Investigation of the near-field and far-field protection effect of face masks using micro-scale and macro-scale CFD simulations

Abstract

Due to the corona pandemic, the wearing of masks is mandatory in many fields of life. Inhaling and exhaling while wearing a mask can be stressful over a long period of time, especially during strenuous exertions - even for healthy persons. Providing masks with a low pressure drop at a high filtration efficiency is crucial for persons with preexisting trouble breathing who are especially vulnerable. Therefore, the aim of this work is to investigate both the near-field and the far-field protection effect of an existing medical and FFP 2 mask.
The set-up of the CFD model is carried out in 3 stages corresponding to 3 spatial scales. In the first stage, based on µCT scans, individual fibers of mask materials are resolved and filtration efficiency as well as macro-scale material parameters are determined by micro-scale simulation. Stage 2 focusses on the near field of a mask and takes the different mask shapes into account as well as the results of stage 1. The simulations serve for determining pressure loss of the complete mask including the effect of the shape of the mask. Last but not least, in stage three, the exhalation and inhalation of aerosols through a mask is investigated in order to determine the far-field reduction of aerosol concentration by the mask. For this purpose, the flow field corresponding to different aerosol generation processes such as breathing, talking and coughing is simulated using a Eulerian approach and a specific particle distribution for every case is injected after the steady-state flow solution is established (Lagrangian approach).
Simulation results of pressure drop and filtration efficiency of medical and FFP2 masks are shown and validated by comparison to experimental data. We investigate the influence of the shape of the mask, the leakage due to a bad fit of the mask as well as the effect of different aerosol injection scenarios (breathing, coughing, talking) on the reduction of the far-field aerosol particle concentration allowing to assess the protection effect of the different types of masks.

Full text

Investigation of the near-field and far-field protection effect of face
masks using micro-scale and macro-scale CFD simulations
André Baumann, Dennis Hoch, Jennifer Niessner
Institute for Flow in Additively Manufactured Porous Media (ISAPS), Heilbronn
University of Applied Science,Max-Planck-Straße 39, 74081 Heilbronn, Germany
ABSTRACT
Due to the corona pandemic, the wearing of masks is mandatory in many fields of life.
Inhaling and exhaling while wearing a mask can be stressful over a long period of time,
especially during strenuous exertions - even for healthy persons. Providing masks with
a low pressure drop at a high filtration efficiency is crucial for persons with preexisting
trouble breathing who are especially vulnerable. Therefore, the aim of this work is to
investigate both the near-field and the far-field protection effect of an existing medical
and FFP 2 mask.
The set-up of the CFD model is carried out in 3 stages corresponding to 3 spatial
scales. In the first stage, based on µCT scans, individual fibers of mask materials are
resolved and filtration efficiency as well as macro-scale material parameters are
determined by micro-scale simulation. Stage 2 focusses on the near field of a mask
and takes the different mask shapes into account as well as the results of stage 1. The
simulations serve for determining pressure loss of the complete mask including the
effect of the shape of the mask. Last but not least, in stage three, the exhalation and
inhalation of aerosols through a mask is investigated in order to determine the far-field
reduction of aerosol concentration by the mask. For this purpose, the flow field
corresponding to different aerosol generation processes such as breathing, talking and
coughing is simulated using a Eulerian approach and a specific particle distribution for
every case is injected after the steady-state flow solution is established (Lagrangian
approach).
Simulation results of pressure drop and filtration efficiency of medical and FFP2 masks
are shown and validated by comparison to experimental data. We investigate the
influence of the shape of the mask, the leakage due to a bad fit of the mask as well as
the effect of different aerosol injection scenarios (breathing, coughing, talking) on the
reduction of the far-field aerosol particle concentration allowing to assess the
protection effect of the different types of masks.
Left-hand side: micro-scale simulations to determine fractional filtration efficiency and
far-field macro-scale simulation to account for the reduction of aerosol particle
concentration.