Aerosol Deposition in 90° Circular Tube Bends with Laminar Flows: Effects of Inertial Impaction and Gravitational Settling

Abstract

As studied by many authors, the behavior of particles in aerosol flow through bent tubes is relevant to a variety of technological developments for practical applications. The present work is no exception, motivated by the need of understanding ink droplet loss during mist transport in Aerosol Jet® printing. While the majority of works in the literature have considered particle deposition in tube bends with the tube-flow Reynolds number Re > 1000, the mist flow in transport channels of Aerosol Jet® printer often has Re < 100. Here, the effects of inertial impaction and gravitational settling with laminar flows in 90° bends are examined using an OpenFOAM® CFD package, for Re ~ 50 to 1000. The computational code is verified by comparing with the experimental result of Pui et al. for Re = 1000. Besides inertial impaction due to the centrifugal forces in bends, the effect of gravitational settling is shown to become increasingly significant with reduction of tube-flow velocity, which can also be quite sensitive to the bend orientation when the mist flow rate is low. For situations of downward bend or upward inlet, where the gravitational force and centrifugal force oppose each other, the effect of gravitational settling appears relatively insignificant. However, the particle deposition efficiency is generally enhanced in upward bends or bends with downward inlet, where the gravitational force and centrifugal force reinforce each other, exhibiting large deviations from the zero-g case, especially at lower flow velocities (i.e., smaller Froude number).