Alton

I'm with Jim on this one. You can have all the subject matter experts,
theory, math, periodic tables to argue the thermo point. I know from
personal experiences that when the helium rich mix hits my chest in the dry
suit, I get a cooler feeling then when air or argon is used - period. I am
colder at the end of the dive when a helium rich mix was used - dumb on my
part. Did it once and won't do it again.

David

>-----Original Message-----
>From: Alton J. Hall, Jr. [mailto:ahall@da*.co*]
>Sent: Tuesday, February 20, 2001 1:39 AM
>To: Jim Cobb
>Cc: Matthias Voss; moorea(uol); techdiver@aquanaut.com
>Subject: Re: More about breathing Helium thermal loss
>
>
>For what it is worth, I recently was involved in a case in
>which the thermal
>capacity of Helium and it's effect on a diver breathing it
>(i.e. it's insulation
>qualities were not discussed) was debated between two experts.
>In the final
>analysis the experts opinion was that the effect was minimal if any.
>
>Alton
>
>Jim Cobb wrote:
>
>> Matt-
>>
>> Damn engineers... ;)
>>
>> The point is that often I see folks on this list delving
>into the obscure
>> theory behind this and that but miss the big picture. By the
>way you seem to
>> be saying that helium is a good heat transfer medium in
>addition to being a
>> poor insulator, I really can't wrap my brain around this
>one. And can we
>> really use gases that get warm on expansion for diving? You
>worked up tables
>> for them yet?
>>
>> Like I said, I am no physicist (or engineer) but have
>certainly felt the icy
>> cold blast of air out of a regulator chill me to my bones.
>It feels good in
>> the summer and like death in the winter.
>>
>> Hows this for an engineering project, take an ice diver with
>a frozen first
>> and the have him thaw it by breathing on it. Then compare
>the time it took
>> for the first to freeze and compare how long it took for it
>to thaw from him
>> breathing on it. At least you will get a dive out of it.
>>
>>    Jim
>>
>>  -------------------------------------------------------------------
>>  Learn About Trimix at http://www.cisatlantic.com/trimix/
>>
>> > From: mat.voss@t-*.de* (Matthias Voss)
>> > Organization: Harry Haller Memorial Fund
>> > Date: Wed, 21 Feb 2001 19:25:38 +0100
>> > To: Jim Cobb <cobber@ci*.co*>
>> > Cc: "moorea(uol)" <moorea@uo*.co*.br*>, techdiver@aquanaut.com
>> > Subject: Re: More about breathing Helium thermal loss
>> >
>> > Jim,
>> >
>> >
>> >
>> >> On a more practical note, when breathing open circuit, as the gas
>> >> expands from the tanks to the outlet of the second stage,
>it cools.
>> >
>> > Some gases, like nitrogen, Oxygen, do. They do it within
>the limits of
>> > our diving environment. That is, bottle pressure 50 to
>200bar, ambient
>> > pressure from 1 to 15 bar, ambient temperature from zero to 30 °C.
>> >
>> > Other gases do not. It is rather fizzical, but there are
>gases which get
>> > warmer when they expand , in our kind of settings. In
>other settings ,
>> > any gas does. They just show a different behaviour

>cooling or heating)
>> > for different pessure/ temperature settings). I have to
>look it up how
>> > much helium is concerned here, but is definitely plays a role.
>> > For the temperature effect, remember that the heat
>capacity refers to
>> > mass, not to volume. We breathe volume, though, so please
>adjust the
>> > math to that.
>> >
>> > The real issue about heat loss is, we do not have
>temperature sensors in
>> > our lungs ewhich tell us we should warm up a bit. This may lead to
>> > dangerous lowering of body temperature, apathy, drowsiness.
>> >
>> >
>> >
>> >> This is the same principle that air conditioners work on.
>> > Well, yes. But these work with gases ( freon) which dangle
>near their
>> > point of condensation)
>> >
>> >
>> >
>> > This would
>> >> be the primary source of heat loss rather than the
>composition of the
>> >> gas being breathed.
>> >
>> > I feel the prime source is evaporation of water. Anybody
>care to do the
>> > calc?
>> >
>> >>
>> >> If you have ever tried a rebreather, one thing that immediately
>> >> strikes you is how warm and humid your breathing air is.
>> > This pertains to mix as well.
>> >
>> >
>> >
>> > Another
>> >> comment is that thermal transfer infers that you are
>moving heat from
>> >> A to B, certainly not a factor when the heat has nowhere
>to go, i.e.
>> >> inside your lungs. While in a drysuit the transfer is
>from your body
>> >> to the water which surrounds you.
>> >
>> > In a rebreather , B is the water surrounding the loop.
>> >
>> >
>> >>
>> >> As far as gas of various mixtures acting as a heat transport
>> >> mechanism, the expansion cooling effect has far more
>consequences on
>> >> heat loss on a diver than the composition of your
>breathing gas to the
>> >> point of rendering it inconsequential.
>> >
>> > Could you prove that ?
>> >
>> > Matthias
>> > ( no physicist, only an engineer)
>> >
>> >
>> >
>> >> I am no physicist but this seems to be fairly obvious to me.
>> >>
>> >> Jim
>> >
>>
>> --
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