water velocity required to prevent freezing
water velocity required to prevent freezing
(OP)
Simple,
I need to move ~10,000 usgpm of water over 3000 feet, in subartic conditions, 24/7 run conditions.
Negligible head (10m +/-) plus line loss.
Heat trace and insulated pipe not an option due to cost.
Mining application
Anybody have a minimum flow velocity to prevent line freezing,
Probably sclair DR17, water at low single digits (C). Ambient air temp -20C and warmer.
ANy ideas?
I'll put this in civil as well.
h_r
I need to move ~10,000 usgpm of water over 3000 feet, in subartic conditions, 24/7 run conditions.
Negligible head (10m +/-) plus line loss.
Heat trace and insulated pipe not an option due to cost.
Mining application
Anybody have a minimum flow velocity to prevent line freezing,
Probably sclair DR17, water at low single digits (C). Ambient air temp -20C and warmer.
ANy ideas?
I'll put this in civil as well.
h_r





RE: water velocity required to prevent freezing
From your question it sounds like you are counting on heating due to frictional resistance. I think that heating will be negligible, unless you go to a quite small pipe/high velocity, so that pumping energy is providing heating. You didn't mention initial temperature, that's important.
You might try some simulation at http://www.pipeinsulation.org/
but that may not account for friction heating.
RE: water velocity required to prevent freezing
It gives an equation for time it takes for water to freeze in a pipe.
It mentions that if the flow of the water is sufficient to offset the heat loss - freezing will not occur.
RE: water velocity required to prevent freezing
Then see what velocity the water in that 1 foot section would have to travel before it froze.
If say the calculation came out the water would freeze in 60 minutes, then the velocity required would have to be 50 feet per minute (3000 ft / 60 minutes).
Convert the gpm to velocity given your pipe size and that will tell you if 10,000 gpm is enough.
RE: water velocity required to prevent freezing
All I need is your line size. Note that the chart goes up to 18" pipe, and is for 100 feet of pipe.
The example used in the book is an 8" line, 250 feet long. The chart says 5 GPM, so it's 5 X 2.5 = 12.5 GPM
For wind velocities over 15 mph, it states that the flow rates taken from the chart should be doubled.
RE: water velocity required to prevent freezing
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RE: water velocity required to prevent freezing
Even with considerable velocity, given enough time (distance) and heat loss water lines can freeze solid. Line blockage can be due to both annular ice formation and frazil ice which can clump together at obstructions.
RE: water velocity required to prevent freezing
The important point about the book is that it contains a formula so that hrdrok has a reference to use when he makes his calculation. A reference is better than an anonymous post.
"Introduction to cold regions engineering" also shows on page 435 that water mains with 2 ft/sec velocity have been successfully used. On page 434, the book states that insulation to keep the freezing isotherm within the insulation is too expensive.
If you feel the book is in error, perhaps you can put a review on amazon.
RE: water velocity required to prevent freezing
While we obviously have very little information and this is indeed an interesting exercise for any thermodynamically inclined amongst, from the outside looking in (I guess there could be much we don't know/uniqueness about the specific application) this seems like somewhat risky business, and there would be at least some possibility of inconvenience and maybe even some unexpected "cost" if/when? the line freezes.