High pressure micro plasma discharge: Effect of conjugate heat transfer

In recent years there has been growing interest in high pressure non-thermal micro plasma discharge utilizing the Paschen´s `pd´ scaling law. At high pressures these plasma discharges were found to be sufficiently “warmer” than the classical non-thermal discharge even though they maintain non-equilibrium characteristics, making it critical to resolve the neutral gas heating in the system. In this current work high pressure micro plasma discharge were simulated using a one dimensional hybrid multi-physics model. The model included charged and neutral species conservation with detailed gas phase chemistry, self-consistent solution of the electric field, electron and neutral gas temperature as well as an external circuit model. In addition, conjugate heat transfer in the electrode was also considered. Simulations were carried out for a DC micro plasma discharge over a broad range of pressure, inter-electrode separation and electrode material for a He-N₂ feed gas. Special attention was given on the conjugate heat transfer aspect and its effect on the gas temperature and the plasma characteristics predictions (i.e. electron density, voltage-current characteristics). Unlike the conventional and widely accepted isothermal wall boundary conditions, predictions with the conjugate heat transfer model indicated significantly different gas temperature and plasma characteristics. The gas temperature prediction from the conjugate heat transfer model was found to be in good agreement with experimental measurements.