Die vorliegende Habilitationsschrift stellt den erreichten Stand der CFD-basierten Modellierung ein- und mehrphasiger Hochtemperaturprozesse dar. Die hierzu vorgelegten Arbeiten umfassen die Hochdruck-Partialoxidation von Erdgas, die Vergasung fester Einsatzstoffe in einem endothermen Flugstromreaktor und in einem mehrstufigen Wirbelschichtprozess sowie die Synthesegasaufbereitung in einem neuen Quenchreaktor. Der Forschungsschwerpunkt reicht dabei von der Entwicklung neuer Korrelationen zur Beschreibung der Strömungskräfte und des Wärmeübergangs basierend auf partikelaufgelösten Rechenmodellen über die Modellierung der thermochemischen Konversion reaktiver Einzelpartikel bis hin zur Berechnung und Optimierung unterschiedlicher Hochtemperaturreaktoren. / This habilitation thesis discusses the state of the art for the CFD modeling of single-phase and multi-phase high-temperature processes. The presented publications comprise the high-pressure partial oxidation of natural gas, the gasification of solid fuels in entrained-flow gasifiers and multi-stage fluidized-bed gasifier as well as the syngas treatment in a new quench reactor. The scientific approach covers the development of new correlations for flow forces and heat transfer based on particle-resolved numerical models, the modeling of the thermochemical conversion of reactive single particles, and the calculation and optimization of different high-temperature processes.

Multiphase flows abound in nature and enterprises. Our daily interactions with fluids - washing, drinking, and cooking, for example - occur at a free surface and within the realm of multiphase flows. The applications of multiphase flows within the context of emulsions, which are caused by mixing two immiscible fluids, have been of interest since the nineteenth century: compartmentalizing one fluid in another is particularly of interest in applications in pharmaceutical, materials, microfluidics, chemical, and biological engineering. Even more control in compartmentalization and delivery can be obtained through the usage of double emulsions, which are emulsions of smaller drops (i.e., inner drop) within larger drops (i.e., outer drop). The goal of this work is to understand the dynamic behavior of compound drops in confined flow at low Reynolds numbers. These behaviors include the migration patterns, limit cycles, and equilibrium locations in confined flows such as channel flows.<br> <br>Firstly, we look at non-concentric compound drops that are subject to simple shear flows. The eccentricity in the inner drop is either within the place of shear, normal to the plane of shear, or mixed. We show unreported motions that persist throughout time regardless of the initial eccentricity, given that the deformations of the inner and outer drops are small. Understanding the temporal dynamics of compound drops within the simple shear flow, one of the simplest background flows that may be imposed, allows us to probe at the dynamics of more complicated background flows.<br> <br>Secondly, we look at the lateral migration of compound drops in a Poiseuille flow. Depending on the initial condition, we show that there are multiple equilibria. We also show that the majority of initial configurations results in the compound drop with symmetry about the short wall direction. We then show the time it takes for the interfaces to merge if a given initial configuration does not reach the aforementioned symmetry.<br> <br>Thirdly, while the different equilibria of compound drops offer some positional differences at different radii ratio, we show that the lift force profiles at non-equilibrium locations offer distinctly different results for compound drops with different radii ratio. We then look at how this effect is greater than changes that arise due to viscosity ratio changes, and offer insights on what may create such a change in the lift force profile.

The aluminothermic (AT) process utilises a self-propagating high-temperature synthesis (SHS) type reaction for producing primarily thermite steel and alumina slag at high temperatures during the welding of rails. In this work, an investigation on the early stages of the aluminothermic process, the separation of AT reaction products and mould filling has been carried out, using both experimental and computational methods to predict the time duration of a complete separation and to obtain a better understanding of the internal multiphase flow within the crucible and mould. The decomposition of AT reaction products after the combustion and the subsequent mould filling by thermite steel and alumina slag have been simulated numerically, using a diffusive phase field and volume-of-fluid model. However, to minimize numerical errors on the input parameters of the high- temperature multiphase flow, a careful review on transport properties has been made. Missing data, e.g. the contact angle of thermite steel on waterglass-bonded mould and crucible wall material has been investigated experimentally. Being further necessary for the prediction of the separation time of AT reaction products in compacted thermite, results on the propagation front velocity show a decreasing trend with increasing initial compact temperature. Further, the combustion front velocity is used for a subsequent analysis of the separation time, which is obtained from the phase distribution of thermite steel, alumina slag and intermetallic compounds, using a combustion front quenching (CFQ) methodology. Moreover, geometric modifications on the crucible and mould have been developed for a reduction in changeover time, as well as an optimized multiphase flow field. Their performance during crucible discharge and mould filling has been verified numerically. Furthermore, alumina slag inclusions have been tracked within the mould using a volume-of-fluid approach with their final positions being verified through an authentic welding. / Während des aluminothermischen (AT) Prozesses findet eine SHS-Reaktion Anwendung, um primär Thermitstahl und Aluminiumoxidschlacke bei hohen Temperaturen für das Verschweißen von Bahnschienen herzustellen. In dieser Arbeit wurden Anfangsstadien, welche die Separation der AT-Reaktionsprodukte sowie das Füllen der Gießform einbeziehen, unter Anwendung von sowohl experimentellen als auch numerischen Verfahren untersucht. Damit konnte die Zeitdauer einer kompletten Separation ermittelt und ein genaueres Verständnis der Mehrphasenströmung in Tiegel und Gießform erlangt werden. Die Separation der AT-Reaktionsprodukte nach der aluminothermischen Reaktion und die anschließende Formfüllung wurden mit einem diffusen Phasenfeld und einem Volume-of-Fluid-Modell numerisch berechnet. Für die Minimierung numerischer Fehler in den Eingangsgrößen dieser Hochtemperatur-Mehrphasenströmungen wurde eine intensive Literaturrecherche durchgeführt und fehlende Parameter, wie zum Beispiel die Kontaktwinkel von Thermitstahl auf Wasserglas gebundenem Form- und Tiegelmaterial, wurden experimentell ermittelt. Messungen der Reaktionsfrontgeschwindigkeit in gepresstem Thermit sind notwendig für eine Vorhersage der Separationszeit der AT-Reaktionsprodukte, und die Ergebnisse zeigen einen linear abfallenden Trend mit zunehmender Anfangstemperatur des verdichteten Materials. In dieser Arbeit wurde die Geschwindigkeit der Reaktionsfront verwendet, um aus der Phasenverteilung von Thermitstahl, Aluminiumoxidschlacke und intermetallischen Verbindungen als Ergebnis des CFQ-Experimentes die Separationszeit in verdichtetem Thermit zu approximieren. Es wurden Modifikationen an Tiegel und Gießform erprobt, die für eine Verbesserung der internen Strömungsführung sowie für die Reduzierung der Umrüstzeit sorgen sollen. Die Effizienz dieser Veränderungen wurde anschließend mit numerischen Methoden überprüft. Des Weiteren konnten durch eine Realschweißung die numerisch vorhergesagten finalen Positionen von Schlackeeinschlüssen innerhalb der Gießform verifiziert werden.

Environmental pollution has become a global concern as consequence of industrializa-tion and urbanization. The ongoing subsurface contamination by dense non-aqueous phase liquids (DNAPLs) bears tremendous hazardous potential for humans and ecosys-tems including aquifer systems. Intended or accidental spill events have led to a vast number of registered sites affected by DNAPL type chemicals. Despite the existence of novel techniques for their exploration, characterization and remediation, economical constraints often limit efforts for risk prevention or reduction, so that information and data to characterize highly complex DNAPL contamination scenarios are often insuffi-cient and compensated by natural attenuation of groundwater-dissolved contaminant plumes. Especially, knowledge on the DNAPL source zone geometry (SZG) and source zone formation are critically required yet very scarce. Against the previously stated background, this cumulative doctoral dissertation critically examined the processes of DNAPL source zone formation at laboratory scale. A comprehensive literature review identified current limitations and open research questions in the latter research field, revealing evidence for the relevance of SZG for plume response at different scales. Giv-en only a limited number of published studies related to DNAPL source zone formation, two simplified experimental setups mimicking source zone formation in an initially fully water-saturated aquifer were developed and intensively tested. The performance of aqueous and non-wetting phase dyes was evaluated for DNAPL release into three non-consolidated porous media using reflective optical imaging in combination with a cus-tom-made image processing and analysis (IPA) framework. The latter suite allowed for the generation of physically plausible DNAPL saturation distributions with determinable level of uncertainty. Then, a limited number of DNAPL release experiments were per-formed under controlled ambient as well as with boundary and initial conditions to generate robust observation data, while further adopting the IPA framework. The latter data was introduced into a numerical multiphase flow model. While most system pa-rameters could be directly determined, the parameters defining the capillary pressure-saturation and relative permeability-saturation retention curves were inversely deline-ated through a classical Monte Carlo analysis. Overall, the successfully calibrated nu-merical setup mimicking the transient DNAPL source zone formation allowed to quanti-fy uncertainties related to the experiment, IPA framework and model setup configura-tion. In addition, a number of new research questions pointing towards future im-provements of laboratory-scale methodologies to understand DNAPL contamination were derived. Especially in light of numerous existing contaminated sites with unclear history and even more vague future, given by potential impacts through climate change and anthropogenic activity, an increasing need for sophisticated strategies to better un-derstand DNAPL contamination and to reduce hazard potential is expected.:Statement I List of publications II Abstract VI Acknowledgements and funding information IX List of figures XIII List of tables XIV Abbreviations and symbols used in the main text XV 1 Introduction and background 1-1 1.1 Motivation of this thesis 1-1 1.2 Incorporation of this thesis in research projects 1-4 1.3 Definition of objectives and workflow strategy of this thesis 1-5 1.4 Formal structure of this thesis 1-11 2 Existing knowledge on DNAPL contamination 2-1 3 Fundamentals of DNAPL migration in porous media 3-1 3.1 Basic concepts for multiphase flow in porous media 3-1 3.2 Capillary pressure-saturation correlation 3-3 3.3 Relative permeability-saturation correlation 3-5 3.4 Balance equations for laminar fluid phase flow in porous media 3-7 4 Core research complex A : Development of a framework for the semi-automatized generation of DNAPL saturation distribution observation data 4-1 5 Core research complex B : Experimental and model-based simulation of DNAPL source zone formation 5-1 6 Summary and conclusions 6-1 6.1 Summary of perceptions for each main section of this thesis 6-1 6.2 New research questions with regard to DNAPL source zone formation at the laboratory scale 6-5 6.3 General recommendations for future works related to DNAPL contamination 6-8 References Ref-1 Appendix I : ENGELMANN ET AL. (2019a) App I-1 Published journal article App I-1 Appendix II : ENGELMANN ET AL. (2019b) App II-1 Published journal article App II-1 Electronic Supplementary Material 1 : Unprocessed raw TIFF format images used for IPA frame-work evaluation App II-26 Electronic Supplementary Material 2 : Sensitivities for color model change and binary conversion algorithms App II-36 Electronic Supplementary Material 3 :Relevance of spatially non-uniform illumination correction and background exclusion App II-76 Appendix III : ENGELMANN ET AL. (2021) App III-1 Published journal article App III-1 Electronic Supplementary Material 1 : Unprocessed raw TIFF format images for IPA framework ap-plication App III-30 Electronic Supplementary Material 2 : Processed images with all intermediate steps of IPA frame-work application App III-58 Electronic Supplementary Material 3 : IPA fitness App III-86 Electronic Supplementary Material 4 : Partial objective functions App III-87 Electronic Supplementary Material 5 : Model verification App III-93

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Bei oberflächennahen geothermischen Anwendungen kommt es zu Temperaturveränderungen im Untergrund, um Wärme zu gewinnen oder zu speichern. Die dadurch verursachten thermischen Auswirkungen können die thermischen, hydraulischen und chemischen Bedingungen des Untergrunds verändern und sich auf die Systemleistung auswirken. Die Situation wird noch komplizierter, wenn die Grundwasserleiter unterschiedlich gesättigt sind und eine Verunreinigung des Untergrunds vorliegt. In dieser Arbeit werden vollständig gekoppelte Wärme- und Stofftransportmodelle angewandt, um die Wechselwirkung zwischen oberflächennahen geothermischen Anwendungen und der unterirdischen Umgebung besser zu charakterisieren. Es werden drei verschiedene Szenarien untersucht. Zunächst werden die thermischen Auswirkungen und die Nachhaltigkeit einer intensiven oberflächennahen geothermischen Nutzung in einem Wohngebiet über einen Zeitraum von 24 Jahren bewertet. Überwachungsdaten des Standorts werden in das Modell integriert, und die Bedeutung standortspezifscher Kenntnisse für die Planung wird hervorgehoben. Zweitens wird der gekoppelte Feuchtigkeits- und Wärmetransport eines Erdwärmespeichersystems (BTES) untersucht. Es wird eine Sensitivitätsanalyse durchgeführt und die Wärmeentzugsefzienz zwischen verschiedenen Szenarien verglichen. Bei Austrocknung oder starker Gasphasenkonvektion werden signifkante Änderungen im Wärmetransportverhalten erwartet. Drittens wird ein nichtisothermes Drei-Komponenten-Zweiphasenströmungsmodell abgeleitet und mit der Finite-Elemente-Methode implementiert. Die Validierung des numerischen Modells bestätigt seine Fähigkeit, die gekoppelte Strömung sowie den Wärme- und Stofftransport in einem ungespannten Grundwasserleiter zu simulieren, der einem BTES-Betrieb ausgesetzt ist. Insbesondere wird das Potenzial für die thermisch verstärkte Verflüchtigung von Trichlorethylen (TCE) in wässriger Phase bewertet. Da durch die Wärmezufuhr eine Auftriebsströmung induziert wird, nimmt die Verringerung der Schadstoffmasse erheblich zu und erreicht nach fünf Jahren mehr als 70 %. Die in dieser Arbeit gewonnenen Erkenntnisse können durch die Verbesserung ihrer ökologischen und ökonomischen Leistungen zu einer breiteren Akzeptanz von Technologien der flachen Geothermie beitragen. / Shallow geothermal applications induce temperature changes in the subsurface for heat extraction or storage purposes. Their induced thermal impacts may alter the thermal, hydraulic, and chemical conditions of the subsurface and feedback on the system performance. The situation is further complicated in variably saturated aquifers and when subsurface contamination exists. In this work, fully coupled heat and mass transport models are applied to improve the characterization of interaction between shallow geothermal applications and the subsurface environment. Three different scenarios are investigated. First, the thermal impact and sustainability of intensive shallow geothermal exploitation in a residential area is evaluated over a 24-year period. Monitoring data from the site is integrated into the model and the importance of site-specifc knowledge for planning is highlighted. Second, the coupled moisture and heat transfer of a soil borehole thermal energy storage (BTES) system is explored. A sensitivity analysis is performed and the heat extraction efciency is compared among various scenarios. Signifcant changes in the heat transport behavior are expected when drying out or strong gas phase convection occurs. Third, a non-isothermal three-component two-phase flow model is derived and implemented with the fnite element method. Validation of the numerical model confrms its ability to simulate the coupled flow, heat and mass transport in an unconfned aquifer subject to BTES operation. In particular, the potential for thermally-enhanced volatilization of aqueousphase trichloroethylene (TCE) is assessed. As buoyant flow is induced due to heat injection, reduction of the contaminant mass grows considerably, reaching more than 70% after fve years. The fndings obtained from this thesis can contribute to a wider adoption of shallow geothermal technologies through the enhancement of their environmental and economical services.

[pt] Nas últimas décadas, grandes investimentos foram feitos no desenvolvimento de modelos e métodos numéricos para prever e analisar os diferentes aspectos do processo de recuperação de óleo e gás. Neste contexto, os simuladores modernos devem ser capazes de incorporar uma grande variedade de opções para responder questões relacionadas ao gerenciamento de reservatórios de forma rápida e precisa. Neste trabalho, nós apresentamos um simulador de reservatórios baseado em uma arquitetura de plugins, onde diferentes formulações, solvers e modelos podem ser desenvolvidos, estendidos e aprimorados. A partir desta abordagem, utilizamos o modelo black-oil para implementar técnicas tradicionais e do estado da arte, como os métodos totalmente e adaptativamente implícito, os métodos de Newton-Raphson e Newton Inexato, controladores heurístico e PID para passo de tempo adaptativo e aproximações de fluxo de um ponto baseados no potencial de fase tradicional e C1-contínuo. Diversas configurações de plugins foram testadas e validadas com simuladores comerciais e seus desempenhos foram utilizados para determinar quais as mais adequadas para resolver problemas de escoamento multifásico. / [en] During the last decades, large investments were made towards the development of numerical models and methods to forecast and analyze the different aspects of oil and gas recovery. In this context, modern simulators must be able to incorporate a wide variety of options to answer questions related to reservoir management accurately and effectively. In this work, we present a reservoir simulator based on a plugin architecture, where different formulations, solvers, and models can be developed, extended, and enhanced. With this approach, we use the black-oil model to implement traditional and state-of-the-art techniques, including fully- and adaptiveimplicit methods, heuristic and PID time-step controllers, Newton-Raphson and Inexact Newton, and C1-continuous and conventional phase-potential single-point upstream weighting. Several plugin configurations were tested and validated with commercial simulators, and their performances were used to determine which are the most suitable to solve multiphase flow problems.

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Roterugnar är cylindriska kärl som används för att höja materials temperaturer i en kontinuerlig process som kallas för kalcinering. Roterugnar kan tillämpas i olika processer såsom reduktion av oxidmalm samt återvinning av farligt avfall. Fördelen med roterugnar ligger i dess förmåga att hantera råmaterial som sträcker sig från slam till granulära material med en mängd olika partikelstorlekar, och därigenom upprätthålla distinkta miljöer såsom en bädd av fasta partiklar som samexisterar med ett oxiderande fribord. Sex olika bäddbeteende har dokumenterats med avseende på fyllningsgrad samt Froude nummer. Syftet med denna studie var att utveckla en tvådimensionell suspensions modell med CFD genom att använda den kommersiella mjukvaran COMSOL 5.5 för att simulera de två faser, gas och fast, som en blandad fas efter verk av Philips et. al., Physics of Fluids A: Fluid Dynamics 4.1 (1992) 30-40 och Acrivos &amp; Zhang., International Journal Multiphase Flow 20.3 (1994) 579-591. Denna modell undersöktes genom att jämföra den med de dokumenterade flödesregimerna samt genom parameter som partikelstorlek, partikeldensitet och viskositeten hos gas i flödesregimen känd som rullande läge. Dessutom undersöktes temperaturprofilen för den roterande ugnen genom att utforska hur blandningsvariationer av den fasta bädden i den roterande ugnen påverkas av värmeöverföringen när värme tillförs från väggen under rullande läge. Resultaten av den tvådimensionella suspension modellen visade att det var bara möjligt att simulera glidläge korrekt; andra lägen kunde inte beskrivas som dokumenterat i litteraturen. Det indikeras att vilovinkeln och viskösa krafter i den roterande ugnen var låga vilket resulterade i att suspensions modellen inte kunde avbilda exakt de återstående flödesregimerna som dokumenterat. Till exempel avbildades rullningsläget mer likt forsandeläge då partiklarna fall fritt efter höjning av bädden. Partikelstorlek och partikeldensitet har visat sig ha en betydande påverkan på suspensions modellen eftersom de viskösa krafterna blir låga för en partikelstorlek och partikeldensitet under 0,4 mm respektive 1500 kg/m3. Angående gasens viskositet visades det sig att ju närmare värdet 2.055e-3 (Pa*s) den blev desto större blev sedimentationsflödet vilket resulterade i att bäddpartiklarna dras ner och förblir där. Suspensions modellen kunde således simulera en fast och flytande fas och inte en gasfas som avsett. Slutligen visade temperaturanalysen att påverkan av den termiska konduktiviteten var mer signifikant än den specifika värmekapaciteten i intervallet 1 - 50 (W/(m*K)) respektive 300 - 800 (J/(kg*K)) på grund av den tid det tog att nå en homogen temperaturprofil. / Rotary kilns are cylindrical vessels used to raise materials temperature in a continuous process known as calcination. Rotary kilns find application in various processes such as reduction of oxide ore and hazardous waste reclamation. The advantage of the rotary kiln lies in its ability to handle feedstock ranging from slurries to granular materials with a variety of particle size, thereby maintaining distinct environments such as a bed of solid particles coexisting with an oxidising freeboard. Six different bed behaviours within the kiln have been documented with respect to the filling degree and Froude number. The aim of this study was to develop a two-dimensional suspension model with CFD by using the commercial software COMSOL 5.5 to simulate the two phases, gas and solid, as a mixed phase, following the works of Philips et. al., Physics of Fluids A:  Fluid Dynamics 4.1 (1992) 30-40 and Acrivos &amp; Zhang., International Journal Multiphase Flow 20.3 (1994) 579-591. This model was investigated by comparing it against the documented flow regimes as well as through parameters such as particle size, particle density and viscosity of gas in the flow regime known as rolling mode. In addition, the temperature profile of the rotary kiln was investigated by exploring how the mixture variation of the solid bed within the rotary kiln affects the heat transfer when heat is supplied from the wall during a rolling mode. The results of the two-dimensional suspension model showed that it was only possible to simulate the slipping mode accurately; others mode could not be described as documented in literature. It is indicated that the angle of repose and viscous forces within the rotary kiln were low resulting in the suspension model not being able to accurately depict the remaining flow regimes as documented. For instance, the rolling mode was depicted more as a cataracting mode due to the free fall of particles after elevation of the bed. The particle size and the particle density were found to have a significant impact on the suspension model as the viscous forces became low for a particle size and particle density below 0.4 mm and 1500 kg/m3 respectively. As for the viscosity of gas it was found that the closer it got to the value 2.055e-3 (Pa*s) the sedimentation flux became too large resulting in the bed particles being pulled down and remaining there. Thus, the suspension model could simulate a solid and liquid phase and not a gas phase as intended. Lastly, the temperature analysis revealed that the impact of the thermal conductivity was more significant than the specific heat capacity in the range of 1 - 50 (W/(m*K)) and 300 - 800 (J/(kg*K)) respectively, due to the time it took to reach a homogeneous temperature profile.

[pt] Os custos de instalação e as taxas de produção ao longo da vida de um reservatório de óleo e gás são influenciados diretamente pela localização, quantidade e capacidade das Unidades Estacionárias de Produção (UEPs). A distância entre um poço e a UEP a qual foi alocado é um fator impactante na perda de carga a que os fluídos são submetidos. A dissipação de energia aumenta quando essa distância é maior e todo o sistema de produção recebe a interferência negativa desta perda, o que compromete as taxas de recuperação. A necessidade de respeitar as restrições de capacidade das UEPs faz com que outras decisões precisem ser tomadas no mesmo momento em que se decide a localização de cada uma. Este trabalho descreve um modelo baseado em Algoritmos Genéticos para a otimização simultânea da quantidade, localização e dimensionamento de Unidades Estacionárias de Produção (UEPs). Para lidar com as restrições lineares e não lineares do problema utiliza-se a técnica chamada de GENOCOP III - Genetic Algorithm for Numerical Optimization of Constrained Problems e funções de penalidade. O objetivo da otimização é maximizar o Valor Presente Líquido (VPL) que depende da curva de produção de cada configuração obtida como possível solução. Para obter a curva de produção são realizadas simulações de reservatório que utilizam tabelas de escoamento multifásico para representar o sistema de produção externo ao reservatório. O modelo de solução foi testado em um modelo de reservatório baseado em um caso real. Os resultados encontrados indicam que a utilização deste modelo de solução como ferramenta pode auxiliar a tomada de decisão dos especialistas responsáveis pelo desenvolvimento de campos de petróleo. / [en] Installation costs and production rates over the life of an oil and gas reservoir are directly influenced by the location, number and capacity of the Production Units. The distance between a well and the Production Unit to which it has been allocated is an important factor in the loss of fluids pressure. The power dissipation increases when the distance is bigger and the entire production system receives the negative interference of this loss, compromising recovery rates. There is a need to take into account restrictions that apply to the capacity of Production Unit at the same time as there localization are decided. This paper describes a model with genetic algorithms for the simultaneous optimization of the quantity, location and sizing of Production Units. To deal with the constraints of the problem we use a technique called GENOCOP III - Genetic Algorithm for Numerical Optimization of Constrained Problems. The goal of the optimization is to maximize the Net Present Value (NPV) which depends on the production curve of each configuration obtained as a possible solution. The production curves are obtained by reservoir simulations with multiphase flow tables that represent the system external to the reservoir. The solution model was tested in a reservoir model based on a real case. The results indicate that using this solution model as a tool can assist the decision making of experts responsible for oil field development.