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10th INTERNATIONAL CONFERENCE AND SEMINAR EDM’2009, SECTION IV, JULY 1-6, ERLAGOL
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Effectiveness Increase of Ultrasonic Cavitational Processing of Viscous Liquid Media Vladimir N. Khmelev, Senior Member, IEEE, Sergey S. Khmelev, Denis S. Abramenko, Sergey N. Tsyganok Biysk Technological Institute (branch) Altai State Technical University after I.I. Polzunov, Biysk, Russia Abstract – The article is devoted to the problems which can occur during the ultrasonic processing of liquid media with high damping of ultrasonic vibrations. The disadvantages of existing equipment are shown. The new ways of ultrasonic cavitational processing of viscous media are offered; they let to realize new technological processes, which are impossible in ordinary conditions without ultrasonic influence. Index Terms – Ultrasound, viscous liquid, thin layer, resonance intervals, cavitation.
I. INTRODUCTION
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PPLICATION OF HIGH-INTENSITY ultrasonic vibrations lets to realize or to intensify different stages of production, treatment and modification of high-molecular compounds. Numerous laboratory research [1, 2] proves, that ultrasonic vibrations let to speed up the processes of polymerization and depolymerization, mixing of melts, obtaining of grease lubricants, paints, dissolving of slime deposits, dispersion and even distribution of solid substances in polymeric materials and technical oils. One of the most perspective trends of ultrasonic vibrations application while developing new polymeric materials is dispersion of clusters and even distribution of nanoparticles in viscous polymer and resins during the obtaining of nanocomposites. Technology of process acceleration and obtaining of new materials are in contact insertion of ultrasonic vibrations directly into produced polymeric material. It is known, that there are some variants of contact insertion of ultrasonic vibrations in liquid media. The most commonly used ones are treatment by immersion of the working tool of the vibrating system into processed volume or treatment in flow reactors, containing flowing chamber and ultrasonic radiator. Speed and quality of obtained material are defined by parameters of immersing ultrasonic vibrations and possibility of their spreading in the technological volume.
Ultrasonic influence is so effective and unique, that similar results can be reached by high-speed mixing and low-frequency vibration. The uniqueness of the influence is ensured by the possibility of cavitation appearing in liquid media. Laboratory and industrial researches of different technological processes helped to establish, that necessary criterion of realization and acceleration of processes in liquid media under the action of ultrasound is developing and maintaining of cavitational process in liquid, which can occur, if intensity of ultrasonic vibrations exceeds the defined value [3]. While realizing the cavitational process in liquid and liquid-dispersed media steam and gas bubbles are formed and collapsed, that creates shock waves and emissions, which provides maximum energy influence on liquid around it in the stage of collapse. II. PROBLEM STATEMENT Unfortunately resources of high-intensity ultrasonic vibrations for intensification of different processes and production of new polymeric materials are not widely used as there is a lack of special equipment, which is able to provide with cavitational mode of viscous polymeric materials treatment. The reasons of this are connected with fundamental physical limitations occurring in polymeric materials while realizing ultrasonic technologies. Limitations can be explained by irregularly high damping of ultrasonic vibrations in viscous materials. Such damping restricts the spreading area of ultrasonic vibrations and size of the zones, where vibration intensity reaches the values that are enough to realize the cavitational process. It is evident that even in the case of realization of cavitational process in small volume near the irradiating surface and intensive mixing of processing technological media the productivity will be low, which is not acceptable for industrial application. It is also not possible to ensure the processing uniformity of whole media volume.
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TSYGANOK et al.: EFFECTIVENESS INCREASE OF ULTRASONIC CAVITATIONAL PROCESSING…
In view of high intensity of ultrasonic treatment while accelerating processes and obtaining new material it is very important to develop new ways of immersion and spreading of ultrasonic vibrations in the media with high damping and to implement developing methods in ultrasonic devices suitable for industrial application in different industries. Beforehand it is necessary to develop general requirements to power parameters of designing devices. Consider the available ones. III. THEORY As it was shown, the high damping of ultrasonic vibrations in polymeric materials restricted the use of them in processing of large volumes. The evident method of viscous media processing is their treatment in flow reactors containing flowing chamber and radiator of ultrasonic vibrations. The distinguishing characteristic is that the distance from radiator to reflecting surface of the flowing chamber does not exceed the space on which ultrasonic vibrations produced in the volume do not damp to the amplitude that is not enough to appear cavitation. Such method can be conventionally called processing in “thin layers”. However, even small volumes of viscous liquids are not possible to process in “thin layers” with the application of modern ultrasonic equipment. The necessity of creating ultrasonic vibrations in viscous liquids with intensity more than 20 W/cm2 for realization of cavitational mode is determined the necessity of work used in practice ultrasonic devices at in admissible power modes. Why does it happen? Practically all modern ultrasonic devices are made according to similar construction arrangements; they have similar functional capabilities and the similar power parameters. Consider the possibility of application of the device with 1000 W power (device “Volna-M” model UZTA-1/22-OM). Such device uses doublehalf-wave irradiating system with working mushroom-shaped ending (40 mm diameter) making piston-like vibrations. If the irradiation area is 25 cm2, for cavitational mode it is necessary to irradiate in processing viscous liquid no less than 500 W of acoustic energy. If the efficiency does not exceed 30% while immersing vibrations in viscous media, the consumed power has to transcend 1500 W that is more than consumed power of the device. Because of this during the developing and using devices for viscous media under the equal conditions it is necessary to lessen the irradiating surface area of the working tool. If the diameter of mushroomlike irradiator is 30 mm (irradiation area 15 cm2) and intensity is defined, consumed power of the device should be no more than 1000 W. But it results in volume increase of simultaneously processed liquid.
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To increase the volume of simultaneously processed volumes of viscous liquids it is important to increase the area of radiating surface. Evident solution of this problem is synchronous use of several ultrasonic devices. For practical realization ultrasonic device “Potok-3” model UZAP-2,5/22-OP is designed and widely applied. Viscous liquid in one technological volume is processed by three simultaneously working ultrasonic vibrating systems. View and draft of technological volume of the device “Potok-3” is presented in Fig. 1 and Fig.2 respectively.
Fig.1. View of the technological volume of the device “Potok-3”.
Fig.2. Draft of the technological volume of the device “Potok-3”.
As the production of identical vibrating system is not possible power supply of simultaneously working systems have to accomplish from three separate generators. The distinguishing characteristic of studied devices is the processing of viscous liquids in “thin layers”. The main disadvantage of such method is in the following. If many liquids different in their properties are processed, there is a need to create different devices and flowing chambers and to set the value of requisite and sufficient layer for each liquid. The solution of the problem can be the treatment of liquid viscous media through resonance interval. Thus in the moment of occurring vibrations on the
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10th INTERNATIONAL CONFERENCE AND SEMINAR EDM’2009, SECTION IV, JULY 1-6, ERLAGOL
surface of the working irradiating tool the space from this surface to reflected wall of the reactor multiplies λ/4 in liquid filling reactor. When in liquid ultrasonic field is formed, which pressure amplitude exceeds the threshold of cavitation origination Pm, cavitational cloud appears there. In processed volume under irradiating surface acoustic properties of the media essentially change and as a result resonant conditions change. In this case it is necessary to change the space from reflected wall by moving the working irradiating tool and to state resonance size in the cavitation mode. During such processing it is possible to achieve resonance condition in different liquid media at the distances exceeding some λ/4. Besides parallel connection of separate vibrating systems the vibrating system with many half-wave irradiator can be designed. It is a system with sequentially butt-jointed separate half-wave elements [4]. The devices “Bulava-P” model UZUP-3/22-OP can be an example of using such systems. Distinguishing characteristic of their ultrasonic vibrating systems is that working irradiating is made in the form of rod consisting of tandem area of cylindricity. Irradiation of ultrasonic vibrations is carried out from the irradiator surface in the zone of crossing between cylindrical areas of different diameter. Ultrasonic vibrating system is fastened to axis of reactor flowing chamber along flow direction of fluid motion. Developed surface of irradiation lets to process large volume of liquid in unit of time. Application of multipack piezoelectric transducer [5], where energy of several piezoelectric transducers summarized in irradiating tool, allows achieving the intensity of ultrasonic vibrations up to 20 W/cm2. The creation of this construction having the area of irradiating surface up to 200 cm helps to enter ultrasonic vibrations with power more than 3000 W in media, while supplying electric oscillations the power is no less than 8000 W. While realizing ultrasonic flowing reactor on the basis of such irradiator effective processing of all volume of viscous liquid is possible only in the case of uninterrupted change of liquid in volumes between neighboring parts of irradiator of larger section. To fulfill such change in cylindrical volume is impossible even at low speed of flow taking into account mixing influence of ultrasonic vibrations and their spreading owing to multiple reflections. In such case small volumes of liquid are processed, which are between zones of larger diameter, and the main volume of flowing liquid is not influenced by ultrasound. Elimination of mentioned defects is possible while realizing following technical solution, when ultrasonic vibrations direct to the volume of chamber providing multiple reflection of ultrasonic vibrations from internal surface of flowing chamber and areas
of irradiator and creation the conditions for vibration spreading, which in turn help to get resonant amplification of ultrasonic vibrations. Design and principle of operation of developed ultrasonic flow reactor are demonstrated in Fig. 3 and Fig. 4.
Fig.3. Design of flow reactor.
Fig.4. Principle of operation of ultrasonic flow reactor.
Ultrasonic flow reactor made according to scheme operates in the following way. Processed liquid comes into the cavity through cylindrical grid element 4, which provides even distribution and speed of liquid flowing along the cross-section area of flowing chamber. During the operation ultrasonic vibrations are formed 11 due to piston motions made by surfaces of smooth transitions 9. Direction of ultrasonic vibration spreading is at right angle to the surfaces of smooth transitions. Thus the form of transitions determines the direction of ultrasonic vibration spreading 11, that lets to change the direction of irradiating vibrations in the volume of the reactor. The form of smooth transitions 9 provides the direction of ultrasonic vibrations into internal volume of the flowing chamber and it also reduces flow resistance. Besides spreading in given direction radial and exponential forms of smooth transitions
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can help to focus ultrasonic vibrations 11. The reflectors of ultrasound 10 are situated in such a way that they provide the reflection of ultrasonic vibrations along the lines of reflectors areas with less section and also into chamber volume between reflectors of ultrasound. So the even distribution of ultrasonic vibrations in internal volume of the flowing chamber can be achieved. Form of the irradiator and internal surface of the flowing chamber provides the creation of chamber sequence; each one has conditions for resonant amplification of spreading ultrasonic vibrations. In the internal volume of flowing chamber ultrasonic field with the intensity enough for creation and keeping of developed cavitation mode in all space between walls of the flowing chamber and irradiator surface is generated. Thus offered technological solution helps to increase the efficiency of liquid media processing providing even treatment of volume.
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Vladimir N. Khmelev (SM’04) - prorector at Biysk technological institute, professor, Full Doctor of Science (ultrasound). Honored inventor of Russia. Laureate of Russian Government premium for achievements in science and engineering. Area of scientific interests is application of ultrasound for an intensification of technological processes. IEEE member since 2000, IEEE Senior Member since 2004. His biography published in 7th issue of book “Who is who in scientific and engineering”. Sergey S. Khmelev was born in Prokopievsk, Russia, 1985. Now he is student of Biysk Technological Institute. His research interest is design and construction ultrasonic oscillation system.
Denis S. Abramenko. He is received engineer’s degree from BTI AltSTU in 2005.
IV. CONCLUSION As a result of carried out experiments it was found out that existing ultrasonic equipment is not suitable for cavitational processing of viscous liquid media, because of necessity to work in inadmissible power modes and low efficiency of the process. New method of ultrasonic processing of viscous fluid media in flow reactors with irradiator of extended type and flowing chamber was offered. The flowing chamber had the internal surface which made the conditions for resonant amplification of propagating vibrations. The use of obtained data helps to design, develop and introduce ultrasonic technological equipment in industry. It provides the efficiency increase of viscous media processing, allows realizing new technological processes which are not possible to accomplish in common conditions without ultrasonic influence.
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[2]
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[5]
Khmelev, V.N. Ultrasonic multipurpose and specialised devices for an intensification of technological processes in the industry / V.N. Khmelev, A.V. Shalunov [and others]. – Barnaul: AltGTU, 2007. – 416 p. Khmelev V.N., Popova O.V. Multifunctional ultrasonic devices and their application in small industries, agriculture and household / Monograph - Barnaul.: AltGTU 1997, 168 p. (in Russian). Ultrasonic technology / B.А. Agranat. – М.: Metallurgy, 1974. – 505 p. Khmelev, V.N. High Power Ultrasonic Oscillatory Systems / V.N. Khmelev // International Workshops and Tutorials on Electron Devices and Materials EDM'2007 / NSTU. – Novosibirsk, 2007. Ultrasonic oscillation system: pat. 2332266 Russian Federation: Khmelev V.N., Savin I.I., Tsyganok S.N., Barsukov R.V., Lebedev А.N.; Biysk Technological Institute (branch) Altai State Technical University after I.I. Polzunov.
Sergey N. Tsyganok was born in Biysk, Russia, 1975. Now he is Ph.D (Machinery), he received degree on information measuring engineering and technologies from Altay State Technical University, key specialist of electronics. Laureate of Russian Government premium for achievements in science and engineering. His main research interest is development of high -effective multifunctional oscillators for ultrasonic technological devices.
