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URL: https://pubmed.ncbi.nlm.nih.gov/35340680/

⇱ Risk assessment of COVID infection by respiratory droplets from cough for various ventilation scenarios inside an elevator: An OpenFOAM-based computational fluid dynamics analysis - PubMed

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Abstract

Respiratory droplets-which may contain disease spreading virus-exhaled during speaking, coughing, or sneezing are one of the significant causes for the spread of the ongoing COVID-19 pandemic. The droplet dispersion depends on the surrounding air velocity, ambient temperature, and relative humidity. In a confined space like an elevator, the risk of transmission becomes higher when there is an infected person inside the elevator with other individuals. In this work, a numerical investigation is carried out in a three-dimensional domain resembling an elevator using OpenFoam. Three different modes of air ventilation, viz., quiescent, axial exhaust draft, and exhaust fan, have been considered to investigate the effect of ventilation on droplet transmission for two different climatic conditions (30 , 50% relative humidity and 10 , 90% relative humidity). The risk assessment is quantified using a risk factor based on the time-averaged droplet count present near the passenger's hand to head region (risky height zone). The risk factor drops from 40% in a quiescent scenario to 0% in an exhaust fan ventilation condition in a hot dry environment. In general, cold humid conditions are safer than hot dry conditions as the droplets settle down quickly below the risky height zone owing to their larger masses maintained by negligible evaporation. However, an exhaust fan renders the domain in a hot dry ambience completely safe (risk factor, 0%) in 5.5 s whereas it takes 7.48 s for a cold humid ambience.

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Figures

👁 FIG. 1.
FIG. 1.
(a) The whole computational domain. (b) Isometric view of the passenger in the domain. (c) Mouth of the passenger modeled as a rectangular aperture.
👁 FIG. 2.
FIG. 2.
The entire coughing phenomenon.
👁 FIG. 3.
FIG. 3.
(a) Validation of droplet evaporation model including crystallization with literature data and (b) validation of droplet size distribution with literature data at t = 0.6 s.
👁 FIG. 4.
FIG. 4.
(a)–(f) Droplet dispersion in the domain at various time instants for all the scenarios of both the ambiences. Multimedia views:
👁 FIG. 5.
FIG. 5.
(a)–(d) Droplet size distribution in the domain at various time instants for all the scenarios of both the ambiences.
👁 FIG. 6.
FIG. 6.
Cross-sectional plane AB.
👁 FIG. 7.
FIG. 7.
Velocity contours at plane AB (of Fig. 6) along with droplets, at various instances of scenario 2 for the hot dry ambience.
👁 FIG. 8.
FIG. 8.
Temperature contoured velocity vector plots at plane AB (of Fig. 6) at different time instances, of scenario 2 for the hot dry ambience.
👁 FIG. 9.
FIG. 9.
Temperature contoured velocity vector plots at plane AB (of Fig. 6) at different time instances, of scenario 3 for the hot dry ambience.
👁 FIG. 10.
FIG. 10.
Velocity contours at plane AB (of Fig. 6) along with droplets, at various instances of scenario 3 for the hot dry ambience.
👁 FIG. 11.
FIG. 11.
Droplet fate at various time instants for all the scenarios of both the ambiences.
👁 FIG. 12.
FIG. 12.
Risk factor for various scenarios along with the elucidation of the time averaging process for the computation of risk factor in the bottom right corner.
👁 FIG. 13.
FIG. 13.
(a)–(f) Height distribution of suspended particles for various scenarios of both the ambiences at the end of 10 s.
👁 FIG. 14.
FIG. 14.
(a) and (b) Radial distance distribution in the risky height zone for the quiescent and axial exhaust scenarios of the hot dry ambience at the end of 10 s. (c) and (d) Radial distance distribution in the risky height zone for the quiescent and axial exhaust scenarios of the cold humid ambience at the end of 10 s.
👁 FIG. 15.
FIG. 15.
Percentage of suspended droplets that have fully evaporated to droplet nuclei at different time instances for various scenarios for the hot dry ambience.
👁 FIG. 16.
FIG. 16.
Percentage of suspended virusols in the risky height zone at different time instances for various scenarios for the hot dry ambience.
👁 FIG. 17.
FIG. 17.
(a)–(d) Radial location tracking and diameter of the suspended particles in the risky height zone after 10 s, for different scenarios of both the ambiences.
👁 FIG. 18.
FIG. 18.
(a) and (b) Radial distribution of virusols suspended in the risky height zone after 10 s, for different scenarios of the hot dry ambience.
👁 FIG. 19.
FIG. 19.
(a) Location of slice CD and line AB. (b) Comparison of velocity profile (Vy) of different mesh sizes at line AB. (c) Comparison of velocity contours of different mesh sizes at slice CD for coarse, medium, and fine mesh sizes, respectively, from left to right.
👁 FIG. 20.
FIG. 20.
(a) Comparisons of droplet distributions for coarse, medium, and fine mesh sizes, respectively, from left to right. (b) Comparisons of risk factors for coarse, medium, and fine mesh sizes, respectively, from left to right.
👁 FIG. 21.
FIG. 21.
(a) Adopted mesh, (b) refinements at various locations of the adopted mesh, and (c) mesh section showing gradual refinement of mesh near the mouth of the passenger.

References

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