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LAN_403

2Spoons

Thu Sept 06 2012, 11:20PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

Because simply buying LN2 is not the point of the exercise. The whole idea is to try to diy LN2.

IamSmooth

Thu Sept 06 2012, 11:37PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Microwatt wrote ...

why don;t you spare yourself the trouble and cost and just buy the ln2. i heard its cheap and you can bubble oxygen through it to make liquid 02

The whole point is I want to make it like Linde did in the 1800's. I don't care about the liquid N2. It's the journey; not the destination.

I have found some scuba/paintball compressors that have a reasonable flow, are oil free and have a psi over 2000. I just don't want to spend $3k to do it.

Microwatt

Fri Sept 07 2012, 03:44AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Posts: 224

I got an idea take an ordinary air compressor, have the heads milled or rods extended so that you can get a really tiny squish zone at the top. do your calculations and see if you can get it to 100 bar of pressure. I am sure that you can find a way to solder up a big head volume to increase the compression ratio.

Ash Small

Fri Sept 07 2012, 06:29AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Microwatt wrote ...

I got an idea take an ordinary air compressor, have the heads milled or rods extended so that you can get a really tiny squish zone at the top. do your calculations and see if you can get it to 100 bar of pressure. I am sure that you can find a way to solder up a big head volume to increase the compression ratio.

I wouldn't recommend this route. There are a lot of other factors to be considered. You can't just 'up the compression' without a complete re-design of the compressor. You could end up with shrapnel flying everywhere.

Shrad

Fri Sept 07 2012, 06:41AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780

I have been told, while searching for compressors, that car air conditioning compressors have better properties than the typical fridge compressor, and that the most common fault on these is the shaft tip breaking at the coupling point, leaving a part of the shaft still usable if it was threaded or coupled somewhat to a suitable drive

I have asked several times in my neighborhood though, and still no compressor in sight..

2Spoons

Sat Sept 08 2012, 02:23AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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The nice thing about car compressors is that the motor would be external, which makes cooling simple. Should be possible to find a couple at a wreckers yard.

Marko

Sat Sept 08 2012, 04:31PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys,

It's somewhat defeating that only now I have realized something about joule cycle and the fact that it doesn't even work with an ideal gas...
I guess we need some more creativity fuel here to devise something more hobbyst-friendly and not involving multikilodollar compressors or cryocoolers.

Would it be possible to attain a thermodynamic cycle similar to stirling cycle, while still using a compressor as a prime mover? As far as I see for this to work with helium, it has to do work on something other than itself. As we don't really care about efficiency that much, the energy probably doesn't have to be returned to the source but could be dissipated by a heatsink as well.

Simplest thin I thought of would be some sort of a cylinder into which compressed gas is let in and expands pushing a piston against a load (perhaps a gas again). Not sure if that'd be much simpler than a stirling engine though!

On the other hand, while I was interested into this topic a while ago someone posted an interesting website involving a cooler with multiple fridge compressors and a special mixture of gasses which included nitrogen - anyone remembers that?

Marko

IamSmooth

Mon Sept 17 2012, 08:10PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Well, I acquired an oil-free compressor that can do over 3000 psi for a nice price. I am on my way.

For my regenerative coil I plan to wrap plastic tubing around 1/4 seamless steel. Does anyone have a suggestion what plastic tubing is tolerant to very low temperatures. I looked at McMaster Carr and could only find tubing that goes to -40C.

EDIT:

I am currently researching teflon tubing. This may be promising.

2Spoons

Tue Sept 18 2012, 02:27AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Teflon would be the first one I'd think of. Quick search suggests its good to -200C. Truth is you can probably use anything, as long as you don't try to flex it when cold.

Well done on the compressor - I am now officially envious!

Ash Small

Tue Sept 18 2012, 02:48PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Marko wrote ...

On the other hand, while I was interested into this topic a while ago someone posted an interesting website involving a cooler with multiple fridge compressors and a special mixture of gasses which included nitrogen - anyone remembers that?

I remember that, or something similar. I mentioned it earlier in this thread. I think it was to cool a cold trap on a vacuum system someone had built for coating a telescope lens (or mirror, or whatever it is that they coat).

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