Flow calculations for small tubes 3/16 with looong lengths 650 f

Weezbo

it may be better to consider a slightly different plan.

Ron Alexson

Flow calculation for 650 ft of 3/16 ID nylon tube

Hi Have a strange request to run a 1/4" nylon tube through a return and supply water line. The purpose is that on occassion, if everyone is not vigulent, the lines freeze up. The function of the tube is to circulate glycoled boiler fluid when an emergency occurs (about three time per year). The tube that will fit through all the various fittings etc is a 1/4" OD nylon tube with a 3/16" ID. The tube will be contineous without fittings along the run for a total of about 650 feet and will be a closed loop off the circulator system. The main feeder line is 2" and if this works then all is well BUT if the flow in the heater tube is too small and does not supply enough heat to exceed the heat loss then the effort will be wasted. Once the ice in the line is thawed enough to allow even a small flow the water temp will look after the rest, the problem occurs typically over night on very cold (-20 or colder) and the flow is shut off completely for an extended period of time.Hope you can help and thanks in advance for your efforts.
Ron.

Alan(CaliforniaRadiant)Forbes

System Syzer

My Bell & Gossett System Syzer only goes down to 3/8" copper tubing which has a 1/4" i.d.; a bit larger than your nylon tubing. Friction loss is 9.5 feet of head per 100 ft., so for 650 feet, you would need a pump that could overcome 62 feet of head, 1 gpm; somewhat larger for your smaller tubing. That's gonna be a big, expensive pump.

Have you thought about heat tape under fiberglass insulation?

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bob_25

flow

Alan and Ron, Al I believe the tube sizes on the syzer are nominal ID. I looked at a chart in a swagelock manual and they give 2.8PSI per 100ft at .1 gpm. That works out to about 42' of head at .1 gpm for 650'. If the lines you are trying to protect are potable water this is a bad idea. bob

Joe Mattiello

Taco 009 circulators in series

You can put Two Taco, 009 circulators in series to overcome the frictional losses. This is an economical alternative to a larger perhaps multistage pump.

Joe Mattiello
Technical Service Technician

Mike T., Swampeast MO

Am not certain

But I think your velocity would have to be unachievably high to prevent all of the heat in that little tube from being liberated WAY before you hit the end of the big tube.

In other words your delta-t would probably remain infinite (meaning coming out at same temp as water in the big tube) at any achievable flow rate.

I don't think it's the heat loss from the big pipe that is the problem--it is the heat loss from the little pipe surrounded by all of that water...

Think it would be sort of like expecting to circulate water through 650' of ½" fin baseboard fast enough to wind up with a 20° delta-t!

Ken_8

Why not simply put a

small dia. return line from the far-end, back to the source. A simple recirc. line?

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hr

I'd like to see

the fitting that allows the inner tube to go in and out of the larger tube?

Think I would attach a piece of PAP to the outside and insulate the whole assembly. I'm not sure nylon would be a good match with glycol, anyways.

hot rod

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Alan(CaliforniaRadiant)Forbes

Bob

You're right; it's 3/8" nominal; don't know what I was thinking.

I like Ken's idea with the recirculating line. Good things come from the shores of the mighty Passaic.

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