Calc Pressure Drop in nested pipe

[TMEldridge]

I have a application where a 2" sch 80 pipe is running inside a 10" sch 40 pipeline. How can I calculate the pressure drop with this internal interference? I've used equivalent cross-sectional area, but it seems the velocity profile, amount of wetted steel, etc would have a greater effect. Any ideas?

 

[RWF7437]

Have you tried using the Manning equation and calculating the actual hydraulic radius ( area/wetted perimeter )? Solve for the slope, which is the slope of the hydraulic grade line.

good luck

 

[TMEldridge]

Is there a modification to Manning for pressure flow? This is a fuelling line in Steel pipe, operating at medium pressure. Or a modification to the Darcy formula for equivalent area?

 

[RWF7437]

The Manning equation applies to both pressure flow and open channel flow, so long as you remember that the S is the slope of the hydraulic grade line, not the slope of the pipe. It applies to the flow of water usually. It can be modified for other fluids taking into account the viscosity and density differences.

Funny situation here... why are pipes "nested" and how are they nested, concentrically or is the smaller pipe laying in the bottom of the larger pipe. You got strange plumbers in your part of the world !

Good luck

 

[TMEldridge]

The pipes nested are actually for a buried vertical product run where the interior pipe is a contractor's low point drain standpipe running inside the main run. Intresting idea, since he saves a full-size tee, cap, and thread-o-let as opposed to the traditional low-point buried drain arrangement. But I've never seen this before, so I'm wandering in approximation territory for losses.

 

[RWF7437]

Here's link to several flow calculators that may help.

http://www.lmnoeng.com/darcy.htm

Good luck