Kuang C. Lin

Inhalation of airborne fibers such as asbestos has been a concern for toxicological response that can affect lung tissues. This study aims at developing a computational model that predicts experimental measurements for fibrous particle filtration in nylon mesh screens and elucidates the physics underlying particle dynamics. The filtration process is operated at the constant airflow of 7 cm/s for particles with aerodynamic diameters between 0.8 and 10 μm corresponding to the particle length between 11.4 and 54.3 μm and particle diameter between 0.6 and 8.5 μm. The aerodynamic diameter characterizes particle sizes having different shapes and densities with a single dimension. This two-dimensional (2D) computational model with a single fiber represents the infinite array of screen fibers parallel to each other and screen collection efficiency is estimated by a previously proposed formula taking into account particle laden flow crossing two crossed fibers. The orientations of fibrous particles in a three-dimensional form are projected to the 2D plane and analyzed in the cross-sectional view of a screen. The simulations generally well predict experimental profiles of the screen collection efficiency as a function the aerodynamic diameter and screen pore size. The analyses carried out contain the distribution of particle fraction deposited along fiber surface, particle pathlines, particle distribution in the gas flow, and breakdown of forces acting on a single particle.

The computational study reported here is motivated by a desire to develop a computer model for predicting and analyzing experimental screen collection efficiency of wire-mesh filters for microparticles (up to 100 µm). The operational parameters include the particle size of 0.3 to 100 μm, screen opening size of 11 to 160 μm, fiber diameter of 33 to 60 μm and superficial velocity of 0.48 cm/s. We use a simplified 2-D model with the hybrid lattice-Boltzmann Lagrangian method to describe flow crossing a single fiber in a periodic cell of a wire screen. The newly proposed formula of the screen collection efficiency representing particle deposition on two crossed fibers in each screen cell effectively predicts the experimental data with good accuracy. The quality factor analysis that determines a filter performance is adopted to evaluate the interplay between the energy needed for gas transport and collection efficiency. In addition, the detailed analyses are given for particle deposition pattern and transport behavior in terms of particle fraction profiles and flow fields. Finally, the degree of individual forces acting on each particle traveling in the gas flow is revealed. Copyright © 2022 American Association for Aerosol Research

While previous experimental studies revealed the existence of optimal heat transfer performance in natural convection of magnetohydrodynamic (MHD) nanofluid flows, it is believed that this phenomenon is not unique in different levels of magnetic flux density. In order to prove this speculation, we numerically investigate the influence of the magnetic field on steady natural convection of aluminum-oxide (Al₂O₃) nanofluids inside an enclosure. The MHD flow model without the consideration of nanofluids is well validated against theoretical, numerical, and experimental results. The nanofluid in the present investigation has temperature-dependent physical properties and is modeled by a two-phase mixture considering thermophoresis and Brownian diffusion. While varying the volume fraction of nanoparticles from 0 to 6%, we methodically examine the effect of the Hartmann number on the heat transfer performance through the thermal behavior map in terms of the Hartmann–Rayleigh plane. Depending on the combination of magnetic intensity and buoyancy-induced flow, the nanofluid heat transfer with the addition of various concentrations of nanoparticles can be categorized into two patterns separated by a critical Hartmann number: the presence of a maximum Nusselt number (Type A) and continuously increased heat transfer rates (Type B) over a wide range of the Rayleigh number from 10³ to 10⁶ and the Hartmann number from 0 to 300. Described by a piecewise-defined function, the critical Hartmann number is exponentially proportional to the Rayleigh number from 10⁴ to 10⁶ and rises linearly in a logarithmic scale with elevating the Rayleigh number from 10³ to 10⁴.