FLow rate and pressure in a non-round pipe

[brianpeters]

I am interested in calculating flow rate and pressure drop in 3/8" nominal copper tubing that has been rolled to produce a cross-section that is roughly rectangular with half circular ends.

Geometry example

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I have calculated the reduction in cross-section assuming a constant circumfrence and wall thickness.

round tube data

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flattened tube data

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This gives me a cross-secton area reduction of 37-50% depending on the ASTM B88 type of soft copper tube used as the basis geometry.

I presume that a linear extrapolation from the results from a normal tube based on cross-section change would not give me a good estimate of actual flow and pressure for this geometry due to frictional effects remaining constant or perhaps increasing even as the flow at constant pressure drops due to area reduction.

Can you recommend how to approach this problem ?

THanks and Regards,
Brian Peters

Check out ITER.ORG to see what this is a very small piece of.

[PipeFlowCalcs]

You should use hydraulic diameter Dh=4A/P

A - cross section area
P - wetted perimeter

With Dh you should use Bernoulli equation to calculate pressure drop

[brianpeters]

Thanks Zoran,

I guess I should have read a bit more carefully, I see it was in the posted material.


I take it that for series connnected piping runs the pressure drops just sum.

But for parallel runs haveing a common inlet and outlet can you calculate total pressure drop similar to parallel resistance?

I.E. if p1 and p2 are known pressure drops calculated individually for two legs of parallel piping would this be true,

Ptotal = p1*p2/(p1+p2)

or how would you calculate it?

regards, and thanks again
Brian