Dynamic Plasma-Liquid System with Discharge in Reverse Vortex Flow of Tornado Type

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1 20 International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011 Dynamic Plasma-Liquid System with Discharge in Reverse Vortex Flow of Tornado Type O. A. Nedybaliuk, V. Ya. Chernyak, S. V. Olszewski, and E. V. Martysh Department of Physical Electronics, Taras Shevchenko National University of Kyiv, Ukraine Abstract When a liquid is a subject to sufficiently strong vortex air flow, it can be induced the special features for discharge in such system. Here, we reported experiments and calculating that enable a comprehensive picture of the distinctions between such type of discharge and other discharge at high pressure. Behavior of this discharge is operated by simple macro-parameters. It has, probably, both fundamental and practical implications. Keywords Plasma, plasma-liquid system, discharge, temperature, reverse vortex flow I. INTRODUCTION Atmospheric pressure plasmas can be created by various types of discharges: transverse arc [1]; discharge in gas channel with liquid wall [2] and others. But most of them aren t sufficiently stable. Stabilization of discharge in the high pressure powerful plasmatron is attained by vortex flow of gas [3]. In the low-powered high pressure discharges the reverse vortex flow tornado type can be used for the space stabilization [4]. Previous investigations were performed only for discharges with solid-state electrodes. And we haven t any information about discharges with liquid electrodes, which were stabilized by gas reverse vortex flow. II. EXPERIMENTAL SETUP Plasma-liquid system reactor was prepared with the DC discharge in a reverse vortex gas flow of tornado type with a "liquid" electrode (TORNADO-LE) as is shown in Fig. 1. It consists of a cylindrical quartz vessel (1) by diameter of 90 mm and height of 50 mm, sealed by the flanges at the top (2) and at the bottom (3). The vessel was filled by the work liquid (4) through the inlet pipe (5) and the level of liquid was controlled by the spray pump. The basic cylindrical T-shaped stainless steel water-cooled electrode (6) on the lower flange (3) made from stainless steel is fully immersed in the liquid. The electrode on the upper flange (2) made from duralumin had a special copper hub (11) with the axial nozzle (7) by diameter 2 mm and length of 6 mm. The gas was injected into the vessel through the orifice (8) in the upper flange (2) tangentially to the cylinder wall (l) and created a reverse vortex flow of tornado type, so the rotating gas (9) went down to the liquid surface and moved to the central axis where flowed out through the nozzle (7) in the form of jet (10) into the quartz chamber (12). Since the area of minimal static pressure above the Corresponding author: Oleg Nedybaliuk address: oanedybaliuk@gmail.com Presented at the Third Central European Symposium on Plasma Chemistry, in August 2009 liquid surface during the vortex gas flow is located near the central axis, it creates the column of liquid at the gasliquid interface in the form of the cone with the height of ~ 5-10 mm above the liquid surface (without electric discharge). The voltage was supplied between the upper electrode (2) and the lower electrode (6) in the liquid with the help of the DC power source (PS) powered up to 10 kv. Two modes of the discharge operation were studied: the mode with liquid cathode (LC) and the mode with solid cathode (SC): + is on the flange (2) in the LC mode, and - is on the flange (2) in the SC mode. The conditions of breakdown in the discharge chamber were regulated by three parameters: by the level of the work liquid; by the gas flow rate G; and by the value of voltage U. The ignition of discharge usually began from the appearance of the axial streamer; the time of establishment of the self-sustained mode of operation was ~1-2 s. The range of discharge currents varied within ma. The pressure in the discharge chamber during the discharge operation was ~ 1.2 bar; the static pressure outside the reactor was ~ 1 bar. The elongated ~ 5 cm plasma torch (10) was formed during the discharge burning in the camera. The high-speed photo camera Nikon L100 was used in supervision for the process of discharge ignition and existence. The emission spectroscopy was used for plasma diagnostics. Emission spectra were measured with system that was made up of light guide (13), spectrum device with CCD-line and PC. The spectrometer worked in range nm with resolution 0.6 nm. PC was used as a control device for measuring and data processing. III. RESULTS AND DISCUSSION Total pressure inside system was 1.2 bar and outside was 1 bar. It has two components: static and dynamic. Air flow velocity on circumference is lower than on the system main axe. The area of low pressure formed at the

2 Nedybaliuk et al. 21 Fig. 1. Scheme of plasma-liquid system with discharge in reverse vortex flow of tornado type. system center. That is one of some reasons liquid cone formation (Fig. 2a). The exposure time for the photographs in Fig. 2 was 33 ms. When air flow is larger than G = 150 cm 3 /s drops emission started from cone tip. Their diameter is mm (Fig. 2b). If air flow prolonged its increasing the frequency of drops emission from cone tip will grow up. We have breakdown between on top bush and immersed in water electrode, when applied voltage from power source (PS) exceeds the breakdown voltage U b (Fig. 2c). The height of liquid surface was 40 mm. Breakdown voltage U b = 5.5 kv in LC regime and U b = 4.5 kv in SC regime. Discharge exists in stationary а) b) e) state after 1-2 s. The discharge parameters are: current 300 ma, voltage 2.8 kv and air flow was G = 110 cm 3 /s (Fig. 2d). In this situation discharge is accompanied by electrolysis. Discharge on 3-rd second after breakdown (Fig. 2e). The surface of immersed electrode is an area of bubbles formation. Formed bubbles pick up from this surface to contact area plasma - liquid. Volume with bubbles is growing after sixth second (Fig. 2f). There is no bubbles formation in contact area plasma - liquid. Investigations of water electrolysis without discharge were conducted also. Grid from stainless steel (diameter - 12 mm, step between wires - 4 mm) was putted on the liquid surface. The diameter of grid is closed to contact plasma/liquid diameter. This grid was grounded and potential of immersed electrode was negative. The system parameters are: current 300 ma, voltage 600 V and air flow was G = 110 cm 3 /s. Bubbles were formed near grid and near immersed electrode. Bubbles filled the whole volume between grid and immersed electrode on the 7-th second (Fig. 3b). They didn t leave the liquid but moved to the chamber walls, reflected from it and came back. c) a) b) d) Fig. 2. Photos of experimental plant: stationary cone (a); drops emission from cone tip (b); breakdown of gas gape (c); discharge exists in stationary state after 1-2 s (d); discharge on 3-rd second after breakdown (e); discharge on sixth second after breakdown (f). f) Fig. 3. Water electrolysis under current 300 ma, voltage 600 V: (а) t = 3 s after start of electrolysis; (b) t = 7 s after start of electrolysis. Volt-ampere characteristics were measured under various air flows for two regimes LC and SC (Fig. 4). Volt-ampere characteristics that shown in Fig. 4a were

3 22 International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011 measured for cause when cathode was metal, and voltampere characteristics that shown in Fig. 4b - for cause when cathode is liquid. The measurements of absorption spectra were conducted for distillate water in LC regime. Processed water inside chamber and condensate were investigated. Glass refrigerator was installed at chamber outlet (Fig. 1, 12) and condensed there. The temperature at the inner surface of the refrigerator was 20 ºC. Measurements of absorption spectra conducted no later than two minutes after processing. The absorption coefficients are presented on Fig. 5 for processed water in chamber and condensed water in refrigerator. Energy contribution to discharge was 50 kj. The discharge condensed liquid outside of reactor. Concentration of hydrogen peroxide outside of reactor (0.2%) is 15 times higher than inside (0.014%). Absorption coefficients of different hydrogen peroxide distilled water mixtures were measured previously. Hydrogen peroxide concentration as a function of absorption coefficient was plotted. Concentration of hydrogen peroxide was measured by absorption coefficient. The nitrous acid (HNO 2 ) is presented in condensate. But there are no traces of this acid in absorption spectra inside system. If energy contribution has enlargement up to 100 kj the concentration of hydrogen peroxide inside system is unchanged. Fig 4. Volt-ampere characteristics under various air flows: (a) SC regime; (b) LC regime. Fig. 5. The absorption coefficients of processing water in plasmaliquid system with reverse vortex flow: (a) Condensed water and water inside chamber with energy contribution 50 kj; (b) Water inside chamber with energy contribution 50 kj and 100 kj. parameters are: Current 300 ma, voltage 2.8 kv, LC regime and air flow was G = 110 cm 3 /s. The hydrogen peroxide exists in liquid inside of reactor and in

4 Nedybaliuk et al. 23 Fig. 6. Typical emission spectra outside and inside plasma reactor under air flow = 110 cm 3 /s; current = 300 ma and voltage = 2.8 kv. Typical emission spectra in plasma-liquid system with reverse vortex flow are shown on Fig. 6. Measurements were conducted on the outside (nozzle outlet) and inside (at the middle distance between liquid surface and on top bush) reactor. On emission spectrum present bands of hydroxyl (OH) and nitrogen molecule, lines of atomic oxygen, hydrogen and copper. Band of nitrogen molecule N 2 (С-В) and lines of copper Cu were absent on emission spectra on the inside of reactor. Lines of copper were absent, because material of solid electrode has been taken away through nozzle by gas stream outside of reactor. Band of nitrogen molecule was absent, probably, because the ratio N 2 /H 2 O is higher outside of reactor than inside. Also, it can be connected with kinetics in plasma-chemical of reaction metal with plasma-generate gas in plasma torch. The temperature of excited electron levels population T e was determinate by oxygen lines. System inside has T e = 5000 ± 500 К and outside T e = 4500 ± 500 К [3]. Experimental data processing by original procedure [5] was used for determination of temperature vibrational Т v and rotational Т r excited levels population. Plasma emission spectra inside and on the outside reactor are shown on Fig. 7. Experimental data are designated by Fig. 7. Emission spectra of band OH experimental measured and calculated by SPECAIR program inside and on the outside reactor. (inside - T r = 4000 K, T v = 4000 K, T e = 5000 K; outside - T r = 3200 K, T v = 4400 K, T e = 4500 K)

5 24 International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011 ratio (В-С)/А. If it is growing, vibrational temperature is growing also. Temperature vibrational excited levels population on the outside reactor (T v = 4400 K) is larger than inside (T v = 4000 K). Temperatures for the discharge in gas channel with liquid wall [2] were Т r = 3500 ± 500 К, Т v = 4000 ± 500 К, T e = 6000 ± 500 К, for the transverse arc plasma - Т r = 2000 ± 500 К, Т v = 4000 ± 500 К, T e = 6000 ± 500 К, for the discharge in reverse vortex flow inside of reactor - Т r = 4000 ± 200 К, Т v = 4000 ± 200 К, T e = 5000 ± 500 К and outside - Т r =3200±200 К, Т v = 4400 ± 200 К, T e = 4500 ± 500 К. Plasma on the outside reactor Т r < Т v < T e is more non-isothermic than inside Т r = Т v < T e. Plasma nonequilibrium in dynamic plasma-liquid system reverse vortex flow is less than exists in transverse arc plasma and gas channel with liquid wall discharge. Fig. 8. Emission spectra experimental measured and calculated by SPECAIR program. markers and computation results by full line. Emission spectra were measured inside and on the outside reactor and calculated with SPECAIR program [6]. Until T r sensing tail of hydroxyl band is shading into infrared space. Temperature vibrational excited levels population on the outside reactor (T r = 3200 K) less than inside one (T r = 4000 K). The temperature of vibrational excited levels population of hydroxyl band ОН (А-Х) from plasma emission spectra in the wavelength range nm were determined by the procedure [5]. They are presented on Fig. 8. Emission spectrum is presented on Fig. 9 for hydroxyl band ОН (А-Х) regions that are depended from variations of temperature vibrational excited levels population. Vibrational temperature is determined by Fig. 9. Emission spectrum hydroxyl band ОН (А-Х) regions that are depended from variations of temperature vibrational excited levels population [5] IV. CONCLUSION Lines of copper Cu were absent on emission spectra on the inside of reactor. Temperatures of excited levels of plasma in reverse vortex flow outside (Т r = 3200 ± 200 К, Т v = 4400 ± 200 К, T e = 4500 ± 500 К) and inside (Т r = 4000 ± 200 К, Т v = 4000 ± 200 К, T e = 5000 ± 500 К) of reactor were measured. Plasma on the outside reactor Т r < Т v < T e is more non-isothermic than inside Т r = Т v < T e. Plasma nonequilibrium in dynamic plasma-liquid system reverse vortex flow is less than exists in transverse arc plasma and gas channel with liquid wall discharge. Concentration of hydrogen peroxide in condensed liquid outside of reactor was higher on order than in liquid inside of reactor. REFERENCES [1] I. V. Prisyazhnevich, V. Ya. Chernyak, V. V. Yukhymenko, V. V. Naumov, S. Matejcik, J. D. Scalný, and M. Sabo, "Study of Non-Isothermality of Atmospheric Plasma in Transverse Arc Discharge," Ukrainian Journal of Physics, vol. 52, pp , [2] I. V. Prisyazhnevich, V. Ya. Chernyak, J. D. Scalný, S. Matejcik, V. Yukhymenko, S. Olszevsky, and V. Naumov, "Sources of Nonequlibrium Plasma at Atmospheric Pressure," Ukrainian Journal of Physics, vol. 53, pp , [3] A. S. Koroteev, V. M. Mironov, and Yu. S. Svirchyk, Plasmatrons: constructions, characteristics, calculation. M., 1993, 286 pp. (in Russian). [4] C. S. Kalra, M. Kossitsyn, K. Iskenderova, and A. Chirokov, Y. I. Cho, A. Gutsol, and A. Fridman, "Electrical discharges in the Reverse Vortex Flow Thornado Discharges," in Proc. 16th International Symposium on Plasma Chemistry, Taormina, Available: ations/documents/ispc tornado.pdf [5] I. V. Prisyazhnevich, V. Ya. Chernyak, S. V. Olszewsky, and Ok. V. Solomenko, "Determination of excitation temperatures for vibrational and rotational molecular levels in an atmosphericpressure gas-discharge plasma," Ukrainian Journal of Physics, vol. 55, pp , [6] C. O. Laux. Available: