@article{gautam_kumar_tafreshi_pourdeyhimi_2024, title={A simple approach to simulate corona-charged electret filters}, volume={176}, ISSN={["1879-1964"]}, url={https://doi.org/10.1016/j.jaerosci.2023.106293}, DOI={10.1016/j.jaerosci.2023.106293}, abstractNote={This paper presents a novel computational model devised to simulate how different ways of corona-charging a fibrous filter can impact its aerosol collection efficiency. The model assigns different bipolar charges to the fibers in the media based on how the corona-generated negative ions impact these fibers they travel from the corona needles towards the grounded surface underneath the media. The charge assignment process is based on observations made from simulating the electrohydrodynamic field around the corona needles. With the fibers virtually charged, the trajectory of positively and negatively charged aerosol particles, ranging in size from 30 to 500 nm, were simulated across the filter thickness to quantify the effect of fiber charge distribution on the filter efficiency. The performance of our virtual filter was found to be better when it was exposed to the corona ions on both the face and back sides. More interestingly, it was found that the filtration efficiency of the filter was dependent on the order by which its face and back sides were charged. The filter was observed to capture smaller particles (less than 150 nm) more efficiently when it was first charged on the face side and then charged on the back side. The opposite effect was observed when the charging order was reversed. This difference in filtration performance was found to arise from the differences in the solid volume fraction of the filter across its thickness.}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Gautam, S. and Kumar, A. and Tafreshi, H. V. and Pourdeyhimi, B.}, year={2024}, month={Feb} }
 @article{gautam_kumar_tafreshi_pourdeyhimi_2024, title={Designing Multi-Layer electret filters via numerical simulation}, volume={286}, ISSN={["1873-4405"]}, url={https://doi.org/10.1016/j.ces.2023.119680}, DOI={10.1016/j.ces.2023.119680}, abstractNote={The deposition of neutral and charged particles inside an electrostatically charged filter can affect its performance by decreasing its ability to capture additional particles and by increasing its pressure drop. The particle-loaded behavior of a composite filter comprised of three fibrous layers is studied in this paper using a macroscale simulation approach. Each of these fibrous layers were assumed to have fibers with the same amount of charge but different charge polarities of only unipolar positive, only unipolar negative, or only bipolar. The charged layers were stacked on top of one another in three different configurations with respect to the flow direction and their filtration efficiency and pressure drop were compared during particle loading with neutralized particles (having the Boltzmann equilibrium charge distribution), singly-charged particles, and neutral particles. Our simulations revealed that placing the bipolarly-charged layer downstream of the unipolarly charged layers helps to lower the negative impact of particle deposition on pressure drop and filtration efficiency of the resulting composite filter. This study introduces a design tool, which can be used to optimize the configuration of a composite filter to enhance the particle capture efficiency and minimize pressure drop.}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Gautam, S. and Kumar, A. and Tafreshi, H. V. and Pourdeyhimi, B.}, year={2024}, month={Mar} }
 @article{rahman_gautam_tafreshi_pourdeyhimi_2024, title={The role of 3D electrostatic field in modeling the electrospinning process}, volume={135}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0187859}, DOI={10.1063/5.0187859}, abstractNote={Electrospinning is a cost-effective but very intricate method of producing polymeric nanofibers at room temperature. Unfortunately however, it is extremely difficult to predict the diameter or other properties of the fibers produced via electrospinning a prior. In this paper, we present a new approach to simulate fiber formation during electrospinning. Our work builds on the mathematical framework that was originally developed by Reneker and Yarin in 2000. Our approach incorporates the 3D electrostatic field that surrounds the fiber in a Lagrangian discrete particle tracking algorithm that tracks the trajectory of the fiber in air and predicts its deposition velocity and diameter. We investigate the effects of electrostatic field spatial variation on fiber electrospinning and compare our results with those obtained using a constant electrostatic field, the traditional approach, and with experiments (conducted using polyurethane). We considered three different electrospinning configurations of single-needle-plate-collector, single-needle-drum-collector, and two-needles-drum-collector to investigate how different electrostatic fields impact fiber formation. The computational model developed in this work helps to advance the current state of the art in modeling the electrospinning process.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Rahman, S. M. and Gautam, S. and Tafreshi, H. V. and Pourdeyhimi, B.}, year={2024}, month={Jan} }
 @article{kumar_gautam_atri_tafreshi_pourdeyhimi_2023, title={Importance of Dipole Orientation in Electrostatic Aerosol Filtration}, volume={39}, ISSN={["1520-5827"]}, url={https://doi.org/10.1021/acs.langmuir.3c02016}, DOI={10.1021/acs.langmuir.3c02016}, abstractNote={Electrostatic charge is a major part of modern-day aerosol filtration media (e.g., N95 respirators and surgical facemasks) that has remained poorly understood due to its complicated physics. As such, charging a fibrous material has relied on empiricism in dire need of a mathematical foundation to further advance product design and optimization. In this concern, we have conducted a series of numerical simulations to improve our understanding of how an electrostatically charged fiber captures airborne particles and to quantify how the fiber's dipole orientation impacts its capture efficiency. Special attention was paid to the role of Coulomb and dielectrophoretic forces in the capture of particles of different charge polarities (e.g., particles having a Boltzmann charge distribution). Simulation results were compared with the predictions of the popular empirical correlations from the literature and discussed in detail. Predictions of the empirical correlations better agreed with the simulation results obtained for fibers with a dipole perpendicular to the flow direction rather than for fibers with a dipole parallel to the flow. This indicates that such empirical correlations are more suitable for filters charged via contact electrification (friction charging), where the dipoles are mostly perpendicular to the flow direction, and less suitable for corona-charged media, where the fiber dipoles are generally parallel to the flow direction.}, number={49}, journal={LANGMUIR}, author={Kumar, A. and Gautam, S. and Atri, S. and Tafreshi, H. V. and Pourdeyhimi, B.}, year={2023}, month={Nov}, pages={17653–17663} }
 @article{jamali_atri_gautam_saleh_tafreshi_pourdeyhimi_2023, title={Macroscale modeling of electrostatically charged facemasks}, volume={4}, ISSN={["1521-7388"]}, url={https://publons.com/wos-op/publon/65200080/}, DOI={10.1080/02786826.2023.2203188}, abstractNote={Abstract In this study, the instantaneous collection efficiency and pressure drop of an N95 facemask is numerically simulated in a setting similar (but not identical) to that used by NIOSH to certify N95 respirators. More specifically, a CPU-friendly macroscale model is developed, for the first time, to simulate the performance of an electrostatically-charged facemask when the mask is clean and when it is loaded with neutral or neutralized nanoparticles. The simulations were performed using ANSYS software enhanced with in-house subroutines, and they were calibrated using the experimental data reported in the literature for the initial efficiency of N95 masks. In addition, a correction factor was developed for the Kozeny-Carman permeability equation to expand its application to the case of nanoparticle-deposits, where the dendrites porosity is very high and the aerodynamic slip is expected to occur. Copyright © 2023 American Association for Aerosol Research}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Jamali, M. and Atri, S. and Gautam, S. and Saleh, A. M. and Tafreshi, H. V. and Pourdeyhimi, B.}, year={2023}, month={Apr} }
 @article{gautam_saleh_tafreshi_radney_pourdeyhimi_2023, title={Macroscale simulation of particle loading in electrostatically charged filters}, volume={173}, ISSN={["1879-1964"]}, url={https://doi.org/10.1016/j.jaerosci.2023.106212}, DOI={10.1016/j.jaerosci.2023.106212}, abstractNote={Existing studies have shown that particle collection efficiency of a charged filter tends to decrease with particle loading to a certain extent, then increase with further loading. This contrasts with pressure drop which monotonically increases with particle loading. This trend in particle collection efficiency is due to a variety of factors including, but not limited to, neutralization and aerodynamic shielding of the fibers' electrostatic field. The current paper presents a semi-empirical macroscale simulation method to predict the instantaneous pressure drop and particle collection efficiency of an electrostatically charged filter during the early stages of particle loading. The simulations were performed by using ANSYS software enhanced with a series of in-house subroutines. The simulation results are compared with experimental data (for calibration and validation) obtained from testing a bipolarly-charged (55 μC m−2) polypropylene filter exposed to different levels of nanoparticle loadings. The filter media was loaded (both experimentally and computationally) with polydisperse NaCl nanoparticles (count median diameter of 75 nm) having charge values of ±1e. The loaded media were then tested (experimentally and computationally) with NaCl nanoparticles spanning 10 nm–500 nm in electrical mobility diameter (from TSI 3160 filter tester) having a Fuchs charge distribution. In addition, a high-porosity conditional factor was developed for the Kozeny-Carman permeability equation to expand its application to the case of nanoparticle deposits, where the dendrites’ porosity is very high, and aerodynamic slip is expected to occur.}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Gautam, S. and Saleh, A. M. and Tafreshi, H. V. and Radney, J. G. and Pourdeyhimi, B.}, year={2023}, month={Sep} }