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Old 26-04-2007, 12:40 AM posted to rec.aquaria.freshwater.plants
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Default dry ice as co2 source any thoughts if so, how or y not




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Old 26-04-2007, 12:36 PM posted to rec.aquaria.freshwater.plants
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Default dry ice as co2 source any thoughts if so, how or y not

it works but way to good, in less than 2hr's I about suffocated my mollies I
need a gang valve or sumthing to reduce the flow of co2, still looking for
ideas though




"Jeffery Moyer" wrote in message
...




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Old 10-05-2007, 03:47 AM posted to rec.aquaria.freshwater.plants
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Default dry ice as co2 source any thoughts if so, how or y not

On Apr 26, 7:36 am, "Jeffery Moyer" wrote:
it works but way to good, in less than 2hr's I about suffocated my mollies I
need a gang valve or sumthing to reduce the flow of co2, still looking for
ideas though

"Jeffery Moyer" wrote in message

...



Just to give you an idea of what you are looking at...

When held at room temperature solid CO2 will expand completely into a
much larger volume of gas. To prevent this you must either supply
enough volume for it to expand into ( a big tank) or apply enough
pressure to liquify it. WHen compressed at about five atmospheres (to
the best of my memory) CO2 will liquify at room temperature, so what
happens is the solid melts, expanding slightly into the liquid, which
evaporates into the container to maintain a constant vapor pressure of
about 5 atm (or around 75 psia). That's about 60 psi about the
pressure in your house, so you need some gear that will be able to
handle that. Such equipment is already sold for planted tanks, though
they usually assume you want to use a commercially supplied CO2
canister.

Maybe... you could maintain a CO2 bubble under an inverted glass by
placing tiny pieces of dry ice under it. This assumes you have easy
access to dry ice, other wise I would just buy canisters.

Oh, and your story about the mollys cracked me up. I would have
warned you if I had read your first post in time.

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Old 10-05-2007, 08:51 PM posted to rec.aquaria.freshwater.plants
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Default dry ice as co2 source any thoughts if so, how or y not

Vreejack wrote:
When held at room temperature solid CO2 will expand completely into a
much larger volume of gas. To prevent this you must either supply
enough volume for it to expand into ( a big tank) or apply enough
pressure to liquify it. WHen compressed at about five atmospheres (to
the best of my memory) CO2 will liquify at room temperature, so what
happens is the solid melts, expanding slightly into the liquid, which
evaporates into the container to maintain a constant vapor pressure of
about 5 atm (or around 75 psia). That's about 60 psi about the
pressure in your house, so you need some gear that will be able to
handle that. Such equipment is already sold for planted tanks, though
they usually assume you want to use a commercially supplied CO2
canister.



You're of by more than an order of magnitude. The liquid CO2 will
continue to expand until it reaches about 60 bar (~900 psi) at room
temperature. Put it in a sealed container that cannot withstand that
pressure and it will explode.

Best regards,
Bob
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Old 11-05-2007, 01:22 AM posted to rec.aquaria.freshwater.plants
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Default dry ice as co2 source any thoughts if so, how or y not

On May 10, 3:51 pm, zxcvbob wrote:
Vreejack wrote:
When held at room temperature solid CO2 will expand completely into a
much larger volume of gas. To prevent this you must either supply
enough volume for it to expand into ( a big tank) or apply enough
pressure to liquify it. WHen compressed at about five atmospheres (to
the best of my memory) CO2 will liquify at room temperature, so what
happens is the solid melts, expanding slightly into the liquid, which
evaporates into the container to maintain a constant vapor pressure of
about 5 atm (or around 75 psia). That's about 60 psi about the
pressure in your house, so you need some gear that will be able to
handle that. Such equipment is already sold for planted tanks, though
they usually assume you want to use a commercially supplied CO2
canister.


You're of by more than an order of magnitude. The liquid CO2 will
continue to expand until it reaches about 60 bar (~900 psi) at room
temperature. Put it in a sealed container that cannot withstand that
pressure and it will explode.

Best regards,
Bob


Seems so. I had the axes reversed on that tiny phase diagram and was
looking at the solidus line instead of the liquidus. So the solid CO2
will continue to sublimate straight to gas, building up pressure
absorbing heat from the room until one of three things happens.

1) The container will fail due to overpressurization.

2) All of the solid sublimates into a gas below ~900psi which slowly
warms to room temperature.

3) The pressure rises and the temperature drops as the gas
sublimates. As the pressure rises above five atmospheres--if the
temperature drops to about -56C--the CO2 will start to condense. If
the temperature does not drop that low then the condensation will
start at a higher pressure, but once condensation occurs the pressure
will be controlled by heat coming in from the outside, which will re-
evaporate the liquid CO2 forcing it to condense at a an higher
pressure. The result is that the system will follow the liquid/gas
line of the phase diagram until it reaches room temperature, at the
pressure Bob mentioned (~900 psi).

12 gram CO2 canisters get charged to about 900-1000 psi, so there you
go. At room temperature some of it will be liquid or on the
threshold.

At 70 degrees F, CO2 obtains a gas pressure of 852.8 psi.

I used to use CO2 fire extinguishers with liquid CO2 in them. Actually
I used them to make carbonated ice coffee, but that's neither here nor
there.




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