Author(s)

JAMES Q. FENG

Abstract

The Aerosol Jet® direct-write technology enables microscale printing of functional inks on various substrates with complex shapes, which is of great interest in many applications. It deposits the ink material in a form of high-speed collimated mist stream of fine droplets with diameters typically ranging from 1 to 5 microns, through a deposition nozzle connected via mist transport pathways to a liquid atomizer. Because the liquid atomization process often produces droplets with a wide size distribution having diameters much larger than 5 microns, removal of large ink droplets becomes the primary task of mist transport pathway design in the Aerosol Jet® system development, especially for printing fine features down to the 10 micron range. In the same time, the mist transport pathways must allow smaller droplets to pass through for desired ink material throughput. Therefore, it is important to understand the physical principles for mist transport pathway design based on multiphase mist flow analysis. With simplified models of particles flowing with a carrier gas in straight tubes of various inclination angles, convenient analytical formulas can be derived (even with particle inertia effect included to describe trajectories of large droplets), for calculating the rate of removal of droplets of given sizes due to gravitational sedimentation as a function of tube diameter and length. Rather intricate effect of particle inertia on gravitational wall deposition is revealed by the analytical results. For mist pathways of more complicated geometries, an OpenFOAM® lagrangian solver is used for the mist flow simulation, to gain insights into the wall deposition behaviour of ink droplets during mist transport from the liquid atomizer to the ink deposition nozzle. Applications of such mist flow analysis for mist transport channel design are illustrated with practical examples.

Keywords

Aerosol Jet®, gravitational sedimentation, mist of microdroplets, mist transport, Open-FOAM® lagrangian solver, particle-laden flow, wall deposition