New approach to assessing nanofiber-based air filters efficiency across variable airflow velocities

Abstract

Filtration is a fundamental method in aerosol science for separating unwanted particles, mainly through air filters. Since the onset of the SARS-CoV-2 pandemic in 2019, there has been an increased demand for high- efficiency, low-cost nanofiber-based respirators capable of filtering particles within the size range of viruses and bacteria. The quality factor QF is the critical parameter for evaluating these respirators' practical effectiveness. QF integrates filtration efficiency with a tolerable pressure drop for the respiratory process. Typically, this pressure drop is reported as a function of the flow rate for a given respirator. However, the physical mechanism of filtration is governed by the mean frontal airflow velocity, which depends not only on the flow rate but also on the membrane area, a parameter often unknown in practical applications. The aerosol flow rate influences filtration efficiency and pressure drop through the membrane, yet a comprehensive physical description of this process has been lacking. Therefore, we developed a mathematical-physical model for filtration using a nanofibrous membrane that accounts for all relevant physical mechanisms. This model provides a more accurate definition of the quality factor. Our findings indicate that filtration efficiency does not reach 100 %, even at near-zero air velocities, and that efficiency approaches an asymptotic plateau at high velocities. When fitted to experimental data from various filters using a three-parameters approach, the model's predictions show strong agreement, particularly within the central region of the uncertainty band.