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Name: Joseph F.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 2001


Question:
We all know that moving water does not freeze. My question is, at what point does the temperature overtake the moving water? Is there a correlation between the volume, velocity and the temperature of the environment. An example: if I need a hose above ground and have it on all the time is there a temperature that it would freeze and at what velocity with the water need to maintain to keep it from freezing? I am hoping for some type of equation that would tell me this information.


Replies:
What you describe is a very complex problem. Running water will freeze provided that the rate at which heat is removed from the cold surface exceeds the heat required to transform water at 0 C. to ice at 0 C. However, the dynamics of this process will be very complicated depending upon the temperature of the cold surface and the hydrodynamics of the water flow across that surface (which could be air). Every sleet or hail storm involves the freezing of liquid water to ice under very turbulent conditions, for example. I do not think you will find any "simple" equation to describe such processes.

Vince Calder


With visions of huge chunks of ice floating down the Missouri River, I must differ on your point that "moving water does not freeze." Now leaving a hose running, which seems to be the gist of your question, is another story. Here, you have water that is supplied from a source that is above the freezing point of water. For example, my well brings up water at maybe, 50? Degrees Fahrenheit. If I run it through a hose on the ground, how slow can I turn it down before the water freezes up in the hose? The main variables in this would seem to be a) the ability of the hose conduct heat, b) the length of hose, c) the outside temperature, and d) the velocity of the water. As the water moves through the hose, it will lose energy to the surroundings; if it loses enough energy, it will freeze up. But alas, I don't know of any simple equation to predict this. Interesting question though. It does seem that one could work out an equation for this. Perhaps a civil engineer has to deal with questions like this.

Paul Mahoney, Ph.D.


Joseph,

It would be very difficult to develop an equation to approximate what you are looking for here. There are far too many variables, some of which I am listing below:

1. inside diameter of the hose

2. material composition of the hose (some insulate better than others

3.mini-environment of the hose (exposed to sunlight, exposed to wind, lying in insulating grass, lying on non-insulated hard surface)

4. velocity of the flowing water

5. temperature of the incoming water (which could provide a "melting' effect on the forming ice

As you can see, depending upon these and other characteristics of your scenario, you can have a range of outcomes...some where the hose could freeze solid, others where no freezing was able to happen at all.

Suffice it to say that if you hold all of the variables constant except flow velocity you may be able to develop an experiment and plot flow vs. time for water flow from the outer end of the hose to cease( frozen hose); from that you could develop your desired equation.

This is a tough one...good luck.

Thanks for using NEWTON!

Ric Rupnik



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