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Abstract—The characteristics of a multiple argon bubble jet in which a streamer is generated by a dc pulsed discharge have been experimentally clarified ...
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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011

Characterization of a Multiple Bubble Jet With a Streamer Discharge Hideya Nishiyama, Ryosuke Nagai, and Hidemasa Takana

Abstract—The characteristics of a multiple argon bubble jet in which a streamer is generated by a dc pulsed discharge have been experimentally clarified through discharge visualization in a bubble and decolorization of a methylene blue solution. There are two types of streamer behavior in a bubble jet in which discharge propagation is along the top and bottom interfaces of the bubble and along the sidewall of the bubble. The methylene blue solution is successfully decolorized by a discharged bubble jet in 20 min. Index Terms—Bubble jet, radicals, streamer discharge, water treatment.

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N recent years, a great deal of interest has been shown in the application of electrical discharges in bubbling water to oxidize persistent harmful contaminants using O and OH radicals [1]. The direct injection method of O and OH radicals into the solution, which are produced by a streamer discharge in bubbles, is very effective in improving the decomposition efficiency in liquid, because these radicals have a very short lifetime in atmospheric air and oxygen [2]. Therefore, it is very important to clarify the discharge structure in the bubble, the bubble jet dynamics, and the decomposition characteristics for synthetic water treatment. In this paper, a multiple bubble jet system encapsulating radicals with strong oxidization generated by a dc pulsed discharge in the bubbles is successfully constructed for methylene blue solution decomposition. Multiple bubble jet behavior with luminescence and complex streamer behavior in a bubble are successfully visualized. Finally, decolorization of the methylene blue solution is effectively confirmed by using a multiple bubble jet with reactive radicals. Fig. 1 shows a schematic of the experimental setup. The gas feeding quartz vertical tube has a 6.0-mm outside diameter and a 4.0-mm inside diameter. It has five holes with a 0.5-mm inside diameter in line in the tube sidewall with a 10-mm spacing to generate a multiple bubble jet. There are a grounded cylindrical tungsten cathode with a 3-mm diameter inside the

Manuscript received December 1, 2010; revised April 14, 2011; accepted April 15, 2011. Date of publication July 25, 2011; date of current version November 9, 2011. This work was supported in part by the Global Center of Excellence Program Grant “World Center of Education and Research for Trans-Disciplinary Flow Dynamics” and in part by the Japan Society for the Promotion of Science under a Grant-in-Aid for Challenging Exploratory Research (No. 20656032). The authors are with the Institute of Fluid Science, Tohoku University, Sendai 980-8577, Japan. Digital Object Identifier 10.1109/TPS.2011.2160367

Fig. 1.

Schematic of a multiple bubble jet with a discharge system.

quartz tube and a copper plate anode with an applied high voltage at the bottom of the reactor. The feeding gas is argon with 4.0 SL/min, and the solution is water with 0.55 L. The applied dc pulsed voltage is 6 kV at 1000 Hz. The electrical conductivity of pure water is 300 μS/m. Fig. 2(a) shows the photo of a multiple argon bubble jet with a discharge. There is clear luminescence between the cylindrical cathode and the side holes of the quartz tube in a gas phase. Furthermore, many microbubbles are generated in the downstream discharge region. Fig. 2(b) and (c) shows the streamer propagation inside a single bubble in a few millimeters size with complex deformation of a bubble gas–liquid interface, which is an enlarged photo of a discharged single bubble taken by a high-speed camera with 50 000 frames/s. There are two particular propagating patterns of the streamer path inside a bubble interface depending on the bubble size and shape, the applied voltage, and its polarity, as well as the mean free path of ionizing photons [3]. One is the propagation only along the top and bottom curved interfaces of the bubble, and the other is that along the sidewall of the bubble. Fig. 3(a)–(d) shows the time evolution of decolorization of a methylene blue solution by a multiple argon bubble jet system with a discharge. Decolorization is easily achieved in 20 min by radicals with strong oxidization in a solution.

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NISHIYAMA et al.: CHARACTERIZATION OF A MULTIPLE BUBBLE JET WITH A DISCHARGE

Fig. 2.

(a) Multiple argon bubble jet with a streamer discharge. (b) and (c) Streamer propagation inside a discharged single bubble.

Fig. 3.

Time evolution of decolorization of a methylene blue solution. (a) 0 min. (b) 10 min. (c) 20 min. (d) 30 min.

R EFERENCES [1] H. Katayama, H. Honma, N. Nakagawara, and K. Yasuoka, “Decomposition of persistent organics in water using a gas–liquid two-phase flow plasma reactor,” IEEE Trans. Plasma Sci., vol. 37, no. 6, pp. 897–904, Jun. 2009.

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[2] A. Yamatake, J. Fletcher, and K. Yasuoka, “Water treatment by fast oxygen radical flow with dc-driven microhollow cathode discharge,” IEEE Trans. Plasma Sci., vol. 34, no. 4, pp. 1375–1381, Aug. 2006. [3] N. Yu. Babaeva and M. J. Kushner, “Structure of positive streamers inside gaseous bubbles immersed in liquids,” J. Phys. D, Appl. Phys., vol. 42, no. 13, p. 132 003, Jul. 2009.