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  1. #1
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    why useful "perpettum mobile" is not possible in thermodynamics ?



    Maybe it sounds naiive, but still.
    With a typical COP of a heat pump = 3 and it's heat energy produced, for instance = 3kW, why is not it possible to utilise just 1 kW of the heat but the other 2 kW of the heat energy produced to convert back into 1 kW of the electrical energy to power up the heat pump itself ?



  2. #2
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    In one word,

    Losses.

    Sorry, nothing created by humans will run lossless.

    There is another flaw in your reasoning, the heat pump doesn't actually generate the 3 kW in your example above. It uses 1 kW of electrical energy to transfer 3 kW of thermal energy...




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  3. #3
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    Clear. Thank you.

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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    Why could not all the 3 kW of the heat energy transferred from the outside into inside be converted into 1kW of the electric energy feeding the heat pump ? (including losses)

  5. #5
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    OK,
    What would you utilise to transform the thermal energy (heat) in to electrical or mechanical energy?



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  6. #6
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    Thermocouple effect, or some other means.

  7. #7
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    Look at energy transfer as if there is always some drawback.
    If you fill a clean dry pint glass with water and then transfer the water to another container, you will not transfer the whole 1 pint. Some of the water will stick to the original container, meaning that you have transfered less than you originally put in.

    It's the same with energy. Daltons First Law of Thermodynmics states that energy cannot be created or destroyed - only transfered. The transfer always uses some of the energy so the total transfered is always less than the initial value.

    For perpetual motion, you must achieve at least the same energy transfer in and out...but that's not possible.

    On fridge systems, the energy input to drive the compressor is measured against the energy transfered by the refrigerant.. the 2 are quite seperate...i.e. there is no excess energy that can be recovered to do other work, unless you look at the heat energy rejected from the condenser as waste heat
    I'm back on the Pale

  8. #8
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    Re: why useful "perpettum mobile" is not possible in thermodynamics ?

    How much heat is required to produce 1 kW electricity ?

    Wiki answers'
    "Best Answer"

    Probably 1.5 to 2 Kw, depending on efficiency.





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    Last edited by Yuri B.; 20-10-2012 at 05:04 PM.

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