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Aerosol agitation: Quantifying the hydrodynamic stressors on particulates encapsulated in small droplets

Oliver McRae1, Kenneth R. Mead2, and James C. Bird1,*

  • 1Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
  • 2Division of Field Studies and Engineering, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, Ohio 45226, USA

  • *jbird@bu.edu
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Phys. Rev. Fluids 6, L031601 – Published 8 March, 2021

DOI: https://doi.org/10.1103/PhysRevFluids.6.L031601

Abstract

Lower respiratory tract infections originate from multiple aerosol sources, varying from droplets erupting from bursting bubbles in a toilet or those produced by human speech. A key component of the aerosol-based infection pathway—from source to potential host—is the survival of the pathogen during aerosolization. Due to their finite-time instability, pinch-off processes occurring during aerosolization have the potential to rapidly accelerate the fluid into focused regions of these droplets, stress objects therein, and if powerful enough, disrupt biological life. However, the extent that a pathogen will be exposed to damaging hydrodynamic stressors during the aerosolization process is unknown. Here we compute the probability that particulates will be exposed to a hydrodynamic stressor during the generation of droplets that range in size from one to 100 microns. For example, particulates in water droplets less than 5 μm have a 50% chance of being subjected to an energy dissipation rate in excess of 1011 W/m3, hydrodynamic stresses in excess of 104 Pa, and strain rates in excess of 107 s−1, values known to damage certain biological cells. Using a combination of numerical simulations and self-similar dynamics, we show how the exposure within a droplet can be generally predicted from its size, surface tension, and density, even across different aerosolization mechanisms. Collectively, these results introduce aerosol agitation as a potential factor in pathogen transmission and implicate the pinch-off singularity flow as setting the distribution of hydrodynamic stressors experienced within the droplet.

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Phys. Rev. Fluids 6, L031601– Published 8 March, 2021
  • Received 30 August 2020
  • Accepted 11 February 2021
Article part of CHORUS
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