抄録
For measuring the flow velocity of sheath region of an arc burning through a polyethylene tube (PE arc), we obseved the in-flight motion of non-vaporized bulky carbon particles which are ablated from the tube wall and emit strong continuum in the sheath region at the tube exit. The velocity was calculated from the time difference during which the particles passed through two slits located along the arc axis. The experimental parameters are arc current (DC 5 to 15A), tube inner diameter (2 and 4mm) and tube length (10 to 30mm).
The results show that the sheath flow velocity of PE arc increases with increasing arc current, decreases with increasing tube diameter and increases in proportion to tube length. The maximum value of the velocity is about 300m/s at 15A, 2mm in tube diameter and 30mm in tube length. Mass of the polyethylene tube was measured before and after arcing, and the mean velocity across the cross-section of the tube is roughly estimated from the mass difference assuming that the gas temperature is uniform inside the tube. The tendency of the estimated characteristics of flow velocity versus tube length agrees with the measured one. Also, it is deduced from the experimental results that the flow velocity inside the tube is proportional to axial distance from the tube center.
