A sheathed virtual impactor – Microseparator for improved separation of sub- and supercritical sized particles

Abstract

In the separation process of airborne microbial particles, a typical virtual impactor with sheath flow is effective to lower the critical diameter and minimize wall loss. However, a considerable fraction of undesired subcritical particles smaller than the critical diameter are gathered in the minor flow. To address this issue, this article presents a novel microseparator to reduce subcritical particle content while preserving the typical virtual impactor's advantages. The microseparator made of a microfluidic chip adopts a core-aerosol-sheath configuration in which the core and sheath flows raised from clean airflow confine the distribution of microparticles in the aerosol flow towards the core region of the microchannel but away from the center axis. Such configuration effectively decreases the subcritical particle content in the minor flow. The improvement of the proposed microseparator is quantified by comparing the performance with the typical virtual impactor numerically and experimentally at the same critical diameter. At the critical diameters of 0.35 μm, 0.42 μm, 0.52 μm, and 0.6 μm, we find that, firstly, the ratios of subcritical particle content to total particle content (Csp) of our device are 5.24%, 4.74%, 12.34%, and 7.76% smaller than those of typical virtual impactor, respectively. Secondly, the corresponding reduction ratios of subcritical particle (Rsp) of our device are 25.87%, 21.20%, 40.31%, and 33.92%. Lastly, the maximum wall loss of the proposed microseparator in the collection probe is slightly smaller than the typical one, while the operation range of minor flow is enlarged with the premise of maintaining low subcritical particle collection efficiency.