Numerical Computation on the Generation of CH3 and H Radicals by the Thermal Plasma Decomposition of Hydrocarbons

Abstract

A two-dimensional numerical analysis on the thermal decomposition of methane (CH4) by Ar/H2 thermal plasmas has been carried out using a FLUENT code to nd out the effects of thermal plasma fields on the production rates of CH3 and H radicals during the CH4 decomposition process in a dc arc-jet diamond CVD. In the numerical analysis, the partial di erential equations describing conservations of mass, momentum, and energy as well as mass of individual chemical species are taken into account along with the K-epsilon turbulence model. The numerical calculations are performed in the following consecutive procedure. In the first step, the thermal plasma fields inside a reaction chamber are calculated from the inlet boundary conditions without considering chemical reactions. Uniform profiles of the plasma temperature and velocity at the torch exit are assumed as the inlet boundary conditions in this step. Next in the second calculation step, the chemical kinetic equations, involving 13 species and 25 reactions, are solved in the environment of the calculated two-dimensional plasma fields to give the concentration fields of all chemical species generated in the CH4 decomposition process. The calculated results show that the developed plasma elds inside the reaction chamber strongly depend on the reaction chamber geometry, and significantly affect the concentration fields and generation rates of the decomposed radicals, such as CH3 and H.