The study of haemodynamics, or the mechanics of blood flow, has been a topic of significant interest since ancient times, as it provides critical insights into both the normal functioning of the circulatory system and the mechanisms underlying various diseases. A robust scientific understanding of these dynamics facilitates the development of innovative prevention and intervention strategies, such as advanced, less invasive surgical techniques and cost-effective medical devices, which can dramatically improve global health outcomes. Over the centuries, experimental, analytical, and, more recently, computational methods have enhanced our knowledge of cardiovascular and cerebrovascular conditions, leading to improved diagnostic and therapeutic approaches that enhance life quality and expectancy.

Despite these advancements, substantial challenges remain, particularly in diagnosing and understanding haemodynamic complications such as stroke, stenosis, and regurgitation. Modern imaging techniques like MRI and sonography are limited by spatial and temporal resolution, requiring significant hardware improvements to overcome these constraints. Moreover, while analytical models have evolved to address the complex nature of blood flow and vessel behavior, they often struggle to accurately represent in vivo scenarios, especially in areas like the cerebral vasculature that are difficult to image. The presence of anomalies such as medial calcifications - which are responsible behind numerous life altering conditions and diseases such as, diabetes, kidney disease and hypertension - further complicates the accurate modeling of blood flow dynamics by introducing departure from axisymmetry, changes in material properties of the tissue and impacting the physics at localized scale.

To address the impact of medial calcifications, this thesis presents a detailed approach starting with the development of a three-dimensional (3D) model that represents the physiological fluid-structure interaction (FSI) phenomenon of pulsatile blood flow through an Internal Carotid Artery (ICA) with medial calcification. ICA is a critical vessel within the Circle of Willis which itself is one of the most crucial cerebro-vascular networks. Following this, a physics based one-dimensional (1D) Reduced Order Model (ROM) is developed, integrated with which is a data-driven constitutive modelling framework trained on the 3D simulation data, to account for changes in material proeprties introduced by medial calcifications. This ROM aims to provide a computationally efficient yet accurate representation of the physiological changes caused by medial calcifications. The thesis includes a comprehensive theoretical framework, detailed validation and verification processes, and comparisons between the 1D and 3D models to ensure accuracy and clinical relevance. The overarching goal is to create a well-validated ROM that maintains essential physical details while reducing computational costs, with an emphasis on evaluating its performance in clinical scenarios and exploring its potential applications and future research directions.

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.

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.

Pigs are devices that are transported from time to time through a pipeline, mainly to either clean the pipeline or to inspect the integrity of the pipeline wall. Conventional models for the friction between the pig and the pipe wall, as used in the oil and gas industry, are often criticized for their inaccuracies. To obtain a more accurate model, this thesis investigates the detailed physics behind the frictional forces. The effect of the sliding conditions on the wall-normal force and on the friction force was investigated by conducting 1D lubricated sliding experiments for a rubber lip moving along a metal surface and by performing model simulations, including a parameter sensitivity study. The experiments were conducted for dry water, dodecane and castor oil under varying sliding velocities and loads. The loads were measured with a dual axis transducer and the lubrication film was observed during the experiments with a microscope set-up. The experimental results consist of friction forces for various configurations, which show that the frictional behaviour depends strongly on the lubrication regime in which the rubber lip is operating. The friction coefficients for the boundary lubrication regime and the mixed lubrication regime were measured and compared with results from the model. Among the tested fluids, castor oil showed a non-proportional decrease in friction force when the sliding velocity was increased. This decrease in friction force was interpreted as a transition from the boundary lubrication regime to the mixed lubrication regime. The other tested fluids remained in the boundary lubrication regime in the experimental runs. A validation study was performed by fitting the friction model to the experimental results. Only the dry friction coefficients are in good agreement with the model. Both the water and dodecane experiments show a slight increase for the friction coefficient with increasing lubrication factor and are in mediocre agreement with the friction model. The castor oil experiments are in the mixed lubrication regime of the Stribeck curve and are in reasonable agreement with the model. The results can be linked to the oil and gas industry as pigs can operate in different regimes of the Stribeck curve. Stalled pigs can be the result of transitions from the mixed lubrication regime to the boundary lubrication regime. This can happen when a pig is momentarily slowed down in the pipeline. Recommendations for future experimental work are: performing experiments at higher sliding velocities, using an emulsion as lubricant and finding suitable methods to calibrate models that have a range of input parameters. This work was carried out by the author at the Shell Technology Centre in Amsterdam. The supervision by the Shell staff and the support obtained in carrying out the experiments in the Shell lab are greatly acknowledged.

Zero Emission Fuels (ZEF B.V.) is a start-up working to build a sustainable methanol micro-plant. Carbon dioxide and water are obtained from atmosphere. Hydrogen is obtained from captured water through alkaline electrolysis and the hydrogen is used for methanol production. The alkaline electrolyser should run at 50 bar and 90°C with 30% KOH as the electrolyte. It is a multi-cell design and the electricity supplied to the electrolyser leaks within the system through the electrolyte. This is the energy supplied to the system not being used for splitting water into hydrogen and oxygen. Leaking current and flow scale with the length and the radius of any channel in the system and contradict each other in terms of requirements.
This study focuses on characterising the electrolyser to validate a modified version of the existing Matlab model at a channel in the system for two different dimensions of the channel. The Matlab model predicts
the flow and the leaking currents in the system. Estimating the flow in the system is essential to validate the model and using the model, the leaking currents are estimated. Experiments were performed on a single cell version of the electrolyser at atmospheric pressure to obtain the flow and thermal characteristics. Comsol simulations were ran on the single cell system to support the Matlab results.
The heating curve of the system was obtained at four different points in the system to check for the necessity of insulation. The system went up to 56°C at the hottest point in the system after 2 hours. This confirmed for the necessity of insulation. The diameter of the bubbles at the electrode were measured and compared to the estimated diameter in Matlab. They were 34% off. The flow part of the experiments were done at a lower current density to simulate 50 bar flow at 1 bar. The flow rate of the electrolyte was estimated using high speed cameras and tracking fluorescent particles at one of the channels in the system. The values of the flow rate from Comsol, Matlab and Comsol were 25% away from each other whereas Matlab and experiments were 65% away from each other. The mass flow rate predicted by Comsol was in between Matlab and experiments. The absence of a temperature network to estimate temperature at every part of the system, the approximate geometry and ignoring smaller resistances to flow in the Matlab model are responsible for the offset.
Leaking currents were estimated in the single and multi-cell system using Matlab. The power lost due to leaking currents were higher in the multi-cell system as compared to the single cell system. The reduction in leaking currents by using gas slugs was estimated and the current design achieves the electrical efficiency of 99%. Recommendations were to make the channel diameter larger and remove the part of the channel that is in the cell. Further modifications to the Matlab and Comsol model were suggested to improve the prediction. Experiments related to multi-cell setup have to be done to estimate the actual electrical efficiency of the system and validate the Matlab model.

Renewable energy projects, such as wind and solar (PV) parks, are rapidly being built to replace fossil fuel based energy sources. The major drawback of electricity production from renewable sources is that they are intermittent and therefore lead to amismatch between the supply and the demand of energy. Energy storage in the form of hydrogen production is a potential candidate to overcome this problem. However, due to its lowvolumetric energy density, hydrogen must be compressed to use it for storage or transportation purposes. HYET BV has developed an Electrochemical Hydrogen Compressor (EHC) that is capable of compressing hydrogen up to P = 1000 bar, and have the potential of bringing compression costs down to 3 kWh/kg. As the compressed hydrogen is saturated with water, it must be dehydrated before it is used for refuelling Fuel Cell Electric Vehicles (FCEV), as the ISO 14687-2:2012 standard has limited the water concentration to 5 ¹mol water per mol gas mixture. In this work, a landscaping studywas performed to search for potential drying methods, includingmembrane separation, adsorption, absorption and cooling. To select the best method for hydrogen dehydration, it is essential to have a good understanding of the thermodynamics at the given pressure conditions, beginningwith the saturated water content in compressed hydrogen. To the best of our knowledge, the only experimental data describing the water content in the H2-H2O mixture for pressures exceeding 300 bar are from 1927 and are limited to T = 323.15K [J. Am. Chem. Soc., 1927, 49, pp 65-78]. In this thesis, it was concluded that conventional Equations of State (EoS) failed to predict the equilibrium coexistence compositions of the liquid and gas phase. Therefore, molecular simulations were used, which adequately predicted the water content in compressed hydrogen. The second part of this thesis was to select the best drying method for hydrogen dehydration. Previous work showed that absorption using Ionic Liquids (IL) could be an interesting alternative to traditional dryingmethods. Therefore, absorption experiments were performed on the ILs 1-Ethyl-3-methylimidazolium acetate [EMIM][Acetate], 1-Butyl-3-methylimidazoliumchloride [BMIM][Chloride], and 1-Butyl-3-methylimidazolium octyl sulfate [BMIM][Octyl Sulfate] to test the feasibility of ILs for hydrogen dehydration. The ILs were selected on stability, safety, and on the activity coefficient of water in the given IL. The experiments showed that ILs can be used as an absorbent to dry hydrogen gas. A part from the initial selection criteria, the experiments showed that surface tension is an important criterion for future IL selection, as it is strongly related to foam production. Finally, the very hygroscopic ILs tested turned out to be capable of absorbing large amounts of water, but a lot of energy was required to regenerate the ILs, making them less attractive as a potential absorbent.

As an alternative energy carrier alongside electricity, hydrogen is considered one of the key factors in the impending required changes in the energy system transition. Due to the decrease in natural gas extraction in the Netherlands, the reuse of the natural gas network which eventually will become available for hydrogen transmission has emerged as a topic, recently. Although it seems to be possible to reuse the existing natural gas transmission network for the transmission of hydrogen, a quantitative risk analysis is still lacking and there is uncertainty about the safety of hydrogen transmission. This report aims to quantify the risk of the reuse of an existing natural gas pipeline for 100% hydrogen transmission and compare it with the natural gas case. A risk analysis entails the quantification of both the probability of failure and the adverse consequences. This research investigated the current methodology to determine the probability of failure for hydrogen transmission and proposed a new calculation method using a Bayesian network and historical natural gas data to derive new failure frequencies. The consequence of failure for both hydrogen and natural gas will be modelled using the SAFETI-NL; the influence of the gas different characteristics on the lethality will be quantified and risk values are produced, assuming the probability of failure to be similar for both gases when transported through natural gas pipelines. This research illustrated the promising application of a Bayesian network is a promising method to derive failure frequencies while taking into the significant influence of the pipeline characteristics. However, from the results, it emerges that further research is required with more redundant data. Also, future research should investigate the application of natural gas data since some failure scenarios are not entirely independent of the transmission gas, which could result in less favourable failure frequencies. Furthermore, calculations in SAFETI-NL have shown that hydrogen release is associated with a shorter duration and lower release power than natural gas, resulting in less significant consequences in the vicinity of the pipelines. Also, the low weight and high diffusive coefficient of hydrogen cause the consequences to decrease much faster with distance. As a result, there is concluded that hydrogen transmission is accompanied by lower risk values than natural gas, assuming the failure frequencies to be similar when both gases transported through natural gas pipelines. Although, numerous input parameters affect the risk values determined, of which at least the probability of ignition for hydrogen release has to be investigated in future research.