[TheForge] Vapor/Gas (Was: Building a propane forge)

[Mike]

> A 'vaporized liquid' IS A GAS!  That's how it works.

I have to agree with Bruce and Craig that stuff is either gas or
liquid. [1]

BUT that's under user-friendly conditions in which everything stays
where you put it while you scrutinize it.

Between the surface of the liquid propane in a tank and the feathery
tip of the flame in the forge, there's a whole string of dynamic
processes going on that are very far from equilibrium.  Stuff is
*happening*.  

In particular, there's turbulence happening.  Every time the stuff in
the pipe goes around a corner, through a diameter change or over a
rough spot, there's turbulence.  If the stuff is moving fast enough,
there will be turbulence even in a straight, smooth pipe.  Where
there's turbulence, there are sudden, chaotic changes in pressure. In
a river or garden hose, this won't make much difference but in
propane, which is not too far in temp/pressure from a liquid phase
anyhow, there will be significant changes in temperature where those
changes in pressure happen.  All these little variations in T and
P are happening in your 1/2" or 3/4" pipe, that is, a great many
changes on a very small scale.

I suspect that the reason propane techs say that "vapor" isn't "gas"
is this: All that turbulence results in the spontaneous condensation
of aerosol-sized liquid droplets in places and ways sufficiently
unpredictable that it's indistinguishable from random.  Changing the
flow rate, pipe diameter, shape of turns joints or fittings, inside
surface finish, kind of regulator etc etc would change the effect but
probably not eliminate it.  

If this effect does, in fact, exist, it may be undesirable to
eliminate it since a mix of gas and micron-sized droplets at a
give flow rate would move energy into the burned faster than pure gas
would.

So "vapor" is the same as "gas" except when the engineers need to
highjack "vapor" so they can give a name to some stuff involved in a
messy, poorly understood dynamic process.

My guess, FWIW,
- Mike


[1] Ignoring, for the moment, solids, plasmas, neutronium,
    administratium, quantum bogodynamics and various irrelevant
    ambiguous cases such as glasses.

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer@tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

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