dP Flow Measurement on Elbow in pipeline

[AntonTRN]

I would like to measure flow by means of the dP over an Elbow. The 36" steel pipeline is used for cooling water. Temperature is around 30 deg c . I would like to have a formula which gives the dP as function of the flow. The max flow speed is approx 2 m/s
Thanks.

note it is a long radius elbow

 

[JLSeagull]

NPS 10 seems to be the limited corner tap data available in the API MPMS 14.3.4. This is the Manual of Petroleum Measurement Standards: Chapter 14-Natural Gas Fluids Measurement Section 3-Concentric, Square-Edged Orifice Meters; Part 4-Background, Development, Implementation Procedures and Subroutine Documentation. I don't recall trying corner taps on large lines and I have not even thought about the fluid phase details for a while.

 

[danw2]

Mr. Upp and LaNasa devote 2 paragraphs and a graphic to describe inner and outer elbow taps that create a DP in their "Fluid Flow Measurement: A Practical Guide to Accurate Flow Measurement", 2nd Ed. (pages 181-182)

Maybe you could characterize the DP range with a rented clamp-on flow meter upstream?

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Elbow Meters

As fluid flows around an elbow, centrifugal force makes pressure on the outside wall higher than pressure on the inside wall. This pressure difference is proportional to flow, and its coefficient can be estimated from knowledge of elbow dimensions. For more accurate measurement, an elbow (with at least 10 diameters of straight pipe upstream - straightening vanes are recommended to stabilize swirling flow - and 5 diameters downstream) should be flow calibrated. If welds on an inlet elbow and pressure taps are carefully made, elbows will calibrate with a very stable calibration curve.

These units, however, are more often used for flow control (high repeatability) rather than for accurate flow measurement. Piping systems already have elbows present, and their use as a meter adds no pressure loss not already present. But normal pipeline velocities do not generate differentials (normal maximum about 9 inches), and this limits accuracy and severely limits rangeability.

 

[glowing]

talk to your meter supplier. If they can not calculate that out and provide a datasheet, it is time for a new vendor.

 

[hacksaw]

elbow taps are fine for monitoring flow where accuracy is not a concern, ASME calculations (old), Miller, and even spinks handbooks are good sources