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

Wed Feb 18 12:51:00 2004

I have to think that some of this liquid, vapor, and gas discussion stems
from the fact that as propane gas exits a tube into the air we can see a
stream of material exiting the orifice. I have always assumed this "visible"
stream is cause by the difference in refractive index between air and
propane gas, not particles, or droplets of propane.

As far as propane coming off the top of a tank, it exits as a gas, if the
tank is upside down liquid will exit and actual liquid will exit out the
tube opening into the atmosphere as the tube becomes very cold.

Restated

It is at that interface of propane gas to air where the refractive index
difference bends light making propane as a gas appear visible, lending
people to assume it isn't a gas at that point..

Mike McKim.

----- Original Message ----- 
From: "Bruce Freeman" <[email protected]>
To: <[email protected]>
Sent: Wednesday, February 18, 2004 11:35 AM
Subject: [TheForge] Gas vs Vapor vs ??? (was: Building a propane forge)

> 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
>
> >>> [email protected] 2/17/2004 5:58:56 PM >>>
>
> In a message dated 2/17/2004 1:50:58 PM Pacific Standard Time,
> [email protected] 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
>
>
>
>
>
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