From Fuel Droplets in Jet Engines to
Pathogen-carrying Droplets in the Air by Dr Pedro Magalhães de Oliveira (2015), College Research Associate
A
t around the time COVID-19 first hit the UK, I was at Heathrow Airport waiting to board a long-haul flight. I remember the uncertainty caused by the new virus in the air, manifested on passengers’ faces as we saw that those headed to Asia were all wearing masks. Little did I know, I would soon discover why wearing such a simple piece of protective equipment was of vital importance to contain the spread of the virus, as I embarked on a much more important journey: shifting part of my research from aerospace propulsion to the transmission of the SARS-CoV-2 virus. There are fundamental principles that help us understand the behaviour of a droplet, or particle, in an airflow. George Gabriel Stokes (1819–1903), a Fellow at Pembroke College and one of the fathers of modern fluid mechanics, defined some of the physical laws that describe the motion of flows and the motion of particles as they experience a surrounding viscous flow. While large droplets fall through the air, if a particle is
10 Magdalene Matters
small and light enough, it will closely follow the surrounding fluid due to the drag it experiences. Before COVID-19, I applied such concepts to my daily research to predict, for example, how fuel droplets impact the propagation of a flame in an aeroengine combustor. When I first learnt that the SARS-CoV-2 virus was likely transmitted through droplets and that important outbreaks were taking place indoors, I immediately knew what that meant: “if these droplets are small enough, the virus can remain suspended in air for hours!” I remember telling my partner Maria as we read one of the first articles out in the New York Times, hungry for information as most people at the time. It turns out that humans exhale droplets of different sizes during a sneeze, a cough, talking and even during breathing. These are produced in different parts of the body: large droplets in the mouth, medium to fine droplets in the vocal cords, and really fine droplets are produced deep in the lungs,
