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Clandestine-Chemist
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DIY Sub Zero C freezer?
Hello all! I have been poking around here a minute and decided to finally post my first question:
I will be handling some proteins soon. Not very large. 191 amino acid recombinant protein. And i was curious to know if there was a way to mod a
normal freezer/ chest freezer etc. to sub zero (preferably up to -20C) for storage of these proteins and eventually DNA storage.
Lab freezers really break the bank and there has to be some way to take advantage of the technology at hand.
Thanks much!
Formaldehyde is NOT seawater -_-
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Twospoons
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An ordinary deep freeze runs at -18C. Simply tweaking the thermostat might get you down to -20C.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Clandestine-Chemist
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Interesting, thanks!
Formaldehyde is NOT seawater -_-
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The_Davster
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My deep freeze goes below(perhaps 5-7degrees) the -20C minimum measurement point on my thermometer. You might get lucky with different
brands/different ages of freezers.
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MagicJigPipe
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I concur. My freezer goes down to -26F (-32C). That's so close to being able to condense ammonia I too have wondered if I could make it go just a
bit lower.
That makes me think. I know in the northern US, Canada and Alaska the temperature sometimes falls below this. It would be interesting to condense
ammonia outside without artificial cooling.
I could store methylamines in my freezer! Which also makes me wonder, has anyone here successfully condensed and stored anhydrous NO2/N2O4? That
would be interesting. Is it a red liquid?
[Edited on 19-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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bio2
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Install the proper range after market thermostat. These are available at commercial refrigeration suppliers in several ranges and configurations.
You should be able to go 10-15 degrees below the "standard" minimum temp without
damaging the compressor but the capacity will reduce somewhat.
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CyrusGrey
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You could put a chunk or two of dry ice in an ordinary freezer to get it even lower. This would be temporary of course, but dry ice is cheap.
If you want something more long term you might take apart a couple freezers and connect the cooling units together in some way. You could try in
paralell (By having multiple cooling units go directly inside the freezer) or in series (By having one cooling unit's heat sink connected to the next
one's cold sink) or some combonation of the two.
EDIT: posted at the same time as Bio2. I think his suggestion is better.
[Edited on 20-3-2008 by CyrusGrey]
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not_important
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| Quote: | Originally posted by CyrusGrey...
If you want something more long term you might take apart a couple freezers and connect the cooling units together in some way. You could try in
paralell (By having multiple cooling units go directly inside the freezer) or in series (By having one cooling unit's heat sink connected to the next
one's cold sink) or some combonation of the two.
...
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Parallel would just increase the amount of heat that can be transfered. You cool the enclosure and contents down faster, but it limits at the same
temperature. Only if the enclosure is not well insulated, leaking enough heat that a single cooling unit, of the type available, can't keep up with
the inflow. A single larger unit accomplishes the same thing.
Series might help, but only if the cooling unit works at the lower temperature. The cooling effect comes from the evaporation of the refrigerant,
most common ones boil at -15 to -30 C under the operating conditions.
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Clandestine-Chemist
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Excellent, so in reality i can just get a small-ish chest freezer and attach the aftermarket thermostat? I guess that would set me back less than 2
bills USD not bad. I can still put food in it :-p.
Formaldehyde is NOT seawater -_-
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7he3ngineer
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| Quote: |
I can still put food in it :-p.
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I wouldn't. I'd fork out the 4 bills USD, and keep my food seperate... What are the ultimate rules of lab safety!
Josh
Engineers aren\'t boring people, we\'re just interested in boring things!
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-jeffB
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| Quote: | Originally posted by CyrusGrey
If you want something more long term you might take apart a couple freezers and connect the cooling units together in some way. You could try in
paralell (By having multiple cooling units go directly inside the freezer) or in series (By having one cooling unit's heat sink connected to the next
one's cold sink) or some combonation of the two.
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Unlikely to work. Most freezers specify both upper and lower limits on ambient temperature. It seems like chilling the hot loop would improve
efficiency and performance, but it doesn't work in practice -- if the working fluid is too cold coming into the compressor, it can't function
properly. I'm not sure whether it's just a problem with the coolant behavior, or the lubricant, or something else.
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-jeffB
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| Quote: | Originally posted by MagicJigPipe
has anyone here successfully condensed and stored anhydrous NO2/N2O4? That would be interesting. Is it a red liquid?
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It's NO2 that's red. At colder temperatures, the equilibrium shifts toward N2O4, which is colorless. As a liquid, it's nearly pure N2O4. I'd expect
it to be nearly colorless. I've always wanted to try this experiment, too, but it's probably just as well for my health that I haven't. 
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Mr. Wizard
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The temperature of the cool side of a freezer is limited by the boiling point of the refrigerant and the lowest pressure that can be maintained on the
'low' or cooling side of the freezer. A refrigerant boiling in a vacuum will be colder than one boiling at say 30 psi. Most systems do not run a
complete vacuum on the low side, as it isn't efficient to have a pump trying to 'scavenge' a vacuum on one side and maintain a condensing head
pressure on the other. On older Freon 12 cars for example, the 'low' side could be anywhere from 30 to 50 psi which resulted in a temperature of
30-50 degrees F. It happens that the temperature number is about the same as the pressure in these systems, so I can make these generalizations. I
know they aren't exact. The point is, at the lower pressures, when the system is low on freon, it gets very cold, but the system doesn't work very
well in total amount of heat transferred. You might be able to tweak a freezer to give a slightly lower temperature, at the expense of it running all
the time trying to move BTUs out of the freezer with much less refrigerant. It may not even stay cold in the summer time, but would be very cold in
the winter. The hardware may not allow the lower temperature, as temperature controlled expansion valves will simply shut off when they get too cold,
while the older, and cheaper simple orifices will operate like this. In summary, if you knew this much or more about refrigeration you would be
remarking how I got it all wrong, and if you don't then this isn't enough information to make any modifications 
Another path to sub zero would be to use a Peltier cooling device such as a portable car cooler , and set it to run inside the freezer. The freezer
will have to be able to dump the waste heat from the other cooler. I don't know if these units have a set thermostat or if they just run
continuously. Obviously the thermostat would have to be disabled, or modified. Lubrication of the fan motor will also have to be considered. I
believe some Peltier junctions cease to operate at very low temperatures (-100C ?) A normal freezer may not be able to dump all the extra heat , so
don't do this with a freezer full of food and come back in two days wondering where all that water came from.
[Edited on by Mr. Wizard]
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ScienceGeek
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| Quote: | Originally posted by -jeffB
| Quote: | Originally posted by MagicJigPipe
has anyone here successfully condensed and stored anhydrous NO2/N2O4? That would be interesting. Is it a red liquid?
|
It's NO2 that's red. At colder temperatures, the equilibrium shifts toward N2O4, which is colorless. As a liquid, it's nearly pure N2O4. I'd expect
it to be nearly colorless. I've always wanted to try this experiment, too, but it's probably just as well for my health that I haven't. |
I flash- froze a large amount of NO2 using liquid Nitrogen. I obtained a dark- blue liquid, due to the prescence of Dinitrogen Trioxide
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-jeffB
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| Quote: | Originally posted by ScienceGeek
I flash- froze a large amount of NO2 using liquid Nitrogen. I obtained a dark- blue liquid, due to the prescence of Dinitrogen Trioxide
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Ah, that's another one I always wanted to try for! Do you suppose you got it because your NO2 was heavily contaminated with NO, or perhaps was
partially reduced to NO by other contaminants?
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-jeffB
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| Quote: | Originally posted by Mr. Wizard
Another path to sub zero would be to use a Peltier cooling device such as a portable car cooler , and set it to run inside the freezer. The freezer
will have to be able to dump the waste heat from the other cooler. I don't know if these units have a set thermostat or if they just run
continuously. Obviously the thermostat would have to be disabled, or modified. Lubrication of the fan motor will also have to be considered. I
believe some Peltier junctions cease to operate at very low temperatures (-100C ?) |
I think most Peltier stacks also have a minimum cold-junction temperature, and like other coolers, the colder the cold side, the less heat they can
move. I've seen listings for specialized multi-stage Peltier devices that go as low as -100C, but most won't go that low. I would expect an ordinary
device to fail at those extremes -- it might simply not work because of the electronic properties of the active semiconductor, or it might be
physically destroyed by thermal/mechanical stress and increased brittleness. On the other hand, such devices are cheap enough now that it might be
worth experimenting.
Instead of trying to keep the fan running at low temps, I'd find a way to more directly couple the device's hot side to the freezer's cold side. If
you felt very daring, you could try to set up an ethanol- or acetone-based liquid-cooling loop.
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tumadre
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From what little I know about the subject, I'm thinking the efficiency will decrease as the temperature goes down, because the thermal conductivity
will increase by a factor of ~2 or so from 300K to 200K.
Same for most semiconductors, although I don't know which ones specifically. link here
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MagicJigPipe
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I wonder how much those dry ice freezers are that they have at grocery stores to keep the dry ice in? It would be GREAT if I could find one that was
getting rid of one. I think the dry ice company (Penguin here) rents out the freezer the same way a vending machine or arcade game company rents out
their equipment. So maybe I could (or anyone could) call the dry ice company to see if they have any damaged or surplus freezers they want to sell.
(for anyone from southern Louisiana, just replace "freezer" with "icebox" )
[Edited on 20-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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not_important
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I'm not sure how important changes in thermal conductivity, but the greater the temperature differential in a Peltier device the less heat it can move
and the less efficient it is. This is compensated for by stacking devices in thermal-series, reducing the temperature difference across a given
device. But the devices are not all that efficient to start with, so each warmer layer must pump increasingly greater amounts of heat.
If you're really into TEC, look here
http://www.ferrotec.com/products/thermal/modules/
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Mr. Wizard
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This one will drop 125 *C, but I don't know what the lower limit is. If you assume ambient is 20*C it will get down to below -100*C. Maybe its just
wishful thinking or reading too much into the specs written on the Melcor box.
46 volts Dc Max 9 amps max 30*C/layer
125*C T Wafer Cut
I got this at a techno swap meet a few years ago, before eBay killed that sort of thing.
I'm guessing, but I think it was military avionics
http://www.melcor.com/mstage.html
[Edited on by Mr. Wizard]
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undead_alchemist
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What you want is a R502 system, as this is a low temp refrigerant.
Or if you get an old system, you could try to refit it with propane, it
This company sells retrofit kits.
http://www.foxtoolsupply.com/HC-502a.htm
http://www.duracool.com/Duracool/refrigerants.html
http://www.duracool.com/ecom/shoppingcart.html
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-jeffB
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| Quote: | Originally posted by MagicJigPipe
I wonder how much those dry ice freezers are that they have at grocery stores to keep the dry ice in? |
Freezers? In our local store at least, it's just a very heavily insulated box. Same way with the dry-ice bin upstairs in my work building. The
electricity and upkeep on a -77C freezer would probably cost more than the dry ice lost to evaporation in a well-insulated box.
I think these are the folks who provided the box in our local store:
http://www.airgas.com/content/products.aspx?id=9002008002015
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MagicJigPipe
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You're probably right as I haven't paid much attention to these "boxes". Yeah, I just looked at the picture, that's it. I just never thought about
the fact that letting it sublime slowly would be cheaper than keeping it below -109 degrees.
My mistake.
[Edited on 21-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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bio2
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Problem with Peltiers, other than those already mentioned, is the capacity for the size and current draw is really piss-poor.
Take a look at the capacity specs, if you can find them, as
it seems the makers don't want you to know, lol.
A mechanical refrigeration device has magnitudes more
output for the size and power consumption.
Peltiers have many specialized uses and chest freezers
isn't one of them.
Ever use one of the "ice chest" type Peltier 12 volt coolers?
If so that will tell you a lot. These pathetic little devices
are power hogs, take forever too cool down and if you don't
open the lid for a few days it might finally get down to 5 degrees.
I ran one of these for over a year non-stop at 140% output
so I know a little about them.
Still they have their purpose. Just don't expect to put a case of warm beer in one and expect to have a nice cold beer for a couple days.
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Cloner
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Peltiers can be used in cascade, creating a much lower temperature than normal freezers. Their use is limited to test tube sized samples and I agree
wholeheartedly with the poster above. I made a freezer that could come at -80 degrees from ambient with only the thermocouple in it. Unfortunately,
insulating did not really help beyond a certain degree, as the electrical wire was the main leakage route. I never managed to find a fix for this
problem.
However, since peltiers generate a temperature gradient, putting a battery powered peltier of limited gradient inside a normal freezer should get you
from -20 to -40 with a much better capacity than my experiment.
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