Paper Number
VP48
Session
Pre-recorded Flash Presentations (virtual)
Title
Saliva rheology and its effect on aerosol generation during sneezing
Presentation Date and Time
All Week (Asynchronous) Any Time
Track / Room
Pre-recorded Presentation / Virtual
Authors
- Rodriguez Hakim, Mariana (ETH Zürich, Department of Materials)
- Räz, Linard (ETH Zürich, Department of Materials)
- Vermant, Jan (ETH Zurich, Materials Departement)
Author and Affiliation Lines
Mariana Rodriguez Hakim, Linard Räz and Jan Vermant
Department of Materials, ETH Zürich, Zürich, Zürich 8049, Switzerland
Speaker / Presenter
Rodriguez Hakim, Mariana
Keywords
experimental methods; applied rheology; biological materials; flow-induced instabilities; non-Newtonian fluids; polymer solutions; rheology methods
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]. Experiments are conducted with human saliva provided by different donors, and the resulting sheet morphologies are compared to commercially available saliva substitutes. We quantify the effect of viscoelasticity via oscillatory shear and extensional rheology experiments. Due to the radial flow profile that is established within the sheet, extensional stresses dominate over shear stresses. We summarize our results in terms of the dimensionless Weber, Reynolds, and Deborah numbers. We find that for a given solution, the sheet-to-ligament and the ligament-to-aerosol transitions are primarily determined by the Weber number. The magnitude of this transition Weber number is directly correlated to the elasticity of the solution, quantified by the Deborah number. 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 a diminished saliva elasticity 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).