Transient CFD Simulation of an RF Plasma Torch with Oscillatory Water-Ethanol Injection

In this paper, the effect of oscillatory water-ethanol injection on the temperature, velocity and species profiles of a thermal plasma jet is investigated by using a time-dependant 2D-axisymmetric Computational Fluid Dynamics model. The model concerns a TEKNA PL-35 RF Plasma torch operated with an argon-oxygen mixture and accounts for the presence of species such as electrons, atoms, molecules, and ions. The water-ethanol solution is injected with a sinusoidal velocity into the plasma core through a probe, simulating the characteristic fluctuations of a peristaltic pump. Model validation is performed based on comparisons with numerical results available in literature, showing good conformity. The effects of sinusoidal frequency and amplitude, water-ethanol mixture molar concentration and operating pressure on plasma characteristics such as electron density and temperature distribution, are analyzed. The results indicate that oscillatory water-ethanol injection leads to a reduction in plasma temperature, particularly at the outlet of the injection tube, while decreasing the temperature gradient at the plasma torch outlet. Furthermore, the study reveals that higher torch pressure increases electron density and promotes energy transfer, stabilizing the plasma. This, in turn, could lead to more uniform heating of precursor materials, which is crucial for applications like coating deposition and powder synthesis.