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Electrospray droplets generation and application
A. Jaworek, A.T. Sobczyk, A. Krupa, A. Marchewicz, A. Krella, T. Czech
Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-231 Gdańsk, Poland
Keywords: EHD spraying, electrospraying, thin solid film, nanoparticles
Electrospraying is a physical process of liquid atomization to fine droplets by electrical forces acting on the surface of liquid at a capillary nozzle outlet. Due to these forces the jet elongates to a fine filament and disperses into fine droplets. An electrospray system consists usually of a stainless-steel or glass capillary nozzle maintained at high electric potential and a counter electrode. By varying the voltage applied to the nozzle and adjusting the flow rate of the liquid, the charge and size of droplets can be controlled. Electrospraying technique allows production of micron-sized droplets that can be applied in the technology of fine particles (powders) production or for the deposition of thin solid films. The solid particles or film are obtained after solvent evaporation from electrosprayed solution or colloidal suspension which is electrosprayed. Because the droplets are electrically charged, the droplets coagulation is avoided. The advantage of charged spray in thin film deposition is that the aerosol disperses uniformly within the space between the nozzle and the substrate that facilitates thin and uniform film deposition.
The electrospraying has the following advantages over conventional mechanical atomizers:
1. Droplet size is smaller than that available from conventional mechanical atomizers, and can be in the nanometer range,
2. Standard deviation of the size distribution of droplets is usually small that means nearly uniform droplets are produced,
3. Charged droplets are self-dispersing in space (due to their mutual repulsion), resulting also in the absence of droplet coagulation,
4. Motion of the charged droplets can be controlled by electric field allowing focusing the aerosol,
5. The deposition efficiency of a charged spray on an object is order of magnitudes higher than for un-charged droplets.
The droplets produced by electrospraying are charged up to a fraction of the Rayleigh limit, which is the magnitude of charge on the droplet that produces the electrostatic force, which overcomes the surface tension force and leads to the droplet fission. This charge is given by the following equation:
2/130 )16(2 rQ lR εσπ=
in which σl is the liquid surface tension, ε0 is the
electric permittivity of the free space, and r is the droplet radius.
This paper discusses practical aspects of the applications of electrospraying to thin film deposition or fine powder production. It is shown that a mode of spraying plays a crucial role in properties of charged droplets: their electric charge and size, and their dispersion in the interelectrode space. Regarding thin film deposition, the mode influences the film quality: its uniformity, number and size of voids, etc. In the case of nanoparticles production, the mode of spraying defines monodispersity and morphology of these particles. Modes generating smallest droplets of uniform size distribution, such as cone-jet and multijet, are preferred in these technological processes.
Thin solid film or solid particles can also be produced from a precursor, which is decomposed at high temperatures in the aerosol phase or on the substrate to obtain the required product. For inorganic films or particles usually suspensions of metal oxide or sulfides are used. Metal chlorides, nitrates, or acetates dissolved in water, methanol, ethanol, or their mixtures, or metal-organic salts dissolved in organic solvents are used as precursors for metal-ceramic products.
It should be mentioned that electrospraying is also an effective way for nanocomposite films production. Nanocomposite in this specific case means a film formed from nanosized, chemically non-reacting components (particles, crystallites, nanofibers) differing in mechanical, electrical, thermal, physical and chemical properties, which have micro-sized or bulk properties different from their building blocks. Nanocomposite film can be produced by simultaneous spraying of these components or consecutive deposition of layer-by-layer of two or more materials onto the substrate.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A02
Electrohydrodynamic Atomization from a Conical Tip Emitter
C. Lübbert1, W. Peukert
1 and J.C.M. Marijnissen
2
1Chair of Particle Technology, University of Erlangen (FAU), Cauerstr.4, 09131, Erlangen, Germany
2Aerosol Consultancy, The Netherlands
Keywords: Electrospray, micro-dripping, printing
Electrohydrodynamic atomization in the cone
jet mode is well known as a method which is able to
provide narrow distributed aerosols in the size range
from a few nanometer for highly conductive liquids
such as ionic liquids (Ki Ku, 2009) and 100µm for
insulating liquids like oils (Ganan-Calvo,1997). The
major disadvantage of electrostatic atomization is the
low throughput of liquid which is typically in the
range between µL/h to mL/h and which can only be
increased by parallelization. Therefore, EHDA has
only limited application in technical particle
synthesis. For coating and characterization
applications, however, EHDA is an attractive tool
(Jaworek, 2009).
Here, we show that electrohydrodynamic
atomization of low conductivity liquids from solid
conical emitters (Fig. 1) might increase the field of
applications for the electrospray by outstanding spray
properties.
Figure 1: Photograph of a typical stainless steel
emitter and a schematic sketch of the arrangement
For triacetin as example we show, that:
1. The flow rate can be reduced to values much
smaller than the minimum flow rate required
for operation the stable cone jet mode.
2. The emission mode changes what we assume
to be the micro dripping mode. Here, the
droplet formation takes place directly at the
emitter tip.
3. Due to the outstandingly periodic emission
(Fig. 2) and mono-mobility of the produced
droplets, the particles can be kept aligned
“on the fly” over comparably long distances
in the few centimetre range which allows for
aligned particle deposition (Fig. 3).
The emission has been studied by light scattering of
the emitted particles close to the emitter tip and by a
high speed camera. The emission frequency
increased with increasing potential and decreasing
liquid flow rate. The required electric potential of the
emitter for stable emission decreased with decreasing
flow rate.
Figure 2: Light scattering signals as obtained in a
distance of three millimeters from the emitter tip.
Microdripping and intermittent microdripping at
0,3mL/h and the cone jet mode at minimum flow rate
of 2.3mL/h for the triacetin.
For low emitter voltages the microdripping
becomes intermittent and larger and smaller droplets
are emitted in a very regular alternating manner.
Furthermore, we studied the break-up of the
emitted particle jet as a function of the drift zone
field strength. The required electric field in the drift
zone showed good agreement with a simple
analytical prediction. The alignment of the particles
was evaluated by deposition patterns of particles
captured on silicon wafers at a distance of 3.5cm
from the emitter tip.
Figure 3: 17µm particles (patch diameter 22.4µm) as
captured at a distance of 3.5 cm from the emitter.
The outstanding monodispersity and monomobility
of the produced particles and the simplicity of
determining their particle size by measuring the
emission frequency make them ideal candidates as
well for calibration purposes as also for printing and
patterned deposition applications.
Ki Ku, B., L., Fernandez de la Mora,J. (2009). J.
Aerosol Sci.Technol.,Vol. 43, 241-249.
Ganan-Calvo, A. M., Davila J. and Barrero A.,
(1997), J. Aerosol Sci., Vol. 28, No. 2, 249-275.
Jaworek, A., Sobczyk A.T. (2008), J. Electrostat.
Vol. 66, No. 3-4, pp. 197-219.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A04
Effect of Liquid Electrical Conductivities and Neutralizer strength on EHDA
Sanjay Singh1, Arshad Khan2, Amruta Koli2, B.K Sapra2 and Y.S Mayya3 1Radiation Safety Systems Division, 2Radiological Physics and Advisory Division,
3Department of Chemical Engineering, IIT Bombay, Mumbai
Bhabha Atomic Research Centre, Mumbai-400085, India Email: [email protected]
Keywords: Size distribution, conductivity, neutraliser, EHDA
Introduction: Electro-hydrodynamic Atomization (EHDA) is the
phenomenon of disintegration of liquid surface on
application of electric potential with the ability to
produce fine size droplets with narrow size
distribution. The main parameters that affect the
process of atomization are the applied potential, the
liquid flow rate and physical properties of liquid,
such as the electrical conductivity, viscosity, surface tension, and dielectric constant (Fernandez de la
Mora & Loscertales, 1994). Liquid electrical
conductivity is the most important parameter for
controlling both stability of the electro-spray and size
of the droplet (Tang & Gomez, 1996, Hayati et al.,
1986). A few experimental investigations have been
carried out mainly with low electrical conductivity
and lower electrical permittivity solution. This study
focuses on behavior of electro spray of solutions
having higher conductivity. Additionally, effect of
droplet neutralizer strength has also been addressed.
Results and discussion: a) Effect of Liquid Conductivity: Experiments have
been performed using indigenously developed EHDA
system (Figure 1). The selected liquid for this study
was Ethylene Glycol, this choice was motivated to
investigate elctrospray behaviour of high electrical
permittivity and low vapour pressure liquid. The
generated aerosols were neutralized using Am-241
radioactive source and sizing was carried out using GRIMM make SMPS.
Figure 1: Schematic of the EHDA system used for the
study
Results shown in Figure 2 depict that the size
distribution shifts towards the lower side as the
conductivity increases. The mode decreases about 60
% in this case. This very high compared to a decrease
of 15 % for heptanes (Tang & Gamez, 1996).
0.00E+00
2.00E+04
4.00E+04
6.00E+04
8.00E+04
1.00E+05
1.20E+05
1.40E+05
1.60E+05
1.80E+05
10 100 1000
dN
/dLo
gD
p P
art
icle
/cc
Droplet Diameter (nm)
Size distribution of EG droplet at flow rate of 40 µµµµL/h
26 µS/cm
50 µS/cm
150 µS/cm
240 µS/cm
Figure 2: Change in the droplet size distribution for
varying conductivity of Ethylene Glycol solution
b) Effect of Neutralizer Strength: Ethylene Glycol
was sprayed at liquid flow rate of 40 mL/h and
electrical conductivity 150 µS/cm. The neutraliser
strength was varied form 0 to 8 µCi and results are
shown in Fig. 4. It is seen that aerosol concentration increases with increase of neutralization strength.
This is because the electrodepositing of neutralised
aerosols is reduced. Although, no significant shift of
mode of the distribution is seen, however distribution
became narrower with increase of liquid
conductivity.
0.00E+00
2.00E+04
4.00E+04
6.00E+04
8.00E+04
1.00E+05
1.20E+05
1.40E+05
10 100
DN
/dLo
gD
p (
Pa
rtic
le/c
c)
Droplet Diameter (nm)
No Neutralizer
3 micro-Ci
6 micro-Ci
8 micro-Ci
Figure 3: Droplet size distribution for varying
strengths of neutralizer
References: Fernandez de la Mora & Loscertales I. G. (1994),
J. Fluid Mech. 260, 155-184.
Tang K & Gomez A. (1996). J of Colloid and
Interface Science 184, 500-511.
Hayati I., Bailey A. I., Tadros Th. F. (1986),
J. Colloid & Interface Science, 117(1), 205 -221.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A06
Numerical simulations of evaporating electrosprays with Coulomb explosions
Ajith Kumar Arumugham-Achari1, Jordi Grifoll1 and Joan Rosell-Llompart 1,2
1Departament d'Enginyeria Química, Universitat Rovira i Virgili, Tarragona, 43007, Spain 2ICREA (Catalan Institution for Research and Advanced Studies), Barcelona, 08010, Spain
Keywords: electrospray, numerical simulation, spray dynamics, evaporation, Coulomb explosions
Presenting author email: [email protected]
Electrosprays are constituted of highly charged microdroplets which are created by the action of electrostatic forces on a liquid. The droplets' motion does work on the surrounding gas, causing it to flow (Arumugham-Achari et al., 2013). Here we consider how this induced gas motion influences droplet evaporation, and how the resulting changes in spray dynamics, in turn, modify the induced gas flow. The model is, thus, fully coupled. In addition, it considers droplets' Coulomb explosions. Any droplet below a critical diameter is transformed into vapor and highly mobile charged species (e.g., ions). In previous studies, solvent evaporation was considered, but for zero gas velocity and low volatility liquids (Wilhelm et al. 2003). Coupling a numerical scheme based on the vorticity-streamfunction method to describe the Eulerian gas flow dynamics, and a non-equilibrium Langmuir-Knudsen (LK) evaporation model for sprays (Miller et al., 1998) to a numerically efficient Lagrangian particle dynamics model (Grifoll and Rosell-Llompart, 2013), the vapor and "ion" source rates for the electrospray are computed. Thence, the vapor and ion-charge transport equations are solved through upwind discretization schemes, employing suitable boundary conditions. A final steady state solution is obtained iteratively through a series of coupled time-averaged pseudo-steady state solutions in all the three frameworks (for droplets, gas, and vapor transports). The computational time is greatly reduced by the suitable choice of droplet dynamics method, as well as by the use of the LK non-equilibrium evaporation model. Results We have applied this methodology to unimodal electrosprays that follow the scaling laws of Gañan-Calvo (2004). The droplets are assumed to undergo Coulomb explosions on reaching their Rayleigh limit. Figure 1(a) shows a snapshot of a simulated methanol electrospray evaporating under the induced air flow, where dots (droplets) change color upon reaching the first instance of Rayleigh limit. The resulting Coulomb explosions boost the production rate of "ions" charge (C/m3/s), shown in Fig. 1(b). Subsequent bands of increased "ion" rate correspond to second, third, etc Coulomb explosion events. In this simulation, exploding droplets are assumed to discharge 2% of their mass (Fernández de la Mora, 1996) with progenies carrying 70% of their Rayleigh charge limits (Hunter and Ray, 2009). At the final steady state, an electrospray of around 16000 droplets in the absence of evaporation
reduces to a system of around 8000 droplets plus "ionic" charge. Hence, these simulations reveal that significant evaporation is experienced by such a volatile electrospray, and further highlight the importance of accounting for Coulomb explosions, as well as gas flow. These results could be all the more important in the simulation of sources used for electrospray ionization mass spectrometry (ESI-MS), for which forced flow could be trivially incorporated into our model. Acknowledgements Ministerio de Educación y Ciencia (Spain), project DPI2012-35687. Generalitat de Catalunya, ref. 2009SGR-01529. A.K.A. acknowledges a Universitat Rovira i Virgili Ph.D. scholarship.
r (m)
0.000 0.005 0.010 0.015 0.020 0.025 0.030
z (m
)
0.000
0.005
0.010
0.015
0.020
0.025
r (m)
0.0050.0100.0150.0200.0250.030
0.000
0.005
0.010
0.015
0.020
0.025
0.030
(a) (b) Figure 1. (a) Snapshot of evaporating methanol electrospray droplets (d10= 8 μm) and induced air flow streamlines. (b) "Ion" charge source rate (from particles with d < 1 μm).
References Arumugham-Achari, A.K., Grifoll, J. and Rosell-
Llompart, J. (2013) J. Aer. Sci. 65, 121-133. Fernández de la Mora., J. (1996) J. Coll. Int. Sci. 178,
209-218. Gañán-Calvo, A.M. (2004) J.Fluid Mech. 507, 203-212a Grifoll, J. Rosell-Llompart, J. (2012) J. Aer. Sci. 47, 78-
93. Hunter, H.C. and Ray, A.K. (2009) Phys. Chem. Chem.
Phys. 11, 6156-6165. Miller, R.S., Harstad, K. and Bellan. J. (1998) Int. J.
Mult. Phys. Flow 24, 1025-1055. Wilhelm, O., Madler, L. and Pratsinis, S.E. (2003) J.
Aer. Sci. 34, 815-836.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A03
Metal recovery with ionic liquids in combination with electro-hydrodynamic
atomization
Dries Parmentier1,2
, Sybrand J. Metz1, Maaike C. Kroon
2, Jan C. M. Marijnissen
3, Luewton L F
Agostinho1,4
1 Wetsus Centre of excellence for sustainable water technology, Agora 1, 8900 CC Leeuwarden, The Netherlands 2Separation Technology Group Department of Chemical Engineering and Chemistry, Eindhoven University of
Technology, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands 3Aerosol Consultancy, Zaart 11, 4819 ED Breda, the Netherlands
4NHL University of Applied Sciences, Rengerslaan 10, 8900CB, Leeuwarden, The Netherlands
Keywords: Electrospray, Ionic Liquids, Metal Recovery
The use of ionic liquids (ILs) as a selective
extractant to recover metal salts from water is a
promising technique. This concept is based on
the principle that it is more energy efficient to
selective remove the minority compounds
(salt) from the saline liquid stream than
otherwise. Nowadays, metal extraction is done
by physical mixing of the water phase with
hydrophobic ILs (Parmentier et al, 2013 and
Wellens et al, 2013) In this research, we
investigated whether electro-hydrodynamic
atomization (EHDA, or electrospraying) can
effectively enhance metal extraction by ILs.
The experiments were conducted using a
double cylinder configuration and EHDA
conditions were adjusted to provide an
intermittent cone-jet mode (Grace and
Marijnissen, 1994), i.e. bigger IL + solution
interface. Results showed that whenworking in
the mentioned mode with a nozzle-ring
configuration, nozzle grounded, ring charged
at 5kV and volumes of 1.2 mL/h and 1 mL/h
IL and aqueous solution respectively, the
extraction efficiency using electrospray was
comparable to that of using physical mixing
(mechanical stirrer). However the selectivity
towards transition metals was improved with
EHDA.
This work was performed in the TTIW-
cooperation framework of Wetsus, centre of
excellence for sustainable water technology
(www.wetsus.nl). Wetsus is funded by the
Dutch Ministry of Economic Affairs. The
authors would like to thank the participants of
the research theme salt for the fruitful
discussions and their financial support.
Reference list:
1. Parmentier, D., S.J. Metz, and M.C.
Kroon, Tetraalkylammonium oleate
and linoleate based ionic liquids:
promising extractants for metal salts.
Green Chemistry, 2013. 15(1): p. 205-
209.
2. Wellens, S., et al., A continuous ionic
liquid extraction process for the
separation of cobalt from nickel.
Green Chemistry, 2013. 15(11): p.
3160-3164.
3. J. M. Grace, J.C.M.M., A review of
liquid atomization by electrical means.
Journal of Aerosol Science, 1994.
25(6): p. 1005-1019.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A08
Computational Modelling Techniques for Electrospray Atomisation
Narvez-Munoz, C. 1, Lajhar, F.1. Bargiacchi M.1, Schiava D'Albano G.G.2, Ryan, C.2, Cooper D.1, Watkins, P.1, Revell A.1 and Smith K.1
1 School of Mechanical Aerospace and Civil Engineering , University of Manchester, M13 9PL, Manchester, UK
2 School of Engineering and Materials Science , Queen Mary University of London, E1 4NS, London, UK.
Keywords: electrospray, computational modelling, experimental. Electrospray atomization is a technique whereby strong electric fields (~106 V/m) are applied to a fluid in order to generate an isotropic and ultra fine spray of the fluid. Owing to the uniform size of the spray droplets and the high degree of control over droplet size this technique can be exploited in a wide range of applications from spacecraft propulsion (Alexander, 2007) to high resolution printing (Paine, 2007) and novel drug delivery systems (Gañan Calvo, 1999) Spray properties can be controlled by the applied field. Of particular note is the influence of the electric field on the mass flow rate in an electrospray. Previous experimental work (Ryan, 20012; Ryan 2009; Smith, 2006) has established that the applied field can be used to control the flow rate of an electrospray and thus provide fine control over the spray properties, such as emitted droplet size, which would be highly desirable in a range of applications. However electrospray is a complex multiphase flow that involves strongly coupled electric and fluid flow fields and liquid/gas interfaces that cannot be solved purely by analytical techniques (Ryan, 2009). This results in a need for accurate computational models that can be used to predict spray behaviour for specific geometric and conditions. Ongoing work on the development of a Lattice Boltzmann model (LBM) using the open source software PALABOS, as well as models developed from commercial packages such as COMSOL, STAR CCD and ANSYS are discussed and compared to experimental data. One of the attractions of the LBM is the direct manner in which multiphase flow can be captured. The inherent multi-scale nature of this phenomenon (from millimetres down to almost molecular level) adds complexity to any numerical analysis due to mesh refinement however already established refinement algorithms for LBM may be employed (Mehl, 2011). In the LBM work the Shan-Chen model (Shan, 1993) is used to describe the liquid / gas interface and the coupled electric field is solved via an LBM-like algorithm. Figure 1 illustrates a Taylor cone like formation simulated using this method.
Figure 1. Simulation of Taylor cone using LBM method in PALABOS. Alexander M.S., Smith K, Paine M.D., Stark J.P.
(2007) Journal of Propulsion and Power. 23(5)pp1042-1048.
Gañan Calvo A.M, (1999) Journal of Aerosol Science. 30(7), 973
Mehl, Neckel & Neumann (2011) Int. J. Numer. Meth. Fluids; 65:67–86
Paine M.D., Alexander M.S., Smith K, Wang M.J., Stark J. (2007) Journal of Aerosol Science. 38.pp315-324.
Ryan C.N., Smith K, Stark J.P.. (2012). Journal of Applied Physics. Vol. 112. Issue 11. 114510.
Ryan C.N., Smith K, Alexander M.S., Stark J.P. (2009) Journal of Physics D: Applied Physics. 42.155504.
Shan, Chen (1993) Phys Rev E 47, 1815-1819 Smith K, Alexander M.S., Stark J.P. (2006) Physics
of Fluids. Vol. 18. 09214.
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A01
Demonstration model for the liberation of energy during the break-up of intermolecular
bonds in water by electrospraying.
Jan C.M. Marijnissen
1 , Luewton L.F. Agostinho
2, Gerrit Oudakker
3 and Sjaak Verdoold
4
1 Aerosol Consultancy, Zaart 11, 4819 ED Breda, the Netherlands
2 NHL, University of Applied Sciences, Rengerslaan 10, P.O. Box 1080, 8900 CB Leeuwarden, the
Netherlands 3 Tetradon b.v. The Netherlands
4 Sciver, Wilgenstraat 38, 2861 TP Bergambacht, the Netherlands
Keywords: Electrospraying, electrospray turbine, hydrogen bonds, liberation of energy.
Hathaway e.a (1998) and Graneau e.a. (2000)
report that pulsed high current arcs in water
result in water droplets, which exhibit more
kinetic energy than the electrical energy
supplied to create the explosion. They claim
that the liberation of the extra energy is the
release of potential energy in hydrogen bonds
in water. In case of water arc explosions only
indirect energy measurements can be
performed.
To make direct energy measurements possible
Verdoold (2012) and Graneau e.a. (2011) used
Electro HydroDynamic Atomization (EHDA
or electrospraying) to break bulk water up
into small droplets. In the experiments
electrostatic forces (together with other forces)
create a thin jet of water, which breaks up into
small droplets. By measurements and/or
calculations a complete energy balance,
including maximum uncertainties, could be
made. The energy gain for the break-up of
water was demonstrated very clearly. For the
break-up of ethanol (which always contains
some water) it was also apparent, but the gain
was less.
The next type of experiment is towards
demonstrating the possibility of generating
usable energy. For this purpose a table top
electrospray turbine is built, in which the
movement, created by up-breaking jets of four
water electrosprays, is brought over to the
rotor of a small generator. The electrospray
nozzles are positioned symmetrically in a
plane perpendicular to the rotor axis with their
jet outlets on a circle. Both the power input by
the High Voltage (HV) source and the power
output from the generator are measured. The
final goal of the experiment is a system, in
where the energy from the generator will
power the HV source, thus that the liberation
of the potential energy in the hydrogen bonds
in the water is made available.
The building up of the experimental turbine
has been made possibe by Elstatik
(Elektrostatik/Explosionsschutz,Odenthal,
Germany)
References:
G. Hathaway, P. Graneau and N. Graneau, J.
Plasma Phys. 60, 775 (1998)
P. Graneau, N. Graneau, G. Hathaway, and
R.L. Hull, J. Plasma Phys. 63, 115 (2000)
S. Verdoold, PhD thesis, TU Delft (2012)
N. Graneau, S. Verdoold, G. Oudakker, C.U.
Yurteri and J.C.M.Marijnissen, J. Appl. Phys.
109, 034908 (2011)
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A07
Characterization of droplets produced by electrospray emulsification
Anne Kamau1, Jan C.M. Marijnissen
2, Luewton L.F. Agostinho
1,3
1 Wetsus Centre of excellence for sustainable water technology, Agora 1, 8900 CC Leeuwarden, The
Netherlands 2 Aerosol Consultancy, Zaart 11, 4819 ED Breda, the Netherlands
3 NHL, University of Applied Sciences, Rengerslaan 10, P.O. Box 1080, 8900 CB Leeuwarden, the
Netherlands
Keywords: Electrospray, emulsification, droplet characterization
Electrohydrodynamic atomization (EHDA)
provides a novel way to enhance the dispersion
of droplets in an emulsion and improve its
quality. The effectiveness of this technique is
demonstrated in this study. Various liquid-
liquid combinations for emulsions were
selected to determine their behavior during
EHDA. For the liquid pair that produced a
stable cone-jet mode, it was further
characterized in terms of the droplet diameter
and size distribution, the emulsion quality,
electrical energy requirements and the
suitability of applying theoretical scaling laws
to predict the droplet size and spray current.
The ethylene glycol-hexane system was found
to generate stable cone-jet mode between 6 and
8 kV for a range of flow rate of 0.5- 4.0 mL/h.
In this mode, the measured average droplet
diameter was found to range from 2- 14μm and
a bimodal size distribution was observed. The
droplet dispersion into the continuous phase
was enhanced by the electric field and the self-
repulsion. The stability of the droplets in the
continuous phase was found to increase in the
presence of a surfactant (Tween 80).
Preliminary results showed that the electric
energy requirements were in the scale of
106J/m
3. The average droplet diameter was
found to scale with the liquid flow rate as in
d~Q0.33
and the dimensionless current scaled
with the flow rate by I/I0~ (Q/Q0)0.5
. This study
establishes that EHDA can be effectively used
in the preparation of emulsions.
This work was performed in the TTIW-
cooperation framework of Wetsus, centre of
excellence for sustainable water technology
(www.wetsus.nl). Wetsus is funded by the
Dutch Ministry of Economic Affairs. The
authors would like to thank the participants of
the research theme salt for the fruitful
discussions and their financial support.
Reference List
Barnes and I. Gentle, Interfacial Science - An
introduction. Oxford University Press. 2005
Mc Clements, Critical review of techniques
and methodologies for characterization of
emulsion stability. Critical Reviews in Food
Science and Nutrition. 2007. 47(7): p 611-649
J. F. Hughes and I. D. Pavey, Electrostatic
emulsification. Journal of
electrostatics.1981.10: p 45-55
Geerse, Applications of electrospray: From
people to plants. PhD Theis.2003
Cite abstract as Author(s) (2014), Title, Aerosol Technology 2014, Karlsruhe, Abstract T270A09