James and all,

Let's be realistic.

Set me the MINIMUM possible spec that you would find useful and I'll 
see whether I can make a realistically realisable proposal for it. 
This is an *absolute minimum* spec real device, not a toy, that would 
be borderline acceptable as a demonstrator that Stirling had its 
place.

Bear in mind the alternatives.

Bear in mind that peak *POSSIBLE* theoretical efficiency is 
(Thot-Tcol)/Thot in absolute degrees. (ie Degrees in Kelvin, or 
Centigrade plus 273, or
 Fahrenheit plus 590 (if you must). A good working point is 600K 
giving 50% Carnot efficiency. Actual will be lower, much lower or much 
much lower than that. To be fair start with the best you can hope for 
from the best diesel you know and halve it. That makes allowance for 
100 years odd development and millions of dollars of production costs 
to startup and more.

I'd say that 10% was commendable and 20% was frabjous.
I'd say that 5% was proof of concept reasonable.

Consider the *minimum* possible mechanical power out that would be 
useful - more than just a toy. I'd say 10's of watts would be a fair 
starting point. 50 Watts good. 100 Watts excellent. At 10% 100 Watts 
out is 1 kW in. At that rate a 7 kg Propane bottle would last say 50 
hours. And run a laptop and a radio and ... . Or charge an RV 
accessories battery at 8A or so.  Useful.

Note that many hydrocarbons deliver AROUND 10 kWh/kg. Good wood and 
coal similar. Hydrogen far more, but not what we are really looking at 
here. Various not so good fuels still rate in the 5 kWh/kg range. So a 
good burner MIGHT use say 200 grams of wood an hour. That's not a lot 
of wood!

Whats the absolute largest you'd accept.
What's the absolute heaviest you'd accept.

Bear in mind that you need to cool this to 200 K = 27C at the cold 
end.
Bear in mind that cooling source needs to be lowe rto allow for delta 
t.
A stream would help.

BUT if you allowed cold end to rise about 100C you can use it for 
boiling water source, thereby making it really useful. And steam 
generation sets a rather practical cold end cooling method if desired.

For a 600K hot end with 100C = 400K cold end that takes Carnot 
efficiency down to (600-400)/600 = 33%. To get back to 50% Carnot Z 
you need 800 hot = about 500C hot end.

So. Lets hear people's reasonable specs for weight, size, power and 
efficiency that THEY think would make a Stirling a viable small energy 
converter. Bear in mind that you can make that hot end temperature any 
way you like. Unlike an IC engine where you need just right diesel or 
petrol or LPG or whatever, here you simply need to deliver 300C plus 
via solar, petrol, biodiesel, used cooking oil, used sump oil, diesel, 
wood, saw dust, fluidised bed garbage, coal, coke, dung, rice husks, 
lp or other g or whatever. If you can burn it and make the temperature 
and energy level required the Stirling will use it.

Let's negotiate this spec DOWN to a level that the majority would 
grudgingly accept and then lets see if it looks like it can be done. 
Cost hasn't bene mentioned. By all means suggest cost in 1 / 10 / 1000 
/ 100,000,000 quantities. (Prototype, small trial, small group, 
yeeha). 100 million of these could be rather useful.

Also suggest reasonable spec for reliability in whatever terms desired 
and maintenance effort and cost. Be fair.



        Russell






-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist