Modeling of particle movement and thermal behavior in a high-velocity oxy-fuel (HVOF) spraying process

摘要

Fluid and particle dynamics of a high velocity oxy-fuel (HVOF) spraying system are analyzed numerically and experimentally. The HV 2000 Praxair gun is selected for HVOF deposition. The carrier gas and solid spherical particles are injected through the center of a combustion chamber. The mixture of propylene and oxygen is introduced from an annulus of the combustion chamber, where it is ignited by a spark plug. The chemical reaction produces the gas mixture of temperature around 3000K. After the gas mixture enters in a converging nozzle, its velocity increases sharply. A flame jet forms and shock waves are observed in the ambient air after the gas mixture leaves the nozzle. A compressible, k - ε turbulent model is employed, and the combustion process is modeled using an instantaneous chemistry model. The particles are heated and accelerated by the chemical products. Particles are modeled as a lumped-heat-capacity model. An iterative, implicit, finite-volume numerical method is employed to solve the coupled gas and particle equations inside and outside the gun. The gas temperature, velocity and Mach number distributions are presented at different locations. The particle temperature, velocity and trajectory are also presented. The particle behaviors of different sizes are analyzed. At the exit of the computational domain, high particle velocities (400 - 650 m/s) are obtained depending on the particle size. Most particles undergo melting before they leave the nozzle. The particle temperature is below the melting point at the exit of the computational domain. The numerical results compare well with the experimental data from Molybdenum and tungsten carbide particles measured by DPV 2000.