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JP2002066550

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DESCRIPTION JP2002066550
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
water treatment apparatus which generates cavitation by ultrasonic waves in film-like water and
disinfects microorganisms in water by the action of cavitation.
[0002]
2. Description of the Related Art In water treatment, it has been pointed out that chlorination,
which has been widely adopted conventionally, is not very effective in the sterilization of
pathogenic microorganisms excellent in chlorine resistance such as cryptosporidium. As a means
capable of sterilizing pathogenic microbes, a water treatment method using cavitation with
ultrasonic waves of 20 kHz or more is known, for example, from European Patent Publication
567,225.
[0003]
Cavitation, which is a cause of the bactericidal effect in the water treatment method by ultrasonic
waves, is a phenomenon in which bubbles such as oxygen or the like present in the water are
generated as nuclei by fluctuations in pressure. As described in "Ultrasonic Technology
Handbook (New Edition): The Nikkan Kogyo Shimbun, 1991, p. 844-p. 858", the impact pressure
generated when the bubbles generated by cavitation are crushed causes the water to submerge.
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It is widely known that microbes of bacteria are mechanically destroyed.
[0004]
SUMMARY OF THE INVENTION In order to impart the action of cavitation to microorganisms in
water with a high probability and to improve the sterilization efficiency, the present inventors
have applied in Japanese Patent Application No. 11-182903 and Japanese Patent Application No.
2000-163137. , A water treatment device is shown which generates cavitation in filmy water.
[0005]
Ultrasonic cavitation can generate cavitation with less energy if a relatively low frequency of 100
kHz or less is used, and furthermore, the mechanical destructive action of cavitation is strong.
In the water treatment apparatus using ultrasonic waves as described above, it is considered
preferable to use ultrasonic waves of 100 kHz or less, but in any case ultrasonic waves of a single
frequency are used.
[0006]
Usually, there are many bubbles of different sizes in water, and the bubbles with radius of several
tens of μm are the most frequent. When such cavitation is irradiated with ultrasonic waves of
100 kHz or less in such water to generate cavitation, bubbles of several μm to several hundreds
of μm are crushed efficiently and strong shock waves are generated, but the diameter is small or
the diameter is large. The bubbles reduce the impact force when crushed or do not crush.
[0007]
In the above-described water treatment apparatus, since ultrasonic waves of a single frequency
are used, some of the bubbles of various sizes contained in the water are crushed. In order to
destroy microorganisms in water efficiently, it is better to crush as many bubbles as possible and
generate a large impact pressure in many places.
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[0008]
It is an object of the present invention to crush bubbles in various sizes contained in water and
generate strong impact pressure in a water treatment apparatus for generating cavitation in
membrane water and sterilizing microorganisms in the water. The present invention is to provide
a water treatment apparatus for efficiently sterilizing microorganisms in water by generating at a
place.
[0009]
[Means for Solving the Problems] As described in "Ultrasonic Technology Handbook (New
Edition): Nikkan Kogyo Shimbun, 1991, p. 1085-p. 1086", the bubbles vibrate. When doing so,
bubbles will grow and grow due to rectified diffusion.
This effect is most pronounced in resonant bubbles. Therefore, in the water treatment apparatus
of the present invention, ultrasonic waves having a frequency of 100 kHz or more are irradiated,
small bubbles are grown by rectified diffusion, and the existence frequency (density of bubbles of
several μm to several hundreds μm) which can be crushed at a frequency of 100 kHz or less
Increase). Then, by irradiating an ultrasonic wave of 100 kHz or less, many of the bubbles
present in the water are crushed.
[0010]
The water treatment apparatus of the present invention comprises a reaction vessel having first
and second portions having a rotational symmetry axis and having a rotational symmetry axis.
The opening on the side of the first part of the reaction vessel is covered by a first lid with an
inlet for water, and the opening on the side of the second part of the reaction vessel is a second
lid with an outlet for water It is covered with
[0011]
A first cylinder of a first ultrasonic vibrator having a rotational symmetry axis formed by
sequentially coupling a first ultrasonic transducer, a first vibration transmitter, and a first
cylinder is a first cylinder. The rotational symmetry axis of the ultrasonic vibrator and the
rotational symmetry axis of the reaction container are made to coincide with each other, and are
contained in the first portion of the reaction container and supported by the first lid.
04-05-2019
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[0012]
A second cylinder of a second ultrasonic vibrator having a rotational symmetry axis formed by
sequentially coupling a second ultrasonic transducer, a second vibration transmitter and a
second cylinder is a second cylinder. The rotational symmetry axis of the ultrasonic vibrator and
the rotational symmetry axis of the reaction vessel are made to coincide with each other, and one
end face of the first cylinder and one end face of the second cylinder face each other. And is
supported by the second lid.
[0013]
The first ultrasonic vibrator is driven at a frequency of 100 kHz or more, and the second
ultrasonic vibrator is driven at a frequency of 100 kHz or less.
The distance between the inner surface of the reaction vessel constituting the first part and the
side surface of the first cylinder is equal to or less than (1/4) the wavelength of the sound wave
in water determined by the frequency of vibration of the first ultrasonic vibrator. The distance
between the inner surface of the reaction vessel constituting the second portion and the side
surface of the second cylinder is equal to or less than (1/4) the wavelength of the sound wave in
water determined by the frequency of vibration of the second ultrasonic vibrator. I assume.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be
described in detail with reference to the drawings.
[0015]
FIG. 1 is a cross-sectional view showing an embodiment of the water treatment apparatus of the
present invention.
The reaction vessel 10 has an axis of rotational symmetry, and has an adjacent first portion 11
and a second portion 12 each having an axis of rotational symmetry.
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The cross section perpendicular to the rotational symmetry axis of the first portion 11 and the
second portion 12 of the reaction vessel 10 is a circle. In order to make the inside of the reaction
vessel 10 watertight, the opening of the first part 11 is closed by a first lid 21 and the opening of
the second part 12 is closed by a second lid 22.
[0016]
The first lid 21 is provided with a first ultrasonic vibrator 31 formed by sequentially coupling a
first ultrasonic transducer 313 connected to a drive power supply (not shown), a vibration
transmitter 312, and a cylinder 311. , Are coupled by a flange provided on the vibration
transmitter 312. The first ultrasonic vibrator 31 is disposed coaxially with the reaction vessel 10
and the first lid 12, and is disposed so that the cylinder 311 is contained in the first portion 11 of
the reaction vessel 10.
[0017]
In the second lid 22, a second ultrasonic vibrator 32 formed by sequentially coupling a second
ultrasonic transducer 321 connected to a drive power supply (not shown), a vibration transmitter
322 and a cylinder 323 is provided. , And are coupled by a flange provided to the vibration
transmitter 322. The second ultrasonic vibrator 32 is disposed coaxially with the reaction vessel
10 and the second lid 22, and is disposed so that the cylinder 323 is contained in the second
portion 12 of the reaction vessel 10.
[0018]
Water entering the reaction vessel 10 through the water distribution pipes 411 and 412 passes
through the water distribution pipe 413 provided on the first lid 21 and enters the first portion
11 of the reaction vessel 10 first. The ultrasonic vibrator 31 vibrates at a frequency of 100 kHz
or more, and the water introduced into the first portion 11 vibrates the first ultrasonic vibrator
31 particularly between the side surface of the cylinder 311 and the inner surface of the reaction
vessel 10 In addition, air bubbles of various sizes present in the water also vibrate.
[0019]
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As described in "Ultrasonic Technology Handbook (new edition): Nikkan Kogyo Shimbun, 1991,
p. 1085-p. 1086", the respiratory vibration of this bubble is a non-linear vibration and the
comparison is Small size bubbles grow into large bubbles by the effect of rectified diffusion.
Therefore, when the water transfers from the first portion 11 to the second portion 12, the water
contains many bubbles of several μm to several hundreds of μm.
[0020]
In the water thus flowing to the second portion 12, the ultrasonic vibration of the second
ultrasonic vibrator 32, in particular, the ultrasonic vibration of 100 kHz or less between the side
surface of the cylinder 323 and the inner surface of the reaction vessel 10 Is given. The water in
the second portion 12 is crushed by ultrasonic waves of 100 kHz or less, and contains many
bubbles of several μm to several hundreds of μm that can generate a strong impact pressure.
For this reason, the microorganisms present in water are efficiently and efficiently subjected to
the impact pressure and are mechanically destroyed.
[0021]
Thus, the water sterilized in the second portion 12 is drained to the pipes 422 and 421 through
the water distribution pipe 423 provided on the second lid 22.
[0022]
Next, the frequencies of the first ultrasonic vibrators 31 and 32 will be described with reference
to FIGS.
2 to 6 show the theoretical analysis results when the bubble is assumed to be spherically
symmetric. Assuming that the pressure inside the bubble is uniform, the vapor pressure of water
is constant, and there is no diffusion of gas inside and outside the bubble, the equation of motion
of the bubble is (Equation 1) (see J. B. Kellerand M. Miksis: Bubble oscillation of large amplitude,
Journal of Acoustics Society of America, Vol. 68, No. 2, 1980, p. 628-p. 633).
[0023]
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(D2R / dt2) {R (1-M) + 4m / r0c0} + (1/2) (dR / dt) 2 (3-M) = (1 / r0) {Pv- ( 1 + M) P0 + (1-3 kM)
(P0 + 2s / R0) x (R0 / R) 3k-2s / R-4mRt / R + Psinw (t + R / c0)} (Equation 1) (Equation 1), where
R is the bubble radius , R 0 is the initial radius of the bubble, t is the time, P is the pressure
amplitude of the sound field, and w is each frequency of the sound field. r0 (= 1000 kg / m3) is
the density of water, m (= 1. 31 x 10-3 Pa s) is the viscosity coefficient of water, s (= 7.2 x 10-2 N
/ m) is the surface tension of water, Pv (= 1.227 kPa) is the vapor pressure of water, c0 (= 1466
m / s) is the speed of sound in water, k (= 1.33) is the specific heat ratio of gas, M (= (dR / dt) /
c0) is It is the Mach number.
[0024]
For example, the frequency of ultrasonic waves in the second portion 12 of the reaction vessel
10 for the purpose of sterilization is 20 kHz (w = 3.14 × 10 5 rad / s), and the pressure
amplitude of the sound field is P = 1.2. It is assumed that x 105 Pa.
[0025]
With respect to the change in sound pressure shown in FIG. 2 (A), the temporal variation of the
bubble radius with a radius of 10 μm is as shown in FIG. 2 (B). It becomes like 2 (C).
From the results shown in FIG. 2, it can be seen that the bubble collapses in about a half cycle,
and a shock wave pulse is generated due to the change in the moving velocity of the large bubble
wall generated at that time.
[0026]
The same analysis was performed with the initial radius of the bubbles changed to 5 μm, 3 μm
and 2 μm, and the obtained results are shown in FIGS. 3 (A) to 3 (C) and 4 (A) to 4 respectively.
(C), shown in FIG. 5 (A) to FIG. 5 (C).
[0027]
From the results shown in FIG. 2 to FIG. 5, the impact pressure at the time of bubble collapse
does not change much between the bubble having the radius of 10 μm at the beginning and the
bubble having the radius of 5 μm at the beginning.
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[0028]
It can be seen that in the case of the bubble having the radius of 3 μm at the beginning, the
impact pressure becomes smaller, and in the case of the bubble having the radius of 2 μm at the
beginning, the bubble collapse is not observed.
[0029]
Therefore, when the second portion 12 of the reaction vessel 10 is irradiated with ultrasonic
waves of 20 kHz, the bubbles having a radius of 3 μm or less in the first portion 11 can be
grown into bubbles having a radius of about 5 μm. The presence frequency (density) of bubbles
collapsing in the part 12 of 2 can be increased and the efficiency of sterilization becomes better.
[0030]
6 (A) to 6 (C), assuming that the pressure amplitude of the sound field is P = 1.2 × 105 Pa and
assuming the same as the above analysis, the frequency 900 kHz, the initial radius of the bubble
3 μm Analysis result in the case of
Under this condition, the bubbles gradually increase to a maximum radius of about 7 μm.
Also, the change in sound pressure in the sound field and the change in bubble radius are in
phase.
Such a state is a state in which the bubble is in resonance, and the change in bubble radius per
cycle shows that the time during which the radius is larger than the initial radius is smaller than
the initial radius Longer than.
Therefore, the gas diffuses from the water into the bubble, and the pressure in the bubble
gradually rises, resulting in so-called rectified diffusion in which the initial radius increases.
[0031]
From the above, for example, in the first portion 11, the first ultrasonic vibrator 31 is vibrated at
900 kHz to increase the existence frequency (density) of the bubbles having the initial radius of
about 5 μm, By vibrating the second ultrasonic vibrator 32 at 20 kHz in the second portion 12
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and collapsing air bubbles of 5 μm or more, an efficient sterilizing effect can be obtained.
[0032]
Since relatively small bubbles are grown in the first portion 11, the frequency of the first
ultrasonic vibrator 31 is necessarily higher than the frequency of the second ultrasonic vibrator
32.
It is desirable that the frequency of the second ultrasonic vibrator 32 be 100 kHz or less at which
the mechanical destruction action of cavitation is high, so the frequency of the first ultrasonic
vibrator 31 is preferably 100 kHz or more.
[0033]
In the first portion 11 and the second portion, air bubbles are present, and when the vibration of
the air bubbles becomes strong, a part of the water changes to gas, so that the specific acoustic
impedance of the apparent water changes. Based on the theoretical analysis of the bubble
described above, for example, assuming that the initial radius of the bubble is 4 μm and the
presence frequency (density) of the bubble is 1010 / m 3, water and bubbles at a frequency of
25 kHz The values of the real part and the imaginary part of the time-averaged intrinsic acoustic
impedance (cc) of the mixed fluid with are respectively shown for the acoustic power as shown in
FIG.
[0034]
As the acoustic power changes, the specific acoustic impedance (と c) of the mixture of water and
air bubbles greatly changes in both the real part and the imaginary part. In the water treatment
apparatus of the embodiment of the present invention, in the first portion 11 and the second
portion 12 in the reaction vessel 10, separate roles of bubble growth and bubble collapse are
shared. As the first part does not need to crush the air bubbles, the acoustic power may be small
and in the second part 12 relatively large acoustic power is required. Therefore, the specific
acoustic impedance of the mixture of water and air bubbles present in the first part 11 and the
specific acoustic impedance of the mixture of water and air bubbles present in the second part
12 are largely different. Therefore, it is desirable to separate drive power supplies (not shown)
04-05-2019
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for driving the first ultrasonic vibrator 31 and the second ultrasonic vibrator 32.
[0035]
Since cavitation occurs in areas with large sound pressure fluctuations, the generation is usually
remarkable near the ultrasonic vibration surface or in the antinodes of the sound pressure of the
standing wave sound field, but the bubbles in water are uniformly distributed Therefore, it is
considered that the distance between the side surface of the cylinder 311 and the cylinder 323
and the inner surface of the reaction vessel 10 is water at each frequency of the first ultrasonic
vibrator 31 and the second ultrasonic vibrator 32, respectively. It is desirable to set it to (1/4) or
less of the wavelength of.
[0036]
As described above, in the water treatment apparatus of the present invention, relatively small air
bubbles can grow in the first portion, and can be crushed in the second portion to generate a
strong impact pressure. As water with increased bubble density flows to the second part and is
further irradiated with ultrasonic vibration, the microorganisms in the water are given high
probability of mechanical destruction of cavitation, and efficient sterilization You can get the
effect.
In addition, since small bubbles are grown, and the sound pressure distribution in the area where
microbes are sterilized is uniform, the sound pressure distribution in the area where the bubbles
grow and the cavitation generation distribution in the sterilizing area have no spots, and the
efficiency Can grow bubbles and destroy microorganisms more efficiently.
[0037]
Brief description of the drawings
[0038]
1 is a cross-sectional view showing an embodiment of the water treatment apparatus of the
present invention.
[0039]
2 is a diagram showing the analysis result of the radial movement of the bubble in the
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embodiment of the present invention.
[0040]
FIG. 3 is a diagram showing another analysis result of radial movement of bubbles in the
embodiment of the present invention.
[0041]
4 is a diagram showing another analysis result of the radial movement of the bubble in the
embodiment of the present invention.
[0042]
5 is a diagram showing another analysis result of the radial movement of the bubble in the
embodiment of the present invention.
[0043]
6 is a diagram showing another analysis result of the radial motion of the bubble in the
embodiment of the present invention.
[0044]
7 is a diagram showing the relationship between the specific acoustic impedance and the
acoustic power of the mixture of water and air bubbles in the embodiment of the present
invention.
[0045]
Explanation of sign
[0046]
DESCRIPTION OF SYMBOLS 10 ... Reaction container, 11 ... 1st part, 12 ... 2nd part, 21 ... 1st
cover, 22 ... 2nd cover, 31 ... 1st ultrasonic vibration body, 311 ... 1st cylinder, 312: first vibration
transmitter, 313: first ultrasonic transducer, 32: second ultrasonic transducer, 321: second
ultrasonic transducer, 322: second vibration transmitter, 323: Second cylinder, 411-413, 421423 ... piping.
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