Fluidized bed reactors are catalytic multiphase reactors capable of processing large volumes with relatively high mass and heat transfer, which is appealing to a variety of industries. The presence of voids, in this case gas bubbles, within these systems can be detrimental to the efficiency and are desired to be minimized. Further fundamental understanding of the bubbles is necessary to model, design, and control them. However, the study of bubbles is difficult, as these beds are typically opaque and 3D. Current studies of bubbles within fluidized beds are often limited to use of quasi-2D set ups, specialized particles, or internal measuring devices. This research utilizes a newly constructed experimental setup consisting of three x-ray source and flat panel detector pairs that produce 2D projections. This setup allows for investigation into the bubble dynamics inside a 3D cylindrical column with industrial particles. The possibilities and limitations of the use of 2D projections to obtain fully 3D time-resolved reconstructions were explored through simple 3D reconstructions of injections of single bubbles. These 3D reconstructions showed the potential of the setup for 3D time-resolved studies of the bubble dynamics and laid the groundwork for future studies. Apart from the ability to obtain 3D reconstructions, the 2D projections can be used to study the dynamics of the bubbles. In this research, 2D projections of an injection of a single bubble were used to develop a deeper fundamental understanding of the shape, motion, and dynamics of an individual bubble traversing through a bed. The bubble shape and size were obtained through a horizontal slicing technique, which assumes axis-symmetry around the vertical axis. Different background fluidization levels, injection volumes, injection velocities, particles, and column diameters were investigated. An analysis of the individual bubble trajectories and the statistical averages provided insight into the interconnection of these factors. The two previously studied bubble stages, formation and rising, were observed. The rising stage was observed to have two regions, stable and unstable. The stable region, following the formation stage, occurs when the motion of the bubble is essentially rectilinear. The unstable region, following the stable region, occurs when the bubble moves sideways while traversing the column in an irregular motion. A simple analogy to gas bubbles in a liquid was drawn, suggesting the bubble cloud, or particles surrounding the bubble, plays a vital role, especially in the formation of the bubble. Standard correlations for the bubble rise velocity based on a constant bubble Froude number were found to be insufficient at accurately describing the bubble velocity and dynamics. The Froude number for individual bubbles appears to be non constant and dependent on parameters that have not been previously considered, like the level of background fluidization.

Chemical process industries face challenges in monitoring and controlling complex operations. Current `visualization' techniques require extensive data and computational efforts, which may not always be feasible. Moreover, these techniques often lack detailed insights into the underlying physics. This thesis explores an a priori integral approach that can reconstruct scalar or vector fields using sparse sensor measurements. The approach is conceptually built on the mathematical constraints associated with Helmholtz-Hodge Decomposition together with the physical laws. To illustrate this, temperature field reconstructions are considered in steady heat transfer systems, including scenarios with either heat generation or forced convection, using discrete data obtained from flow-following sensors.

A generalized framework is developed using hypothetical heat sources (potentials), with parameters of the heat potentials being determined from the values of the temperature field measured at limited discrete points. Infinitely many reconstructed solutions are possible and the arrangement, population, intensity, and size of the hypothetical heat potentials are the issues of interest that influence the reconstructed solution. Two concrete possibilities are presented for simplification (linearization) by limiting the issues associated with these potentials. The optimal values of unknowns are determined using sparse sensor measurements in a linear system of equations, with the help of `training’. The framework-assisted reconstructed fields demonstrate accurate predictions of uniform and smooth temperature distribution, while utilizing only a small number of sensor measurements, and minimal computational effort. This validates the effectiveness of an integral approach.

In more complex situations, like locally uneven fields or sharp convective currents, the framework-assisted reconstructions focus primarily on the dominant phenomena and do not capture specific (or, local) characteristics. This highlights the inherent limitations associated with the simplification of a non-linear problem. Potential improvements regarding the treatment of issues associated with heat potentials are suggested for developing a more versatile framework.

The performance of the source framework developed in this work, based on an integral approach, is compared with the Hidden Fluid Mechanics algorithm, a recently developed physics-informed neural network framework, based on a differential approach. This comparison highlights the strength of the source frameworks and the integral approach to `visualize' simple and smooth domains, in terms of computational expense and accuracy, particularly when dealing with a limited number of measurements. Integrating physics-constrained field functions, developed in this work, into a neural network architecture can present an intriguing avenue for framework optimization. Additionally, gradual enhancements in domain complexity can be explored to expand the applicability of the framework.

Presented works describe a novel approach to assess mixing in a stirred vessel using light-based tomography. The study is driven by key research questions: What are the obstacles in three-dimensional dynamic tracer distribution reconstruction? How should the experimental equipment be constructed to obtain the best possible data from three cameras recording the back-lit stirred tank? How can raw images be processed to isolate the ray-dye interaction? And, how can relevant mixing information be obtained from projections and reconstructed volumetric data? The research begins with a short introduction of traditional mixing measurement techniques, establishing the context and relevance of the work. The theoretical background of the study is then presented, including the principles of tomographic reconstruction and the main algorithms used in the process. The methodology involves the use of synthetic data obtained from LES for the framework and baseline creation followed by the acquisition of experimental data. A significant part of the methodology is dedicated to image pre-processing, which incorporates as main steps the inverted grayscale transformation, brightness normalization, background removal using image similarity metrics and object removal with the use of a neural network. The use of the simplistic forward model based on the Lambert-Beer law is described, followed by the implementation of the projection matrix-free Simultaneous Algebraic Reconstruction Technique. The outcomes of both synthetic and experimental data reconstruction are presented and despite the shortcomings of the used experimental setup the 2D and 3D mixing maps were created, supported by the local Coefficient of Variance calculation to gain further insight into the process. The conclusions highlight the potential of light-based tomography for evaluating mixing while acknowledging the need for significant refinement and validation of the methodology. Recommendations include the improvement of imaging, equipment modifications, and reconstruction implementation. ii

This thesis is aimed at developing a fundamental understanding of the key physical mechanisms associated with swirling gas-liquid flow in a vertical pipe, in order to construct a mechanistic model for predicting the flow behaviour. The model is based on quasi-1D reasoning, in analogy to the classical models for gas-liquid flow without swirl. As a benchmark case, it is used to investigate the onset of columnar flow patterns that are characteristic to swirling multiphase flow, for low gas input flows.

Experimental investigation of swirling vertical gas-liquid flow regimes. Different columnar flow patterns were observed and were used to construct flow regime maps. Four swirl elements were used to investigate the effect of swirl intensity on the flow regimes. An attempt was made to model the transitions between these columnar flow patterns.

Particle-laden internal turbulent flows are very commonplace, for example, in petrochemical flow lines, oil wells and so on. From an engineering view point, modelling such flows in a 3D or even 2D fashion may not be reasonable in terms of computational cost, especially when the flow domain is sufficiently long, and a large number of grid cells are needed to resolve the flow field. On the other hand, ID models are quite fast but only take into account the stream-wise variations of the flow characteristics, without providing any information on their cross-sectional distribution. In this work, a novel quasi-ID modelling framework was introduced, which is able to capture the flow field in both stream-wise and cross-stream directions and yet stay computationally more efficient than the 3D or 2D models. The quasi-ID modelling framework was developed based on the one-way coupling of a RANS model for the single-phase turbulent flow with an Eulerian model for the transport of the dispersed particle phase. The nucleation, agglomeration and breakup events were also taken into considera¬tion through the generic population balance equation, the solution of which was provided using the direct quadrature method of moments. The results of the quasi-ID single-phase flow model were verified and shown to be in accordance with those of the AN SYS Fluent 2D model for different test cases. The computational cost analysis revealed that the simulation CPU time of the quasi-ID model increases linearly with the number of streamwise grid cells (Nx), whereas that of the 2D model scales with Nx1.6, implying that the quasi-ID model will perform faster than the 2D model from a certain number of grid cells on. The quasi-ID multi-phase-flow tool was then used to address the transport and deposition of asphaltenes in oil wells, as an example of particle-laden internal turbulent flows. To this end, a simulation test case was set up with several simplifications, and the results were compared with those of a simpler ID model in the literature, as the benchmark. Due to the lack of an appropriate model for the collision efficiency of asphaltene particles, a model associated with liquid droplets was adopted and tuned to obtain a match between the results of this study and the benchmark. The outcome of the sensitivity analysis demonstrated that the collision efficiency plays an important role in determining the asphaltenes deposition profile along the well bore and needs to be modeled accurately.

For many decades, conventional gravitational separators have been the backbone of the fluid separation in the oil and gas industry. The stricter environment regulation for purification of the recycled water, together with a tighter profitable margin of the produced oil, requires more efficient and faster separators. Inline swirl separator uses centrifugal acceleration up to hundreds of gravitational accelerations to perform separation in a much faster time. However, its efficiency is still lower than the industry expectations. There are essential geometric parameters such as swirl intensity and the collector tube, and vital operating conditions such as flow-rate at the entrance and mass flow-rate at each exit that impact the dynamics behavior of swirl flow in the pipe. The dynamic behavior of the swirl flow determines the efficiency of the apparatus. Thus, the main objective is to understand the dynamics of the single-phase swirl flow in the pipe and determine an inline swirl separator that presents sufficient efficiency. The first part of the study focuses on a better understanding of the dynamic behavior of the swirl flow in a pipe. The second part utilizes the results from the first stage to determine an inline swirl separator that presents sufficient efficiency. The performed numerical study suggests that the dynamic behavior of swirl flows in a pipe is determined by the intensity of the swirl flow, which is quantified by the swirl number. The swirl intensity shapes the axial velocity profile at the core of the vortex. When the swirl number increases beyond a critical number, a columnar vortex appears, with a reverse flow along with the center of the entire tube. The swirl intensity decays along the wall of the pipe; the swirl intensity and the decay of it form the shape of the axial velocity profile. In case the disturbance of the flow results in a stagnation point at the vortex axis, it may develop a vortex breakdown. The vortex breakdown in high Reynolds numbers ( Reb > 100,000) is a function of the swirl number, and the instability at the vortex core increases by increasing the swirl intensity. Furthermore, the results show that the stability of the vortex is a function of the Reynolds number. Considerable reduction of the Reynolds number kicks in the effect of viscous forces, which stabilize the vortex core. Reynolds and swirl numbers determine the dynamic of the low Reynolds number but turbulent, swirl flow. Therefore, the industry needs to rely on Reynolds Averaged Navier-Stokes (RANS) simulations; Direct Numerical Simulation predictions obtained at much lower Reynolds numbers may not predict the occurrence of the vortex breakdown inside the pipe. These findings show that there are essential design considerations, which determine the efficiency of the swirl separator. Thus, a combination of the geometry parameters and the swirl flow characteristics should be considered to avoid the reverse flow zone and vortex breakdown inside the inline separator. One of the vital elements of the inline swirl separator is the collector tube. The study shows that the collector tube at the neutral flow split, with no bias of the mass flow-rate at each outlet, changes the velocity to the extent that he reverse flow zone for Sw=0.5 is eliminated. Pressure actuators can control the flow; therefore, controlling the flow split at both outlets. The numerical results show that an additional percentage of flow split enhances efficiency by eliminating the reverse flow zone for the higher swirl numbers. Additionally, the study reveals the counter effect of the extreme flow splits, which hinders the efficiency of the inline swirl separator. These optimal settings for the geometry of this research were found at swirl number 1.6 and flow split of 50%.

A numerical study has been done on a rectangle in a 2D pipe flow. Therefore a Matlab code is made from scratch on basis of the SIMPLE algorithm. In the appendix is explained step by step exactly how all equations are implemented in Matlab. Focusing on low Reynolds numbers (1<Re<80) are different simulations made of the flow with the rectangle. Different heights of the rectangle in the pipe in a pressure driven flow are considered. Drag, lift and torque coefficients that were obtained from these simulations are plotted against the Reynolds number. Furthermore are shear flows as a consequence of a moving wall considered. Plots and other data of the dimensionless coefficients are included. The goal to make a good simulation of the flow past a rectangle is achieved. Different possible improvements to the code have been opposed, so it can be improved in the future to make also simulations of more complex geometries than a rectangle.

The world’s ever-increasing demand for energy and the inevitable depletion of the available fossil resources in the foreseeable future lead to an increasing necessity to optimize the exploitation of oil fields. The in-line liquid-liquid swirl separator is a separation method that is interesting for two reasons: It separates oil and water faster than the conventional settling tank and the fact that it is placed in-line is a practical advantage. In this report a study has been conducted on the modelling of an in-line liquid-liquid swirl separator using a mechanistic model. This model can be used as a thinking tool to better understand the separation performance of an in-line swirl separator: which parameters play an important role, what are the key processes? This model could also serve as an engineering design tool to optimize the swirl separator for industrial use. The goal of this research is to build a solid foundation for a relatively uncomplicated mechanistic model to describe the underlying physical processes of an in-line swirl separator.
To model the process of separating an oil-water mixture using an in-line liquid-liquid swirl separator different research steps have been taken. The first step was building a base model. The idea of this model was to provide a solid foundation for a more sophisticated model. Based on the findings from this base model and by comparing the base model results to results from CFD simulations and experimental results, a more sophisticated model has been built. In this report this model is referred to as the swirl decay model. These models calculate the separation efficiency based on certain key parameters. To find the efficiency, the trajectory of the particle in the axial and radial directions are modelled based on a balance of forces constructed under the assumption of a quasi-steady state. From these trajectories it is possible to determine whether an oil droplet starting at a certain radial position at the beginning of the swirl tube ends up in the collection tube at the end of the pipe.
The mechanistic model that was built in this research manages to capture the general processes involved in an in-line swirl separator, although the calculated efficiency values are generally larger than the experimental values. However, in order to capture the whole process, several features should be added to the model. These improvements include: more accurately determining the swirl decay coefficient, finding a way to model the droplet size distribution, model droplet coalescence and breakup, implementing a way to alter the flow split.

This study aims to get a better understanding of the passing phenomena of a rising gas bubble passing through a liquid-liquid interface. This is done experimentally with a narrow column by capturing the rising gas bubble with high speed imaging. The light phase consists of silicone oil and the heavy phase
consists of water with different glycerine concentrations. The viscosity ratio of the liquids and the size of the bubbles were varied in the experiments. Experimental results show the effect of liquid viscosity and bubble size, represented as the Reynolds number, on the retention time at the interface. Moreover results show the shape of the bubble when moving through the phases and compares the experimental results with bubbles in infinite medium. The results also gave interesting insights into conditions where the bubble passing the interface was encapsulated by heavy liquid.

In this master thesis a CFD model targetting the combustion in cement kilns is developed. The model is implemented in OpenFoam