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This one seems to cause some very negative comments.



 
 
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  #41  
Old February 3rd 05, 08:22 PM
Elaine T
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spiral_72 wrote:
1 LITTLE PERCENT!!!???!!! WHAT'S UP WITH THAT?

Actually, the ONLY thing I am concerned about is I throw the ice in
this dude....cork it..... have it build up pressure and the CO2 only
lasts five minutes. I have no idea what the equivalent gas volume a 1
pound chunk of dry ice has.


Well, the volume depends on the temperature but the ideal gas law lets
you calculate it. (more or less)

pv=nrt
p = pressure in atmosphteres
v = volume in litres
n = number of moles
r = a constant = 0.08205 L atm / (mol·K)
t = temperature in degrees K.

C02 is 44 g/mol and a pound is 454 grams so you have about 10 moles of
C02. At standard temperature and pressure (273K or 0C and 1 atm), one
mole of gas is 22.4 L of volume. So your 1 lb block would sublime to
occupy 231 litres of volume at freezing.

You can use the number of moles, your tank volume, the temps in the
tank, and this equation to predict the actual pressure in your tank in
atmospheres.

--
__ Elaine T __
__' http://eethomp.com/fish.html '__

  #42  
Old February 4th 05, 01:53 AM
Dan White
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"Elaine T" wrote in message
. ..
spiral_72 wrote:
1 LITTLE PERCENT!!!???!!! WHAT'S UP WITH THAT?

Actually, the ONLY thing I am concerned about is I throw the ice in
this dude....cork it..... have it build up pressure and the CO2 only
lasts five minutes. I have no idea what the equivalent gas volume a 1
pound chunk of dry ice has.


Well, the volume depends on the temperature but the ideal gas law lets
you calculate it. (more or less)

pv=nrt
p = pressure in atmosphteres
v = volume in litres
n = number of moles
r = a constant = 0.08205 L atm / (mol·K)
t = temperature in degrees K.

C02 is 44 g/mol and a pound is 454 grams so you have about 10 moles of
C02. At standard temperature and pressure (273K or 0C and 1 atm), one
mole of gas is 22.4 L of volume. So your 1 lb block would sublime to
occupy 231 litres of volume at freezing.

You can use the number of moles, your tank volume, the temps in the
tank, and this equation to predict the actual pressure in your tank in
atmospheres.


....and you've already provided the volume and pressure, so he can just solve
for the new pressure after finding out his cylinder volume. P1V1 = P2V2 as
you know, so

(1 atm)(231 litres) = P2(cylinder volume). This is the pressure at 0C.
Spiral - just divide each side by the temperature (T1 = 273 and T2 = room
temp or whatever you want) and solve for P2 if you want to know your
pressure at different temperatures. You might need to look at a property
diagram for CO2 to make sure your results are correct. If you calculate
your pressures to be too high, for example, you might be getting a phase
change in reality.

dwhite


  #43  
Old February 4th 05, 01:56 AM
Dan White
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"spiral_72" wrote in message
oups.com...
Oh, for those wanting an update...... Hopefully I will be able to cut
threads today over lunch for the tank pressure gauge. I will hopefully
weld the top on it tonight.and hopefully I will have some news, good or
bad, by Monday morning.


1 percent.... good grief.


Hey, I thought 25% chance of leaky welds was an insult! You obviously do
something like this for a living, so I have to think you will make good
welds and threads. But then again, you might be a troll!

dwhite


  #44  
Old February 4th 05, 04:08 AM
Joe Crowder
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"Dan White" wrote in message
...
"spiral_72" wrote in message
oups.com...
Actually, yea..... I thought about that. I really don't know what to
expect. I would suppose a material could be brought to a low enough
temp causing that material to become brittle. Water, plastic, chewing
gum, lots of stuff becomes brittle at a low enough temp. Any idea what
that temp is for steel?


I haven't looked that up -- maybe it can be found by googling. It

probably
depends on the type of steel, although they might all be in the same
neighborhood. I checked on dry ice the other day and I think it sublimes
at -78.5 deg C at atmospheric pressure, and warmer at higher pressure, but
you'd need an equilibrium diagram for that. -78.5 C should be the worst
case though.

dwhite


Dodge the whole embrittlement problem by putting down a layer of 1/4" - 1"
thick styrofoam between the dry-ice and the base of the tank. It should not
affect the volume capacity significantly, but it will keep the steel at a
reasonable temperature. It will slow down your melt rate quite a bit, but
that's probably not a bad thing anyways.

You could use a ceramic or hard plastic insulator too, but I'd be concerned
about the additional shrapnel when the tank explodes ;-)

Joe


  #45  
Old February 4th 05, 02:40 PM
spiral_72
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Hey, I cut a nice plug for the top yesterday. I ended up with one inch
of 1"-40 threads on a 1.25" dia plug. I bored a 1/8" hole through the
plug, down the centerline. Finally I bored a 7/16" - 1" deep hole and
cut threads for 1/4" pipe. I mounted my pressure gauge in the top of
the plug.

All I can find at the moment is a 0-60bar gauge... 800 something psi I
think. It is actually a borrowed gauge, that's why I mounted it in the
plug. I figured that's better than trying to fix a big gaping hole in
the tank when a new gauge requires an assortment of fittings to thread
1/4" pipe. The fitting on this gauge is brass instead of steel. I don't
gat any warm fuzzies from that, but I guess we'll see. After all I am
testing Da Bomb outside right?

The neighbors have goats..... I wonder how goats respond to 1/4" steel
debris traveling at the speed of sound? and a shock wave?

"Da Bomb" = "Da Goat Bomb"

  #46  
Old February 5th 05, 10:40 AM
Elaine T
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spiral_72 wrote:

The neighbors have goats..... I wonder how goats respond to 1/4" steel
debris traveling at the speed of sound? and a shock wave?

"Da Bomb" = "Da Goat Bomb"

I have a sudden very odd mental picture of goats in flak jackets!

--
__ Elaine T __
__' http://eethomp.com/fish.html '__

  #47  
Old February 7th 05, 04:45 PM
spiral_72
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IT WORKS!!! IT WORKS!!! IT WORKS!!!

AHA! o.k....... the news.

Things didn't start out well at all. I cross threaded my plug (I have
no idea how) and at 40 threads per inch..... they were pretty much
immediately wasted, which means the top of the tank was wasted,
cause'it's welded in. In an effort to ward off defeat I welded the plug
in the top of the tank. Hey, I had to make a new one anyways, right?

Next problem was, how the heck am I supposed to get the dry ice in the
tank? Anyways to make a long story short....
I put about 1/2 a pound of dry ice and about 1/4 cup of water in a hole
for 3/8"pipe and put the regulator back on, closed the bleed valve and
closed the regulator. it took about 60 seconds to steadily build 60psi
at which point I found a leak. In my hurry I forgot to put teflon tape
back on the regulator pipe (where I inserted the ice). CRAP!
I had to leave, The previous problems took too long. I was already 10
minutes later for an appointment. I dropped everything and left.
Hopefully tomorrow I can start the tank repair.

I will note that 1/2 pound of dry ice sublimates into A LOT of
volume... I actually bled off all the pressure at one point and closed
the valve again. The pressure built back steadily to around 60psi and
held. Very cool stuff.... I can't wait to fix my tank. I wish I knew a
better way to cap the thing. Any ideas? Remember, it could be about
1200psi we are talking about.

 




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