LU|ZONE|UL Collection:
https://zone.biblio.laurentian.ca/handle/10219/3637
2024-03-29T08:33:00ZNumerical modeling and investigations of oxygen transport in microcirculation
https://zone.biblio.laurentian.ca/handle/10219/4113
Title: Numerical modeling and investigations of oxygen transport in microcirculation
Authors: Abbasi Amiri, Farhad
Abstract: 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.2023-05-18T00:00:00ZApplication of laser bessel beams in velocity measurements
https://zone.biblio.laurentian.ca/handle/10219/4026
Title: Application of laser bessel beams in velocity measurements
Authors: Sakah, Mahmud
Abstract: 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.2022-06-24T00:00:00ZComputational modelling of membrane viscosity for immersed boundary simulations of red blood cell dynamics
https://zone.biblio.laurentian.ca/handle/10219/3831
Title: Computational modelling of membrane viscosity for immersed boundary simulations of red blood cell dynamics
Authors: Li, Ping
Abstract: 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,2021-01-29T00:00:00ZUV/Photocatalyst based photoreactor design for water treatment
https://zone.biblio.laurentian.ca/handle/10219/3638
Title: UV/Photocatalyst based photoreactor design for water treatment
Authors: Yongmei, Jiao
Abstract: 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.2020-12-15T00:00:00Z