Behavior Of Ferrofluids Research Articles

Thermal behavior of ferrofluids in a microfin tube with rotating magnetic fields: Experimental analysis and artificial intelligence modeling strategies

The utilization of various tools by researchers to enhance heat transfer (HT) in fluid flow is steadily on the rise. These tools encompass both active and passive methods. This study involved an experimental examination of HT and fluid flow within a micro-fin tube. The strategies were implemented to improve Nu: ferrofluid, micro-fins, and a rotating magnetic field. Before implementation, the magnetic ferrofluid was evaluated for particle size and stability. The results were validated, demonstrating a good correlation with the anticipated outcomes. The use of a microfin tube and ferrofluid can enhance HT about 7–14 % and 7–22 %, respectively. Additionally, a rotating magnetic field can improve HT by approximately 10%–37 %. An empirical correlation derived from experimental data is introduced for Nu prediction. Additionally, employing artificial intelligence techniques such as ANFIS and GMDH, the Nu has been successfully estimated, showcasing the effectiveness of these models in predicting Nu.

Investigation of natural convection heat transfer in various structures of a partitioned triple porous enclosure under permanent magnetic field

Using porous media is an efficient technique aimed at enhancing heat transfer in engineering systems. Replacing conventional fluids by ferrofluids and applying external magnetic fields through magnets is another method for heat transfer control. In this regard, understanding the behavior of ferrofluids through porous media in the presence of magnets is important. The present study aims at providing a thorough analysis of the properties of heat transfer resulting from the combination of buoyancy driven convection and thermomagnetic convection in a porous enclosure. The equations governing the two types of convection in the fluid as well as the conduction in the solid matrix are presented in the dimensionless form and solved numerically. The control volume finite element method has been used to solve the governing equations. The influence of various parameters such as the magnetic Rayleigh number, the porosity, Darcy number, and the interfacial heat transfer coefficient on the flow and temperature contours and on the Nusselt number is then investigated. For low interface coefficient, the heat transfer in the fluid is enhanced when the overall porosity in the cavity is raised, while for high coefficients, the porosity of the bottom porous layer is the main parameter affecting the heat transfer.

The effects of thermal radiation, thermal conductivity, and variable viscosity on ferrofluid in porous medium under magnetic field

Purpose This study aims to analyze the two-dimensional ferrofluid flow in porous media. The effects of changes in parameters such as permeability parameter, buoyancy parameter, Reynolds and Prandtl numbers, radiation parameter, velocity slip parameter, energy dissipation parameter and viscosity parameter on the velocity and temperature profile are displayed numerically and graphically. Design/methodology/approach By using simplification, nonlinear differential equations are converted into ordinary nonlinear equations. Modeling is done in the Cartesian coordinate system. The finite element method (FEM) and the Akbari-Ganji method (AGM) are used to solve the present problem. The finite element model determines each parameter’s effect on the fluid’s velocity and temperature. Findings The results show that if the viscosity parameter increases, the temperature of the fluid increases, but the velocity of the fluid decreases. As can be seen in the figures, by increasing the permeability parameter, a reduction in velocity and an enhancement in fluid temperature are observed. When the Reynolds number increases, an increase in fluid velocity and temperature is observed. If the speed slip parameter increases, the speed decreases, and as the energy dissipation parameter increases, the temperature also increases. Originality/value When considering factors like thermal conductivity and variable viscosity in this context, they can significantly impact velocity slippage conditions. The primary objective of the present study is to assess the influence of thermal conductivity parameters and variable viscosity within a porous medium on ferrofluid behavior. This particular flow configuration is chosen due to the essential role of ferrofluids and their extensive use in engineering, industry and medicine.

Simulation of ferrofluid behavior under the efficacy of magnetic field through a porous complex container

Numerical code based on steam function formulation for scrutinizing the nanomaterial flow and heat transfer within the porous container with sinusoidal hot surface has been developed in this study. The model involves the impression of Lorentz force and buoyancy force has the main role in movement of nanomaterial. Shape of nano-powders and their concentrations have been selected as two other factors. The validation test has been done according to the previous paper which means that present code has good accommodation. In presence of Ha, the Nu declines about 26.5 %. Augmenting Ra in absence of Ha, makes Nu to increase about 28.64 %. When Ha = 0 and 15, loading nanoparticles makes the Nu enhance about 28.18 % and 42.82 %. Augmenting m causes the Nu to increase around 11.94 % and outputs showed that loading nanoparticles has greater impact in presence of magnetic field.

Steady-State and Dynamic Rheological Properties of a Mineral Oil-Based Ferrofluid

In this study, nanoparticles were suspended in L-AN32 total loss system oil. The thixotropic yield behavior and viscoelastic behavior of ferrofluid were analyzed by steady-state and dynamic methods and explained according to the microscopic mechanism of magneto-rheology. The Herschel–Bulkley (H–B) model was used to fit the ferrofluid flow curves, and the observed static yield stress was greater than the dynamic yield stress. Both the static and dynamic yield stress values increased as the magnetic field increased, and the corresponding shear thinning viscosity curve increased more significantly as the magnetic field strength increased. The amplitude scanning results show that the linear viscoelastic region (LVE) is reached when the shear stress is 10%. The frequency scanning results showed that the storage modulus increased with the increase of the frequency at first. The storage modulus increased steadily at a higher frequency range, while the loss modulus increased slowly at the initial stage and rapidly at the later stage. In the amplitude sweep and frequency sweep experiments, the energy storage modulus and loss modulus are enhanced with the decrease of temperature. These findings are helpful to better understand the microscopic mechanism of magneto-rheology of ferrofluids, and also provide guidance for many practical applications.

A simplified phase-field lattice Boltzmann method with a self-corrected magnetic field for the evolution of spike structures in ferrofluids

This research presents a numerical analysis of the normal field instability for an initially flat layer of ferrofluid under the influence of magnetic field. A coupling between the simplified lattice Boltzmann method and the self-correcting procedure is developed to capture the velocity field and magnetic field. The proposed method has the ability to simulate complex hedgehog and comb-like spike structures without using an additional magnetization equation. A single dipole permanent magnet is defined instead of multiple point dipoles which makes this method much simpler and more efficient compared to the numerical approaches available in the literature. A comparison between the simulation results and experimental findings is provided to verify the validity of our method. A criterion for the prediction of spikes is presented for uniform magnetic fields. This study also investigates the effects of different types of magnetic fields, their strengths, and the effect of surrounding non-magnetic fluid on the spike structures. Moreover, the description of magnetic field lines, distribution of magnetic flux density, and energy estimation are also provided in this work which gives a useful insight into the hydrodynamic as well as the magnetostatic behavior of ferrofluids.

Heat Flow Characteristics of Ferrofluid in Magnetic Field Patterns for Electric Vehicle Power Electronics Cooling

The ferrofluid is a kind of nanofluid that has magnetization properties in addition to excellent thermophysical properties, which has resulted in an effective performance trend in cooling applications. In the present study, experiments are conducted to investigate the heat flow characteristics of ferrofluid based on thermomagnetic convection under the influence of different magnetic field patterns. The temperature and heat dissipation characteristics are compared for ferrofluid under the influence of no-magnet, I, L, and T magnetic field patterns. The results reveal that the heat gets accumulated within ferrofluid near the heating part in the case of no magnet, whereas the heat flows through ferrofluid under the influence of different magnetic field patterns without any external force. Owing to the thermomagnetic convection characteristic of ferrofluid, the heat dissipates from the heating block and reaches the cooling block by following the path of the I magnetic field pattern. However, in the case of the L and T magnetic field patterns, the thermomagnetic convection characteristic of ferrofluid drives the heat from the heating block to the endpoint location of the pattern instead of the cooling block. The asymmetrical heat dissipation in the case of the L magnetic field pattern and the symmetrical heat dissipation in the case of the T magnetic field pattern are observed following the magnetization path of ferrofluid in the respective cases. The results confirm that the direction of heat flow could be controlled based on the type of magnetic field pattern and its path by utilizing the thermomagnetic behavior of ferrofluid. The proposed lab-scale experimental set-up and results database could be utilized to design an automatic energy transport system for the cooling of power conversion devices in electric vehicles.

Numerical and experimental investigation of a magnetic micromixer under microwires and uniform magnetic field

With the development in biomedical and biotechnological areas, novel and efficient microfluidic devices integrated with sufficient and rapid mixing function have been attracting enormous scientific attention as versatile and robust platform for low cost and non-contact biological analysis and diagnose. Here, we design and fabricate a magnetic micromixer integrated with special designed microwires, a Y-shaped microchannel and uniform magnetic field for realizing rapid mixing between ferrofluid and deionized water. A comprehensive analysis on the dynamic behavior of ferrofluid is performed by using 3D Eulerian-Eulerian model. Good consistency between experiment and numerical results demonstrates that the enhanced mixing in the presence of longitudinally arranged microwires is due to the introduction of eddies, whose impacts are strengthened with the increase of the number of microwires (nw). However, increasing nw requires a long microchannel and long time to complete mixing. In order to further improve the mixing performance of our micromixer, a horizontally arranged microwire combined with a particular uniform magnetic field is proposed to provide enough magnetic force for enhancing the mixing of ferrofluid and deionized water, receiving optimal mixing efficiency 99.06%. The flexible tunability of external uniform magnetic field enables desired performance of our designed system.

Modelling and Simulation of Flow and Heat Transfer of Ferrofluid under Magnetic Field of Neodymium Block Magnet

Neodymium magnets are the strongest type of permanent magnet commercially available. This investigation aims to numerically study the behavior of ferrofluids in the presence of neodymium block magnets which could be used in a wide range of applications. The problem formulation is derived using the principles of ferrohydrodynamics (FHD) and magnetohydrodynamics (MHD), and the finite volume method is employed for solving the equations. The flow of water-Fe3O4 magnetic nanofluid at 250≤Re≤2300 in a three-dimensional channel under heat flux exposed to a block neodymium magnet is considered. The results indicate that the magnet can significantly affect the flow field and heat transfer while FHD effects are completely dominant and MHD effects are ignorable. In the presence of the magnet, a secondary flow is created, which is more significant for low Reynolds numbers. Applying the magnetic field increases the heat transfer so that at Re=250, where the heat transfer is low, it can increase the Nusselt number by a factor of 2. Moreover, the magnetic field substantially increases the wall skin friction. Considering both the increments of heat transfer and friction, the Reynolds number of 1500 has the maximum thermal performance factor. With increasing Reynolds number or distance between the magnet and channel, the magnetic effect decreases. It is found that the thermal performance factor is increased by reducing the distance of the magnet and channel. In addition, if the height of the magnet is decreased by half (from 1 cm to 0.5 cm), the thermal performance factor improves by 6%.

Numerical Investigation of Ferrofluid Preparation during In-Vitro Culture of Cancer Therapy for Magnetic Nanoparticle Hyperthermia.

Recently, in-vitro studies of magnetic nanoparticle (MNP) hyperthermia have attracted significant attention because of the severity of this cancer therapy for in-vivo culture. Accurate temperature evaluation is one of the key challenges of MNP hyperthermia. Hence, numerical studies play a crucial role in evaluating the thermal behavior of ferrofluids. As a result, the optimum therapeutic conditions can be achieved. The presented research work aims to develop a comprehensive numerical model that directly correlates the MNP hyperthermia parameters to the thermal response of the in-vitro model using optimization through linear response theory (LRT). For that purpose, the ferrofluid solution is evaluated based on various parameters, and the temperature distribution of the system is estimated in space and time. Consequently, the optimum conditions for the ferrofluid preparation are estimated based on experimental and mathematical findings. The reliability of the presented model is evaluated via the correlation analysis between magnetic and calorimetric methods for the specific loss power (SLP) and intrinsic loss power (ILP) calculations. Besides, the presented numerical model is verified with our experimental setup. In summary, the proposed model offers a novel approach to investigate the thermal diffusion of a non-adiabatic ferrofluid sample intended for MNP hyperthermia in cancer treatment.

Parallel superposition rheology on the yielding behaviors of ferrofluids

The microscopic mechanism behind the yielding behaviors of ferrofluids is still blurred, lacking a research method to monitor the structural evolution under a varying steady shear stress. In the present work, parallel superposition rheometry was first used to evaluate the viscoelastic behaviors of ferrofluids during the yielding process. The existence of a linear viscoelastic region in storage moduli curve under very low steady shear stresses demonstrates that gap-spanning structures dominate the rheological behaviors of ferrofluids under weak hydrodynamic interaction. The disappearance of the peak in loss moduli of ferrofluids with relative low particle volume concentration was spotted, indicating that the decomposition of gap-spanning structures can be completed through different paths in ferrofluid system. A sudden drop in the storage moduli was observed under the sweep of steady stress, magnetic field strength or temperature respectively, which is regarded as the sign of transition from thick columnar structures to single chains. By examining the combined effect of magnetic field strength and temperature, a fixed yield stress of ferrofluids was thought to reflect a critical contrast between the thermal and magnetic interaction level.

Water-Dispersible Fe3O4 Nanoparticles Modified with Controlled Numbers of Carboxyl Moieties for Magnetic Induction Heating

Monodisperse Fe3O4 nanoparticles (NPs) with excellent water dispersibility and stability were prepared by the introduction of the carboxyl group (−COOH) on the surface of the as-prepared oleyl-capped Fe3O4 NPs. Controlled introduction of the COOH moieties on the NP surface was carried out by a simple ligand exchange reaction using two types of phosphonic acid ligands with dodecyl moiety and the terminal COOH group. The degree of modification of the COOH group on the particle surface was controlled by tuning the molar ratios of the two phosphonic acids. During the ligand exchange reaction, no change was observed in the crystal structure and morphology of the Fe3O4 NPs. The results of Fourier transform infrared (FT-IR) spectroscopy confirmed that the two ligands were bound to the Fe3O4 NP surface through their phosphoric acid functional groups. The surface coverage and molar ratios of the two ligands were evaluated by thermal gravimetric analysis (TGA) and via proton nuclear magnetic resonance (1H NMR) measurements, respectively. Results obtained from the thermal analyses were consistent with the initial molar ratios of the ligands used in the reaction, which reflect on the efficiency of the developed ligand exchange process. Our COOH-modified Fe3O4 NPs could be dispersed in water by deprotonation for over 6 months and exhibit a typical ferrofluid behavior without the addition of other surfactants and dispersants, showing high dispersion stability. Furthermore, the magnetic induction heating performance of the Fe3O4 NPs in aqueous dispersions was evaluated and the specific absorption rate (SAR) value was estimated to be 38.3 W/g Fe. These results suggest that our COOH-modified Fe3O4 NPs with the desired number of COOH surface moieties can be advantageous for applications such as precise surface design, water-based ferrofluid, and hyperthermia treatment.

Water-Based Fe3O4 Ferrofluid Flow Between Two Rotating Disks with Variable Viscosity and Variable Thermal Conductivity

The impact of variable viscosity and variable conductivity is presented on the water-based Fe3O4 nanofluid flow between two parallel stretchable rotating disks. The stretching and rotating rates of both disks play an essential role in velocity distribution and heat transfer study. The similarity transformation is utilized to customize the momentum and energy equations into nonlinear-coupled differential equations with some influential dimensionless physical parameters. The nonlinear-coupled differential equations of the transformed system are solved numerically through the finite element method using COMSOL Multiphysics. The outcomes for velocity and temperature distributions are shown in the presence of considered physical parameters in the flow. Enhancing the stretching of disks, rotation speed, and variable thermal conductivity enhances the temperature of nanofluid. Permeability parameter, ferromagnetic interaction numbers, and Reynolds numbers also have a major role in the velocity and temperature distributions. Strengthening the rotation number, ferromagnetic interaction number and Reynolds number amplifies the friction on the surface of the disk and shrinks the local heat transfer rate. The rheological behavior of ferrofluid and the role of variable thermal conductivity in the present study might be useful to select the best possible nanofluid for medical purposes.

Conductivity and energy change in Carreau nanofluid flow along with magnetic dipole and Darcy-Forchheimer relation

The current research article explores the bio-convection magnetized Carreau-nanofluid flow utilizing activation energy and magnetic dipole. Magnetic nanomaterials have significant effect on the magnetized behavior of ferrofluids which leads to robust the changes in fluid viscosity and thermophysical characteristics. Darcy-Forchheimer flow model is also present. Thermal conductivity of nanofluid is dependent on the temperature. Brownian motion and thermophoresis aspects are also accounted. The PDEs are reduced to set of ODEs via appropriate functions. Numerical solutions are achieved with the help of the famous bvp4c solver a built-in function in MATLAB. Numerous flow parameters are graphically and numerically presented with physical significance. The proposed findings could be useful for applications of extrusion systems, organic compounds, improved energy generation and improved manufacturing techniques.

The influence of thixotropy on the magnetorheological property of oil-based ferrofluid

A Fe3O4 hydrocarbon oil-based ferrofluid was synthesized and its magnetorheological behavior was investigated. The ferrofluid exhibits shear thinning behavior under different magnetic fields and a significant hysteresis effect was observed from the viscosity-shear rate flow curves due to the thixotropy of ferrofluid. The thixotropic behavior is induced by the presence and evolution of the microstructures in the ferrofluid. Moreover, the experimental results demonstrate that the viscosity of the ferrofluid decreases with increasing magnetic field when the magnetic field is below 81 mT. This is followed by an abrupt increase in the viscosity when the magnetic field increases to 124 mT. However, the viscosity again decreases as the magnetic field continue to increase beyond 124 mT. We reveal the negative correlations between viscosity and magnetic fields. The unusual magnetorheological behavior of the ferrofluid is due to the joint effect of thixotropy and magnetic fields. These findings provide a new perspective on the rheological behaviors of ferrofluids that takes the thixotropic effect into consideration.

Chain Formation and Phase Separation in Ferrofluids: The Influence on Viscous Properties.

Ferrofluids have attracted considerable interest from researchers and engineers due to their rich set of unique physical properties that are valuable for many industrial and biomedical applications. Many phenomena and features of ferrofluids’ behavior are determined by internal structural transformations in the ensembles of particles, which occur due to the magnetic interaction between the particles. An applied magnetic field induces formations, such as linear chains and bulk columns, that become elongated along the field. In turn, these structures dramatically change the rheological and other physical properties of these fluids. A deep and clear understanding of the main features and laws of the transformations is necessary for the understanding and explanation of the macroscopic properties and behavior of ferrofluids. In this paper, we present an overview of experimental and theoretical works on the internal transformations in these systems, as well as on the effect of the internal structures on the rheological effects in the fluids.

On evaluation of magnetic field effect on the formation of nanoparticles clusters inside aqueous magnetite nanofluid: An experimental study and comprehensive modeling

This experimental study is conducted to explore the rheological behavior of magnetite-water ferrofluid in the attendance of an external magnetic field (MF). Tetramethylammonium hydroxide is used as surfactant to increase the stability of prepared ferrofluids. The impacts of MF strength (0–480 G) and volume concentration of nanoparticles (0.3–1.5%) on the outcomes are examined. It was found that as the shear rate increases, the viscosity decreases sharply and then tends to a fixed number and therefore, the magnetite-water has non-Newtonian pseudoplastic behavior. It was also found that the application of the MF both increases the viscosity and enhances the non-Newtonian behavior of the ferrofluid. Moreover, it was found that the rise of nanoparticle concentration (φ) leads to the increase of ferrofluid viscosity. Then, the artificial neural network is applied to develop a prediction model for the rheological behavior of water- magnetite ferrofluid in both the absence and attendance of an external MF based on the obtained experimental data. The outcomes revealed that the developed models are capable of predicting the outputs in the absence and attendance of an external MF with R2 value of 0.9772 and 0.9692.

Non-contact and liquid–liquid interfacing triboelectric nanogenerator for self-powered water/liquid level sensing

Abstract Triboelectric nanogenerators (TENG) based on liquid-solid or solid-solid contact have attracted much attention in sensing applications recently. However, the stain caused from external environment and high friction over triboelectric interface are two important issues yet to be solved. To address these issues, a novel magnetic field assisted non-contact TENG is designed by driving the motion of ferrofluid in a sealed tube under an external magnetic field without direct contact. The as-designed TENG can separate the external mechanical motion from the inner triboelectric process, thereby solving the potential stain problem over the triboelectric interface from external environment. Furthermore, a lubricant oil layer is introduced between ferrofluid and substrate to construct a liquid–liquid triboelectric interface, which facilitates the sliding behavior of ferrofluid. This design helps to extend the range of linear relationship between triboelectric current peak value and the ferrofluid motion velocity over its surface, thereby breaking the motion velocity measurement limit of TENG as a velocity sensor. Finally, its potential application is demonstrated as a self-powered water/liquid level sensor. This work provides a novel type of non-contact TENG, and shows triboelectrification on liquid–liquid contact. The novel TENG could be further applied as a highly sensitive sensor in harsh environment.

Preparation and magneto-optical behavior of ferrofluids with anisometric particles

Nanoparticles of barium hexaferrite have been synthesized by hydrothermal method. Copper and cobalt ferrite nanoparticles have been prepared via a novel coprecipitation technique. The particles were characterized by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, magnetic granulometry, wide angle x-ray diffraction, small angle x-ray scattering, small angle neutron scattering. For preparation of the ferrofluids, relatively large nanoplates have been stabilized by a double layer. A stabilization method has been developed and the stable ferrofluids with large particles have been obtained. Magneto-optical effects in the ferrofluids containing both spherical and anisometric ferrite nanoparticles have been studied. The ferrofluids with relatively large nanoplates—61 and 51 nm—have been found to be efficient magneto-optical media. Magneto-optical response in these media has been shown to be one or two orders of magnitude higher, than the one in the colloids with particle size about 10 nm. Characteristic frequencies and aggregate sizes have been determined using experimental data.

Study on the yielding behaviors of ferrofluids: a very shear thinning phenomenon.

The yielding behaviors of the ferrofluids are vital for many applications. However, previous studies have mainly focused on the magnetoviscous effect under relatively high shear rates and rarely involved the yielding process of ferrofluids under very low shear rates. In this study, ferrofluid samples of different particle volume concentrations were prepared and their shear thinning behaviors within a wide shear stress range were systematically studied under various magnetic field strengths and temperatures. The very shear thinning phenomenon of ferrofluids was first observed and its microscopic mechanism was analyzed. A precipitous fall-off stage as the mark of yielding appeared between the low shear and high shear plateaus in the viscosity curves of ferrofluids. The precipitous fall-off stage in the viscosity curves became steeper with the increase of the magnetic field strength or decrease in the temperature. For ferrofluids with relatively low particle volume concentrations, the high viscosity limit under the low shear region disappeared when temperature exceeded a certain value and was interpreted as the disappearance of the equilibrium columnar structures under high Brownian thermal interaction level. A composite Ellis model was proved to be suitable for the fitting of different types of yield stresses and a structural number, Sn was proposed for the dimensionless analysis of the shear thinning behaviors of ferrofluids. The findings in this study contribute to a better understanding of the microscopic mechanism of yielding behaviors of ferrofluids and also provide guidance for many practical applications.