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Re: you guys are asholes

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On 3/20/16 10:27 AM, James McGinn wrote:
> I'm not so sure it's right to equate water vapor with steam.


   Sublimation, evaporation and boiling all create water vapor, the
   gaseous phase of water.


   The physics and thermodynamics of steam – the long version
> http://geosci.uchicago.edu/~moyer/GEOS24705/Notes/SteamNotes.pdf

> Second, what is steam? The English language is a little fuzzy here.
> Some definitions say that any water vapor (H2O in gaseous form
> instead of liquid) is steam. By that definition, the atmosphere
> itself is a very low-temperature steam engine. Other definitions say
> that steam is water vapor if the water vapor happens to be boiling.
> (Which brings up another question: what does "boiling" mean?)
> Finally, a third definition says that steam is "pressurized water
> vapor", i.e. water vapor at a pressure higher than 1 atmosphere.
> Those are incompatible definitions, which makes clear thinking
> difficult.

> Let's start with the question of what boiling is, and even before
> that, how vapors and liquids interact.

> We all know from our experience that the atmosphere contains some
> water vapor at all times, even at temperatures well below what we
> might think of as the "boiling point". We talk about the humidity,
> and know what a humid day feels like.

> In a very qualitative explanation: whenever/wherever there is liquid
> water, some of the water molecules "want" to be in gas phase. If you
> bring a pot of water into very dry air and wait, you'll find that
> some water from the pot evaporates (i.e. some of the molecules move
> into the gas phase), until eventually the liquid and vapor reach
> "equilibrium". At that point the liquid water and vapor are somehow
> in the state they "want" to be in and their proportions stay
> constant.

> If you heat up that pot of water, however, more water "wants" to move
> into the gas phase. You have some intuitive sense that hot air holds
> more water vapor: a hot summer Chicago day feels damp to you, while
> cold winter air feels dry.

> The amount of water that evaporates as you warm the water is
> described by a very simple and beautiful relationship, named after
> its two independent discoverers, Clausius and Clapeyron. The
> Clausius-Clapeyron equations states that the equilibrium "partial
> pressure" over liquid water -- the pressure that you'd measure if you
> had only water vapor and no extraneous air molecules -- is a function
> only of temperature.


   There is much more, James.


-- 

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you guys are asholes "James McGinn" <iwetmyself@yourhouse.com> - 2016-03-20 15:27 +0000
  Re: Why do you think you are not ? Poutnik <poutnik4nntp@gmail.com> - 2016-03-20 18:13 +0100
    Re: Why do you think you are not ? James McGinn <jimmcginn9@gmail.com> - 2016-03-20 10:17 -0700
      Re: Why do you think you are not ? Sam Wormley <swormley1@gmail.com> - 2016-03-20 14:51 -0500
  Re: you guys are asholes Sam Wormley <swormley1@gmail.com> - 2016-03-20 14:37 -0500

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