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Thermodynamics

Discussion in 'Off Topic' started by doug, Oct 8, 2008.

  1. doug

    doug Administrator / Head Moderator

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    Ehh... not to be a stickler, but thermodynamics are always a factor. Like it or not, the topics of energy efficiency and transduction fall under the umbrella of the subject labeled as Thermodynamics. My guess is it's an historical point and that likely these principles where first quantitatively illustrated with heat engines. Although heat transfer is not always involved, the "principles of thermodynamics" permiate all of physics.
     
  2. GSP

    GSP Member

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    Doug,

    I appreciate your thoughtful comment, which helped me to think a little bit deeper about the subject. I must admit I'm a little confused. I suspect you have a deeper, more fundamental, scientific understanding of the subject than I do. I'd appreciate your thoughts on the following:

    1) Efficiency: Does thermodynamics explain the details of the I2R and Iron losses in an electric car? I think of this as being Electrical Engineering.

    2) Transduction: Certainly thermodynamics explains the conversion of heat to mechanical energy. Does thermodynamics also explain the conversion of electrical energy to mechanical energy (and visa versa) in a Motor/Generator? I thought Maxwell's equations (electrodynamics) would be used here.

    3) Heat Transfer: I consider this also to be a different discipline than Thermodynamics. Would you agree?

    Thanks for your thoughts,

    GSP

    PS. Even if this is all thermodynamics, it still didn't kill the electric car (as Mr. Flint incorrectly asserts), which have much better energy conversion efficiency than ICE cars. The challenge for electric cars is that batteries don't have the specific energy of a gas tank! :smile:
     
  3. doug

    doug Administrator / Head Moderator

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    Sure. :smile: Like many things, it comes down to language. From what you've said, I guess there's a difference between the subject of Thermodynamics (what one might say meaning a course an undergrad sophomore physics student might take or a section in a chemistry textbook), and what physicists think of as the "principles of thermodynamics." In the former, one would probably cover topics like heat engines and the Carnot cycle, define terms like "adiabatic" and "isentropic," and learn some algebraic (somewhat hand-wavy) equations to do some basic calculations. The latter refers to deeper, fundamental rules of the universe kind of stuff, which is codified in 3, 4, or 5 laws (depending on who's doing the codifying). You'd cover these Laws of Thermodynamics in a Thermodynamics course, but their scope is much wider than that.

    The most relevant ones for us are those labeled as the First and Second Laws of Thermodynamics. The First Law is about the conservation of energy. The take home message being that the best you can do with any closed system is to break even. The Second Law is more mysterious since it has to do with entropy, which can be an almost philosophical concept (although we have some nice mathematical expressions for it in statistical mechanics and in information theory). But the take home message for us with this Law is that you can't even break even. I.e. there are always losses. (This was surely a great disappointment to those trying to make perpetual motion machines at the time this principle was discovered.)

    So maybe you get my point now. Though, you'd probably best use the mathematical tools taught in an electrodynamics course for the examples you mention, or the math of nuclear physics to calculate the efficiency of a fission reactor, or the latest theories on quantum gravity to see what happens to information when it goes down a black hole, these are all governed by the First and Second Laws of Thermodynamics.

    If, for example, these principles had first been discovered within the context of E&M theory, they might have been called the "Laws of Electrodynamics." But history is such as it is.

    I guess I meant to say "heat flow." I was just referring to the Greek etomology of the word "thermodynamics" which means something like heat-change/motion. However, I can think of a few examples where you would talk about heat transfer in the context of a thermodynamics course. I suppose if we were talking about practical thermal conductivity, you might better describe it with solid state physics or materials science (both of which are still governed by the principles of thermodynamics :wink:).

    Agreed!
     
  4. GSP

    GSP Member

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    Thanks Doug for the detailed, and very helpful, explanation. :smile: I guess, as you suggest, it does come down to:

    1) Language

    2) What was covered in my sophomore thermo class, vs. the wide applicability of the first and second law. :wink:

    GSP
     
  5. TEG

    TEG TMC Moderator

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  6. daniel

    daniel Active Member

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    From the British comedy team of Flaunders and Swan, several decades ago:

    "You can't move heat from a cooler to a hotter;
    you can try it if you like but you far better not-er,
    cuz the heat in the cooler will get hotter as a rule-er,
    and that's a physical law!

    "Heat is work and work's a curse.
    And all the heat in the universe
    is gonna cool down, cuz it can't increase,
    and there'll be no more work and there'll be perfect peace.

    "That's entropy, man. That's entropy."
     
  7. dpeilow

    dpeilow Moderator

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  8. Doug_G

    Doug_G Lead Moderator

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    Doh!!!! :rolleyes:
     
  9. doug

    doug Administrator / Head Moderator

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    Oh man... Well I'm gonna give him the benefit of the doubt and assume the interviewer misheard him. Probably he said something like:
    This makes more sense because Boyle's law is taught as part of thermo and he was probably trying mention British scientists. Otherwise mentioning Boyle's law seems rather random.

    Loved this comment, though:
     
  10. Norbert

    Norbert TSLA will win

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    Nothing against the first law of thermodynamics, but I'd propose that it was more the 'conservation of money', than the 'conservation of energy', which "killed the electric car". Just wanted to point out the obvious, given that probably most here saw the movie. :)

    At that time, car manufacturers where unwilling to finance the continued development of EVs all by themselves (except perhaps in the lab, as Nissan did for battery development), and found a way out of it. Of course the then current state of battery technology made it difficult, but why would a society shy away from this difficulty? The constant improvement of battery technology was already apparent. Ironically it is being pointed out, all the time, that Tesla as a company is not yet making profit. However, the best I know, Tesla is the primary company demonstrating the real-world possibility of building and selling highway capable ("real") electric cars ..... with profit.

    And they demonstrated this as a start-up. Companies like GM, Toyota, or Ford, should have been able to do so easier and sooner... if the actual reason had been the battery technology itself, as it becomes convenient to say nowadays.

    Perhaps, the insight that electric cars can be desirable even with home charging only (without a charging infrastructure), was necessary for Tesla to get to this point. However, that point is now (more or less) history, and I believe the next thing to demonstrate is that a working infrastructure can be done, in the real world, as well. And implicitly, to demonstrate that EVs are not a niche product by nature. In the US, it seems that the Leaf with a range of 70-100 miles and 50 kW charging isn't completely convincing yet (in regard to this second step), but the Model S will likely make that point, and even if not, it won't be far. After that, it will be primarily about reducing cost for a wider market share, while the Model S will already make profit.

    Many EV critics appear to have doubts that it will... and to me, that confirms the point above.

    At the same time, another factor is that solar energy is now getting closer to grid parity (being profitable enough), and that adds a lot of enthusiasm to the equation.
     

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