Numerical Approach and Optimization of the Combustion and Injection Techniques in High Velocity Suspension Flame Spraying (HVSFS)

The interest in submicron and nano-structured layers applied by thermal spray technologies on different surfaces has been significantly increased during the last decade. Conventional HVOF spraying processes are not suitable to achieve submicron and nano-particles.

Therefore, High Velocity Suspension Flame Spraying (HVSFS) has been developed for the processing of nano structured spray material to achieve dense surface layers in supersonic mode with a refined micro- or nano-structure, from which superior mechanical and physical properties are expected. However, the chemical and thermodynamic phenomena occurring in the HVSFS reacting flow field are a challenging, multidisciplinary issue. This study is intended to analyze and understand the HVSFS combustion and flow dynamic system on the basis of a CFD model and numerical calculation. Simulation of these phenomena can yield the mass fractions and densities of combustion reactants and products as well as temperature, pressure and particle size and velocity, depending on the position in the combustion chamber and expansion nozzle. In this way, modeling and simulation is suitable to analyze the relevant set of parameters describing the complete spraying process, i. e. the energy balance being influenced by the different combustion mechanisms and the particle properties in the spray jet and during impact on the surface. The final aim is an optimization of the process parameters by variations during simulation experiments. The model considers the following phenomena: combustion of the fuel gas (premixed oxygen/propane), heat, momentum and mass transfer between the flame and the suspension droplets (organic solvent and particles), as well as the injection, vaporization and combustion of the suspension organic solvent.