Multiphase flow denotes the simultaneous flow of two or more physically distinct and immiscible substances and it can be widely found in several engineering applications, for instance, power generation, chemical engineering and crude oil extraction and processing. In many of those applications, multiphase flows determine safety and efficiency aspects of processes and plants where they occur. Therefore, the measurement and imaging of multiphase flows has received much attention in recent years, largely driven by a need of many industry branches to accurately quantify, predict and control the flow of multiphase mixtures. Moreover, multiphase flow measurements also form the basis in which models and simulations can be developed and validated. In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10 000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10 000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:23836 |
| Date | 11 August 2008 |
| Creators | Da Silva, Marco Jose |
| Contributors | Gerlach, Gerald, Hampel, Uwe, Yang, Wuqiang |
| Publisher | Technische Universität Dresden, Forschungszentrum Dresden-Rossendorf e.V. |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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