# Physicists help needed!!! Current technology limitations.

Discussion in 'General Science & Technology' started by Tirstan, Nov 15, 2005.

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1. ### MetaKronRegistered Senior Member

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5,502
It's misleading. Maybe the party line on this changed, which would shock me, but most of my life when I read about it, the Carnot number was taken to mean much like the maximum fuel efficiency. Another way to say it is that the Carnot percentage equals the percentage of the available heat that you can possibly use. Anyone who is somewhat knowledgeable would automatically say that the amount of heat available is that amount that is over the ambient temperature.

The habit is to take the Carnot number as the maximum possible fuel efficiency. I can't tell you if that habit has changed, but it definitely prevailed in all the literature that I used to read. Reading the equation, for example, if you get a result of 10 percent from the equation, that supposedly means that you can only get 10 percent fuel efficiency. This means that you get 10 percent of 10 percent and you wonder how we can afford to get from one place to another, not that we actually can. This is taken to mean that the use of low temperature differential heat sources is futile, and fuel efficiency goes up the higher your hotside temperature.

I have also seen complicated explanations of why 10 percent of 10 percent that remind me of the epicycle explanation of planetary retrograde motion.

Right now people sell Stirling engines and their advertising says that they're like 7 percent efficient. I don't know if there's a law or what, but if hotside temperature and cold side temperature are such that their Carnot number is 7 percent, then some people will say that they have to say that their engine is 7 percent efficient, even if 100 calories worth of fuel gave you 100 calories useful energy at the output. This seems to me like the kind of mathematical trick that some people use to say that they have invented perpetual motion but in reverse.

http://en.wikipedia.org/wiki/Carnot_heat_engine

3. ### loki_ghostRegistered Senior Member

Messages:
89

i don't know the difference between diesel and gas. we probably ''hit the throttle'' just in case we choose for the ''next'' dimension. we have to choose for gas, diesel is not an option, too many carbonmonooxide. invest in catalysts?
kevlar? after 2012 we go for steam and ''zero-point'' energy.

regards,

loki (greenpeace-member).

5. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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23,198
to MetaKron:
Your post today at 20 after the hour reflects a lot of misunderstanding about Carnot cycles and related things, but the wikipedia reference you gave is good.

I think it a little formal for you (and many others also) as it is built on entropy, which few really understand.

The four numbered text paragraphs next to the first Temperature vs. Entropy diagram are better. They are more easily understood in a Pressure vs. Volume diagram, - I gave them in my post of 13 Dec. at 11 minutes after the hour and suggested how one can also prove that the Carnot cycle is the best for converting the low grade heat energy into high grade mechanical energy (or electrical energy etc)

The proof given in wikipedia with entropy is more mathematical and easier to demonstrate mathematically than one built on the cycle shown in a P vs. V diagram of it, but if you do take the trouble to go thru the one I suggested, you will understand because you understand that pressure pushing on a moving piston is doing work and in the two compressive legs of the cycle the flywheel is losing energy to compress the working fluid - no complex understand of entropy required.