Numerical investigation on effects of nanoparticles on liquid feedstock behavior in High Velocity Oxygen Fuel (HVOF) suspension spraying

Suspension feedstock in high velocity oxy-fuel flame jets has opened a new area of research with great potential for advanced coatings. Understanding the suspension behavior in such a multidisciplinary process is a key factor in producing repeatable and controllable coatings. In this study, the effects of solid nanoparticles, suspended in liquid feedstock, on suspension fragmentation, vaporization rate and gas dynamics are investigated in the High Velocity Oxygen Fuel (HVOF) suspension spraying process by numerical modeling. The model consists of several sub-models that include pre-mixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling aerodynamic droplet break-up and evaporation, heat and mass transfer between liquid droplets and gas phase. Moreover, the thermo-physical properties of suspension (mixture of solid nanoparticles and liquid solvent) are calculated from theoretical models. The results show that small droplets carrying high nanoparticle concentrations develop higher surface tension and result in less fragmentation. The recommended ethanol droplet size at high nanoparticle loadings is found to be 50 μm due to the high evaporation rate in the mid-section of the nozzle. For larger droplets, severe fragmentation occurs inside the combustion chamber (CC) while complete evaporation takes place in the free jet region outside the gun.