Study of nozzle influence on aerosol deposition (AD) by using 3D CFD simulations

In aerosol deposition, fine ceramic powders in sizes of less than typically 5 µm are deposited as coating at room temperature. The use of such fine powders, however, requires that aerosol deposition has to be performed under vacuum. According to experimental results, coating formation by aerosol deposition only occurs if particle velocities exceed a material specific threshold velocity. Thus, knowledge on attained velocities over acceleration in the nozzle and under the expansion into vacuum is essential for deriving conditions for successful deposition. In the present study, 3D CFD simulations were used in order to investigate the key parameters in powder acceleration. Three different nozzle geometries were investigated: a convergent nozzle, a convergent-divergent nozzle, and a convergent nozzle followed by straight flow towards exit. In addition, a new nozzle geometry is proposed. Within this comparison, the convergent nozzle leads to the lowest gas and particle velocities. Highest velocities are gained by combining convergent, straight and divergent sections for gas and powder acceleration. In next steps, a prototype of such optimized geometry well be produced and tested in order to validate the modelling results and studying possibly improved higher deposition rates.