Analysis of a high-velocity oxygen-fuel (HVOF) thermal spray torch .1. Numerical formulation

The fluid and particle dynamics of a high-velocity oxygen-fuel torch are analyzed using computational fluid dynamic techniques, The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder feed, The injection nozzle is axisymmetric with powder and a carrier gas injected on the centerline, premixed fuel and oxygen fed from an annulus, and air cooling injected from an annulus along the interior surface of the aircap, The aircap is a conically converging nozzle that achieves choked flow conditions at the exit; a supersonic, underexpanded jet develops externally, A two-dimensional, axisymmetric geometry is assumed; the equations for mass, momentum, and energy conservation are solved for both the gas and the particle phases, The combustion process is modeled using approximate equilibrium chemistry with dissociation of the gas with a total of nine species, Turbulent flow is modeled by a two-equation model for turbulent kinetic energy and dissipation rate that includes compressibility effects on turbulent dissipation, Particles are modeled as a lumped-heat-capacity system and are considered to melt upon attaining the required latent heat of fusion, An iterative, implicit, finite-volume numerical method is used to solve the coupled gas and particle equations inside and outside the torch, A companion paper presents the results of the numerical simulation and discusses in detail the gas and particle dynamics.