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Researchers from Florida Atlantic University’s College of Engineering and Computer Science conducted an experiment using flow visualization to demonstrate how far a cough travels and how long it lingers in the air. Flow visualization is a method that enables flow patterns, such as a stream of particles from a cough, to become visible in fluids like air and water since they are transparent. Various techniques using flow visualization make these patterns visible to the naked eye.
In a laboratory setting, the researchers were able to visually demonstrate a mechanically emulated cough/sneeze jet from an orifice representing the mouth and the associated particle-laden airflow using a mannequin and other props.
“Our goal was to demonstrate the fate of smaller size particles that are present in the exhaled jet of a cough. We used a mixture of distilled water and glycerin to represent the synthetic fog that made up the content of the cough-jet that was expelled from the mannequin’s nose and mouth during our experiment,” said Manhar Dhanak, Ph.D., a professor, chair of FAU’s Department of Ocean and Mechanical Engineering, and director of FAU’s SeaTech, who conducted the study with Siddhartha Verma, Ph.D., an assistant professor in FAU’s Department of Ocean and Mechanical Engineering. “The fog is initially warmer than the ambient air, just as in the case of an exhaled cough-jet, however, it cools as it travels through the air.”
Particles and droplets that result from a human cough or sneeze typically range in size from 5 to 500 microns. The larger particles fall to the ground within a short distance due to gravity, but smaller particles can be carried longer distances by prevailing breezes of air. The particulates making up the fog from the fog machine Dhanak and Verma used in the emulation of the cough-jet ranged in size from 10 to 20 microns.
To visualize the particles from the exhaled air in the mannequin and film the cough jet, the researchers used LED and laser lights. The visualization highlights the structure of the jets and provides the distances over which the jets extend from the source.
“Preliminary results from our experiment reveal that significant concentrations of small particles from a turbulent jet such as from a heavy cough/sneeze can linger in still air for more than one minute. It only took the particles a couple of seconds to travel 3 feet; in about 12 seconds it reached 6 feet and in about 41 seconds it reached around 9 feet,” said Verma.
For a heavy cough, the researchers found that particles can even travel up to 12 feet. A lighter cough does not travel as far.
“In the case of light coughing, it can lead to formation of vortex rings in which the particles and droplets ejected in the cough-jet remain confined to evolving toroidal flow structures,” said Dhanak. “The rings appear to travel 1 to 9 feet or more before getting diffused and breaking up. We found that wearing a face mask doesn’t stop the particles 100 percent, but it does slow down the cough jets.”
Dhanak and Verma say that additional research is required to refine the emulation of the coughing action as well as the visualization of the airflow in order to better quantify their results.
“Initial results from the experiment that professors Dhanak and Verma conducted have important implications for how we protect the public from this highly infectious disease,” said Stella Batalama, Ph.D., dean of FAU’s College of Engineering and Computer Science. “There is currently a gap in knowledge over how COVID-19 spreads as well as a scientific debate about how the disease moves in the air. This experiment will help to shed more light on the spread of the disease through aerosols. Moreover, it underscores why it is so essential to cover your cough and sneezes and to wear a face mask when you are out in public settings.”
– FAU –
About FAU’s College of Engineering and Computer Science:
The FAU College of Engineering and Computer Science is internationally recognized for cutting edge research and education in the areas of computer science and artificial intelligence (AI), computer engineering, electrical engineering, bioengineering, civil, environmental and geomatics engineering, mechanical engineering, and ocean engineering. Research conducted by the faculty and their teams expose students to technology innovations that push the current state-of-the art of the disciplines. The College research efforts are supported by the National Science Foundation (NSF), the National Institutes of Health (NIH), the Department of Defense (DOD), the Department of Transportation (DOT), the Department of Education (DOEd), the State of Florida, and industry. The FAU College of Engineering and Computer Science offers degrees with a modern twist that bear specializations in areas of national priority such as AI, cybersecurity, internet-of-things, transportation and supply chain management, and data science. New degree programs include Masters of Science in AI (first in Florida), Masters of Science in Data Science and Analytics, and the new Professional Masters of Science degree in computer science for working professionals. For more information about the College, please visit eng.fau.edu.
About FAU’s Department of Ocean and Mechanical Engineering:
The Department of Ocean and Mechanical Engineering (OME) offers exciting programs at the undergraduate and graduate levels in both ocean and mechanical engineering, and serves a diverse population of undergraduate and graduate students. At the undergraduate level, programs are grounded in engineering fundamentals with an emphasis for hands-on experience. OME strives to instill and cultivate knowledge, character, imagination, creativity, and innovation as the main traits in its graduates. Students are active in various local, national, and international design competitions including the Formula SAE Race Car event, human powered submarine races, assistive technologies, alternative energy and many other exciting topics. At the graduate level, OME offers Masters and PhD degrees in both ocean and mechanical engineering. OME is heavily involved in research and scholarly activities funded by industry, state and federal agencies. Research focus areas include, but are not limited to: autonomous marine vehicles, underwater acoustic imaging and communication, physical oceanography, hydrodynamics and acoustics of marine vehicles, robotics and controls, alternative energy (solar, wind and ocean), materials (nano, composite, and corrosion), helicopter dynamics and structures. A high percentage of OME graduate students are supported by research funds as well as teaching assistantships. World class faculty and their student groups conduct research either on FAU’s Boca Raton campus or in the state-of-the-art Institute for Ocean and Systems Engineering called SeaTech located in Dania Beach.
About Florida Atlantic University: Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, the University, with an annual economic impact of $6.3 billion, serves more than 30,000 undergraduate and graduate students at sites throughout its six-county service region in southeast Florida. FAU’s world-class teaching and research faculty serves students through 10 colleges: the Dorothy F. Schmidt College of Arts and Letters, the College of Business, the College for Design and Social Inquiry, the College of Education, the College of Engineering and Computer Science, the Graduate College, the Harriet L. Wilkes Honors College, the Charles E. Schmidt College of Medicine, the Christine E. Lynn College of Nursing and the Charles E. Schmidt College of Science. FAU is ranked as a High Research Activity institution by the Carnegie Foundation for the Advancement of Teaching. The University is placing special focus on the rapid development of critical areas that form the basis of its strategic plan: Healthy aging, biotech, coastal and marine issues, neuroscience, regenerative medicine, informatics, lifespan and the environment. These areas provide opportunities for faculty and students to build upon FAU’s existing strengths in research and scholarship. For more information, visit fau.edu.
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