Numerical investigation of enhanced ultrafine particle collection in quartz crystal microbalance with electric fields

Abstract

To improve ultrafine particle (UFPs) collection and thus measurement of mass concentrations, we developed a sensitive quartz crystal microbalance (QCM), capable of measuring mass at the nanogram level: an electrostatic force was applied to draw particles to a target position, so that all charged particles in the collection zone were measured. In its design, the COMSOL Multiphysics simulation was used to investigate airflow, electric field strength distribution, particle trajectory, particle deposition position, and collection efficiency within the collection zone inside the QCM detector. The airflow pattern exhibited dominant streamlines that flowed vertically through the nozzles and then horizontally along the QCM plate. This configuration directed UFPs along the streamlines, enhancing their deposition onto the plate. The multi-nozzle design also provided a uniform electric field throughout the collection zone, with average electric field strengths over the QCM surface ranged from 399.9 kV/m to 666.4 kV/m. Increasing the applied voltage and particle charge enhanced both velocity and collection efficiency. Varying particle size was also examined, showing that smaller particles were more responsive to electrostatic forces, as indicated by higher particle terminal velocities. The simulated collection efficiency for 30–100 nm particles agreed strongly with predictions from the Deutsch-Anderson equation, where the percentage error between experimental and theoretical results ranged from 4.1 % to 18.3 %. This confirmed that electrostatic force played a significant role in improving the collection efficiency of QCM detectors for UFPs.