I've heard that turning on faucets to a slight drip will prevent pipes from freezing, but I've never understood why this is the case. Can anyone out there help me to understand? Thanks!
Heat – Why Does a Slight Drip of Water Prevent Pipes from Freezing?
freezingheatwater
Related Solutions
If the temperature is not much below freezing, the rate of heat transfer from your plants (and particularly from the earth around their roots) is low, if there is a lot of water present, the high heat of fusion means that it will take a long time to actually freeze much of it. So maybe the plant makes it through the night without too much damage.
Note that if it doesn't warm up enough the next day the second night will kill them because it starts close to freezing.
(source: engineeringtoolbox.com)
The graph(blue lines are what you want) only goes till $50^o C$, but we can extrapolate and say that the oxygen level will become a fifth or so by the time the water reaches its boiling point.
The solubility comes from Henry's law, but I don't know the temperature dependance of the proportionality constant $k_H$--I'll check it out tomorrow and edit it in..
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Best Answer
Pipes are damaged when ice forms a complete blockage, and the expansion of water trapped by it puts too much pressure on them.
Now, ice is a pretty good thermal insulator, so once a little ice forms on the inside of the pipe further freezing proceeds slowly. If the water is flowing there will not be enough time for it to freeze between leaving the (relatively warm and protected) underground run and exiting the pipe at the dripping faucet. Thus the pipe never freezes all the way through, no blockage forms and excess pressure is never applied.