flow through annulus

[henerythe8th]

Attempting to determine the maximum flowrate that can pass through the annulus created when a 2 1/2 inch SCH40 pipe is placed inside a 4 inch SCH40 pipe 16 feet long in a vertical orientation. The 4 inch pipe is connected to a box that normally feeds the flow down another tube that is inside the 2 1/2 pipe. In a "what if" the supply pipe leaks scenario the flow will need to be diverted back to the tank that this is all attached to. Minimal head will be involved. Any ideas?

 

[zdas04]

There are a couple of different definitions that give you the very different answers.

The "wetted perimiter" method

Area = (Pi/4)*(ID(outer)^2 - OD(inner))
WettedPerimeter=Pi(ID(outer)+OD(inner))

EffectiveDiameter = 4(Area)/WettedPerimeter

The petroleum engineering method uses:

EffectiveDia=((OD+ID)^2 * (OD-ID)^3)^(1/5)

The Petroleum method will give you effective diameters that are about 40% higher.

To use either one, calculate your effective diameter and then just use it in any of the fluid-flow equations that call for ID.

I've found that using the PE method gives me excellent correlation to measured data in vertical flow. The Wetted perimeter method is used on the Profesional Engineer exam and I've not found it to match measured data very well.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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