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L. TATOULIAN , J-P. BORRA

Effect of nozzle geometry on operating ranges (V,Q) in cone-jet mode of EHD Atomisation. 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. OUTLINE. Goals and means Experimental set-up

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L. TATOULIAN , J-P. BORRA

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  1. Effect of nozzle geometry on operating ranges (V,Q) in cone-jet mode of EHD Atomisation 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.

  2. OUTLINE • 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

  3. GOALS and MEANS 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)

  4. Without Electric Field With Electric Field mm NOZZLE NOZZLE Capillary pressure EHD EQUILIBRIUM for CONE & JET FORMAT° Capilary pressure Electric pressure (normal and tangential) Viscous stress Hydrodynamic and gravity pressures HYDRODYNAMIC JET BREAK-UP Charged droplets Neutral droplet Fd ~ µm Fd ~ mm Electro-Hydro-Dynamic Atomisation : Physical principle

  5. Experimental SET-UP Production system Investigation technique DC High voltage supply Oscilloscope R=10Mohm Liquid pump HV probe NOZZLE Measuring volume Phase Doppler Anemometry (PDA) Laser beam SPRAY PLANE Size measurement

  6. Succession of EHDA spraying modes 5 ml/h & Dout = 2 mm DVcone-jet Vmin Cone-jet mode 7 kV Vmax 12.5 kV dripping, µdripping, intermitent cone-jet . Multi Cone-jet Mode V

  7. dN dLogdp 0.1 1 10 (V,Q) operating ranges Q fixed CONE-JET MODE Vincreases V fixed Unstable modes Unstable modes Q increases VARICOSE KINK dN / dLog dp Monodispersity Polydispersity VARICOSE (axysimetric) KINK (asymetric) dp Particle diameter (µm) 0.1 1 10

  8. Outer nozzle diameter 8mm 2mm 3.1mm r2 r1 V,Q fixed r1; r2 Charge density Dout & Scone FOR CONE JET MODE - higher Vmin and Qmin - larger (V,Q) ranges IN CONE JET MODE - No dependance of DQ(VARICOSE) - Dependance of DQ(KINK) as outer diameter increases with outer diameter

  9. 1.3mm 0.4mm r V,Q fixed Din r Inner nozzle diameter 1) - Vmin sligthly increases - Qmin slightly decreases - No dependance of (V,Q) ranges 2)Possible obstruction of nozzle tip 3)Stabilisation of liquid jet as inner diameter decreases

  10. Nozzle geometry: a way to control the droplet size ? Dout = 8mm Dout = 3.1mm Dout = 2mm • 1) Dp = f (Qliq n) • 2) A Qliq fixe, Dp # f(D out) • 3) DQ (VARIOSE) • => Dd var. • 4) DQ(KINK) • => Dd kink # f( Dout) Dp theoretical ~ Q liq 1/3 with Dout KINK VARICOSE Qmax varicose = 9 ml/h

  11. CONCLUSIONS AND PERSPECTIVES • CONCLUSIONS • For a given conductivity, cone-jet mode exists only within an appropriate (V,Q) operating ranges • Outer nozzle diameter increases (V,Q) ranges • DQ(varicose)independant of nozzle geometry • DQ(kink) is larger as outer diameter increases • APPLICATIONS • Thin film Deposition at Atmospheric Pressure in air • Powder Production

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