Ferrofluid Particles Research Articles

Analyzing heat transfer behavior in two-dimensional Darcy–Forchheimer porous medium using magnetized nanoparticles

This study investigates the two-dimensional boundary layer flow and heat transfer of an incompressible fluid over a plate embedded in a Darcy–Forchheimer porous medium of magnetite ternary hybrid ferrofluid in the presence of suction or injection. It uniquely includes the effects of thermal radiation and viscous dissipation in the energy equation, offering a comprehensive analysis of the phenomena involved. The research focuses on three nanoparticle (NP) combinations of ferrofluid particles ( Fe 3 O 4 ) and metal oxide NPs ( CuO / TiO 2 ) dispersed in an aquatic base fluid with different volume fractions. The governing nonlinear partial differential equations are transformed into ordinary differential equations via similarity transformations and solved using the Runge–Kutta-based shooting technique. The study evaluates key physical quantities, such as the skin friction coefficient and Nusselt number, and examines the effects of dimensionless parameters, including the absorbent Reynolds number (Re), expansion ratio (α), Peclet number (Pe), Eckert number (Ec), NP volume fractions ( φ 1 , φ 2 , and φ 3 ) , porous medium parameter (r), and Darcy-porous medium parameter (F), on velocity and temperature profiles. The results indicate that increasing the porous medium parameters r and F leads to opposite shear stress effects in the dual-porosity medium. Higher Peclet number (Pe) and Eckert number (Ec) values enhance heat transfer rates within the thermal boundary layers. Moreover, elevated Reynolds number (Re) and expansion ratio (α) values result in opposing radial velocity profiles within the momentum boundary layers. This comprehensive analysis provides valuable insights into the complex interactions governing ternary ferrofluid flow and thermal performance in dual-porosity media, contributing to advancements in fluid system applications.

Hydrothermal characteristics of ferrofluid in a wavy chamber with magnetic field-dependent viscosity: Effects of moving walls

The present investigation aims to scrutinize the role of different moving walls on the hydrothermal characteristics and thermal performance of a Fe3O4-H2O ferrofluid within a wavy chamber under mixed convection. Notably, the study also takes into consideration the effects of a magnetic field and internal heat generation or absorption phenomena. To achieve this, a numerical simulation employing a compact finite difference method is conducted, focusing on key factors such as the Richardson number (0.1≤Ri≤100), Hartmann number (0≤Ha≤30), magnetic orientation (00≤γ≤900), Grashof number (Gr=104), solid concentrations (0≤ϕnp≤0.04), magnetic number (0≤δ0≤1), Prandtl number (Pr=6.8377), and internal heat generation parameter (−2≤Q≤2). All of this is undertaken while carefully managing the ferromagnetic particle volume fraction. The primary aim is to assess how different types of moving walls affect the transport behavior of the ferrofluid and to determine the impacts of the magnetic field on the hydrothermal characteristics of the ferrofluid. The outcomes of this investigation reveal that the presence of moving walls leads to a non-uniform temperature distribution within the ferrofluid, significantly affecting the overall transport behavior. The addition of ferrofluid particles to the base fluid results in noteworthy enhancements in the average Nusselt numbers, signifying improved convective heat transfer efficiency. Specifically, Case-I experienced an increase of up to 3.21%, Case-II showed an improvement of 0.93%, Case-III exhibited a rise of 1.70%, and Case-IV demonstrated the highest enhancement of 20.71%. Furthermore, the inclusion of magnetic field-dependent viscosity and the internal heat generation coefficient significantly influences the behavior of the ferrofluid. The findings from this study hold paramount importance for the design and optimization of heat transfer systems that employ ferrofluids and have the potential to contribute to the development of novel technologies with a wide range of industrial applications.

Modeling shape deformation of ferrofluid ring section and secondary flow in ferrofluid seals with rectangular polar teeth using BEM and FVM

The focus of this study is on modeling the shape deformation of ferrofluid ring sections and secondary flows in ferrofluid seals with a rectangular polar tooth. These factors determine the sealing capability and homogenization of particles in ferrofluids. The model consists of governing equations for ferrofluid flows, the balance equation of normal stresses on ferrofluid free surfaces, the magnetic field equations and the ferrofluid volume equation. To solve the mathematical model, a method utilizing a combination of boundary element method and finite volume method is proposed. Discretizing the azimuthal velocity equation with boundary element method enables efficient determination of ferrofluid-ring section shape deformation. Furthermore, a discretely fitting method is proposed to solve the issue of lack of analytic expressions for the magnetic field distribution in sealing structures with rectangular polar teeth. Numerical tests of the magnetic field and azimuthal velocity distribution verify the validity and accuracy of the proposed solution method. Numerical experiments conducted on an actual ferrofluid sealing structure show that increasing the rotational speed of the shaft, in conjunction with effect of the centrifugal force, leads to deformation of the ferrofluid-ring section shape and reduces the contact area between the ferrofluid ring and shaft. This results in a decrease in pressure resistance. Typically, at a speed of 10 m/s, the pressure resistance falls by around 20%. The maximum value of secondary-flow velocity is significantly affected by the rotational speed of the shaft, although it does not exceed 0.8% of the linear velocity on the shaft surface in our study.

A highly stretchable and sintering-free liquid metal composite conductor enabled by ferrofluid

Stretchable and highly conductive elastomers with intrinsically deformable liquid metal (LM) fillers exhibit promising potential in soft electronics, wearables, human-machine interfaces, and soft robotics. However, conventional LM-elastomer (LME) conductors require a high loading ratio of LM and the post-sintering to rupture LM particles to achieve electric conductivity, which results in high LM consumption and process complexity. In this work, we presented a straightforward and post-sintering-free method that utilizes magnetic aggregation to fabricate stretchable LME conductors. This was achieved by dispersing LM ferrofluid into the elastomer precursor, followed by applying the magnetic field to induce the aggregation and interconnection of the LM ferrofluid particles to form conductive pathways. This method not only simplifies the preparation of initially conductive LME but also reduces the LM loading ratio. The resulting conductive LME composites show high stretchability (up to 650% strain), high conductance stability, and magnetic responsiveness. The stretchable LME conductors were demonstrated in various applications, including the creation of flexible microcircuits, a magnetically controlled soft switch, and a soft hydrogel actuator for grasping tasks. We believe the stretchable LME conductors may find wide applications in electronic skins, soft sensors, and soft machines.

Morphological Effects on Natural Convection Heat Transfer of Magnesium Ferrite Ferrofluid

This investigation intends to analyze the influence of nanoparticles morphology on the magnetic flux dependent thermo-physical properties and magnetohydrodynamic free convection heat transfer performance of water-based magnesium ferrite ferrofluid under various volume fractions. The thermo-physical parameters of the ferrofluid suspended with cube shaped particles are examined at 25 °C using KD2 pro thermal analyzer, Ostwald viscometer and specific gravity bottle under magnetic flux. The free convection heat transfer is obtained using heat pipes assisted cubical enclosure. Without the influence of magnetic flux, the thermal conductivity of the ferrofluid was improved by a maximum of 12.75% at a volume fraction of 0.15%. At the same time, the maximum viscosity and density were raised by 32.92% and 6.11% at a volume fraction of 0.20% in comparison with water. Under the influence of 350 Gauss, thermal conductivity, and viscosity of ferrofluid enhanced by 21.81% and 37.41% while the density decreased by 4.91%. It was revealed that the addition of cube-shaped magnesium ferrite particles in ferrofluid improved the thermo-physical properties. The optimum concentration for maximum heat transfer is reduced to 0.025% with the use of cube shaped particles compared to other types of nanoparticles reported in previous studies.

Bubbling of Ferrofluid Droplets via Coupled Magnetic and Sound Fields

AbstractBubbles play essential roles in many natural and industrial processes because of the unique effects of their films on heat–mass transfer and their soft confined geometry for interfacial assembly or phase transitions. Here, a technique for noncontact bubbling via coupling of sound and magnetic fields in acoustic levitation is reported. An acoustically levitated ferrofluid droplet can be transformed into a closed bubble in a controlled manner. It has been found that the magnetic field pulls the flattened ferrofluid film downward, and making it deviate from its initial levitation position determined by the balance between acoustic radiation force and gravity. This results in variation in acoustic radiation pressure on the film surface and generates an upwards torque on the levitated film, leading to buckling and subsequent bubble transition via acoustic resonance. Moreover, the levitated ferrofluid bubble can remain unburst in the sound field for minutes to enable its complete evaporation; thus, solid hollow shells form. This work provides insight for understanding the coupled effect of sound and magnetic fields on ferrofluid drops and sheds light on evaporation‐driven self‐assembly of ferrofluid particles into shell structures

A Method and Apparatus for Measuring the Magnetization Relaxation Times of Ferrofluids

A definite value of the magnetization relaxation time for a ferrofluid is important to scrutinize its flow phenomenon in the presence of magnetic fields. A method for measuring the magnetization relaxation time is present in this article, which is achieved via the measurement of the field component perpendicular to the applied magnetic field in rigidly rotational ferrofluids. In order to establish the relationship among the relaxation time, the flow vorticity and the field component in a ferrofluid filled in the gap between two rotating cylinders, the distributions of flow velocity, magnetic field, and magnetization field in this configuration are derived analytically. An apparatus to implement the proposed method is set up. After calibration using one ferrofluid, the magnetization relaxation times of the other two ferrofluids are measured on the apparatus to test its feasibility. The results show that the relative errors are 2.1% and 6.1%, respectively, in comparison with that obtained by the dynamic light scatting technique. In contrast, the present method does not need to determine the size distribution of particles in ferrofluids, while only the initial magnetic susceptibility and a calibrated coefficient are required in advance. The corresponding apparatus is robust and the results can be read out easily.

Self-diffusion in bidisperse systems of magnetic nanoparticles.

In the present paper, we study the self-diffusion of aggregating magnetic particles in bidisperse ferrofluids. We employ density functional theory (DFT) and coarse-grained molecular dynamics (MD) simulations to investigate the impact of granulometric composition of the system on the cluster self-diffusion. We find that the presence of small particles leads to the overall increase of the self-diffusion rate of clusters due the change in cluster size and composition.

Three-dimensional numerical analysis of focusing and separation of diamagnetic particles in ferrofluid

Focusing and separation of particles and cells by magnetophoresis are important steps in many applications. In simple terms, the magnetophoresis can be classified into a positive one and a negative one. The most important characteristic of negative magnetophoresis is that particles and cells can be manipulated in a label-free manner. In this paper, continuous separation based on negative magnetophoresis is studied numerically using a three-dimensional model considering the interaction between particles and the ferrofluid. Firstly, the separation of two sized particles is investigated with a straight microchannel with two opposite permanent magnets for focusing particles before their separation by another bias magnet. Then the influence of size and position of permanent magnets and geometry of microchannel are investigated to achieve a better particle separation. Moreover, the effects of the concentration of the ferrofluid, the size difference of the particles, the magnet-channel distance and the flow velocity on the particle separation are analyzed.

Microstructurally-guided explicit continuum models for isotropic magnetorheological elastomers with iron particles

This work provides a family of explicit phenomenological models both in the F−H and F−B variable space. These models are derived directly from an analytical implicit homogenization model for isotropic magnetorheological elastomers (MREs), which, in turn, is assessed via full-field numerical simulations. The proposed phenomenological models are constructed so that they recover the same purely mechanical, initial and saturation magnetization and initial magnetostriction response of the analytical homogenization model for all sets of material parameters, such as the particle volume fraction and the material properties of the constituents (e.g., the matrix shear modulus, the magnetic susceptibility and magnetization saturation of the particles). The functional form of the proposed phenomenological models is based on simple energy functions with small number of calibration parameters thus allowing for the description of magnetoelastic solids more generally such as anisotropic (with particle-chains) ones, polymers comprising ferrofluid particles or particle clusters. This, in turn, makes them suitable to probe a large set of experimental or numerical results. The models of the present study show that in isotropic MREs, the entire magnetization response is insensitive to the shear modulus of the matrix material even when the latter ranges between 0.003-0.3MPa, while the magnetostriction response is extremely sensitive to the mechanical properties of the matrix material.

Two families of explicit models constructed from a homogenization solution for the magnetoelastic response of MREs containing iron and ferrofluid particles

This work puts forth two families of fully explicit continuum or phenomenological models that are constructed by approximating an analytical (but implicit) homogenization solution recently derived for the free-energy function describing the macroscopic magnetoelastic response of two classes of MREs comprised of an isotropic incompressible elastomer filled with a random isotropic distribution of: (i) spherical iron particles and (ii) spherical ferrofluid particles. Both families are given in terms of free-energy functions WH=WH(F,H) that depend on the deformation gradient F and the Lagrangian magnetic field H and are constructed so as to agree identically with the homogenization solution for small and large applied magnetic fields, this for arbitrary finite deformations and arbitrary volume fractions c of particles in the entire physical range c∈[0,1]. The accuracy of the proposed phenomenological models is assessed inter alia via the direct comparison of their predictions with that of the homogenization solution for a boundary-value problem of both fundamental and practical significance: the magnetostriction response of a spherical MRE specimen subject to a remotely applied uniform magnetic field.

Electric response of cells containing ferrofluid particles

The Poisson-Nernst-Planck model for electrolytic solutions is generalized to take into account the difference in the diffusion coefficients and in the electric charge of the ions dissolved in an insulating liquid. The electric impedance of the cell is evaluated by considering the case in which the electric charge transfer from the cell to the external circuit is proportional to the surface electric field. An analytical expression for the electric impedance of the cell is derived. The model is used to interpret experimental data relevant to cell of kerosene doped with ferrofluid particles. We show that the impedance spectroscopy data can be well interpreted by the proposed model. An estimation of the electric conductivity of the system kerosene based ferrofluid is reported and compared with the value obtained by means of the analysis based on equivalent electric circuits. A few considerations on the applicability of Debye’s model with a dc conductivity to our data are reported.

Heat transfer enhancement and migration of ferrofluid due to electric force inside a porous medium with complex geometry

The migration of ferrofluid particles due to an electric field within a porous space is examined. An algorithm was developed for CVFEM to solve the coupled equations. The properties of Fe3O4–ethylene glycol nanofluid are dependent on the electric field and on the shape of the nanoparticles. The energy equation seems more interesting in the presence of a radiative term. The influence of nanoparticles’ shape, voltage, radiation parameter and Darcy number on nanofluid thermal behavior has been described. Average Nusselt number increases with expansion of the thermal radiation in the system. Enhancing the shape factor causes the Nusselt number to increase. The Darcy number yields more random patterns of isotherms.

Numerical method for analysis of the correlation between ferrofluid optical transmission and its intrinsic properties

Abstract A numerical method to simulate the ferrofluid particle distribution evolution is presented. Also, the optical transmission of the distributions obtained is calculated by two numerical methods. The first one consists on a numerical propagation of an electromagnetic wave through the sample. The second one analyzes the aggregates’ mean length to obtain the optical transmission through a mixture law. As an illustration of the possibilities of the method developed, it is applied to analyze how ferrofluid optical transmission changes after magnetic field application depend on intrinsic properties of the colloid such as its nanoparticle concentration and surfactant repulsion represented by means of the final distances between consecutive particles forming chains. Changes in the attenuation factor of these samples show the trends expected from the Literature.

Determining Parameters of a Ferrofluid Based on the Temperature Dependence of Microwave Reflection Spectrum with Allowance for the Formed Agglomerates of Ferromagnetic Nanoparticles

The possibility of simultaneously determining four parameters of a ferrofluid (permittivity, the volume fraction of solid phase, loss tangent, and the diameter of ferrofluid particles) based on the temperature dependence of microwave reflection spectrum has been investigated. It has been shown that taking the dimensions and spatial arrangement of magnetite-nanoparticle agglomerates into account improves the accuracy of determining the parameters.

CFD modeling and sensitivity analysis of heat transfer enhancement of a ferrofluid flow in the presence of a magnetic field

In this paper, a numerical method is developed to simulate the effect of an external magnetic field on convection heat transfer of a ferrofluid flow inside a rectangular duct. This model is two-dimensional, steady-state, laminar and incompressible. Simple finite volume method is used to couple and solve continuity, momentum and energy equations. In the first part of this paper, it is observed that ferrofluid particles movement along the magnetic field of a line dipole changes the streamline patterns and enhances heat transfer. In the second part of this paper, a sensitivity analysis is performed to investigate the effects of Reynolds number, magnetic field strength, location, and number of line dipoles on the convection heat transfer. It is observed that cooling rate is higher at larger Reynolds numbers while increasing magnetic field strength would not necessarily result in noticeable improvement in heat transfer. It is also noticed that magnetic field strength should be large enough to merge small vortexes and to create large circulation zones inside the duct. Our simulation also revealed that heat transfer could be augmented by adding line dipoles on high-temperature regions closer to the duct inlet.

Influence of behaviors of magnetic particles in ferrofluids under alternating magnetic fields on harmonic responses

We describe the relationship between the excitation frequency dependence of harmonic signal intensity under alternating magnetic fields and the hydrodynamic size of magnetic particles in ferrofluids. The hydrodynamic size estimated from magnetic susceptibility increases with the increase in ion and particle concentrations in the ferrofluids. The excitation frequency dependence of the fifth-harmonic signal intensity exhibits a minimum point at a certain frequency. The frequency of the minimum point shifts to the lower-frequency range, and after reaching the minimum, it increases with the increase in ion and particle concentrations, reflecting the increase in hydrodynamic size owing to the aggregation of magnetic particles. These behaviors may be useful for applications in ion sensing by a magnetic technique.

Label-Free Alignment of Nonmagnetic Particles in a Small Uniform Magnetic Field.

Label-free manipulation of biological entities can minimize damage, increase viability and improve efficiency of subsequent analysis. Understanding the mechanism of interaction between magnetic and nonmagnetic particles in an inverse ferrofluid can provide a mechanism of label-free manipulation of such entities in a uniform magnetic field. The magnetic force, induced by relative magnetic susceptibility difference between nonmagnetic particles and surrounding magnetic particles as well as particle-particle interaction were studied. Label-free alignment of nonmagnetic particles can be achieved by higher magnetic field strength (Ba), smaller particle spacing (R), larger particle size (rp1), and higher relative magnetic permeability difference between particle and the surrounding fluid (Rμr). Rμr can be used to predict the direction of the magnetic force between both magnetic and nonmagnetic particles. A sandwich structure, containing alternate layers of magnetic and nonmagnetic particle chains, was studied. This work can be used for manipulation of nonmagnetic particles in lab-on-a-chip applications.

A general result for the magnetoelastic response of isotropic suspensions of iron and ferrofluid particles in rubber, with applications to spherical and cylindrical specimens

This paper puts forth an approximate solution for the effective free-energy function describing the homogenized (or macroscopic) magnetoelastic response of magnetorheological elastomers comprised of non-Gaussian rubbers filled with isotropic suspensions of either iron or ferrofluid particles. The solution is general in that it applies to N=2 and 3 space dimensions and any arbitrary (non-percolative) isotropic suspension of filler particles. By construction, it is exact in the limit of small deformations and moderate magnetic fields. For finite deformations and finite magnetic fields, its accuracy is demonstrated by means of direct comparisons with full-field simulations for two prominent cases: (i) isotropic suspensions of circular particles and (ii) isotropic suspensions of spherical particles.With the combined objectives of demonstrating the possible benefits of using ferrofluid particles in lieu of the more conventional iron particles as fillers and gaining insight into recent experimental results, the proposed homogenization-based constitutive model is deployed to generate numerical solutions for boundary-value problems of both fundamental and practical significance: those consisting of magnetorheological elastomer specimens of spherical and cylindrical shape that are immersed in air and subjected to a remotely applied uniform magnetic field. It is found that magnetorheological elastomers filled with ferrofluid particles can exhibit magnetostrictive capabilities far superior to those of magnetorheological elastomers filled with iron particles. The results also reveal that the deformation and magnetic fields are highly heterogenous within the specimens and strongly dependent on the shape of these, specially for magnetorheological elastomers filled with iron particles. From an applications perspective, this evidence makes it plain that attempts at designing magnetrostrictive devices based on magnetorheological elastomers need to be approached, in general, as structural problems, and not simply as materials design problems.

Effect of alternating magnetic field on unsteady MHD mixed convection and entropy generation of ferro fluid in a linearly heated two-sided cavity

This work considers the numerical study of unsteady MHD convection of cobalt-kerosene ferro fluid in a linearly heated two-sided cavity and in the presence of constant and alternating magnetic elds. An accurate nite volume method is adapted to solve the governing equations for this problem. The fluid flow and heat transfercharacteristics are studied for a wide range of Richardson numbers (0:01  Ri  10) and Hartmann numbers (0  Ha  100). The volumetric fraction of nanoscale ferromagnetic particles in ferro fluid also varies between 0:0   0:2, while the size of those nanoparticles is fixed at 45 nm. In addition, di fferent alternating magnetic fields with various periods and phase deviations are utilized to study the eff ect of time-periodic magnetic field on the flow characteristics and heat transfer. The entropy generation and Bejan number are also evaluated to study the e ect of key parameters and temporal variation of magnetic field on various fluid irreversibilities. The results show that applying time-periodic magnetic fi eld has remarkably influenced the fluid characteristics, the fluid irreversibilities, and heat transfer within the cavity. Meanwhile, the influence of phase deviation on heat transfer seems to be insigni cant.