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725Re: Dippy bird

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  • Phil Karn
    Dec 3, 2002
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      --- In AMBIENTENERGY@y..., "marvinjasoncarter"
      <marvinjasoncarter@y...> wrote:
      > Mr. Phil,
      > I've been thinking about your statement which says "when the water
      > runs out, the bird stops even though there is plenty of heat left
      > the atmosphere." I have heard this said before and don't
      > what it proves.
      > Would this not also be true of a steam Locomotive? If it were to
      > run out of water, it too would stop even though there were plenty
      > heat left. Once and for all, what exactly does this prove?

      Good question. There's a *very big* difference between the toy bird
      and the steam locomotive. Unlike the toy bird, the steam locomotive is
      burning fuel that keeps a boiler at a temperature well above ambient.
      The steam from this boiler is used to do work against a piston, and is
      then released into the atmosphere.

      It would be theoretically possible to build a steam locomotive that,
      instead of releasing the spent steam into the atmosphere, condenses it
      back to liquid water that could be recycled back into the boiler. The
      condensor would be essentially a radiator that would absorb the waste
      heat from the steam and radiate it to the atmosphere.

      The problem is that such a radiator would be too big and bulky to be
      practical on a locomotive. But this is exactly how many large
      stationary power plants operate; that's why they have those big
      cooling towers and/or are located next to a river, lake or ocean. Such
      plants have considerably greater efficiency than gas turbine or
      internal combustion engines that simply vent their combustion products
      to the environment.

      You can close the loop with a condensor in such a steam plant because
      of the external source of energy that heats the boiler, and the fact
      that the spent steam is well above ambient temperature. Find a good
      way to pass that heat to the environment, and the water will condense
      on its own.

      But you can't do this with the toy bird because the water vapor is
      already at or below ambient temperature. It won't cool any further on
      its own, so it won't return on its own to the liquid state. So the
      liquid water becomes a consumable; when you use it up, the bird stops.

      Once again, we see that the second law must be obeyed.

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