Ok so Dry Ice is dirt cheap anyway. I can buy it or ask my friendly lab for a Thermos Flask of it. But I'm sure that is not the case for everyone!
Ok so you can buy dry ice makers... bags that attach to a special adapter onto a syphon liquid CO2 cylider but then you have to get a large syphon
cylinder and thats rentable or outright purchase. And these adapters are quite pricey $100 or so.
I have just discovered an easier way!
I purchased a CO2 cylinder for Soda Stream. Wanted to empty it, removed the annoying valve, fill with gas of more interest and replace with a decent
propper valve! Well in order to do that I had to purchase a soda syphon with the correct valve fittings in order to empty the CO2. This cost £35.
Whilst emptying the cylinder, if you turn it upside down you get dry ice snow.
Naturally I tied a sock to the nozzel and collected a teaspoon of dry ice very quickly. The sock lets too much snow escape to collect sizeable
quantity but couple second burst you have at least a teaspoon.
I think a felt bag would be best. Well worth it if you can collect say 50-100cc dry ice in a go.
I will experiment a bit. The refills only cost £3.99 here so if you can get a small, handy, quantity of dry ice form these as and when needed I think
it would be well worth people considering.stateofhack - 4-1-2009 at 13:03
That is very intresting! I am having a hard time trying to get what your doing exactly could we see some pictures?panziandi - 4-1-2009 at 13:23
What I am doing? I am emptying a high pressure steel lecture bottle of CO2 for a soda syphon in order to remove the patented valve fill with liquified
gas replace with a standard lecture bottle valve and have the gas on tap, like Sauron has been intending to do himself.
Why I am posting about dry ice? This is because I found that dry ice can be made easily by this method and may be useful for people to do if they need
dry ice at a moments notice and can not buy it!stateofhack - 4-1-2009 at 14:40
Ah thanks for that, makes more sense. I also checked a it online..everything is much clearer!
Thanks!497 - 4-1-2009 at 15:06
How cheap do you think you can make it?
Right now it's about -45*C where I am, I wonder how much better the yield would be?Magpie - 4-1-2009 at 15:22
I think what he is saying is that he has a bottle of liquid CO2 normally used to issue gaseous CO2 from the valve on top of the bottle. By turning
the bottle upside down he issues liquid CO2 which partially turns into solid CO2 snow. Is this correct panziandi?panziandi - 4-1-2009 at 16:32
Magpie you are correct! I believe the contents to be liquid CO2!
After a while the dry ice stopped forming, I believe because the liquid CO2 contained in the bottle converted to pressurized gaseous CO2 within the
bottle so at room temperature no liquid CO2 left the bottle to form dry ice.
497: Dare I say I think you are lucky to be at -45*C ... You will certainly insulate the dry ice as it forms better than I did at room temperature! I
would suggest something thicker than a sock since the high pressure pushes the snow through the material. Perhaps somehow making a contical adapter to
the soda syphon nozzel could spread the snow out, larger volume = lower pressure = less force.
I have no idea as to the conversion % yield ... online says 25% yield from specially manufactured adapters for dry ice making in this way.... I'd say
if carefully done with a decent method of collection and low temperature/insulation you could perhaps get an ok quantity.
It seems quite convenient. I have tried getting dry ice from disposable welding CO2 cylinders with no success but these soda syphon ones seem to work!Sauron - 4-1-2009 at 19:13
While some gas suppliers may try to charge you drayage for a 6 m3 cylinder (48 L) I purchase mine outright with the standard CGA320 valve and dip
tube. Charged with liquid CO2 this is still dirt cheap.
I did buy a Frigimat Jr (dry ice snow maker) and figured out that it can be duplicated for about $30. The brass fittings are all standard stuff, one
required modification (drilling a single 1/8" hole) and the cone is a plastic cup of approx size and shape.
Big frigging deal!
The important thing is that the dry ice come out only when you need it (JIT) and in slurriable form rather than in big blocks.497 - 4-1-2009 at 20:49
Quote:
The important thing is that the dry ice come out only when you need it (JIT) and in slurriable form rather than in big blocks.
Yes that would be nice. I can buy it cheap ($3/lb IIRC), but it's in big blocks which are hard to deal with..Sauron - 4-1-2009 at 21:29
And impossible to store. They will just sublime away, use it or lose it.
The liquid storage, just in time conversion to dry ice granules sor slurrying in acetone, is the way to go. Gagage chemist disagrees because he was
disappointed with how much he got out of a cyclinder. But refills are cheap, and if you own your cylinder and valve ($50) and assemble your own
Frigimat Jr clone, ($25) there are no other costs.
You need:
A CGA320 regulator nut and nipple w/nylon sealing washer. $6
Some are 1/4 NPTM, some 3/8 NPTM, the specs below assume 1/4
A 45 degree elbow to fit same (mine, 1/4" NPTF)
A reducing adapter 3/8 NPTF x 1/4 NPTM
A plug 3/8 NPTM. Drill a longitudinal hole 1/8" through.
Washers, a plastic cone and suitable heavy duty woven PE bags, a hose clamp to hold bag on cone.
That is IT.
Remember to open valve ONLY 3/4 of a turn. NOT 3 or 4 turns!
Wear cryo gloves, liquid CO2 will hurt you.
A dip tube on inlet of valve is REQUIRED. Also known as an outtage tube. You want liquid not gas coming through this device.not_important - 5-1-2009 at 01:38
Wonder if you could get better yields if you could rig a heat exchanger to use the escaping CO2 gas to cool the pressurised CO2 before it was
expanded?Sauron - 5-1-2009 at 02:38
Replacing a simple cheap device with a more complex one?
Diminishing returns surely.watson.fawkes - 5-1-2009 at 15:22
Quote:
Originally posted by not_important
Wonder if you could get better yields if you could rig a heat exchanger to use the escaping CO2 gas to cool the pressurised CO2 before it was
expanded?
If I understand you correctly, you're talking about using the excess expansion energy that doesn't
go into phase change as a desuperheater for the feed liquid. Right?
It would work physically, but I think the mass-transfer rates vs. the heat-transfer rates won't work in your favor. Perhaps it might if operated
rather more slowly than most people have the patience for. I'd have to run numbers to know for sure.
Then again, it's true that the fixed costs for such a system are likely not beneficial at the small scale. But it does inspire another idea. (1) Buy a
small chest freezer for the CO<sub>2</sub> tank. (2) Optional (for convenience). Pierce the wall of the freezer with a liquid line and put
the tap on the outside. (3) More Optional (for performance). Hack the thermostat to keep the interior temperature at right above the boiling point of
the refrigerant, presumably R-134a. This one is pretty cheap to build and operate. It's a certainly has diminishing returns--paying fixed costs and
some operating one for better gas efficiency. It may well be economical for some people, particular if you count inconvenience costs of refilling the
tank.
could we see some pictures?