Hui Zhu

Fibrous filters are widely used for aerosol control; however, the coupled effects of elliptical fiber geometry and orientation on diffusion-dominated nanoparticle capture and efficiency–resistance optimization remain insufficiently understood. This study develops a numerical framework to investigate the effects of fiber aspect ratio (ε = 1–4), attack angle (θ = 0–90°), packing density (C = 0.01–0.10), and particle diameter (d_p = 0.01–1 μm) on the diffusional collection efficiency, pressure drop, and quality factor of elliptical fibers. The airflow field is solved under steady laminar conditions, and particle trajectories are simulated using a Langevin-based Brownian motion model. The results show that elliptical fibers with moderate aspect ratios (ε ≤ 2) exhibit filtration characteristics comparable to circular fibers, whereas highly elongated fibers (ε = 4) provide enhanced particle capture by modifying near-fiber flow structures and increasing particle–fiber interactions. However, the benefits of increased aspect ratio depend strongly on fiber orientation and must be balanced against the associated pressure-drop penalty. Quality factor analysis reveals that the streamwise-aligned elliptical fiber configuration (ε = 4 and θ = 0°) achieves the best overall performance within the investigated parameter range by maintaining high collection efficiency while minimizing aerodynamic resistance. These findings demonstrate that elliptical fiber optimization requires simultaneous consideration of geometry and orientation and provide mechanistic guidance for designing energy-efficient fibrous filtration materials.

This paper incorporates various currently known collection mechanisms (including Brownian diffusion, interception effect, inertial impaction, thermophoresis, diffusiophoresis, and electrostatic interaction) into the calculation of the total collection efficiency to analyze their impacts on the scavenging coefficient. The turbulent effect is introduced into the parametric study of the scavenging coefficient. Combining the local raindrop size distribution and aerosol size distribution, a theoretical prediction model for multi-fraction aerosol scavenging by rainfall is established and verified and corrected with measured data. The main conclusions are as follows: For particles within the accumulation mode range, the influence of the collision efficiency needs to be carefully considered. When studying the scavenging coefficient, it is necessary to combine the locally measured raindrop size distribution and aerosol size distribution. The influence of the aerosol size distribution on the scavenging coefficient under different seasonal conditions in the same area can be neglected. When the turbulent effect is introduced, the theoretical prediction is closer to the actual situation. In comparison with the actual measured PM_2.5 values in Guangzhou City, Hefei City, and Tianjin City, the temporal variation characteristics of PM_2.5 estimated by the theoretical model exhibit a substantial degree of consistency with the trends revealed by the measurement results. Additionally, a linear correlation is discernible between the scavenging coefficients obtained from field measurements in these three regions and those calculated by the theoretical model. Specifically, the equations of the linear relationships are Λ_s = 0.498 × 10⁻⁵ + 1.025Λ_m; Λ_s = 1.035Λ_m − 0.036 × 10⁻⁵; and Λ_s = 0.903Λ_m − 1.11 × 10⁻⁵.