Heliiox Through Compressor

Pelagian

Hey Mike

Thanks for that, but I'm a little confused.

Are saying the compressor is gonna have to work harder to compress the helium or that because the helium is gonna be compressed more that it's gonna produce more heat?

I thought S.H.C. was the energy rerquired to raise the temp of a unit of gas. Given that He changes temp quicker than N2 wouldn't it cool down quicker as well?

Thanks again for you help

Seb

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Sutty

Not sure that the higher specific heat capacity of He will make it hotter when compressed by the same ratio as N2 or O2 (but don't think so). However the thermal conductivity is definitely higher too (more than double) so the higher temperature produced by compression will be transferred much more effectively to the container - in this case the compressor.
I don't dive trimix myself (yet), but has anyone noticed if their cylinders feel hotter after a He rich fill?
Neil

PeteS

And from the PDF quoted:-

"It is not clear at this time what caused the failure."

So, although O2 is very, err, "iffy" through a compressor, helium probably isn't.

The He temperature rise during pumping may cause problems with valves and seals and pistons, etc, but I personally don't see any explosion risk from He. At all.

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Pete S.

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MikeH

Actually, the compressor will more easily compress Helium than air....simply listening to the operation of a compressor and measuring various temps(especially the electric drive motor) running pure Helium through it as opposed to air will make most people a believer in this. The cylinder heads, however, will be significantly hotter. This is primarily because the Helium is compressed more, creating more heat, and the Helium is able to hold more heat than the same volume of air. To prove this to yourself, measure the temperature of a cylinder with only air compressed into it immediately after the fill is finished, then measure the temperature of a cylinder with pure Helium compressed into it from the same compressor.

Technically, you're correct. Where does that energy come from, though? It comes from the compression of the Helium molecules. I attempted to use the term SHC(rather than going into exact specifics) to make it easier to understand. I honestly didn't think anybody would call me out on it...

Theoretically, yes. You would think that since the Helium molecules absorb heat so much faster than air that they would cool much more quickly than an air cylinder....but when it comes to filling SCUBA cylinders, that doesn't occur. I, personally, believe that this is simply due to the material the cylinder is made of absorbing the heat and releasing it at the same rate regardless of the gas in the cylinder....but some of my buddies disagree with me, and have their own theories.

I'm always happy to pass on the knowlege that I have....BUT...in this case, you must understand that this knowledge is self taught and based mostly on personal experience, and the rest on theory. Don't take it as fact, since a large portion of it is simply my opinion based on experience and knowledge I have obtained.

Mike

MikeH

The problem that occurs based on Helium temp rise is NOT due to the Helium itself....it's due to the Oxygen content that is in there with the Helium. Helium is an inert gas....therefore, it will NOT cause or support combustion. Oxygen is not a "flammable" gas. It simply fuels fires caused by other flammable materials that happen to ignite based on pressure and heat. Without Oxygen, nothing can burn....but with a Heliox mix(for example), the Helium can create the heat, another subtance can cause the ignition source, and the Oxygen can fuel the fire.

Mike