Freezing of water pipes in operation

[babooman]

Dear all,

I am trying to determine whether a water pipe in a cold climate can freeze even if the line is in operation continuously.

I understand that the water in a pipe not in operation (no movement) gets frozen quicker than the water in a pipe in operation (it's circulating) but I can't find some kind of relationship or equation to determine it. Any suggestion or idea?

Thanks in advance.

 

[cloa]

This comes to kinectics of ice freezing but given some undercool to exceed the kinectic energy its all going to freeze given enough time .Even the US department of Energy scientists think this is a tough problem requiring modelling.

http://www.newton.dep.anl.gov/askasci/gen01/gen01174.htm

By the way, still water in your pipeline will not freeze quickly when under 0C- it takes a considerable undercool maybe -40C depending on the materials of pipe and their surface roughness and any solid contaminants in the water to seed freezing and then as it propagates the temperature quickly rises to 0C. That's why they use cloud seeders much lower undercool to freeze.

 

[TheBlacksmith]

I don't see why not. Depending on the flow rate and temperatures of the water and the climate, the pipe should ice from the outside in until it is obstructed. May not be flowing water, but industries use "freeze seals' with liquid nitrogen all the time to make a stop valve in a pipe run for repairs.

 

[babooman]

Thank you for the replies. I see that freezing may be a risk even in flowing pipes but very tough to estimate or assess.

For stationary liquids I usually estimate the time for freezing a certain % of the water mass using ISO 12241, and was trying to find a reference or rule of thumb to know the impact of the liquid flow in the freezing time calculations.

 

[zdas04]

For flowing lines, you have to estimate the rate of heat transfer. This is not easy, I usually calculate thermal entry length to see if the line is still above some required sub-cooling (I usually use 0F or 32F sub-cool) level. If it is then I feel like I have a reasonable chance of not freezing. If it is below that magic number then I start looking at insulation and heat tracing.

David

 

[waterpipe]

The others have mentioned difficulties involved in such a "calculation". However, there are certain design/code considerations. You mentioned a water pipe in a cold climate. AWWA M11 states:" Desigu practice should not be determined by the saying that "running water doesn't freeze." Water in a pipeline will freeze, running or not, if its temperature drops a fraction of a degree below 32F (0C)."

Under some circumstances, water may not turn to ice even when the temperature is as low as 28 to 29F (around -2C) but as stated by others, this condition cannot be predicted.

Please note that water containing only ice particles may cause serious trouble because it can block a valve. So the problem is not a full freeze but even before reaching to this point. So it is recommended to keep the water few degrees above 0C to be on the safe side.

 

[Compositepro]

The reason than "running water will not freeze" is that in most cases the source of the water is warmer than freezing. This is a common but unstated assumption, particularly when applied to building plumbing.