RU2540608C1 - Method for ultrasonic cavitational processing of liquid media - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method for ultrasonic cavitational processing of liquid media, wherein a resonance acoustic cavitation mode is formed within a flowing mechanical vibration channel system; generation of sound vibrations is carried out in an in-phase manner at each side of the channel with an amplitude greater than the acoustic cavitation threshold for a moving liquid medium. The channel system has at least four rectangular sides with a section in the plan view in the form of a rhombus. Sides with resonant natural vibrations at the same frequency or different frequencies are arranged such that together they form a cylindrical focusing concentrator of acoustic energy in the central area of the channel system.

EFFECT: invention increases acoustic wave intensity in the processed liquid medium while maintaining or increasing the volume of the processed liquid medium in the channel system.

1 tbl, 7 dwg

Description

The invention relates to the field of cavitation treatment of liquid media, as well as environments where the specific content of water or other liquid phase exceeds ~ 40-50% of the total mass. Liquid media may contain solid inclusions (suspensions). Acoustic ultrasonic cavitation is effectively used in a number of areas of the economy, where the following processes are implemented / 1-5 /:

- dispersion;

- homogenization and emulsification;

- mixing;

- disintegration;

- deagglomeration.

In practice, this covers the processes of obtaining multicomponent media (emulsions, suspensions, aqueous solutions and systems), ultrasonic sterilization (disinfection) of water, milk, other products, cleaning of instruments and medical supplies, etc.

The method of processing liquid media, which is implemented in the scheme of an ultrasonic reactor, can be taken as a prototype / 1 /. It consists in the fact that an ultrasonic wave is created in the volume of a liquid using a rod emitter, at the end of which there is a source of oscillations, as a rule, a piezoelectric emitter. There are many options for calculating the shape of the rod emitter and the possibility of attaching several piezoelectric emitters at its end, but all of them are aimed at increasing the amplitude of the oscillations of the rod at the lower end and on the side walls / 8 /. This is due to the fact that the developed cavitation zone in practice is measured by the dimensions of several centimeters from the surface of the oscillations. Therefore, the bottom of the rod is considered the most effective zone, since a standing wave is formed in the processed fluid between the flat end of the emitter and the flat bottom. It is noted that the diameter of the end face is difficult to make in sizes larger than 50-70 mm. Radiation from the cylindrical surface of the rod has a significantly lower amplitude of oscillations and a cylindrical divergence. Taking into account the reflected acoustic waves from the walls of the external cylinder-cup, it can be estimated that it is practically impossible to obtain the optimal regime of a stable standing plane coherent ultrasonic wave in the processed liquid medium, by analogy with a small area between the end of the emitter and the bottom of the cylinder-cup. The complex picture of transmitted and reflected ultrasonic waves in the medium, the absence of wave coherence and energy concentration at one frequency leads to the fact that it is almost impossible to obtain emulsions with a dispersed phase size of less than 1.0 μm, the homogeneity level does not exceed 15-20% in the main mode. Moreover, the volume of the processed fluid is limited.

Another alternative method of ultrasonic cavitation treatment of liquid media is implemented in rotary-pulsating homogenizers / 2 /.

In the sounding chamber, due to periodically occurring alternating motions of the fluid from the rotating stator-rotor system, an ultrasonic wave with cavitation effects occurs. This is an intermediate option between acoustic and hydrodynamic cavitation. Such homogenizers are currently most widely used. They are quite simple, allow you to process large volumes of liquid, much cheaper than ultrasonic counterparts. Good high-speed homogenizers allow emulsions with a dispersed phase size of ~ 1.5 μm in the main mode, the level of homogeneity does not exceed 10-15%. However, this method also has a number of fundamental limitations. This is due to the low efficiency of electromechanical systems (up to 10%), which limits the power of the ultrasonic wave to 1.5-2 W / cm ² , does not allow working with viscous media, with the processing of static volumes of liquid (in the volume of the stator-rotor), suspensions containing solid inclusions, and a number of other fundamental restrictions.

The closest in essence is a method of obtaining an emulsion cosmetic product according to patent No. 2419414 of 09/08/2010.

The principal difference of this method from others is the use of the resonant properties of a mechanical oscillatory system of a rectangular channel with large side a and small side b, respectively, to generate an acoustic wave in liquid media, sound vibrations are generated in phase on both opposite sides a with an amplitude exceeding the acoustic threshold cavitation, the frequency f of sound vibrations is chosen equal to the resonant frequency of the entire channel, with a smaller distance b between kami channel selected multiple quarter wavelength, is excited in a given environment. In the prototype, between the sides a, a quasi-plane standing wave is formed in the fluid being treated, and due to reflection from the opposite side, the pressure difference in the positive and negative phase can be amplified. If the width b is equal to half the wavelength in the liquid, the maximum gain can be 4 times (taking into account two sides).

The disadvantages of this method is the restriction on the gain of the acoustic wave in the processed liquid medium while limiting the volume of this liquid medium. Indeed, to obtain high-intensity acoustic fields, for example, at a frequency of 25 kHz, half the wavelength in water will be ~ 3 cm (size b), width a will be ~ 11.5 cm, that is, in a channel system with dimensions of 100 * 11.5 * 3 cm will be possible simultaneous processing of not more than 3.45 liters of liquid, similar in its characteristics to water. The gain of the acoustic wave is limited, the only way is to increase the amplitude of the oscillations of the channel system. As a rule, this causes great difficulties.

The aim of the invention is to increase the intensity of the acoustic wave in the processed liquid medium while maintaining or increasing the volume of the processed liquid medium in the channel system.

This goal is achieved by the fact that in the method of ultrasonic cavitation processing of liquid media, in which the resonant acoustic cavitation mode is formed inside the flow-through mechanical oscillatory system-channel, the generation of sound vibrations is carried out in-phase on each side of the channel with an amplitude exceeding the acoustic cavitation threshold for a moving liquid medium, the channel system has at least four rectangular sides with a cross-section in the plan in the form of a rhombus, while the sides performing resonant self-oscillations on one oh or different frequencies, arranged so that together form a cylindrical concentrator focusing the acoustic energy in the center region-channel system.

It is known / 4, p. 167 / that it is advisable to use cylindrical focusing emitters for flow cavitation treatment of liquids, which create a coherent in-phase convergent front - a cylindrical front of an acoustic wave. The closed cylindrical focusing emitters / 4, p. 183 / made of piezoceramics given in this work, using both bending and radial vibrations, have received very limited distribution in practice. This is due to the relatively high frequency of radial vibrations (hundreds of kHz) and their small amplitude.

For an industrial scale, the level of cavitation treatment of liquid media should be measured in cubic meters and tens of cubic meters per hour. In this case, the range of the most effective frequencies lies from 20 kHz to 40 kHz.

Such volumes require a cross-section of the channels where cavitation treatment of liquid media occurs, measured in tens of square centimeters.

At the same time, it is necessary that the radial vibrations be the maximum possible in amplitude and coherent.

To implement the proposed method, we consider a channel system whose cylindrical (round) section can be approximated by a set of chords. In the simplest case, it will be four rectangular sides forming a square, rhombus or trapezoid. It was shown in / 4, p. 169 / that the gain of a converging cylindrical wave in intensity and vibrational velocity in the focal plane has an optimal opening angle of ~ 60 degrees. Accordingly, the angle between the two radiated surfaces should be 120 degrees. The simplified approximation of the circle by an equilateral triangle shows that in this case the opening angle will be 30 degrees, which reduces the gain by 2 times (~ 50% of the maximum). The approximation of a circle by a square (opening angle of 45 degrees) gives intermediate results with a gain (~ 75% of the maximum). Figure 1 presents the dependence from work / 4, p. 182 /, showing the maximum achievable vibrational velocity on the focal axis of the vibrational velocity of its surface in the presence of attenuation of the acoustic wave in the medium. As you know / 3, p. 15 /, the intensity of the sound wave is proportional to the square of the vibrational velocity. For typical intensity values of ~ 10 W / cm ² (water), the amplitude of the vibrational velocity is ~ 36.7 cm / s / 3, p. 120 /. The maximum achievable speed gain can be ~ 15 (in FIG. 1). This is significantly higher than in the prototype, even if we take into account factors that reduce this coefficient. It should be noted that amplification is effective at low vibrational velocities of the surface of a cylindrical emitter, which is very important. By creating small vibrations on each side that form a converging cylindrical wave, high intensities of the acoustic wave will be observed in the center of the channel system (on the focal line). Implementation of the proposed method can be performed in different ways. Figure 2 and Figure 3 presents the prepared for work elements (sections) of the oscillatory system-channel, forming a spherical wave converging to the center of the channel. In the first case, the channel system has a cross section in the form of a rhombus (angles of 120 and 60 degrees), in the second case, in the form of a regular hexagon (angles of 120 degrees). The shape of the regular hexagon can be attributed to one of the most optimal.

The resonant acoustic cavitation mode is formed inside the flow-through mechanical oscillatory system-channel, the sound vibrations are generated in-phase on each side of the channel with an amplitude exceeding the acoustic cavitation threshold for a moving liquid medium. The channel system must have at least four rectangular sides with a cross-section in the form of a rhombus, while the parties performing resonant self-oscillations at one or different frequencies are arranged so that together they form a cylindrical focusing acoustic energy concentrator in the central zone of the channel system.

Figure 4 shows a General view of an industrial installation with diamond-shaped channels. The installation has 14 individual oscillatory channels with a capacity of ~ 4 liters each. At the same time, ~ 56 liters of liquid can undergo cavitation treatment. Each channel consists of 4 faces, bent on a special machine with subsequent welding to ensure tightness.

Each face of the channel system is a rectangle that has certain length and width dimensions depending on the operating frequency. The working frequency is close to the first harmonic of the oscillations of the rectangular membrane, which can be determined by the ratio / 6 /

where c is the propagation velocity of elastic waves;

k _x , k _y are wave numbers whose values are determined by the boundary conditions;

L _x is the length of the side of the plate directed along the axis Ox;

L _y is the length of the side of the plate directed along the axis Oy;

j _x , j _y is an integer equal to 1 for the first harmonic of the oscillations.

The channels are made of AISI 316 stainless steel (analogue 12X10HT), with a longitudinal wave velocity of ~ 5800 m / s.

As shown by numerous experiments, in systems with an infinite number of degrees of freedom, which include plates and membranes, at certain frequencies and magnitude of the dynamic deflection amplitude, the modes of forced oscillations (linear and nonlinear), forced oscillations with additional parametric resonances or self-oscillations can be realized / 7 , 8/.

To ensure the coherence of a converging cylindrical wave, it is best to implement a self-oscillation regime.

The self-oscillation regime should be characterized by a maximum amplitude of oscillations, a minimum power consumption, and a dominant harmonic of oscillations, which substantially prevails over the others. The energy for maintaining self-oscillations is provided by an external power exciter of ultrasonic vibrations / 9, p. 175 /, in particular, piezoelectric exciters connected to an industrial ultrasonic oscillator UZG 2-22, which are serially produced by a number of domestic enterprises. The UZG 2-22 generator is convenient in that it allows you to manually determine the frequency of self-oscillations, since it has an indicator of power consumption associated with the power given to the load. To control the amplitude of oscillations, when determining the frequency of self-oscillations, a measuring path is used from piezo-accelerometers of type 4344 (or type AR-12, AR-33, manufactured in Russia), an amplifier 2635 from Bruel & Kjaer, a digital Velleman oscilloscope with registration of signals to a personal computer.

It was found that the frequency of self-oscillations is not equal to the frequency of the first harmonic of membrane oscillations, as defined above. As defined in the prototype method, the effect of the attached mass, nonlinear damping and nonlinear elasticity is very significant.

According to the set of processed experimental data for frequencies from 22 kHz to 40 kHz and the use of typical piezoelectric exciters (the masses are close to each other), the frequency correction was 1.5-2.5 kHz towards higher frequencies.

As a practical application of the efficiency of a converging cylindrical wave, the data of the following experiment are presented.

Table 1 shows a typical formulation of a cosmetic emulsion.

As an emulsifier, the NMF ingredient is used, which can form both direct and inverse emulsion during homogenization.

Figure 5 shows a micrograph of the emulsion during homogenization in an oscillating channel system (prototype) at low power (~ 50-70 W / liter) at a frequency of 25 kHz. It can be seen that this is a typical direct oil-in-water emulsion.

Figure 6 shows an emulsion of the same formulation prepared in a diamond-shaped channel. The specific energy consumption is close to the previous version (~ 50-70 W / liter), frequency 25 kHz. It can be seen that the phase turned around in the emulsion, that is, it became inverse.

This was due to an increase in the intensity of cavitation treatment, due to the effect of a converging cylindrical wave.

Figure 7 presents the scale of the object micrometer with a division value of 10 μm.

In this method, it is possible to implement a mode of operation with different frequencies.

In this case, the simplest profile will have a section in the form of a trapezoid or the same rhombus. Otherwise, the methodology for determining the vibration frequencies and sizes of the rectangular sides of the channel system remains the same. To synchronize the operation of generators with different frequencies, it is necessary to use a clock generator. This scheme is most easily implemented at multiple frequencies, for example 22 kHz and 44 kHz, and so on.

Thus, the proposed method of ultrasonic cavitation treatment of liquid media allows you to increase the intensity of the acoustic wave in the processed liquid medium while maintaining or increasing the volume of the processed liquid medium in the channel system.

LITERATURE

1. Bronin F.A. Investigation of cavitation destruction and dispersion of solids in a high-intensity ultrasonic field. Abstract for the degree of candidate of technical sciences, MISIS, 1967.

2. Chervyakov V.M., Only V.G. The use of hydrodynamic and cavitation phenomena in rotary devices. - M.: Mechanical Engineering, 2008.

3. Bergman L. Ultrasound and its application in science and technology. - M .: Foreign literature, 1956.

4. Rosenberg L.D. Focusing ultrasound emitters. Part 3. In the book. Sources of powerful ultrasound. Ed. Rosenberg L.D. M .: Nauka, 1967.

5. Khmelev V.N., Popova O.V. Multifunctional ultrasonic devices and their application in small industrial, agricultural and household conditions: scientific monograph, Alt. Gos. Tech. University of I.I. Polzunova. - Barnaul: Publishing house of Altai State Technical University.

6. Koshlyakov N.S., Gliner E.B., Smirnov M.M. Partial differential equations of mathematical physics. M .: Higher school, 1970.

7. Obukhov A.N. Parametric excitation of self-oscillations in vibrating machines. Abstract for the degree of candidate of technical sciences. Institute of Engineering, M., 2007.

8. Izrailovich M.Ya., Obukhov A.N. Parametric self-oscillation control. M .: Publishing House URSS, 2010.

9. Volmir A.S. Nonlinear dynamics of plates and shells. M .: Nauka, 1972.

Claims (1)

A method of ultrasonic cavitation treatment of liquid media, in which the resonant acoustic cavitation mode is formed inside a flowing mechanical oscillatory system of a channel, the generation of sound vibrations is carried out in-phase on each side of the channel with an amplitude exceeding the acoustic cavitation threshold for a moving liquid medium, characterized in that the channel system has at least four rectangular sides with a cross-section in the plan in the form of a rhombus, while the sides performing resonant self-oscillations on one or different x frequencies are arranged in such a way that together they form a cylindrical focusing acoustic energy concentrator in the central zone of the channel system.

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