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Acetic Acid
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Methods of cooling?
I made a thread some time ago about how to heat stuff to ridiculous ends, but I'm still confused about how to cool it. I know how to make an ice bath
and put my beaker in it, but that only gets down to 0-5C. I know what dry ice and liquid nitrogen are, but I'm not sure how to get them, and I'm not
sure how to keep them cold. Anyone care to share their experiences?
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Megamarko94
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dont worry about keeping liquid nitrogen and dry ice cold they will stay cold by them self..
liquid nitrogen must be kept in container called dewar its a container with double walls and vacuum in the between. (never keep it in close container
because it will go boom from it going to gas stage)
you can put thermal foil around block of dryice to keep it solid longer.
i dont think they sell liquid nitrogen to individual
[Edited on 3-9-2011 by Megamarko94]
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Acetic Acid
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I feared that... and it's hard enough to get dry ice as well because I'm under 18 >.<
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Megamarko94
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and dewars are pretty expensive...
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UKnowNotWatUDo
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Dry ice can be mixed with acetone (or sometimes ethanol) to make a cooling bath which will keep your reaction mixture at about -78C. If you can't buy
dry ice directly you might try getting someone to buy it for you. I wouldn't imagine it would be that hard to find someone to buy you something as
innocuous as dry ice. Maybe a friend or parent?
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Acetic Acid
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Ah yes, I remember a youtube video where this guy froze acetone with liquid nitrogen. Same concept I guess?
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Endimion17
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Quote: Originally posted by Acetic Acid  | | I made a thread some time ago about how to heat stuff to ridiculous ends, but I'm still confused about how to cool it. I know how to make an ice bath
and put my beaker in it, but that only gets down to 0-5C. I know what dry ice and liquid nitrogen are, but I'm not sure how to get them, and I'm not
sure how to keep them cold. Anyone care to share their experiences? |
Here, knock yourself out. 
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Megamarko94
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i think that guy was nurdrage...
[Edited on 3-9-2011 by Megamarko94]
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Acetic Acid
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Thanks! Isn't it possible to get calcium chloride as road salt?? Now I know why :->
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Endimion17
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Don't mention it.
No, road salt is a mixture of calcium and sodium chloride.
But relatively pure calcium chloride is that stuff you buy for removing moisture in damp rooms. For some reason, that tends to be expensive where I
live.
It's usually packed in some synthetic cloth and is placed in special trays.
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Acetic Acid
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barley81
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A brand is Damp-Rid sold at Home Depot, it comes in cartons and cylindrical plastic containers with snap-on lids. Just thought I'd add something...
Also if you can find an Airgas near your home, it will carry pellets of dry ice, sold in boxes for $10.
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ziqquratu
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Dewars are cheap - as long as you buy them in the form of a Thermos flask or similar.
As mentioned, though - do NOT seal any container which holds dry ice or liquid nitrogen, or it WILL explode, violently! A loose-fitting polystyrene
foam plug serves as an excellent cap - it should allow gas to escape, but on the off chance it does seal (eg if it's wet and you get an ice seal
forming), it should pop out under low pressure and cause much less damage than an exploding flask.
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Endimion17
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I've never seen a big thermos flask. Only up to 2 liters, and that's only for keeping a sample right before you do the experiment. The larger the
flask, the longer it keeps the stuff at the same temperature. That's why Dewars are 50, 100 liters etc.
If he's going to work with LN2, either he has to have a quick access to a near filling station, or buy a real Dewar.
Dry ice can be stored in iceboxes with styrofoam walls added. Again, the more you have, the better.
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Dr.Bob
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You can get dry ice at many grocery stores or ice cream places (especially if they sell ice cream cakes). Our Kroger's sells it, for one example.
We have plenty of places nearby that sell it. Just look in the phone book (a paper thing invented before the internet) under dry ice. It is not
regulated as far as I know. You could also try searching Google maps for dry ice.
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Neil
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Curiously the larger the vessel the shorter it keeps 'the stuff'. more surface area, a 1L dewar losses less N2 then a 25L dewar in the same period.
But with a larger vessel you have more of the stuff so losing a bit of it isn't much of a worry. If you get to use half the nitrogen out of a 180L
dewar you are doing very well.
Getting small dewers that are insulated as well as the large dewars is the trick, most of them are not nearly as good.
Calcium chloride is sold by people who sell cement in cold climates, it is also sold where people use it as a additive to remove dust from gravel
roads during hot dry summers.
Dollar stores often carry small containers of it as a 'drying agent' ditto with boat or RV stores.
The last bag I bought of it was around 34$ for 65 Lb and it was labeled for treating summer roads.
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Panache
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conc sulfuric poured onto crushed ice is a super cooling bath for freezing something in a pinch, the normal precautions concerning sulfuric pertain,
afterwards you'll have a solution of sulphuric acid that can be used as sulphuric acid solutions are. Driving off the water at temp allows you to
repeat the process with fresh ice.
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Sedit
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I never had luck with H2SO4 on ice, Concentrated Sulfuric worked worse then dilute. HCl onto snow on the other hand worked wonders.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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sternman318
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| Quote: Originally posted by UKnowNotWatUDo | | Dry ice can be mixed with acetone (or sometimes ethanol) to make a cooling bath which will keep your reaction mixture at about -78C. If you can't buy
dry ice directly you might try getting someone to buy it for you. I wouldn't imagine it would be that hard to find someone to buy you something as
innocuous as dry ice. Maybe a friend or parent? |
Here is a video http://www.youtube.com/watch?v=d11TFkeqbwY
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Acetic Acid
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I bought some "DampRid Moisture Absorber Refill". I got 4 pounds for $5.29 from my local Publix. Opening it up, the chips look like pure calcium
chloride, and when I left some in a beaker overnight they were a solution by the morning. How do I chill the solution to its freezing point, though?
My freezer won't cut the mustard. Do I leave it in a dry ice bath until it freezes?
[Edited on 10-9-2011 by Acetic Acid]
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Neil
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UTFSE
http://en.wikipedia.org/wiki/Cooling_bath
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Acetic Acid
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Show me where that page tells me how to freeze a mixture of CaCl2 and ice. Oh wait...
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Chordate
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Alternatively, you can get into refrigeration technology.
A good basic tutorial is here:
http://www.refrigerationbasics.com/1024x768/rb2.htm
Look to the "end of the fridge pump questions" thread for some basics on how to get cheap compressors.
A basic fridge compressor or AC unit can get you quite a ways, but if you are willing to play with some exotic refrigerants you can start looking into
cascade cooling(the use of several refrigerants in a loop, with each evaporator cooling the condenser of the next coolant phase). This sort of
cooling, with two units and good refrigerant selection can produce temperatures low enough to freeze carbon dioxide and produce dry ice, or provide a
cooling coil which could easily cool an acetone reservoir and allow cryogenic temperatures.
Some people have even used cascade cooling and a small cryocooler to produce liquid nitrogen DIY style, but it should be noted that this will also
condense liquid oxygen and as such is a rather dangerous extreme
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unionised
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| Quote: Originally posted by Neil | Curiously the larger the vessel the shorter it keeps 'the stuff'. more surface area, a 1L dewar losses less N2 then a 25L dewar in the same period.
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Not always.
http://www.flinnsci.com/store/scripts/prodView.asp?idproduct...
In any event, if you have, for example, 100 litres of liquid N2 to look after you will have more of it left at the end of the week if you put it in
one 100 L dewar rather than 100 1 litre ones.
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Endimion17
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| Quote: Originally posted by Neil | Curiously the larger the vessel the shorter it keeps 'the stuff'. more surface area, a 1L dewar losses less N2 then a 25L dewar in the same period.
But with a larger vessel you have more of the stuff so losing a bit of it isn't much of a worry. If you get to use half the nitrogen out of a 180L
dewar you are doing very well.
Getting small dewers that are insulated as well as the large dewars is the trick, most of them are not nearly as good. |
That's simply not true and I'm stunned to read this.
If that was true, it would be stored in small vessels. Economy argument.
And another argument, this time natural one, is that surface grows slower than volume, if the body is close to being spherical, which is the case of
LN2 tanks.
LN2 is spent by increasing its storage tank surface. Nitrogen inside LN2 does not evaporate. Only the layers touching the vessel do.
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