Less Wasted Energy than Carnot Cycle? wth?

[ymboc]

From a link lifted from that hardware news portal people love to hate.... "Scully's design employs lasers, mirrors and a concept known as "quantum coherence" to drive a piston with less wasted energy than in the Carnot model."

The article goes onto say...

Scully makes clear that they have not rewritten the laws of physics -- the second law of thermodynamics is not violated, he says, and perpetual motion is still a dream.

Warning: Impending ignorance

How is it possible to design a cycle "with less wasted energy" than the Carnot cycle -- I thought that the definition behind the carnot cycle was that it didn't waste any energy.... and if that is infact the case (if my memory serves) how is it possible to design a cycle 'more efficient' than the carnot cycle without violating second law.

If anyone knows where the full 'real' text for this is or can explain how such things are possible in quantum theory.. well, please shoot me a line...

Cheers

[gmat]

The mechanical (or chemical) work involved in Carnot cycle is never 100% efficient, you always have *at least* heat losses somewhere (Joule effect).

[ymboc]

Having read your post and then the second sentance on the topic of the carnot cycle from my thermo textbook... I feel awfully ignorant.

Thanks for straightening me out though... this looks like one of those mistakes I wont be forgetting.

sigh...

[futRtrubL]

While it is true that energy is lost to increase/maintian entropy in a Carnot cycle there is no energy "wasted" it is the theoretical limit dictated by thermodynamics. So I have a problem with them saying that they can have better efficiency than the Carnot cycle. Net entropy would have to decrease in such a case which would violate second law.

Entropy;
1. You cannot win.
2. You cannot brake even.
3. You cannot leave the game.

[Alchemy]

Originally posted by futRtrubL

Entropy;
1. You cannot win.
2. You cannot brake even.
3. You cannot leave the game.

Actually, those are the three laws of thermodynamics.

1. Energy is always conserved (You get what you give)
2. Real systems tend toward a state of decreasing available energy - a good definition takes quite a bit more background, so I won't give one here (You actually get less than what you give)
3. The entropy of all pure perfect crystals is zero at absolute zero (You can get what you give if this could happen, but it can't, so don't worry about it)

Alchemy

[futRtrubL]

Sorry I meant thermodynamics and not entropy, 1;45 am is not the best time for me ;']

Edward

[gmat]

I think they made that claim considering that real implementations of the Carnot cycle require some kind of mechanical device, or a chemical reaction - well, an engine - to perform the compression stage.
Their system seems to use far less mechanical components, thus involving far less losses due to mechanical constraints.
In other words, if you measure the overall efficiency (work fed / work produced) of the system, you always get less than 100%.
A good example is the Sterling engine, its efficiency is excellent but nowhere near 100%.
The only system i know that is more than 100% efficient is the breeder reactor. But again it's a special way of looking at figures, even a breeder reactor does not violate thermodynamics laws.