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Title: The Effects Of Reynolds NUMBER,WALL ROUGHNESS,AND Profile Asymmetry On Single- And Multi- Path Ultrasonic Meters
Author: Klaus J. Zanker
Source: 1999 North Sea Flow Measurement Workshop
Year Published: 1999
Abstract: A simple power law velocity profile is used to study the effects of pipe roughness and Reynolds Number (Re) on ultrasonic meter performance. Considered here are two measurement methods. The first utilize a single bounce path through the pipe center, and is common to multipath as well as single path meters. The second employs four parallel chordal paths, (e.g. Daniel SeniorSonic). The single path centerline measurement requires typical corrections from 4% to 8% for changes in velocity profile due to variations in pipe roughness and Re. A correction for Re can be calculated from additional information on fluid density and viscosity, but changes of roughness with time cannot be measured, and hence cannot be corrected. It will be shown that the four path meter does an excellent job of integrating the velocity profile to give the correct flow rate over a wide range of both Re and roughness. A mathematically generated profile similar to that from a single bend is used to study the effects of asymmetry on the performance of both measurements. The centerline measurement varies over about 1.5%, depending on the path orientation relative to the asymmetry. Unfortunately applying a typical Re correction then creates a bias error of about 4%. In contrast, the four path meter accurately integrates the velocity profile to give an answer within 0.2% of the flow irrespective of orientation. Furthermore the four-path meter is capable of recognizing the changes in operating conditions.

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