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Air conditioning may be spreading COVID   The Healthy You: Health and Fitness Polls

Started Jul-11 by Showtalk; 296 views.
Showtalk
Staff

From: Showtalk

Jul-11

This could be one reason why hot states were hit hardest this summer.

Yeah, definitely.

“What we’ve been recommending to minimize risk indoors is to provide 100% outside air, which you can’t do if you’re trying to heat or cool because it just costs way too much money,” she said.

Another strategy to reduce the risk of being indoors is to kill airborne viruses with special wall or ceiling mounted boxes that emit short-range UV radiation. This kind of UV light doesn’t damage skin the way sunlight does, but still zaps harmful germs. These so-called upper-room germicidal systems have successfully controlled outbreaks of other airborne viruses, like tuberculosis, Nardell says."

and if the 210 to 222 nanometer UV light sources are too expensive or have too long of a lead time to acquire and install, the ordinary quartz envelope 255 nanometer mercury vapor line "fluorescent lamps" will get the job done as long as the air passes around light baffles in the air handlers so the radiation doesn't come into the rest of the room and burn people.

Essentially wiring those up is just like wiring up fluorescent lights - you have the fixtures and ballasts and starters, but the fixtures are placed inside the (ideally metal) ductwork, as this hard UV will decompose most plastics as well.

Counterflow heat exchangers can also be used but they are still pretty expensive. they need an enormous amount of fairly thin thermally conductive metal to separate the incoming and outgoing air streams to and from the outside.

https://www.sciencedirect.com/topics/engineering/counterflow-heat-exchanger

...

4.9.1.1 Ideal, reversible heat transfer

Ideal reversible heat transfer can be approached in a counterflow heat exchanger. In this type of device, the temperature difference between the two streams is kept to a minimum, because the hot ‘source’ fluid on entering the heat exchanger is in closest contact to the ‘sink’ fluid which is leaving the device, and vice versa. The processes involved are depicted by two almost coincident lines from 1 to 2 in Fig. 4.10. ...

Figure 4.10. Reversible heat transfer in a counterflow heat exchanger. (a) Schematic diagram of heat exchanger; (b) Processes shown on Ts diagram.

In this ideal process, it will be assumed that, at all times, the fluid receiving the heat is at temperature, T, while the temperature of the source of heat is at all times at temperature, T + δT, i.e. T1c is δT less than T2h etc. From the First Law of Thermodynamics it is obvious that, if the boundaries of the control volume are insulated from the surroundings, the energy transferred from the hot stream must be equal to the energy received by the cold stream. This means that the areas under the curves in Fig. 4.10 must be equal; in this case they are identical. The exergy change of the hot stream is then given by

(4.53)ΔBh=B2hB1h=(A2hA0)(A1hA0)=A2hA1h=(U+p0VT0S)2h(U+p0VT0S)1h=(U2hU1h)
...[Message truncated]
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Showtalk
Staff

From: Showtalk

Jul-15

I remembered about UV and heat, I had some things I needed  to use, and could not effectively disinfect, so I put them outside in the hot sun and flipped them after a few hours, then brought it all in. I never worried at all about the virus being on it.

  • Edited July 15, 2020 4:02 pm  by  Showtalk

Yeah. I've got some heavy duty industrial air conditioners with metal innards that I could probably install a UV lamp inside, like shining on the back of the evaporator cores. Hard UV doesn't faze aluminum or copper or other metals, but it plays havoc on plastic. So the light has to thoroughly irradiate all the air that passes through its sphere of influence, but not illuminate plastic parts (or people or furnishings) elsewhere.

I've got an 18 inch UV light. Might even be able to find another hard UV light on Ebay.

Yep. Not finding the 18 inch lamp that goes in a fluorescent desk light or similar fixture any more. You just use it instead of a regular fluorescent light. But I found these:
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=germicidal+lamp+quartz&_sacat=0

About 45 bucks delivered.

https://www.ebay.com/itm/38W-UVC-Ozone-Ultraviolet-Germicidal-Lamp-Remote-UV-Sterilization-Quartz-Lights/402324567985?hash=item5dac69b7b1:g:4uUAAOSw3C5e6caQ

But note the "Engrish" in the description:

"Germicidal light produces the-ozone during work.the-Ozone can sterilize places where ultraviolet light cannot reach, but the-ozone is harmful to the human body. After disinfection, room needs ventilation of 60 minutes. We recommend to use it for cabinets"

Nowhere does it state the wavelength, but it is most likely the UV-C mercury vapor emission line at 254 nanometers that does all the heavy lifting.

...

Low-pressure lamps are very similar to a fluorescent lamp, with a wavelength of 253.7 nm (1182.5 THz).

The most common form of germicidal lamp looks similar to an ordinary fluorescent lamp but the tube contains no fluorescent phosphor. In addition, rather than being made of ordinary borosilicate glass, the tube is made of fused quartz or vycor 791.3 glass. These two changes combine to allow the 253.7 nm ultraviolet light produced by the mercury arc to pass out of the lamp unmodified (whereas, in common fluorescent lamps, it causes the phosphor to fluoresce, producing visible light). Germicidal lamps still produce a small amount of visible light due to other mercury radiation bands.

Showtalk
Staff

From: Showtalk

Jul-15

That is why I used a natural light source, outdoors.

Natural sunlight has mostly UVA and UVB, which, while they can kill pathogens, do so much more slowly than UVC. UVC wavelengths tend to pass only short distances through air, so they only reach the surface at high altitudes, and they both cause severe sunburn and also cause cataract formations.

This is one reason so many residents in the high Himalayas and Andes develop cataracts and also skin cancers well beyond the average - because the ultra thin air lets more of the hard UVC reach the surface, and the intensity of UVB and UVA is much greater than would reach sea level.

The air also attenuates the longer UV wavelengths well enough that at the surface of the Dead Sea, that extra 1,100 feet of air below sea level acts like a high SPF sun block and they say people can lie out in the sun all day and not be burned. Surface air pressure down there is more than 16 PSI, or about 5x the pressure you would find on Mt Everest.

The most germicidal wavelengths that severely disrupt viruses are blocked completely by the ozone layer in the upper atmosphere, and the ozone is actually formed by this very radiation. This also limits the distance these short wavelengths can travel in air near the ground, as the radiation produces ozone, which is opaque at those wavelengths. The ozone itself is also rather corrosive to living material. The extra oxygen atom is easily dislodged producing a free radical that is very reactive, and this just rips apart many materials as it seeks something to bond with and balance its outer electron shell to get to a neutral charge again.

Most of the ozone at sea level pressures decays back into 02, with two O3 molecules breaking off the surplus oxygen atoms which then combine with one another to form three O2 molecules which are far more stable and comprise 21% of the air.

Of course ozone has that "electric smell" everyone is so familiar with that accompanies nearby lightning strikes, and arcing old timey electric motor commutators, and from such metal working operations as electric arc welding and plasma cutting.

At the earth's surface, ozone is considered a pollutant, and it irritates eyes and lungs when inhaled even if fairly low concentrations.

The infamous Los Angeles smog of the 1970s was a nasty brew of partial combustion hydrocarbon byproducts, tetraethyl lead, nitrous oxides, and ozone along with a bunch of other irritating and toxic materials such as nanoparticles and smoke (another product of incomplete combustion)

Showtalk
Staff

From: Showtalk

Jul-16

Doesn’t the virus die if it dries out? I thought it needed moisture to stay alive.

Jeri (azpaints)

From: Jeri (azpaints)

Jul-16

I can't find a precise answer but it is known to transmit from surfaces for several minutes which would seem to indicate it is active when dry or reactivates when exposed to moisture, maybe.

It depends on the virus species. I think most of them degrade fairly fast when they dry out, but others can survive even as a crystalline material, much like a dry seed, for potentially thousands of years.

https://www.pbs.org/newshour/science/how-long-do-cold-and-flu-viruses-stay-contagious-on-public-surfaces

... “Viruses tend to be more stable in environments for which they’re known to reproduce,” Auwaerter said. “If they live in warm, moist environments — for example, in your nostrils, in your throat, in your bronchial tree — they’re more stable. But when they’re exposed to a different material or to a non-moist environment, they can break down.” ... This is why cold and flu viruses remain infectious on non-porous surfaces like light switches and countertops longer than porous surfaces like fabric and tissues. Porous surfaces suck moisture away from the viruses, causing the structures to collapse. ...

https://www.mayoclinic.org/diseases-conditions/flu/expert-answers/infectious-disease/faq-20057907

Showtalk
Staff

From: Showtalk

Jul-16

They have guess but aren’t sure. I’ve heard everything from a few hours to three weeks.

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