Established in 2020 Wednesday, October 27, 2021

Droplets with coronaviruses last longer than previously thought
Computer simulations show, how long small droplets can remain suspended in the air. Image courtesy: Vienna University of Technology.

VIENNA.- It is easier to get infected in winter than in summer—this is true for the Corona pandemic, for influenza and for other viral diseases. Relative humidity plays an important role in this. Outdoors, it is much higher outside in winter than in summer, as can be seen from the fact that our breath condenses into droplets in the cold air.

Previous models assumed that only large droplets pose a relevant risk of infection because small droplets evaporate quickly. At TU Wien, however, in cooperation with the University of Padova, it has now been shown that this is not true: Due to the high humidity of the air we breathe, even small droplets can remain in the air much longer than previously assumed. The study was published in the scientific journal PNAS.

Simulations and plastic heads
Prof. Alfredo Soldati and his team at the Institute of Fluid Mechanics and Heat Transfer TU Wien are researching flows that are composed of different components—so called "multiphase flows." This includes the air that an infected person exhales when sneezing: the infectious viruses are in liquid droplets of different sizes, with gas in between.

This mixture leads to a relatively complicated flow behavior: Both droplets and gas move, both components influence each other, and the droplets can evaporate and become gas themselves. To get to the bottom of these effects, computer simulations were developed, in which the dispersion of droplets and breathing air can be calculated at different environmental parameters, for example at different temperatures and humidity.

In addition, experiments were conducted A nozzle with an electromagnetically controlled valve was installed in a plastic head to spray a mixture of droplets and gas in a precisely defined manner. The process was recorded with high-speed cameras, so it was possible to measure exactly which droplets remained in the air and for how long. Francesco Picano's team at the University of Padua was also involved in the research project.

Humid breathing air makes droplets hover longer
"We found that small droplets stay in the air an order of magnitude longer than previously thought," says Alfredo Soldati. "There's a simple reason for this: the evaporation rate of droplets is not determined by the average relative humidity of the environment, but by the local humidity directly at the droplet's location." The exhaled air is much more humid than the ambient air, and this exhaled humidity causes small droplets to evaporate more slowly. When the first droplets evaporate, this locally leads to higher humidity, further slowing down the further evaporation process of other droplets.

"This does mean that small droplets are infectious for longer than assumed, but that should not be a reason for pessimism," says Alfredo Soldati. "It just shows us that you have to study such phenomena in the correct way to understand them. Only then can we make scientifically sound recommendations, for example regarding masks and safety distances."

Today's News

September 20, 2021

World's first discovery of liquid directional steering on a bio-inspired surface

Discovery highlights the complex lifestyles of frontline immune cells

Skeletal muscle grown in a dish offers insight into neuromuscular diseases

Fossil bird with fancy tail feathers shows that sometimes, it's survival of the sexiest

Droplets with coronaviruses last longer than previously thought

Mushballs stash away missing ammonia on Uranus and Neptune

Rare artefacts discovered on the Murray River

New physics research reveals fresh complexities about electron behavior in materials

Behold the humble water flea, locked in a battle of mythological proportions

SARS-CoV-2 is evolving to get better at becoming airborne, new study shows

Jaws: How an African ray-finned fish is helping us to rethink the fundamentals of evolution

Link between inflammation and pancreatic cancer development uncovered

Researchers infuse bacteria with silver to improve power efficiency in fuel cells

New discovery about meteorites informs atmospheric entry threat assessment

Game-changer for clean hydrogen production

The microbial molecule that turns plants into zombies

Fiber tracking method delivers important new insights into turbulence

How do cells acquire their shapes? A new mechanism identified


Editor & Publisher: Jose Villarreal
Art Director: Juan José Sepúlveda Ramírez

Tell a Friend
Dear User, please complete the form below in order to recommend the ResearchNews newsletter to someone you know.
Please complete all fields marked *.
Sending Mail
Sending Successful