Dynamic Behavior of Arc Voltage and Electro-thermal Efficiency in Atmospheric Pressure Non-transferred Arc Plasma Torches under Different Degrees of Anode Cooling

Unusually, high electro-thermal efficiency, observed under certain cooling rates of the anode boundary layer in a typical non-transferred arc argon plasma torch, is reported. The behavior is reproducible at different arc currents and gas flow rates. To understand the origin of such behavior, total arc voltage, which bears an overall signature of the internal arc dynamics, has been analyzed using tools of dynamical analysis such as frequency space behavior, phase space dynamics, correlation dimension and Lyapunov exponent under different rates of anode cooling. Simultaneous emission spectroscopic investigation of the plasma temperature at the nozzle exit and fast photographic study of the anode boundary layer have been carried out for better insight. Observed significant variation in the dominant frequency components with change in cooling rates gives concrete signature of onset on new dynamics induced by anode cooling. Vivid differences in the dynamics are brought out in phase space representations. True natures of the dynamics are obtained through the estimated values of correlation dimension and Lyapunov exponents.