Turbulence controlled high-power arcs with different electron and gas temperatures

Abstract

Experiments with high-power arcs interacting with a sonic high-pressure gas flow suggest an energy dissipation mechanism much more effective than thermal conduction and radiation. It is shown that the arc behavior is almost completely controlled by turbulence phenomena. By means of a phenomenological turbulence theory, an expression for the turbulent heat conductivity is derived which is used to solve the energy balance. The static arc voltage and the temperature profiles calculated for currents up to 50 kA and pressures of some 100 N/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (≈ 10 atmospheres) depend on a characteristic turbulence length that is determined by comparison with the experiments. For radially blasted arcs with a length of a few centimeters, this turbulence length is shown to be constant over a wide range of current and pressure but varying with the arc geometry. The high energy dissipation leads to arc voltage gradients that may attain several kilovolts per centimeter. Such high gradients imply deviations from local thermal equilibrium, especially at smaller currents. For such a case, the solution of the energy balance requires the calculation of nonequilibrium plasma composition and transport properties for plasmas with different electron and gas temperatures. Numerical calculations have been performed for nitrogen.