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RE: If an oxygen molecule...

> Charley Bay wrote:
> > Additional gas is forced into the water through
> > pressure.
> 
> and
> 
> > There are pockets of air in almost all pipes that
> > result from bacterial and chemical reaction, or
> > from turbidity in the system (stop and go flow
> > traffic, pressure changes, turbidity around bends
> > and diameter steps.)  These pockets are forced
> > into the water at higher pressure, and "de-gass"
> > at lower pressure.  If you're a drop of water en
> > route to a faucet, you really have a violent ride
> > (if you can keep yourself together at all ;-).
> 
> > More practically, plumbers know that it's always
the
> > hot water pipes that freeze and bust in the
winter,
> > because they came from the hot water heater and
> > cooled, they have more dissolved gas, so it takes
> > a smaller energy change to freeze the pipe (more
> > gas, less water, gas has a lower specific heat
> > value for a temperature change.)
> 
Douglas Guynn replied:
> I still don't understand where the gasses come from.

> Possibly, a small amount may be generated by some 
> chemical reaction after the water enters 
> the pipes. I would like to believe there are VERY
> limited spontaneous chemical reactions in the water
> one drinks.

Oh, I think I see what you're saying:  If the pipes
are a sealed system, and the surface of the water
tower is at atmosphere, how do additional gasses
keep getting forced into the system?

Remember, filling the 200 foot water tower will 
require a 100psi pump (or higher) at the base
of the tower.  Just as water moving over rapids
are super-saturated, municipality water systems
usually have super-saturated water because they
are processing a lot of capacity and ensure
mixing of fluoride, chlorine/chloramine, and any
other treatments necessary to make it safely
potable.  So, as this super-saturated water enters
the piping system, the pressures go up and down
over various parts and pockets of "de-gassed"
gas appear throughout.

Unrelatedly, I recently learned our municipality 
spends about $100K US/year just for fluoride for 
our water (supplies a population of about 100K.)

I don't have any good quantitation on the volume
of gas, but it's safe to say most of the water
in the supply system is sitting at 40psi or higher.
Normal "atmosphere" is usually 14.7psi.  So, there
is some room for saturated gas to de-gas in our
tanks after that water change.  Of course, we're
now back to your central issue of, "if the pipes
don't leak, where does the gas come from when
the surface of the water at the top of the tower
is at 14.7psi?"

I'll guess at the pumps to fill the tower, and
the super-saturated state of the supply water,
and the assumption that the system is in constant
motion so degassing water is comming from everywhere.
Maybe somebody else can jump in here.

> As to the hot/cold water freezing issue, here is
> a link to an interesting article on the subject;
>
>http://www.urbanlegends.com/science/hot_water_freezes_faster.html
> 

Cool!  I had no idea evaporation was such an issue
(26% in one case!)  Of course, if it's in your 
pipes, then it seems evaporation is minimized 
(it's a sealed container) and the biggest issue
will be the dissolved gasses in freezing the
hot water pipes before the cold.

full of hot air,
--charley


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