Freezing at Low Temps

[mongo blongo]

I am thinking of building a machine that can freeze anhydrous nitric acid out of a mixture of Dichloromethane and HNO3 at around -50 degC. I am thinking of this because I have no other way of achieving such low temps (can't get dry ice). It would also be more convenient to use.
It would be great if anyone knows of any methods that could achieve this.

At the moment I am thinking that a normal household freezer is a good place to start.
Maybe some condensers,coiled up, from a few freezers could be used together cooling a small volume container?
What about taking out the thermostat? Does anyone know what kind of temps a freezer could drop to without the thermostat interrupting it?

I have also seen a machine in a wine shop. I don't know what it's called but it looks expensive. It is used to chill bottles of wine in about 30 seconds (it must get very cold for that). It has two holes for the bottles to fit and in the holes are these cooler jackets which I presume are filled with Ethylene Glycol. They are cooled by the machine in probably the same way a freezer does.
I probably can't afford something like this but I just thought it was worth mentioning.
Another machine called a microtome also has some kind of powerful cooling system. I used to use one in a quality control laboratory for a plastics company that I worked for. It was used to freeze and slice very thin samples of plastic sheet. It could drop to -40 degC with the top open. But again that thing would cost a fortune.

So does anyone have any ideas about achieving such low temps without resorting to dry ice and other hard to find chems?
Thanks :)

[Al Nobel]

The only way I know to reach such low temperatures is to get access to liquid N2 (which sould be nearly impossible).I dont think that there exists a way to reach such low temperatures without spending lots of money.

[A43tg37]

There are a few ways of achieving temperatures that low without dry ice or liquid nitrogen, they have been pretty extensively discussed on the Hive, mostly for use in things like liquefying ammonia:

Refrigerators/freezers

Hive post 378139 (just this one post). About modifying refrigeration apparatus (and a couple of other things) for use as very low temp lab coolers. It has many good references, including one from The Scientific American Amateur Scientist column (another good reason that the Amateur Scientist CD should be group-purchased for the FTP, in my opinion).

Peltier Coolers

Hive posts 296588 (and the entire thread it's part of, which also includes useful US patents and a simple chemical reaction that can supposedly get down to -55C) and 180583 (again, including the entire thread it's part of). Although Peltier coolers aren't exactly cheap, if the claims in this thread are true, they are capable of some very low temperatures.

Also, if you can't get dry ice, why not just make some? Edmund Scientifc ( <a href="http://www.scientificsonline.com/ec/Products/Display.cfm?CategoryID=317291" target="_blank">http://www.scientificsonline.com/ec/Products/Display.cfm?CategoryID=317291</a> ) and Polyfoam ( <a href="http://www.polyfoam.com/dry_ice_makers.html" target="_blank">http://www.polyfoam.com/dry_ice_makers.html</a> ) both sell dry ice makers that only require a tank of carbon dioxide to hook up to. Although both models cost slightly above a hundred dollars (US dollars), they would be well worth it in the long run for one who couldn't get dry ice.

<small>[ January 25, 2003, 08:20 PM: Message edited by: A43tg37 ]</small>

[mongo blongo]

A43tg37- Thanks dude! I was not aware of dry ice makers. That seems to be the easiest option. I will look into it.

[VX]

A dry ice maker is a waste of money! To make dry ice, just get a cylinder of CO2, open the valve with a cloth or something over it to collect the solid dry ice.... That’s it. The only advantage I can think of is that the machine may improve efficiency, but for $100 surely it's not worth it?

The modified freezer could be a good way to go, especially if modified to either change the setting of the thermostat to a lower temp, or if temperature is not crucial completely remove it and cause it to run constantly.

[nbk2000]

Cracking open a CO2 cylinder doesn't work for making Dry Ice. The valve orfice quickly freezes up and stops the flow. :( The dry ice maker has something in the valve that keeps it from clogging, allowing the dry ice to form.

[mongo blongo]

Well I am thinking of getting my own valve and making some contraption which will do the same thing because it's too expensive for me.
US Patent <a href="http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=5,528,907.WKU.&OS=PN/5,528,907&RS=PN/5,528,907" target="_blank">5,528,907 </a> describes how the machine works. I haven't read the whole thing yet but it may yield some clues on how the valve stops itself from clogging up. For some reason the images don't work for me. <img border="0" title="" alt="[Frown]" src="frown.gif" />

[a_bab]

As a matter of fact you only need to adapt a 30 cm tube at the CO2 tank, and you need a cloth sack as well. The tube should be about 3 cm wide. Try it, it works; the dry ice is formed on the tube walls and it'll fall in the sack. The valve won't get clogged because of the presure. And the valve should be wide opened !

<small>[ February 04, 2003, 12:51 PM: Message edited by: a_bab ]</small>

[PEROMAN]

A mix of calcium chloride(it wasnot written , hydrous or unhydrous, but i think CaCl2*6H2O) with ice gives -55C

[Al Koholic]

CaCl2 giving -55C by mixing with ice?? I don't think so...

Maybe you are thinking of its effect on freezing point depression. Even then it still won't prevent freezing of water down to -55C. Ethylene Glycol is the way to go here. Even still, you would have to mix the ethylene glycol with ice that is already at -55 or below...

Actually, now that I think about it, CaCl2 dissolving in water produces heat.

Al

<small>[ February 05, 2003, 01:36 AM: Message edited by: Al Koholic ]</small>

[PEROMAN]

It's written in a book ! It's not my emagination!
Unhydrous CaCl2 dissolves it water with heating , but here is CaCl2*6H2O .

[J]

Which book?

[PEROMAN]

J , it must be written in every normal chemical book
I read it in chemical encyclopedia (russian) (you dont know it)
There is written :mix of 1.5 weight parts of CaCl2*6H2O + 1 weight part of snow or crushed ice can decrease t to -55C

Also you can find it with any e-net searching system(www.yahoo.com ...) - just write " cooling mixtures"
for example go here <a href="http://home.t-online.de/home/KS-Info/cool.htm" target="_blank">http://home.t-online.de/home/KS-Info/cool.htm</a>
or <a href="http://www.nl.fishersci.com/TechZone/Tables/chemicals.htm" target="_blank">http://www.nl.fishersci.com/TechZone/Tables/chemicals.htm</a>
<img border="0" title="" alt="[Wink]" src="wink.gif" />

[mongo blongo]

Yes I have also seen this in many places. Actually I may as well give it a go and see what happens. I will get some chalk and neutralize it with HCl and evaporate till dryness to get some Calcium Chloride. I will probably have to keep the bath and everything well insulated with polystyrene or something.

[PEROMAN]

Remember ! You need only CaCl2*6H2O !
If you dry it at big t , it can demompose(even can give some HCl).
But if you keep CaCl2*6H2O on air for some time , it would take water from air and become liquid
So there is a problem to obtain CaCl2*6H2O . It's worth to read some books about it...

<small>[ February 05, 2003, 10:25 AM: Message edited by: PEROMAN ]</small>

[Anthony]

I would assume that dehumidifer refills would be anydrous calcium chloride? If so, its £1-2 for a kilo from practically anywhere.

[VX]

It would be easy to make CaCl2(6H20) from anhydrous calcium chloride. Simply start with one mole of CaCl2 (111g) and to this add 6 moles of water (108g)(108ml), mix well and leave for a while in a sealed container.

[Mr Cool]

My freezer gets below -20*C on its lowest setting, it could probably go lower in theory.
I've seen CaCl2 for de-icing roads in B&Q, it was a tub of several kg for a few £.
This would probably be cold enough for cloud chambers, which would be nice since I have more productive things to do when I occaisionally get dry ice.

[Al Koholic]

I stand corrected. I neglected to note that due to its hydrated state, CaCl2.6H2O will not cause an increase in the temperature of a solution as will the anhydrous form.

Anhydrous CaCl2 forms the hexahydrate when dissolving and in the process releases large amounts of heat.

Hydrous CaCl2 simply produces a state change from crystalline to solute. Since it already carries its water onboard so to speak, the dH of solution is quite positive then.

I wasn't aware of this property of hydrous CaCl2 before, thanks guys.

[metafractal]

Flipping through my MERCK: Tables for the Laboratory (A source to trust if any), I found the following table:

4 Water + 1 Potassium Chloride lowers temperature from +20 to -12
1 Water + 1 Ammonium Nitrate " " " +10 " -15
1 Water + 1 Sodium Nitrate
+ 1 ammonium Chloride " " " +8 " -24
3 Ice (ground) + 1 Sodium-
Chloride " " " 0 " -21
1. 2 Ice (ground) + 1 Magnesium-
Chloride
(MgCl2.7 H2O) " " " 0 " -34
1. 2 Ice (ground) + 2 Calcium-
Chloride
(CaCl2.6 H2O) " " " 0 " -39
1. 4 Ice (ground) + 2 Calcium-
Chloride
(CaCcl2.6 H20) " " " 0 " -55
Methanol or Acetone + Dry Ice " " " +15 " -77
Diethyl Ether + Dry Ice " " " +15 " -100

No measurements were given for the last to, so assume that exact proportions are unimportant and just use commonsense.
Almost all the chemicals stated are easily available to the amateur chemist.
I had never really thought about preciseley measuring a freezing mixture, but this table shows how vital it is. Until now, A salt ice bath for me has always been shake a bit of NaCl on some ice cubes in water...

God I love this book, I've started carrying it around with me everywhere I go! It is a wonderful resource and it fits right in your pocket. If you see it, by all means do get it (I cant imagine that it would cost more than ~$5US). It is entitled:
"Tables for the Laboratory", by MERCK, and deceptiveley contains a large amount of information. I will upload it to the ftp when I feel ready to request ftp rights and are granted them, but I doubt that it will be of any particular use if we've got the full MERCK index up there, as its main appeal is convenience.

[Al Koholic]

Sounds like a good book to have around! Im going to have to obtain me a copy. It would be great to have a little pocket sized book like that with all kinds of interesting info in!

Where did you obtain your copy? I'll bet it can be gotten from any major book retailer...

[mongo blongo]

After some research I have designed some kind of freezing system which could be made out of easily available materials.
I don't know how cold it will get but *hopefully* very cold. I also don't know how much it will cost to make but I think it would make an interesting project.

<a href="ftp://ewf:sd332gf@209.195.155.80/hosted%20images/Mongo%20Blongo/freeze.jpg" target="_blank">Here</a> is a picture of the design and it is explained below.

Materials & equipment used:

1. Compressor pump - This can be easily salvaged from a fridge or freezer. Just take a trip down the scrap yard and you can find one for free.
2. Tubing - What you need is tubing that can stand a lot of pressure. Some 1/4" copper tubing (hardware store) should do the trick.
3. V1 & Outlet1- This is just a normal gas valve. You can get small brass valves from a hardware store.
4. V2 - This is a variable gas valve. In this setup it is being used as an explanation valve in place of a capillary tube. The need for variable valve will become apparent later.
5. PG1 & PG2 - These are gas gauges which are needed to monitor the pressures involved. I think these may be a bit expensive though.
6. Inlet1 - This I am not sure about. This valve depends on the source of refrigerant used.
7. Refrigerant - Here you can use any practical refrigerant you want. I think Freon, Propane, Butane(?) would be a good choice.
8. Ethylene Glycol - This is used a heat conductive bath which will remain liquid at low temperatures. Also known as anti-freeze from a hardware store.
9. Insulation - You can use any insulation you want as long as it works well. Polystyrene should work ok.
10.Plastic container - I will leave this up to you.
11.Mix container - This is the container which will contain the material that you want to freeze. If you are using DCM/HNO3 mix then make sure it is made out of a resistant material. I suggest Teflon or polypropylene. I have read that certain metals will react with Dichloromethane so I would rule out metals.
You can attach a sieve with the handle removed to the container. This is so that when the HNO3 is frozen you can QUICKLY pour out the DCM and the HNO3 crystals will remain.

Operation

1.Once you have built this setup, the first thing you will have to do is evacuate all the air ot of the system. To do this first close V1 and inlet1 then fully open V2 and the outlet valve. Switch on the pump. The air will be sucked out of the system and pushed out of outlet1. After a few mins the system will become a vacuum. Then close the outlet valve.

2.Now you will have to charge the system with your chosen refrigerant. To do this you will first have to get some data for your refrigerant. You will need to know the critical pressure (the pressure at witch your refrigerant changes from a gas into a liquid.
Open V1 and fully close V2. Introduce your refrigerant into inlet1 (like from a propane gas cannister or something) with the pump still running. Do this until you get a reading Just over your critical pressure on PG2 then close the inlet valve. This now means that the red side is now filled with LIQUID refrigerant.
Close V1 and switch the pump off. Leave V2 closed and re-introduce your refrigerant until you get a reading of about half(?) your critical pressure on PG1 and close inlet1. You now have your refrigerant in the form of a GAS on the blue side. The system is now charged.

3. Now the system is just about ready to work. First fully open the variable valve (V2) and V1 and PG1 and PG2 should be reading the same pressures. The blue side should start to feel a little cold.
Turn the pump on. Now slowly close V2 until you get a reading just over your critical pressure on PG2. PG1 should then be well below the critical pressure. Once you have got these pressures and it is stable leave V2 in this position.That is why I said to use a variable valve.
It should also be possible to change the temp with V2.
The blue side should get very cold and frost up as the liquid refrigerant is being forced into a gas on that side absorbing heat.
As the gas is being compressed into a liquid on the red side it will give off heat. This is why you need to cool this side somehow eg. an ice bath.
If it is not cooled then it temp could rise over the critical temperature of your refrigerant which means over this temp, it can not change back into a liquid no matter what pressure you put on it. The efficiency of your system will be GREATLY reduced.

I think I have covered everything here.Did I make any mistakes?
So what does people think of this then?

[mongo blongo]

On a separate note. While I was researching the Peltier Effect I found<a href="http://www.sharperimage.com/us/en/catalog/productview.jhtml?sku=GF200" target="_blank">this.</a>I have found cheaper ones elsewhere but all you have to do is take out the thermostat. :)

[Al Koholic]

Your reasoning looks accurate. It sounds (and is) basically like you have built a new (hopefully more badass) refrigerator from the compressor. The thing is Im not sure if you could get it any colder than a normal refrigerator already would unless the liquid---&gt;gas expanded into a larger chamber than the original refrigerator did, leading to most heat absorbtion due to lower pressure. I think thats how it would work but I very very well could be wrong.

Other than that it looks good and your operating procedure makes sense.

Im not sure that you need an ice bath. Common refrigerators do not require one because of the large surface area provided for heat exchange by the coiled tubes on the back of the fridge.

Thinking of even lower temps here than required to freeze HNO3 (if im not mistaken, don't have merck here now), what about the potential of a system like this to liquify ammonia? I was contemplating a system like this which would work dry ice and ethylene glycol (or acetone, ethyl ether, etc) and a pump to run the fluid through and cause a stream of NH3 running through a tube to condense. The collection container could easily be immersed in the freezing mixture if needed as well. NH3(l) would be wonderful to create even just for the sake of creating it.

[Sparky]

Sounds hard, but you can do it I have faith. Just two points:

I have only had one experience using butane as a coolant and it wasn't so good. My dad's car leaked all it's coolant and it was a really hot summer day so he decided to try putting in butane instead, with some propane to raise the pressure. It worked for a while but after an hour and a half or so the compressor was ruined. Butane (and propane too of course) doesn't have the lubricants needed to let the compressor run without destroying itself. I think you can buy the lubricants but I don't know if they would separate out of butane or what since they are meant to be added to freon.

A good coolant could be hard to get. Propane's boiling point is barely good enough at around -42 C - you want around -50 right? Methane boils at around -161 but the hard part is getting it. It is sold for cars that run off natural gas but it may be highly compressed and not actually liquid I'm not sure. Ammonia at only -33 probably wouldn't be a good choice especially because of it's health effects - you're bound to get a leak sometime.

<small>[ February 17, 2003, 05:34 PM: Message edited by: Sparky ]</small>

[mongo blongo]

Al Koholic- I was thinking about a larger gauge wire too. I am not sure either about "lower pressure = more heat absorption". Does anyone know? I think that it is just plainly the transition of state. and it only absorbs a specific amount of heat for the transition.

Sparky- What I want is to get to at least 42 deg C (freezing point of HNO3) but 50 deg C would be more favorable. :)
I also don't think the boiling point of the refrigerant comes into play here. Remember we are talking about high and low pressures. The boiling point changes at different pressures. As long as the blue side is below the critical pressure you can be sure that it is a gas no matter what temperature it is. Hence the amount of heat absorbed will be the same all along in theory?. The temp inside the container however will depend on insulation. You want as less heat as possible getting in. You only want what heat is left in the container to be absorbed. So there will be an equilibrium at some point when the heat getting in will equal the heat absorbed. So this equilibrium will depend on the heat getting in so the insulation will play a big part on the lowest temp possible rather than the boiling point of the refrigerant becoming a factor.

[Anthony]

I could well be wrong here, but I think it's the differential in pressure that dictates how much heat is absorbed. I.e. 1000psi to 14.7psi would abosrb more heat than 100psi to 1psi. If nothing else there's a greater atmospheric volume of gas for a given volume compressed.

I reckon it would get colder than a standard fridge because you have a lot less area to absorb heat to, and might be better insulated. Basically you're cramming all your "coldness" into a smaller space :)

I think the ice water is a good idea, it'd make it easier for the compressor to liquify the gas again.

All AFAIK - I don't know much about refrigeration.

[vulture]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">I am not sure either about "lower pressure = more heat absorption". Does anyone know? I think that it is just plainly the transition of state. and it only absorbs a specific amount of heat for the transition.</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">It's true if you lower the boiling point of the coolant you are using to the temperature you are wanting to achieve. Transition of state will cause significant heat absorbtion while the temperature of the coolant stays constant.
However, there are a few drawbacks.
Once the vapor carries the energy, it's going to get rid of it sometime by condensing and then it will lose alot of heat while staying at the same temperature then. If this happens where it shouldn't be happening then you'll be warming up.
Also, reduced pressure means lower heat conduction and thus the coolant will need more time to absorb the same amount of heat.

<small>[ February 18, 2003, 01:02 PM: Message edited by: vulture ]</small>

[Tuatara]

mongo blongo

Boiling point of your refrigerant is important - most commerial / industrial heatpumps utilize the liquid/gas phase change for shifting heat. This results in a much better COP than simply changing gas pressure. A plain gas phase only system does work , its just not very efficient. Back to boiling point - this is one of the reasons heatpumps require different refrigerants in differant sitations, eg R12 for a -25C freezer, R22 for air conditioners.

If you want to go really cold, do it the way Carl von Linde did it!
<a href="http://www.chemheritage.org/EducationalServices/chemach/tpg/cvl.html" target="_blank">Carl von Linde</a> (hope i put the link in right - first post here you know :) )

He liquified air with nothing more than a compressor, a couple of heat exchangers and an expansion valve. I've been wanting to try this myself with my salvaged refrigeration compressor, but its currently running my air-brush. I think a steady supply of LOX would be a great thing to have in one's garage :D

Peltier coolers can be used, they can also be stacked for lower temps but they are not efficient. Some specs from the Farnell Catalogue
heatpump capacity: 70W
Delta T : 68C
supply current 7.4A
supply voltage 14.7 V

So you'd be looking at over 100W of electrical power to pump 70W of heat, so on the hot side of your peltier you've got to get rid of 170W <img border="0" title="" alt="[Eek!]" src="eek.gif" /> . Oh, and you wont get maximum delta T at maximum heat transfer rate.

Sparky - your dad's car's cooler died because the compressor oil must be miscible in the refrigerant. This is also why you can't just replace R12 with R134a - you have to strip the whole cooler down, clean it out completely, change all the seals change to the correct oil, and then the compressor might last longer than a week.

[Marvin]

Boiling point of a liquid changes with pressure, so if you take water water as an example you can get down to neerly 100 degrees below its boiling point in atmospheric pressure. The lower the pressure, the lower the temperature at which it boils, and so the minimum temp you can reach with that system. Its true to say that latent heat of vapourisation doesnt change much with pressure, but this does affect the power you can shift with the system. The reason is you arnt dealing with constant rates of liquid flow, you are compressing gas, for a given compressor volume, the lower the pressure at its inlet, the lower the total amount of high pressure gas/liquid gets to the other side, and the total heat you can remove is less. Usually around the triple point a given coolent becomes unworkable, and solids block the flow anyway.

Peltiers can produce temperatures differences of around 70C, but the colder the hot side, the lower the difference they can produce, and so they dont stack well. Additionally the power they remove is roughly in line with the percentage of the max capcity they dont use. For example a device rated at 70W, with a max difference of 70C will pump 70W at no temperature difference. Cooling the cold side to half the difference, say -15C with a hot side of 20C, will pump half of the power, 35 watts. taking the cold side down to -40, and the device will pump only 7 Watts. They cannot be overspecced, increasing the voltage/current will only make it perform worse. You still have to supply 70W of power to the device, and remove that plus the heat pumped from the hot side. They ant very power friendly, but they are solid state and very reliable unless you fry them (operation with no heatsink, and for these apps only watercooling is feasable).

Try looking into vortex tubes for this application, its possible they can be cascaded to produce -50C at power.

[mongo blongo]

Those vortex tubes are mad! I can't seem to find any pressures that the gas must be. I take it that higher pressure would produce more heat and then gives more cooling to the cold jet?
Could they be improvised or do they need very accurate construction?

Also I just tried the Calcium Chloride-6-Hydrate reaction many times and the lowest temp I could get was -25 deg C! <img border="0" title="" alt="[Frown]" src="frown.gif" />

[Tuatara]

I spent some time looking into vortex tubes a while back, simply because it seemed such a beautifully simple idea. The only pressure spec I recall was that the pressure be greater than 1.3atm, which isn't very much. As for building one, it didn't look like huge amounts of precision were required to make it work, though making one that works well might be another story. I gather the discovery was rather accidental, as there is still some controversy over exactly why the things work at all. Its not exactly an intuitive process.
I could find very liitle design info - but I would guess that you will get lower temps with a smaller hole at the cold end, at the expense of cooling capacity.

I believe they are not that efficient, but they are very, very simple and reliable.

Go have a play in your machine shop :)

[Tuatara]

I've just remebered another rather neat idea for cooling. Its called a pulse tube, and basically works like a Stirling engine/heatpump, but uses audio frequencies. These things can be used to cool SQUIDs to around 4 Kelvin (no thats not a typo). I lost all my links when I got made redundant 2 years ago, but if you search google for 'pulsetube' or 'TADOPTR' (I've forgotton what the acronym stands for) you should find lots of info, including diagrams,design info, simulation software etc. Should be very easy to make - its just a tube with a loudspeaker at one end, closed at the other end, with some stainless mesh in the middle, and a couple of heat exhangers.

[firebreether]

A note about refrigerants. For as low a temp as possible you'll want to use materials with very low boiling points, but hvae critical point temps above 30* C. You wouldnt want to turn your refrigerator off, and the temperature climbs past the critical temperature, so the pressure just keeps climbing and clinbing, until boom, and your refrigerator's tubes explode. Suffice to say, that wouldnt be a good situation.

Heres a list of ones i would use (besides the freons of course :p )
N₂O, Propane, NH₃, other hydrocarbons.......

I would stay away from peltier coolers if i was you though, stick with normal refrigerators.

TADOPTR = thermo-acoustically driven orifice pulse tube refrigerator, im just looking up stuff on it, yay google!

here is a simple picture showing the schematic, that was found here, which explains it more <a href="http://irtek.arc.nasa.gov/WhatisOPT.html" target="_blank">here</a>
<img src="http://irtek.arc.nasa.gov/OPTsketch.gif" alt=" - " />

<small>[ February 19, 2003, 01:11 AM: Message edited by: firebreether ]</small>