ChemNewbie (Hive Bee)
07-05-03 12:57
No 444740
      Ultra-low temp refrigeration system design  Bookmark   

I recently put together a small refrigeration system capable of cooling a highly insulated SS cylinder of acetone to around -25C. It basically consisted of a small refrigerator compressor, 1/4" copper tubing for the evaporator/heat exchanger along with a little warm water to aid in evaporation, small dia. copper capillary tubing was used in place of a thermal expansion valve, and 1/4" copper tubing was also used for the condenser. I have used 134a, R22, and propane as refrigerants with little or no difference between any of them in terms of temperature. This little system works damn good for what it is, (basically a solvent chiller) I just can't get it down to the -35C or so required for NH3 liquefaction. I was wondering if anyone knew of any good cryogenic/ultra-low temp refrigeration schematics, or design information floating around on the net. Swic has done a lot of searching, and has found several pages dealing with this subject, but they all stop short of giving detailed schematics for their "proprietary" systems. They all work on vapor pressure refrigeration principles, although some do utilize multiple compressors, and I think this may be the key to actually reaching super low temps. I do happen to be an electrical tech, and a refrigeration mech, so I should have no problems putting together any system I want, given the proper schematics, and design details. Also, I am licensed, and have special EPA certification (don't even ask) so I am able to get any refrigerant I may need, no questions asked, to to make this happen. "Well if that's the case, why don't you just go buy a tank of NH3?" you ask. I could do that, and I have done that in the past, for refrigeration purposes. Basically it's just something I want to do. And once I get it up and working to efficiently condense NH3, I'll do a write up, and include the details of the rest of my generator system, which will produce 100ml of liquid ammonia in about 10 minutes using dry ice. I personally think that performing a Birch reduction of pseudoephedrine is, on orders of magnitude, easier, and more OTC than all the tedious, meticulous cleaning and detail work required for success in any HI/I2 reduction.  (It is also much more dangerous and shouldn't be attempted by anyone who hasn't studied the procedure thoroughly) I've also been doing some reading lately on the electrolytic production of solvated electrons in NH3, which DOES NOT require any sort of special divided cell, so should be totally doable if I (or someone else) can come up with a suitable electrolyte that doesn't snatch up so many electrons.  Anyhow, if anyone has any comments or suggestions please don't hesitate to post them.


Just fuckin'do it already
07-05-03 20:54
No 444813
      CO2  Bookmark   

You might consider using CO2 for this, either alone or as second stage added to your setup now.
- easy to aquire
- nonpoisonous
- nonflammable
- a bigger bottle as backup ensures the cooling also if the cooling device should have a malefunction.

You will know how to setup this. The pressure should be no problem if standard parts are used which are readily available because of the wide use of CO2 - from gastronomy to welding to aquaristic - everywhere.

Honi soit qui mal y pense
(Hive Bee)
07-06-03 07:17
No 444881
      RE: Warm water  Bookmark   

Yes I know the warm water is ghetto, and shouldn't be there, but too much liquid refrigerant was making it back to the compressor, so I had to do something. A larger condensor is probably in order, along with an adjustable TXV valve instead of capillary tubing on the low side. Those two adjustments alone might be enough to drop it another ten degrees.

A two stage system using a different gas as a second refrigerant has been considered, althoguh I don't think it's necessary for this purpose. It would be cool to build though, and I might give it a shot later on.

An NH3 absorbtion type system has also been considered, and I definately plan on building one of these, for times when there are power failures etc. cause they don't require a compressor/electricity to run.


Just fuckin'do it already
07-06-03 16:21
No 445010
      IcyBall  Bookmark   

For the NH3 adsorber do a websearch on "IcyBall" - lots of interesting stuff including HowTo´s and the following patents:
Patent US1740737
Patent US1811523
Patents include construction drawings.


Honi soit qui mal y pense
(Hive Bee)
07-06-03 21:41
No 445102
      Yeah those are cool...  Bookmark   

I already have a couple of empty fire extinguisher bottles to use for the evaporator/generator. Now I just gotta get off my ass and build it. Or better, just quit trying to build so much shit at once. I have a least 5 different (chemistry/meth related)projects going at any given time, and my basement's beginning to look like something out of an old Frankenstein movie. Fuckin' drugs'll do that to ya though. Oh well, time to go boil something...

Just fuckin'do it already
07-21-03 22:32
No 448975
      cheap commercial source for -40C chiller  Bookmark   

High end pc enthusiast cpu coolers. kryotech used to make one called G2 (no longer - but used still available), another company (google for it) makes one that has vapochill in the name.

They have tiny little vapor cycle refrigeration units AND peltiers, AND control electronics AND monitoring software.

They run on 12vdc.

They're small and quiet.

SWIM saw some on ebay for cheap (search vapochill - or was it vapochili? *grin*)