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Continuous flow reaction using micro-reactors is a valued technology due to its excellent mass and heat transfer performance, reduced reactor volume, handling capacity of hazardous reactions, and many other process intensifications. These intensifications opportunities interest the fine chemicals, pharmaceuticals producers and other multiphase reaction users who currently use batch processes or already use continuous flow. In this thesis, elements of passive and active mixing are investigated for the application of immiscible liquid-liquid systems. In the first study, the effects of geometrical arrangements of a residence time between mixing units on the interphase mass transfer rates are evaluated with four different immiscible liquid-liquid systems. A presentation of an algorithm for the optimal selection of a reactor and its operating conditions is given in order to enable easy and improved use of one’s micro-reactor. In the second study, the impact of a secondary pulse flow on interphase mass transfer is investigated. A coil without internal baffles is used as the oscillatory-flow coil reactor with a continuous active mixing source. The best application for the reactor is determined using a comparison to other complementary continuous flow platforms in the toolbox approach. The novel advancements presented here will help lead new molecular discoveries and connect the laboratory science scale to the process engineering production scale.

A volume-filtered Large-Eddy Simulation (LES) of oscillatory flow over a rippled mobile bed is conducted using an Euler-Lagrange approach. As in unsteady marine flows over sedimentary beds, the experimental data, referenced in this work for validation, shows quasi-steady state ripples in the sand bed under oscillatory flow. This work approximately reproduces this configuration with a sinusoidal pressure gradient driven flow and a sinusoidally rippled bed of particles. The LES equations, which are volume-filtered to account for the effect of the particles, are solved on an Eulerian grid, and the particles are tracked in a Lagrangian framework. In the Discrete Particle Method (DPM) used in this work, the particle collisions are handled by a soft-sphere model, and the liquid and solid phases are coupled through volume fraction and momentum exchange terms. Comparison of the numerical results to the experimental data show that the LES-DPM is capable of capturing the mesoscale features of the flow. The large scale shedding of vortices from the ripple peaks are observed in both datasets, which is reflected in the good quantitative agreement between the wall-normal flow statistics, and good qualitative agreement in ripple shape evolution. Additionally, the numerical data provides three insights into the complex interaction between the three-dimensional flow dynamics and bed morphology: (1) there is no observable distinction between reptating and saltating particle velocities, angular velocities or observed Shields parameters; (2) the potential motion of the mobile bed may create issues in the estimation of the bed shear stress used in classical models; and, (3) a helical pairing of vortices is observed, heretofore not known to have to have been identified in this type of flow configuration.

Thermoacoustic devices are a group of systems that make use of the thermoacoustic effect to achieve an energy conversion between thermal and acoustic energy. The thermoacoustic effect occurs when a solid boundary is introduced into an acoustic field, and a non-zero net heat transportation takes place while the net mass transfer remains null. Thermoacoustic technologies are gaining an increasing research interest because of their potential applications for building alternative prime movers or heat pumps which do not use working fluids causing environmental damage and require very little maintenance due to their lack of moving part. However, the operation of this type of system is yet to be fully understood: fluid flow and heat transfer processes within the system components such as thermoacoustic stacks and heat exchangers still require a lot of attention. The performance of the system working with relatively low amplitude acoustic wave can be predicted by the linear thermoacoustic theory, which is already well developed. However, a high amplitude acoustic wave is usually required in order to achieve high power density or high power output. Unfortunately, the performance of such systems can be seriously degraded due to nonlinear effects, such as turbulence, minor loss or high proportion of harmonics. The lack of understanding of these effects impedes the design and construction of high efficiency systems. The work described in this thesis is focused on the study of flow phenomena taking place around parallel plate stack placed in a standing wave thermoacoustic resonator, by using advanced flow diagnostics techniques such as particle image velocimetry (PIV) and hot wire anemometry (HWA). In order to carry out the experimental study, a standing wave thermoacoustic device working at relatively low frequency of 13.1Hz was designed, commissioned and tested. The frequency response of this device was carefully investigated and compared with the analytical results using linear acoustic equations and a linear model of the loudspeaker. A further comparison with the analytical results obtained with the modelling tool DeltaEC (Design Environment for Low-amplitude Thermoacoustic Energy Conversion) was also presented. The resonator was driven from low to large pressure amplitudes with drive ratios up to 10%. A good agreement is obtained for small amplitudes, but the discrepancies become larger when the driving amplitude is increased. The analysis reveals that the large discrepancy at high amplitude can be attributed to minor losses. Following the above preliminary work, a more comprehensive study of the flow field around parallel-plate stacks was conducted by means of PIV and HWA. It was shown that the flow around the two studied parallel-plate stacks exhibits rather complicated flow features when the amplitude of the acoustic oscillation varies. Symmetrical and asymmetrical vortex shedding phenomena are observed and two distinct modes of generating 'vortex streets' are identified. It shown that a velocity related parameter such as the Reynolds number, defined on the plate thickness and the velocity amplitude at the entrance to the stack, and a geometrical parameter are not sufficient to define the flow characteristics in this type of flow problem. It is also proposed to introduce an extra frequency related parameter such as the Keulegan-Carpenter number (KC) and to carry out a similarity analysis in order to understand better the physics behind the flow phenomena and their controlling parameters. Typical ensemble-averaged velocity fields are used in the analysis above. However, the detailed flow features obtained from the ensemble averaged flow fields and the instantaneous flow fields could be different in a substantial way. The flow behaviour, its kinematics, dynamics and scales of turbulence, therefore are further investigated by using the classical Reynolds decomposition to separate the instantaneous velocity fields into ensemble-averaged mean velocity fields and fluctuations in a set of predetermined phases within an oscillation cycle. The mean velocity field and the fluctuation intensity distributions are investigated over the acoustic oscillation cycle. By using fast Fourier transform (FFT) spatial filtering techniques, the velocity fluctuation is further divided into large- and small-scale fluctuations, and their physical significance is discussed. The physics behind the flow phenomena are further studied by carrying out an analysis of the wake flow during the ejection part of the flow cycle, where either closed re-circulating vortices or alternating vortex shedding can be observed. A similarity analysis of the governing Navier-Stokes equations is then undertaken in order to derive the similarity criteria governing the wake flow behaviour. Similarity numbers including two types of Reynolds number, the KC number and a non-dimensional stack configuration parameter are considered. The influence of these parameters on the flow behaviour is discussed by investigating the experimental data obtained, along with additional data from literature.

The performance evaluation and parametric studies of an Inertance Tube Pulse Tube Refrigerator (IPTR) are performed for different length-to-diameter ratios, with the Computational Fluid Dynamics (CFD) package FLUENT. The integrated model consists of individual models of the components, namely, the compressor, compressor cooler, regenerator, cold heat exchanger, pulse tube, warm heat exchanger, inertance tube and the reservoir. The formulation consists of the governing equations expressing the conservation of mass, momentum and energy with axi-symmetry assumption and relations for the variable thermophysical properties of the working medium and the regenerator matrix, and friction factor and heat transfer coefficients in oscillatory flows. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of heat exchangers and the regenerator which are treated as porous zones. In addition, the wall thickness of the components is also accounted for. Dynamic meshing is used to model the compressor zone. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the overall performance. The thermal non-equilibrium results in a higher cold heat exchanger temperature due to inefficiencies. The dynamic characteristics of pulse tube are analyzed by introducing a time constant. The study is extended to other types of PTRs, namely, the Orifice type Pulse Tube Refrigerator (OPTR), Double Inlet type Pulse Tube Refrigerator (DIPTR) and a PTR with parallel combination of inertance tube and orifice (OIPTR). The focus of the second phase of analysis is the pulse tube region. The oscillatory flow and temperature fields in an open-ended pipe driven by a time-wise sinusoidally varying pressure at one end and subjected to an ambient-to-cryogenic temperature difference across the ends, is numerically studied both with and without the inclusion of buoyancy effects. Conjugate effects arising out of the interaction of oscillatory flow with heat conduction in the pipe wall are taken into account by considering a finite thickness wall with an insulated exterior surface. Parametric studies are conducted with frequencies in the range 5-15 Hz for an end-to-end temperature difference of 200 K. As the pressure amplitude increases, the temperature difference between the wall and the fluid decreases due to mixing at the cold end. The pressure amplitude and the frequency have negligible effect on the time averaged Nusselt number. The effect of buoyancy is studied for hot side up and cold side up configurations. It is found that the time averaged Nusselt number does not change significantly with orientation or Rayleigh number. Sharp changes in Nusselt number and velocity profiles and an increase in energy transfer through solid and gas were observed when natural convection comes into play with hot end placed down. Cooldown experiments are conducted on a preliminary experimental setup. Comparison of the numerical and experimental cooldown curves disclosed a number of areas where improvement is required, primarily the leakage past the piston and the design of the heat exchangers. The setup is being improved to bring out a second and improved version for attaining the lower cold heat exchanger temperature.

Wormlike micelles are viscoelastic fluids that present an intermediate behavior between solids and ordinary liquids since they are elastic at short time scales but flow easily at large time scales. In opposition to Newtonian fluids, which have constant viscosity, these fluids usually exhibit a non-Newtonian response with a rate-dependent shear viscosity. Wall-bounded oscillatory flows of Newtonian and complex fluids are found in many practical situations. Oscillatory pipe flows are especially important in physiology in connection with the circulatory and respiratory systems of human beings, as well as in industrial processes such as fluid pumping, secondary oil recovery or filtration, and in acoustics. Pulsating flows are of particular interest also in the rheological characterization of complex fluids. We analyze the laminar oscillatory flow of viscoelastic fluids using the Maxwell and Oldroyd-B models. We have shown that in wall-bounded oscillatory flows of viscoelastic fluids the two characteristic lengths of the Ferry waves, the damping length and wavelength, together with the characteristic separation of the walls, define all the flow properties for fluid models with a linear shear-stress equation in unidirectional flow. In wall-bounded settings there exists the possibility that shear waves generated at different locations superpose themselves before decaying so that the shear waves interfere, giving rise to a resonant flow at well defined frequencies of driving. The theoretical predictions obtained for the laminar velocity profiles are validated by carrying out time-resolved Particle Image Velocimetry (PIV) experiments in a vertical pipe at small driving amplitudes. The oscillatory pipe flow has been investigated in the whole range of experimentally accessible driving frequencies and amplitudes, and classified in three main flow regimes: laminar, vortical, and non-axisymmetric vortical. By ramping up and down the driving amplitude at constant frequency we have been able to characterize the transition from laminar to more complex flows, under controlled driving conditions. The first hydrodynamic instability occurs when the laminar base flow becomes unstable against the formation of axisymmetric toroidal vortices that appear distributed along the cylinder. The calculation of root-mean-square fluctuations in the vertical direction, of the vertical and radial components of the velocity (averaged in time or over the tube diameter) has allowed to determine the critical amplitude at which the instability sets in with high accuracy. In the vortical flow an abrupt increase of the fluctuations is observed, that accounts for the loss of the vertical translational symmetry and the formation of vortices in the flow. This transition exhibits hysteresis when the driving amplitude is ramped up and down, which makes us presume that the bifurcation from the laminar flow has a subcritical nature. A second hydrodynamic instability occurs when the vortical flow loses the axial symmetry. In this flow regime the vortices are heavily distorted and no longer axisymmetric. The velocity and vorticity maps of the vortical flow measured in a meridional plane of the tube appear periodic in time, on time scales comparable to the driving period. Interestingly, the vortex formation is favored in the acceleration phases of the piston oscillation. Besides, we have uncovered a spatio-temporal dynamics on long time scales (much larger than the relaxation time of the fluid) that substantially modifies the flow organization. This slow dynamics is more effective in the bottom half of the cylinder, specially next to the driving piston. A global inspection of the vortical flow along the tube length reveals that the instability takes place earlier in the bottom part of the tube, in the vicinity of the driving piston. At increasing the driving amplitude the boundary between laminar and vortical flow progressively raises towards the top regions. And above a critical driving amplitude the entire fluid flow is vortical. The mechanism triggering the hydrodynamic instability from the laminar to the axisymmetric vortical flow is not yet clear. / L'objectiu d'aquesta Tesi és estudiar el flux oscil•latori vertical en fluids micel•lars. Els fluids micel•lars són fluids complexos amb propietats viscoelàstiques, de manera que mostren un comportament intermedi entre els sòlids i els líquids: són elàstics a escales de temps curtes però flueixen a escales de temps més llargues. En contraposició als fluids Newtonians, que tenen una viscositat constant, els fluids complexos mostren un comportament no-Newtonià, amb una viscositat que depèn del ritme de deformació. El fluxos oscil•latoris de fluids Newtonians o complexos en geometries confinades són especialment importants en fisiologia, en relació amb el sistema circulatori i respiratori d'éssers humans, i també en processos industrials com el bombejat de fluids, l'extracció de petroli, i en particular són interessants en la caracterització reològica de fluids complexos. Primer estudiem el flux oscil•latori des d'una perspectiva teòrica i analitzem el flux laminar de fluids viscoelàstics utilitzant els models de Maxwell i Oldroyd-B en un tub vertical. Hem mostrat que en fluxos confinats existeix la possibilitat que les ones de cisalla generades a les diferents parets se sobreposin abans d'esmorteir-se i que eventualment donin lloc a un fenomen de ressonància. Les prediccions teòriques obtingudes pel flux laminar són validades duent a terme experiments de Velocimetria d'Imatges de Partícules (PIV) en un tub vertical, per amplituds petites del forçament oscil•latori. Quan s'incrementa l'amplitud de l'oscil•lació el flux laminar evoluciona cap a fluxos que presenten una dependència espai-temporal més complexa. Fent rampes d'amplitud creixent a una freqüència fixada hem pogut caracteritzar experimentalment la transició del flux laminar a aquests fluxos més complexos, sota condicions de forçament ben controlades. La primera inestabilitat apareix quan el flux laminar esdevé inestable amb la corresponent formació d'anells de vorticitat apilats al llarg del tub. Es manifesta una segona inestabilitat per amplituds del forçament més grans, per la qual el flux vortical perd la simetria axial. En aquest nou règim els vòrtex estan fortament distorsionats i no són axisimètrics. Fent rampes d’amplitud creixent i decreixent hem observat que aquestes dues transicions presenten histèresi, i que per tant són de caràcter subcrític.

Understanding the mechanisms of cardiovascular disease progression is essential in developing novel therapies to combat this disease that contributes to 1 in 3 deaths in the United States every year. Endothelial dysfunction and its effects on vessel growth and remodeling are key factors in the progression and localization of atherosclerosis. Much of our understanding in this area has come from in-vivo and in-vitro experiments however perfused organ culture systems provide an alternative approach. Organ culture systems can provide a more controlled mechanical and biochemical environment compared to in-vivo models. This study focused on furthering development of this organ culture model by introducing a novel device to produce flow waveforms at the high frequencies and low mean flows seen in the mouse model. The device is capable of monitoring pressure, flow, diameter, and nitric oxide release. Each individual mechanism in the system was integrated via a computer using a custom Labview interface. The performance of the device was characterized by developing physiologic, physiologic-oscillatory, low, low-oscillatory waveforms and sinusoidal waveforms at frequencies ranging from 1-10 Hz. Overall this system provides a robust model to test the effects of flow on various biological markers both in real-time and after culture.

<div>Studying the motion of cells and investigating their migration patterns in inertial microchannels have been of great interest among researchers because of their numerous biological applications such as sorting, separating, and filtering them. A great drawback in conventional microfluidics is the inability to focus extremely small biological particles and pathogens in the order of sub-micron and nanometers due to the requirement of designing an impractically elongated microchannel, which could be in the order of a few meters in extreme cases. This restriction is because of the inverse correlation between the cube of the particle size and the theoretically required channel length. Exploiting an oscillatory flow is one solution to this issue where the total distance that the particle needs to travel to focus is virtually extended beyond the physical length of the device. Due to the present symmetry in such flow, the directions of the lift forces acting on the particle remain the same, making the particle focusing feasible. </div><div><br></div><div>Here, we present results of simulation of such oscillatory flows of a single capsule in a rectangular microchannel containing a Newtonian fluid. A 3D front-tracking method has been implemented to numerically study the dynamics of the capsule in the channel of interest. Several cases have been simulated to quantify the influence of the parameters involved in this problem such as the channel flow rate, capsule deformability, frequency of oscillation, and the type of applied mechanism for inducing flow oscillations. In all cases, the capsule blockage ratio and the initial location are the same, and it is tracked until it reaches its equilibrium position. The capability to focus the capsule in a short microchannel with oscillatory flow has been observed for capsule deformabilities and mechanisms to induce the oscillations used in our study. Nevertheless, there is a limit to the channel flow rate beyond which, there is no single focal point for the capsule. Another advantage of having an oscillatory microchannel flow is the ability to control the capsule focal point by changing the oscillation frequency according to the cases presented in the current study. The capsule focusing point also depends on its deformability, flow rate, and the form of the imposed periodic pressure gradient; more deformable capsules with lower maximum velocity focus closer to the channel center. Also, the difference between the capsule equilibrium point in steady and oscillatory flows is affected by the capsule stiffness and the device flow rate. Furthermore, increasing the oscillation frequency, capsule rigidity, and system flow rate shorten the essential device length. </div><div><br></div><div>Although the oscillation frequency can provide us with new particle equilibrium positions, especially ones between the channel center and wall that can be very beneficial for separation purposes, it has the shortcoming of having a zero net throughput. To address this restriction, a steady component has been added to the formerly defined oscillatory flow to make it pulsating. Furthermore, this type of flow adds more new equilibrium points because it behaves similarly to a pure oscillatory flow with an equivalent frequency in that regard. They also enable the presence of droplets at high Ca or Re that could break up in the steady or a very low-frequency regime. Therefore, we perform new numerical simulations of a deformable droplet suspended in steady, oscillatory, and pulsating microchannel flows. We have observed fluctuations in the trajectory of the drop and have shown that the amplitude of these oscillations, the average of the oscillatory deformation, and the average migration velocity decrease by increasing the frequency. The dependence of the drop focal point on the shape of the velocity profile has been investigated as well. It has been explored that this equilibrium position moves towards the wall in a plug-like profile, which is the case at very high frequencies. Moreover, due to the expensive cost of these simulations, a recursive version of the Multi Fidelity Gaussian processes (MFGP) has been used to replace the numerous high-fidelity (or fine-grid) simulations that cannot be afforded numerically. The MFGP algorithm is used to predict the equilibrium distance of the drop from the channel center for a wide range of the input parameters, namely Ca and frequency, at a constant Re. It performs exceptionally well by having an average R^2 score of 0.986 on 500 random test sets.</div><div><br></div><div>The presence of lift forces is the main factor that defines the dynamics of the drop in the microchannel. The last part of this work will be dedicated to extracting the active lift force profiles and identify their relationships with the parameters involved to shed light on the underlying physics. This will be based on a novel methodology that solely depends on the drop trajectory. Assuming a constant Re, we then compare steady lift forces at different Ca numbers and oscillatory ones at the same constant Ca. We will then define analytical equations for the obtained lift profiles using non-linear regression and predict their key coefficients over a continuous range of inputs using MFGP.</div>

[pt] Nessa pesquisa, desenvolvemos uma nova metodologia para analizar materiais nos regimes oscilatórios linear e quasilinear. Foi mostrado que poucos experimentos reológicos são necessários. Além disso, a análise de dados apresentada é objetiva já apenas processamentos simples são necessários para avaliar as funções materiais. Esse fato contrasta com grande parte das análises de escoamento oscilatório de alta amplitude, tendo em vista que essas metodologias requerem manipulação matemática complexa dos dados. Por fim, a metodologia desenvolvida também apresenta grande evolução com relação às metodologias utilizadas anteriormente para analisar materiais no regime QL-LAOS. / [en] In this research, we developed a novel methodology to analyze materials in the linear and quasilinear oscillatory regimes (constant structure motions). It was shown that very few rheometric experiments are necessary. Furthermore, data analysis presented on this thesis is straightforward as raw data obtained from the rheometer requires simple data processing before being input into the equations that evaluate the material functions. This fact is in contrast with most large amplitude oscillatory shear analysis methods since they aim to analyze structure-changing motions and this requires complex mathematical manipulation of data. At last, both experimental methodology and data analysis presented in this research are much simpler than the previous methodologies used to analyze materials in the QL-LAOS regime.