Why is Argon Chosen for Double Glazing?

[exchemist]

I’ve just had some new windows fitted which have argon between the two layers of glass. I can’t find a good explanation for this on line. I would expect the heat capacity to be lower than for air, as argon is monatomic, but this does not seem likely to be relevant. Would argon conduct heat less well and if so, why? Some “explanations” say the higher density of argon is an advantage but I can’t immediately see why. I can see that an inert gas would not react over time with components of the frame and seals, but this does not seem to be the chief reason for its use. Lower heat and sound conduction seem to be the reasons given, but why would this be?
 

Does anyone know?

[swansont]

It does have lower heat conduction; Kr is even lower. Probably a function of the higher mass - diffusion rates should be dependent on that.

[exchemist]

21 minutes ago, swansont said:

It does have lower heat conduction; Kr is even lower. Probably a function of the higher mass - diffusion rates should be dependent on that.

Ah yes, higher mass would reduce diffusion rate. Re sound, I suppose an interface with a denser medium would create some partial reflection. But that’s just a guess. 

[Genady]

From my SCUBA diving days, I remember that argon was used for dry suit inflation in cold water diving because of its thermal insulation and non-corrosive properties as well as its low cost.

[sethoflagos]

2 hours ago, swansont said:

It does have lower heat conduction; Kr is even lower. Probably a function of the higher mass - diffusion rates should be dependent on that.

Add to this that gas thermal conductivity is directly proportional to C_V favouring selection of the low specific heat monatomic gases, and that argon is relatively cheaply available from air liquidation facilities.

[exchemist]

5 minutes ago, sethoflagos said:

Add to this that gas thermal conductivity is directly proportional to C_V favouring selection of the low specific heat monatomic gases, and that argon is relatively cheaply available from air liquidation facilities.

Ah that's interesting. I didn't realise thermal conductivity of gases was proportional to specific heat capacity. So it is something to do with 3/2R rather than 5/2R, after all.

[sethoflagos]

55 minutes ago, exchemist said:

Ah that's interesting. I didn't realise thermal conductivity of gases was proportional to specific heat capacity. So it is something to do with 3/2R rather than 5/2R, after all.

You might find this article on Prandtl number interesting and relevant.

https://www.sciencedirect.com/topics/engineering/prandtl-number

Edit: actually don't. Some of the numbers are out by several orders of magnitude (!)

But the Wikipedia page on Prandtl number is okay for the first few paragraphs.

 

Edited April 29 by sethoflagos