"Everything there is to know" about Peltiers including free design 
software for use as heaters, coolers and thermoelectric generators

        http://www.melcor.com/index.html

Product prices are rather high alas.

Their TEG design software shows that my target power output is 
achievable with a sensible albeit rather more costly than desired 
number of Melcor units. Even at (only) 100C hotside performance is 
bearable. Results with NNB (no-name-brand) modules yet to be seen.

At 113 C *COLD* side and 200C hot side efficiency drops nastily (as 
expected) to about 2.5% BUT this shows you can run with boiling water 
as your coolant and a flame source as the hot side. The software will 
not let you design for Th > 200C (funnily enough).

At 15C cold and 200C hot and a matched load, effciency of around 8% is 
achievable. (20% of Carnot efficiency of 40%). This is a commendable 
result.

The greatest challenge is liable to be getting a suitably low thermal 
resistance cold side heat sink.

eg at 200C hot, 15C ambient and 92 C cold side (!!!) using air cooling 
a 0.1 C/W cold side heat sink is needed.
For 29.2 Watts out (my spec was 2A at 14V) heat flow is 800 Watt for 
3.6% efficiency..

At 20% net efficency an 8kg LPG bottle would last about 20 hours :-(.

Going to a 0.01 C/W nonexisteum heat pipe heatsink (or a stream) gives 
matched load efficiency of 7.7% (double)

Matched to unmatched load efficiencies can vary by a factor of over 
2:1 so use of a variable input-voltage power converter inverter to 
allow source tuning seems wise.


My 10 x 68 W no-name-brand Peltier modules turned up yesterday. 
Haven't tried them yet. Stay tuned ... .


        Russell





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