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

No description available.

Trois techniques de mesure différentes ont été utilisées pour étudier la distribution des fluides dans un lit fixe : la tomographie à fils, le collecteur de liquide et un ensemble de thermistances. La tomographie à fils, dont la première application dans le cadre des lits fixes est décrite ici, a permis, tout comme le collecteur de liquide, d’obtenir des résultats intéressants concernant l’influence de paramètres tels que la distribution initiale, le type de chargement et les débits de fluides sur la distribution du liquide. L’étude a notamment montré l’importance de bien définir la maldistribution de liquide en termes de la grandeur mesurée et a apporté un regard critique vis-à-vis des consensus généraux concernant l’effet sur la distribution de liquide de paramètres tels que le débit de gaz (dont les expériences ont montré qu’elle dépend du distributeur utilisé) et le type de chargement (l’hypothèse selon laquelle le chargement dense disperse mieux le liquide dans la direction radiale par rapport au chargement lâche n’a pas été vérifié). Une étude réalisée en régime à haute interaction a permis aussi d’observer la relation étroite qui existe entre la distribution initiale et le régime d’écoulement / Three different measuring techniques were used to study the fluid distribution inside a trickle-bed reactor: the wire mesh tomography, the liquid collector and a set of thermistors. The liquid collector and specially the wire mesh tomography, whose first application in trickle bed reactors is described here, yielded interesting results concerning the influence of variables such as the initial liquid distribution, the loading method and the fluid flow rates on liquid maldistribution. Among the main observations, the study illustrates the importance of well defining liquid maldistribution in terms of the measured quantity and prompts to some caution when referring to some “normally accepted facts” like the advantages in terms of liquid distribution obtained when increasing the gas flow rate (which depends, according to this study, on the quality of initial liquid distribution) or when using a dense loading of the catalyst (the hypothesis according to which, compared with a sock loading, dense loading favors radial dispersion was not verified by the study). Also, a study performed under high interaction conditions showed the intimate relationship between the inlet distribution and the flow regime observed inside the reactor

Master of Science / Department of Mechanical and Nuclear Engineering / Steven J. Eckels / Membrane dehumidification and evaporative cooling applications have the potential to significantly improve the energy efficiency of air conditioning equipment. The use of wire mesh media in such membrane applications is feasible but has not been studied extensively. Therefore, the aim of this work is to investigate the heat and mass transfer performance of several different wire mesh media in membrane based dehumidification and evaporative cooling. There were six wire mesh membranes tested in an experimental facility. The wire mesh membranes vary with respect to percent open area, wire diameter, pore size and material. Two non-permeable, solid membranes were also tested in the facility and compared with the wire mesh membranes. The test section of the experimental facility consists of a narrow air duct and a plate apparatus. The membrane samples were fashioned into rectangular plates and installed into the test section. The plate membranes separate liquid water and air flow streams. The inlet air temperature and humidity are altered to produce condensation or evaporation at the membrane surface. The average convective heat and mass transfer coefficient of the air boundary layer is measured for each of the experimental plates. Membrane based dehumidification and evaporative cooling were accomplished using the wire mesh media. However, the wire mesh membranes did not exhibit any significant differences in their performance. The mesh plates were compared with the solid plate membranes and it was discovered that the solid plates exhibited significantly higher heat transfer coefficients during condensation conditions. This result most likely is due to the formation of large water droplets on the solid plates during condensation. The experimental data is then compared to analytical predictions of the heat and mass transfer coefficients developed from several heat transfer correlations and by invoking the heat and mass transfer analogy. The experimental data is also compared directly with the heat and mass transfer analogy. It was found that the data did not compare well with the heat and mass transfer analogy. This result is attributed to the fact that the membrane surface limits the amount of direct exposure to the gas-liquid interface.

The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar. The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-04-03T19:47:15Z No. of bitstreams: 1 JoseBatistaDeSalesFilho_DISSERT.pdf: 5253037 bytes, checksum: 306cef0f9ed7e39467276cd7982f3884 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-04-06T19:49:23Z (GMT) No. of bitstreams: 1 JoseBatistaDeSalesFilho_DISSERT.pdf: 5253037 bytes, checksum: 306cef0f9ed7e39467276cd7982f3884 (MD5) / Made available in DSpace on 2017-04-06T19:49:23Z (GMT). No. of bitstreams: 1 JoseBatistaDeSalesFilho_DISSERT.pdf: 5253037 bytes, checksum: 306cef0f9ed7e39467276cd7982f3884 (MD5) Previous issue date: 2016-12-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Em diversos campos da ind?stria petroqu?mica e nuclear, o controle e monitoramento de escoamentos compostos de misturas de ?leo, g?s e ?gua (escoamentos multif?sicos) v?m motivando o desenvolvimento de t?cnicas de investiga??o baseadas na gera??o de imagens por tomografia. Fen?menos como propaga??o de bolhas de g?s possuem din?micas r?pidas que exigem dos sistemas de monitoramento uma boa resolu??o temporal. Com o intuito de melhorar tais requisitos temporais em rela??o as t?cnicas de imagem j? consolidadas, foram desenvolvidos sensores do tipo wire-mesh ao longo da ?ltima d?cada. Estes sensores, que s?o inseridos dentro das tubula??es, s?o constitu?dos por uma malha de eletrodos que realizam medi??es de imped?ncia el?trica, que pode ser convertida nas propriedades el?tricas dos fluidos. Apesar da caracter?stica intrusiva, imagens do fluxo multif?sico s?o geradas sem a necessidade de algoritmos iterativos de reconstru??o. ? proposto neste trabalho um circuito integrado (CI) para realizar o condicionamento de uma malha de sensores wire-mesh 4x4, aplicado ? determina??o da fra??o de fases em fluxos multif?sicos. A integra??o reduz o tamanho dos circuitos de condicionamento, comparado ?s implementa??es dos sistemas existentes que utilizam componentes discretos, e tamb?m oferece op??es de customiza??o para melhorar o consumo de energia. O chip ? composto dos seguintes blocos: um amplificador de interface, que converte as correntes provenientes dos sensores em tens?o; um demodulador s?ncrono a fase, que fornece sinais de tens?o em fase e em quadratura que s?o fun??es das propriedades el?tricas dos fluidos (permissividade e condutividade); e de um filtro passa-baixas que antecede a convers?o anal?gico-digital, a ser feita fora do chip. O foco deste trabalho ? apresentar o projeto dos blocos do amplificador de interface e do filtro passa-baixas. O circuito integrado foi projetado para uma tecnologia CMOS padr?o de 130 nm. A valida??o do funcionamento do circuito ? feita a partir de simula??es p?s-leiaute. / In many petrochemical and nuclear industry applications, monitoring of streaming oil-watergas- mixtures (multiphase flows) has been motivating the development of investigation methods based on tomographic imaging. Some investigated phenomena, such as gas bubble propagation, feature fast-changing dynamics, thus demanding a good time resolution of monitoring systems. In order to achieve faster imaging methods compared to established tomographic techniques, wire-mesh sensors were developed over the last decade. These sensors, which are inserted inside pipelines, are composed of an electrode mesh that performs electric impedance measurements, which can be converted in fluid electrical properties. Despite their intrusive nature, multiphase flow images can be generated without iterative reconstruction algorithms. It is proposed in this work an integrated circuit (IC) to perform a 4x4 wire-mesh sensor signal conditioning, applied to phase fraction calculations of multiphase flows. The circuit integration reduce the size of conditioning circuits, in comparison with established systems which use discrete components, and also offers customization options to enhance power consumption efficiency. The chip comprises the following blocks: an interface amplifier that converts the sensor output currents into voltage signals; a phase syncronous demodulator, which provides in-phase and quadrature voltage signals that are functions of the main fluid electrical parameters (permittivity and conductivity); and a low-pass filter, prior to the off-chip analog-to-digital conversion. This work focuses on the project of the interface amplifier and the low-pass filter. The circuit was designed for a 130-nm standard CMOS technology. The IC validation is performed via post-layout simulations.

The objective of the present thesis research is to apply state-of-the-art experimental and data analysis techniques to the study of gas-liquid pipe flows, with a focus on conditions occurring in header-feeder systems of nuclear reactors under different accident scenarios. Novel experimental techniques have been proposed for the identification of the flow regime and measurement of the flow rates of both phases in gas-liquid flows. These techniques were automated, non-intrusive and economical, which ensured that their use would be feasible in industrial as well as laboratory settings. Measurements of differential pressure and the gas and liquid flow rates were collected in vertical upwards air-water flow at near-atmospheric pressure. It was demonstrated that the probability density function of the normalized differential pressure was indicative of the flow regime and using non-linear dimensionality reduction (the Elastic Maps Algorithm), it was possible to automate the process of identifying the flow regime from the differential pressure signal. The relationship between the probability density function and the power spectral density of normalized differential pressure with the gas and liquid flow rates in air-water pipe flow was also established and a machine learning algorithm (using Independent Component Analysis and Artificial Neural Networks) was proposed for the estimation of the phase flow rates from these properties. The proposed methods were adapted for use with single and dual conductivity wire-mesh sensors in vertical upwards and downwards air--water flows. A thorough evaluation of the performance and measurement uncertainty of wire-mesh sensors in gas-liquid flows was also performed. Lastly, measurements of the flow distribution in feeder tubes supplied with air-water mixtures by a simplified header model were collected and correlated to the observed flow patterns in the header.

The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar. The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.

Am 14. Oktober 1999 wurde in Rossendorf die dritte Veranstaltung in einer Serie von Workshops über Meßtechnik für stationäre und transiente Mehrphasenströmungen durchgeführt. Dieses Jahr kann auf auf 11 interessante Vorträge zurückgeblickt werden. Besonders hervorzuheben sind die beiden Hauptvorträge, die von Herrn Professor Hetsroni aus Haifa und Herrn Dr. Sengpiel aus Karlsruhe gehalten wurden. Erneut lag ein wichtiger Schwerpunkt auf Meßverfahren, die räumliche Verteilungen von Phasenanteilen und Geschwindigkeiten sowie die Größe von Partikeln bzw. Blasen der dispersen Phase zugänglich machen. So wurde über einen dreidimensional arbeitenden Röntgentomographen, ein Verfahren zur Messung von Geschwindigkeitsprofilen mit Gittersensoren und eine Methode zur simultanen Messung von Blasengrößen sowie Feldern von Gas- und Flüssigkeitsgeschwindigkeit mit einer optischen Partikelverfolgungstechnik vorgetragen. Daneben wurden interessante Entwicklungen auf dem Gebiet der lokalen Sonden vorgestellt, wie z.B. eine Elektrodiffusionssonde. Neue meßtechnische Ansätze waren ebenfalls vertreten; hervorzuheben ist der Versuch, die Methode der optischen Tomographie für die Untersuchung von Zweiphasenströmungen nutzbar zu machen. Der Tagungsband enthält die folgenden Beiträge: S. John, R. Wilfer, N. Räbiger, Universität Bremen, Messung hydrodynamischer Parameter in Mehrphasenströmungen bei hohen Dispersphasengehalten mit Hilfe der Elektrodiffusionsmeßtechnik E. Krepper, A. Aszodi, Forschungszentrum Rossendorf, Temperatur- und Dampfgehaltsverteilungen bei Sieden in seitlich beheizten Tanks D. Hoppe, Forschungszentrum Rossendorf, Ein akustisches Resonanzverfahren zur Klassifizierung von Füllständen W. Sengpiel, V. Heinzel, M. Simon, Forschungszentrum Karlsruhe, Messungen der Eigenschaften von kontinuierlicher und disperser Phase in Luft-Wasser-Blasenströmungen R. Eschrich, VDI, Die Probestromentnahme zur Bestimmung der dispersen Phase einer Zweiphasenströmung U. Hampel, TU Dresden, Optische Tomographie O. Borchers, C. Busch, G. Eigenberger, Universität Stuttgart, Analyse der Hydrodynamik in Blasenströmungen mit einer Bildverarbeitungsmethode C. Zippe, Forschungszentrum Rossendorf, Beobachtung der Wechselwirkung von Blasen mit Gittersensoren mit einer Hochgeschwindigkeits-Videokamera H.-M. Prasser, Forschungszentrum Rossendorf, Geschwindigkeits- und Durchflußmessung mit Gittersensoren

Am 14. Oktober 1999 wurde in Rossendorf die dritte Veranstaltung in einer Serie von Workshops über Meßtechnik für stationäre und transiente Mehrphasenströmungen durchgeführt. Dieses Jahr kann auf auf 11 interessante Vorträge zurückgeblickt werden. Besonders hervorzuheben sind die beiden Hauptvorträge, die von Herrn Professor Hetsroni aus Haifa und Herrn Dr. Sengpiel aus Karlsruhe gehalten wurden. Erneut lag ein wichtiger Schwerpunkt auf Meßverfahren, die räumliche Verteilungen von Phasenanteilen und Geschwindigkeiten sowie die Größe von Partikeln bzw. Blasen der dispersen Phase zugänglich machen. So wurde über einen dreidimensional arbeitenden Röntgentomographen, ein Verfahren zur Messung von Geschwindigkeitsprofilen mit Gittersensoren und eine Methode zur simultanen Messung von Blasengrößen sowie Feldern von Gas- und Flüssigkeitsgeschwindigkeit mit einer optischen Partikelverfolgungstechnik vorgetragen. Daneben wurden interessante Entwicklungen auf dem Gebiet der lokalen Sonden vorgestellt, wie z.B. eine Elektrodiffusionssonde. Neue meßtechnische Ansätze waren ebenfalls vertreten; hervorzuheben ist der Versuch, die Methode der optischen Tomographie für die Untersuchung von Zweiphasenströmungen nutzbar zu machen. Der Tagungsband enthält die folgenden Beiträge: S. John, R. Wilfer, N. Räbiger, Universität Bremen, Messung hydrodynamischer Parameter in Mehrphasenströmungen bei hohen Dispersphasengehalten mit Hilfe der Elektrodiffusionsmeßtechnik E. Krepper, A. Aszodi, Forschungszentrum Rossendorf, Temperatur- und Dampfgehaltsverteilungen bei Sieden in seitlich beheizten Tanks D. Hoppe, Forschungszentrum Rossendorf, Ein akustisches Resonanzverfahren zur Klassifizierung von Füllständen W. Sengpiel, V. Heinzel, M. Simon, Forschungszentrum Karlsruhe, Messungen der Eigenschaften von kontinuierlicher und disperser Phase in Luft-Wasser-Blasenströmungen R. Eschrich, VDI, Die Probestromentnahme zur Bestimmung der dispersen Phase einer Zweiphasenströmung U. Hampel, TU Dresden, Optische Tomographie O. Borchers, C. Busch, G. Eigenberger, Universität Stuttgart, Analyse der Hydrodynamik in Blasenströmungen mit einer Bildverarbeitungsmethode C. Zippe, Forschungszentrum Rossendorf, Beobachtung der Wechselwirkung von Blasen mit Gittersensoren mit einer Hochgeschwindigkeits-Videokamera H.-M. Prasser, Forschungszentrum Rossendorf, Geschwindigkeits- und Durchflußmessung mit Gittersensoren