TheIdeanator
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Building a cold trap
Recently I acquired a working 10,000btu/hr (2.9kW) window ac unit to make a cold trap out of. The only instance I've seen of this is here. Has anyone else done this sort of project?
“I will show you fear in a handful of dust.”
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Ubya
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https://youtu.be/mzeRvdnIP-I
if you were able to put two smaller units in series (and change the refrigerant accordingly) you could get much lower temperatures, equivalent of dry
ice and ethanol. to get -70 or -80 celsius with just one stage you would need a really big pressure difference in the system, and so a big and watts
sucking compressor
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XeonTheMGPony
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Here ya go, cold traps are harder then ya think to get a good design going but worth it.
Attachment: Alcohol_Cold_Trap.pdf (684kB)
This file has been downloaded 422 times
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XeonTheMGPony
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Quote: Originally posted by Ubya  | https://youtu.be/mzeRvdnIP-I
if you were able to put two smaller units in series (and change the refrigerant accordingly) you could get much lower temperatures, equivalent of dry
ice and ethanol. to get -70 or -80 celsius with just one stage you would need a really big pressure difference in the system, and so a big and watts
sucking compressor |
and a short lived inefficient unit while at it! A simple 3 stage auto cascade will do this much better, or even a 2 stage cascade system with much
improved energy utilization.
The gasses are the most expensive part, first stage propane and N-Butane can be used (The N-Butane @ 0.5c boiling point, is used for compressor
cooling at the small cost of a tiny bit of capacity)
Second stage could be R-507 or R-410a for a happy -50c range for the easier to source gasses.
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Ubya
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mhh well this is interesting, i did not think of this design, much appreciated thank you
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RogueRose
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If you want a really good lab grade cold trap (like the one in the first video link) check out surplus auctions for Universities and colleges. I see
these quite often and they usually don't sell for a whole lot, maybe $50-100 at times (and obviously more for some newer larger models). They often
sell as "untested" but they are usually pulled from working labs as I've never heard anyone buying one that hasn't functioned - unless it was sold as
such.
Maybe even look for a broken one and repair it?
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TheIdeanator
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I wish there were more pictures there, I can't tell what's really going on. It seems considerably more complicated than I'm willing to troubleshoot
with the cascading heat exchangers and mixed refrigerant. I was just going to re-route the plumbing and hope for the best.
“I will show you fear in a handful of dust.”
― T.S. Eliot
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Ubya
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| Quote: Originally posted by TheIdeanator |
I wish there were more pictures there, I can't tell what's really going on. It seems considerably more complicated than I'm willing to troubleshoot
with the cascading heat exchangers and mixed refrigerant. I was just going to re-route the plumbing and hope for the best. |
an air conditioner does not produce sub zero temperatures on the evaporator, otherwise it would frost during normal operation. re-routing the plumbing
would be ok if you wanted to make a water cooler for distillations,
but to freeze water or organic solvents in a vacuum you need lower temperatures, that's why dry ice and acetone or liquid nitrogen are used for this
porpuse
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TheIdeanator
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| Quote: Originally posted by Ubya | | Quote: Originally posted by TheIdeanator |
I wish there were more pictures there, I can't tell what's really going on. It seems considerably more complicated than I'm willing to troubleshoot
with the cascading heat exchangers and mixed refrigerant. I was just going to re-route the plumbing and hope for the best. |
an air conditioner does not produce sub zero temperatures on the evaporator, otherwise it would frost during normal operation. re-routing the plumbing
would be ok if you wanted to make a water cooler for distillations,
but to freeze water or organic solvents in a vacuum you need lower temperatures, that's why dry ice and acetone or liquid nitrogen are used for this
porpuse |
They can, actually,
https://advanced-air.com/uploads/Coil_Frost_656_DJFss.jpg
but when sized and charged appropriately they shouldn't because it hinders their effectiveness as an AC.
The system in the video I linked was icing over and he shows the thermocouple on the cooler itself running at -38 °C which is ~4 °C above the bp of
propane (the refrigerant he's using).
[Edited on 21-10-2018 by TheIdeanator]
“I will show you fear in a handful of dust.”
― T.S. Eliot
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