Effect of nozzle shape on the performance of high velocity oxygen-fuel thermal spray system

Numerical analysis is performed to predict the gas dynamic behaviors in a HVOF (high velocity oxygen-fuel) thermal spray gun in which oxygen and fuel are burnt in combustion chamber linked to nozzle. The analysis is applied to investigate the axisymmetric, steady-state, turbulent, and chemically combusting flow both within the torch and in a free jet region between the torch and the substrate to be coated. The combustion is modeled using a single-step and eddy-dissipation model which is assumed that the reaction rate is limited by the turbulent mixing rate of fuel and oxidant, or the reaction is instantaneous as the reactants are mixed together. The computational fluid dynamics (CFD) model is also used to elucidate the effect of various nozzle configurations. Using a commercial code, FLUENT which uses FVM (finite volume method) and SIMPLE algorithm, governing equations have been solved for the pressure, velocity and temperature distributions in the HVOF thermal spray gun.