Nanofluid Flow in Porous Media

Studies of fluid flow and heat transfer in a porous medium have been the subject of continuous interest for the past several decades because of the wide range of applications, such as geothermal systems, drying technologies, production of thermal isolators, control of pollutant spread in groundwater, insulation of buildings, solar power collectors, design of nuclear reactors, and compact heat exchangers, etc. There are several models for simulating porous media such as the Darcy model, Non-Darcy model, and non-equilibrium model. In porous media applications, such as the environmental impact of buried nuclear heat-generating waste, chemical reactors, thermal energy transport/storage systems, the cooling of electronic devices, etc., a temperature discrepancy between the solid matrix and the saturating fluid has been observed and recognized

New magnetic stimulation routes with magnetic nanoparticles from process intensification in chemical engineering

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2012-2013.Les nanoparticules magnétiques (NPM) suscitent un vif intérêt dans plusieurs branches de l’ingénierie et de la recherche. En effet, la taille de ces dernières ainsi que leur propriétés magnétiques lorsqu’en suspension permettent leur manipulation à distance en utilisant des champs magnétiques externes appropriés. Cela ouvre la voie à l’activation de fonctionnalités supplémentaires lorsqu’ancrées à des catalyseurs métalliques, des enzymes ou des agents thérapeutiques. Conséquemment, les NPM ont été impliquées au sein de plusieurs applications dans lesquelles le mélange à l’échelle microscopique est une problématique importante, par exemple dans les réactions catalytiques, la séparation et l’administration de médicaments. Le présent travail de thèse explore l’utilisation de NPM en tant que dispositifs nanométriques pour manipuler le mélange à l’échelle microscopique lorsque le système complet est soumis à des champs magnétiques. Toutes les expérimentations ont été menées à l’intérieur d’un électro-aimant à bobines tubulaire statique possédant deux pôles et trois phases. Ce dernier génère des champs magnétiques rotatifs uniformes (CMR), des champs magnétiques oscillatoires (CMO) ainsi que des champs magnétiques stationnaires (CMS). En premier lieu, une technique de mélange dans laquelle un CMR transforme des NPM en agitateurs nanométriques créant de petits tourbillons dans la phase liquide est présentée. L’utilisation de cette technique permet l’augmentation du coefficient de diffusion de l’eau quiescente dans une cellule de diffusion statique jusqu’à 200 fois. Les études systématiques des paramètres d’opération révèlent que l’ampleur de l’augmentation dépend de la fraction volumique en NPM ainsi que de la force et de la fréquence du champ magnétique. En second lieu, un écoulement convectif est utilisé afin de comprendre l’effet du couple hydrodynamique sur le comportement des NPM en champs magnétiques. Des tests de distribution de temps de séjour par impulsion sont effectués avec et sans champ magnétique dans le but d’examiner la dispersion axiale d’un écoulement laminaire de Poiseuille à l’intérieur d’un tube capillaire (Tests de dispersion de Taylor). Les résultats obtenus démontrent que le mélange latéral au long du tube est favorisé en présence de NPM et d’un champ magnétique. De plus, l’effet hydrodynamique observé de ce mélange latéral sur le profil de vitesse laminaire est interprété comme provenant d’une approche d’un profil de vitesse plat similaire à celui d’un écoulement piston. À l’aide de la même technique, l’effet des CMO et des CMS sur la dispersion de Taylor et sur le profil de vitesse laminaire est aussi examiné en écoulement capillaire. Alors que les CMO n’induisent pas de mélange nano-convectif dans le capillaire et ont un impact négligeable sur la dispersion axiale, les CMS pour leur part, détériorent le mélange latéral du traceur et créent des profils de vitesse déviant de la forme parabolique vers une forme plus saillie. Une discussion détaillée de la vorticité du fluide en fonction de l’orientation du champ magnétique est aussi présentée. Finalement, un écoulement multiphasique est étudié en ciblant le transfert de matière gaz-liquide entre des bulles de Taylor d’oxygène et la phase liquide, composée d’une solution diluée de NPM, à l’intérieur de tubes capillaires soumis à des CMR, des CMO et des CMS. Les résultats indiquent que les NPM qui tournent sous l’action d’un CMR améliorent le mélange dans le film lubrificateur qui entoure les bulles de Taylor comme cela est révélé par une augmentation mesurable du kLa. À l’opposé, les CMS immobilisent les NPM, menant à des taux de transfert de matière systématiquement plus faibles alors que les CMO n’ont pas d’effet détectable sur le coefficient de transfert de matière. Par ailleurs, l’interaction entre le couple magnétique et le couple hydrodynamique nécessaire pour dominer la direction de rotation des NPM est tirée de ces résultats.Magnetic nanoparticles (MNPs) have attracted significant interest in diverse areas of engineering and research. Particle size and magnetic properties of suspended MNPs in a suspension allow their manipulation at a distance using appropriate external magnetic fields. In particular by enabling additional functionality in forms anchored to metal catalysts, enzymes or therapeutic drug agents. Owing to this feature, MNPs have been involved in many applications where mixing in micro-scale is also a critical issue, e.g., catalytic reaction, separation and drug delivery. This thesis explores MNPs as nano-scale devices to manipulate mixing in micro-scale when the whole system is subject to magnetic fields. All the experiments were performed in tubular two-pole, three-phase stator winding magnet, generating uniform rotating magnetic field (RMF), oscillating magnetic field (OMF) and stationary magnetic field (SMF). Initially, we present a mixing technique in which a RMF converts MNPs into nano-stirrers generating small vortices in liquid phase. Using this technique, self-diffusion coefficient of motionless water in a static diffusion cell was intensified up to 200 folds. Systematic studies of operating parameters revealed that the extent of enhancement depends on MNP volume fraction, and strength and frequency in magnetic field. In order to understand the effect of hydrodynamic torque on the MNPs behavior under magnetic fields, convective flow was also included. As such, axial dispersion of pressure-driven laminar Poiseuille flows in a capillary tube (Taylor dispersion test) was examined through a series of impulse (residence time distribution) RTD tests with and without RMF. This resulted in lateral mixing along the channel that was promoted relative to that in absence of MNPs or magnetic field. Moreover, we interpreted the observed hydrodynamic effects of such lateral mixing on laminar velocity profile as resulting from an approach to plug flow-like flat velocity profile. Using the same technique, the effect of OMF and SMF on Taylor dispersion and laminar velocity profile was examined in capillary flows. OMF did not induce nano-convective mixing in the capillary and had negligible impact on axial dispersion. On the contrary, SMF deteriorated lateral mixing of solute tracer and led to velocity profiles deviating from parabolic shape towards more protruded ones. A detailed discussion of magnetic field orientation versus fluid vorticity vector was presented. Finally a multiphase flow case concerned gas-liquid mass transfer from oxygen Taylor bubbles to the liquid in capillaries which was studied using dilute concentration of MNPs as the liquid phase under RMF, OMF and SMF. Experimental results implied that spinning MNPs under RMF improved mixing in the lubricating film that surrounds Taylor bubbles which reflected in a measurable enhancement of kLa. On the contrary, SMF pinned MNPs leading to systematically degraded gas-liquid mass transfer rates whereas axial oscillating magnetic field had no detectable effects on the mass transfer coefficient. Moreover, interaction between magnetic torque and hydrodynamic torque to dominate MNP spin direction was conceived from these results

Numerical study of slip and radiative effects on magnetic Fe3O4-water-based nanofluid flow from a nonlinear stretching sheet in porous media with Soret and Dufour diffusion

Increasingly sophisticated techniques are being developed for the manufacture of functional nanomaterials. A growing interest is also developing in magnetic nanofluid coatings which contain magnetite nanoparticles suspended in a base fluid and are responsive to external magnetic fields. These nanomaterials are “smart” and their synthesis features high-temperature environments in which radiative heat transfer is present. Diffusion processes in the extruded nanomaterial sheet also feature Soret and Dufour (cross) diffusion effects. Filtration media are also utilized to control the heat, mass and momentum characteristics of extruded nanomaterials and porous media impedance effects arise. Magnetite nanofluids have also been shown to exhibit hydrodynamic wall slip which can arise due to non-adherence of the nanofluid to the boundary. Motivated by the multi-physical nature of magnetic nanomaterial manufacturing transport phenomena, in this paper, we develop a mathematical model to analyze the collective influence of hydrodynamic slip, radiative heat flux and cross-diffusion effects on transport phenomena in ferric oxide (Fe3O4-water) magnetic nanofluid flow from a nonlinear stretching porous sheet in porous media. Hydrodynamic slip is included. Porous media drag is simulated with the Darcy model. Viscous magnetohydrodynamic theory is used to simulate Lorentzian magnetic drag effects. The Rosseland diffusion flux model is employed for thermal radiative effects. A set of appropriate similarity transformation variables are deployed to convert the original partial differential boundary value problem into an ordinary differential boundary value problem. The numerical solution of the coupled, multi-degree, nonlinear problem is achieved with an efficient shooting technique in MATLAB symbolic software. The physical influences of Hartmann (magnetic) number, Prandtl number, Richardson number, Soret (thermo-diffusive) number, permeability parameter, concentration buoyancy ratio, radiation parameter, Dufour (diffuso-thermal) parameter, momentum slip parameter and Schmidt number on transport characteristics (e.g. velocity, nanoparticle concentration and temperature profiles) are investigated, visualized and presented graphically. Flow deceleration is induced with increasing Hartmann number and wall slip, whereas flow acceleration is generated with greater Richardson number and buoyancy ratio parameter. Temperatures are elevated with increasing Dufour number and radiative parameter. Concentration magnitudes are enhanced with Soret number, whereas they are depleted with greater Schmidt number. Validation of the MATLAB computations with special cases of the general model is included. Further validation with generalized differential quadrature (GDQ) is also included

Particle Manipulation Via Optical Forces and Engineering Soft-Matter Systems With Tunable Nonlinearities.

One of the most intriguing properties of light-matter interaction is the ability of an electromagnetic field to exert mechanical forces on polarizable objects. This phenomenon is a direct consequence of the fact that light carries momentum, which in turn can be transferred to matter. Mediated by scattering, this interaction usually manifests itself as a “pushing force” in the direction of beam propagation. However, it is possible to judiciously engineer these optical forces, either by tailoring particle polarizability, and/or by structuring the incident light field. As a simple example, a tightly focused laser beam demonstrates strong gradient forces, which may attract and even trap particles with positive polarizability in the focal volume. The opposite occurs in the regime of negative polarizability, where particles are expelled from the regions of highest intensity. Based on this fundamental principle, one can actively shape the beam using spatial light modulators to manipulate individual objects as well as ensembles of particles suspended in a liquid. In the latter case, a modulation of the local particle concentration is associated with changes of the effective refractive index. The result is an artificial nonlinear medium, whose Kerr-type response can be readily tuned by the parameters of its constituent particles. In the course of this work, we introduce a new class of synthetic colloidal suspensions exhibiting negative polarizabilities, and observe for the first time robust propagation and enhanced transmission of self-trapped light over long distances. Such light penetration in strongly scattering environments is enabled by the interplay between optical forces and self-activated transparency effects. We explore various approaches to the design of negative-polarizability arrangements, including purely dielectric as well as metallic and hybrid nanoparticles. In particular, we find that plasmonic resonances allow for extremely high and spectrally tunable polarizabilities, leading to unique nonlinear light-matter interactions. Here, for the first time we were able to observe plasmonic resonant solitons over more than 25 diffraction lengths, in colloidal nanosuspensions

A MODEL ON MHD CONVECTIVE TIN-OXIDE (TiO2) NANOFLUID FLOW OVER A CYLINDERICAL POROUS PLATE

Abstract: In this study, a model of MHD convective tin-oxide(TiO2) nanofluid flow over a cylindrical porous plate was examined. The governing equations of continuity, momentum, energy, and concentration modelled in terms of partial differential equations with boundary conditions were non-dimensionalised using the Buckingham’s π-theorem and then were transformed into ordinary differential equations using the regular perturbation technique, each of these equations was solved in isolation using Frobenius Method which gave the analytic solutions. The solutions obtained for the momentum, energy, and concentration were subjected to analysis which gave the results for the temperature profile, concentration profile, and velocity profile graphically. It was observed that, when the radiation parameter was increased, the temperature profile dropped; as the chemical reaction was increased, the concentration profile and the velocity profile were reduced; again as the magnetic field number was increased, it lowered the profile of the velocity. The velocity profile was enhanced with an increase in the porosity parameter, and this, as a result, tended to increase in the size of the pore spaces of the porous medium; the concentration profile, temperature profile, and velocity profile all improved as the nanofluid volume fraction increased. Keywords: Nanofluid, MHD flow, Convection, Cylindrical Porous Plate, Analytical Solutions. Title: A MODEL ON MHD CONVECTIVE TIN-OXIDE (TiO2) NANOFLUID FLOW OVER A CYLINDERICAL POROUS PLATE Author: Tombotamunoa W. J. Lawson, Isobeye George, Alalibo T. Ngiangia International Journal of Mathematics and Physical Sciences Research ISSN 2348-5736 (Online) Vol. 11, Issue 1, April 2023 - September 2023 Page No: 101-121 Research Publish Journals Website: www.researchpublish.com Published Date: 20-September-2023 DOI: https://doi.org/10.5281/zenodo.8362486 Paper Download Link (Source) https://www.researchpublish.com/papers/a-model-on-mhd-convective-tin-oxide-tio2-nanofluid-flow-over-a-cylinderical-porous-plateInternational Journal of Mathematics and Physical Sciences Research, ISSN 2348-5736 (Online), Research Publish Journals, Website: www.researchpublish.co

Mass Transport via Thermoplasmonics

When a metallic nanoparticle is illuminated with light under resonant conditions, the free electron gas oscillates in such a way that substantial amplification of the local electric field amplitude is achieved – this is known as a plasmonic resonance. This resonance enhances both the optical scattering as well as absorption. In many applications, the enhanced scattering can facilitate efficient coupling between the near-field and the far-field, which enables optical interrogation of nanoscale volumes. Simultaneously, however, the enhanced absorption results in localized heating and substantial temperature gradients. The resulting temperature profile can drive other thermal processes, some beneficial others detrimental. Thermoplasmonics is the study of these plasmonically enhanced thermal processes. Elevated temperatures increase the Brownian motion of small particles. Moreover, if large temperature gradients are present, then a process known as thermophoresis is likely to occur. Thermophoresis tends to cause a local depletion of Brownian particles around a hot region. From the context of “conventional” plasmonic applications (like molecular sensing), these thermally driven mass transport mechanisms are adverse side effects since they reduce the interaction rate between the plasmonic system and the analyte. An investigation of thermal effects in plasmonic optical tweezers showed that the increased Brownian motion essentially negated the optical tweezing effect, resulting in an overall insensitivity between the resonance condition of the antenna and the particle confinement when evaluated in terms of the local temperature increase. Additionally, a significant thermophoretic depletion of analytes occurred, extending tens of microns from the plasmonic structure. This depletion acts in opposition to the plasmonically enhanced optical forces, which are restricted to a region of only a few hundred nanometres.However, thermoplasmonic effects can also be used for advantageous means. Once example is by driving thermocapillary flows directed towards the plasmonic system, thereby facilitating the efficient accumulation of analytes. One method of employing this effect is to superheat a plasmonic particle to a high enough temperature such that a bubble is nucleated. Once a bubble is formed, thermocapillary effects at the bubble interface drive fluid motion with a flow profile similar to that of a Stokeslet. This fluid flow can be utilized for analyte accumulation near the plasmonic structure. In addition to the thermocapillary induced flow, it was found that even more intense flow speeds were achieved immediately upon nucleation due to the mechanical action of the bubble. This transient peak in flow speed was approximately an order of magnitude faster than the subsequent persistent (thermocapillary) flow. By designing the plasmonic nanoparticle so that the Laplace pressure restricted the ultimate bubble size, these bubbles could be kept small enough to permit high modulation rates and maximize the relative effect of the peak transient flow

Momentum exchange between light and nanostructured matter

An object\u27s translational and rotational motion is associated with linear and angular momenta. When multiple objects interact the exchange of momentum dictates the new system\u27s motion. Since light, despite being massless, carries both linear and angular momentum it too can partake in this momentum exchange and mechanically affect matter in tangible ways. Due to conservation of momentum, any such exchange must be reciprocal, and the light therefore acquires an opposing momentum component. Hence, light and matter are inextricably connected and one can be manipulated to induce interesting effects to the other. Naturally, any such effect is facilitated by having strongly enhanced light-matter interaction, which for visible light is something that is obtained when nanostructured matter supports optical resonances. This thesis explores this reciprocal relationship and how nanostructured matter can be utilised to augment these phenomena.Once focused by a strong lens, light can form optical tweezers which through optical forces and torques can confine and manipulate small particles in space. Metallic nanorods trapped in two dimensions against a cover glass can receive enough angular momentum from circularly polarised light to rotate with frequencies of several tens of kilohertz. In the first paper of this thesis, the photothermal effects associated with such optical rotations are studied to observe elevated thermal environments and morphological changes to the nanorod. Moreover, to elucidate upon the interactions between the trapped particle and the nearby glass surface, in the thesis\u27 second paper a study is conducted to quantify the separation distance between the two under different trapping conditions. The particle is found to be confined ~30-90 nm away from the surface.The momentum exchange from a single nanoparticle to a light beam is negligible. However, by tailoring the response of an array of nanoparticles, phase-gradient metasurfaces can be constructed that collectively and controllably alter the incoming light\u27s momentum in a macroscopically significant way, potentially enabling a paradigm shift to flat optical components. In the thesis\u27 third paper, a novel fabrication technique to build such metasurfaces in a patternable polymer resist is investigated. The technique is shown to produce efficient, large-scale, potentially flexible, substrate-independent flat optical devices with reduced fabricational complexity, required time, and cost.At present, optical metasurfaces are commonly viewed as stationary objects that manipulate light just like common optical components, but do not themselves react to the light\u27s changed momentum. In the last paper of this thesis, it is realised that this is an overlooked potential source of optical force and torque. By incorporating a beam-steering metasurface into a microparticle, a new type of nanoscopic robot – a metavehicle – is invented. Its propulsion and steering are based on metasurface-induced optical momentum transfer and the metavehicle is shown to be driven in complex shapes even while transporting microscopic cargo

Focused optical beams for driving and sensing helical and biological microobjects

A novel and interesting approach to detect microfluidic dynamics at a very small scale is given by optically trapped particles that are used as optofluidic sensors for microfluidic flows. These flows are generated by artificial as well as living microobjects, which possess their own dynamics at the nanoscale. Optical forces acting on a small particle in a laser beam can evoke a three dimensional trapping of the particle. This phenomenon is called optical tweezing and is a consequence of the momentum transfer from incident photons to the confined object. An optically confined particle shows Brownian motion in an optical tweezer, but is prevented from long term diffusion. A careful analysis of the motion of the confined particle allows a precise detection of microfluidic flows generated by an artificial or living source in the close vicinity of the particle. Thus, the particle can be used as a sensitive optofluidic detector. For this aim, several optical tweezers at different wavelengths are integrated into a dark-field microscope, combined with a high speed camera, to achieve a precise detection of the motion of the center-of-mass of the trapped particle. With this unique experimental system, a gold sphere is used as an optofluidic nanosensor to analyze for the first time the microfluidic oscillations generated by a biological sample. Here, a freely swimming larva of Copepods serves as the living source of flow. However, even if the trapping laser wavelength is off-resonant to the plasmon resonance of the flow detector, a finite heating of the gold nanoparticle occurs which reduces the sensitivity of detection. To increase the sensitivity of the optofluidic detection, a non-absorbing, dielectric microparticle is introduced as the optofluidic sensor for the microflows. It enables a quantitative, two dimensional mapping of the vectorial velocity field around a microscale oscillator in an aqueous environment. This paves the way for an alternative and sensitive detection approach for the microfluidic dynamics of artificial and living objects at a very small scale. To this aim and as a first step, an optically trapped microhelix serves as a model system for the mechanical and dynamical properties of a living microorganism. An optical tweezer is implemented for initiating a light-driven rotation of the chiral microobject in an aqueous environment and the optofluidic detection of its flow field is established. The method is then adopted for the measurement of the microfluidic flow generated by a biological system with similar dynamics, in this case a bacterium. The experimental approach is used to quantify the time-dependent changes of the flow generated by the flagella bundle rotation at a single cell level. This is achieved by observing the hydrodynamic interaction between a dielectric particle and a bacterium that are both trapped next to each other in a dual beam optical tweezer. This novel experimental technique allows the extraction of quantitative information on bacterial motility without the necessity of observing the bacterium directly. These findings can be of great relevance for an understanding of the response of different strains of bacteria to environmental changes and to discriminate between different states of bacterial activity

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals