Ultra-fast Imaging of Two-Phase Flow in Structured Monolith Reactors; Techniques and Data Analysis

This thesis will address the use of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques to probe the “monolith reactor”, which consists of a structured catalyst over which reactions may occur. This reactor has emerged as a potential alternative to more traditional chemical engineering systems such as trickle bed and slurry reactors. However, being a relatively new design, its associated flow phenomena and design procedures are not rigorously understood, which is retarding its acceptance in industry. Traditional observations are unable to provide the necessary information for design since the systems are opaque and dynamic. Therefore, NMR is proposed as an ideal tool to probe these systems in detail. The theory of NMR is summarised and the development of novel NMR techniques is presented. Novel techniques are validated in simple systems, and tested in more complex systems to ascertain their quantitative nature, and to find their limitations. These techniques are improvements over existing techniques in that they either decrease the acquisition time (allowing the observation of dynamically-changing systems) or allow us to probe systems in different ways to extract useful information. The goal of this research is to better understand the flow phenomena present in such systems, and to use this information to design better, more efficient, more controllable industrial reactors. The analysis of the NMR data acquired is discussed in detail, and several novel image-processing techniques have been developed to aid in the quantification of features within the images, and also to measure quantities such as holdup and velocity. These novel techniques are validated, and then applied to the systems of interest. Various configurations of monolith reactor, ranging from low flow rate systems to more challenging (and more industrially relevant) turbulent systems, are probed using these methods, and the contrasting flow phenomena and performance of these systems are discussed, with a view to optimisation of the choice of design parameters

Experimental and computational study of two-phase slug flow

This thesis presents a computational and experimental investigation of horizontal gas-liquid two-phase slug flow. The overall aim of the present project was to carry out analytical and computational studies to model the processes of slug initiation, growth and collapse in horizontal pipes. The literature of two-phase flow, with a focus on slug flow, is reviewed. A “Benchmark exercise” of predicting the horizontal two-phase slug flow on the WASP (Water, Air, Sand and Petroleum) facility was set up for CFD simulations with the aim of investigating the capability of CFD codes in the prediction of slug flow characteristics in large scale pipe (78 mm ID, 37 m long). Six CFD codes (TRIOMPH, LedaFlow, STAR-CD, TransAT, FLUENT and CFX) were participated in this exercise. The complex nature of the slug flow mechanism and the relatively large-scale of the associated modelling domain contribute to the challenges of this CFD exercise; this is particularly challenging for three-dimensional simulations. It has proven difficult to carry out direct comparisons between the performances of the various codes; this is due to the difference in the assumptions and approximations made in each case. Successive slugging was captured by most of the CFD codes, apart from CFX in which the flow was remaining stratified. In terms of flow characteristics, comparison against the measurements was mainly focused on the distribution of slug frequency at various locations. Satisfactory agreement was obtained by the 1D code TRIOMPH, whereas the rest of the codes were failed to reproduce the observed trend of slug frequency distribution. The ability of the TRIOMPH code in the prediction of horizontal slug flow is limited in a restrain region, where the two-fluid equations employed in the code has to be well-posed, therefore a validation case study was examined. For a well-posed system, a unique solution can be obtained, whereas for an ill-posed system, the solution would become mesh dependent. However, the lack of unique solution of the ill-posed case can be altered by applying unsteady inlet condition prescribed in terms of a train of slugs, which can be generated by an alternative code namely slug-tracking code. CFD prediction of horizontal slug flow in a channel with rectangular cross-section (100 mm x 30 mm x 8000 mm) was systematically studied using STAR-CCM+. The experimental data was provided by Forschungszentrum Rossendorf (FZD) from Germany. Mesh sensitivity and parametric study were conducted to determine the settings that optimise accuracy and stability. The polyhedral mesh was found to give a fast and better convergence of the numerical solutions. A sufficient small grid size is important in order to resolve the velocity gradient throughout the two fluids. The onset of interfacial instability, wave growth, and slug generation processes were captured in the simulation. However, the predicted slug initiation site was shifted further downstream than the actual site observed in the experiment, leading to the discrepancy in the prediction of the flow characteristics. Experimental studies on slug initiation and their subsequent development were carried out on the LOWPRSS (Low Pressure) facility at Imperial College London. The motion of the slug is followed using high-speed imaging and conductivity probes for air-oil and air-water systems, respectively. The slug frequency results demonstrate that rapid initiation events occur near the inlet region, and the slug frequency exhibits a maximum at intermediate axial distances before eventually reaching an approximately constant value at sufficiently large distances downstream of the inlet. Particular attention was given to the slug initiation mechanism observed using the LOWPRESS facility. Together with a set of air-water slug flow data obtained on the WASP facility, the influence of inlet geometry was examined. It was shown that the inlet geometry significantly influences slug initiation; however, the effect of inlet geometry on the slug development reduces along the pipe length. Beyond a certain distance, slug frequency approaches a constant value invariant with inlet geometry.Open Acces

Smart Flow Control Processes in Micro Scale

In recent years, microfluidic devices with a large surface-to-volume ratio have witnessed rapid development, allowing them to be successfully utilized in many engineering applications. A smart control process has been proposed for many years, while many new innovations and enabling technologies have been developed for smart flow control, especially concerning “smart flow control” at the microscale. This Special Issue aims to highlight the current research trends related to this topic, presenting a collection of 33 papers from leading scholars in this field. Among these include studies and demonstrations of flow characteristics in pumps or valves as well as dynamic performance in roiling mill systems or jet systems to the optimal design of special components in smart control systems

Image stitching algorithm based on feature extraction

This paper proposes a novel edge-based stitching method to detect moving objects and construct\ud mosaics from images. The method is a coarse-to-fine scheme which first estimates a\ud good initialization of camera parameters with two complementary methods and then refines\ud the solution through an optimization process. The two complementary methods are the edge\ud alignment and correspondence-based approaches, respectively. The edge alignment method\ud estimates desired image translations by checking the consistencies of edge positions between\ud images. This method has better capabilities to overcome larger displacements and lighting variations\ud between images. The correspondence-based approach estimates desired parameters from\ud a set of correspondences by using a new feature extraction scheme and a new correspondence\ud building method. The method can solve more general camera motions than the edge alignment\ud method. Since these two methods are complementary to each other, the desired initial estimate\ud can be obtained more robustly. After that, a Monte-Carlo style method is then proposed for\ud integrating these two methods together. In this approach, a grid partition scheme is proposed to\ud increase the accuracy of each try for finding the correct parameters. After that, an optimization\ud process is then applied to refine the above initial parameters. Different from other optimization\ud methods minimizing errors on the whole images, the proposed scheme minimizes errors only on\ud positions of features points. Since the found initialization is very close to the exact solution and\ud only errors on feature positions are considered, the optimization process can be achieved very\ud quickly. Experimental results are provided to verify the superiority of the proposed method

Liquid recirculation & mass transfer beneath ventilated cavities in vertical two-phase downflows

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Selected Papers from the 9th World Congress on Industrial Process Tomography

Industrial process tomography (IPT) is becoming an important tool for Industry 4.0. It consists of multidimensional sensor technologies and methods that aim to provide unparalleled internal information on industrial processes used in many sectors. This book showcases a selection of papers at the forefront of the latest developments in such technologies

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

Understanding magmatic processes and their timescales beneath the Tongariro Volcanic Centre through microanalytical investigations of the tephra record : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Sciences at Massey University, (Manawatū Campus), Palmerston North, New Zealand

Appendix A1 Published methodology was removed as it is ©Microscopy Society of America 2018. It may be accessed at https://doi.org/10.1017/S1431927618015428The Tongariro Volcanic Centre (TgVC) is a complex volcanic system located at the southern end of the Taupo Volcanic Zone in New Zealand, and has produced historical explosive eruptions of different eruptive styles. Its three ski fields and its iconic Tongariro Alpine Crossing attract more than 130,000 visitors annually. The last eruption occurred in 2012 on the northern flank of Tongariro, at the Te Maari vent. Due to the lack of precursory activity, this eruption could have turned into a tragedy if it had happened during day time. Previous studies have focused on the TgVC phenocrysts, which do not provide insights into shallow magmatic processes, essential to mitigate the resulting volcanic hazards. To understand magma ascent processes and their associated timescales, the textures and compositions of the micrometre-sized crystal cargo (i.e. microlites and micro-phenocrysts) carried during explosive eruptions are investigated, along with their conditions of crystallisation [i.e. P-T-X(H₂O)], which are constrained using hygrothermobarometry and MELTS modelling. Glass shards from five tephra formations spanning from c. 12 ka BP to 1996 AD, associated with explosive eruptions ranging from Strombolian to Plinian in style, are studied here. High resolution images and chemical maps of the tephras and the crystals are acquired using scanning electron microscopy (SEM) and secondary ion mass spectrometry. The variety of disequilibrium textures and compositions found in the micro-phenocrysts (< 100 μm) indicates multiple events of magma mixing, magma recharge, pressure fluctuations, and suggests an antecrystic origin. Crystal size distribution (CSD) of 60,000 microlites (< 30 μm) of plagioclase and pyroxene are generated from back-scattered-electron (BSE) images using a semi-automatic method developed here to undertake this study, employing the Weka Trainable Segmentation plugin to ImageJ. Combined with a well-constrained growth rate, crystallisation times are derived and indicate that microlites crystallised 2 to 4 days before the eruption, regardless of the eruption style. Microlite crystallisation occurred between mid-crustal depths and the surface (average of c. 4 km), at unusually high temperature for arc magmas of intermediate composition (average of 1076 °C), and at low water contents (average of 0.4 wt%). Considering the inferred depths and the crystallisation times of 2 to 4 days, ascent rates of only up to 9 cm s⁻¹ prior to shallow water exsolution are calculated. Vent exit velocities are not exceeding 27 m s⁻¹ after complete water exsolution, too slow to feed explosive eruptions characterised by supersonic exit velocities. This research proposes a new conceptual model for the magmatic plumbing system beneath TgVC, where the microlitic crystal cargos result from multiple intrusions of aphyric melts through dykes, which most of the time stall and evolve at depth as deep as the mid-crust. Eventually, a magma injection percolates through previous intrusions and entrains crystals of differing textures and histories. Dykes feeding volcanism funnel into a narrow cylinder towards the surface, allowing acceleration and triggering explosive eruptions. Therefore, the conduit geometry at TgVC is a key controlling factor on the explosivity, with narrower conduits resulting in more explosive eruptions, suggesting that volatile-poor magmas can still trigger explosive eruptions. This study supports that vertical foliation of the igneous upper crust is consistent with dyking and thus may be more common than typically acknowledged