Paper Number
BF17
Session
Biomaterials and Bio-fluid Dynamics
Title
Effects of saliva elasticity and expiration velocity on aerosol formation upon sneezing
Presentation Date and Time
October 11, 2022 (Tuesday) 2:50
Track / Room
Track 4 / Michigan AB
Authors
- Rodriguez-Hakim, Mariana (ETH Zürich, Department of Materials)
- Räz, Linard (ETH Zürich, Department of Materials)
- Vermant, Jan (ETH Zürich, Materials)
Author and Affiliation Lines
Mariana Rodriguez-Hakim, Linard Räz and Jan Vermant
Department of Materials, ETH Zürich, Zürich, Switzerland
Speaker / Presenter
Rodriguez-Hakim, Mariana
Keywords
experimental methods; bio-fluids; biomaterials; flow-induced instabilities; polymer solutions
Text of Abstract
Aerosols and droplets that are produced upon sneezing, coughing, or speaking can lead to the transmission of contagious diseases such as COVID-19, influenza, and tuberculosis. The mechanism of droplet formation during sneezing has been previously documented, revealing that the mucus volume is initially expelled as a flat sheet, which destabilizes into filaments that subsequently break up into droplets [1]. Less than 1% of the total salivary mass is composed of mucins, a high molecular weight protein that renders mucus viscoelastic. The presence of mucins influences the dynamics of filament stretching by retarding the onset of droplet formation. The process of aerosol formation during sneezing is systematically replicated using an impinging jet setup, where the collision of two liquid jets forms a thin fluid sheet that can subsequently fragment into ligaments and droplets [2]. This setup enables us to investigate a range of dynamic conditions, quantified by the dimensionless Deborah (De), Weber (We), and Reynolds (Re) numbers, which encompass those experienced during sneezing. We conduct experiments using saliva from different healthy human donors, which exhibit significant variations in their elasticity, as quantified via capillary breakup extensional rheology (CaBER) experiments. We summarize the results from all donors in terms of the dimensionless We, Re, and De. We find that sheet destabilization into aerosols is proportional to We, which provides a measure of the inertia (or velocity) of a sneeze, and inversely proportional to De, which quantifies the elasticity of the fluid. This is particularly relevant for human saliva, since the Deborah numbers among donors can differ by up to two orders of magnitude. Thus, higher ejecta velocities and diminished saliva elasticities facilitate the formation of aerosols upon sneezing. [1] B. E. Scharfman et al., Exp Fluids 57, 24 (2016). [2] J. W. M. Bush and A. E. Hasha, J. of Fluid Mech., 511 (2004).