## 3 Results and Discussion
Micro-particle deposition is important to consider in reusable face masks, and therefore washing instructions should be followed carefully. However, over washing can damage the fabric, so the manufacturer's end-of-life instructions should be followed. The spray is an aerosol mist of liquid with a size range of 0.05 \(\upmu\)m to 1 \(\upmu\)m, giving a polydisperse distribution of particles. The pore size allows small particles to penetrate the mask; larger particles deposited upon the mask surface, as shown in (Figure 3(a-l)). Figure 3m displays the velocity of each mask and of its layers in bar chart form. For this, an average velocity at entry was required for the three-dimensional velocity profile over the rectangular duct area. The maximum entry velocity (\(v_{1}\)) at the air duct mid-position is shown. For each mask, the first velocity bar displayed is that for the whole mask, followed by bars representing the individual layers. Overall, the results show that the filtration efficiencies of multi-layered masks are greater than those of their individual layers. The comparison between the exit velocities (m/s) of each whole mask is as follows: _FFP3_ (0.4 m/s) and _FFP2_ (0.5 m/s) have the greatest values, whereas the lowest is that of the _Antiviral_ mask (1.8 m/s). The _Surgical_ and _Silk_ masks have similar exit velocities (1.6 m/s), and the _Reusable Cotton_ exit velocity is slightly lower at 1.3 m/s. This indicates that the greatest filtering efficiency applies at the lowest exit velocity (see Figure 3m and Table 1). Figure 3: _Cont._  
Figure 3n demonstrates the average pore size of each mask as a whole and for its individual layers. The first block of bars applies to the six whole masks, followed by individual layers depicted by the color key. As whole masks, the _FFP3_ was the least porous (912 um), whereas the _Reusable Cotton_ was the most porous (4936 um). As an example, \(\
u_{0}=37.76\), \(\
u_{1}=8.65\) (m/s), and F = 31%. These values for the first layer of the _surgical_ mask are judged to be a realistic estimate of the passage of air (face velocity) through a porous face mask layer. An estimate of the total area of the pores based upon the SEM analysis is assumed to be distributed evenly as an average calculation within the air duct rectangular area. Here, the average porosity (pore size) of each layer of six different masks and of each whole mask was calculated and is shown in Table 1. These averages lie in a range of 2.5-24% of the average value of between five to fifteen SEM measurements, which are shown in the bar chart (see Figure 3n) [36]. Figure 4 is a mesh study of a surgical face mask, showing the three different mesh zones (mask, mannequin head, and exterior) for the convergency of the results. This phenomenon is due to the mask's structure. To conclude, according to the simulations,  
Figure 3: The sprayed aerosol micro-particles on the outside layer of: (**a,b**) Surgical; (**c,d**) Reusable Cotton; (**e,f**) FFP2; (**g,h**) FFP3; (**i,j**) Antiviral; (**k,l**) Silk masks. (**m,n**) Graphs show the exit velocity of whole and individual layers (**m**); and the pore size of whole and individual layers (**n**). the masks with the highest filtering capabilities for particles (<5 \(\upmu\)m) are _FFP3_ and _FFP2_. This is substantiated by the direct measurement of pore size and fiber diameter given in Figure 2. These findings confirmed earlier studies on mask layer transmissibility [1]. The volume fraction of water is used to evaluate the water permeability of the six different face masks. Figure 5a-f show the velocity profile distribution from the source to the wearer along the horizontal y-axis. The velocity in the proximity of the wearer's face is reduced drastically. The droplets represent the water distribution within the flow. The size of the droplets was set to 5 \(\upmu\)m according to the present results and previous studies [37,38]. Different analyses were used in series in order to evaluate which mask reduces better the volume fraction of H\({}_{2}\)O at the wearer's face.