| ホーム | 渡辺教授 | 研究 | 業績 | 装置 | メンバー | 卒業生 | 学生業績 |
| 講義 | 学会報告 | 入学希望者 | トピックス | サイトマップ |

論文題目「Arc Temperature Fluctuation Near the Electrodes of Multiphase AC Arc by High-speed Camera with Band-pass Filter」

Chang Jungie

1．Introduction
　Thermal plasma has considerable applications such as nanomaterials synthesis and waste treatment due to its unique characteristics including high enthalpy, high energy densities, high temperature, and high chemical reactivity. In comparison with the conventional DC arc plasma torch, the multiphase AC arc (MPA) have higher energy efficiency, slower gas flow velocity, and larger plasma volume, and so on.
　Arc temperature of the MPA is a key parameter for the practical use of industrial applications. The high-speed camera system with band pass filter (BPF) has been successfully used to measure the arc temperature of the central region of the MPA. The effect of the working pressure and the driving frequency on the temperature in the MPA has also been visualized and investigated by the high-speed camera. The results indicate that the arc temperature of the central region increases with the increase of the driving frequency and the decease of the working pressure. However, the specific temperature distribution of the arc near the electrodes of the MPA has not been understood. Exploring the arc temperature near the electrode can serve as the reference of the heat transfer mechanism between the arc and the electrode in the AC arc plasma.
　In this study, a new arc temperature measurement method is proposed to measure and investigate the arc temperature fluctuation near the electrodes of MPA. The arc temperature fluctuation near the electrodes of MPA under different currents is further investigated by comparing with a diode-rectified multiphase AC arc (DRMPA) which is an innovative AC arc plasma with lower electrode erosion rate.

2．Experimental
　The setup consists of 12 electrodes, an arc chamber, exhaust gas system, a cooling-water system, and AC power supply. Electrodes are symmetrically arranged by the angle of 30deg to enlarge the plasma area. In this study, six lower electrodes are used to generate the arc in MPA and DRMPA. The arc current is 150, 200, and 250 A. The distance between the electrodes is 80 mm. Ar (10 L/min) is used as the plasma gas on the observed electrodes (lower electrode). The electrode of W-2wt%La2O3 is used. The electrode diameter is 10 mm.
　The arc temperature can be deduced from the ratio of the total arc emission intensity in various spectral ranges. The total arc emission from thermal plasma can be classified into line emission and continuous emission. A high-speed camera combined with suitable BPF is used for observing arc temperature fluctuation near the electrodes of MPA and DRMPA.
　In the observation system with high-speed camera, employed BPFs’ wavelength ranges are 440 ± 5 nm and 480 ± 5 nm where the main emissions from arc above 15,000 K are line emission of single-charged argon ion. The intensity ratio of combination of line and continuum emissions in various wavelength ranges are obtained. The arc temperature is calculated based on the relationship between the intensity ratio and electron temperature. The frame rate of the high speed camera is set up to 5,000fps and the fluctuation of arc temperature near the electrodes is measured by ms order.

3．Results and Discussion
　The arc temperature distribution was calculated for MPA and DRMPA near the electrodes in Ar atmospheres with the electrode of W-2wt%La2O3 in an AC cycle at IRMS 250. The arc temperature near the electrode fluctuates in the range from 15,000 K to 20,000 K in the cathodic period.
　The arc temperatures near the electrode at maximum current in the cathodic period at specific position of MPA and DRMPA are compared. The arc temperature at specific position of DRMPA is lower than that of MPA in cathodic period. The arc temperature near the electrodes increases with the increase of arc current in MPA and DRMPA. This is because the higher arc current leads to higher current density in the arc. Therefore, higher Joule heating leads to higher arc temperature.
　The effect of the arc current on the coefficient of variation (CV) value of arc temperature at the specific position in cathodic period in MPA and DRMPA was investigated. The CV value of arc temperature decreases with the increases of arc current. The CV value of the arc temperature of MPA is higher than that of DRMPA. This larger temperature fluctuation in MPA originates from more significant arc swinging motion in MPA than that in DRMPA.
　The existence probability of area of arc above 15,000 K in cathodic period in MPA and DRMPA was estimated. The existence probability of area of arc above 15,000 K in DRMPA is higher MPA under the same current. This fact is owing to the effective work function of the electrode tip. The electrode tip of MPA is molten by the heat transfer at anodic period. Therefore, molten electrode tip has W as its main component with a work function of 4.5 eV. On the other hand, the electrode tip of DRMPA is mainly covered by the liquid La2O3 with a work function of 3.1 eV. Therefore, the current density of arc in DRMPA is higher than that in MPA. Thus, the high-temperature area in DRMPA is larger.

4. Conclusion
　In this study, the arc temperature fluctuation near the electrodes has been successfully measured by a high-speed camera system combing the new arc temperature measurement considering continuums emission. The arc temperature near the electrode fluctuates in the range from 15,000 K to 20,000 K in the cathodic period. DRMPA has been expected to apply in various material process due to the higher arc temperature and larger high-temperature area than MPA.

国際学会