How Scientists Studied Cough Droplets To Model Covid-19 Spread

Studies applied fluid dynamics experiments to show how the respiratory droplets dried and formed aerosols, and how virus particles are distributed within them.

How Scientists Studied Cough Droplets To Model Covid-19 Spread

When the COVID-19 pandemic struck the world, IIT-Bombay Professor Rajneesh Bhardwaj was studying how droplets evaporated for applications in spray cooling and inkjet printing, and his collaborator Amit Agrawal was working on point-of-care medical devices and electronic cooling.

But once it became clear that the pandemic was mainly spreading through cough and sneeze aerosols from infected individuals, the duo began applying their knowledge to understand the evaporation of respiratory droplets from surfaces and the spread of cough clouds.

"Our plans were to continue in the domain of thermal and fluid engineering. However, the pandemic came as an opportunity to diversify and explore other research areas. We thought of extending and applying our knowledge to several unanswered questions in the context of COVID-19," Agrawal, Institute Chair Professor from the Department of Mechanical Engineering, IIT-Bombay, told PTI.

Bhardwaj and Agrawal, both experts in the field of fluid mechanics, said their understanding of the motion of fluids helped them model how the novel coronavirus spread.

"Air and water are the most common fluids, and also the carrier of most viruses and bacteria, it is not that surprising that the subject is playing an important role in understanding and managing the current pandemic," Bhardwaj told PTI.

Numerous studies, over the course of the COVID-19 pandemic, applied principles of fluid mechanics to provide scores of important insights about the distance over which different size respiratory droplets travel, the safe distance between people, and the efficacy of various types of masks in reducing the transfer of contaminated droplets.

Scientists also probed into the process by which larger droplets underwent evaporation and subsequently precipitation to turn into microdroplets called aerosols.

"During this process, big droplets settle on the ground after a short distance in flight while the smaller ones remain airborne for a longer period forming aerosols," explained Saptarshi Basu, from the Indian Institute of Science (IISc), Bengaluru.

"In short, the entire story of droplets leading to infections is a fluid dynamics problem," Basu, Chair Professor in the Department of Mechanical Engineering, told PTI.

Two studies by Basu and his team, both published in the journal Physics of Fluids, applied fluid dynamics experiments to show how the respiratory droplets dried and formed aerosols, and how virus particles are distributed within them.

According to the IISc scientist, factors such as people's mask wearing behaviour, social distancing, population density, and movement of individuals contribute significantly to the infection rate and severity in a region.

However, he believes some of the primary contributors include how respiratory droplets evaporate after ejection, how far they travel, and how they disperse.

"All the above control how droplets can infect other people and norms like safe distance for social distancing," said Basu, who has been studying the physics of droplets in applications ranging from 3D printing, surface patterning, combustion, and biomedical engineering.

As economies slowly opened across the world post lockdowns, and travel restrictions eased, scientists and engineers also applied fluid mechanics to shed light on the indoor spread of the coronavirus.

Scientists, led by Verghese Mathai from the University of Massachusetts-Amherst, US, performed computer simulations to understand the aerosol spread of the coronavirus inside car cabins.

"I had gained industrial experience with this specific type of computational fluid dynamics simulations while I was in India, and my suggestion to use these simulations was primarily motivated by the fact that we could not perform experiments due to the stay-at-home orders, and the pandemic situation required results with a short turnaround time," Mathai said.

The scientists could quickly apply principles used to test flows inside an aircraft engine and suggest the safest way to prevent possible transmission of COVID-19 when people travel in cars in a study published in the journal Science.

"This is an excellent example of how the pandemic made researchers revisit their complementary skills and come together to work on an important topic," Mathai said.

"So this simulation approach can be extended to trains or buses and we can answer important questions about airflows and aerosol type of particles. We can also look into confined buildings, or long queues of people and how potentially pathogen laden airflows around them might get diluted," he said.

Several studies, published in the journal Physics of Fluids, helped predict how the virus spread at different conditions, such as temperature, carbon dioxide concentration, and humidity.

"Those predictions allowed us to identify critical situations for virus transmission," explained Douglas Fontes from the University of Central Florida in the US.

"As the models better represent the real phenomena, we can use them to determine better safety measures for specific conditions, people, and type of disease," Fontes told PTI.

According to Fontes, future simulations could detail the physical properties of mucus, tissue structures within respiratory systems, and how they interact with each other.

"The better our knowledge of the biological characteristics associated with respiratory events that transport diseases, the better our capacity to accurately model how disease transmission through droplet dispersion occurs," he added.