Viscoelasticity reduces the droplet size in mucosalivary film fragmentation during intense respiratory events

TL;DR

This study investigates how the viscoelastic properties of mucosalivary fluids influence droplet size during respiratory events, revealing that viscoelasticity leads to smaller droplets due to thinner, more uniform bag-like structures during fragmentation.

Contribution

It demonstrates experimentally and numerically that viscoelasticity affects the size of aerosol droplets by altering the thickness of bag-like structures during fluid fragmentation.

Findings

Viscoelastic fluids produce smaller aerosol droplets than Newtonian fluids.

Viscoelastic bags inflate larger but rupture into smaller droplets.

Thinner, more uniform sheets in viscoelastic fluids lead to reduced droplet size.

Abstract

We examine the fundamental fluid dynamical mechanisms dictating the generation of bioaerosols in the human trachea during intense respiratory events such as coughing and sneezing, with an emphasis on the role played by the mucosalivary fluid viscoelasticity. An experimental investigation of the shear-induced fragmentation of a mucosalivary-mimetic fluid in a confined geometry reveals that viscoelastic liquids undergo atomization in a manner akin to Newtonian liquids -- via the formation of bag-like structures -- which ultimately rupture through the appearance of retracting holes on the bag surface. Droplets are produced via the unstable retraction of liquid rims bounding these holes. However, in comparison to Newtonian liquids, viscoelastic bags inflate to larger sizes -- implying thinner sheets and, consequently smaller droplets upon rupture. Numerical simulations support that the smaller droplets can be attributed to the thinner sheets, with a more uniform thickness, for viscoelastic bags prior to rupture. Hence, we highlight the role of the viscoelasticity in determining the thickness of the intermediate bag-like structures, which, in turn, govern the droplet size distribution of the expelled aerosol.