The Flow Physics of Face Masks

Abstract

Although face masks have been used for over a century to provide protection against airborne pathogens and pollutants, close scrutiny of their effectiveness has peaked in the past two years in response to the COVID-19 pandemic. The simplicity of face masks belies the complexity of the physical phenomena that determine their effectiveness as a defense against airborne infections. This complexity is rooted in the fact that the effectiveness of face masks depends on the combined effects of respiratory aerodynamics, filtration flow physics, droplet dynamics and their interactions with porous materials, structural dynamics, physiology, and even human behavior. At its core, however, the face mask is a flow-handling device, and in the current review, we take a flow-physics-centric view of face masks and the key phenomena that underlie their function. We summarize the state-of-the-art in experimental measurements, as well as the growing body of computational studies that have contributed to our understanding of the factors that determine the effectiveness of face masks. The review also lays out some of the important open questions and technical challenges associated with the effectiveness of face masks. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 55 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Design and Evaluation of Face Mask Filtration: Mechanisms, Formulas, and Fluid Dynamics Simulations

“…It should be noted that the permeability of the porous media also plays an important role. In fact, as the porosity of the mask filter decreases, its permeability decreases, and the pressure drop increases [34].…”

Double Layered Compressible Masks

“…Permeability results are available for mask materials, largely coming out of the textile industry [6]. A recent review of the fluid dynamics-centric materials can be found in the work of Rajat et al [8]. The work presented in the current paper involves flow through a compressible filter which was studied by Köry et al [5] in the context of industrial filtering.…”

“…Previous work Face masks have been used for centuries to provide protection from pollutants and pathogens, but attempts to understand the physics of the flow and the filtration physics in this context are more recent, with an enormous increase in activity since the advent of the COVID-19 pandemic. The associated fluid dynamics is complicated involving, as it does, scales varying from nanometres (fibre diameter) to metres (the distance travelled by a respiratory jet), with structural dynamics, droplet and particle dynamics, and even electrostatics playing a role [8]. Computational mask flow experiments have been undertaken using real world observations [1].…”