VASIMR

[MSimon]

These devices can achieve very high fractions of Camot efficiency at
relatively low operating temperatures.

http://etd.lib.ttu.edu/theses/available ... 017807.pdf

Carnot efficency is just used as a reference point.
"Carnot cycle" does not apply to this systems, but "Carnot Efficency" can be used as a reference tool to express their potentiality (in certain way similar to what the mach number is for jetplanes).

Go back and read Maxwell's Demon. If it is thermal energy you can't beat Carnot. Think about it: If you could beat Carnot you could endlessly pump energy from a low temp sink to a high temp one and come up with unlimited energy.

I'm sorry. But unless you get a Demon with supernatural powers (Allah wills it) it can't be done.

If The Energy Is Thermal You Can't Beat Carnot

http://en.wikipedia.org/wiki/Maxwell%27s_demon

This stuff has been publicly known since 1871. About 140 years. I guess they don't teach it in school any more.

[Giorgio]

Giorgio,

I'm going to be a little snide here (as is my won't) and claim that you not only didn't get Carnot in school (or statistical thermodynamics for that matter) you didn't even read carefully the beginning of the article you suggested.

You probably didn't understand in school that Carnot IS NOT a godsend limit for anything that happens in the universe. It applies to "thermal engines" working between "thermal reservoirs".

Carnot Theorem:
No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs.

Try to read it a couple of times, until you get clear that it refers to a THERMAL ENGINE OPERATING BETWEEN TWO THERMAL RESERVOIRS.

As soon as you go out of those boundaries, you can kiss carnot theorem and carnot efficency goodbye.
AMTEC is such an example, humans are another example.

I mean seriously guys. Except for a 12 week course in Nuke Power School I have not "officially" studied thermodynamics. None the less every few months I drag out my thermo books for exciting bed time reading. Yeah. I'm strange.

So let me put it to you straight. When it comes to thermal energy you can't beat Carnot. For further reading on the subject may I suggest a look at Maxwell's Demon. Yeah. James Clerk Maxwell.

I think it all comes down to the perniciousness of education. Being uneducated I'm sure I am more than sufficiently ignorant of any topic I might care to study. It keeps me on my toes. Educated people get complacent. It is especially bad when they think they know something that ain't so.

As you are so eager to learn, go back to study some thermodynamics and try to "understand" where you can apply the related laws and were not.

[Giorgio]

Carnot efficency is just used as a reference point.
"Carnot cycle" does not apply to this systems, but "Carnot Efficency" can be used as a reference tool to express their potentiality (in certain way similar to what the mach number is for jetplanes).

Go back and read Maxwell's Demon. If it is thermal energy you can't beat Carnot. Think about it: If you could beat Carnot you could endlessly pump energy from a low temp sink to a high temp one and come up with unlimited energy.

I'm sorry. But unless you get a Demon with supernatural powers (Allah wills it) it can't be done.

If The Energy Is Thermal You Can't Beat Carnot

http://en.wikipedia.org/wiki/Maxwell%27s_demon

This stuff has been publicly known since 1871. About 140 years. I guess they don't teach it in school any more.

Are you kidding me?

Go back to read what I have posted until now.
AMTEC is a TERMOCHEMICAL reaction!

Where did I ever say that we are beating Carnot on a thermal machine?

[MSimon]

You probably didn't understand in school that Carnot IS NOT a godsend limit for anything that happens in the universe. It applies to "thermal engines" working between "thermal reservoirs".

And the device you linked to is a thermal engine working between thermal reservoirs.

Temperature-Entropy Diagrams are provided. Quite a clue.

[MSimon]

AMTEC is a TERMOCHEMICAL reaction!

Nope. It is a heat engine. There are no reactants introduced into the system. All reactants are created thermally. It is a thermal system.

Seriously. RTFM.

Suppose we eliminated the fuel cell mechanism and replaced it with a black box. And I told you the black box could cool the cold side and warm the hot side you would tell me I'm nuts. Or suppose I told you the black box could exceed Carnot efficiency. Nuts again. Labeling the black box "chemicals" changes nothing.

There is no chemical reaction which can substitute for Maxwell's Demon.

I'm going to leave you now. I'll let others with degrees have a go at you.

You might want to contact the author of the paper though. Just to check.

[Giorgio]

AMTEC is a TERMOCHEMICAL reaction!

Nope. It is a heat engine. There are no reactants introduced into the system. All reactants are created thermally. It is a thermal system.

Seriously. RTFM.

Suppose we eliminated the fuel cell mechanism and replaced it with a black box. And I told you the black box could cool the cold side and warm the hot side you would tell me I'm nuts. Or suppose I told you the black box could exceed Carnot efficiency. Nuts again. Labeling the black box "chemicals" changes nothing.

There is no chemical reaction which can substitute for Maxwell's Demon.

I'm going to leave you now. I'll let others with degrees have a go at you.

You might want to contact the author of the paper though. Just to check.

Seriously, you are proving that you do not have a clue on how the AMTEC work, and clearly are not willing to try even to grasp the basic knowledge of that system. Oh well, your problem, this is not certainly going to change my life.

[MSimon]

OK. I'll let you go at it.

You have a hot reservoir. You have a cold reservoir. You are extracting energy.

Please explain to this uneducated feller how you can beat Carnot. Obviously I am in serious need of an education on the matter. Provide one. If you can. Show me how you can reduce entropy. Or at least beat Carnot.

I wonder why folks running chemical plants with thermal energy aren't all over this.

[Giorgio]

OK. I'll let you go at it.

You have a hot reservoir. You have a cold reservoir. You are extracting energy.

Please explain to this uneducated feller how you can beat Carnot. Obviously I am in serious need of an education on the matter. Provide one. If you can. Show me how you can reduce entropy. Or at least beat Carnot.

I wonder why folks running chemical plants with thermal energy aren't all over this.

Please explain the folks here why you keep saying that I affirmed that I can beat carnot efficiency on a thermal engine.

Please provide a quote where I said that.

English might not be my mother language, but I think my posts were clear enough. Try to read them again.

I wonder why people who have no arguments keep trying to put in the mouth of other people words they did not say just for the sake to prove that they have knowledge.

[MSimon]

Giorgio asks:

Please explain the folks here why you keep saying that I affirmed that I can beat carnot efficiency on a thermal engine.

Please provide a quote where I said that.

viewtopic.php?p=35802#35802

viewtopic.php?p=35795#35795

This one is particularly good:

viewtopic.php?p=35775#35775

"the AMTEC cell, being an electrochemical converter of heat to electricity, has no moving parts and is not limited to Carnot-cycle efficiency."

I hate to break the news to you but the lack of moving parts does not mean it is not a heat engine.

Now I know you got that from the abstract. But you know what I think? The abstract is flat out wrong.

If you are operating between an energy source and an energy sink using the heat energy and temperature difference to do work (on electrons or mechanical shafts - makes no difference) you can't beat Carnot.

There is nothing special about a chemical vs a mechanical engine when it comes to Carnot. Carnot uses black boxes.

[Giorgio]

Giorgio asks:

Please explain the folks here why you keep saying that I affirmed that I can beat carnot efficiency on a thermal engine.

Please provide a quote where I said that.

viewtopic.php?p=35802#35802
viewtopic.php?p=35795#35795

There is nothing written there about what you are stating. Please quote the words, I am curious to see.

This one is particularly good:

viewtopic.php?p=35775#35775

"the AMTEC cell, being an electrochemical converter of heat to electricity, has no moving parts and is not limited to Carnot-cycle efficiency."

I hate to break the news to you but the lack of moving parts does not mean it is not a heat engine.

Now I know you got that from the abstract. But you know what I think? The abstract is flat out wrong.

If you are operating between an energy source and an energy sink using the heat energy and temperature difference to do work (on electrons or mechanical shafts - makes no difference) you can't beat Carnot.

There is nothing special about a chemical vs a mechanical engine when it comes to Carnot. Carnot uses black boxes.

Plain flat wrong, becouse Carnot is referred to "heat reservoirs and heat sinks" and not to "Energy Source and Energy Sink"
This completely proves your poor knowledge and lack of comprehension of what a Carnot Cycle and Carnot Efficiency is all about.
Do you understand the exact meaning and the difference of those definitions?

But wait, for sure you will not accept this from someone that you believe did not even take thermodynamic at university, so I will let someone else explain this to you:

Prof. Christopher F. Edwards, professor of Mechanical Engineering at Stanford University:
http://gcep.stanford.edu/pdfs/8fZLzZEhu ... rds_04.pdf
or
http://gcep.stanford.edu/pdfs/i6W09tDtK ... rds_07.pdf

The introduction looks tailored for you:

....based on the realization that current internal combustion engines have been designed based upon an incorrect premise that they are subject to limitations based on the Carnot efficiency.
This misconception persists because these engines are often modeled as heat engines subject to Carnot limitations, when in fact, they are chemically reactive engines which are not subject to Carnot proscriptions. The Carnot misconception has led to erroneous conclusions about the architecture of efficient combustion engines.
The most serious of these is that it is necessary to make the peak temperature in the cycle as high as possible (so as to improve the Carnot limit).
That this is not correct is confirmed by experiences with homogeneous-charge compression-ignition (HCCI) engines—engines that achieve higher efficiency than their SI counterparts while reducing the peak temperature. The ultimate example of both the inapplicability of the Carnot criterion and the benefits of low-temperature reaction is the fuel-cell—a reactive engine with first-law efficiency potential in excess of 90% when operated at low temperatures.

Is it clear enough now?

Please, study some more thermodynamic, understand the difference between the various definitions, learn when and "where" you can apply Carnot, and after we can discuss this a little bit more.

Or you can write a mail to Prof. Edwards and ask him, maybe he will find some time to explain.

[MSimon]

Please explain to me how this:

If you are operating between an energy source and an energy sink using the heat energy and temperature difference to do work (on electrons or mechanical shafts - makes no difference) you can't beat Carnot.

There is nothing special about a chemical vs a mechanical engine when it comes to Carnot. Carnot uses black boxes.

Is different from this:

Plain flat wrong, becouse Carnot is referred to "heat reservoirs and heat sinks" and not to "Energy Source and Energy Sink"
This completely proves your poor knowledge and lack of comprehension of what a Carnot Cycle and Carnot Efficiency is all about.
Do you understand the exact meaning and the difference of those definitions?

And the automobile is a chemical engine that is not limited by Carnot? I'd like to know why auto engineers have not been using these methods to figure out how to double auto efficiency. They fight for .1% improvements and you claim they should be looking for factors of 2X. How did they miss the obvious?

Unless you are saying that using the gasoline in some fuel cell will be different. If so I agree. Direct use of chemical energy is not limited by Carnot.

But this engine you link to is not a direct user of chemical energy. It uses thermal energy. Thus the Carnot limitation.

[Giorgio]

This:

energy source and an energy sink.

has nothing to do with Carnot.

And the automobile is a chemical engine that is not limited by Carnot? I'd like to know why auto engineers have not been using these methods to figure out how to double auto efficiency. They fight for .1% improvements and you claim they should be looking for factors of 2X. How did they miss the obvious?

Simple, becouse is not easy and we do not have yet the right materials which is what I stated in my first post of this thread.
If you take the time to read those 40 pages from Prof. Edwards, at the end you can read:

A key result of this project, as discussed in Sections 1 through 3, is that we now understand what is required to develop a simple-cycle combustion engine with 75% efficiency:
... omissis.....
If successful, this work will pave the way for the design of ultra-efficient engine

Unless you are saying that using the gasoline in some fuel cell will be different. If so I agree. Direct use of chemical energy is not limited by Carnot.

But this engine you link to is not a direct user of chemical energy. It uses thermal energy. Thus the Carnot limitation.

Always from the same PDF:

....... we began to develop a fundamental understanding of the architectural requirements for a simple-cycle engine driven by unrestrained reactions and their implications on the engine efficiency, bridging the abstract notion of resource exergy and the second-law limit for specific engine design.

[R.Nkolo]

STS-135: NASA managers discuss mission outline ahead of approval decision
July 9th, 2010 by Chris Bergin

although the late June 2011 flight may allow for launching the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine, which would be tested by aiding the ISS altitude control – such as reboosts.

The engine – otherwise know as an Electro-thermal Plasma Thruster or Electro-thermal Magnetoplasma engine – uses radio waves to ionize and to heat propellant and magnetic fields to accelerate the resulting plasma to generate thrust.

However, due to the power requirements at the ISS, the engine will only be put through minimal testing. Several other working assumptions are also pre-empted for the notional mission, which will undergo evaluation during Monday’s meeting.

[WizWom]

If it is thermal energy you can't beat Carnot. Think about it: If you could beat Carnot you could endlessly pump energy from a low temp sink to a high temp one and come up with unlimited energy.

Technically, if you can use the universe as an energy sink (drawing in from a cold source) the Carnot efficiency of your delta-T between high temp and exhaust is misleading

[D Tibbets]

If it is thermal energy you can't beat Carnot. Think about it: If you could beat Carnot you could endlessly pump energy from a low temp sink to a high temp one and come up with unlimited energy.

Technically, if you can use the universe as an energy sink (drawing in from a cold source) the Carnot efficiency of your delta-T between high temp and exhaust is misleading

Um, that makes sense to a degree. If your heat sink is ~ 3 degrees K, you have a larger temperature differential. But, that is also missleading. I think the gradient would be limited by the temperature range in your energy exchange medium. Generally water for power plants. So long as you stay in its gasous form, your bottom temperature is essentially the boiling point of water (100 degrees C or 376 (?) degrees K). The top temperature is limited by the containment materials that can stand that temperature and pressure (pressure is important as that determines the energy density (sort of like in a Polywell), and/ or the limits of the fuel (can't heat the water past the temperature of the burning fuel).

Dan Tibbets