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Numerical Analysis of the Impact of the Use of Personal Protective Equipment on the Face in the Process of Pollutants Spreading Emitted During Breathing

Anna Bulińska
Anna Bulińska
, 
Stanisław Kocik
Stanisław Kocik
 and 
Zbigniew Buliński
Zbigniew Buliński
   | Apr 24, 2023
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Published Online: Apr 24, 2023
Page range: 113 - 130
Received: Nov 10, 2022
Accepted: Feb 27, 2023
DOI: https://doi.org/10.2478/acee-2023-0009
Keywords
© 2023 Anna Bulińska et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1.

Example of geometry showing the torso and head of a human with the fabric mask
Example of geometry showing the torso and head of a human with the fabric mask

Figure 2.

Examples of Personal Protective Equipment used in research, A – full face shield, B – small face shield, C – material mask, D- no PPE
Examples of Personal Protective Equipment used in research, A – full face shield, B – small face shield, C – material mask, D- no PPE

Figure 3.

Refined computational mesh on the cross-section of the numerical model. Geometry with a small face shield
Refined computational mesh on the cross-section of the numerical model. Geometry with a small face shield

Figure 4.

Refined computational mesh on the cross-section of the numerical model. Geometry with a fabric mask
Refined computational mesh on the cross-section of the numerical model. Geometry with a fabric mask

Figure 5.

Computing domain with marked location of the top surface
Computing domain with marked location of the top surface

Figure 6.

Graph of CO2 concentration changes in time on the upper surface of the computational domain for 4 different numerical mesh for two breathing periods at pseudo-steady state
Graph of CO2 concentration changes in time on the upper surface of the computational domain for 4 different numerical mesh for two breathing periods at pseudo-steady state

Figure 7.

Graph of average CO2 concentration at the top surface as a function of a number of mesh cells
Graph of average CO2 concentration at the top surface as a function of a number of mesh cells

Figure 8.

Example of CO2 concentration changes in time at the surface of the nostrils, during breathing, as it is described by developed UDF
Example of CO2 concentration changes in time at the surface of the nostrils, during breathing, as it is described by developed UDF

Figure 9.

Characteristic time points in the breathing cycle used in results analysis
Characteristic time points in the breathing cycle used in results analysis

Figure 10.

Location of section plane for results visualization
Location of section plane for results visualization

Figure 11.

Contours of CO2 concentration in the numerical domain during inhalation for the 21st breathing cycle
Contours of CO2 concentration in the numerical domain during inhalation for the 21st breathing cycle

Figure 12.

Contours of CO2 concentration in the numerical domain during exhalation
Contours of CO2 concentration in the numerical domain during exhalation

Figure 13.

Pathlines coloured with CO2 concentration in the numerical domain during exhalation
Pathlines coloured with CO2 concentration in the numerical domain during exhalation

Figure 14.

Contours of CO2 concentration in the numerical domain during the pause between exhalation and inhalation
Contours of CO2 concentration in the numerical domain during the pause between exhalation and inhalation

Figure 15.

Contours of temperature (K) and velocity (m/s) on the example of models without any PPE and with a face shield located 40 mm from the face, during the pause between exhalation and inhalation
Contours of temperature (K) and velocity (m/s) on the example of models without any PPE and with a face shield located 40 mm from the face, during the pause between exhalation and inhalation

Figure 16.

Time-varying CO2 concentration monitored on the surface of the nostrils
Time-varying CO2 concentration monitored on the surface of the nostrils

Figure 17.

Distributions of CO2 concentration ranges during the inhalation phase
Distributions of CO2 concentration ranges during the inhalation phase

List of boundary conditions with specifications

Element: Type of boundary conditions Conditions related to the conservation of momentum Thermal conditions
Nostrils Mass-flow inlet Mass flux defined by the user Temperature defined by the user, T = 307 K
Face shield surface Wall Standard fixed walls Zero heat flux
Fabric mask Porous Jump Porous materialThickness: 0.5 mmFace permeability: 9.8−10 m2 Zero heat flux
Body surface Wall Standard fixed walls Heat flux 40 W/m2
The outer surface of the numerical domain Pressure-outlet Standard conditions T = 293 K

Grid parameters used for grid independence study

Mesh: 1.1 1.2 1.3 1.4
Element Size [mm]: 20 15.4 11.5 8.8
Sizing [mm]: 5 3.8 2.9 2.2
Number of elements: 887 932 1 643 675 2 886 498 5 251 038

List of parameters describing the quality of meshes

Model Number of elements Average skewness Average orthogonal quality
Reference model without PPE 2 485 096 0.181 0.817
Model with shield covering nose and mouth 2 637 907 0.183 0.814
Model with face shield, 15 mm far from face 2 779 952 0.185 0.812
Model with face shield, 40 mm far from face 2 811 042 0.186 0.811
Model with a fabric mask 907 944 0 (skewness parameter is not applicable for polyhedral mashes) 0.96526

Results of the mesh independence study

Mesh Number of cells, Millions Mesh refinement ratio Solution, ppm Observed discretisation order GCI
1.1 0.888 - 725.5 - -
1.2 1.644 0.81 750.0 - 0.123
1.3 2.886 0.83 767.7 1.63 0.086
1.4 5.251 0.82 784.0 - 0.077
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