Derivation of a new dimensionless design criterion for MEMS-based low-flow micro virtual impactors

Abstract

To respond to the spread of respiratory infectious diseases, a low-flow particle classification device capable of accurately classifying and measuring the concentration of airborne bioaerosols is required. In this study, a micro virtual impactor (μVI) capable of stable operation even at a low flow rate of 50 mL/min was designed to address the problem of bioaerosol damage or evaporation under high-flow conditions, and a new design criterion was proposed. The μVIs with cutoff sizes of 0.3, 1.0, and 2.5 μm were fabricated, and numerical and experimental analyses were conducted to compare their wall losses and collection efficiencies. While the width of the acceleration nozzle had been used as the characteristic length in previous studies, the hydraulic diameter of the acceleration nozzle was adopted in this study, and a dimensionless criterion of √(Stk50) = 0.865 was derived to determine the cutoff size. Simulation and experimental results for the μVIs designed based on this criterion agreed within an error range of 0.4–6%, verifying the accuracy of the proposed design method. Therefore, the new design criterion proposed in this study was demonstrated to overcome the limitations of previous design methods and to provide a practical guideline for designing μVIs optimized for low-flow bioaerosol classification. The results are expected to contribute to the miniaturization and precision improvement of future portable bioaerosol detectors and fine particle classification devices.