第 2 章 多相交流アークにおける電極消耗現象の可視化
2.4 まとめ
本章では，多相交流アークにおける電極消耗現象に着目し，高速度カメラとバンドパス フィルターを用いることで液滴飛散現象と電極金属蒸発現象を観察した．また，電極消耗 機構をより理解するため，電極温度測定方法を確立した．以下に得られた知見を述べる．
(1) 高速度カメラにより電極からの熱放射を観測し，二色放射測温法を用いて電極温度を 算出した．得られた電極温度は最大±100 K 程，±2.5%程の誤差を含み，多相交流ア ーク放電中の電極温度測定が可能である．
(2) 液滴飛散現象の観察により，粒径250 μm以上の液滴は陰極時にのみ発生しており，多 相交流アークにおける液滴飛散による消耗は，主に陰極時に生じる．
(3) 電極金属であるタングステンの蒸発挙動の観察により，陽極時にタングステン蒸気が 細く局所的に発生している様子が確認された．また，タングステン蒸気は電場の影響
45
を強く受けるため，蒸発による消耗は主に陽極時に生じる．
46 参考文献
[1] M. Tanaka, T. Ikeba, Y. Liu, S. Choi, and T. Watanabe: Investigation of Electrode Erosion Mechanism of Multi-Phase AC Arc by High-Speed Video Camera, Journal of Physics:
Conference Series, 441, 012015 (2013).
[2] T. Hashizume, M. Tanaka, and T. Watanabe: Investigation of Electrode Erosion Mechanism of Multi-Phase AC Arc by High-Speed Video Camera, Quarterly Journal of the Japan Welding Society, 33, 44s-48s (2015).
[3] N. A. Sanders and E. Pfender: Measurements of anode falls and anode heat transfer in atmospheric pressure high intensity arcs, Journal of Physics D: Applied Physics, 55, 714-722 (1984).
[4] J. J. Lowke, R. Morrow, and J. Haidar: A simplified unified theory of arcs and their electrodes, Journal of Physics D: Applied Physics, 30, 1449-1454 (1997).
[5] A. A. Sadek, M. Ushio, and F. Matsuda: Effect of rare earth metal oxide additions to tungsten electrodes, Metallurgical Transactions A, 21, 3221-3236 (1990).
[6] M. Usio, A. A. Sadek, and F. Matsuda: Comparison of temperature and work function measurements obtained with different GTA electrodes, Plasma Chemistry and Plasma Processing, 11, 81-101 (1991).
[7] M. Tanaka, M. Ushio, M. Ikeuchi, and Y. Kagebayashi: In situ measurements of electrode work functions in free-burning arcs during operation at atmospheric pressure, Journal of Physics D: Applied Physics, 38, 29-35 (2005).
[8] V. A. Nemchinsky and W. S. Severance: Cathode erosion in high-current high-pressure arc, Journal of Physics D: Applied Physics, 36, 704-712 (2003).
47
Table 2.1 Experimental conditions and measurement conditions for electrode temperature measurement.
Number of Phase Plasma Gas
Arc Current (each electrode) Power
Power (each electrode) Ar Flow Rate (each electrodes)
Electrode
High-speed camera Band-pass filter
Frame rate Shutter speed
Plasma conditions
12-Phase 100 A 45 ～ 50 kW
3.5 L/min
2.0wt%ThO
2-W (φ6.0 mm) Measurement Conditions
3～4 kW
Ar 60 L/min, Air 200 L/min
FASTCAM SA5 (Photron) 785 nm (±2.5 nm ), 880 nm (±5 nm)
5000 fps
40 µs
48
Table 2.2 Experimental conditions and measurement conditions for observation of droplet ejection.
Number of Phase Plasma Gas
Arc Current (each electrode) Power
Power (each electrode) Ar Flow Rate (each electrodes)
Electrode
High-speed camera Band-pass filter
Frame rate Shutter speed
Plasma conditions
12-Phase
Ar 60 L/min, Air 200 L/min 100 A
45～50 kW 3～4 kW 3.5 L/min
2.0wt%ThO
2-W (φ6.0 mm) Measurement Conditions
FASTCAM SA5 (Photron) 785 nm (±2.5 nm )
5000 fps
40 µs
49
Table 2.3 Experimental conditions and measurement conditions for observation of metal vapor.
Number of Phase Plasma Gas
Arc Current (each electrode) Power
Power (each electrode) Ar Flow Rate (each electrodes)
Electrode
High-speed camera Band-pass filter
Frame rate Shutter speed
Plasma conditions
12-Phase
Ar 60 L/min, Air 200 L/min 100 A
45 ～ 50 kW 3 ～ 4 kW 3.5 L/min
2.0wt%ThO
2-W (φ6.0 mm) Measurement Conditions
FASTCAM SA5 (Photron) 393 nm (±1.5 nm )，738 nm (±1.5 nm )
5000 fps
50 µs
50
Table 2.4 Experimental conditions and measurement conditions in DC arc.
Plasma Gas Arc Current
Power Electrode
High-speed camera Band-pass filter
Frame rate Shutter speed
785 nm (±2.5 nm ), 880 nm (±5 nm) 10000 fps
40 µs 100 A 2～3 kW
2.0wt%ThO
2-W (φ6.0 mm) Ar 50% - H
250%
Plasma conditions
Measurement Conditions
FASTCAM SA5 (Photron)
51
Fig. 2.1 Photograph of multiphase AC arc apparatus.
52
Fig. 2.2 Schematic image of experimental setup.
53
Fig. 2.3 Ideal voltage of each electrodes.
54
Fig. 2.4 Electrical circuit diagram and schematic connection diagram of the plasma reactor.
55
Fig. 2.5 Snapshot of electrode configuration of 12-phase arc during arc discharge.
56
Fig. 2.6 Schematic image of plasma torch of multiphase AC arc.
57
Fig. 2.7 Electrode condition before arc ignition. (a) Upper view, (b) Front view.
(b)
58
Fig. 2.8 Schematic image of experimental setup of emission spectroscopy.
59
Fig. 2.9 Schematic image of experimental setup of observation of droplet ejection.
60
Fig. 2.10 Measurement point of emission spectroscopy.
61
Fig. 2.11 Emission spectrum from electrode region of 6-phases arc.
62
Fig. 2.12 Emission spectrum focusing on 785 nm for observation of thermal radiation from electrode.
63
Fig. 2.13 Schematic image of observation of thermal radiation from electrode.
64
Fig. 2.14 Schematic diagram of high-speed camera system with band-pass filters.
65
Fig. 2.15 Relationship between intensity ratio and calculated temperature.
66
Fig. 2.16 Emission spectrum focusing on 785 nm for observation of thermal radiation from electrode.
0.0 2.0 10
34.0 10
36.0 10
38.0 10
31.0 10
41.2 10
41.4 10
4770 780 790 800
In ten sit y [-]
Wavelength [nm]
Ar I Ar I
Ar I
Ar I
Ar I
(a)
67
Fig. 2.17 Electrode temperature measurement system.
68
Fig. 2.18 (a) Transmission of band-pass filter and (b) Influence of FWHM on intensity.
69
Fig. 2.19 High-speed snapshots of electrode at anodic period (a), (b) and synchronized current waveforms (c).
70
Fig. 2.20 Radial profiles of the measured intensity for the continuum and the sum of the line and continuum radiation at the anodic period.
71
Fig. 2.21 High-speed snapshots of electrode at cathodic period (a), (b) and synchronized current waveforms (c).
72
Fig. 2.22 Radial profiles of the measured intensity for the continuum and the sum of the line and continuum radiation at the cathodic period.
73
Fig. 2.23 Relationship between emissivity of tungsten and wavelength.
0.36 0.38 0.40 0.42 0.44 0.46 0.48
500 600 700 800 900 1000
2000 K 2200 K 2400 K 2600 K 2800 K
E m iss ivi ty [-]
Wavelength [nm]
74
Fig. 2.24 Relationship between intensity ration and temperature.
75
Fig. 2.25 Temperature errors caused by the continuum radiation and tungsten emissivity at the anodic (a) and the cathodic period (b).
76
Fig. 2.26 Emission spectrum from electrode region of 6-phases arc.
77
Fig. 2.27 Emission spectrum focusing on 785 nm for observation of W vapor.
78
Fig. 2.28 Measurement system of intensity of W vapor.
79
Fig. 2.29 High-speed snapshots (a) and temperature distributions (b) of W electrode, and synchronized current waveform (c).
80
Fig. 2.30 Temperature variation of electrode tip during an AC cycle.
3600 3700 3800 3900 4000 4100 4200
T e m p e ra tu re [ K ]
(n-1) (n-1/2) n (n+1/2) (n+1)
Phase
81
Fig. 2.31 Representative snapshots of electrode surface and corresponding temperature
distributions of ThO2 doped W electrode tip at cathodic period in multiphase AC arc (a), (b) and DC arc (c), (d).
82
Fig. 2.32 Axial distributions of electrode temperature from electrode tip in multiphase AC arc and DC arc.
83
Fig. 2.33 Schematic diagram of electrode phenomena in DC arc (a) and multiphase AC arc (b).
84
Fig. 2.34 Representative snapshots of electrode surface (a) at the cathodic period and synchronized waveforms of current and voltage (b).
85
Fig. 2.35 Representative snapshots of small droplets (a) and large droplets (b).
86
Fig. 2.36 Number-weighted droplet size distribution (a) and volume-weighted droplet size distribution (b).
87
Fig. 2.37 Time transient of the number of the ejected droplets during AC cycles.
88
Fig. 2.38 Time transient of the volume of the ejected droplets during AC cycles.
89
Fig. 2.39 Representative high-speed images of W vapor (a), Ar (b), relative intensity distributions of W to Ar (c), and synchronized current waveform (d).
90
Fig. 2.40 Time variation of area of W vapor during an AC cycle.
91
Fig. 2.41 Estimated rate of W evaporation during an AC cycle.
92
93