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Administration of nasal cannula therapy tasks providers with periodically monitoring their patients and adjusting settings according to patient needs. Conventionally, providers monitor a patient's oxygen demand using pulse oximetry and a qualitative assessment of the patient's work of breathing. The motivation for this research is to augment the traditional qualitative assessment of work of breathing with a quantitative measurement of a patient's tidal volume, the volume of air inhaled with each breath. This thesis presents a novel approach to measure tidal volume using a nasal cannula with built-in pressure sensors. Pressure waveforms obtained from continuous measurement of the pressure at the tip of the cannula are used to estimate nasal flowrates, and these nasal flowrates are time-integrated to estimate tidal volumes. Computational fluid dynamics (CFD) models were used to simulate fluid flow in a simplified nasal passage undergoing nasal cannula therapy. These simulations used a range of flow conditions characteristic of both low-flow and high-flow nasal cannula treatments. The simulations produced a transformation from cannula tip pressure to instantaneous nasal flowrate, and this transformation was evaluated using a matching empirical experiment. This empirical experiment used a matching physical geometry with a similar range of flow conditions, and the transformation obtained from CFD was able to estimate the actual tidal volumes with 85% accuracy. This study showed that continuous pressure measurement at the tip of a nasal cannula produces enough information to estimate nasal flowrates and tidal volumes. No similar studies were found during the literature review, so an accuracy of 85% is promising for this stage. If this technique could be made more accurate and deployed in an unobtrusive way, the resulting nasal cannula device could be used to continuously, comfortably monitor patients' tidal volumes. / Master of Science / Oxygen therapy is the most common prescription in hospitals across the United States, and the most common form of oxygen therapy is nasal cannula therapy. Administration of nasal cannula therapy requires providers to periodically assess their patients' oxygen saturations and work of breathing. Oxygen saturation can be quantitatively monitored using pulse oximetry but work of breathing must be qualitatively monitored using visual exams or walking tests. The motivation of this research is to augment this qualitative assessment with a quantitative metric. In our research, we chose the volume of inhaled air (the "tidal volume") as a proxy metric for a patient's work of breathing. This thesis presents our attempt to use a nasal cannula augmented with pressure sensors to estimate the tidal volume of a mannequin undergoing nasal cannula therapy. Our concept is that more intense inhalations/exhalations produce larger pressure swings at the tip of the nasal cannula. For this proof-of-concept study, a simplified nasal passage geometry was used. Pressure waveforms obtained from continuous measurement of the pressure at the tip of the cannula are used to estimate nasal flowrates, and these nasal flowrates are time-integrated to estimate tidal volumes. Computational fluid dynamics (CFD) simulations were used to predict how the cannula tip pressure changes as a function of nasal flowrates and cannula flowrates, then this relationship was tested using a matching empirical experiment. This matching empirical experiment showed that our technique of estimating tidal volumes was 85% accurate. This study showed that continuous pressure measurement at the tip of a nasal cannula produces enough information to estimate nasal flowrates and tidal volumes. No similar studies were found during the literature review, so an accuracy of 85% is promising for this stage. If this technique could be made more accurate and deployed in an unobtrusive way, the resulting nasal cannula device could be used to continuously, comfortably monitor patients' tidal volumes.

Climate change and rising temperatures is a well-known problem. To tackle global warming a transition from fossil fuels to renewable and reliable energy sources is necessary. Hydrogen, in fuel cells, is proposed to replace diesel and gasoline in the transport sector. Hydrogen is a pure fuel and the fuel cells only emit water and heat as a byproductbyproduct. Combined with electric motors, the hydrogen fuel cell can be 2-3 times more efficient compared to combustion engines fueled by gasoline. The performance of the fuel cell is affected by how the individual parts of the cell are designed. There are some difficulties in manufacturing complex geometries which requires require a forming in more than one step.  The goal isis to investigate, with the help of COMSOL Multiphysics software, how the performance of the fuel cell is affected by the shaped geometry at the cathode side of the flow plate. A numerical model is developeding will be made with varying parameters on the measurement of the cross-sections of the channels where pressure drop and flow distribution for ten different geometries isarewill be investigated. The model iswas built in the COMSOL Multiphysics 6.1 Software and includes a three-dimensional geometry consisting of a gas channel and a gas diffusion layer. The flow is laminar and the gas diffusion layer is set as a porous medium.  The results show that geometries with less sharp edges have lower pressure drops and more uniform flow distribution compared to geometries with sharper edges. The geometry with the sharpest edges has the highest pressure drop of 4.8 Pa/mm and the geometry with rounder edges has the lowest of 3.8 Pa/mm. A relationship between pressure drop and cross-sectional area can be found. With increasing radius and increasing cross-sectional area will the pressure drop decrease. The Reynolds number is higher for sharper geometries since the average velocity in the channels is higher, which also gives a lower friction factor. The length of the top flat becomes less for rounder geometries, which positively affects uniform flow distribution. The geometries with rounder edges have the most uniform distribution at the top of the gas diffusion layer and the sharpest geometry has the least uniform distribution. The deviation from the mean velocity is lower for sharper geometries, mainly because the velocities in the gas diffusion layer are lower. Sensitivity analysis was made over the mass flow rate and mesh, showing that the pressure drop is proportional to the mass flow rate and it becomes higher with less fine mesh.  Less fine mesh also gives lower velocities in the gas diffusion layer. Further studies can be made on how the gas diffusion layer behaves in the fuel cell when adding clamping force to the stack when putting it together and investigate if and how it affects pressure drop and flow distribution. The environmental benefit can be crucial if the performance of the fuel cells improves and motivates the investments which is are needed for, among other things, the infrastructure. / Klimatförändringar och stigande temperaturer är ett välkänt problem. För att ta itu med den globala uppvärmningen är en övergång från fossila bränslen till förnybara och pålitliga energikällor nödvändigt. Vätgas,  går bland annat att användas ii bland annat bränsleceller och , skulle kunna ersätta diesel och bensin inom transportsektorn. Vätgas är ett rent bränsle och bränslecellerna släpper bara ut vatten och värme som biprodukter. I kombination med elmotorer kan vätgasbränslecellen vara 2–3 gånger mer effektiva jämfört med förbränningsmotorer som drivs av bensin. Bränslecellens prestanda påverkas av hur de enskilda delarna av cellen är utformade. Det finns vissa svårigheter att tillverka komponenter med komplexa geometrier som kräver formning i fler än ett steg. Målet är att med hjälp av programvaran COMSOL Multiphysics undersöka hur bränslecellens prestanda påverkas av den formade geometrin på katodsidan av flödesplattan. En numerisk modellering kommer att utförasgöras utifrån med varierande parametrar därpå måtten hos kanalernas tvärsnitt varieras. Tdär tryckfall och flödesfördelning hos tio olika geometrier kommer att undersökas. Modellen byggdes i COMSOL Multiphysics 6.1 Software och inkluderar en tredimensionell geometri bestående av en gaskanal och ett gasdiffusionsskikt. Flödet är laminärt och gasdiffusionsskiktet antas vara ett poröst medium. Resultaten visar att geometrier med mindre skarpa kanter ger lägre tryckfall och jämnare flödesfördelning jämfört med geometrier med skarpare kanter. Geometrin med skarpast kanter har det högsta tryckfallet på 4.8 Pa/mm och geometrin med rundare kanter har ett tryckfall på 3.8 Pa/mm. Ett samband mellan tryckfall och tvärsnittsarea kan hittas då ökad radie och ökad tvärsnittsarea ger en minskning i tryckfall. Reynoldstalet är högre för skarpare geometrier eftersom medelhastigheten i kanalerna är högre, vilket också ger en lägre friktionsfaktor. Längden på toppen av kanalerna blir mindre för rundare geometrier, vilket påverkar flödesfördelningen positivt. Geometrierna med rundare kanter har den mest jämna fördelningen i toppen av gasdiffusionsskiktet och den skarpaste geometrin har den minst jämna fördelningen. Avvikelsen från medelhastigheten är lägre för skarpare geometrier, främst på grund av att hastigheterna i gasdiffusionslagret är lägre. Känslighetsanalys gjordes över storleken på massflödet och noggrannheten i meshen, vilket visar att tryckfallet är proportionellt mot massflödet och att det blir högre med mindre noggrann mesh. Mindre noggrann mesh ger också lägre hastigheter i gasdiffusionsskiktet. Ytterligare studier kan göras om hur gasdiffusionslagret beter sig i bränslecellen vid sammanpressning av alla delar i cellen och undersöka om och hur det påverkar tryckfall och flödesfördelning. Fördelen för miljönMiljönyttan kan vara stor om bränslecellernas prestanda förbättras och på så vis kan motivera de investeringar som behövs för utbyggnaden av bland annat infrastrukturen.

Engineering applications of unconventional fuels like HFOs require a detailed understanding of the physics associated with their evaporation. The processing of HFOs involves forming a spray; therefore, studying droplets is of particular interest. The work described in this dissertation tackles two of the most obscure aspects associated with HFOs modelling. The first aspect is the identification of a valid chemical description of the structure of the fuel. In particular, the author focused on finding a methodology that allows identifying a discrete surrogate to describe the complex pool of molecules of which the fuels are made. The second part of the work was devoted to understand and model thermally-induced secondary breakup, which is the primary cause of deviation from the "d2" that multi-component droplet experience. The formulation of a surrogate was successfully achieved by developing and implementing a new algorithm that allows building a surrogate from a set of easily accessible physical properties. A new methodology for the post-processing of experimental data was formulated. The methodology consists of studying the evolution of the normalized distance of the interface from the droplet’s centroid instead of its diameter. The new approach allowed the separation between interface deformation and expansion/shrinking. The information was then processed using the dynamic mode decomposition to separate the stochastic contribution associated with secondary atomization and the deterministic contribution of vaporization. Finally, thermally induced secondary atomization was studied using a CFD code appositely developed. The code is based on the geometric Volume of Fluid (VoF) method and consists of a compressible, multi-phase, multi-component solver in which phase change is considered. The novelty in the proposed approach is that the evaporation source term and the surface tension force are evaluated directly from the geometrically reconstructed interface. The code was validated against the exact solution of analytically solvable problems and experimental data. The solver was then used to study HFO secondary breakup and perform a parametric analysis that helped to understand the problem’s physics. A possible application of this framework is the formulation of sub-models to be applied in spray calculations.

This thesis reports on a numerical investigation into the three-dimensional flow divergence around a high solidity vertical axis wind turbine. Three-dimensional unsteady Reynolds averaged Navier-Stokes simulations of an H-type vertical axis wind turbine were used to examine the impact of turbine aspect ratio and tip speed ratio on the flow divergence. The turbine height was changed to alter the turbine aspect ratio, while keeping the diameter constant, to ensure that the solidity and tip speed ratio values were comparable between the different aspect ratios tested. The power output of the turbine consistently increased with aspect ratio and the optimal tip speed ratio for peak performance was negligibly affected. The flow divergence results showed that larger aspect ratio turbines had significantly more flow divergence with a 1 m/s entrance velocity difference between the smallest and largest cases. These two results where contradictory as a larger aspect ratio turbine was more efficient even though it had a smaller fraction of the upstream flow entering the upwind pass. The reason for this result was that impact of the tip effects, which caused a power reduction near the end of the blades. The distance from the blade tips that experienced a power reduction was constant for turbines of aspect ratio one and greater, resulting in a smaller turbine having a greater fraction of its height effected by the tips. This caused the overall power output for a smaller aspect ratio turbine to be lower even though its centre performance was higher, due to an increased entrance velocity. The change in flow divergence with tip speed ratio was also examined to better understand the driving force behind the divergence. It was found that the turbine power output was not the direct cause of flow divergence. The blade forces, specifically the force generated in the upstream direction had a strong linear correlation with the upstream flow divergence. / Thesis / Master of Applied Science (MASc)

Yes / In a novel development on previous computational fluid dynamics studies, the work reported here used an Eulerian two-fluid model with the shear stress transport k–ω turbulence closure model and bubble interaction models to simulate aeration tank performance at full scale and to identify process performance issues resulting from design parameters and operating conditions. The current operating scenario was found to produce a fully developed spiral flow. Reduction of the airflow rates to the average and minimum design values led to a deterioration of the mixing conditions and formation of extended unaerated fluid regions. The influence of bubble-induced mixing on the reactor performance was further assessed via simulations of the residence time distribution of the fluid. Internal flow recirculation ensured long contact times between the phases; however, hindered axial mixing and the presence of dead zones were also identified. Finally, two optimization schemes based on modified design and operating scenarios were evaluated. The adjustment of the airflow distribution between the control zones led to improved mixing and a 20% improvement to the mass transfer coefficient. Upgrading the diffuser grid was found to be an expensive and ineffective solution, leading to worsening of the mixing conditions and yielding the lowest mass transfer coefficient compared with the other optimization schemes studied. / College of Engineering and Physical Sciences, University of Birmingham, UK