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Improved guidelines of indoor airborne transmission taking into account departure from the well-mixed assumption

Jorge S. Salinas*, K. A. Krishnaprasad, N. Zgheib, and S. Balachandar†

  • Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, USA

  • *josalinas@ufl.edu
  • †bala1s@ufl.edu
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Phys. Rev. Fluids 7, 064309 – Published 30 June, 2022

DOI: https://doi.org/10.1103/PhysRevFluids.7.064309

Abstract

The well-mixed assumption has been widely used in predicting the spread of infectious diseases in indoor spaces. It is to be expected that a perfect well-mixed state will not be achieved in an indoor space at any reasonable level of ventilation. This work evaluates the well-mixed assumption by comparing the theory with results from large eddy simulations. The robustness of the well-mixed theory is established by comparing at four different levels. The comparison also points out systematic departures in pathogen concentration which can be accurately accounted for with an easily implementable correction factor to quantities such as cumulative exposure time. With the well-mixed model as the baseline, the correction factor can be used to account for additional important problem-specific details. We demonstrate that more accurately accounting for variability in pathogen concentration can help obtain improved estimates for enhanced guidelines of indoor airborne transmission. We further demonstrate that at source-sink separation distances smaller than 5 m, the well-mixed theory on average underestimates the risk of contagion, while for distances larger than about 5 m, the well-mixed theory's prediction, on average, is overly restrictive.

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  72. The present room-scale LES does not resolve the early jet-scale ejection physics. Thus, the source must be interpreted as post-ejection source, at the point where the room-scale ventilation flow dominates the jet flow. This difference is small in case of breathing or soft speaking. For more intense ejection, one must include the effect of the jet phase with an analysis similar to that given in Eq. (7) of Ref. [8] (2022).

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Phys. Rev. Fluids 7, 064309– Published 30 June, 2022
  • Received 18 April 2022
  • Accepted 14 June 2022
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