Particle dispersion induced by vortical interactions in a particle-laden upward jet with a partial crossflow

Abstract

Abstract

Particle leakage through the exhalation valve on a face mask under flow conditions mimicking human breathing: A critical assessment

“…τ p is derived based on the force balance between the Stokes drag force and gravitational body force on the particle under the condition of . The flow timescale was defined as , where D h is the hydraulic diameter of the jet nozzle and U is the jet bulk velocity ( Fessler and Eaton, 1997 ; Lau and Nathan, 2014 ; Park and Park, 2021 ). In previous studies, silicon particles were used to mimic airborne contaminants: dusts (PM 2.5 ), fumes, mist (solution being sprayed), microplastics, and bioaerosols (small respiratory droplets, and viral particles) ( Bakand et al , 2005 ; Yang et al , 2007 ; Morawska et al , 2009 ; Johnson et al , 2011 ; Prata, 2018 ).…”

“…Droplets less than m evaporate rapidly (in s) at room temperature, form nuclei, and are transported as passive scalars ( Bhagat et al , 2020 ; Jarvis, 2020 ; Mittal et al , 2020b ). The particle size is evaluated with a particle size analyzer (Mastersizer 2000; Marvern Panalytical Ltd.) for a sample (10 g) of particles, and it has a Gaussian distribution with a standard deviation of 15% ( Park and Park, 2021 ). In Table I , we provide important parameters characterizing the present experimental and flow conditions.…”

“…In the same region of interest (ROI) for the airflow measurement, the particle distributions were measured using planar nephelometry (PN) ( Birzer et al , 2012 ; Lau and Nathan, 2014 ; Park and Park, 2021 ) ( Fig. 5 ).…”

“…According to 42 CFR part 84 (USA), air leakage into the respirator from the exhalation valve should not exceed 30 ml/min under a constant suction head of 25 mmH 2 O. Although the amount of air leakage is controlled, the aerodynamic behavior (concentration, dispersion, and trapping) of particles (solid, fluid, or biological; Tang et al, 1992 ; Eaton and Fessler, 1994 ; Marchioli and Soldati, 2002 ; Gibert et al , 2012 ; Liu et al , 2020 ; Park and Park, 2021 ) that accompanies the operation of the valve in flow conditions mimicking actual human breathing is unknown. However, it is critical to ensure that the penetration of particles through the exhalation valve does not compromise the filtering efficiency of the face mask.…”

“…However because our ultimate aim is to develop a face mask that both achieves high-efficiency shielding and easy breathing, we need to understand how particles penetrate the valve beyond simple visualizations or statistical analyses. Knowledge of flow-induced particle dynamics, such as the preferential concentration and sweeping, is mature enough to tackle this issue ( Leighton and Acrivos, 1987 ; Eaton and Fessler, 1994 ; Monchaux et al , 2010 ; Lau and Nathan, 2014 ; Park and Park, 2021 ). Therefore, in this study, we experimentally investigate airflow through an exhalation valve and associated particle dynamics (penetration and concentration) mimicking realistic human breathing in terms of airflow rate and direction.…”