Engineering - Doctoral Theses

Permanent URI for this collectionhttps://laurentian.scholaris.ca/handle/10219/3637

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Numerical modeling and investigations of oxygen transport in microcirculation
(2023-05-18) Abbasi Amiri, Farhad
Several aspects are involved in the oxygen transport in capillaries, such as the red blood cell (RBC) membrane mechanics, the cytoplasm/plasma flow fields, and the mass transport across the semipermeable deformable membrane. The transport process is also influenced by association and dissociation kinetics, which considers the interaction between oxygen and hemoglobin molecules within the RBCs. Therefore, a model of oxygen transport must include these factors to accurately represent the process. In chapter 1, the microcirculation system, human RBC structure and properties, and oxygenhemoglobin kinetics have been briefly introduced to provide basic background information for oxygen transport process in microcirculation. Then, the effects of several important factors (RBC shape, plasma/cytoplasm convective effect, RBC membrane treatment) on gas transport in microcirculation have been reviewed. The literature review has shown that an efficient and robust numerical scheme for simulating oxygen transport in capillaries is missing and the effects of RBC properties and behaviors have not been well addressed. The motivation of this Ph.D. research is to develop a transport model to study the effects of various RBC flows on oxygen transport in capillaries. Several specific research objectives have been outlined in Section 1.5. In Chapter 2, we propose a new method called the immersed membrane method for mass transfer across flexible semipermeable membranes. This method is based on the classical immersed boundary method used for interaction between structures and flow, and it replaces the sharp interface of the membrane with an artificial fluid layer. This layer does not affect the fluid flow or the membrane deformation, but it does add resistance to mass transiii fer, based on the membrane’s original permeability. By using this approach, we can solve the mass transfer problem using a single numerical scheme on the same Eulerian mesh, and we can avoid the complicated interface treatment required for the membrane interface condition. We also validated this method by comparing numerical results with theoretical solutions, and satisfactory agreement has been observed. In Chapter 3, we consider a tank-treading capsule in shear flow, which is generated with two parallel plates moving in opposite directions: the top plate represents the core of RBCs in a microvessel with a high oxygen pressure (PO2 ), while the bottom plate represents the microvessel wall with a lower PO2 . Numerical simulations are conducted to investigate the individual and combined effects of cytoplasm convection and oxygen-hemoglobin (O2-Hb) reaction on the oxygen transport efficiency across the tank-treading capsule, and different PO2 situations and shear rates are also tested. In Chapter 4, we conduct numerical simulations for the blood flow and RBC deformation along a capillary and the oxygen transfer from RBCs to the surrounding tissue. We look at different values of capillary hematocrit, the oxygen tension in the arterioles, and metabolic rate of oxygen consumption. Our results show that there are two competing factors that affect the tissue oxygenation while the capillary hematocrit increases: the positive effect of higher RBC density and the negative effect of the slower RBC movement; and the relevant strength of these two mechanisms is related to the oxygen-hemoglobin reaction and hemoglobin concentration and affinity in cytoplasm. In Chapter 5, we simulate the oxygen uptake processes in stopped-flow experiments with different cell shapes, membrane permeability and unstirred layer thickness considered. Our results show that the uptake process from the spherical model is much slower than those from the ellipsoidal and biconcave shapers, meaning that results form previous studies using spherical cell models may need to be revisited. Also we find that it is difficult to distinguish the individual influences from the membrane permeability and unstirred layer, and more comprehensive models will be required for future studies. At last, in Chapter 6, concluding statements and future work based on the research results are presented.
Application of laser bessel beams in velocity measurements
(2022-06-24) Sakah, Mahmud
In this thesis we explore the use of Laser Bessel beams in solid surface and fluid velocity measurements. We present a novel simple technique to measure two velocity components of a solid surface, using a Bessel beam Laser Doppler Velocimetry (LDV) system. The experiments examined the intersection of similar two Bessel beams to generate interference fringes at the intersection region. These fringes, along with the Bessel beam fringes can be used in a simple LDV system to measure two velocity components. We also explored the use of single Bessel beams for measurement of fluid flow velocity in a horizontal transparent smooth straight circular pipe using forward scattering Laser Bessel velocimetry (LBV). The measurements were validated using a commercial LDV system. In order to produce an acceptable spatial resolution for fluid flow measurements, we investigated experimentally and numerically the use of Durnin rings (annular slits) with finite width to produce nearly Bessel beams with limited transverse profile extent and depth of field (DOF). One purpose of the work was to develop the suitability of laser Bessel Velocimetry for flow conditions where velocity measurements by alternative instrumentation were not feasible or were subject to optical access limitation. We also demonstrated, a significant advantage in using a single Bessel beam to measure the total velocity of two-dimensional flows.
Computational modelling of membrane viscosity for immersed boundary simulations of red blood cell dynamics
(2021-01-29) Li, Ping
Although tremendous efforts have been devoted to modelling various membrane properties, few studies considered the membrane viscous effects. Meanwhile, immersed boundary method (IBM) has been a popular choice for simulating the motion of deformable cells in flow for the convenience of incorporating the flow-membrane interaction. Unfortunately, the direct implementation of membrane viscosity in IBM suffers severe numerical instability. In this thesis, three numerical schemes for implementing membrane viscosity in IBM are developed. Furthermore, the effects of membrane viscosity on the capsule dynamics in shear flow have been examined in detail. In Chapter 1, the biomechanical properties of red blood cells (RBCs) are introduced followed with a literature review. Also, the motivations and objectives, the structure of this thesis, and the contributions of the candidate are described. In Chapter 2, a finite-difference approach is proposed for implementing membrane viscosity in IBM. To improve the simulation stability, an artificial elastic element is added in series to the viscous component in the membrane mechanics. The detailed mathematical description and key steps for its implementation in immersed boundary programs are provided. Validation tests show a good agreement with analytical solutions and previous calculations. The accuracy dependence on membrane mesh resolution and simulation time step is also examined. In Chapter 3, two other schemes are proposed based on the convolution integral expression of the Maxwell viscoelastic element. Several carefully designed tests are conducted and the results show that the three schemes have nearly identical performances in accuracy,
UV/Photocatalyst based photoreactor design for water treatment
(2020-12-15) Yongmei, Jiao
A germicidal ultraviolet (UV-C)/photocatalyst based advanced oxidation process (AOP) has potential to disinfect and mineralize waterborne organic pollutants without generating disinfection by-products. But low efficiency has hindered application of this technology. In this study, I have looked to improve the AOP process through use of enhanced photocatalytic surfaces and reactor design. The intention is that the resulting improvements will help in combating the effects of water eutrophication due to global warming, which is often accompanied by accelerated cyanobacterial (blue-green algae) growth and waterway contamination by their toxins. An acidic anatase titanium dioxide (TiO2) slurry doped with tungsten oxide (WO3) or rutile TiO2 was coated onto stainless steel plates, and annealed at 460, 500, and 540°C in a muffled furnace. The coatings were ~10 µm thick and demonstrated good durability. This method enabled bandgap reduction to the visible light spectrum for all coatings, with the smallest bandgap being 2.48 eV. The higher annealing temperatures resulted in rougher coated surfaces, which had negative effect on photocatalytic activities. Methylene blue (MB) degradation tests under UV-C showed that the coatings annealed in 460°C had the best performance and with a rate constant of 5.59 h-1. An UV-C/TiO2 based photocatalytic reactor with a corrugated configuration was designed to accommodate a larger photocatalytic surface per unit volume. With TiO2 coated corrugated plates, a 70 % MB solution was degraded within the first 10 minutes with the highest photonic efficiency of 2.83 %. A light absorption model was developed and validated with light intensity measurements. A set of corrugated photocatalytic reactors with the same surface area, but different geometries were analyzed and the one with flatter configuration showed better energy absorption capacity. A household scale UV-C/TiO2 reactor was then designed for drinking water treatment. A 3D UV-C absorption model, that agreed well with light intensity measurements, was used to predict light energy absorbed by the photocatalyst coatings and to optimize reactor design. The system degraded a synthesized raw water pollutant (uracil) and the organic matter in lake water by 34.2 % and 33.2 % respectively in 24 minutes, and also concurrently inactivated Escherichia coli.
Recovery and repurposing of low-grade thermal resources in the mining and mineral processing industry
(2020-10-29) McLean, Shannon Heather
A substantial quantity of energy is currently lost as waste heat to the atmosphere in the mining and mineral processing industry. The recovery and application of this waste heat to on-site processes is an opportunity to reduce primary fuel usage, operational cost and environmental impacts. To investigate this, research has been conducted within a nickel smelter’s sulphuric acid plant, where operational data was collected on a process water cooling loop that incorporates cooling tower systems. The cooling towers discharge in excess of 50 MW of heat without any recovery. Collected data was then used to develop a model to quantify the potential for low-grade heat recovery and repurposing within the sulphuric acid manufacturing process. Heat pumps were examined as a method to repurpose this waste heat, and use it to replace electric heaters currently used in the mist precipitators and weak acid stripper. The model allows for an economic and environmental impact comparison between various recovery and application scenarios. Results obtained from the model indicated that the implementation of a heat pump system would provide a reduction in annual operating costs that allows a payback period of 3 years. Furthermore, there would be from less primary energy consumption a reduction in CO2 emissions of about 42% from heat pump operation compared to electric heaters for the system. To further quantify environmental benefits from implementing the proposed recovery strategy, a comparative life-cycle assessment (LCA) model was also constructed and applied to the sulphuric acid plant. The LCA showed a 20% reduction in emissions in the cooling tower and heating system would be achieved from the impact categories of global warming, acidification, eutrophication, and human toxicity potentials. This includes emissions from cooling tower fans and water pumps, as well as the mist precipitator air heating. The concepts and models can be applied to a wide range of energy intensive industrial sectors, to help identify and quantify reductions in consumption and improvements in long-term sustainability performance.

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