What temperature does moving water freeze at?

[robphippen]

Having thought a little about this, I am guessing that the additional kinetic energy in moving water means that it would freeze at a higher temperature than stationary water. Is that right?

 

[turbo]

Look at little brooks and streams. Did the moving waters freeze before the still waters?

 

[robphippen]

Yes, that's exactly the point. What I would rally like to know is if there is a known relationship between velocity of water and it's freezing point. Temperature is in general a measure of the (randomised) kinetic energy of water molecules. So I have wondered exactly how the non random kinetic energy of moving water affects it's freezing point.

 

[Studiot]

Flow movement does not directly affect freezing point.

If you conduct a thermal melting/freezing experiment in lab you stir the pot.

Suspended/dissolved material does affect (lower) freezing point and moving water can carry a greater load.
Further, moving water is subject to frictional heating, like anything else, so if you probe the temperature of a moving stream you will find it is above zero C, even when the local environment is below.

 

[robphippen]

Having thought it through a little more, I've realized that I was doing some muddy thinking. If all the molecules in some water are moving in the same direction, it won't affect the effective water temperature at all. To state the obvious, a glass of water in a jet plane doesn't boil a when the plane takes off, and yet the water molecules are all moving rather quickly! It's all to do with how fast they are moving relative to each other - their tendency to fly apart. This does not change for the water in the glass in the jet, and out won't change either for flowing water (apart from the valid comments made about the heating effect of the moving water coming into contact with eg the edges of whatever it it's in)

 

[Studiot]

Good thinking, Rob.