Failure to recognise when an aerosol isn't a droplet 26

[LittleInch]

FacEngrPE dropped this in an obscure post and it reads very well.

Basically the whole epidemiological world though various dieses and viruses were spread by "droplets" which landed on surfaces and then infected people or were sneezed at you.

And a lot of times they are probably right.

But there was a magic 5 micron cut off between droplets and aerosols. Why? Read on

https://www.wired.com/story/the-tee...t-helped-covid-kill/?utm_source=pocket-newtab

So is this a disaster - Well you tell me.
But it goes to show that just because a lot of people write something, it doesn't mean that they originally got the wrong end of the stick and then the error repeats itself until it becomes fact.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LionelHutz]

It's a little sad that engineers have to argue about r/3 being a constant or not. That seemed rather obvious it's not to me.

 

[TugboatEng]

Speaking of censoring scientists:

"Even if the letter in Science was well intentioned, its authors should have thought more about how it would feed into the divisive political environment surrounding this issue, says Angela Rasmussen, a virologist at the University of Saskatchewan in Saskatoon, Canada."

https://www.nature.com/articles/d41586-021-01383-3

 

[zeusfaber]

....says a rentagob in an editorial in a rival (interesting - that came out as "viral" the first time I typed it) rag.

Never been convinced that putting journalistic opinion-pieces in publications where the majority of the content is peer-reviewed is all that clever.

A.

 

[TugboatEng]

Yeah, I was surprised to see that one in Nature. They've been a pretty good source of information those that want to read and learn about the virus vs be told about it.

 

[1503-44]

The ratio is constant, not the individual variables. I dont know what anyone else was thinking and don't care. Its mass that matters, no "matter" what size the sphere is or the density it takes. Speaking of constants, some even want density to be constant, but that's OK, but then you have to make temperature a constant too.

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[TugboatEng]

What about flux? The surface to mass ratio certainly has an effect on how rapidly heat transfers.

 

[1503-44]

If surface area increased by the cube of the mass, you might have something there.

The rise in surface area doesn't keep up with the increase in mass inside the sphere. It just gets more and more difficult to get enough heat into the sphere to heat the ever more increasing mass inside.

And we all know in our hearts that a smaller drop of water evaporates faster than a larger one .. we do know that, right?

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I take no responsibility for any damages or injuries of any kind that may result.

 

[dik]

It may not be linear with small particles... don't know if it is... would suspect that it wasn't.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LionelHutz]

Constant - a quantity or parameter that does not change its value whatever the value of the variables, under a given set of conditions.

r/3 is not a constant. You're just arguing for the sake of arguing if you continue to claim otherwise.

 

[LionelHutz]

I also doubt the majority of people are living in houses or working in offices that vary much in temperature. I'm also doubting freezing water droplets are much of a concern in those environments.

 

[Alistair_Heaton]

They are a factor in air conditioning I seem to remember. You can get super cooled droplets to boot.

We quiet often get snow coming out the vents when the aircraft cooling systems come on.

There is loads of stuff on airborne droplets researched by NASA centred round icing of aircraft.

 

[1503-44]

Lionel, what I said, look up there, was Ar/V = 3. 3 is a constant, so the ratio Ar/v is constant = 3. Just as circumference / radius is a constant = Pi. Why I said that was to address Tug's question about flux in advance. Heat flux across the increasing surface area will not keep pace with the increase of the mass inside the sphere, thus it is more difficult to evaporate larger spheres than smaller ones.

As for what constants are, or are not ...
Ar/V =3 is just as much a constant for spheres as C/d = π for circle's.

https://en.m.wikipedia.org/wiki/Pi[/URL]]π is commonly defined as the ratio of a circle's circumference C to its diameter d. The ratio C/d is constant, regardless of the circle's size. For example, if a circle has twice the diameter of another circle, it will also have twice the circumference, preserving the ratio C/d.

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[FacEngrPE]

It is really difficult to get snow out of a air conditioning evaporator as evaporator temperatures lower than zero C make the water stick to the coils as ice. Most jet aircraft - particularly larger one use air cycle machines, where air is the working fluid. As the cold is created by expanding the air, any ice will be formed as snow, and unless removed mechanically in the moisture separator will blow into the cabin.

https://www.aircraftsystemstech.com/2017/05/aircraft-air-conditioning-systems.html

I can see temperature excursions on startup making snow while the controls are catching up with the operating physics.

In the context of the current discussion the cold temperatures in the air machine at the moisture separator (and the low amounts of moisture in the ambient air at altitude) ensure low cabin air moisture levels.

 

[Alistair_Heaton]

It's quite impressive when it does it.

You can also give the whole cabin 1 meter viz if you have been sitting on a hot ramp near the sea and then turn it on.

As you say on start up the duct temp plummets and then you get oscillations for about five mins.

 

[Lou Scannon]

I have a car that used to blow snow out of the A/C vents from time to time with its original R12 system. That was in not so humid SoCal, too.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[1503-44]

Can't beat Houston for that effect. If the freon got a bit low, or if a window was open, you'd got a mini North Pole under the hood.

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[waross]

How about the volume to surface area of a cylinder?
If I double the diameter of a conductor, I have twice the surface area and four times the cross-sectional area.
If I maintain the same current density and increase the current four times, I have four times as much heat generated but only twice as much surface area to conduct and radiate the heat. The wire will run hotter. This is reflected in the ampacity tables.
Every designer who has saved on copper by using multiple smaller conductors rather than one larger conductor for heavy currents has taken advantage of this even if he did not understand it. I'm going to go out on a limb and suggest that in the case of a sphere, the effect may increase exponentially. A square factor to a cube factor or an exponent of 2 to an exponent of 3.
A pseudo-ratio that changes when units are considered and varied may be a misleading assertion.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

LOL, Ar/V is quite obviously not the area/volume ratio.

Using the circumference to diameter ratio comparison to try and prove that the area to volume ratio is constant is a logical fallacy.

The rise in surface area doesn't keep up with the increase in mass inside the sphere. It just gets more and more difficult to get enough heat into the sphere to heat the ever more increasing mass inside.

You also just re-stated the reverse of what was posted after saying it was wrong by posting the claim that the volume to surface area ratio is constant.

Everyone else can understand that volume and density of water have a rather close relationship but you are arguing about that too.

At this point, it's rather obvious you're just posting argumentative crap for the sake of being argumentative so there's not much point responding about this again.

 

[1503-44]

Ok maybe the wrong formula. I got that from Moon161 and didnt check it. My fault.
You must remember that I never wanted to talk about the surface area anyway. Nor the volume. I said it wasn't important every time.

Its only the mass! And that part is quite true then and still is. I am not arguing about anything other than that. Which nobody has ever contradicted. I do think if you have the right formula, you can probably work out the S:V ratio is constant, but I will say again, that is totally irrelevent, so its fine with me if you don't want to talk anymore about that. I never did.

I find your comment a bit trolly as well. The difference is kind of why you need two terms to relate the different properties. "Everyone else can understand that volume and density of water have a rather close relationship but you are arguing about that too." Do you really think I dont "understand" the difference? You don't think that's a kind of troll behavior?


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[RedSnake]

Could someone please explain what this article is about, I can't read it, and I have tried to find somewhere it is possible, no luck.
Thanks in advance.

Best Regards Anna



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein