Some advances in thermoelectric devices have come along recently[1].
In particular "rough" silicon nano-wires[2] are apparently producing
ZT values greater than 1, and the US DoD apparently has expectations
that values greater than 2 are on the horizon[3]. Further the
solicitation by the US Navy is looking to produce a first generation
thermoelectric generator prototype with 20% efficiency. On the
domestic front the various news articles relating to these advances
mention much more efficient heating and cooling (more efficient than
current mechanical refrigeration and heat pumping). In one article a
researcher mentioned going from room temperature to liquid nitrogen
temperatures in a single stage thermoelectric device used for
refrigeration.
Some questions:
How much more efficient would these devices be than the normal
mechanical method of transferring heat? (i.e. compression of gasses.)
Which I suppose we would also need to know the overall efficiency of
those mechanical means.
What is the thermal efficiency of a single stage thermoelectric device
generating electricity with a ZT of about 2? I was seeing older
references for efficiencies in the range of 10% to 18%, but they did
not seem to be in reference to the rough silicon nano-wire technique.
Since these can be operated in series and work down to below body
temperature, what application do they have for cooling the interior of
a spacecraft?
As a follow-up to the above question. Assuming that sufficient
miniaturization were to be possible, could multiple stages of these
devices be used to reduce the emissions of a spacecraft down to say 50
Kelvin? The charts from an article in _Nature_[4] seem to indicate
that they work down to roughly 25 Kelvin, albeit at a dismal
efficiency. (Of course we'd have to ignore the prohibitive mass that
this would entail, but would it work at all?)
Finally, using that electricity that is generated by the multi-stage
thermoelectric generator suggested would just generate more heat of
course. Conservation of energy says that the energy is still there
even if you do turn it into a different form. So are there ways to
store electricity easier than to store heat? Or a way of getting rid
of electricity that is easier than getting rid of heat?
1. http://www.azonano.com/news.asp?newsID=5640
http://www.lbl.gov/Science-Articles/Archive/MSD-silicon-nanowires.html
2.
http://web.mac.com/majumdargroup/iWeb/Site/Main_files/NANOTECH%20ALERT%20--%20JANUARY%2018,%202008.html#2
3. http://www.navysbir.com/n07_1/n071-086.htm
4.
http://www.nature.com/nature/journal/v451/n7175/fig_tab/nature06381_F2.html
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