CFD simulations to improve the aerosol tangential inlet of a Differential Mobility Analyzer

Abstract

Differential Mobility Analyzers (DMA) have been studied for decades to classify a wide range of particle sizes. Its correct behavior is determined by the resolution, influenced by Brownian diffusion losses, distortions in the electric and flow field. The design configuration, especially inlets and outlets, can be a reason of these effects, affecting the DMA reliability. One of these configurations is the tangential inlet for polydisperse aerosol, used in the Vienna-type DMA. The use of a tangential inlet reduces the residence time and favored the aerosol flow distribution in the classification chamber. However, in this configuration swirl effects of non-uniform particle behaviors had previously been observed.In this work, the 3D-Computational Fluid-Dynamics has been used to analyze the distortions expected of this DMA in previous studies. The proposed methodology had allowed determining its correct operation and thus, to develop new designs optimizing their operation. The procedure includes the simulation by Ansys Workbench v15.0 and the method to determine an adequate behavior, including the effect on the particle distribution and penetration towards the classification chamber, and the effect on the transfer function. The calculation results have allowed the design of alternative geometries of the aerosol inlet keeping the tangentiality. Using the new geometry, the flow distribution has improved removing the flow disturbances, the particle penetration has increased until 15% and the particle distribution has deviated from the ideal one only in a 2% in some cases. The best behavior has been observed especially at high flow rates and lower particle sizes.