CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

L. TATOULIAN, J-P. BORRA

Laboratoire de Physique des Gaz et des Plasmas, UMR 8578, Ecole Supélec, Plateau de Moulon, 91192 Gif-Sur-Yvette Cedex, France.

Effect of nozzle geometry on operating ranges (V,Q) in

cone-jet mode of EHD Atomisation

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

• Goals and means

• Experimental set-up

• Operating ranges (V,Q) for given geometry & conductivity

• Droplet properties

• Influence of nozzle geometry on (V,Q) operating ranges

• Conclusions and applications

OUTLINE

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

GOALS

• Control the size distribution of droplets by nozzle geometry:

– Operating ranges (Voltage (V)-liquid flow rate (Q)) of EHDA in cone-jet mode, for a given nozzle geometry

– Influence of nozzle geometry on operating ranges (V,Q)

MEANS

• Nozzle (Dout = [1.8-8] mm; Din = [0.4-1.3] mm)

• Liquid pump (Q = [0-100] mL/h)

• DC high voltage supply (V = [0-15] kV)

• Diagnostics (visual, electric & granulometric)

GOALS and MEANS

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

Electro-Hydro-Dynamic Atomisation : Physical principle

Neutral droplet

Hydrodynamic and gravity pressures

Without Electric Field

Capilary pressure

Viscous stress

NOZZLE

mm

d ~ mm

Charged droplets

Electric pressure (normal and tangential)

With Electric Field

NOZZLE

Capillarypressure

d ~ µm

EHD EQUILIBRIUM for CONE & JET FORMAT°

HYDRODYNAMICJET BREAK-UP

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

Experimental SET-UPProduction systemProduction system Investigation techniqueInvestigation technique

DC High voltage supply Oscilloscope

Liquid pump HV probe

SPRAY

NOZZLE

PLANE

R=10Mohm

Phase DopplerAnemometry

(PDA)Laser beam

Size measurement

Measuring volume

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

0

20

40

60

80

100

120

140

0 5 10 15Voltage (kV)

Cur

rent

(nA

)

ETHANOL

Succession of EHDA spraying modes

Vcone-jet

V

Vmin Cone-jet mode7 kV

Vmax12.5 kV

dripping, µdripping, intermitent cone-jet .

Multi Cone-jet Mode

5 ml/h & Dout = 2 mm

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

0

2

4

6

8

10

12

14

16

0 5 10 15Liquid flow rate (ml/h)

Vol

tage

(kV

)

Dripping

Multi cone-jet

CONE-JET MODE

(V,Q) operating ranges

Q fixed

V fixed Unstable modes

Unstable modes

Vincreases

Q increases

VARICOSE(axysimetric)

KINK(asymetric)

MonodispersitydNdLogdp

0.1 1 10dp Particle diameter (µm)

dN / dLog dp

Polydispersity

0.1 1 10

KINKVARICOSE

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

Outer nozzle diameter

FOR CONE JET MODE- higher Vmin and Qmin- larger (V,Q) ranges

IN CONE JET MODE- No dependance of Q(VARICOSE)

- Dependance of Q(KINK)

r1

2mm 3.1mm 8mm

DoutV,Q fixed r1; r2

SconeCharge density

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100

Liquid flow rate (ml/h)

Vol

tage

(kV

)

KINKVARICOSE

CONE-JET MODE

Qmax varicose = 9mL/h

&

as outer diameter increases

with outer diameter

r2

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

Inner nozzle diameter

01234567

0 0,5 1 1,5 2 2,5Liquid flow rate (ml/h)

Vol

tage

(kV

)

VARICOSE KINK

CONE-JET MODE

1) - Vmin sligthly increases - Qmin slightly decreases - No dependance of (V,Q) ranges 2) Possible obstruction of nozzle tip3) Stabilisation of liquid jet

as inner diameter decreases

r

1.3mm 0.4mm

V,Q fixedrDin

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

Nozzle geometry: a way to control thedroplet size ?

0

5

10

15

20

0 10 20 30 40Liquid flow rate (ml/h)

Vol

tage

(kV

)

0

10

20

30

40

50

0 10 20 30 40Liquid flow rate (ml/h)

Diam

eter (

µm)

VARICOSE KINK

Dout = 8mmDout = 3.1mmDout = 2mm

1) Dp = f (Qliq n)

2) A Qliq fixe, Dp # f(D out)

3) Q (VARIOSE) => d var.

4) Q(KINK) => d kink

with Dout

# f( Dout)

Qmax varicose = 9 ml/h

Dp theoretical ~ Q liq 1/3

CNRS/L.P.G.P./Equipe DECHARGE ELECTRIQUE ET ENVIRONNEMENT 5th Electrohydrodynamics International Workshop

• CONCLUSIONS

– For a given conductivity, cone-jet mode exists only within an appropriate (V,Q) operating ranges

– Outer nozzle diameter increases (V,Q) ranges

– Q(varicose) independant of nozzle geometry

– Q(kink) is larger as outer diameter increases

• APPLICATIONS

– Thin film Deposition at Atmospheric Pressure in air

– Powder Production

CONCLUSIONS AND PERSPECTIVES