Shear-induced particle migration was investigated by using a continuum diffusive -flux model for the creep flow of nickel powder filled polymers, which are viscous with shear-thinning characteristic. The model, together with flow equations, was employed for solving the non-Newtonian flow patterns and non-uniform particle concentration distribution of mono-modal suspensions in a pressure-driven tube flow. Particle volume fraction and velocity fields for the non-homogenous shear flow field were predicted for 40% particle volume fraction. The model captures the trends found in experimental investigations. / Singapore-MIT Alliance (SMA)

A sports field construction method that uses a geotextile to support the root zone atop a synthetic drainage structure is an alternative to the common design that uses gravel drainage material to support the root zone. A study was conducted to address the concern that fine particles in the root zone may migrate under the influence of percolating water, clog geotextile pores, and restrict the amount of water drained from a sports field. In test columns, six root zone mixtures with different particle size distributions were combined with ten geotextiles with different opening sizes to produce 60 replicated treatments. Water flow through the root zone mixture-geotextile combinations in the test columns was evaluated over a six-month period. Change in permeability was assessed by monitoring the temporal distribution of drainage from a 25-mm pulse of water applied to 300-mm deep root zone mixture in the test column. Particles in drainage water were analyzed for size distribution. The study revealed that drainage rates were affected more by drainage trough the root zone mixture than through the geotextile. The amount and particle size distribution of particles in drainage water were influenced more by root zone mixture than by geotextile. It appeared that in the establishment phase of a sports field that fine particles in the root zone may present more of a problem to clogging of the root zone pores than clogging of the geotextile pores.

<div> <div> <div> <p>The motion of synthetic capsules and living cells in microchannels has been the subject of numerous studies in the last decade due to its significance in engineer- ing and biomedical applications. Cell sorting and separation are common processes that are used for various purposes such as separation of leukocytes from blood used in DNA sequencing. Isolation of rare cells in blood is needed for early diagnosis of lethal diseases such as cancer. Cell isolation and enrichment will also provide a better platform to biologists to study and analyze various properties of living cells. Thus, there is a high demand for developing techniques to precisely control trajectories of the cells and manipulate them in a desired manner. Microfluidic devices provide a platform to achieve aforementioned needs while overcoming challenges such as sample contamination, cost and complexity of the procedures. In many of these applications, the background fluid is non-Newtonian due to the presence of DNA and proteins, or polymers are added to control the trajectory of the cells. In this work, we first provide a fundamental study on the dynamics of a single deformable capsule in a viscoelastic matrix under a simple shear flow. Furthermore, we investigate the motion of a single cell and suspension of cells in microchannels. The effects of cell size, inertia, cell volume fraction, cell deformability and fluid elasticity are explored. Our findings on capsule motion in the viscoelastic medium suggest that the use of constant-viscosity viscoelastic fluid pushes the cells toward the channel centerline which can be used in microfluidic devices used for cell focusing such as cytometers. However, viscoelastic fluid with shear-thinning characteristics and drives the flowing cells toward the channel wall. Particle motion in viscoelastic matrix equilibrium positions of the particle in the microchannel for a wide range of inertial and elastic effects. These fundamental studies can provide insight on the role of rheological properties of the fluid that can be tuned to control the motion of the cells and particles for efficient design of microfluidic devices. </p> </div> </div> </div>

<p>The major issue concerns how the different lignosulfonate types changes the rheological properties of the cement based material (concrete, mortar and cement paste) as a function of temperature and time. In such terms, it is demonstrated that the high molecular weight lignosulfonates performs far better than the low molecular weight ones. The former type also performs considerable better compared to a naphthalene based polymer. </p><p>The above investigation is done with help from the second part of this thesis, which identifies some of the parameters p1, p2,... affecting the shear viscosity η = η ( p1, p2,...) of the cement based material. This is done by investigating the thixotropic behavior of cement paste mixed with either lignosulfonates or naphthalene. The thixotropic behavior is directly related to coagulation, dispersion and re-coagulation of the cement particles. In making the analysis, a modification is applied to the Hattori-Izumi theory, which is a theory about the bookkeeping of the number of reversible coagulated connections between the cement particles. The modification consist, among other things, of include a fading memory to the analysis. That is, the cement paste is allowed to remember its recent past. By a combination of experimental results and numerical simulations, it is demonstrated that such memory term is very important.</p><p>An experimental error is present during a viscometric measurement on concrete (a coaxial cylinders viscometer is used). The error is generated by particle migration. Investigating and compensating for this error constitutes the third part of this thesis. Realizing the nature of this error, some corrections are applied. However, with these corrections, one is only extracting the viscometric values of a "fat'' concrete that surrounds the inner cylinder of the viscometer after the particle migration is basically complete, and not of the concrete in the original homogenous state.</p>

The major issue concerns how the different lignosulfonate types changes the rheological properties of the cement based material (concrete, mortar and cement paste) as a function of temperature and time. In such terms, it is demonstrated that the high molecular weight lignosulfonates performs far better than the low molecular weight ones. The former type also performs considerable better compared to a naphthalene based polymer. The above investigation is done with help from the second part of this thesis, which identifies some of the parameters p1, p2,... affecting the shear viscosity η = η ( p1, p2,...) of the cement based material. This is done by investigating the thixotropic behavior of cement paste mixed with either lignosulfonates or naphthalene. The thixotropic behavior is directly related to coagulation, dispersion and re-coagulation of the cement particles. In making the analysis, a modification is applied to the Hattori-Izumi theory, which is a theory about the bookkeeping of the number of reversible coagulated connections between the cement particles. The modification consist, among other things, of include a fading memory to the analysis. That is, the cement paste is allowed to remember its recent past. By a combination of experimental results and numerical simulations, it is demonstrated that such memory term is very important. An experimental error is present during a viscometric measurement on concrete (a coaxial cylinders viscometer is used). The error is generated by particle migration. Investigating and compensating for this error constitutes the third part of this thesis. Realizing the nature of this error, some corrections are applied. However, with these corrections, one is only extracting the viscometric values of a "fat'' concrete that surrounds the inner cylinder of the viscometer after the particle migration is basically complete, and not of the concrete in the original homogenous state.

<div><div>This thesis analyzed three fundamental fluid dynamics problems arising from multiphase flows that may be encountered in hydraulically fractured flow passages. During hydraulic fracturing (``fracking''), complex fluids laden with proppants are pumped into tight rock formations. Flow passages in these formation are naturally heterogeneous with geometric variations, which become even more pronounced due to fracking. Upon increasing the flow area (and, thus, the conductivity of the rock), crude oil, shale gas or other hydrocarbons can then flow out of the formation more easily. In this context, we encounter the following three fluid mechanical phenomena: fluid--fluid interfacial instabilities, flow-wise variation of the hydraulic conductivity, and particle migration in the pumped fluids. </div><div><br></div><div>First, we studied the (in)stability of the interface between two immiscible liquids in angled (tapered) Hele-Shaw cells, as model of a non-uniform flow passage. We derived an expression for the growth rate of perturbations to the flat interface and for the critical capillary number, as functions of the small gap gradient (taper). On this basis, we formulated a three-regime theory to describe the interface's stability. Specifically, we found a new regime in which the growth rate changes from negative to positive (converging cells), or from positive to negative (diverging cells), thus the interface's stability can change type at some location in the cell. We conducted three-dimensional OpenFOAM simulations of the Navier--Stokes equations, using the continuous surface force method, to validate the theory.</div><div><br></div><div>Next, we investigated the flow-wise variation of the hydraulic conductivity inside a non-uniformly shaped fracture with permeable walls. Using lubrication theory for viscous flow, in conjunction with the Beavers--Joseph--Saffman boundary condition at the permeable walls, we obtained an analytical expression for the velocity profile, conductivity, and wall permeation velocity. The new expression highlights the effects of geometric variation, </div><div>the permeability of the walls, </div><div>and the effect of flow inertia.</div><div>The theory was validated against OpenFOAM simulations of the Navier--Stokes equations subject to a tensorial slip boundary condition.</div><div><br></div><div>Finally, we extended the utility of phenomenological models for particle migration in shear flow using the physics-informed neural networks (PINNs) approach. We first verified the approach for solving the inverse problem of radial particle migration in a non-Brownian suspension in an annular Couette flow. Then, we applied this approach to both non-Brownian and Brownian suspensions in Poiseuille slot flow, for which a definitive calibration of the phenomenological migration model has been lacking. Using PINNs, we identified the unknown/empirical parameters in the physical model, showing that (unlike assumptions made in the literature) they depend on the bulk volume fraction and shear P\'eclet number. </div></div>

Heat transfer and flow characteristics of phase change material slurry flow in microchannels with constant heat flux at the base were investigated. The phase change process was included in the energy equation using the effective specific heat method. A parametric study was conducted numerically by varying the base fluid type, particle concentration, particle size, channel dimensions, inlet temperature, base heat flux and melting range of PCM. The particle distribution inside the microchannels was simulated using the diffusive flux model and its effect on the overall thermal performance of microchannels was investigated. Experimental investigation was conducted in microchannels of 101 [micro]m width and 533 [micro]m height with water as base fluid and n-Octadecane as PCM to validate the key conclusions of the numerical model. Since the flow is not fully developed in case of microchannels (specifically manifold microchannels, which are the key focus of the present study), thermal performance is not as obtained in conventional channels where the length of the channel is large (compared to length of microchannels). It was found that the thermal conductivity of the base fluid plays an important role in determining the thermal performance of slurry. The effect of particle distribution can be neglected in the numerical model under some cases. The performance of slurry depends on the heat flux, purity of PCM, inlet temperature of the fluid, and base fluid thermal conductivity. Hence, there is an application dependent optimum condition of these parameters that is required to obtain the maximum thermal performance of PCM slurry flows in microchannels.

En 1970, George K. Batchelor suggérait que la connaissance des lois de l'hydrodynamique rendait possible la dérivation de propriétés rhéologiques macroscopiques telle la viscosité, à partir de la connaissance de la microstructure d'une suspension de particules. Quarante ans plus tard, ses espoirs ne se sont pas concrétisés et la rhéologie des suspensions,notamment en régime concentré, reste un domaine de recherche très actif.Considérant des suspensions modèles de particules non colloïdales dans un liquide newtonien, le travail expérimental réalisé au cours de cette thèse s'est d'abord attaché à unifier les concepts classiquement définies en rhéologie des suspensions et ceux issus des récentes avancées sur les écoulements granulaires. Dans ce but, un dispositif original de cisaillement à pression imposée a été développé et a permis une caractérisation claire des équations constitutives en régime très dense.Par la suite, des configurations d'écoulements à surface libre ont été utilisées pour la mesure des deux différences de contraintes normales.Enfin, la mise en cohérence de l'ensemble des résultats expérimentaux donne une formulation complète et cohérente de la rhéologie des suspensions non colloïdales. / In 1970, George K. Batchelor suggested that the knowledge of the laws of hydrodynamics made ​​possible the derivation of macroscopic rheological properties such as the effective viscosity, from the knowledge of the microstructure of a suspension of particles. Forty years later, his hopes have not materialized and the rheology of suspensions, particularly in the concentrated regime, remains an area of ​​active research. Considering suspensions of non-colloidal particles in a Newtonian liquid, the experimental work in this thesis was first attached to unify the concepts traditionally defined rheology of suspensions and those from recent advances on granular flows. For this purpose, an original of shear imposed pressure was developed and showed a clear characterization of constitutive equations in the dense regime. Subsequently, the configurations of free surface flows have been used for the measurement of both normal stress differences. Finally, the coherence of all the experimental results gives a complete and consistent formulation of the rheology of non-colloidal suspensions.

A hybrid FEM/FDM algorithm for particle migration of quasi-steady flow in concentrated suspension materials is proposed in this study. This hybrid FEM/FDM algorithm in which the planar variables, such as pressure field, are described in terms of finite element method, and gapwise variables of temperature, density concentration and time derivatives are expressed by finite difference method. The particle concentration inhomogeneities can be predicted, which is ignored by the existing injection molding simulation packages. Simulation results indicated that powder concentration variation could be significant in practical processing in PIM. / Singapore-MIT Alliance (SMA)

The correlation between concrete rheological parameters and its pumping behavior under consideration of the so-called lubricating layer has been investigated for decades. In this thesis, flow-induced particle migration (FIPM) was studied in-depth, as the main underlying mechanism for the formation of the lubricating layer. Conventionally vibrated and self-compacting concretes were chosen as the target mixtures. Furthermore, cementitious model concretes, containing colored glass beads, were proposed to obtain further insights into the FIPM and its impact on pumping. The mixtures were differentiating with regard to particle volume fractions, mortars composition, maximum particle size and particle size distributions. In the experiments, various established methods were used to characterize the rheological properties and the pumping behavior of the concretes. New methodologies for estimating the thickness of the lubricating layer and the particle distribution in pumped cross-sections were proposed as well. The rheological properties and pumping behavior of real and model concretes were in agreement with the state-of-the-art literature. Based on the radial particle distributions, it was illustrated that the particle migration intensifies by increasing the particle size and decreasing the total volume fraction of solid particles. Furthermore, in highly-concentrated poly-dispersed model concretes, the particle concentration curves consist of a sudden jump close to the pipe wall and a relatively uniform distribution in the inner zone of the pipe. In these cases, the influence of FIPM on overall flow behavior cannot be neglected. Moreover, it was shown that the lubricating layer thickness is not constant for all concrete mixtures. For poly-dispersed suspensions, the shear-induced particle migration (SIPM) has a stronger impact than the wall for forming the lubricating layer. Finally, it was concluded that a solid-liquid threshold of 1 to 2 mm is a reliable choice when investigating concrete pipe flow. The faster the concrete is pumped or the lower the yield stress of the constitutive mortar is, the smaller is the solid-liquid threshold. Based on the experimental findings, a first-order physical correlation between pumping parameters (pressure and discharge rate), particle properties (volume fraction and packing properties) and lubricating layer properties (thickness and viscosity) was proposed. Accordingly, for a simple flow topology with a shearing lubricating layer and an extruding yield stress concrete, the lubricating layer thickness was computed from the competition between shear-induced fluxes of particles. In agreement with the driving equations of SIPM, it was assumed that the first flux correlates with the internal stress gradient in the plug concrete whereas the counteracting particle flux correlates with the shear rate in the lubricating layer. The model was validated for two flow types, pipe flow in the Sliper and Couette flow in a co-axial tribometer. The proposed model can capture the observed main features and their evolutions despite the absence of any fitting parameters.