Facing shortages of personal protective equipment, some clinicians have advocated the use of barrier enclosures (typically mounted over the head, with and without suction) to contain aerosol emissions from coronavirus disease 2019 (COVID‐19) patients. There is, however, little evidence for its usefulness. To test the effectiveness of such a device, we built a manikin that can expire micron‐sized aerosols at flow rates close to physiological conditions. We then placed the manikin inside the enclosure and used a laser sheet to visualize the aerosol leaking out. We show that with sufficient suction, it is possible to effectively contain aerosol from the manikin, reducing aerosol exposure outside the enclosure by 99%. In contrast, a passive barrier without suction only reduces aerosol exposure by 60%.
A water droplet can bounce off superhydrophobic surfaces
multiple
times before coming to a stop. The energy loss for such droplet rebounds
can be quantified by the ratio of the rebound speed U
R and the initial impact speed U
I; i.e., its restitution coefficient e = U
R/U
I. Despite much
work in this area, a mechanistic explanation for the energy loss for
rebounding droplets is still lacking. Here, we measured e for submillimeter- and millimeter-sized droplets impacting two different
superhydrophobic surfaces over a wide range of U
I (4–700 cm s–1). We proposed simple
scaling laws to explain the observed nonmonotonic dependence of e on U
I. In the limit of low U
I, energy loss is dominated by contact-line
pinning and e is sensitive to the surface wetting
properties, in particular to contact angle hysteresis Δ cos
θ of the surface. In contrast, e is dominated
by inertial-capillary effects and does not depend on Δ cos θ
in the limit of high U
I.
Facing shortages of personal protective equipment, some clinicians have advocated the use of barrier enclosures (typically mounted over the head, with and without suction) to contain aerosol emissions from coronavirus disease 2019 (COVID-19) patients. There is however little evidence for its usefulness. To test the effectiveness of such a device, we built a manikin that can expire micron-sized aerosols at flow rates close to physiological conditions. We then placed the manikin inside the enclosure and used a laser sheet to visualize the aerosol leaking out. We show that with sufficient suction, it is possible to effectively contain aerosol from the manikin even at high flow rates (up to 60 L min−1) of oxygen, reducing aerosol exposure outside the enclosure by 99%. In contrast, a passive barrier without suction only reduces aerosol exposure by 60%.
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