A suspension flow model based on the "suspension balance" approach has been developed. This work modifies the model to allow the solution of suspension flows under general flow conditions. This requires the development of a frame-invariant constitutive model for the particle stress which can take into account the spatially-varying local kinematic conditions. The mass and momentum balances for the bulk suspension and particle phase are solved numerically using a finite volume method. The particle stress is based upon the computed rate of strain and the local kinematic conditions. A nonlocal stress contribution corrects the continuum approximation of the particle phase for finite particle size effects. Local kinematic conditions are accounted through the local ratio of rotation to extension in the flow field. The coordinates for the stress definition are the local principal axes of the rate of strain field. The developed model is applied to a range of problems. (i) Axially-developing conduit flows are computed using both the full two-dimensional solution and the more computationally efficient "marching" method. The model predictions are compared to experimental results for cross-stream particle concentration profiles and axial development lengths. (ii) Model predictions are compared to experiments for wide-gap circular Couette flow of a concentrated suspension in a shear-thinning liquid. With minor modification, the suspension flow model predicts the major trends and results observed in this flow. (iii) Comparisons are made to experiments for an axisymmetric contraction-expansion. Model predictions for a two-dimensional planar contraction flow test the influence of model formulation. The variation of the magnitude of an isotropic particle normal stress with local kinematic conditions and anisotropy in the in-plane normal stresses are both explored. The formulation of the particle phase stress is found to have significant effects on the solid fraction and velocity. (iv) Finally, for a rectangular piston-driven flow and an obstructed channel flow, a "computational suspension dynamics" study explores the effect of particle migration on the bulk flow field, system pressure drop and particle phase composition.

A comprehensive study of heat transfer and pressure drop of refrigerant R410A during condensation and supercritical cooling at near-critical pressures was conducted. Investigations were carried out at five nominal pressures: 0.8, 0.9, 1.0, 1.1 and 1.2xpcrit. The refrigerant was tested in commercially available horizontal smooth tubes of 6.2 and 9.4 mm I.D. Heat transfer coefficients were measured using a thermal amplification technique that measures heat duty accurately while also providing refrigerant heat transfer coefficients with low uncertainties. For condensation tests, local heat transfer coefficients and pressure drops were measured for the mass flux range 200 G 800 kg/m2-s in small quality increments over entire vapor-liquid region. For supercritical tests, local heat transfer coefficients and pressure drops were measured for the same mass flux range as in the condensation tests for temperatures ranging from 30 110oC. Condensation heat transfer coefficients and pressure drops increased with quality and mass flux. The effect of reduced pressure on heat transfer is not very significant, while this effect is more pronounced on the pressure gradient. The flow regime transition criteria of Coleman and Garimella (2003) were used to initially designate the prevailing flow regimes for a given combination of mass flux and quality. The condensation data collected in the present study were primarily in the wavy and annular flow regimes. During supercritical cooling, the sharp variations in thermophysical properties in the vicinity of the critical temperature resulted in sharp peaks in the heat transfer coefficients and sudden jumps in the pressure drop. Based on the characteristics of the specific work of thermal expansion (contraction), the data from the supercritical tests were grouped into three regimes: liquid-like, pseudo-critical transition and gas-like regimes. Flow regime-based heat transfer and pressure drop models were developed for both condensation and supercritical cooling. For condensation, the overall heat transfer model predicts 98% of the data within 15% while the overall pressure drop model predicts 87% of the data within 15%. For supercritical cooling, the heat transfer model predicted 88% of the data within 25% while the pressure gradient model predicts 84% of the data within 25%.

In CANDU reactors, under normal operating conditions, the inlet headers collect and distribute single-phase liquid flow (heavy water) to the fuel cooling channels via the feeders. However, under some postulated loss of coolant accidents, the inlet headers may receive two-phase fluid (steam/water) and the fluid forms a stratified region inside the header. To predict the thermalhydraulic behaviour of headers for the reactor safety analysis, the two-phase flow distribution within the headers and through the feeders must be modelled. In order to analyse the two-phase flow behaviour of a scaled CANDU inlet header / a transparent and instrumented version of a header with 5 feeders was previously built in the Mechanical Engineering Department of Middle East Technical University (METU-Two Phase Flow Test Facility / METU-TPFTF). The aim of this study is to investigate two-phase flow distribution through multiple outlets from such a horizontal drum both numerically and experimentally. For this purpose, three-dimensional incompressible finite difference equations in cylindrical coordinates were derived by using two-fluid model to simulate adiabatic two-phase flow (air/water) in the header numerically. The discretized equations were then programmed into a computer code which was developed specifically for modelling the header type geometry. A method based on the principles of Implicit Multi Field (IMF) technique has been utilised to solve those equations. The solution algorithm was tested by using some numerical benchmark problems. A number of experimental tests covering single and two-phase flow distribution through outlet pairs from the header were performed. Void fractions and flow rates obtained from these tests are in good agreement with the code results. The code also predicts the void fraction and pressure distribution in the header satisfactorily.

This thesis addresses the experimental investigation of the cavitation phenomenon and its main consequences on the normal operation of a safety relief valve (SRV). More particularly, limitation of the mass flux discharged and alteration of the hydraulic fluid forces behavior is of main interest for the proper design and sizing of such devices. In nuclear or thermal engineering systems, the use of SRVs is mandatory since it represents the ultimate protection device before an accident occurs, caused by a sudden pressurization of the system. A careful design and sizing of the SRV is therefore essential. The complete understanding of the physics taking place in the flow through the valve is required to guaranty and optimize the security of the protected process.<p><p>In order to investigate the above effects of cavitation in a SRV, two different orifice sized valves (API 2J3 type and a transparent model based on an API 1 1/2G3 type) are tested in two different experimental facilities expressly built for this purpose. Instead of using a spring, the design of both valves allows the adjustment of the disc at any desired lift. Hence the static behavior of the valves is investigated. Both facilities, operating at different magnitude scales, allow the study of single phase and cavitating flow conditions required to properly determine the most important hydraulic characteristics, and access on any potential scaling effect between both sized SRVs. Experimental techniques used for the determination of the hydraulic characteristics include temperature, flow rate, fluid forces and pressure measurements both upstream and downstream the test sections. <p><p>Results show a similar influence of cavitation on the flow characteristics of both valves, minimizing any potential scaling effect. The liquid pressure recovery factor FL, which is normally used to identify a choked flow condition in a control valve, is experimentally determined for the first time in a SRV. The existence of a local minimum located at small openings of the lift indicates a change on the flow characteristics of both valves, which is related to the location of the minimum cross section of the flow that does not remain constant for every lift position. An extended experimental campaign is performed to analyse the effect of the blowdown ring adjustment located around the nozzle of the API 2J3 valve. Results confirm that the position of the ring has an important contribution for the hydraulic forces acting on the valve disc. <p><p>In the second part of the research, precise optical diagnostic techniques are successfully applied in the transparent valve to locally characterize the flow topology in a SRV experiencing cavitation. These results are innovative and enrich the experimental database available in the literature for the characterization and understanding of the flow physics in such devices. In a first configuration, high speed visualization is applied to observe qualitatively the flow pattern and the inception of liquid vaporization. Particle tracking results suggest that vapor bubbles are formed in the core of vortices detached from the shear layers attached to the valve. These rotational structures promote lower pressure regions allowing the liquid to vaporize. In the second configuration, particle image velocimetry is applied to extract the velocity field in both single phase and cavitating flow conditions. Results of PIV confirm the existence of a submerged jet just downstream the minimum section. This jet is characterized by two non-symmetric shear layers at its sides. Under cavitation conditions, PIV results confirm that vapor bubbles are formed preferentially inside the jet shear layers. The phenomenon of mass flux limitation caused by cavitation is reproduced at small openings of the valve and interaction with the flow topology is highlighted. It is observed that limitation of the flow occurs when the vena contracta is shifted towards the minimum geometrical section of the flow. Finally, instabilities of the flow downstream the critical section are investigated in the frequency domain by means of time resolved data. Results suggest that vortex shedding mechanism is dominated by a constant Strouhal number which is slightly affected by the valve opening. <p><p>In the last part of the research, the methodology used in water is extended and applied to cryogenic liquids. Two different geometries are investigated experimentally and numerically using water and liquid nitrogen as working fluids. Results suggest that both the flow coefficient (determined at single flow conditions), and the liquid recovery factor (used to identify choked flows), are independent on the fluid properties and therefore, an hydraulic similarity relation can be proposed.<p><p>This research project was carried out at the von Karman Institute for Fluid Dynamics (VKI), in Belgium, in close collaboration and with the funding of Centre Technique des Industries Mécaniques (CETIM) in France. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The subject of this PhD thesis is the development of an efficient system that can simultaneously pump and separate a gas-liquid mixture, in particular an oil-air mixture. Two-phase flows are encountered in many applications (petroleum extraction, flow in nuclear power plant pumps, pulp and paper processing, etc.) but this study is mainly focused on lubrication systems of aircraft gas turbine engines.<p><p>The pump and separator system (PASS) for two-phase flows developed in this PhD thesis aims to perform three functions simultaneously:<p>• Send back the oil to the tank (oil pumping)<p>• Separate the air from the oil (de-aeration)<p>• Separate the oil from the air (de-oiling) and release the sealing air into the atmosphere (venting). <p>Particular care is given to the liquid flow rate lost at the gas outlet of the system.<p>Consequently, it could replace the scavenge pumps and oil-air separators existing in present lubrication systems. This modification provides several advantages: simplification of the lubrication circuit, reduction of oil consumption and of the size of the lubrication system.<p><p>This research is divided into three axes: the theoretical study of the important physical mechanisms taking place inside the two-phase flow pump and separator system, the experimental development, tests and optimization of different PASS prototypes, and also the numerical simulations of the two-phase flow inside these prototypes. Although the experiments were the central pillar of this research, the three axes were closely imbricated.<p><p>The PASS design includes three main components:<p>• An inlet chamber with one or several tangential inlets giving a natural centrifugation to the flow,<p>• An impeller (forced centrifugation) with an axial and a radial part followed by a volute chamber,<p>• A metallic foam that lets pass micron and sub-micron droplets and which is followed by an axial vent port.<p><p>The centrifugation causes the liquid (oil) to move radially outwards in an annular body (a liquid ring) generating pressure. The thickness of this liquid ring inside the impeller is mainly determined by the pressure coefficient (related to the back-pressure and the rotational speed). When the back-pressure increases, the thickness of the liquid ring increases too. An advantage of the PASS is that it does not impose any relation between the liquid head and the liquid flow rate, contrary to common centrifugal pump. It self-regulates the radial position of the gas-liquid interface to sustain the operating conditions.<p><p>The de-aeration efficiency mainly depends on the pressure coefficient (for a constant liquid viscosity or temperature) or on the thickness of the liquid ring. The pressure gradient which appears in the liquid rotating in an annular body acts like a dam for the gas phase. Indeed, the gas movement is mainly determined by the pressure field (buoyancy) while the liquid distribution is dominated by centrifugal and Coriolis forces. Buoyancy tends to accumulate the gas phase near low pressure areas (PASS hub, suction side of the blades, clearances between closed impeller and casing).<p><p>The first oil-air PASS prototype produces high viscous losses due to the high peripheral velocity and liquid viscosity. Therefore, the pumping efficiency is poor compared to common impeller pumps. However, the pumping is not the key function of the PASS and a power consumption below 5 kW is acceptable for the application considered in this work. For applications that require lower power consumptions, a reduction of the rotational speed must be considered.<p><p>Thus, the rotational speed and the impeller diameter are two major constraints for the PASS design which determine the de-aeration and pumping efficiencies. The impeller diameter also influences the size of passage sections for the air flow. The air velocity must be kept as low as possible because the entrainment of droplets increases when the air velocity rises (drag forces on droplets). Indeed, this large influence of the air flow rate on the oil consumption (de-oiling efficiency) was demonstrated by a theoretical analysis, the experiments and the CFD simulations. The production of droplets in the inlet pipes when the two-phase flow is annular is a key phenomenon regarding the oil consumption.<p><p>In addition to the air flow rate, other variables also influence the oil consumption:<p>• Air-oil temperature: when the temperature rises, the oil consumption increases because the surface tension and the oil density are reduced. Moreover, as the air density also decreases, the air velocity rises.<p>• Oil flow rate: the oil consumption rises more or less linearly with the oil flow rate. However, the influence of the oil flow rate on the inlet droplet size is uncertain.<p>• Rotational speed: the rotational speed has obviously a strong impact on the oil consumption without metallic foam. However, experiments showed that the metallic foam efficiency is almost independent on the rotational speed. Therefore, the oil consumption with the Retimet foam does not depend on the PASS rotational speed.<p>• Altitude or air density: the oil consumption decreases when the air density is reduced because the drag forces on droplets also decrease.<p>The gas density (altitude) is also supposed to influence the de-aeration efficiency but this could not be tested or simulated in this work (the de-aeration efficiency gets probably better when decreasing the gas density because the buoyancy forces increase).<p><p>Theory, experiments and numerical simulations also allowed the prediction of performance of the first oil-air prototype for real in-flight operating conditions. Two problems have been identified: the de-aeration efficiency at MTO and cruise ratings and the oil leak throughout the vent in cold start and windmilling. To solve them, some modifications of the lubrication system have been suggested. With these modifications, the oil-air PASS should become very efficient and attractive for engine manufacturers. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

This research project was carried out at the von Karman Institute for Fluid Dynamics (VKI), in Belgium, in collaboration and with the funding of Centre Technique des Industries Mécaniques (CETIM) in France.<p>The flow of a mixture of two fluids in pipes can be frequently encountered in nuclear, chemical or mechanical engineering, where gas-liquid eactors, boilers, condensers, evaporators and combustion systems can be used. The presence of section changes or more generally geometrical singularities in pipes may affect significantly the behavior of twophase flow and subsequently the resulting pressure drop and mass flow rate. Therefore, it is an important subject of investigation in particular when the application concerns industrial safety valves.<p>This thesis is intended to provide a thorough research on two-phase (air-water) flow phenomena under various circumstances. The project is split in the following steps. At first, experiments are carried out in simple geometries such as smooth and sudden divergence and convergence singularities. Two experimental facilities are built; one in smaller scale in von Karman Institute and one in larger scale in CETIM. During the first part of the study, relatively simple geometrical discontinuities are investigated. The characterization and modeling of contraction and expansion nozzles (sudden and smooth change of section) is carried out. The pressure evolution is measured and pressure drop correlations are deduced. Flow visualization is also performed with a high-speed camera; the different flow patterns are identified and flow regime maps are established for a specific configuration.<p>A dual optical probe is used to determine the void fraction, bubble size and velocity upstream and downstream the singularities.<p>In the second part of the project, a more complex device, i.e. a Safety Relief Valve (SRV), mainly used in nuclear and chemistry industry, is thoroughly studied. A transparent model of a specific type of safety valve (1 1/2" G 3") is built and investigated in terms of pressure evolution. Additionally, flow rate measurements for several volumetric qualities and valve openings are carried out for air, water and two-phase mixtures. Full optical access allowed identification of the structure of the flow. The results are compared with measurements performed at the original industrial valve. Flowforce analysis is performed revealing that compressible and incompressible flowforces in SRV are inversed above a certain value of valve lift. This value varies with critical pressure ratio, therefore is directly linked to the position at which chocked flow occurs during air valve operation. In two-phase flow, for volumetric quality of air=20%, pure compressible flow behavior, in terms of flowforce, is remarked at full lift. Numerical simulations with commercial CFD code are carried out for air and water in axisymmetric 2D model of the valve in order to verify experimental findings.<p>The subject of modeling the discharge through a throttling device in two-phase flow is an important industrial problem. The proper design and sizing of this apparatus is a crucial issue which would prevent its wrong function or accidental operation failure that could cause a hazardous situation. So far reliability of existing models predicting the pressure drop and flow discharge in two-phase flow through the valve for various flow conditions is questionable. Nowadays, a common practice is widely adopted (standard ISO 4126-10 (2010), API RP 520 (2000)); the Homogeneous Equilibrium Method with the so-called !-method, although it still needs further validation. Additionally, based on !-methodology, Homogeneous Non-Equilibrium model has been proposed by Diener and Schmidt (2004) (HNE-DS), introducing a boiling delay coefficient. The accuracy of the aforementioned models is checked against experimental data both for transparent model and industrial SRV. The HNE-DS methodology is proved to be the most precise among the others. Finally, after application of HNE-DS method for air-water flow with cavitation, it is concluded that the behavior of flashing liquid is simulated in such case. Hence, for the specific tested conditions, this type of flow can be modeled with modified method of Diener and Schmidt (CF-HNE-DS) although further validation of this observation is required. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The majority of technical separation processes for fluid mixtures utilize the principle of rectification. If a two-phase mixture is fed into the column, possibly undesirable flow morphologies or severe droplet carry-over may occur, which detrimentally affect separation efficiency and equipment integrity. Currently, the two-phase flow behavior in feed pipes is hardly predicable and mostly based on empirical or heuristic methods, which do not properly account for a broad range of possible fluid properties and plant dimensions. As a consequence, costly safety margins are applied. Feed pipes to separation columns are often characterized by horizontal inlet nozzles, small length-to-diameter ratios and complex routing, involving elbows or bends. The pipe lengths are too short to enable the two-phase flow to fully develop, which thus, enters the column with unknown flow morphology. Since developing flows have rarely been studied, today’s engineering practice relies on existing predictive methods for fully developed two-phase flows. Graphical methods can hardly represent gradual transitions between flow regimes. Analytical models provide only simplified flow representations of the two-phase flow that have not yet been qualified for developing pipe flow. In this work, a comprehensive experimental database of horizontal water-air flows in two test sections with nominal pipe diameters of D = 50 mm and D = 200 mm and feed pipe lengths in the range 10 < L/D < 75 was established. This way, the data cover developing pipe flows with entrance lengths typical for two-phase feeds of separation columns and more developed flows that are comparable with the extensively studied reference system water-air. A particular focus was put on the effect of pipe bends on the flow morphology up- and downstream. The flow morphology was captured using imaging wire-mesh sensors. A 4D fuzzy algorithm was applied to objectively identify the flow two-phase morphologies. Based on their fuzzy representation, the flow morphologies were classified and a novel 2D visualization technique is proposed to discuss the flow development along the feed pipes. Undesired flow morphologies (intermittent flow and entrainment) during the operation of two-phase feeds are hardly predictable by conventional design tools. The inception of intermittent flows was analyzed using the experimental data. Consequently, the inception criteria based on the required liquid levels for fully developed intermittent flows were adapted for short entrance lengths. The characteristic dynamics of flow morphologies that are known to cause the onset of entrainment were analyzed. Based on wave frequencies, a predictive criterion for the susceptibility of wavy flows for the onset of entrainment is introduced and applied to straight feed pipes and horizontal 90° bends. Among the dozens available, 66 reduced-order models for the prediction of the void fraction were tested for straight feed pipes and horizontal 90° pipe bends. Thereof, the ones most suitable for variable operating conditions and pipe geometries were identified and adapted. Complementary 3D simulations were performed to verify the applicability of numerical codes (VoF, AIAD) for flows with free interfaces. The flow morphologies were successfully reproduced at macroscopic scale, however, the simulation results rank behind reduced-order models considering their quantitative predicting capabilities.:Abstract II Kurzfassung IV Acknowledgement VI Nomenclature VIII Table of Contents XIII 1 Introduction 1 1.1 Thermal separation in view of the 21st century 1 1.2 Engineering and design of rectification plants 2 1.3 Outline of the thesis 4 2 State of the art 5 2.1 Two-phase feeds in thermal separation 5 2.1.1 Feed condition as adjustable parameter 5 2.1.2 Thermohydraulic optimization 8 2.1.3 Hydrodynamic conditioning 9 2.2 Hydrodynamics of two-phase feeds 11 2.2.1 Flow morphologies in feed pipes 11 2.2.2 Droplet entrainment 14 2.2.3 Flow regime maps 17 2.2.4 Consequences for two-phase feeds 19 2.3 Modelling of two-phase feeds 23 2.3.1 Basic definitions 23 2.3.2 Fundamentals of the two-fluid model 25 2.3.3 The interfacial level gradient 29 2.3.4 Analytical models 32 2.3.5 CFD simulations for commercial feed pipes 34 2.4 Objectives of this thesis 36 3 Experimental method and algorithms for flow characterization 37 3.1 Experimental setups 37 3.2 Wire-mesh sensors 40 3.3 Experimental procedure 42 3.4 Data processing 44 3.4.1 Fuzzy flow morphology classification 45 3.4.2 Power spectral density 48 3.5 Measurement uncertainty 49 4 Flow morphologies in different feed pipe geometries 53 4.1 Developing two-phase flow in straight pipes 53 4.2 Effect of pipe curvatures on the flow morphology 55 4.3 Morphology recovery 57 4.4 Conclusions 60 5 Prediction of undesirable flow morphologies in feed pipes 61 5.1 Initiation of intermittent flows 61 5.2 Onset of droplet entrainment 62 5.2.1 Vulnerable flow morphologies 62 5.2.2 Derivation of a criterion for onset of entrainment 64 5.2.3 Adjustment of the criterion for the investigated pipe geometries 67 5.3 Conclusions 70 6 Reduced-order modelling of two-phase feeds 71 6.1 Prediction of void fraction 71 6.2 Liquid levels 75 6.3 Conclusions 78 7 CFD modelling of two-phase feeds 79 7.1 Simulation setup 79 7.2 Multiphase models 82 7.3 Comparison with experimental data 83 7.3.1 Straight pipes 83 7.3.2 Horizontal 90° bends 85 7.4 Conclusions 88 8 Summary and recommendations for future work 89 8.1 Summary 89 8.2 Recommendations for future work 91 References 94 List of figures 113 List of tables 118 Appendix i Scientific publications and contributions xxxiii Eidesstattliche Erklärung xxxvii / Die meisten technischen Verfahren zur Trennung von Flüssigkeitsgemischen beruhen auf dem Prinzip der Rektifikation. Wird ein Zweiphasengemisch in die Trennkolonne eingespeist, können unerwünschte Strömungsmorphologien oder ausgeprägte Tröpfchenverschleppung auftreten, welche sich nachteilig auf die Trennleistung und die Integrität einzelner Anlagenkomponenten auswirken. Derzeit lässt sich das Verhalten solcher Zweiphasenströmungen in Einspeiseleitungen kaum vorhersagen und basiert meist auf empirischen oder heuristischen Methoden, die ein breites Spektrum möglicher Stoffeigenschaften und Anlagendimensionen nicht angemessen berücksichtigen. Infolgedessen müssen kostspielige Sicherheitszuschläge angewendet werden. Einspeiseleitungen von Trennkolonnen sind häufig durch horizontale Eintrittsstutzen, ein geringes Länge-zu-Durchmesser-Verhältnis und eine komplexe Leitungsführung mit Bögen und anderen Normteilen gekennzeichnet. Typische Rohrlängen sind zu kurz, um eine vollständig entwickelte Zweiphasenströmung auszubilden, welche daher mit unbekannter Strömungs-morphologie in die Trennkolonne eintritt. Da derartige Strömungen jedoch bisher nur selten untersucht wurden, verlässt man sich gegenwärtig in der technischen Praxis auf bestehende Vorhersagemethoden für voll entwickelte Zweiphasenströmungen. Grafische Methoden können jedoch die allmählichen Übergänge zwischen Strömungsformen kaum darstellen. Analytische Modelle liefern nur vereinfachte Näherungswerte der Zweiphasenströmung, die noch nicht für sich entwickelnde Rohrströmung qualifiziert wird. In dieser Arbeit wurde eine umfangreiche experimentelle Datenbasis horizontaler Wasser-Luft-Strömungen in zwei Versuchsstrecken mit Rohrinnendurchmessern von D = 50 mm und D = 200 mm und Einlauflängen im Bereich 10 < L/D < 75 erstellt. Auf diese Weise decken die Daten sowohl sich entwickelnde Rohrströmungen mit typischen Einlauflängen für Einspeiseleitungen ab, als auch weiter (in axialer Richtung) entwickelte Strömungen, die mit dem umfangreich untersuchten Referenzsystem Wasser-Luft vergleichbar sind. Die Auswirkung von Rohrbögen auf die Strömungsmorphologie stromauf- und stromabwärts wurde gezielt untersucht. Die Strömungsmorphologie wurde mit bildgebenden Gittersensoren erfasst. Ein 4D-Fuzzy-Algorithmus wurde zur objektiven Identifizierung der Strömungsmorphologien eingesetzt. Auf Grundlage dieser Fuzzy-Darstellung der Strömung wurden die Strömungsmorphologien klassifiziert, und es wurde eine neuartige 2D-Visualisierungstechnik entworfen, mit der die Strömungsentwicklung entlang der Einspeiseleitungen diskutiert wurde. Unerwünschte Strömungsmorphologien (intermittierende Strömung und Tropfenmitriss) während des Betriebs zweiphasiger Einspeisungen sind mit herkömmlichen Auslegungswerkzeugen kaum vorherzusagen. Das Einsetzen intermittierender Strömungen wurde auf Grundlage der experimentellen Daten analysiert. Daraufhin wurden existierende Kriterien, basierend auf den notwendigen Mindestfüllständen, für das Einsetzen intermittierender Strömungen in Abhängigkeit von den untersuchten Einlauflängen angepasst. Die charakteristische Dynamik von Strömungsmorphologien, die Tropfenmittriss hervorrufen, wurde analysiert. Voraussagemethoden zur Vorhersage der Anfälligkeit welliger Strömungen für das Auftreten von Tropfenmitriss wurden auf der Grundlage von Wellenfrequenzen entwickelt und für gerade Einspeiserohre und horizontale 90°-Bögen angewandt. Von den zahlreichen verfügbaren Modellen zur Vorhersage des Gasanteils wurden 66 Modelle reduzierter Ordnung für gerade Einspeiseleitungen und horizontale 90°-Rohrbögen getestet. Davon wurden die für variable Betriebsbedingungen und Rohrgeometrien am besten geeigneten Modelle ermittelt und angepasst. Komplementäre 3D-Simulationen wurden durchgeführt, um die Anwendbarkeit numerischer Codes (VoF, AIAD) für Strömungen mit freien Grenzflächen zu bestätigen. Die Strömungsmorphologien wurden im makroskopischen Maßstab erfolgreich reproduziert, die Simulationsergebnisse bleiben jedoch hinsichtlich ihrer quantitativen Vorhersagekraft hinter den Modellen reduzierter Ordnung zurück.:Abstract II Kurzfassung IV Acknowledgement VI Nomenclature VIII Table of Contents XIII 1 Introduction 1 1.1 Thermal separation in view of the 21st century 1 1.2 Engineering and design of rectification plants 2 1.3 Outline of the thesis 4 2 State of the art 5 2.1 Two-phase feeds in thermal separation 5 2.1.1 Feed condition as adjustable parameter 5 2.1.2 Thermohydraulic optimization 8 2.1.3 Hydrodynamic conditioning 9 2.2 Hydrodynamics of two-phase feeds 11 2.2.1 Flow morphologies in feed pipes 11 2.2.2 Droplet entrainment 14 2.2.3 Flow regime maps 17 2.2.4 Consequences for two-phase feeds 19 2.3 Modelling of two-phase feeds 23 2.3.1 Basic definitions 23 2.3.2 Fundamentals of the two-fluid model 25 2.3.3 The interfacial level gradient 29 2.3.4 Analytical models 32 2.3.5 CFD simulations for commercial feed pipes 34 2.4 Objectives of this thesis 36 3 Experimental method and algorithms for flow characterization 37 3.1 Experimental setups 37 3.2 Wire-mesh sensors 40 3.3 Experimental procedure 42 3.4 Data processing 44 3.4.1 Fuzzy flow morphology classification 45 3.4.2 Power spectral density 48 3.5 Measurement uncertainty 49 4 Flow morphologies in different feed pipe geometries 53 4.1 Developing two-phase flow in straight pipes 53 4.2 Effect of pipe curvatures on the flow morphology 55 4.3 Morphology recovery 57 4.4 Conclusions 60 5 Prediction of undesirable flow morphologies in feed pipes 61 5.1 Initiation of intermittent flows 61 5.2 Onset of droplet entrainment 62 5.2.1 Vulnerable flow morphologies 62 5.2.2 Derivation of a criterion for onset of entrainment 64 5.2.3 Adjustment of the criterion for the investigated pipe geometries 67 5.3 Conclusions 70 6 Reduced-order modelling of two-phase feeds 71 6.1 Prediction of void fraction 71 6.2 Liquid levels 75 6.3 Conclusions 78 7 CFD modelling of two-phase feeds 79 7.1 Simulation setup 79 7.2 Multiphase models 82 7.3 Comparison with experimental data 83 7.3.1 Straight pipes 83 7.3.2 Horizontal 90° bends 85 7.4 Conclusions 88 8 Summary and recommendations for future work 89 8.1 Summary 89 8.2 Recommendations for future work 91 References 94 List of figures 113 List of tables 118 Appendix i Scientific publications and contributions xxxiii Eidesstattliche Erklärung xxxvii

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Call number: LD2668 .T4 1979 H43 / Master of Science