Why is low density important in a the dry suit insulator gas?

[Subcooled]

I just started the free Science of Diving specialty that SSI is offering and one of the statements in the course materials puzzled me: "Argon’s low density and cost make it an inexpensive dry suit insulator."

I understand the negative efftects of high density of the breathing mixture, but why is low density important in a dry suit insulator gas?

We do know that vacuum is a good insulator (only radiation heat can get through) but for gasses low density is not relevant.

The SSI Science of Diving specialty materials would really benefit from proof reading by anyone who has actually studied physics.

Forget everything you learned about suit gas. First of all, argon (the often preferred drysuit gas) is more dense (and more expensive) than air. Second, density does NOT affect the insulation capability, as can be seen from kinetic gas theory. It is the SPECIFIC HEAT CAPACITY and the MEAN FREE PATH that are relevant. Both can be found in tables. It is better yet to just consult thermal conductivity tables.

The course contains both errors and strange claims (such as: "backplate and wing is only for technical diving" - wrong). Most of the matrials is good, though. A critical read is advised.

 

[Subcooled]

Never heard of using Argon as the dry suit gas, but it sure makes sense. How common is Argon usage and what are the recommended usage guidelines?

Flush your drysuit with argon before the dive. Fill - empty - fill - empty - fill.
Unless you do this, most of your suit gas will still be air.

Do not breathe argon. Make sure your mask is against the skin, not against the hood.

 

[Doctor Rig]

I’m not yet a dry suit diver, but from what I know about heat transfer I question whether argon would make a significant difference in diver warmth. Argon has a lower thermal conductivity than air, but heat transfer also occurs through the solid insulation the diver is wearing. Thermal conductivity through a solid is much higher than through a gas.

Using a lower thermal conductivity gas would decrease the amount of heat transfer, as compared to air. But the total heat transfer is the heat transfer through the gas and through the solid insulation that the diver is using. If the dry suit is tightly compressed against skin, then there likely is little gas present. High (gaseous space) loft of insulation like in a down jacket insulates well as there is lots of air and little fiber mass to transfer heat. A fully compressed down jacket would not be warm!

When it’s really cold, maybe the little difference Argon provides makes its use worth it. Maybe someone who is pro-Argon can explain what we’re missing.

 

[formernuke]

Most shops here don't bother with argon. If a diver is using trimix they just fill the 6cf bottle with air for the above stated reasons.

 

[Jack Hammer]

When it’s really cold, maybe the little difference Argon provides makes its use worth it.

Pretty well sums it up, IMO. Unless one is making dives that are incredibly long, really really deep, or in extremely cold water, the added warmth of argon likely wont be noticed. I use air for suit inflation for most my trimix dives.

 

[rjack321]

When it’s really cold, maybe the little difference Argon provides makes its use worth it. Maybe someone who is pro-Argon can explain what we’re missing.

argon has long since fallen out of favor now that heated undergarments are widely available

 

[D_Fresh]

Argon is certainly common enough that there are "Argon, Do Not Breath" labels available... Personally, I'm not a dry suit diver, but have known about its use for quite some time. It's my understanding, as others have stated, that its insulation value is derived from its lack of conductivity. Of course, exactly how much difference felt vs air would depend on how inflated the suit is.

I can see how, for trimix divers in extremely cold environments, it provides an extremely cheap drysuit gas, as it's a very common, readily available, industrial gas. Much cheaper than using trimix for drysuit inflation, and warmer (helium would actually be colder than air).

 

[Subcooled]

I’m not yet a dry suit diver, but from what I know about heat transfer I question whether argon would make a significant difference in diver warmth.

In the Finnish Journal of military medicine a scientific experiment is described, which proves the benefits of argon. Unfortunately, it's in Finnish only.
Ann Med Milit Fenn 2019; Vol. 94, No 2 pp. 11-15

(that article was mentioned in the magazine of the Finnish Diving Federation)

If the dry suit is tightly compressed against skin, then there likely is little gas present.

True. And that's why minimal weights is not an option in arctic diving. More lead. More suit gas.

I am only using air for insulation and I can do 60 - 90 minute dives in +4C water (but after 60 minutes it is not fun anymore). It's worst for toes, because finning requires contact. Electrically heated socks and undersuits exist, though.

Understandably though, electric heating is not favored amongst those who dismantle influence mines

 

[formernuke]

One of the issues with argon is though its readily available from welding supply stores the tanks are lower pressure so it would require a separate booster pump in order to fully fill the inflator tanks which raises the price.

 

[Subcooled]

I found the abstract of that argon experiment in english:
Europe PMC