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

Wed Feb 18 15:49:00 2004

In a message dated 2/18/2004 9:50:42 AM Pacific Standard Time, [email protected] 
writes:
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
>

    Bruce
Now, that's what I call a discussion! Full of meaty details that might be 
employed by someone to come up with a clever improvement I never dreamed of. It 
will take a little time to collect the information and URLs you are requesting 
as everything changes so fast on the Net, but I will back track and provide 
them for you. This discussion is already bringing up good technical stuff that 
someone may pounce on in the next few months.
   These groups remind me of salvage yards; you never know what you're going 
to find next. While cruising one yesterday I came across a giant fuel/air 
naturally aspirated hand torch. It was unused and probably originally cost one or 
two hundred dollars. I had thought of purchasing it just to hang on the garage 
wall (something quaint, but completely outdated). What is interesting about 
the burner is it's mixing chamber. I belong to a casting group and immediately 
appreciated the design. Many on the group would want to use the design to cast 
their burners (they love any excuse to cast something, and this design is 
both peculiar and elegant). Then I wondered what would happen if I changed out 
the inefficient gas tube for a MIG tip accelerator...
    It wasn't easy to put the burner back on the shelf, but it had to be 
done; it's much to early to get sucked into further burner research. As I sit 
here, it calls to me "Mikey, come back and take me home with you. I can teach you 
to fly. There is this island with pirates and you never have to grow up." If 
I'm lucky, someone else will buy it before I break down. Junk addiction is so 
hard.
Mky

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