Electrical and Spectral Characteristics of Falling Film DBD in different gases

B. M. Obradovi , V. Kova evi , and M. M. Kuraica

Faculty of Physics, University of Belgrade, PO Box 368, Belgrade, Serbia

1. IntroductionA coaxial dielectric-barrier-discharge was designed asatmospheric non-thermal plasma reactor for treatment of various water solutions [1]. In this reactor water forms a falling film which is in direct contact with plasma, see Fig1. Such reactor design allowed successful removing of phenols and arsenic from water [2-4]. This reactor is veryefficient because the plasma that is formed above the waterbesides ozone also has UV radiation, radicals (e.g. OH),excited atoms (e.g. O) and molecules, electrons and ions.Existence of so many reactive species in plasma and in water is the reason why electrical discharges that haveplasma in direct contact with water solutions are veryinteresting for many researches. Although the main interestin investigation of this type of discharges is application,there is also curiosity about the difference between the discharges in gas and gas with water. This paper presentsour results in investigation of electrical and spectroscopiccharacteristics of falling film DBD in air, nitrogen, argonand helium.

-20 -15 -10 -5 0 5 10 15 20

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-50

0

50

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Helium

Q (

C)

U (kV)

Helium with water

U (kV)

Fig. 2. Voltage/charge Lissajous figures for discharges in helium

and helium with water.

2. ExperimentA schematic diagram of experimental setup is shown inFig 1. Water flows up through a vertical hollow cylindricalelectrode and flows down making a thin dielectric filmover the electrode. Filamentary discharge is generated inthe protruding gas within 4mm gap between the dielectric

and the water layer by applying voltage of up to 20 kV at50 Hz. For electric characterization of the discharge we used voltage/charge Lissajous figures which contain in-formation about its energy, ignition and decay. One ex-ample of the difference between discharges in helium and helium with water for three values of applied voltages is shown on Fig 2. Analyzing the figure one can concludethat discharge with water has much larger breakdownvoltages and energy consumption. This can be explainedby decreasing of helium metastable density due toquenching with water molecules. Changes of breakdownvoltages for the discharges in argon, nitrogen and air areless pronounced.

References[1] M.M. Kuraica, B.M. Obradovic, D. Manojlovic, D.R.Ostojic and J. Puric, Vacuum, 73, 705 (2004).

[2] D. Manojlovi , D.R. Ostoji , B.M. Obradovi , M.M.Kuraica, V.D. Krsmanovi and J. Puri , Desalination, 213,116 (2007)

[3] B.P. Doj inovi , D. Manojlovi , G.M. Rogli , B.M.Obradovi , M.M. Kuraica and J. Puri , Vacuum, (2008)

[4] D. Manojlovi , A. Popara, B.P. Doj inovi , A. Nikoli ,B.M. Obradovi , M.M. Kuraica and J. Puri , Vacuum(2008)

wat

er

To spectrometer

N2, Ar, He

Fig 1. Experimental setup