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Condesation/Fractional distillation of air

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IamSmooth

Fri Sept 28 2012, 12:54AM

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

Microwatt wrote ...

Do you think one of those pressure washers might work? they do 2000 psi easily and they are cheap.

I did give it some thought, but did not want to rip open a pressure washer. Also, I think they use oil for the compressing cylinders which is no good for cryogenic temperatures.

IamSmooth

Thu Oct 25 2012, 11:16PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Just made my first condensor coil. I need to make one more. As you can see I modified a coil bender to impart another force so I can easily make a helix. All of this will be documented on a web tutorial.

Here is a video of it:

IamSmooth

Sat Oct 27 2012, 05:50PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Klugesmith had a nice idea to use a thermocouple for measuring cryogenic temperatures. My meter only goes down to -58F.

I would have to order one from Mouser or Digikey. Any suggestions for other places that would have this?

If my meter won't go that low, what needs to be done to use the thermocouple probe? I'm guessing I have to put a small voltage across the leads and measure the current flow at various temperatures. Calibration would possibly become an issue.

Ash Small

Sat Oct 27 2012, 06:01PM

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

Type 'T' and type 'K' both go to -200. You don't need to apply a voltage. If you do it becomes a Peltier device.

IamSmooth

Sat Oct 27 2012, 06:02PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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So how does one measure temperature with them? I read a little about them just now. They produce a voltage based on the temperature. So, I would have to measure the voltage produced and correlate this to the temperature?

I also found this

Ash Small

Sat Oct 27 2012, 06:10PM

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

IamSmooth wrote ...

So how does one measure temperature with them? I read a little about them just now. They produce a voltage based on the temperature. So, I would have to measure the voltage produced and correlate this to the temperature?

I also found this

My recent thread on this subject is here:

Although I ended up using thermistors for my project.

EDIT: You have a 'reference junction' and the 'sensor junction', the temperature difference between them results in a voltage, which you measure. Can't get much simpler really, but you do need a sensitive meter for accurate results. You also need to maintain the reference junction at a steady temperature, or utilise some form of compensation. Microprocessors are available that do this for you, and also amplify the signal if required (I believe there are references to these in the thread I linked to).

...

Sat Oct 27 2012, 07:26PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
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The easiest route is probably to use a RTD, you can get thin film ones pretty cheap these days ex

IamSmooth

Sat Oct 27 2012, 09:55PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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I read about these after your link. I did not see how low of a temperature they will accurately measure. There also seems to be a need to calibrate it near the range I plan to use. Has anyone used an RTD at cryogenic temperatures?

I am beginning to think I should just spend the $200 and get a working unit that goes down to -328F.

...

Sat Oct 27 2012, 10:14PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The hel-700 series is specified at +/- 1.5c at -200c (the ones in the ebay auction look to be the high accuracy -1 type, which is +/-1.2c, not that it makes much of a difference).

see

Our cryostats usually use RTDs, they actually work out quite nicely at low temperatures because their response is linear so you get a much larger (relative) change of resistance for a given change in temperature at low temperatures.

To get an idea of what the temperature response looks like check out

although that is for a 100ohm alpha=385 rtd, where as the ebay is a funny 1000ohm alpha=375 device, to a first approximation just multiply the values in the chart by 10

IamSmooth

Sat Oct 27 2012, 11:42PM

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

They seem nice. I don't want to take on a secondary project. Would I be able to simply put an Ohm meter across the leads, measure the resistance and just compare it to a chart to get the temperature? This would give me a solution that only costs a few dollars.

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