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634 KiB

Open AccessArticle

Flow Anisotropy due to Thread-Like Nanoparticle Agglomerations in Dilute Ferrofluids

by Alexander Cali, Wah-Keat Lee, A. David Trubatch and Philip Yecko

Fluids 2017, 2(4), 67; https://doi.org/10.3390/fluids2040067 - 7 Dec 2017

Cited by 1 | Viewed by 3866

Abstract

Improved knowledge of the magnetic field dependent flow properties of nanoparticle-based magnetic fluids is critical to the design of biomedical applications, including drug delivery and cell sorting. To probe the rheology of ferrofluid on a sub-millimeter scale, we examine the paths of 550 [...] Read more.

Improved knowledge of the magnetic field dependent flow properties of nanoparticle-based magnetic fluids is critical to the design of biomedical applications, including drug delivery and cell sorting. To probe the rheology of ferrofluid on a sub-millimeter scale, we examine the paths of 550 μm diameter glass spheres falling due to gravity in dilute ferrofluid, imposing a uniform magnetic field at an angle with respect to the vertical. Visualization of the spheres’ trajectories is achieved using high resolution X-ray phase-contrast imaging, allowing measurement of a terminal velocity while simultaneously revealing the formation of an array of long thread-like accumulations of magnetic nanoparticles. Drag on the sphere is largest when the applied field is normal to the path of the falling sphere, and smallest when the field and trajectory are aligned. A Stokes drag-based analysis is performed to extract an empirical tensorial viscosity from the data. We propose an approximate physical model for the observed anisotropic drag, based on the resistive force theory drag acting on a fixed non-interacting array of slender threads, aligned parallel to the magnetic field. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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3737 KiB

Open AccessArticle

Three-Dimensional Low Reynolds Number Flows near Biological Filtering and Protective Layers

by Christopher Strickland, Laura Miller, Arvind Santhanakrishnan, Christina Hamlet, Nicholas A. Battista and Virginia Pasour

Fluids 2017, 2(4), 62; https://doi.org/10.3390/fluids2040062 - 13 Nov 2017

Cited by 8 | Viewed by 5754

Abstract

Mesoscale filtering and protective layers are replete throughout the natural world. Within the body, arrays of extracellular proteins, microvilli, and cilia can act as both protective layers and mechanosensors. For example, blood flow profiles through the endothelial surface layer determine the amount of [...] Read more.

Mesoscale filtering and protective layers are replete throughout the natural world. Within the body, arrays of extracellular proteins, microvilli, and cilia can act as both protective layers and mechanosensors. For example, blood flow profiles through the endothelial surface layer determine the amount of shear stress felt by the endothelial cells and may alter the rates at which molecules enter and exit the cells. Characterizing the flow profiles through such layers is therefore critical towards understanding the function of such arrays in cell signaling and molecular filtering. External filtering layers are also important to many animals and plants. Trichomes (the hairs or fine outgrowths on plants) can drastically alter both the average wind speed and profile near the leaf’s surface, affecting the rates of nutrient and heat exchange. In this paper, dynamically scaled physical models are used to study the flow profiles outside of arrays of cylinders that represent such filtering and protective layers. In addition, numerical simulations using the Immersed Boundary Method are used to resolve the three-dimensional flows within the layers. The experimental and computational results are compared to analytical results obtained by modeling the layer as a homogeneous porous medium with free flow above the layer. The experimental results show that the bulk flow is well described by simple analytical models. The numerical results show that the spatially averaged flow within the layer is well described by the Brinkman model. The numerical results also demonstrate, however, that the flow can be highly three-dimensional with fluid moving into and out of the layer. These effects are not described by the Brinkman model and may be significant for biologically relevant volume fractions. The results of this paper can be used to understand how variations in density and height of such structures can alter shear stresses and bulk flows. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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13153 KiB

Open AccessArticle

Numerical Study of a 3D Eulerian Monolithic Formulation for Incompressible Fluid-Structures Systems

by Chen-Yu Chiang, Olivier Pironneau, Tony W. H. Sheu and Marc Thiriet

Fluids 2017, 2(2), 34; https://doi.org/10.3390/fluids2020034 - 16 Jun 2017

Cited by 13 | Viewed by 3919

Abstract

An algorithm is derived for a hyperelastic incompressible solid coupled with a Newtonian fluid. It is based on a Eulerian formulation of the full system in which the main variables are the velocities. After a fully implicit discretization in time it is possible [...] Read more.

An algorithm is derived for a hyperelastic incompressible solid coupled with a Newtonian fluid. It is based on a Eulerian formulation of the full system in which the main variables are the velocities. After a fully implicit discretization in time it is possible to eliminate the displacements and solve a variational equation for the velocities and pressures only. The stability of the method depends heavily on the use of characteristic-Galerkin discretization of the total derivatives. For comparison with previous works, the method is tested on a three-dimensional (3D) clamped beam in a pipe filled with a fluid. Convergence is studied numerically on an axisymmetric case. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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1649 KiB

Open AccessArticle

Modeling Superparamagnetic Particles in Blood Flow for Applications in Magnetic Drug Targeting

by Iris Rukshin, Josef Mohrenweiser, Pengtao Yue and Shahriar Afkhami

Fluids 2017, 2(2), 29; https://doi.org/10.3390/fluids2020029 - 4 Jun 2017

Cited by 25 | Viewed by 5187

Abstract

Magnetic drug targeting is a technique that involves the binding of medicine to magnetizable particles to allow for more specific transport to the target location. This has recently come to light as a method of drug delivery that reduces the disadvantages of conventional, [...] Read more.

Magnetic drug targeting is a technique that involves the binding of medicine to magnetizable particles to allow for more specific transport to the target location. This has recently come to light as a method of drug delivery that reduces the disadvantages of conventional, systemic treatments. This study developed a mathematical model for tracking individual superparamagnetic nanoparticles in blood flow in the presence of an externally applied magnetic field. The model considers the magnetic attraction between the particles and the external magnet, influence of power law flow, diffusive interaction between the particles and blood, and random collisions with red blood cells. A stochastic system of differential equations is presented and solved numerically to simulate the paths taken by particles in a blood vessel. This study specifically focused on localized cancer treatment, in which a surface tumor is accessed through smaller blood vessels, which are more conducive to this delivery method due to slower flow velocities and smaller diameters. The probability of the particles reaching the tumor location is found to be directly dependent on ambient factors; thus, diffusion through Brownian motion and red blood cell collisions, different magnetic field and force models, blood viscosities, and release points are considered. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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1263 KiB

Open AccessArticle

Effect of Wall Flexibility on the Deformation during Flow in a Stenosed Coronary Artery

by Laxman Kallekar, Chinthapenta Viswanath and Mohan Anand

Fluids 2017, 2(2), 16; https://doi.org/10.3390/fluids2020016 - 15 Apr 2017

Cited by 17 | Viewed by 5104

Abstract

The effect of varying wall flexibility on the deformation of an artery during steady and pulsatile flow of blood is investigated. The artery geometry is recreated from patient-derived data for a stenosed left coronary artery. Blood flow in the artery is modeled using [...] Read more.

The effect of varying wall flexibility on the deformation of an artery during steady and pulsatile flow of blood is investigated. The artery geometry is recreated from patient-derived data for a stenosed left coronary artery. Blood flow in the artery is modeled using power-law fluid. The fluid-structure interaction of blood flow on artery wall is simulated using ANSYS 16.2, and the resulting wall deformation is documented. A comparison of wall deformation using flexibility models like Rigid, Linear Elastic, Neo-hookean, Mooney-Rivlin and Holzapfel are obtained for teady flow in the artery. The maximum wall deformation in coronary flow onditions predicted by the Holzapfel model is only around 50% that predicted by the Neo-Hookean model. The flow-induced deformations reported here for patient-derived stenosed coronary artery with physiologically accurate model are the first of its kind. These results help immensely in the planning of angioplasty. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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398 KiB

Open AccessArticle

On the Three Dimensional Interaction between Flexible Fibers and Fluid Flow

by Bogdan G. Nita and Ryan Allaire

Fluids 2017, 2(1), 4; https://doi.org/10.3390/fluids2010004 - 22 Jan 2017

Cited by 1 | Viewed by 4334

Abstract

In this paper we discuss the deformation of a flexible fiber clamped to a spherical body and immersed in a flow of fluid moving with a speed ranging between 0 and 50 cm/s by means of three dimensional numerical simulation developed in COMSOL [...] Read more.

In this paper we discuss the deformation of a flexible fiber clamped to a spherical body and immersed in a flow of fluid moving with a speed ranging between 0 and 50 cm/s by means of three dimensional numerical simulation developed in COMSOL . The effects of flow speed and initial configuration angle of the fiber relative to the flow are analyzed. A rigorous analysis of the numerical procedure is performed and our code is benchmarked against well established cases. The flow velocity and pressure are used to compute drag forces upon the fiber. Of particular interest is the behavior of these forces as a function of the flow speed and fiber orientation. The Vogel exponents, which characterize the rate of bending of a fiber in a flow, are found for the various configurations examined here and seem to display interesting variations. These exponents are then compared with our previously studied two-dimensional models. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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1098 KiB

Open AccessArticle

Hydrodynamics of Highly Viscous Flow past a Compound Particle: Analytical Solution

by Longhua Zhao

Fluids 2016, 1(4), 36; https://doi.org/10.3390/fluids1040036 - 12 Nov 2016

Cited by 4 | Viewed by 6468

Abstract

To investigate the translation of a compound particle in a highly viscous, incompressible fluid, we carry out an analytic study on flow past a fixed spherical compound particle. The spherical object is considered to have a rigid kernel covered with a fluid coating. [...] Read more.

To investigate the translation of a compound particle in a highly viscous, incompressible fluid, we carry out an analytic study on flow past a fixed spherical compound particle. The spherical object is considered to have a rigid kernel covered with a fluid coating. The fluid within the coating has a different viscosity from that of the surrounding fluid and is immiscible with the surrounding fluid. The inertia effect is negligible for flows both inside the coating and outside the object. Thus, flows are in the Stokes regime. Taking advantage of the symmetry properties, we reduce the problem in two dimensions and derive the explicit formulae of the stream function in the polar coordinates. The no-slip boundary condition for the rigid kernel and the no interfacial mass transfer and force equilibrium conditions at fluid interfaces are considered. Two extreme cases: the uniform flow past a sphere and the uniform flow past a fluid drop, are reviewed. Then, for the fluid coating the spherical object, we derive the stream functions and investigate the flow field by the contour plots of stream functions. Contours of stream functions show circulation within the fluid coating. Additionally, we compare the drag and the terminal velocity of the object with a rigid sphere or a fluid droplet. Moreover, the extended results regarding the analytical solution for a compound particle with a rigid kernel and multiple layers of fluid coating are reported. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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Review

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10292 KiB

Open AccessReview

Fundamental Rheology of Disperse Systems Based on Single-Particle Mechanics

by Rajinder Pal

Fluids 2016, 1(4), 40; https://doi.org/10.3390/fluids1040040 - 7 Dec 2016

Cited by 21 | Viewed by 6918

Abstract

A comprehensive review of the fundamental rheology of dilute disperse systems is presented. The exact rheological constitutive equations based on rigorous single-particle mechanics are discussed for a variety of disperse systems. The different types of inclusions (disperse phase) considered are: rigid-solid spherical particles [...] Read more.

A comprehensive review of the fundamental rheology of dilute disperse systems is presented. The exact rheological constitutive equations based on rigorous single-particle mechanics are discussed for a variety of disperse systems. The different types of inclusions (disperse phase) considered are: rigid-solid spherical particles with and without electric charge, rigid-porous spherical particles, non-rigid (soft) solid particles, liquid droplets with and without surfactant, bubbles with and without surfactant, capsules, core-shell particles, non-spherical solid particles, and ferromagnetic spherical and non-spherical particles. In general, the state of the art is good in terms of the theoretical development. However, more experimental work is needed to verify the theoretical models and to determine their range of validity. This is especially true for dispersions of porous particles, capsules, core-shell particles, and magnetic particles. The main limitation of the existing theoretical developments on the rheology of disperse systems is that the matrix fluid is generally assumed to be Newtonian in nature. Rigorous theoretical models for the rheology of disperse systems consisting of non-Newtonian fluid as the matrix phase are generally lacking, especially at arbitrary flow strengths. Full article

(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)

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