On Fri, 5 Dec 2014 05:53:54 -0800 (PST), TimR
wrote:

On Thursday, December 4, 2014 5:12:54 PM UTC-5, micky wrote:
Take the same care with the hot water pipes you do with the cold. It
turns out hot water pipes can freeze sooner than cold water.


I'm familiar with the Mpemba effect, but didn't know it applied to water pipes. Is there evidence for this?

I think I first heard about it on this ng, wrt water pipes. It wasn't
called by any special name then, so to search for the post one would
have to look for freeze or frozen and hold and cold water and pipe, and
it's probably not worth it. I don't remember for sure if the poster was
telling about what he heard or what he had happen at his own home.

I think it's for real. Wikip gives a bunch or reports for this as far
back as Aristotle and including Francis Bacon and Descartes.

Wikip things the definition of freezing is important. Agreement on what
is freezing would be important to duplicate these earlier reports, but
it's not important otherwise. Whatever definition is used for hot water
should be used for cold water, Duh.

Of course if you leave the cold water running and don't run the hot
water until it freezes, the hot water will freeze first. No one is
talking about that. It certainly seems possible to me that when water
is heated it changes physically so that it then cools more quickly.
That's a lot less strange than 1000 other things that happen on earth.
I've never been close enough to a bunch of water molecules to see what
happens.

How long the Mpemba effect would last I don't know. If the water bursts
from the pipe, fills the yard, seeps into the drit, makes its way to the
stream, the river, the ocean, and is evaporated by the sun, and then
falls as rain, would that water drawn from a spring, lake, or well still
freeze more quickly than water which had never been heated? We should
use radio transmitters like they use for wild animals to track
individual molecules of water so we can be sure. And how much of the
water in the world has been heated artificially, with fire or electric
heat, above the maximum outdoor temperature. Doesn't someone know what
fraction of all the water that is?