Numerical and experimental comparison of induction thermal plasma characteristics between 0.5 MHz and 4 MHz

Generation of larger and more stable RF plasmas at atmospheric pressure is important in order for their more widespread adoption in industrial applications. The applied frequency is strongly related to the size of the plasma torch, and also to the distributions of temperature, velocity and species concentration. In this work, the results of the investigation of the characteristics in argon-hydrogen plasmas generated at frequencies of 0.5 MHz and 4 MHz are presented by comparing the two-dimensional modeling approach and the observations of the plasma generated in a 80-mm diameter plasma tube. The fields of flow, temperature and concentration of RF thermal plasmas have been calculated by solving the two-dimensional continuity, momentum, energy, and species conservation equations using a SIMPLEC algorithm. The electromagnetic (EM) fields have been analyzed by solving Maxwell's equations on the basis of the two-dimensional modeling approach. An Ar-H₂ atmospheric pressure plasma is successfully operated at 0.5 MHz frequency and up to 75 kW RF power condition. The observations of the plasma region are performed by an air-cooled CCD camera system. Lower induction frequency generates a longer and narrower plasma region. The penetration depth of the time-varying magnetic field into plasmas, namely skin depth, increases with a decrease in frequency. At lower induction frequency, the high temperature region in the plasma exists more inside than at higher induction frequency. Numerical and experimental results show good agreement qualitatively and indicate that lower induction frequency generates a longer and narrower plasma region. The choice of induction frequency is important in determining the optimum torch diameter for the generation of larger RF plasmas.