[TheForge] Building a propane forge

Tue Feb 17 16:51:13 2004

Mikey,

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.

I don't object in the least to the use of the term "vapor."  What you
don't seem to realize it that it is a synonym for "gas."  There is no
difference.  I am aware that some folks choose to use "vapor" to mean a
gas evaporating from a liquid.  However, the distinction is no more
meaningful than the term "permanent gas," which applies to nitrogen,
oxygen, and many other gases.  Those gases can be, and frequently are,
condensed into liquids.  If we reevaporate them, are they then not
"vapors"?   Such distinctions are meaningless.

Now, the term "gas" was coined some centuries ago from the term "chaos"
(or its Latin precursor, no doubt).  It described a phase of matter in
which there was no interaction between the molecules (as there is in
solids and liquids).  Strictly speaking there is some interaction
between gas molecules, but it is of a much lower magnitude than in
solids and liquids and doesn't become important until the gas density
has increased substantially, usually by compression to hundreds or
thousands of psi. 

What you are suggesting is a phase of matter ("vapor") in which there
is some stronger interaction between molecules than for a gas, but which
is not a liquid.  As I mentioned before, there is such a phase: 
supercritical liquid.  However, this phase is well characterized. 
According to the weldingsupply.net (the first website I found that
listed it), the critical point of propane is about 200 F and 600 psig. 
For the propane to be supercritical, you have to equal or exceed both of
those values.  You are not going to exceed them with propane passively
drawn from a normal cylinder.  (To exceed the critical point, you'd have
to  tap the liquid propane  from the bottom of the cylinder and pump it
at high pressure into a heated device.  I could easily do this in the
lab but don't try it at home.)

So I reiterate:  There is no separate "vapor" phase.  Vapor = gas.  Gas
= vapor.

I do not doubt that it takes signifcant energy to disperse propane in
air, but this is simply a reflection of the gas density, not any sort of
clumping, as you describe it.  In my limited experience, the pressure
from a propane cylinder provides plenty of energy for this dispersion. 

I have not the experience with propane to know the cause of the pulsing
you describe, but I would speculate that it is equivalent to the
"bumping" of hot water, known to all Chem 1A students:  If you heat a
beaker of water to boiling, superheating sometimes occurs at the bottom
of the container, and "bumping"occurs.  "Bumpint is the spontaneous
conversion of a small amount of superheated water to gas, accompanied
with a "bump" sound.  (It is dangerous because it is violent and
splatters hot water.)  

Bumping can occur in any liquid heated from below the surface.  In the
case of propane, bumping could carry liquid into the valve and
regulator.  This would cause an effect similar to that seen when working
with a Bernzomatic type hand-held torch bottle, when you accidently tip
the bottle too far.  (I.e,  Liquid spits through the orifice, either
extinguishing the flame, or cutting air aspiration to near zero,
resulting in a large, typically yellow, candle-like flame.)

If my speculation is correct, there would be a relationship between
"freezing up" and pulsing , in that "freezing up" (a misnomer, since the
only freezing will be of water vapor on the outside of the tank) is when
the propane drops below its boiling point at the pressure of the
cylinder.  That is the temperature (range) at which bumping could occur.

(Note to the scientifically bewildered:  The boiling point of any
liquid increases with increasing pressure.  That's why water boils at a
lower temperature in Denver than in NYC.  I could explain this further
if anyone is really interested...)  

Bruce
NJ

>>> [email protected] 2/17/2004 3:27:36 PM >>>

Bruce
NJ
Congratulations, you are the first of many scolders to come. However, I
make 
no apology for using the term "vapor" as it is the definition which the

National Propane Association uses and is the definition adopted by the
National Fire 
Protection Association. Since the later writes the safety codes -- in
close 
consultation and cooperation with the former -- that government
agencies adopt, 
and since the former writes all other technical terms and makes the 
definitions which are used...
you are outvoted.

"The only remaining possibility would be a
mist, or "aerosol", in which liquid droplets are entrained in air.  I
submit that even this is highly unlikely under the conditions of
operation of any burner."

The problems associated with the difference between a true gas and
propane 
vapor (as "the powers that be" use it, I will too) are not only real,
but are 
taken into consideration in LPG equipment construction, and are
frequently 
encountered in cold weather by people using propane to run forges and
furnaces. I 
do not refer to so called "freezing up," which is simply the result of
the 
liquid falling below its boiling point, but of pulsing. The colder the
vapor gets 
the more vapor like, and less gas like, it becomes. 

I think perhaps the problem you are having with my viewpoint -- and
that is 
all it is -- is a mistaken impression about my use of the term
"clumps." I am 
not trying to convey the thought of anything so enormous a a "droplet"
and 
should have made that clear. The particles envisioned are to small to
even be 
seen, but still affect combustion. To keep this friendly (because your
comments 
were very civil, and because I don't want to discourage further
critics), I will 
reiterate that my ideas of the whys and wherefores about the way my
burners 
work are definitely open to question. I am not a scientist, nor a
combustion 
engineer. That the equipment does work, just as stated--complete or
near nearly 
complete primary flame combustion -- and that the rest of the equipment
in the 
book lives up to my claims completely, is all I can guarantee.
Before anyone asks, the qualification "or nearly complete" is not a
back door 
for excuse making. These burners are going to be hand built, not turned
out 
in a factory. Furthermore, unless someone wants to stand around doing
nothing 
more than readjusting the burner, it will vary slightly in performance
from 
minuet to minuet. With acknowledgment of these two limiting factors,
complete 
means complete. 

Again, congratulations on being the first challenger, and please don't

hesitate to call me to account again. When caught in a mistake I will
'fess right up 
to it. More importantly, don't hesitate to try and make a better
burner. That 
is called progress :o)
Mikey

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