Numerical modeling of aerosol deposition process

Aerosol Deposition (AD) method is an emerging coating process for deposition of ceramic particles for industrial applications such as MEMS, fuel cells, optical devices and radio frequency components. In this process, various parameters such as nozzle geometry, powder size and type, pressure inside the deposition chamber, and carrier gas flow rate have significant influence on the in-flight particle behavior before impact, and therefore, on the coating properties. In this study, a two-way coupled Eulerian-Lagrangian model is used to study the effects of gas flow rates and substrate location on the gas flow characteristics, bow shock near the substrate, and more importantly on the particle velocity and trajectory upon impact. The study is carried out with a rectangular sonic nozzle. To validate our simulations, locations of the Mach disks in highly under-expanded free-jet conditions are compared with the theoretical and experimental results in the literature. Two different computational geometries are utilized; a 2D planar and a quarter slice of 3D. It is found that, for the rectangular nozzle, the 3D geometry produces more accurate results and can capture the axis-switching phenomenon. Moreover, it is observed that the gas flow structure as well as the in-flight particle behavior obtained from 2D and 3D geometries are almost identical before the Mach disk. In addition, two different drag expressions are employed and it is shown that the influence of Mach and Knudsen numbers on particle behavior in vacuum condition is significant.