Quantitative analysis of airflow dynamics with masks during breathing using particle image velocimetry*

Detailed quantitative airflow measurements in the vicinity of a person's face while breathing are important for the optimization of mask usage and respiratory protection in diverse settings. 

Using Particle Image Velocimetry (PIV), this study analyzes the role of different masks on airflow dynamics and droplet transport during breathing. The investigation examines mean and maximum velocities, directional changes, airflow patterns, and droplet transport during exhalation.  

2D PIV was employed to measure airflow velocities within the first 11.34 centimeters in front of a person's face, with a resolution of 1.22 mm^2. The study quantitatively analyzes the evolution of breathing by measuring mean and maximum airflow velocities. Without masks, mean airflow velocities reach 1 m/s while exhaling. Cloth masks reduce mean velocities to 0.35-0.4 m/s, while FFP2 masks with exhalation valves maintain 0.4-0.5 m/s. Maximum velocities without masks peak at 4.2 m/s, while cloth masks reduce them to 2 m/s, and FFP2 masks to 2.3 m/s. Cloth masks exhibit a 70% reduction in mean velocities and a 50% reduction in maximum velocities, with an upward airflow direction. FFP2 masks, with a 42.5% reduction, redirect airflow downwards. 

Using the measured airflow velocities as initial velocity, the transport of droplets of a given size (ranging from 5 to 50 microns) will be discussed.