Analyzing known liquid pulverizers which are driven by piezoelectric transducers we obtain that almost all of them are using longitudinal vibrating mode. So we decide to create a dual-effect system which will act as a pump and sprayer. Using FEM analysis the proposed model was analyzed and it is natural longitudinal frequency was found. Modeling results (frequency, displacement) were compared with real parameters of working transducer and they were nearly the same. The main study object was to find how fluid moves through a capillary under ultrasonic vibrations. The experimental results are populated below

P. Vasiljev

English

Journal of Vibroengineering

  VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 2012. VOLUME 14, ISSUE 2. ISSN 1392-8716 
489
771. Ultrasonic systems for liquid pulverizer 
 
Piotr Vasiljev 
Vilnius Pedagogical University, Lithuania 
E-mail: piotr.vasiljev@vpu.lt 
 
(Received 11 September 2011; accepted 14 May 2012) 
 
Abstract. Analyzing known liquid pulverizers which are driven by piezoelectric transducers we 
obtain that almost all of them are using longitudinal vibrating mode. So we decide to create a 
dual-effect system which will act as a pump and sprayer. 
Using FEM analysis the proposed model was analyzed and it is natural longitudinal 
frequency was found. Modeling results (frequency, displacement) were compared with real 
parameters of working transducer and they were nearly the same. The main study object was to 
find how fluid moves through a capillary under ultrasonic vibrations. The experimental results 
are populated below. 
 
Keywords: ultrasonic, piezoelectric, mechanics, cavitations. 
 
Introduction 
 
The possibility of spraying liquids using ultrasonic fluctuations has a large appliance field, 
such as spraying of drugs, wet cleaning, air conditioning, accelerating chemical reactions, 
spraying fuel, molten chemicals for the manufacture fine powders, etc. [1], [2]. 
Quickly developing nano-technology also may find some application of such system for 
spraying nano particles, to make a smooth thin layer, etc. [3]. 
Because of all things mentioned above it is clear that such a system can find it is application 
in scientific research area and also in civil everyday living. 
 
Principle of ultrasonic spraying 
 
Ultrasonic spraying is based on ripping particles by means of cavitation, since small liquid 
particles have small mass they can fly away from the source. So to make liquid spray we need to 
generate a standing wave in elastic body (liquid). Depending on liquid thickness above the 
transducer it is more power needed to create required amplitude to rip some particles from the 
man liquid mass and push it into air. 
 
 
Fig. 1. The separation of droplets from the waves crests 
 
As soon as cavitations threshold, has been reached surface particles starts to separate and 
form a small droplets (Fig. 1.) [2], the average size of aerosol droplets depends on actuators 
driven frequency [1]: 
 
k
aD λ⋅=  (1) 
 
where a - is a proportionality factor, that depends on the liquids viscosity; λk - the length of the 
capillary waves, which is equal to: 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 2012. VOLUME 14, ISSUE 2. ISSN 1392-8716 
490
,
8
3
2f
k
ρ
πσ
λ =
  (2) 
 
where σ - coefficient of liquids surface tension; ρ - liquids density; f - frequency of ultrasonic 
fluctuations. 
From (2) formula follows, that in order to reduce the size of sprayed particles, it is necessary 
to increase the frequency. Depending on frequency particle size may vary from 3 µm to 80 µm 
with respective frequencies of 10 MHz to 20 kHz. 
 
 
Fig. 2. High-frequency ultrasonic dispersion: 1 - tank, 2 - piezoelements, 3 - liquid, 4 - sprayed liquid 
 
 
 
      a)                b) 
Fig. 3. Schematics (a) and real view (b) of sprayer: 
1 - transducer, 2 - piezoelement, 3 - counterweight, 4 -flow channel, 5 - inlet port, 6 - sprayed liquid 
 
Most simple sprayer can be made of tank and two piezoelectric discs polarized by thickness. 
By applying resonance frequency voltage on electrodes liquid can be sprayed from the surface as 
shown on (Fig. 2). 
Mostly, to spray liquid a so called Langiven pack is used. In Langevin pack a piezoelectric 
rings are used instead of discs. The whole system consists of transducer, piezoelectric rings, and 
counterweight which are bolted tightly together. Thus the mechanical displacement significantly 
increases on the transducers end. Because of enormous amplitude difference a Langevin pack 
with a transducer is used in such systems and much more other systems where mechanical 
amplification is needed (Fig. 3). 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
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As literature [4], says the minimum displacement needed to spray liquid from surface is 15 
µm. Therefore used transducer to amplify mechanical displacement and make it enough for 
spraying. However, that reduces the spraying area and productivity. 
 
Ultrasonic sprayers working in closed space 
 
In some cases, liquids need to be sprayed closed space. We studying two types of ultrasonic 
sprayers, which are used not only for spraying liquids, but also delivers liquid to spraying zone. 
The first type – sprayer–pump, pumping is based on ultrasonic capillary effect, when liquid 
is forced to raises up in a capillary tube by cavitation created pressure. By the end of the tube it 
is sprayed. We call such ultrasonic system, a system with a static capillary. 
The second type – is inhaler where capillary is appears in-between vibrating system and 
input element. Such capillary constantly changes it is size (dynamic capillary). 
We have previously proposed ultrasonic spraying systems, working in closed space [5]. Also 
there are some open sprayers – inhalers, full researches on this type of sprayers was not made. 
 
Ultrasonic capillary effect 
 
Transportation – liquid pumping based on the ultrasonic capillary effect [6]. A number of 
tests were made using capillary tubes. Longitudinal and transverse vibrations were applied on a 
glass capillary however liquid pumping was notified using longitudinal vibrations. The glass 
tube was used with a most effective inner diameter according to [6] (0.4 mm.) external diameter 
was (3 mm). 
 
         
a)                                                       b) 
Fig. 4. Colored water raises up in a capillary tube under longitudinal vibrations (a) and a model 
of the same system made using FEM method (b) 
 
The glass tube was glued to ultrasonic transducer. Tube length was adjusted to fit the 
transducers created fluctuations so at the end of the tube we have maximum amplitude (Fig. 4b). 
Fig. 4b shows the modeling result of proposed transducer with a glass capillary. Transducer 
is made of aluminum alloy D16T. It uses ring type piezo elements with such geometry D - 12.7, 
d – 5.5, h-2 mm, type – PI-181. Natural frequency is 62 kHz, burdened with glass capillary 61 
kHz. 
Fig. 5 shows, relation between capillary inner diameter and maximum liquid raise inside it 
with constant power. Four different liquids were tested, almost all have the same values, thus we 
can say that rising level depends mostly on inner capillary inner diameter. 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
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Fig. 5. Liquid rise, level dependence on capillary diameter 
 
During tests with transverse vibrations the level of raised liquid was the same as without 
vibrations. Such a result allows us to propose that enormous amplitudes created at the end of 
capillary tube are needed to create cavitation and as a result liquid raises in a capillary tube. 
 
Sprayer with a static capillary 
 
Researching ultrasonic capillary effect a few tests were made with a static capillary. Such a 
system is shown on Fig. 6 – ultrasonic sprayer. 
 
    
Fig. 6. Half size view schematics and a picture of real working device: 1 - liquid, 2 - vessel,                       
4, 10 - capillary, 5 - spraying surface, 6 - actuator, 7 - piezoelement, 8 - vessel with liquid, 9 - fastening 
 
Sprayer consists of transducer (6), with drilled capillary holes (4, 10) in it. Through the hole 
(10) the liquid enters to vertical capillary hole 4, which, under the influence of ultrasonic 
vibrations, rises on the spraying surface (5). This piezoelectric system is working at resonance 
frequency on the firs mode of longitudinal vibrations. The spraying intensity depends on voltage 
applied to piezo elements. 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
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It should be noted, that liquid at the spraying surface acts as a load to vibrating system 
forcing it is resonance frequency to low, and impedance is rising up (Fig. 7). 
 
Fig. 7. Impedance-frequency characteristics of piezoelectric actuator 
 
Sprayer with a dynamic capillary 
 
Actuators with dynamic capillary are less influenced by the liquid. The capillary is 
constantly varying as input rotor moves at the transducer. The capillary accidently appears in-
between transducer inner wall and rotor. The maximum amplitude of the transducer at it is end 
liquid moves to it through a capillary and eventually sprayed when reaching the top (Fig. 8). 
The actuator is half-wave length, material D16T, the vibration is produced by two 
piezoelectric rings with size of 18×9×2mm, type – PI 181. Rotor for dynamic capillary is made 
from polyurethane. 
 
          
              a)                                    b)                                                       c) 
Fig. 8. Piezoelectric actuator with dynamic capillary: 
a – general view, b – actuator with polyurethane rotor, c – cross-section view 
 
By applying voltage to actuator it is starts to vibrate, the rotor spins and forms a capillary 
between its self and actuators walls. Using this capillary combined with fluctuations liquid is 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 2012. VOLUME 14, ISSUE 2. ISSN 1392-8716 
494
raising up and appears at the top end. The maximum amplitude at top end prays the liquid into 
air. 
Fig. 9 shows the photo of proposed device with actuators top view and vessel for liquid. Fig. 
10 shows actuators model made using FEM – natural fluctuations. 
 
       
Fig. 9. General view – actuator built into the vessel Fig. 10. Natural fluctuations of actuator. FEM 
model 
 
Displacement measurement on the top end of actuator was made using laser vibrometer 
OFV-5000. 
 
 
 
Fig. 11. Displacement distribution on the actuators top surface 
 
As shown on Fig. 11 the green ring on the end of transducer represents maximum 
fluctuations. When liquid appears on this ring or near, it is sprayed off. 
 
 771. ULTRASONIC SYSTEMS FOR LIQUID PULVERIZER. 
P. VASILJEV 
 
 
 
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495
Conclusions 
 
1. As technology develops fast enough it is necessary to proceed performing such tests seeking 
to invent new ultrasonic spraying systems. 
2. The important thing mentioned in this paper is that only longitudinal (high amplitude) 
fluctuations are causing forces to the liquid to move through a capillary tube. 
3. Offered ultrasonic systems with static and dynamic capillary were successfully realized in 
sprayers working in a closed space. 
 
Acknowledgements  
 
This research was supported by the Lithuanian Science Council, Scientific Group Project  
No. MIP-11089.  
 
References 
 
[1] Хмелев В. Н., Шалунов А. В., Шалунова А. В. Ультразвуковое распыление жидкостей. Алт. 
ГТУ Бийск, 2010, 192 с., (in Russian).  
[2] Bubulis A. Theoretical background for the supply and dosing mechanisms under elastic vibrations. 
Ultragarsas, 1(42), 2002, p. 18-21. 
[3] Ultrasound Company [Electronic resource]. Sono-Tek Corporation: http://www.sono-tek.com/ 
[4] Экнадиосянц О. К. Получение аэрозолей. Физические основы ультразвуковой технологии, под 
ред. Л. Д. Розенберга, Москва: Наука, 1970, (in Russian).   
[5] P. Vasiljev, L. Vasiljeva Ultrasound Sprayer. Patent, LT 3845B, 1996. 
[6] Прохоренко П. П. Ультразвуковой капиллярный эффект. Минск: Наука и техника, 1981, 135 с., 
(in Russian). 


Ultrasonic systems for liquid pulverizer

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