Tank design....

[BrainEater]

Hello , I'm new here.....I must say a resource like this is a great find.

Let me start out by saying , I'm pretty much a cryogenics newb , an 'avid hobbiest' lets say

--------

I Have some questions about building a small tank to potentially hold/circulate liquid nitrogen .

It'll help the conversation if I provide some background.

I do computer casemodding/design.

A few years ago I made a computer case from scratch that was designed to submerge a computer in liquid coolant. see;

http://www.hardforum.com/showthread.php?t=802563

Now , while it worked perfectly for 4 months , the temps were not what I was after .

I have done further work ;

Thats a computer running submerged in 99%iso with dry ice.





-------------

This leads me to my questions.


I am building a new tank , because I'm pretty sure this one won't do below -50 c .

- size =( 12"h x 17"l x 7"w )

- It must have a 'window' on one side.

- It's gotta have some sort of removeable piping system for coolant flow / gas exchange...this means fittings n whatnot.

- Related to the above 2 ; all seals need to be fully resistant to 99% isopropanol , with luck LN2........


My initial design would be a welded aluminum box with a re-enforcement rings on both top and side for a bolt on window plate and the drop in motherboard holder.

-Is 1/4" aluminum plate acceptable for what I want to achieve ? Is thinner better ?

-I'll need seals/O-rings for the top and window.What materials should I be looking at ?

-same goes for the piping.I was considering soft copper lines.Galvanic issues aside , any other problems ?

-What about fittings ? brass ok ?


---


Thanks For any input !

=D

 

[iainuts]

Hi Brian,
Looks like you’re into this pretty deep. I wonder what you’re doing with all that computer power. Trying to make a human brain? When it comes alive, please put her on YouTube so we can all get to see it!

I think you’re saying you want to go down to only -50 C, is that right? That’s not generally considered cryogenic, though its low enough that many materials become hard and brittle. I’ll also assume there’s no significant pressure on the tank you’re building, so stresses are not a big issue.

- How are you insulating this? Conventional insulation (ex: closed cell foam) with a vapor barrier will work fine. You need to do something to keep this box cold when below ambient, or you’ll have to refrigerate not just the electronics but all the heat entering from atmosphere. Also, water from the atmosphere will freeze out on the cold surface and eventually you’ll get a buildup of ice in your insulation which reduces the insulations effectiveness and may damage things. Big balls of ice can push things apart and bend stuff, so best to either seal up the insulation with a good vapor barrier or maybe even keep a dry nitrogen blanket on it. If ice builds up, you can always shut the system down, allow it to warm up and dry out.

In general, aluminum, brass, copper, stainless steel (esp.: 300 series) are all good materials for cryogenic temperature as they don’t loose ductility like steel does. Thickness isn’t too important, just so long as it can support the weight and internal pressure, those materials are acceptable.

Fittings: Swagelok, Parker, Hoke, Bi-Lok and others make duel ferrule fittings in both stainless and brass which are good at cryogenic temperature, including liquid nitrogen.

http://www.swagelok.com/search/find_products_home.aspx?RESET=TRUE

http://www.tidyco.co.uk/store/parker_hannifin/tube_fittings/default.asp

http://www.hoke.com/products/fittings/gyrolok/index.htm

http://www.generant.com/bilok_trans.htm

Galvanic Corrosion: Unless your fluid is electrically conductive, and I have to believe it’s not, galvanic corrosion isn’t an issue for brass/aluminum. See also:

http://www.engineersedge.com/galvanic_capatability.htm

http://www.assda.asn.au/asp/index.asp?pgid=18533

Material Compatibility: For material compatibility, check the Parker O-ring handbook. Parker has moved around their site, so my bookmarks don’t work any more and I can’t seem to find it in 3 clicks, so I’ll just point you to Google:

http://www.google.com/search?hl=en&q=parker+o-ring+handbook

The big question is how to set up the glass. Lots of problems. Sealing. Differential thermal contraction. Frost on the window will make it useless. I’ve never had to set up a window like this before, so I can’t give you a perfect solution. Some kind of silica or quartz glass is probably a good solution for material, but sealing it may be difficult. Silicone is good for isopropanol and is your best low temperature material. It can handle -50 C and even at -320, although it gets hard, O-rings are commonly used and will seal well even under pressure. Just make sure you have the proper squeeze on them and the surfaces are smooth to 63 or preferably 32 finish. Check the Parker handbook for details. Probably want to clamp the window. If you’re going to -320 (liquid nitrogen) then doing some analysis on thermal contraction is warranted. The joint may have to be a bit loose to allow for movement between the glass and aluminum structure.

Insulating the window to prevent frost buildup is an issue even at -50 C. Putting a second piece of glass or plastic a few inches away from the sealed window and having some dry nitrogen between the two should eliminate any frost buildup.

 

[BrainEater]

Thanks for the reply !

Lotta good info there.

Actually -50 isnt the goal ; lets say colder than -100 c for the sake of design criteria.Ideally it should tolerate liquid nitrogen , but i'm not convinced the window will allow that.

I should probably state that this tank isnt for full time use , it'll be for short (>6 hours) term use only.

The tank and piping will all be insulated with closed cell foam.

Frost isn't really an issue.In fact , it's almost a bonus , as nothing says super cold like an inch of frost.

I will say , I really like the idea of a 'nitrogen blanket' for the window.

The glass is definitly an issue.I was considering pyrex , but i'll be looking into this more.

---------

Thanks again for the help.I'll get to reading.

 

[dcasto]

Temperature isn't the problem, its energy absorption. The CRAY series computers used Freon so I don't think they went to -20C. You need to use the liquid coolant to remove the heat (energy) to improve processors. Temperatures below )C are very dangerous and no one here is going to support such a plan.
Keep it simple and remove heat, lower temperatures are not what you are looking for. Use concepts of \FORCED CONVECTION\ Google that.

 

[BrainEater]

Hehe

I understand forced convection just fine , I (and the whole industry) use it on almost all computers...And If I was after efficiency , (best ability to carry away heat) I'd be using watercooling , not air.

Actually , Cray computers have used freon,flourinert,liquid ammonia,water,etc,etc,etc in a variety of different methods from closed loop watercooling to refrigerated liquid spraycooling.

The ETA supercomputer (

http://en.wikipedia.org/wiki/ETA-10

) was designed using liquid nitrogen cooling.Using this method , they were able to achieve stable overclocks in excess of 200%...

----------

As far as being dangerous : being cold aint half of it bud.It's submerged in flammable liquid too.
Seriously though ,I do appreciate your concern , but you let me worry about safety k ?

 

[iainuts]

Hey Brian,
Just wondering, why does lower temperature increase clock speed?

Also, why do you need a window at all? Why can't you just put the computer in LIN and run wires out to a monitor/keypad?

If you must have a window, what is it you're looking at? Can the window be in a warm area of the tank, such as a few feet above the LIN bath so you don't have to worry about leakage or low temperature? You might still have low temperatures there but not nearly as low if in the bath itself.

 

[BrainEater]

Decreasing temperature doesnt increase clock speed in itself.

You manually increase the clockspeed of the system.You may also need to increase the voltages to certain components.This causes the heat output of said components to increase , requiring greater cooling.

The current world record overclocks typically use liquid nitrogen on cpu and gpu only.Submerging the entire electronics package should allow greater OC.

----------

I don't really need a window.I'm doing some initial tests with Dry Ice and Isopropanol in a baking pan (The pic from above).....

The window , really is strictly aesthetic.If it doesnt look good , it aint worth doin.

The initial goal is to make an 'actual computer case' designed for sub -100c submersion...The first tests will go to -70c ish......if all goes well , I may employ the Faraday method to achieve -100 ish (evaporating diethyl ether and dry ice)......Achieving actual LN2 submersion may not happen , depending on the results to that point.

At this point I'm trying to decide if fabricating a tank completely from scratch is the way to go ($$)....I might be able to modify some sort of existing structure.....I hafta go check out the local scrapyard.

-----------

ps......It's 'Brain' not "Brian"...my real names Ross.

 

[iainuts]

oops... sorry Brain. Anyway, now you've explained what you're doing a bit better, I think you have two options.

One option is to buy a vacuum insulated 'bucket' and put a styrafoam lid on it. Contact:
1. Cryofab

http://www.cryofab.com/

2. Technifab

http://www.technifab.com/

3. Andonian Cryogenics

http://www.andoniancryogenics.com/

4. ACME Cryogenics

http://www.acmecryo.com/

5. Chart

http://www.chart-ind.com/app_csd.cfm

Lots of others. Expect to pay $1000 to $3000 for a VJ cylinder new, maybe less used.

The other option is to just weld the aluminum sheet and insulate it on the outside. Make it like a bucket and put a styrofoam lid on. Much less expensive!

In either case, you could add the window to the styrafoam lid as it won't have to be sealed.

Fill the tank with liquid nitrogen from your local gas supplier. They sell it in vacuum insulated cylinders. Get some tips on how to use the equipment and make sure you use it in a very well ventilated area, preferably outdoors. You won't need piping and tubing or any of that other stuff. Just fill it once and it should easily last for 6 hours.

 

[BrainEater]

Awesome ! ...great links.

Thanks again ! =D

-----------

If I had my way , I'd have a stainless dewar made to my specs , but thats a lot of $$ , so it's out.

My next choice would be to fabricate the tank from scratch.I do have half of a machine shop in my garage , so that helps , but I cant do the welding myself.

I have my own n2 tank regulator , so I intend to use your 'nitrogen blanket' idea forsure.

I also have my own vacuum pump , so I may consider actually fabricating my own dewar.....we'll see.

--------------------------


I'm in the planning stages of the next test series.I am buying a brand new motherboard that uses polymeric capacitors (cold resistant) , and I'll be attempting to get it to run at -70 c or lower.

If it actually works , i'll begin the real planning for the tank .

I'll have more 'cool' pics soon

 

[EdStainless]

Use two windows with a gap between them (1/4"). Seal the edge of the window unit with silicone, use a silicone o-ring for the spacing. Run a small vacuum pump on the space between the windows, this will be the best insulation that you can get. Make sure that the edge mounting of the window assembly allows motion, such as a clamp ring with seals on the top and bottom sides of the window assembly.
Make the tank as light weight as you can. The stronger that it is the more likely that you will get thermal related stresses high enough to damage things.

Think about double wall case with vacuum between them. You will want to bake it out under vacuum before you get it cold.

You have to be careful cooling the entire mobo. Many of the connectors will not like being cold, they don't fit right.

The key to these systems is to get the highest heat flux at the point of heat generation. The best, in theory is to use a phase change right at those locations. A phase change of LN is the goal. The problem is that you need to make sure that there is never a gas barrier. The requirements for constant supply of LN makes this difficult.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[BrainEater]

Ok !

Thanks For the procedure ! That's pretty much how I was gonna do it.

Yes , the connector issue is something I'm concerned about.Most of them use 'springyness' , and well , we all know about that and cold.
;S
-----

I will also fully agree with your 'phase change of LN2' comment.I am playing around with the idea of submerging the mobo'etc and cooling that to -70 , Then running 2-way (liquid in-gas out)pots to the CPU/GPU.....

Supply of LN2 / dry ice aint an issue.....The rig is only designed to go for short spans , and , well , I have an account at the welding supply shop

 

[BrainEater]

Just a quick question about 'silicone' (aka silicone caulk).

I've seen this mentioned earlier , but how cold can this stuff go ?

I know the best low temp stuff is rated -55 , but I'm curious if anyone has any experience with this at lower temps ?

 

[someguy79]

I'm going to say a couple things that might seem way too obvious:

How are you dealing with the N2 that vaporizes? Do you have a ventilation system of any kind? N2 will not poison you, but can easily displace oxygen so that a person can suffocate even when breathing normally.

Will your tank (LN2 storage, or any others) be sealed or directly vent to atmosphere? Do you have or will you need any sort of pressure relief devices?

 

[BrainEater]

The system will basically be running outside.

It's being designed to be a zero pressure system.Any and all venting will be straight to atmosphere.

 

[BrainEater]

ok...

I have a simple question or two.

I've boiled this down to making a tank that's glass and silicone.....silicone will do -55c that good enough for now.

So , what would be the ideal glass to use ?

I will probably go below -55c lets say -70c.

Is pyrex a good choice or is there something better thats not super expensive ?

tyia ,
brain

 

[danthemeterman]

Hi Brain,
I am new to cryogenics, have been in the liquid Gas industry for 30 years (L.P.Gas) which is considered a cryogenic. My answer may seem idiotic so understand my history. There are many -dewars- for sale on Ebay right now under cryogenics, hope this helps. Also I have had experience with sight flow indicators rated at 100 PSI to -40ish ? These are no longer legal in the industry ,but I know there are a few in some junk piles if you need, I'll look.
There are many knowlegeable people on this sight. I would like to pick some brains. I am in the beginning stages of collecting a particular (?) from the atmosphere.I will need to store this product in a bulk cryo tank. Any pointers would be greatly appreciated. I plan to try to attend the classes in Boulder this summer, any comments ?

 

[BrainEater]

Hi Dan

Thanks for the response.

Over the last couple months I have completed the required research and am in the process of purchasing materials to build my tank.

I am using the original glass tank as an 'outer' tank in a two layer , nitrogen insulated ,tank.Inside this tank I am building a second tank from Tecniglas Borofloat33 (

http://www.tecniglas.com/borofloat.html

) ....I will be sealing it using Momentive RTV567 (

http://www.gesilicones.com/siliconesweb/am1/en/documents/datasheets/1467.html

)



I am actually building my own dewar from a keg , and some stainless pipe , for the resevoir tank.I am building vacuum jacket lines for all the circulation......

I won't get into the ln2 range I don't think , but -100C is a start.

see

http://www.hardwarecanucks.com/forum/worklog/5532-thinktank-revision-2-0-a.html

for the worklog on this project.....