7/30/2023 0 Comments Fluid mask mask pro(c) Values of the radius of curvature κ − 1 of the jet as a function of the flow rate Q with (filled squares) and without (open circles) a mask covering the pipe. The solid lines represent fits of the trajectories approximating the flow, leading to a quadratic shape y = κ x 2 for low flow rates ( Q ≤ 20 L/min) and straight trajectories ( y = 0) for Q = 50 and 80 L/min. (b) Trajectories y ( x ) of cold air jets emanating from a pipe covered by a mask as a function of the flow rate Q ( 2 ≤ Q ≤ 80 L/min). Depending on the imposed flow rate Q, the trajectory of the jet is linear ( y = 0, light purple) or quadratic ( y = κ x 2, in red). The pipe could be open or covered by a 3-ply mask (blue layers) sealed over the end of the tube, as seen in Fig. (a) Sketch of the experiment: a constant flow rate Q of cold air (at the temperature T −) is imposed for 3 s from a pipe of diameter 2 a leading to an initial velocity V 0. Trajectory of a controlled jet of cold air. The horizontal dashed line delimits exhalations ( Q > 0) and inhalations ( Q < 0). Depending on the kind of respiration, the expiratory flow-rate Q reaches a maximum at approximately 15 L/min (i, blue data), 40 L/min (ii, red), or 200 L/min (iii–iv, green and orange). (c) Measurements of the expiratory flow-rate Q ( t) during those four kinds of respirations. While exhaled flow is contained within 1 cm from the mask in the case of soft respirations (i) and (ii), it reaches distances of the order of 10 cm for heavy respiration (iii) and (iv) as CO 2 jets emanate from the mask. (b) Visualization of the exhaled CO 2 for the four kinds of exhalations (i)–(iv) when the subject wears a mask (false colors). From left to right: (i, blue) soft respiration from the nose, (ii, red) mild respiration with an open mouth, (iii, green) heavy respiration, and (iv, orange) blowing. (a) Visualization of the exhaled CO 2 without wearing a mask (false colors). Typical air flows during four distinct exhalations without and with a face mask. By comparing results on human subjects and model experiments, we propose a model to rationalize how a mask changes the air flow, and thus we provide quantitative insights that are useful for descriptions of disease transmission. Therefore, wearing a mask offers a strong mitigation of direct transport of infectious material in addition to providing a filtering function. In addition, we show that the tissue of common surgical face masks has a low permeability, which efficiently transforms the jetlike flows of exhalation produced during breathing or speaking into quasivertical buoyancy-driven flows. We show how a mask confines the exhaled flows within tens of centimeters in front of a person breathing or speaking. In this study, we characterize the aerodynamic effect of the presence of a mask by tracking the air exhaled by a person through a mask, using both infrared imaging and particle image velocimetry performed on illuminated fog droplets surrounding a subject. While their main purpose is to filter pathogenic droplets, masks also represent a porous barrier to exhaled and inhaled air flow. Face masks are used widely to mitigate the spread of infectious diseases.
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