter. Further, even if the cavitation bubbles move violently in the ultrasonic sound field, the bubbles and the behavior can be clearly photographed.

Therefore, it is possible to measure the change in the size of the bubble, and it is possible to estimate the sound pressure. In addition, it is possible to accurately know the fluctuation of the bubble position and the shape of the bubble, and it is possible to know the degree of stability of the sound field from the information. Information on such a sound field can be applied to multi-valve sonoluminescence, which is a sound field in which a large number of cavitation bubbles are present, greatly accelerating chemical reactions,
It can be used for rapid synthesis of pharmaceuticals, development of new materials such as amorphous metals and diamonds, and decomposition of harmful substances such as dioxins and chlorofluorocarbons.

Further, since it is not necessary to use a high-speed camera, observation can be performed at a low cost without being limited by the number of captured images or being limited by temporal resolution.

Further, since a strobe light is used as a light source, a light emitting area can be enlarged, and high-precision axis alignment of an optical system is not required, thereby enabling easy observation.

According to the second aspect of the present invention, the frequency of the signal for oscillating the vibrator is set to an integral multiple of the frequency of the signal for illuminating the strobe light source. The behavior of cavitation bubbles under the same phase can be observed in detail.

According to the third aspect of the present invention, the frequency of the signal for oscillating the vibrator is set to a value slightly different from an integral multiple of the frequency of the signal for causing the strobe light source to emit light. It is possible to continuously and clearly observe the rising cavitation bubbles.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a cavitation bubble observation device of the present invention.

FIG. 2 is a diagram showing the relationship between the phase of cavitation bubbles and the emission timing of strobe light.

FIG. 3 is a diagram illustrating an image of cavitation bubbles when the frequency of a vibrator is observed at 24.4805 kHz.

FIG. 4 is a diagram showing a result of performing image processing on the image of FIG. 3 using a computer and automatically measuring the radius of cavitation bubbles.

FIG. 5 is a diagram showing an image of cavitation bubbles in which cavitation bubbles move violently.

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Claims (5)

[Claims] 1. A cavitation bubble observation device for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves, comprising: an ultrasonic cell including a transparent wall, containing the liquid; and an ultrasonic cell mounted thereon. An oscillator for applying vibration to the ultrasonic cell; a strobe light source disposed on one side of the ultrasonic cell; and an optical element disposed on the other side of the ultrasonic cell, wherein the strobe light source and the ultrasonic cell have the same optical axis. Imaging means having a system, a first signal for vibrating the vibrator at a first frequency,
Signal generating means for generating a second signal for causing the strobe light source to emit light at a second frequency, wherein the strobe light source emits cavitation bubbles generated in the liquid of the ultrasonic cell by the vibration of the vibrator. A cavitation bubble observation device, wherein one screen is imaged at each timing. 2. The method according to claim 1, wherein the first frequency of the first signal is a second frequency.
The cavitation bubble observation device according to claim 1, wherein the cavitation bubble observation device is set to an integral multiple of the second frequency of the signal. 3. The method according to claim 1, wherein the first frequency of the first signal is a second frequency.
2. The cavitation bubble observation device according to claim 1, wherein the value is set to a value slightly different from an integral multiple of the second frequency of the second signal. 4. The cavitation bubble observation device according to claim 1, wherein the cavitation bubble is a single bubble cavitation bubble generated when an ultrasonic sound field in a liquid is set as a standing wave sound field. 5. A cavitation bubble observation method for observing the behavior of cavitation bubbles generated in a liquid by ultrasonic waves, wherein the liquid is an ultrasonic sound field having a predetermined frequency, and the cavitation bubbles generated in the liquid are subjected to a predetermined frequency. A cavitation bubble observation method, wherein one screen is imaged at each light emission timing of a strobe light source that emits light.