Tuesday, August 31, 2021

Thoughts on Improving Air Cleaners for Covid

 With the return of school and offices moms and dads especially are paying increased attention to air cleaners. You can buy small units for not so much money, but they are a couple of hundred dollars, and putting something together out of a fan, some A/C filters and duct tape is easy and a lot less expensive. 

One simple design is called a Corsi-Rosenthal Cube. Eli has been thinking for a while about air filters. The bunny changed out the A/C filters in his house last year and recommended the same to his sadly low number of Twitter followers

September 23, 2020

So where is this going, well Eli would like to suggest three improvements. The first builds off an early 2020 observation that copper, or at least some copper alloys, effectively kills Covid virus. It has been known for some time that viruses are inactivated by copper surfaces. Govind, V., Bharadwaj, S.,  et al. summarize this in their review article Antiviral properties of copper and its alloys to inactivate covid-19 virus. Biometals (2021). https://doi.org/10.1007/s10534-021-00339-4, so, of course it was a natural thing to look at when Covid-19 raised it's ugly heat. N Van Doremalen, T Bushmaker, DH Morris, et al, were the first to publish in March 2020 in the New England Journal of Medicine Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. Eli remembers looking at that then, and since so have about five million others, with 7500 citations.

The EPA has authorized the use of copper for this purpose and already things like copper handrails and doorknobs are on sale as anti-covid devices
Today, the U.S. Environmental Protection Agency (EPA) is announcing that certain copper alloys provide long-term effectiveness against viruses, including SARS-CoV-2, the virus that causes COVID-19. As a result of EPA’s approval, products containing these copper alloys can now be sold and distributed with claims that they kill certain viruses that come into contact with them. This is the first product with residual claims against viruses to be registered for use nationwide. Testing to demonstrate this effectiveness was conducted on harder-to-kill viruses.
Copper, of course comes in all sorts of shapes and sizes. For Eli's application extra fine copper wool appears to be the ticket. You can even get copper wool for cleaning your pots. A layer or two of this stuff on the inside of the Corsi-Rosenthal Cube, or on the inside of your A/C filter would inactivate a lot of Covid-19. Any mechanical engineer could optimize the flows for maximum efficiency. If the size of the copper wire bothers you, it could always be drawn finer but that would really not be necessary. 

Although the wire is much larger than the virus or the aerosols carrying it, because the path through the many layers of the wool would be kinky the odds on an aerosol particle hitting a wire are excellent. It would work the same way as, well N95 masks work, where multiple layers ensure that the aerosols are captured as shown in this video

But because copper is a conductor, there is another, and perhaps more important trick we can use. The N95 mask has a layer which is composed of electrets which attract and capture virus aerosols! But what if there are two layers of copper wool separated by an insulator! They can be charged up with a small battery or some sort of simple power supply. 

So by combining three things
1. Copper inactivation of Covid 19 virus
2. A tortuous path through fine copper wool
3. Static electrical attraction of the virus to the copper wire,
Perhaps a better Covid air filter at low cost and high efficiency. TM-ER

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