MEASUREMENT OF STREAM VELOCITY IN AN ARC

Abstract

In electric arcs, there generally exists a considerable streaming of plasma caused by Lorentz forces generated by self-magnetic fields. The method of measurement of such streaming velocity is described. The arc used is a d-c thermal arc of 105 amp in argon at atmospheric pressure. The temperature of the arc was measured by a spectroscopic method and by a thermocouple, and a temperature distribution ranging from 16,000 to 1500 deg K was obtained. The streaming velocity was evaluated by measurement of the drag of a small plate swept across the arc, using the result of the temperature measurement, the drag coefficient of the plate, and the calculated density and viscosity coefficient of the plasma. At a section 2 mm from the cathode, the evaluated stream velocity was 135 m/sec at the center and 25 m/sec at the edge of the arc column from cathode to anode. The error in measured temperature is estimated at less than 10%, and the error in the measured stream velocity is considered to be less than 17.5%, excluding the error due to some change of the arc discharge caused by inserting the drag measuring plate. (auth)