Sciencemadness Discussion Board - DIY Sub Zero C freezer?

DIY Sub Zero C freezer?

Clandestine-Chemist - 19-3-2008 at 14:33

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!

Twospoons - 19-3-2008 at 16:48

An ordinary deep freeze runs at -18C. Simply tweaking the thermostat might get you down to -20C.

Clandestine-Chemist - 19-3-2008 at 17:50

Interesting, thanks!

The_Davster - 19-3-2008 at 18:52

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.

MagicJigPipe - 19-3-2008 at 20:34

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]

bio2 - 19-3-2008 at 20:42

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.

CyrusGrey - 19-3-2008 at 20:42

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]

not_important - 19-3-2008 at 23:04

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.
...

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.

Clandestine-Chemist - 19-3-2008 at 23:50

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.

7he3ngineer - 20-3-2008 at 00:52

Quote:

I can still put food in it :-p.

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

-jeffB - 20-3-2008 at 06:08

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.

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.

-jeffB - 20-3-2008 at 06:20

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.

Mr. Wizard - 20-3-2008 at 07:37

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]

ScienceGeek - 20-3-2008 at 09:07

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?

I flash- froze a large amount of NO2 using liquid Nitrogen. I obtained a dark- blue liquid, due to the prescence of Dinitrogen Trioxide

-jeffB - 20-3-2008 at 10:37

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

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?

-jeffB - 20-3-2008 at 10:47

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.

tumadre - 20-3-2008 at 14:08

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

MagicJigPipe - 20-3-2008 at 17:31

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]

not_important - 20-3-2008 at 19:06

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/

Mr. Wizard - 20-3-2008 at 19:45

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]

Peltier Stack.jpg - 56kB

undead_alchemist - 20-3-2008 at 20:00

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

-jeffB - 21-3-2008 at 07:22

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

MagicJigPipe - 21-3-2008 at 17:58

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]

bio2 - 22-3-2008 at 12:39

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.

Cloner - 29-3-2008 at 02:34

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.

-jeffB - 30-3-2008 at 19:07

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?

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 N2O4 is colourless and NO2 brown, and that the solid is pure N2O4 which is partly dissociated in the liquid, and more as the temperature rises.

So there, I guess...

amrhamed2 - 27-5-2008 at 12:27

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]

amrhamed2 - 27-5-2008 at 12:33

I saw once a diy system with AC (air-conditioner ) components using the widely available R22 refrigerant and reach -40 degree Celsius

MagicJigPipe - 27-5-2008 at 13:32

Where? Find it for us, please!

Mr. Wizard - 27-5-2008 at 17:33

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.

tumadre - 29-5-2008 at 13:22

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.

MagicJigPipe - 29-5-2008 at 17:45

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.

tumadre - 29-5-2008 at 18:23

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.

MagicJigPipe - 29-5-2008 at 18:38

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]

tumadre - 29-5-2008 at 19:02

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]

MagicJigPipe - 29-5-2008 at 19:16

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).

Mr. Wizard - 29-5-2008 at 20:48

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 ;-)

tumadre - 30-5-2008 at 13:44

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.

MagicJigPipe - 30-5-2008 at 17:16

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.

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]

not_important - 30-5-2008 at 17:21

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.

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.

bio2 - 30-5-2008 at 20:31

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.

cbfull - 16-6-2008 at 17:59

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.

tumadre - 16-6-2008 at 19:43

If only someone sold a small turbo expander.....

cobrasniper555 - 17-6-2008 at 21:26

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)

cbfull - 23-6-2008 at 15:48

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.

pyro6314 - 19-10-2008 at 13:20

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...

nhanlhyn07 - 22-11-2009 at 00:43

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

Michael zhang - 18-11-2016 at 22:33

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

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Dope Amine - 22-11-2016 at 12:39

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").