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Fridge compressor cryocooler

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Marko

Wed Nov 30 2011, 01:04PM

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

Hi guys

Any refrigeration system experts around here?

I'm wondering whether a plausible cooling system with a target temperature <-100*C could be designed out of trash such as old fridge and AC compressors and parts? I know some poeple have refilled those with propane but I need a lot lower temperatures than that.

I can overdrive the compressor to perhaps 2-3 times it's rated power with an inverter but I'm not sure what refrigerant gas could be usable that has a fairly low boiling point.

I also thought of possibility of filling the system with helium and running it vapor phase, as well as cascading compressors. I ofcourse don't know if any of these ideas would work at all!

The result is to be used for cryocooled mosfet experiments.

Cheers,

Marko

Experimentonomen

Wed Nov 30 2011, 04:16PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

For temps that low i'd say you need a pulse tube or strirling cycle cooler. U can get dry ice and i think even LN2 at the gas depot, should be cold enuf for ur needs, and alot cheaper.

Pinky's Brain

Wed Nov 30 2011, 05:40PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

How much power do you have to get rid off? Peltiers are used to cool CCDs to less than that, but only because COP stops mattering for very low power.

PS. looking around, a mixed refrigerant (Kleemenko) is probably the easiest way to construct a DIY cryocooler ... if you look at the numbers in chapter 7 in this book none of it is beyond the capacity of fridge compressors ... getting the refrigerant mix at a reasonable price would probably be the hardest part.

PPS. if you are as lucky as this guy you can find a 140 Watt cryocooler on ebay for 300$ ... but I wouldn't count on it.

Killa-X

Wed Nov 30 2011, 06:53PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

There's a place around here called thermaltron. They specialise in coolers and heaters for stress testing, up to massive ones thatfit a car. I had a tour there and they had ones running negative 200F...using AC compressors. They said their compressors are like refrigerators but on steroids. Just crazy things, loved the tour.

As for C, not sure. But good luck :)

Marko

Wed Nov 30 2011, 07:49PM

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

hi guys

well, I hardly intend spending on specialized cryo equipment - if I can't get satisfactionary result from what I can do with old fridge parts I'll have find a way to ship LN2 over 250km, or just forget about this alltogether! ;)

Marko

PS. the heat pump would need to move from few watts to few hundred watts, depending on duty cycle, I presume I would be stuck on very low duty cycles though :(

Conundrum

Wed Nov 30 2011, 08:43PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Peltier first stage maybe?
With flowing water and a BIG heatsink you can get down to -50C if you use the real monster units from car aircon units.
I just found a possibly working compressor here, so will let you know if this works.
-A

Pinky's Brain

Wed Nov 30 2011, 09:04PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

To get really low with peltiers you have to cascade them.

Microwatt

Sun Dec 04 2011, 04:27PM

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

Not only do you have to cascade them but the lower stack must be bigger that the taller stack. your PT device will look like a pyramid.

Marko

Sun Dec 04 2011, 09:48PM

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

Bleh, peltiers are extremely inefficient, I don't think they are going to be much of an use for the amounts of power I need to transfer... they also seem to lose efficiency at low temperatures.

I'm pretty much only interested into fridge compressor modding, but it looks like there are poor chances for any success with that anyway.

I guess buying LN2 is the only viable option here...

Marko

Pinky's Brain

Sun Dec 04 2011, 11:37PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

One more problem with the compressor option. The compressor itself could probably be used ... but what would you do for the expansion valve? You need a larger pressure drop and it's not exactly designed for cryogenic temperatures either.

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