This article reports the methodology used to develop a high-precision ultrasound transit time flow meter dedicated to liquid hydrocarbons. This kind of flow meter is designed for custody transfer applications requiring accuracy better than 0.15% of reading. We focus here on certain specific points to achieve this accuracy. The transit time method needs to estimate accurately the time delay between signals received by a pair of transducers. In this study, we review different ways of estimating this time delay. We also propose a specific configuration of the flow meter paths. In particular, this configuration compensates for the swirl phenomenon, which has a significant impact on the accuracy of the flow meter. We also propose a theoretical parametric profile to reconstruct the fluid velocity profile in order to perform in situ diagnosis of the flow. The parameters of the model are estimated from the measurements of the flow meter. Simulations and experimental results showed that this method provides characterization of the flow in disturbed and undisturbed flow conditions.
A transit time ultrasonic flowmeter is a very accurate tool to measure the volumetric flowrate of a fluid flowing in a pipe. To estimate the flowrate, the fluid velocity averaged over the cross-section of the pipe has to be estimated from the fluid velocities averaged over the paths of the flowmeter. That is the reason why the velocity profile of the fluid, which depends on not only the Reynolds number but also on the upstream and downstream pipe configuration, is of great interest in transit time flowmetering. In this work, we propose to reconstruct the fluid velocity profile by using the measures of a 18 paths flowmeter measures to offer an in situ diagnostic tool of the flow. We first test tomography methods: filtered back-projection and then an iterative one, the Algebraic Reconstruction Technique (ART). These methods are not really appropriate to our context of incomplete data. We have previously [1] defined a theoretical parametric model of the velocity profile which allows to in situ detect and characterize the asymmetry of the flow. We defined in this work a new parametric model which has a flowrate function of the asymmetry of the profile. It also has the advantage of determining the parameters of the symmetric term of the model in taking into account the asymmetric part of the profile. This new profile is a promising way in increasing the accuracy of the flowmeter in disturbed flow condition by taking into account the additional information provided by the velocity profile reconstruction.
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