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-jeffB
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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?
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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.  |
Not to threadjack, but I've come across a ref that says I was wrong here. I'm looking at Vol I of Sidgwick's The Chemical Elements and their
Compounds, p. 688, where it says:
| Quote: | | The gas is reddish-brown; the liquid boils at 21.1° and is then brown; it becomes paler on cooling, and freezes at -11.2° to a
colourless solid [...] It is evident that N<sub>2</sub>O<sub>4</sub> is colourless and NO<sub>2</sub> brown, and
that the solid is pure N<sub>2</sub>O<sub>4</sub> which is partly dissociated in the liquid, and more as the temperature
rises. |
So there, I guess...
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amrhamed2
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U can consult a HVAC engineer to make a cooling system for u that mimic the commercial immersion coolers ,circulators and chillers with overkill price
Use an appropriate refrigerant of suitable boiling point
Class 1 refrigerant.
By this, I mean they were manufactured for the purpose of being used as a refrigerant and will require a certification to acquire. These require no
additives to compress properly, have a long life span and are for the most part non combustible, BUT they do release chemicals which are dangerous to
the ozone layer.
Here is a list in order of common use.
1. R12 (dichlorodifluoromethane) was the standard in refrigeration for a long time. With a boiling point of slightly under -21C, it was used widely
in automobiles, refrigerators, window air conditioners - just about everything.
2. R22 (chlorodifluoromethane) is the refrigerant that has held the standard for home air conditioning longer than any other and is still in use.
Its boiling point is just under -40C.
These refrigerants have been in use for years and have been proven time and again reliable and efficient; their only down side is they deplete the
ozone layer and thus require special certification. As a result, they are typically only available in 30lb or larger canisters. These refrigerants
come pre-bottled with mineral oil, so your compressor will need to be adjusted accordingly.
Class 2 refrigerants are refrigerants that are commonplace and easy to acquire. These do not require special certification nor do they damage the
ozone layer.
1. R134A(,1,1,2-tetrafluoroethane) has a boiling point of only -26C; it is becoming the new standard in refrigerators, automobiles, and all other
common uses.
2. R290 (propane) is also beginning to make its way in as a mainstream refrigerant. With a boiling point of -42C, it is more of a class 4
refrigerant, but because of its new found common use I have included it in my class 2 list. This is randomly used in things such as freezers - a lot
of hobbyists use it for home built systems.
These refrigerants are quite affordable; also to be noted is that they come bottled alone or with ester oil, require no certification and do not
damage the atmosphere. As a result of these factors, they are readily available to the public.
Class 3 refrigerants are those which have a lower boiling point than standard refrigerants. Often they are hybrid mixtures of class 1, 2 and 4
refrigerants.
1. R404B (pentafluoroethane/1,1,1-trifluoroethane/1,1,2-tetrafluoroethane: 44:52:4%) This is one refrigerant often sought after by overclockers.
With a boiling point of approximately -44C and available in 12oz cans, this can be a nice choice provided you have your certification.
2. R409A (chlorodifluoromethane/2-chloro-1,1,1,2-tetrafluoroethane/1-chloro-1,1-difluoroethane: 60:25:10%) This refrigerant has a boiling
temperature of -47.8C; you have to purchase 30lb cans.
3. R508B (trifluoromethane/hexafluoroethane: 46:54%) This is one of the best readily available high end refrigerants there is. With a boiling point
near -50C, you are lucky to acquire this.
4. R-14 (1,2-dichloro-1,1,2,2-tetrafluoroethane) Ranking in with a boiling temperature approaching that of -150C at 1 bar pressure, this
refrigerant can deep freeze you faster than you can say lickity split. Provided you are running either a cascade cooler or are have a compressor that
can withstand approximately 350psi, it's a pleasure to work with.
These refrigerants have a moderate - substantially lower boiling point than normal refrigerants. Some can be acquired in small amounts, others have to
be purchased in 30lb cylinders.
The biggest issues with refrigerants like R14 is that with its so low boiling point, it requires a lot of pressure to compress to liquid. With this in
mind, it may be better to juice up a system that is running on a lower grade refrigerant by adding 10-25% more.
Class 4 refrigerants are natural gases. These can be acquired from just about any chemical supply place - some can be located in your own home. These
generally have an extremely low boiling point and are difficult to compress due to their weight, but can easily be used as an additive to an existing
system to squeeze it for a few extra degrees. These, as you may have guessed, do not come packed with any kind of oil additive and therefor can be
used in any system.
1. R50 (methane) This a moderately light gas with a boiling point of -162C; it's the base compound for most of today's refrigerants. In its pure
form, it is a bit too light (molecular weight 16) to work with outside of a cascade cooler. Though this can be used in a system of its own, you will
need pressures nearing the 450 mark on a warm day to liquify. Overall a great additive or for use in a cascade cooler.
2. R170 (ethane) This gas has a boiling point of -88C and a molecular weight of 30. It's a much more suitable stand-alone refrigerant than R50.
There are a few commonplace refrigerants that are based on this gas.
3. R744A (nitrous oxide) This is a pretty commonplace gas these days; with a molecular weight of 45 and boiling point of -89C, this definitely
yields some potential, not only as a stand-alone refrigerant but also as a cascade refrigerant.
4. R717 (ammonia) This is used in many commercial refrigeration systems. Although it has a rather low molecular weight (just under 18), its boiling
point of -33C makes it rather easy to work with. The most widely occurring problem with this gas is its smell and, as it is slightly corrosive, extra
precautions must be taken.
5. R740 (argon) Coming in with a weight of approximately 40 and a boiling point of -182C, it is easily compressed and, used in conjunction with 25%
R134, has a weight which is easily used in a standard air condensed system to maintain a boiling temperature below that of -120C with less than 300
psi. This has a lot of common potential.
6. R764 (sulfur dioxide) This gas has the scores - all around molecular weight of 60 and boiling temperature of -76C, although it has toxicity
issues. Given a bit of precaution not to let a lot of this loose into the air, it will easily yield quite impressive results.
These gasses have quite low boiling points, which would make them all great candidates for a cascade cooler. For those of you who don't know, a
cascade cooler is simply a Phase change system that uses another Phase cooler to cool its condenser, so you can use a very low temperature refrigerant
at a decent psi rating.
[Edited on 27-5-2008 by amrhamed2]
[Edited on 27-5-2008 by amrhamed2]
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amrhamed2
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I saw once a diy system with AC (air-conditioner ) components using the widely available R22 refrigerant and reach -40 degree Celsius
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MagicJigPipe
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Where? Find it for us, please!
"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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Mr. Wizard
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Propane boils in that temperature range, at atmospheric pressure. I don't know what the boiling point is in a good vacuum. Propane has been used in
regular automotive air conditioner systems as a 'substitute' for R12. I don't recommend this but it does work. You will have to keep the pressure on
the low side down to get the low temperature.
(<= 1 bar) Normal automotive AC units try to keep the evaporator cool enough to cool the air, but not cold enough to freeze any condensed water on
the evaporator. This will cause a frozen zone that restricts air flow, leading to a solid block of ice on the evaporator. Automotive refrigeration
units are actually quite big and can handle a lot of BTUs ; 3 to 4 tons of ice per 24 hour equivalent, that is a 3 or 4 ton unit.
This chart :
http://www.glacierbay.com/ptchartpropane.asp
says it is possible to get -92F at 22 inches Hg vacuum. As the pressure drops you will need either less propane going through the evaporator or a
bigger pump to scavenge the vapor and keep the pressure low.
I saw a 5 gallon plastic bucket full of boiling propane once. They had drained a big propane tank into the bucket and it had self refrigerated. It
looked just like water, except for the frozen chunks of ice (spit) rolling around in the boiling liquid.
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tumadre
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MJP are you familiar with http://www.refrigeration-engineer.com/forums?
here is a link to a -130 C three stage CPU cooler, but his first stage uses propane @ -50 to -60C
The page is rather long, and in the middle of it he changes the compressors, but if you scroll past the photos, about 2/3rd down the page is the info,
on post#32.
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MagicJigPipe
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This actually disturbs me how he is using a machine that can CONDENSE XENON and FREEZE Et2O and CS2 yet he is using it to squeeze some speed out of a
computer CPU. Arrggggg!!
To each his own but it still frustrates me.
Some day I shall accomplish this. I think it would be the coolest thing in the world to freeze CO2 and condense HX, ethane (this would be a good way
to obtain pure CH4, by condensing natural gas at about -100C) ammonia, propane and chlorine at home without dry ice.
"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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tumadre
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No small potatoes either. that is about 100 Watts at -130C 
Not including the interstage losses and heat picked up by the overheating compressors.
I'm particularly interested in the first stage, I'm partial to liquid chlorine.
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MagicJigPipe
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100 watts? Is that all? I would be happy if it used as much energy as a microwave. Surely it used much more energy than 100 watts. Did you mean
1000?
I mean, if it were 100 watts, I could easily power it with an excersise bike generator.
[Edited on 5-29-2008 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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tumadre
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misunderstanding... 100 watts at -130C translates into a few kilowatts at 30C
edit: i have no idea. but those are not small compressors shown in the photos.
[Edited on 29-5-2008 by tumadre]
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MagicJigPipe
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Okay, I get it now. If it indeed uses a few kilowatts then I have no idea how anyone but a very rich person could afford to run something like that
simply to overclock their computer. I mean, maybe I could run it for a few hours at a time to do some reactions but to run my computer? Bump that!
That would be like running two large A/C units for most of the day everyday. My electric bill is already $120 a month (and that is on months where I
don't do much experimenting).
"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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Mr. Wizard
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I don't know what your rate is but even at 20 cents a kilo watt hour you could run the compressor for 5 hours for a dollar. Skip a meal ;-)
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tumadre
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Wow, definitely didn't know it was that expensive where you guys live.
Right now we pay 7.5 pu for the first ~700? KWh, then 9 pu after. Granted this is in the pacific northwest, thanks to the Columbia river, and dams
that were payed off during WWII.
I would have made my parents buy solar if it were 20, seriously, its 7.5 and i'm trying to convince them wind turbines are cheaper.
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MagicJigPipe
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It's 10.5 cents per kwh here before taxes. My house is only about 1800 square feet but it still costs over $100 (A/C mostly) a month during the
summer time.
I believe the average summer temperature around here is a little less than 90 degrees.
Some info about the climate here:
| Quote: |
Normal Temperatures
(LITTLE ROCK ADAMS AP Weather station, 3.38 miles from Little Rock)
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Max °F 49.5-55.6-64.2-72.9-81.0-89.0-92.8-92.1-85.1-75.1-62.0-52.5-72.7
Mean °F 40.1-45.2-53.4-61.4-70.1-78.4-82.4-81.3-74.4-63.3-51.7-43.2-62.1
Min °F 30.8-34.8-42.6-50.0-59.2-67.8-72.0-70.5-63.6-51.5-41.5-33.9-51.5
Little Rock, AR climate is hot during summer when temperatures tend to be in the 80's and cold during winter when temperatures tend to be in the 40's.
The warmest month of the year is July with an average maximum temperature of 92.80 degrees Fahrenheit, while the coldest month of the year is January
with an average minimum temperature of 30.80 degrees Fahrenheit.
Temperature variations between night and day tend to be moderate during summer with a difference that can reach 21 degrees Fahrenheit, and moderate
during winter with an average difference of 20 degrees Fahrenheit.
The annual average precipitation at Little Rock is 50.93 Inches. Rainfall in is fairly evenly distributed throughout the year. The wettest month of
the year is November with an average rainfall of 5.73 Inches.
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As you can see the average highs for July, August and September are 92.8, 92.1 and 85.1 respectively. I'm sure that doesn't help with my heat removal
costs.
[Edited on 5-30-2008 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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| Quote: | Originally posted by tumadre
...
I would have made my parents buy solar if it were 20, seriously, its 7.5 and i'm trying to convince them wind turbines are cheaper.
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Wind is cheaper, if you go large enough. Within a few meters of the ground the average velocity drops sharply while the direction becomes much more
variable. It's the huge turbines on those tall towers that have costs approaching that of more conventional electric generation; some of the smaller
rigs have a lifespan EROEI of less than unity.
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bio2
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That is true in the short term however, having installed wind turbines from a few KW to over a MW, the makers have settled on smaller units up to a
few hundred kilowatts.
The reason is the maintenance factor. If a 200 foot crane is needed versus a large boom truck the entire scenario becomes unworkable.
Been there, done that.
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cbfull
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This topic really jumped out at me, because I have been trying to tackle a very similar problem with an outdated lab chiller.
I have an old Lauda RMT6 chiller that I got from ebay. It seemed to run just fine and could heat, but no cooling despite the compressor cranking away
(I didn't really expect it to work).
I worked my butt off trying to get it back to working order but it just wasn't going to happen. I paid a skilled HVAC professional to find and repair
any leaks, and he did find a good sized one buried in the tough insulating foam where the coolant heads into the bath. The compressor is just too old
to handle the work, and it has been out of production so long I gave up on trying to find a replacement.
Also the original refrigerant it was designed to use is R12, which is illegal and no one should be using it anyway. Probably the biggest factor
making my efforts seem bleak, is the type of restriction these things use... capillary tube. Home fridge/freezers are made in much the same way as
lab chillers in that they are capillary tube systems. The compressor basically pushes the vapor into a chamber that has a very small outlet (the
capillary), creating a high pressure and thus a high temperature (yikes! thermodynamics!), likewise the compressor is drawing vapor out of the low
side creating a vacuum. This is how the temperature difference is created.
Capillary tube systems are very, very touchy about everything being just right. The amount of refrigerant is very specific, and it is based on
compressor displacement, and the capillary tube length and diameter has to be determined based on these and other factors.
To try and keep this short, if you want to squeeze more cooling out of a unit, you need to push more gas into the high side, making it hotter so you
can dump more heat, and at the same time the pressure would ideally be lowered in the low side causing the temperature to drop. Unfortunately it is
not that simple with a "cap tube" system. The refrigerant behaves in a sort of counter-intuitive way when it exits that long narrow tube. The force
of the liquid boiling INSIDE the tube causes it to shoot out as a vapor at high velocity. The more suction, the further back the tube this can go.
This high-velocity vapor shooting out causes a sort of "kickback" in the tube, causing the liquid flow to actually slow down.
I think what I might have to do with my chiller is just start over from scratch. I'm going to get a compressor with a slightly higher
displacement (for more pressure), get a new capillary (the size being determined by software!), a new drier is a must (moisture is the last thing you
want inside these), and make sure the inside is free of ANY debris that could clog the capillary and shut it down. For refrigerant I will likely use
R502 or maybe even propane. I probably wouldn't even consider trying propane if it weren't for the HVAC guy fixing the leaks. I'm hoping he'll still
be willing to help me when it's time to actually install the new parts (I'm paying him so he should be okay).
Sorry for the long ramble, I got a little overexcited reading over these posts seeing you guys learning the same things I am now.
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tumadre
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If only someone sold a small turbo expander.....
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cobrasniper555
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| Quote: | Originally posted by MagicJigPipe
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] |
Couldn't you use dry ice and a solvent such as Acetone with available reach of -80 degrees C? (Frogfot's Ice-Bath page)
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cbfull
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That is a very common way to make a sub zero bath, we do it all the time at work to trap moisture and organic vapors from contaminating the vacuum
pump oil, and often to trap them for analysis. It should make a bath the same temp as the sublimation temp as dry ice at atmospheric pressure.
I had another idea as far as the sub-zero chiller and my earlier statement. The coldest part of the circuit is where the liquid vaporizes, and if it
is vaporizing in the cap tube then the cap tube will be where it is coldest. That's why this condition is bad. However, if the cap tubing were very
well insulated, that might help stop the flashing in the tube and allow the cold liquid to make it all the way to the evaporation chamber. It's
feasible that you could get away with a slightly larger compressor and a lower T on the cold side. Maybe not, it's just a thought.
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pyro6314
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If you guys are still looking for a really big compressor that seems to be indestructable as well, look for RV A/C units. I worked for a place that
sold/repaired RVs and this spring we got a nasty hail storm. There was literally piles of A/C units that we replaced through insurance claims because
the condensors were flattened and I had my pick of any of them. I have one ghetto rigged as a temporary vacuum pump and it pulls down to ~30"Hg very
quickly. The label says the pressure side can get to 300psi but it keeps climbing past that with the vacuum side at ambient pressure. I relieved it
because I didnt want to damage it. I'm not sure what refridgerant was used so I dont know what is compatable with the lubricant.
Just a thought...
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nhanlhyn07
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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? 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] |
Why is that you think that the dry ice company rents out the freezer the same way a vending machine or arcade game company rents out their equipment?
Can you please share with us some of your idea? Thank you!
________________________
Vending Machines
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Michael zhang
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it is ordinary deep freeze runs at -25C. the thermostat might get you down to -20-25C. I suggest you can go to the URL, maybe can help you:
http://www.pengnantech.com/consumer-products.html
Attachment: AA-024-12 REV 03.pdf (629kB)
This file has been downloaded 517 times
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Dope Amine
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For what it's worth, I got a chest freezer from Home Depot (under $200, I believe) and I was able to get it to go down to about -31 C from the
previous lowest temperature of -20 C. All it took was pulling out the thermostat, removing the sticker that covered the thermostat adjustment screw,
turning it in the direction that caused it to kick on, letting it run until the temperature would go no lower (easiest to check with an infrared
thermometer), and then turning the screw just to the point where the compressor turned off.
The lower temperature improved my separations of botanical extracts (aka "winterization").
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