Multiphase flows are simultaneous flows of two or more immiscible fluids in a pipe or vessel. Multiphase flows occur in a wide variety of industrial applications, such as chemical reactors, power generation, oil and gas production or transportation, etc. In most of these applications, efficiency and process reliability depend not insignificantly on the composition and flow morphology of these multiphase flows. Therefore, accurate determination of parameters such as phase fractions and their spatial distribution, as well as measurement of volumetric or mass flow rates, is essential to optimize and ensure correct operation of the equipment. For a better prediction of flow characteristics of multiphase systems, the development and validation of analytical models and CFD codes for simulations of multiphase flows has been promoted for some time in thermofluid dynamics research. For this purpose, the in-depth analysis of multiphase flows with high spatial and temporal resolution is essential. However, to date, there is no universal sensor that can directly measure all the required flow parameters over the full range of all flow conditions. Therefore, several strategies have been developed to solve this problem. For pure measurement of fluid composition and mixture volume flow, for example, the fluid mixture is often conditioned before measurement by separation into individual phases or by homogenization. However, this does not allow any more information about the flow morphology. In situations where the fluid cannot be preconditioned, for example when investigating bubble size distributions or predicting plug flows, imaging techniques such as wire-mesh sensors therefore play an important role because they provide cross-sectional images of the flow in rapid succession. This information can be used to determine phase distributions and identify flow regimes, which in turn can serve as input to other sensors to find optimal operating points. In addition, such information is important for validating models and numerical simulations.
Although wire-mesh sensors are very attractive and now widely used due to their high spatial and temporal resolution, the measurement signals obtained from the sensor can be corrupted by energy losses and channel crosstalk under certain conditions. Therefore, a better understanding of the real physical conditions when using wire-mesh sensors is essential to improve the measurement accuracy and to extend the range of applications, e.g., for the measurement of media with very high conductivities or for an accurate quantification of individual phases in three-phase flows. In the present work, the current limitations of existing wire-mesh sensor systems are investigated in detail, thus providing a basis for technical improvements and the development of new methods for better interpretation of the measured values of wire-mesh sensors. For this purpose, the electronic measurement principle and the real sensor geometries are first investigated with respect to inherent energy losses and channel crosstalk. Based on mixing models, a method for visualization and quantification of three-phase gas-oil-water flows even in the presence of dispersions is presented. In addition, nonlinearities of wire-mesh sensors are predicted for the first time by a hybrid model based on the finite element method, which also incorporates the real parameters of the electronic components of signal generation and measurement. This model is subsequently used to generate synthetic data and to test new correction methods. Finally, two methods are proposed to compensate for unavoidable energy losses. The first method allows inherent determination of energy losses that cannot be suppressed by further circuit optimization. The second method allows determination of the voltage drop caused by the impedance of the electrodes when measured in highly conductive liquids. Numerical and experimental analyses show an improvement in the measurement accuracy of wire-mesh sensors with respect to the average and local phase fractions. The deviations of the average phase fraction were reduced from more than 15% to less than 2% and the deviations in local measurements from more than 30% to less than 5%.:Abstract 3
Zusammenfassung 5
Statement of authorship 9
Acronyms 13
Symbols 15
1. Introduction 17
2. State of the science and technology 21
3. Wire-mesh sensor and experimental test facilities 43
4. Three-phase flow measurement based on dual-modality wire-mesh sensor 53
5. Wire-mesh sensor model based on finite-element method and circuit simulation 67
6. Analysis of non-linear effects in measurements of wire-mesh sensor 79
7. Methods for improving the measurement accuracy of wire-mesh sensors 87
8. Conclusions and outlook 97
Bibliography 101
Appendices 111
A. List of scientific publications 113
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:89411 |
| Date | 06 February 2024 |
| Creators | de Assis Dias, Felipe |
| Contributors | Hampel, Uwe, Wang, Mi, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 10.1109/ACCESS.2020.3007678, 10.1109/ACCESS.2021.3076966, doi.org/10.1515/teme-2021-0055, 10.1088/1361-6501/ac6ab4, 10.14278/rodare.898, 10.14278/rodare.373, 10.14278/rodare.556, info:eu-repo/grantAgreement/Europäische Sozialfonds/Bereichen Hochschule und Forschung im ESF im Freistaat Sachsen für die Förderperiode 2014 bis 2020/Landesinnovations.: 100316833 / Industrie.: 100316834//Durchflussmessung für mehrphasige Fluide |
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