It is well known that the temperature of a gas increases during compressi=
on. =

In staged compression heat is removed between each compression stage to =

improve the efficiency of the compressor and to reduce the temperatures.

For an isentropic (ideal) compression the following equation apply:
T2 =3D T1 x (V1/V2)^(k-1)

where:
T2 =3D temperature after compression
T1 =3D temperature before compression
V1 =3D volume before
V2 =3D volume after

Air: k=3D1.402
O2: k=3D1.40
He: k=3D1.66
Ar: k=3D1.6

Say: T1=3D300K (=3D27 deg cels), V1/V2 =3D 6

Then:
T2(air) =3D 300 x 6^(1.402-1) =3D 614K (=3D341C)
T2(He) =3D 300 x 6^(1.66-1) =3D 979K (=3D706 C)

The quantity of heat that need to removed from the system is proportional=
 =

to:
T2 x volumetric flow x density x heat capasity of gas

Helium has less density than air, but greater heat capasity, so the produ=
ct: =

volumetric flow x density x heat capasity of gas will be roughly the same=
 =

for Helium and Air.

Conclusion:
Compressing Helium (or argon) using a compressor will generate higher =

temperature and more heat than compressing air. The same effects (but to =
a =

lesser degree) will also be present when compressing trimix.

Note:
The above analysis is rather simplified, and approximate. As a poor man's=
 =

solution, running mystery mix through a compressor is tempting and may, o=
r =

may not, work. It probably results in additional wear&tear on the =

compressor, but I'll be interested to know if any has experience in this =

matter.

 -bjorn-
 ----------
| From: dcrco@jp*.ne*
| To: hgartner@ra*.or*; dennish@wp*.co*.za*
| Cc: techdiver@aquanaut.com
| Subject: Re: Helium & O2 grading was Re: Gobber Grade helium
| Date: 21. November 1997 05:37
|
| I'm not one of the rocket scientists, why do you say it will heat
| excessivly? It seems as if the helium would carry the heat out of the
|  system
| better.
|
| At 07:29 PM 11/19/97 -0700, Harold Gartner wrote:
| >>Why do you need the expensive Haskel. Why can't you cascade your O2 t=
hen
|  top
| >>the rest off with heliair out of your compressor (setup a flowmeter a=
t
|  the
| >>compressor intake then analyze output & adjust flow of helium until y=
ou
|  get
| >>desired mix, send it to the tanks to get final mix) you should be abl=
e =

to
| >>use every bit of the helium without needing a haskel and its simple.
|  Besides
| >>you need the compressor anyway so why buy two expensive items that
|  basicly
| >>do the same thing. We take delivery of our Rix soon and that is what =
we
|  plan
| >>to start working with right away unless somebody comes up with a real=

|  danger
| >>to doing this - if nobody else has tried this then I guess we will be=
 =

the
| >>test dummys :-)
| >>
| >>Fill whips, Rix SA3, haskel & lots of fittings - $8000 +/- vs. Fill =

whips
|  &
| >>Rix SA3 & a few fittings - $2500 +/-
| >>The decision was easy. (We can get several more Rix units with this k=
ind
|  of
| >>pricing if anybody is interested)
| >
| >I own a RIX SA6 and a Haskel pump. Don=B9t try to use the compressor f=
or
|  this
| >purpose. First, it will heat up more than desired and burn up the ring=
s
|  much
| >faster. Those things are bitchy enough to rebuild and you don=B9t want=
 to =

do
|  it
| >more than you need to.
| >
| >I use the Haskel for O2 only and it=B9s O2 clean. As I=B9m using a reb=
reather
|  I
| want
| >full O2 fills (3000-3300 psi) and I cascade my He from 4 storage tanks=
=2E I
| seldom
| >lose any significant amount of He - even when I was doing open circuit=
 =

trimix
|  -
| >this way. If I do get down to the last few hundred psi of the He I can=

|  transfer
| >using the Haskell.
| >
| >Hal
| >
| >Harold H. Gartner III
| >hgartner@ra*.or*
| >
| >--
| >Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'=
=2E
| >Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com=
'.
| >
| >
|
|  --
| Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.=

| Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'=
=2E
| =

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