Measuring of mean electrical conductivity of a plasma volume in hot anode area of DC arc plasma torches
Abstract
Studying thermal processes in the anode area of plasma torches with an external anode helps to extend the lifetime of the whole plasma torch and is important for plasma spraying applications or waste treatment. The anode area of these plasma torches is very visible.
We focused on measurement of electrical conductivity of the plasma in the anode area of a hybrid plasma torch. The plasma is in thermodynamic equilibrium and it is possible to compute the electrical conductivity indirectly from plasma temperature measured for example spectroscopically.
It is not possible, however, to measure the plasma electrical conductivity in the anode area directly by using probes inserted into the plasma. It is because of high plasma temperature (above 10,000 K) and high plasma density (up to 6 g/m3), in this area.
We developed a non-intrusive method of measuring plasma effective electrical conductivity of a small plasma volume above the anode. For our measurements, we used a high-speed camera (frame rate 300,000 fps) and a high-voltage probe (sample rate 80 MHz).
Firstly, we measured plasma effective electrical conductivity in the anode area for various values of electric current, ambient pressure and argon flow rate; and for two configurations of the anode position. Finally, in some case, we compared our measured electrical conductivity data with model electrical conductivity data from computer simulations.
We also found the corresponding plasma temperatures and compared them with the plasma temperatures measured spectroscopically. In both cases, there is a good agreement between them.
Our results provide missing experimental data on the electrical conductivity of the plasma in the hot anode area, suitable for comparisons with computer simulations. The method can be used also for other plasma torches with an external anode.
Moreover, the idea of the method can be further improved in both, theoretical exactness and experimental accuracy.