Transport and Fate of Virus-Laden Particles in a Supermarket
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The transport of virus-laden particles was investigated numerically in an archetypical supermarket configuration of area 1,200 m^2 and ceiling height of 4.5 m. The particles were tracked using a Lagrangian particle tracking code coupled with the computational fluid dynamics (CFD) model Ansys Fluent. Air transport was assumed to occur due to indoor ventilation. Flow dynamics were simulated using the Reynolds-averaged Navier Stokes (RANS) approach. The movement and spreading of 5- and 20-μm particles were studied with 0%, 25%, and 100% attachment efficiencies on surfaces in the supermarket. We found that the indoor airflows can significantly enhance the transport of particles (e.g., >15 m for 5 μm, and >5 m for 20 μm); therefore, the 6-ft (2.0 m) social distance recommended by health experts would not be sufficient to prevent the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We found that the attachment on surfaces reduces the transport of particles significantly within the supermarket, and that an attachment efficiency of 25% results in transport similar to that resulting from 100% efficiency. This suggests that the type of surfaces is not crucial in terms of air transport of particles. We support the existing approaches for reducing exposure between people through the adoption of one-way movement within an aisle. However, we also propose placing display shelves within the aisles in a staggered way to form baffles that would both increase the surface area and block the transport of airborne particles. We found that virus-laden particles could be sucked into the ventilation system through return vents, and could pose potential infection risks for the buildings connected to the same ventilation system. Hence, high-efficiency particulate air (HEPA) filters and pleated filters with a minimum efficiency reporting value (MERV) greater than 12 are recommended.
Published papers for details:
Cui, F., Geng, X., Zervaki, O., Dionysiou, D., Katz, J., Haig, S, Boufadel, M.C. 2021. Transport and fate of virus-laden particles in a supermarket: recommendations for risk reduction of COVID-19 spreading. Journal of environmental engineering 147 (4), 04021007
Figure 1. (Color) 3D view of the computational domain. The supply vents are indicated by the dark red arrows, and the return vents are on the sides, indicated by light blue arrows. The entrance doors are indicated by purple rectangles. There are display shelves of different sizes inside the domain. The domain was stretched in the z-direction to show the geometry clearly.
Figure 2. (Color) Velocity magnitude contours at the slice of x = 2.2, 7.6, 11.6, 18, and 24 m. Note the large velocity magnitude under the supply vents and around the returnvents. The supply vents and returnvents right above the slice contours are indicated by the dark red arrows and light blue arrows, respectively. The entrance doors are indicated by purple rectangles. The domain was stretched in the x-direction to show contours clearly.
Figure 3. (Color) Spatial distribution of 5-μm particles at t = 100, 400, 700, and 1,000 s with a 25% attachment efficiency. The domain was stretched in the z-direction to show the results clearly. The deep blue spheres indicate particles suspended in the air, and the orange, light blue, and yellow spheres indicate the particles attached to the ceiling, display shelves, and ground and sidewalls, respectively. A large number of particles attached to different surfaces and stopped spreading.
Figure 4. (Color) Spatial distribution of 5-μm particles at t = 10, 100, 200, and 300 s with a 100% attachment efficiency observed from x = 0 m and about 3 m downstream the releasing source (x = 0 m, y = 20 m, and z = 1.8 m). The deep blue spheres indicate free transport particles, and the orange, light blue, and yellow spheres indicate the particles attached to the ceiling, display shelves, and ground and sidewalls, respectively.
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