Particle deposition on the convergent nozzle walls of thermal-spray guns

The present study investigates particle depositions on convergent nozzle walls of (HVOF) spray guns, a process that reduces nozzle lifetime and degrades operation stability and reliability. We perform three-dimensional, two-way coupled simulations of reactive particle-laden compressible flow through a typical thermal spray gun nozzle. We determine critical radial particle velocities at which particles deposit on the wall. We characterize critical velocities concerning particle trajectories, particle diameter, and downstream location of particles deviating from the nozzle center. The critical velocity decreases with particle diameter and increases with the downstream location at which particles deviate from the nozzle center. We exclude the possibility that single particle–particle collision events create sufficient radial particle momentum for deposition. We use the gained insights to propose mitigating measures against particle depositions. • Deposit conditions on the nozzle wall vary by feed-powder particle trajectory class. • Impact wall-normal velocity of powder particles is key for particle-wall adhesion. • Critical radial velocity for particle impact rises exponentially with axial position. • Adapted nozzle geometry and wall-normal jets might mitigate deposits. • Single particle collisions do not create sufficient radial momentum for wall impact.