Pan Wang1, Shouqi Yuan This email address is being protected from spambots. You need JavaScript enabled to view it.1, Ning Yang This email address is being protected from spambots. You need JavaScript enabled to view it.2, Aiying Wang3

1 Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China
2 School of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212013, China
3 China National Rice Research Institute, Hangzhou 310006, China

Received: June 19, 2020
Revised: October 22, 2020
Accepted: November 12, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

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Cite this article:

Wang, P., Yuan, S., Yang, N., Wang, A. (2021). Performance Evaluation of a Virtual Impactor with an Additional Pretreatment Structure for Particle Separation. Aerosol Air Qual. Res. 21, 200269.


  • A novel separation method based on microfluidic chip was proposed.
  • A new micro separator including pretreatment and virtual impactor was designed.
  • The collection efficiency curve can be improved obviously by pretreatment structure.


In this paper, a proposed method based on a microfluidic chip that can arrange the collected particles in radial positions according to their sizes before virtual impactor separation was introduced. The main objective of this paper was to design a novel micro-separator structure composed of two major parts: a virtual impactor, and a pretreatment that consists of a sheath flow and a backward-facing step flow configuration. In the separation process, the particles firstly were aggregated on the middle channel by the sheath flow, then ordered in radial position of backward-facing step flow, and finally separated in virtual impactor. To determine the effects of the pretreatment, both simulations and experiments were conducted. A parameter optimization was performed on the micro-separator where the cut-off size of the virtual impactor was 2.5 µm. The results demonstrated that when the flow ratio between inlet flow rate and the total flow rate was set to 50% and the expansion ratio (Er) was 2. The cut-off size of the micro-separator was reduced by 20.77% from 2.436 µm to 1.93 µm, and the wall loss (WL) was acceptable compared with the result only using PM2.5 virtual impactor. The effect of pretreatment on PM1 and PM5 virtual impactor also saw an improvement of collection efficiency even when the additional pretreatment had varying Reynold numbers and nozzle sizes. Accordingly, the stk50 value was reduced by 44.39% from 0.669 to 0.372 by adding pretreatment before the virtual impactor.

Keywords: Microfluidics, Pretreatment, Particle arrangement, Virtual impactor, Collection efficiency

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