Improved ventilation may reduce the risk of transmission of the COVID-19 virus, but many decades-old public school classrooms lack adequate ventilation systems. A systematic modeling study of simple air purifiers using an attached box fan Fluid physics, by AIP Publishing, shows that these inexpensive units can dramatically reduce the amount of virus suspended in these spaces, if used appropriately.
A low cost air filter can be easily constructed from a cardboard frame topped with an air filter and box fan. The air filter is placed between the fan and the cardboard base. The fan is oriented so that air is drawn in from above and forced through the filter, discharging the cleaned air downward.
Investigators measured the flow of clean air from the air cleaning system in experiments conducted in two independent laboratories. Tobacco smoke has been used to simulate the airborne virus, as the virus is known to travel through the air after exhaling in droplets roughly the same size as smoke particles.
The experimental measurements were incorporated into a detailed computational model of a classroom. In addition to the ventilator’s air filter, a ventilation unit known as the HUV, or horizontal ventilator, was included in the simulation. This type of ventilation system is very common in public schools and is usually placed along an exterior wall, drawing air close to the floor and exhausting it at the top to circulate cool air around a room. classroom.
A cloud of viral particles was assumed to enter the simulation from an infected individual. Investigators assumed this person was the instructor and experimented with different locations of the box fan air filter.
“Placing the air filter near the potential infection is the most effective way to reduce the spread of aerosols,” said author Jiarong Hong.
Simulations showed that the best results were obtained by moving both the box fan air filter and the infected instructor to a location near the HUV.
“At this location, due to its proximity to both the infector and the HUV, the air purifier extracts the majority of the aerosols, leaving only a small percentage suspended in the air,” Hong said. .
Although it is best to place the air filter near an infected person, it is not always possible to tell who is infected. In this situation, investigators recommend placing the air filter near the HUV, with the air filter outlet pointing toward the HUV inlet.
“Additionally, we are finding that in large classrooms, distributing multiple air purifiers across the space is more effective in controlling the spread of aerosols than simply increasing the flow of HUV or air purifiers alone.” said Hong.
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