Cheap Cryocooler: Under $150 DIY Ideas

[Kiara]

Can anyone think of a cheap way (under $150) to build a cryocooler? Commercially available ones run about $15-20K and I don't have those kinds of resources.

 

[Vagn]

Can anyone think of a cheap way (under $150) to build a cryocooler? Commercially available ones run about $15-20K and I don't have those kinds of resources.

I'd be very suprised if you succeeded to be quite honest. You would need a coolant to act as a heat sink, the coolant itself would be very expensive and it would use a lot of energy to keep the system cool enough so the maintenance costs alone would probably be prohibitively expensive.

 

[Jim1138]

What temperature do you want to reach? How much volume? How long do you want to maintain the temperature?

 

[Kiara]

What temperature do you want to reach? How much volume? How long do you want to maintain the temperature?

The cryocooler would be for a small superconducting magnet set-up designed to run under 30K. The coolant (helium, of course, but I can't decide whether liquid or gaseous is better) would just need to surround the magnet, so that's a volume of about 0.1 L. The temp would just have to be maintained for perhaps 5 minutes?

 

[Jim1138]

You could just transfer liquid helium from a supplier's dewar. No refrigeration needed. It would boil off rather quickly, of course. I am not sure what the current prices are. I would suspect the $150 would be low.

 

[russ_watters]

Yeah, a thermos bottle (or jug) should work fine.

 

[Kiara]

wow, didn't think of that. thanks for the help!

 

[f95toli]

The cryocooler would be for a small superconducting magnet set-up designed to run under 30K. The coolant (helium, of course, but I can't decide whether liquid or gaseous is better) would just need to surround the magnet, so that's a volume of about 0.1 L. The temp would just have to be maintained for perhaps 5 minutes?

i agree with Jim1138; it would be better to just transfer LHe from a dewar. However, that of course assumes that the the magnet is mounted in a proper He cryostat. There is a HUGE difference between using liquid helium and liquid nitrogen; for the latter you can just use Thermos bottles etc but that does not work with helium.
Also; liquid helium is quite expensive so $150 won't buy you very much (it is $5-10/l); and you'll need quite a lot to cool down the cryostat+magnet (liquid helium is usually delivered in 60l or 120l dewars).

Finally, and I can't stress this enough, make sure you are doing this with someone who has experience handling liquid helium. It is potentially very dangerous if you don't know what you are doing .

Yeah, a thermos bottle (or jug) should work fine.

You are thinking of liquid nitrogen (77K); you can't use Thermos bottles or anything like that for liquid helium which is what you need for temperatures <30K (you use vacuum-insulated transfer tubes to transfer from dewars to the cryostat) .

 

[Vanadium 50]

A thermos is a bad idea for transporting cryogens. None are perfect, and as heat leaks in, the cryogens begin to boil and the pressure in the thermos goes up. I don't know the exact numbers for helium (which will be similar), but LN2 expands almost 700-fold upon boiling. Every place I have worked has banned using a thermos to transport cryogens (and most ban them anywhere near cryogens, just to avoid temptation).

I don't think this will be possible. You are asking to do something 100x cheaper than the standard way. If this were possible and safe, it would be the standard way. Otherwise it's like trying to buy a new car for $20, or lunch for a dime.

 

[f95toli]

A thermos is a bad idea for transporting cryogens.

Again, a Thermos simply won't work for liquid helium. I sometimes use Thermos bottles (without the cap on, obviously, if you close the cap it will explode) for temporarily storing small amounts of liquid nitrogen. But there is simply no way you can use one for liquid helium; you wouldn't even be able to get any liquid in there (besides, how would you even get the helium in there in the first place? It is not like you can actually pour LHe, it would boil off in less then a second).
Storage vessels for liquid helium are made by using a couple of "layers" of vacuum insulation with superinsulation and/or a liquid nitrogen jacket in-between in order to minimize the heat loss; a normal Thermos bottle is nowhere near good enough.

So again. assuming you already have access to the equipment (a proper cryostat for the magnet+transfer tubes, vacuum equipment etc) +the necessary expertise you MIGHT be able to pull this off by simply spending your $150 on liquid helium.

 

[Kiara]

I don't need to go all the way down to 4.2K, just below 30. Could I simply build a conventional refrigeration system using helium gas instead of ammonia?

 

[Q_Goest]

There are some movies on YouTube, made about 50 years ago, that show 2 layers of clear thermos bottles. The first (outer) bottle contains liquid nitrogen as a shield and the inner one contains liquid helium. No cryostat, no MLI or shielding other than the nitrogen. The thermos bottles were clear so you could see the experiment regarding superconductivity inside the inner vessel.

Regarding transportation of liquid helium; for MRI machines, this is done in shielded, 500 liter dewars. The boil off gas is taken through a copper shield that serves the same purpose as a liquid nitrogen shield. They have low pressure “road relief” valves to allow low pressure venting during transport as well as higher pressure ones and burst disks. To transfer the liquid from a dewar to MRI, a vacuum jacketed hose insulated with MLI is used. A valve helps to control flow and a “stinger” (vacuum jacketed tube) is inserted into the top of the dewar which runs all the way to the bottom. A second stinger is inserted into the top of the MRI machine which mates up with a tube inside that goes down to the bottom of the machine. I’m sure you can get smaller dewars. I’m checking on pricing but don’t know when a sales guy can get back to me, but I seriously doubt you’ll get anything for $150.

Regarding how to get 30 K, I’m assuming you knew that a cryocooler required a properly designed cryostat to insert it into, so you already have that much taken care of. If that’s the case, dumping liquid helium into shouldn’t be an issue. If you weren’t aware that a cryocooler needed a cryostat, you might want to explain where you’re at in the design and what you’re trying to accomplish.

Edit: LHe cost ~ $6/liter plus distribution costs. Smallest dewar we have is 60 L.

 

[f95toli]

I don't need to go all the way down to 4.2K, just below 30. Could I simply build a conventional refrigeration system using helium gas instead of ammonia?

There is -unfortunately- nothing that has a boiling temperature between 77K (nitrogen) and 4.2K (helium), so if you are going to use a liquid to cool your magnet you have to use helium. And no, a conventional refrigeration system won't get you anywhere near 30K. Just to give you some idea of the scale: compressors needed to run a typical pulse tube (what you need to get below 30K) are usually rated at about 4kW and are water cooled...A pulse tube is NOT your typical refrigerator.

There are some movies on YouTube, made about 50 years ago, that show 2 layers of clear thermos bottles. The first (outer) bottle contains liquid nitrogen as a shield and the inner one contains liquid helium. No cryostat, no MLI or shielding other than the nitrogen. The thermos bottles were clear so you could see the experiment regarding superconductivity inside the inner vessel.

Cryostats like that are still sometimes used for teaching. I used to be the TA in a course where we used a glass cryostat to demonstrate various properties of liquid helium (including superfluidity) plus the properties of various materials (making indium go superconducting etc). It was quite fun to do and the students liked it a lot. The fact that there is a nitrogen jacket also means that one can discuss thermal radiation and the T^4 law etc.
The nice thing about a glass cryostat is that you can see the liquid helium; I use liquid helium on a daily basis but of course I never get so see it since my cryostats/dewars are all made from several layers of stainless steel.
The drawback with glass cryostats is that they tend to explode after a few years (and no, that is not a joke, the blast shield is there for a reason)

 

[Vanadium 50]

There is -unfortunately- nothing that has a boiling temperature between 77K (nitrogen) and 4.2K (helium)

Neon boils at 27K. There's one other substance, and it boils at 20K. However, it is so dangerous nobody in their right mind would use it as a cryogen. Liquid neon is seldom used, as it's expensive - around $1000/l.

 

[Jim1138]

Can you use a high-temperature superconductor?

 

[Kiara]

Regarding how to get 30 K, I’m assuming you knew that a cryocooler required a properly designed cryostat to insert it into, so you already have that much taken care of. If that’s the case, dumping liquid helium into shouldn’t be an issue. If you weren’t aware that a cryocooler needed a cryostat, you might want to explain where you’re at in the design and what you’re trying to accomplish.

I had a cryostat designed, I was just trying to figure out how to cool the system down.

I'm working with superconductivity electromagnet experiments. High temperature superconducting wires that superconduct above the boiling point of nitrogen can cost $500 a meter. So I decided that constructing a superconducting electromagnet out of Magnesium Diboride (MgB2, superconducts under 39K) and cooling it with helium would be a less expensive alternative.

Perhaps I could cool the system with liquid nitrogen first, and then liquid helium? I only need to keep the temperature below 30K long enough to energize the electromagnet and take some measurements, about 3-4 minutes.

 

[NobodySpecial]

There is -unfortunately- nothing that has a boiling temperature between 77K (nitrogen) and 4.2K (helium),

Liquid hydrogen boils at around 20K - good luck with that ;-0

 

[Q_Goest]

I had a cryostat designed, I was just trying to figure out how to cool the system down.

I'm working with superconductivity electromagnet experiments. High temperature superconducting wires that superconduct above the boiling point of nitrogen can cost $500 a meter. So I decided that constructing a superconducting electromagnet out of Magnesium Diboride (MgB2, superconducts under 39K) and cooling it with helium would be a less expensive alternative.

Perhaps I could cool the system with liquid nitrogen first, and then liquid helium? I only need to keep the temperature below 30K long enough to energize the electromagnet and take some measurements, about 3-4 minutes.

That's generally the way manufacturers of MRI machines do it (or had done it in the past). They're filled with LN2 and then emptied and a vacuum pulled to help remove the residual LN2. I don't see any problem with your approach, cooling down with LN2 first, then throwing in the LHe. Just do some calculations to determine how much LHe you need to cool down. If you have a mass and material type, post it and I can tell you about how much LHe you'll need.

 

[f95toli]

Liquid hydrogen boils at around 20K - good luck with that ;-0

Indeed. but that is not generally considered a useful cryogenic gas...Unless you are a mad scientist, that is
Solid hydrogen (around 12K or so) has been used to cool high precision oscillators (where the mechanical noise due to a boilding liquid would causes problems) but that is the only "sensible" cryogeniuc application of hydrogen that I know of (but it is still dangerous, most of the time they simply use solid nitrogen).

 

[f95toli]

Perhaps I could cool the system with liquid nitrogen first, and then liquid helium? I only need to keep the temperature below 30K long enough to energize the electromagnet and take some measurements, about 3-4 minutes.

Isn't Jc of MgB2 pretty bad at 30K? What is the expected Jc of your cable?
I haven't done any measurements on MgB2 in years (I was somewhat involved in a project during the first few months after it had just been discovered to be a superconductor) so I don't remember any numbers.

Btw, pre-cooling with nitrogen CAN be a good idea; but only if you can blow out ALL (or at elast nearly all) of the nitrogen. The heat capacity of solid nitrogen is pretty bad; meaning you will need a lot of helium to cool down any nitrogen left in the cryostat. I very rarely pre-cool the systems I use with nitrogen; I prefer to simply pre-cool it in the helium vapour for this very reason (I use 200-300l of liquid helium a week; so the extra 30-40l of whatever it is I loose by not using nitrogen to pre-cool when I cool down the system is negligable).


But once again; there shouldn't be any need to tell you this. You DO need someone with practical experience of cryogenics to help you; this stuff is dangerous if you don't know what you are doing.

 

[Kiara]

That's generally the way manufacturers of MRI machines do it (or had done it in the past). They're filled with LN2 and then emptied and a vacuum pulled to help remove the residual LN2. I don't see any problem with your approach, cooling down with LN2 first, then throwing in the LHe. Just do some calculations to determine how much LHe you need to cool down. If you have a mass and material type, post it and I can tell you about how much LHe you'll need.

About 26 grams of MgB2 (an ionic solid), and about 342 grams of a nickel alloy.

Isn't Jc of MgB2 pretty bad at 30K? What is the expected Jc of your cable?
I haven't done any measurements on MgB2 in years (I was somewhat involved in a project during the first few months after it had just been discovered to be a superconductor) so I don't remember any numbers.

Btw, pre-cooling with nitrogen CAN be a good idea; but only if you can blow out ALL (or at elast nearly all) of the nitrogen. The heat capacity of solid nitrogen is pretty bad; meaning you will need a lot of helium to cool down any nitrogen left in the cryostat. I very rarely pre-cool the systems I use with nitrogen; I prefer to simply pre-cool it in the helium vapour for this very reason (I use 200-300l of liquid helium a week; so the extra 30-40l of whatever it is I loose by not using nitrogen to pre-cool when I cool down the system is negligable).

But once again; there shouldn't be any need to tell you this. You DO need someone with practical experience of cryogenics to help you; this stuff is dangerous if you don't know what you are doing.

I ran a few calculations, and the current I'm planning to send through the wires will remain under Jc if the temperature stays under 32K. Also, the magnet is there simply to produce a strong magnetic field, the type of material the magnet's made of doesn't matter. I simply chose MgB2 because it was less expensive than HTS wire. If there were another more practical choice I'd gladly take that.
Also, regarding the practical experience, that's what I'm here for, right? But really, what exactly are the dangers? Frostbite, asphyxiation, and pressure build-up from evaporation can be combated with lots of good insulation and protective gear, good ventilation, and release valves, right? Am I naively missing something?

 

[Q_Goest]

About 26 grams of MgB2 (an ionic solid), and about 342 grams of a nickel alloy.

omg.. that's nothing. Don't you have a cryostat to cool down? Sounds like an unusually light vessel. The hose used for transfer has more mass than that.

If that's really how much the whole thing weighs, don't even worry about using liquid nitrogen. You'll only use a couple liters of liquid helium to cool down your transfer line + your apparatus. It's not worth worrying about.

Regarding dangers, yes I think you covered it all. Primary thing I think is to just take it slow; don't jam the stinger into the dewar which would over-pressurize the dewar and lift a RV. Get some tips from whoever sells you the product. You'll need transfer lines anyway, so you'll probably need to pay for the use of them or have your supplier's technicians do it.

May I ask where you're doing this? Don't have to be too specific.

 

[Kiara]

omg.. that's nothing. Don't you have a cryostat to cool down? Sounds like an unusually light vessel. The hose used for transfer has more mass than that.

If that's really how much the whole thing weighs, don't even worry about using liquid nitrogen. You'll only use a couple liters of liquid helium to cool down your transfer line + your apparatus. It's not worth worrying about.

Regarding dangers, yes I think you covered it all. Primary thing I think is to just take it slow; don't jam the stinger into the dewar which would over-pressurize the dewar and lift a RV. Get some tips from whoever sells you the product. You'll need transfer lines anyway, so you'll probably need to pay for the use of them or have your supplier's technicians do it.

May I ask where you're doing this? Don't have to be too specific.

Well that's just the magnet. I didn't think you meant for me to include the container and the insulation... that'll add a bit. I don't have a location nailed down yet.