Electrospray droplets generation and · PDF file · 2014-05-27Electrospray droplets...

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.


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.


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.


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.


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.


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)


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


Electrospray droplets generation and · PDF file · 2014-05-27Electrospray droplets...

Documents

Transcript of Electrospray droplets generation and · PDF file · 2014-05-27Electrospray droplets...