Relationship between turbulence and freezing?

[johnnykatz]

How fast do i need to pump water in a 10" aluminum pipe to prevent freezing? Assume 32*F inlet temp and 0*F ambient . For my conditions, the temps will vary and T ambient easily gets down to -20*F or more.

 

[xts]

The conditions you gave are just at singularity: 32F is a freezing point, so even smallest amount of heat lost to environment causes freezing.

But even if you ask about inlet water at +1C - the situation still depends on environmental conditions (esp. wind, but also if your pipe gets covered by frost).

Practical answer is: never use uninsulated aluminum pipes to pump cold water if ambient temperature is likely to drop much below 0C

 

[klimatos]

How fast do i need to pump water in a 10" aluminum pipe to prevent freezing? Assume 32*F inlet temp and 0*F ambient . For my conditions, the temps will vary and T ambient easily gets down to -20*F or more.

Why do you think that moving water does not freeze. As a native of Michigan, I can tell you that it freezes quite readily whenever temperature drop below 0°C and icing nuclei are present--moving or not moving.

 

[johnnykatz]

I understand the practical answer and the additional heat loss concepts.
My question aims at how the nature of turbulence affects the freezing point. From my observations, it is much harder to freeze turbulent water (fast moving streams in sub zero temps, ocean water, etc)
Couldn't the concept of supercooling apply here?

 

[xts]

Turbulence has no effect at all.

Effect on fast rivers and ocean is only such, that if they mix, they just drop some temperature in the whole volume, which is large enough to keep them liquid, while still rivers freeze on their surfaces, while close to bottom the water remain at +3C or so.

But even dramatically turbulent water (like waterfalls) freeze - you may see that in northern mountain regions.

 

[johnnykatz]

Turbulence has no effect at all.

Effect on fast rivers and ocean is only such, that if they mix, they just drop some temperature in the whole volume, which is large enough to keep them liquid, while still rivers freeze on their surfaces, while close to bottom the water remain at +3C or so.

But even dramatically turbulent water (like waterfalls) freeze - you may see that in northern mountain regions.

Are you saying that arctic ocean water is warmer than 0C?

 

[xts]

Are you saying that arctic ocean water is warmer than 0C?

Its surface temperature is usually about -2C (but it is still a bit above freezing point of salted water), while at some depth it is about +4C

 

[klimatos]

Its surface temperature is usually about -2C (but it is still a bit above freezing point of salted water), while at some depth it is about +4C

Yes. Water density decreases as temperatures decrease below 3.9°C, so that the colder waters rise to the surface. There, depending upon salinity, they remain liquid until the freezing point is reached.

Since these waters never get much colder than -2°C, they are the warmest environments around in the polar areas. That is why the vast majority of polar life forms are either marine or aquatic.