Computational fluid dynamics (CFD) investigation of the gas–solid flow and performance of Andersen cascade impactor

Abstract

The Andersen cascade impactor (ACI) is a device designed to fractionate aerosols by their aerodynamic diameters. This work developed a computational fluid dynamics (CFD) model to investigate flow characteristics and particle deposition behaviour in an ACI. A novel Iterative Simulation (IS) modelling technique was adopted to map the flow information between the source and target zones of individual models, hence enabling the establishment of flow fields across the whole device as a single domain. Particle trajectories and deposition were evaluated using the Lagrangian tracking approach in conjunction with the application of a kinetic energy criterion (KEc). The model was validated by comparing the simulation results with literature and manufacturer's data. The effect of flow rate was evaluated by using the standard and high flow rates of 28.3 and 60Lmin−1. The results showed that operating the ACI at high flow rates reduced the impactor performance by magnifying the cross-flow interactions and recirculation vortices. The heavy wall losses observed at Stages 2 and 3 of the impactor were attributed to more pronounced recirculation vortices at these stages. Increasing particle deposits underneath Stages 0 and 1 around the central ring of jet outlets can be attributed to counter-current flows arising from the central holes in the plates. These conclusions have significant implications for the design and operation of the ACI.