<p>In aerosol deposition, fine ceramic powders in sizes of less than typically 5&#xa0;μm are deposited as a coating at room temperature. Aerosol deposition must be performed under a vacuum to apply such fine powders and avoid bow shock effects. According to experimental results, coating formation by aerosol deposition only occurs if particle velocities exceed a material-specific threshold velocity. Thus, knowledge of attained particle velocities over acceleration in the nozzle and under the expansion into a vacuum is essential for deriving conditions for successful deposition. In the present study, 3D CFD simulations were used to investigate the key geometric variables in particle acceleration. Three different nozzle geometries were investigated: a converging nozzle, a converging–diverging nozzle, and a converging nozzle followed by a constant cross section toward the exit. In addition, these three nozzle geometries were optimized to maximize the particle impact velocity. The results show that the converging–diverging nozzle supplies the highest particle velocities within this comparison. By the design of optimization, the particle velocities can be improved for all the geometry types. The most promising geometry from the CFD optimization was manufactured and compared to the original one, providing a gain in experimentally measured particle velocity of 24%.</p>

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Nozzle Geometry Optimization for Aerosol Deposition by 3D Computational Fluid Dynamics Simulations

  • Julio Gutiérrez de Frutos,
  • Andreas Elsenberg,
  • Luca Bachnick,
  • Frank Gärtner,
  • Thomas Klassen

摘要

In aerosol deposition, fine ceramic powders in sizes of less than typically 5 μm are deposited as a coating at room temperature. Aerosol deposition must be performed under a vacuum to apply such fine powders and avoid bow shock effects. According to experimental results, coating formation by aerosol deposition only occurs if particle velocities exceed a material-specific threshold velocity. Thus, knowledge of attained particle velocities over acceleration in the nozzle and under the expansion into a vacuum is essential for deriving conditions for successful deposition. In the present study, 3D CFD simulations were used to investigate the key geometric variables in particle acceleration. Three different nozzle geometries were investigated: a converging nozzle, a converging–diverging nozzle, and a converging nozzle followed by a constant cross section toward the exit. In addition, these three nozzle geometries were optimized to maximize the particle impact velocity. The results show that the converging–diverging nozzle supplies the highest particle velocities within this comparison. By the design of optimization, the particle velocities can be improved for all the geometry types. The most promising geometry from the CFD optimization was manufactured and compared to the original one, providing a gain in experimentally measured particle velocity of 24%.