[TheForge] Gas vs Vapor vs ??? (was: Building a propane forge)

[Bruce Freeman]

Mikey,
 
Apology accepted.  Flames do no good on theforge; hot coals are
better.

You say, "they do make the distinction between vapor and gas."  Who's
"they"?  Give me a reference and I'll check it out.
 
A number of other folks have joined in this conversation, with
differing opinions.  Let's review possibilities for what you're calling
"vapor":
 
Pure phases:
Gas
Supercritical fluid (no chance)
Liquid
Solid (no chance)
 
Mixed phases (ignoring solid)
liquid in gas - a mist
gas in liquid  (unlikely when tapping from the top of the tank)
 
Clearly what's coming out of the cylinder and going through the hose to
the burner must be largely gas, with or without entrained liquid. 
There's no practical limit to the size of the liquid droplets that could
be entrained.  But remember that the dynamics of motion of liquid and
gas are different due to density differences.  Hence, if you take a mist
around a 90-degree elbow, you're likely to drop out some liquid on the
walls.
 
Hence, I envision that you're talking about very small (<=5 micron)
droplets entrained in gas.  These would move largely with the flow of
the gas.
 
However, where did these droplets come from?  I've worked with
hydrocarbon solvents, like pentane, a lot, and have never seen any
tendency for spontaneous generation of mists.  Quite the contrary.  They
evaporate so readily that there's no liquid present at all.
 
However, I work at room temperature and pressure.  Once a burner has
been runing for a while, tank temperature will have dropped due to
evaporation of the propane.  Tank pressure will be perhaps 30 psi,
more-or-less constant (unless it freezes up), but this would scarcely
ENcourage the formation of a mist.  Boiling or bumping would encourage a
mist to some small extent, but I'd bet the liquid would tend to drop out
before the mist ever left the propane tank.
 
All this is speculation.  Let me know your source of this information
about propane "vapor," and I'll look into it as time permits.
 
Bruce
NJ

>>> Keporter@aol.com 2/17/2004 5:58:56 PM >>>

In a message dated 2/17/2004 1:50:58 PM Pacific Standard Time, 
FREEMAB@pt.fdah.com writes:
I object to the term "scolder."  I am not scolding you.  I am merely
correcting a misstatement you made.  I don't question your practical
knowledge of your subject otherwise.
Bruce
Then, I apologize for using the term; "scolder" that is. As to the term

"vapor" it is the term the propane industry chooses to use. 
 
They do make the 
distinction between a vapor and a gas. So, who should I believe? You
certainly sound 
scientific. I can follow what you say, though it is hard slogging.
However, 
chances are good that they have scientific people helping to come up
with their 
terms too. Perhaps, it would be helpful for you to ask them for a 
clarification? Please understand that I don't mind being corrected,
especially if that 
correction furthers understanding of these burners. Understanding is
just as 
necessary as experimentation and design to further improvement.
However, its 
seems to me that we have come to an impasse. Perhaps "vapor" was a slip
up on some 
technical writer's part, and perhaps it was not. Until you receive a 
confirmation from them that it was just some glitch, which they have
been unwilling to 
correct, I have to go with the statements of accepted authority.
Otherwise, 
we have chaos. Personally, I'll be interested, either way, in hearing
what they 
have to say to you.
Mikey