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   Undertoad  Saturday Dec 1 01:26 PM

12/1: Coffee cup Stirling engine



Apparently this little gismo has been used to introduce students to the Stirling engine, but I've never seen it. Stirling engines work with a sealed chamber and a piston where one side is hot and the other side cool. So if you place this engine on top of a really steaming hot cup of coffee, it will crank. And if you place this engine on top of a really cold plate of ice chips, it will crank... the opposite direction!

Stirling engines are extremely efficient, entirely clean, but so far they have been impractical to use because in order to be powerful they need a really wide variation in heat - more than just the difference between room temperature and the temperature inside a coffee cup. Apparently they also suffer from taking a long time to get up to speed.

Stirling engines were thought of 160 years ago as an alternative to then-dangerous steam power.



They don't have to look like hobbyist/kit stuff.

I really have to wonder if Douglas Adams (r.i.p.) knew about this coffee cup engine when he wrote (in the <i>Hitchhiker's Guide to the Galaxy</i>) about the infinite improbability drive requiring a really hot cup of tea to operate!



dave  Saturday Dec 1 01:32 PM

Obvious use: stirring coffee.



Count Zero  Saturday Dec 1 01:45 PM

They could use it to heat another cup of coffee, and then put a second engine and connect to the first cup.

I bet no one thought of that !



jaguar  Saturday Dec 1 03:43 PM

I think the second(?) law or thermodymanics would kick in around there...



blase  Saturday Dec 1 03:50 PM

I was looking at these things just yesterday! What a cool engine, if you've got the money here's where you can buy them. They even come in kit form for those DIY types.

http://www.stirlingengine.com

The pic on the front page is of a Stirling engine that runs off the heat of your palm.



blowmeetheclown  Saturday Dec 1 05:18 PM

Quote:
Originally posted by jaguar
I think the second(?) law or thermodymanics would kick in around there...
"In this house we obey the laws of thermodynamics!"
-Homer J Simpson


Count Zero  Saturday Dec 1 09:23 PM

Quote:
Originally posted by jaguar
I think the second(?) law or thermodymanics would kick in around there...
The second law of thermodynamics states that the entropy of a closed system always increases.

Actually, no thermodynamics law directly dictates that perpetual motion isn't possible.

If you try to build a thermodynamic cycle that is ideal, i.e. is the most efficient, you get what is called a Carnot cycle. Everything that is more efficient than that is banned from existence.

My gedanken experiment with two coffee cups and two engines is such a case. :p


CharlieG  Sunday Dec 2 06:45 PM

Quote:
Originally posted by blase


...snip

The pic on the front page is of a Stirling engine that runs off the heat of your palm.
Jerry Howell sell some nice kits for this (if you have your own shop)

http://www.jerry-howell.com/

his "miser" will run on hand heat - in fact I saw one run on the difference in heat betwwen a tale top and the air around it!


jaguar  Tuesday Dec 4 02:29 AM

argh what?
Could have sworn it was that you cannot create or destroy energy...
i'm on holidays i'm not meant to THINK =p



ChrisD  Tuesday Dec 4 02:08 PM

http://www.howstuffworks.com/stirling-engine.htm



Scopulus Argentarius  Wednesday Dec 5 12:42 AM

Quote:
Originally posted by Count Zero


The second law of thermodynamics states that the entropy of a closed system always increases.

Actually, no thermodynamics law directly dictates that perpetual motion isn't possible.

If you try to build a thermodynamic cycle that is ideal, i.e. is the most efficient, you get what is called a Carnot cycle. Everything that is more efficient than that is banned from existence.

My gedanken experiment with two coffee cups and two engines is such a case. :p

Oh...gawd....flashbacks from my Thermodynamics and Statistical Physics class...

mommy please make it go away ...


:-)





(actually the class wasn't so bad)


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