[AR] Re: Peltier specifications
- From: "Anthony Cesaroni" <acesaroni@xxxxxxxxxxx>
- To: <arocket@xxxxxxxxxxxxx>
- Date: Tue, 4 Aug 2015 11:56:12 -0400
Some references.
https://smartech.gatech.edu/.../041.pdf
http://technology.mit.edu/technologies/11653_thermoelectric-micro-cryogenic-cooler
www.cem.msu.edu/.../G6_2_MODULE.pdf
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Peter Fairbrother
Sent: Tuesday, August 04, 2015 11:31 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Peltier specifications
On 04/08/15 03:12, Troy Prideaux wrote:
I once worked out that to cool to LOX temps I would need about 511
cascaded Peltiers, only one of which would be actually working at
proper efficiency ... ouch.
I was under the impression that only specialised peltiers are suitable
for cryo temps.
Yes indeed.
Do you have any links for readily available peltiers that are
suitable?
No, sorry.
That "once" was in about 1974, I was doing a thermodynamic study of theoretical
but non-existent Peltiers - and I do not know whether any suitable Peltiers
even exist nowadays.
Though a few years ago I read something about developments in low temperature
Peltiers - unfortunately, while the operating temperature range was
interestingly low, the Modified Figure of Merit (which determines the number of
Peltiers needed in the chain) wasn't that interesting.
I don't think they were commercially made, though perhaps they might use some
in spacecraft or the like. Useful for a second stage cooler, eg getting to say
40K from 80K if you have lots of available power and lots of 80K sink and a
very low cooling power requirement - but no use for getting to 80K from RT (and
no use for getting to 20K LH2 or 4K LHe from 80K either).
BTW, that 511 is the length of the chain, not necessarily the number of
Peltiers used.
I made the 511 up as I couldn't remember my original figure, but afair it was
something like that. However I just read you can in theory do something useful
with about 30 steps nowadays (the length of the chain is highly dependant on
the MFoM, which has improved since 1974).
Supposing you were using only one size of Peltier, you might have three
Peltiers in one step per Peltier in the previous step; you would then need
about 3^30 or 200 trillion individual Peltiers in total.
The point of all this being that there is no sensible way to get to LOX
temperatures from room temperature using Peltiers.
You can't get there from here.
-- Peter Fairbrother
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