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13Research changes electric parameters of ultrasonic oscillatory systems in process ultrasonic influences on liquid and liquiddisperse mediums
Leonov G.V., Khmelev V.N. (vnh@bti.secna.ru), Barsukov R.V., Khmelev M.V., Tchyganok S.N.
Biysk technological institute.(branch) of the state educational establishment of the high professional education «Altay state technical university by I.I. Polzunov»
1. Introduction.
Efficiency of ultrasonic technologies today does not cause doubts. They allow to solve the problems connected to drilling the fragile materials, welding of polymers, dispersion various liquids. Especially wide distributions get ultrasonic technologies for an intensification of processes in liquid mediums (emulsification, dispersion, degassing, extraction, impregnation etc).
All ultrasonic technological processes which are taking place in liquid mediums, are based on phenomenon of cavitation in the technological mediums, is more exact than a mode of « developed cavitation».
Technological processes in various mediums are realized by means ultrasonic devices consisting the electronic generator and ultrasonic oscillatory system (UOS). Peak efficiency passing of process is provided at the optimum matching of the electronic generator and UOS and accordance working frequency of the generator to resonant frequency UOS.
Various technological mediums have a various influence on parameters of the electronic generator and UOS [1]. The degree of influence of technological mediums is defined by viscosity of the liquid mediums, quantity of firm substance, attenuation of ultrasonic fluctuations. Besides change of parameters UOS occurs at realization of ultrasonic influence (for example, transition from oil or waters in process emulsification, swelling of substances at extracting, etc.).
It is known also, that properties of processable technological mediums change at increase in amplitude of fluctuations that is caused by occurrence and development cavitations processes (formation a cloud of gas bubbles on a radiating surface).
All possible changes of properties of processable technological madiums cause change of own resonant frequency and good quality of UOS, resulting to her mismatch with the electronic generator on frequency and a voltage. Thus the amplitude of fluctuations of ultrasonic oscillatory system essentially decreases and efficiency of realization of processes down to zero is reduced, at not achievement cavitation process.
Thus, at realization of technological processes in various mediums, there is a necessity for the continuous control of properties of processable mediums and continuous reorganization of the generator, according to all possible changes of parameters of technological mediums. Only in this case ultrasonic influence with peak efficiency is provided.
In this connection there was a necessity for carrying out of experimental researches on revealing a degree of influence of various technological mediums on electric parameters of ultrasonic oscillatory systems.
In this connection given article is devoted to carrying out of experimental researches, the analysis of the received results and developments of requirements to parameters and modes of reorganization of electronic generators.
2. Experimental equipment and materials.
At ultrasonic influence on various liquid mediums there is a change of electric parameters UOS. Ranges of change of electric parameters of UOS depends on significance of acoustic loading and modes of ultrasonic influence. For practical measurement and research of electric parameters of oscillatory systems the specialized measuring stand which block diagram is submitted in figure is offered and developed.
As power supply for UOS the generator of electronic fluctuations ultrasonic frequencies, by capacity 400 W was used. Have been used UOS with working tools of two types: cylindrical with the various area of a radiating surface and mushroom-shaped. For carrying out of practical researches the following technological mediums have been used:
- the water medium;
- the water medium under pressure 7 MPa.;
- the air medium;
- solvent;
- engine oil.
The choice of mediums has allowed to sweep a wide range of known liquid mediums with various cavitation durability.
R - sensors for measure currents and voltages; Z - impedance UOS; C - additional capacity; G - the tunable oscillator.
Fig.1 The block diagram for measurement electric parameters of UOS.
The specialized measuring stand, which circuit is submitted in figure 1, will consist of the device of management, resistive gauges, ultrasonic oscillatory system with the piezoelectric converter and the ultrasonic electronic generator. At work of the measuring stand it is carried out:
- collection the current values of electric parameters of ultrasonic oscillatory systems and electronic generators (an electric voltage on piezoceramic elements of ultrasonic oscillatory system, a current consumed by oscillatory system from the electronic generator, a current proceeding on additional capacity C, frequency of electric voltage, value of phase shifts between controllable currents and voltage);
- tuning of frequency of the electronic generator in a range from 15 kHz up to 25 kHz for measuring of frequency characteristics of controllable electric parameters of oscillatory systems which resonant frequencies lay within the limits of this range;
- driving capacity of the electronic generator for measuring parameters of ultrasonic oscillatory systems from parameters of technological mediums in various modes (work in non cavitation mode, on a threshold of origin cavitation, in a mode developed cavitation);
- formation a stream of the received data for his subsequent processing, calculation of new parameters and characteristics, the analysis and visualization on the PC.
For carrying out of experiments, the ultrasonic electronic generator was equipped with electric gauges for measurement of electric parameters of oscillatory systems and electronic generators (an electric voltage on piezoceramic elements of ultrasonic oscillatory system, a current consumed by oscillatory system from the electronic generator, a current proceeding on additional capacity C, as shown in figure 1), electric signals with which go to the device of management.
3. A technique for carrying out of experiments.
Researches have been carried out by two stages.
The first stage consist in reception a gain-frequency characteristic of electric parameters of ultrasonic oscillatory system [2,3] by direct measurements (by means of the analog-digital converters included in the device of management) at various frequencies of a voltage on oscillatory system, accumulation of the measuring information in the device of management (look figure 1) and her subsequent transfer as a consecutive stream of dates on the PC.
Reception of gain-frequency characteristic of electric parameters of oscillatory system is carried out by smooth tuning of frequency of the electronic generator in the set frequency range with continuous measurement of electric parameters of oscillatory system. At width of a frequency range of tuning the electronic generator is 10 kHz, time of his scanning make 5 sec.
Gain-frequency characteristic of electric parameters UOS were measured at different voltage of a feed a ultrasonic oscillatory system. It has allowed for each separate experiment (processing concrete technological mediums with use of the certain type of the working tip) to receive of 250 curves corresponding to different voltage of a feed a oscillatory system.
During carrying out of measurements accumulation and transfer of the measuring information on the consecutive channel (RS-232) to PC for her further processing was provided.
The second stage consist in processing the saved up data, visualization primary given (gain-frequency characteristic), processing of the primary data, reception of new dependences for and their visualization and the analysis. Result of processing of the saved up data are graphic dependences of measured parameters and their numerical values.
4. The analysis of results.
In figure 2 results of experimental researches (gain-frequency characteristic of current a mechanical branch of oscillatory system (b); gain-frequency characteristic of current consumed by oscillatory system from the electronic generator gain-frequency characteristic an electric voltage on piezoceramic elements of ultrasonic oscillatory system (b) for various voltage of a feed oscillatory system).
]. lüA
а)
22000 21 Ii О ZU С«}
Ъ)
(InHV
iM« iiise JJ3« 3mjo лтзо нть zjmo »зя>
c)
Fig.2 Frequency characteristics of electric parameters of ultrasonic oscillatory system.
Dependence of a current of a mechanical branch of oscillatory system on frequency of the electronic generator is received by subtraction of the capacitor current proceeding on electric capacity C (look figure 1) from a current consumed by oscillatory system from the electronic generator (the capacity C at carrying out of experiments gets out equal electric capacity piezoceramic elements of ultrasonic oscillatory system).
From figure 2^ the frequency characteristic of the current consumed by oscillatory system from the electronic generator follows, that, does not reflect resonant properties of oscillatory system, while characteristics of a current of a mechanical branch (figure 2.b) and voltage on piezoceramic elements of oscillatory system (figure 2.c) obviously reflect a resonant functioning of ultrasonic
oscillatory system. In this connection the analysis only frequency characteristics of a current of a mechanical branch of oscillatory system has been carried out.
The analysis of character of the dependences received for various technological mediums at use of the different working tips has allowed to establish, that at increase in a voltage on piezoceramic elements of oscillatory system increases not only amplitude of mechanical fluctuations on resonant frequency, but also occurs as displacement of resonant frequency. The trajectory of movement of the point corresponding to resonant frequency of oscillatory system on a coordinate plane at increase a voltage on piezoceramic elements is individual for every medium and is defined by its properties.
Further results of processing and the analysis of received experimental dependences (gain-frequency characteristic) for various technological mediums (the air medium, acetone, engine oil, water under normal conditions and superfluous pressure) are submitted at use of cylindrical working tips with the various area of a radiating surface and mushroom-shaped working tips with the advanced radiating surface.
In figure 3 dependences of a current of a mechanical branch and resonant frequency of oscillatory system on a voltage on piezoceramic elements of ultrasonic oscillatory system are submitted at use of the cylindrical tool and realization of ultrasonic radiation in various technological mediums.
1600 1400 1200 1000 800 600 400 200 0
200 400
Voltage, V
■woter '
■air •
■solvent
600
■engin oil
22550 22500
•woter '
500 1000 1500 Voltage, V
-air * solvent ■ engin oil
a) b)
Fig.3 Dependences of a current of a mechanical branch and resonant frequency of oscillatory system on a voltage on piezoceramic elements of ultrasonic oscillatory system at use of cylindrical
tools.
0
0
From the received dependences follows (figure 3^), that the current of a mechanical branch of ultrasonic oscillatory system practically linearly depends on a voltage on it piezoceramic elements. The various corner of an inclination of curves is caused by that processable mediums have a various impedance. The big amplitude of mechanical fluctuations (amplitude of a current of a mechanical branch) is achieved in the air medium (the smallest impedance), then in acetone, then in water and in oil (the biggest impedance) with other things being equal (an equal voltage on piesoceramic elements).
The small difference in amplitudes of a current of a mechanical branch at processing various technological mediums with use of cylindrical working tools is connected to that, the area of
radiation has rather small value equal of 1.7 sm2 It is obvious, that the area of acoustic contact to the processable medium, the less its influence on mechanical and electric parameters of oscillatory systems less. Nevertheless, it is visible, that various technological mediums at use of cylindrical working tools, influence size of a current of a mechanical branch.
The curves submitted in figure 3.b, illustrate change of resonant frequency on a measure of increase in a current of a mechanical branch (oscillatory speed) oscillatory system.
As it has been told above, in connection with the small area of acoustic contact of oscillatory system with processable mediums, the impedance of oscillatory system at processing various technological environments varies not essentially. For this reason in all technological mediumss change of resonant frequency of oscillatory system occurs practically in identical limits and changes under the same law.
Work of the generator in case of use of the working tips with the small area of radiations, at processing of the technological mediums considered above, should provide reorganization of frequency in limits not less than 0.2 kHz.
Similar curves, have been received for working tools with the increased surface of radiation, i.e. the working tools close to cylindrical, but having oblique under a corner 300 face radiating surface. However the dependences describing change of amplitude of a current of a mechanical branch a little differ from similar dependences received for the cylindrical tip. It is caused by that the area of radiation 30° cylinders truncated under a corner, all in 1.3 times are more the than area of the basis of the cylindrical tip that as not essentially influences size of a current of a mechanical branch.
For the cut off working tool resonant frequency has grown, that is connected to smaller weight of the attached tool as the truncated cylinder while the range of change of resonant frequency has not changed. Work of the generator in case of use of the working tip as the cylinder with the oblique surface, at processing of the technological environments considered above, as well as for a case with the cylindrical working tool, should provide reorganization of frequency in limits not less than 0.2 kHz.
The most effective way of increase in ultrasonic energy entered into liquid technological mediums is the increase in the area of radiation by means mushroom-shaped the working tools making piston fluctuations.
In figure 4 dependences of resonant frequency of oscillatory system with the mushroom-shaped working tool are submitted at radiation in the air medium, in water under normal conditions, the water medium under static pressure 7 MPa., solvent and engine oil.
22900 22800 22700 22600 22500 22400 22300 22200 22100 22000
500
1000
1500
Voltege, V
■ woter ander pressure 7 MPa
■ woter at normal condition
■ air
22800 22700 22600 22500 22400 22300 22200 22100 22000
■solvent'
500 1000 1500
Voltage, V
■engin oil * air м woter
a) b)
Fig.4 Dependence of resonant frequency UOS with mushroom-shaped working tip from a
voltage of its feed.
0
0
The analysis of the resulted dependences testifies to the following processes.
1. Change (insignificant reduction) resonant frequency in the air medium at use mushroom-shaped working tools as takes place, as well as at use of cylindrical working tools. Change of resonant frequency at work of oscillatory system in the air medium lays in a range of 22790 Hz -22825 Hz.
2. At input of ultrasonic fluctuations in the water medium, the sharp increase in resonant frequency which range of change lays in limits from 22100 Hz up to 22800 Hz is under normal conditions observed. At use of tools with mushroom-shaped working tip in diameter of 25 mm, the water medium environmental him represents for ultrasonic oscillatory system big enough attached weight that reduces resonant frequency of oscillatory system up to value of 22100 Hz. At increase amplitude of fluctuations (at increase in a voltage on piezoceramic elements of oscillatory system) in water starts to arise cavitation, that is connected, first of all, to occurrence cavitations bubbles which loosen the water environment in immediate proximity the working tool, changing thus properties of the liquid medium. At a voltage 800 V resonant frequency of oscillatory system achieves the maximal value of 22800 Hz and corresponds to resonant frequency of oscillatory system in the air medium. At the further increase a voltage resonant frequency of oscillatory system remains to a constant. It testifies that at a voltage 800 V, in the processable water medium the mode advanced cavitation which is characterized steady cavitation field at a radiator is established.
3. Presence of static pressure in the water medium shifts a threshold of occurrence cavitation in area of the big amplitudes of mechanical fluctuations. Absence cavitation at processing water under static pressure 7 MPa. testifies that the liquid which is taking place in immediate proximity from the radiating surface does not change the physical properties and accordingly the size of the equivalent attached weight does not change the value. It proves to be true a constancy of resonant frequency of oscillatory system at increase a voltage at her piezoceramic elements. It is necessary to note, that resonant frequencies at processing water mediums at normal and superfluous pressure upon small voltage of a feed (at absence cavitation in both cases) are equal each other.
The investigated technological mediums represent extreme cases (air, water - a liquid having maximal cavitation effect, water under the pressure, excluding origin of cavitation).
The considered dependences can be added with the data received on other environments and under similar conditions of ultrasonic influence, submitted on figure figure 4.b.
From the dependences submitted in figure 4.b follows, that at radiation in solvent cavitation starts to develop at smaller, than for water and the oil, the having voltage which are not exceeding 550-600 V.
Besides similar measurements have been lead at radiation to the water medium with use mushroom-shaped working tools to diameters 30мм, 35мм and 40мм. Measurements have shown, that with increase in diameter of the working tool (30мм, 35мм, 40мм) ranges of change of resonant frequency of oscillatory system on a measure of development in the medium advanced cavitation have made 1700 Hz, 2300 Hz and 3072 Hz accordingly.
In figure 5. а dependences of amplitude of a current on a resonance in mechanical branch UOS with mushroom-shaped tool from a voltage on her piezoceramic elements received in various mediums are submitted.
500 1000
Voltage, V
1500
500 1000
Voltage, V
■air ■ solvent * woter м engin oil
■engin oil solvent ^^^woter air
a) b)
Fig.5 Dependence of amplitude of a current of mechanical branch УЗКС on resonant frequency and her electric Q-factor from a voltage of feed UOS.
0
0
From the dependences submitted in figure 5^ follows, that dependences of a current of a mechanical branch of oscillatory system at processing various technological mediums have different character. It as it has been shown above, caused by various wave resistance of processable technological mediums. At the same time at use mushroom-shaped working tool, essential difference (in comparison with the similar experiments which have been lead with cylindrical working tools) of amplitude of a current of a mechanical branch at the same voltage of a feed of oscillatory system is observed. It conditioned that mushroom-shaped working tool in diameter of 25 mm has the big surface of acoustic contact to the processable medium (8 sm2) that five times is more than a surface of acoustic contact of the cylindrical tool. In this connection, change of the technological medium (change of an impedance of attached loading) at use of tools with the advanced surface of acoustic contact renders the greater influence on an electric impedance of ultrasonic oscillatory system.
As a mushroom-shaped tools are widely used in practice and at their use parameters of processable mediums render appreciable influence on electric parameters of oscillatory systems for a case of use mushroom-shaped working tip with a diameter 25 mm have been received additional
dependences of electric Q-factor of oscillatory system depending on a voltage on her piesoceramic elements, submitted on figure 5.b.
Dependences illustrate increase in electric Q-factor of oscillatory system at processing various technological mediums, i.e. for various technological mediums curves have different character. With development cavitation, mechanical Q-factor of oscillatory systems increases and comes nearer to mechanical Q-factor of the same oscillatory system at its work in the air medium. Change of Q-factor of oscillatory system corresponds to change of mechanical Q-factor of oscillatory system that speaks electromechanical analogies between mechanical and equivalent electric parameters of oscillatory system.
The steepness of a curve, at processing acetone, speaks weak breaking strength of this technological medium. Thus electric Q-factor of oscillatory system, achieves value of Q-factor of same oscillatory system in the air medium at voltage of a feed of oscillatory system 500 V.
The water and oil are stableness to tensile stress. Voltage at which electric Q-factor of oscillatory system comes nearer to Q-factor in the air medium, at processing water and oil, make a 700 and 800 Volt accordingly.
5. Conclusion.
As a result of the carried out experimental researches of influence of processable technological mediums on electric parameters of oscillatory systems, definitions of ranges of influence and the analysis of the received results it is possible to draw the following conclusions:
1. For increase of efficiency of technological processes in various liquid and it is necessary to carry out continuously reorganization of electric parameters of ultrasonic electronic generators (amplitude and frequency of a voltage of a feed a oscillatory systems) according to all possible changes of electric parameters of ultrasonic oscillatory systems (a current of a mechanical branch, resonant frequency, electric good quality), the caused changes of parameters processable ultrasonic fluctuations of technological mediums.
2. The increase in energy of ultrasonic fluctuations entered into technological mediums possible due to increase in a radiating surface of working tools (for example mushroom-shaped tools) strengthens interrelation of parameters of processable mediums with electric parameters of ultrasonic oscillatory systems and expands ranges of necessary reorganization of parameters of electronic generators.
3. Increase of efficiency of technological processes probably by realization and the control a mode of developed cavitation in processable mediums. Realization a mode of developed cavitation is carried out due to the control of influence of reactive equivalent weight of the attached volume of the liquid medium directly contacting to the radiating surface of the working tool that results in change of resonant frequency of ultrasonic oscillatory system.
References
1. R. V. Barsukov, V. N. Khmelev, S. N. Tchyganok, A.N. Slivin, A.V. Shalunov. Research of influence cavitation mediums on work of the ultrasonic electronic generator. Material of conference « Measurements, automation and modeling in the industry and scientific researches ». - Biysk: AltSTU, 2003. - p.216-226.
2. R. V. Barsukov, V. N. Khmelev, V. V. Shutov. Measuring instrument of electric parameters of ultrasonic oscillatory systems. Material of conference «Scientific-and-engineering works of students», in 2 part. P.1. - Barnaul: AltSTU, 1997. - p.133
3. R. V. Barsukov, V. N. Khmelev, A. V. Knyazev. Measuring complex for studying work of ultrasonic oscillatory systems. Material of conference «Science and education: problems and aspects ». - Biysk: AltSTU, 1999. - p.10-12
