Ferrofluid Flow Research Articles

Application of electromagnets for forced convective heat transfer enhancement of magnetic fluids

The current research aims to numerically investigate the effect of a three-dimensional magnetic field generated by four electromagnets on the convective heat transfer of Fe3O4 /Water ferrofluid in a parallel plate channel. Simulations have been carried out for different ferrofluid flow rates and concentrations, magnetic field intensities, and the electromagnets locations. The obtained numerical results have been compared with the experimental data of our previous work and accuracy of the numerical method has been determined at different conditions. Results show that the external magnetic field induces a quasi-oscillatory fluid motion between the surfaces of the channel that disturbs the thermal boundary layer and increases the heat transfer rate. A maximum of 24% heat transfer enhancement has been obtained at the optimum conditions. It is also concluded that the magnetic field has both increasing and decreasing effect on the fluid local pressure according to the sign of the magnetic field gradient. However, the overall pressure drop does not vary too much with the magnetic field intensity. Moreover, the accuracy analysis implies that the numerical method is more reliable in low magnetic field strengths and low Reynolds numbers.

New insights on boundary layer control using magnetic fluids: A numerical study

This work investigates the effects of an applied magnetic field on the laminar flow of a ferrofluid over a backward-facing step. Both constitutive equation and global magnetization equation for a ferrofluid are considered. The resulting formulation consists in a coupled magnetic-hydrodynamic problem. Computational simulations are carried out in order to explore the physics of the flow and the consistency of theoretical aspects of our formulation. The unidirectional sudden expansion in a ferrofluid flow is investigated numerically under the perspective of Ferrohydrodynamics in a two-dimensional domain using a Finite Volumes Method. The boundary layer detachment induced by the sudden expansion results in a recirculating zone, which has been extensively studied in purely hydrodynamic problems for a wide range of Reynolds numbers. Similar investigations can be found in literature regarding the sudden expansion under the Magnetohydrodynamics framework, but none considering a colloidal suspension of magnetic particles out of the superparamagnetic regime in the framework of Ferrohydrodynamics. The vorticity-stream function formulation is implemented. Our simulations show a clear coupling between the flow vorticity and the magnetization field. We observe a systematic decay on the length of the recirculating zone as we increase the magnetic parameters of the flow, such as the intensity of the applied field and the volume fraction of particles. The results are discussed from a physical perspective in terms of the dynamical non-dimensional parameters. We argue that the reduction of the recirculating region is a direct consequence of the magnetic torque balancing the action of the torque produced by viscous and inertial forces of the flow. For the limiting case of small Reynolds and magnetic Reynolds numbers, the diffusion of vorticity balances the diffusion of the magnetic torque on the flow. This mechanism controls the growth of the recirculating region.

Particle separation in a microchannel by applying magnetic fields and Nickel Sputtering

In the separation process of micro-particles by applying magnetic force, the particle can be separated and diverted depending on its magnetic susceptibility and size. In this paper, the motion of particles with different sizes were analyzed in a microchannel to obtain particle trajectories due to the effects of magnetic fields, Nickel Sputtering and fluid flow. By applying a permanent magnet, temporal movement of non-magnetic particles in a ferrofluid flow inside the T-shape microchannel was investigated. The distribution of the magnetic force on the particles and their trajectories were first confirmed by analytical and empirical data, and then three models (including magnet arrangements and Nickel layer) were presented to increase the separation efficiency by optimizing the magnetic field. Non-magnetic particles of polystyrene with the diameter of 0.2–7 μm and EMG 408 as the ferrofluid have been used in the model. The results show that the separation efficiency in the model with Nickel Sputtering is more than the others. For the proposed models, two threshold values of particle size were reported for the first time; So that all particles with the sizes greater than the first threshold value are completely sorted to the first outlet of the channel, meanwhile; the particles smaller than the second threshold value are only ejected from the second outlet. Therefore, a smart sorting can be accessible by the proposed technique. The particle diameter threshold values in the 1st, 2nd and 3rd models are obtained as 7, 6, 4.5 μm (i.e. first outlet) and 0.35, 0.3, 0.2 μm (i.e. second outlet), respectively. The threshold values were reported in the paper to design different tuning strategies.

Simulation and modeling of second order velocity slip flow of micropolar ferrofluid with Darcy–Forchheimer porous medium

Ferrofluids are made out of nanoscale ferromagnetic particles and known as colloidal liquids suspended on a bearer liquid, normally water (H2O) or an organic solvent i e., kerosene. A typically composition would be 5% magnetic particles, 10% surfactant and 85% bearer liquid. Ferrofluid is utilized in rotary seals in computer hard drives, loudspeakers, and MRI (magnetic resonance imaging). It is trusted this research work may explore the specialist to think of consider new uses for this attractive material. Therefore, such effectiveness in mind, mathematical modeling for the second order velocity slip nonlinear entropy optimized Darcy–Forchheimer flow of ferrofluid (FF) is developed towards a stretched surface. The energy equation is discussed in the presence of heat source/sink, dissipation and Ohmic heating or Joule heating. Numerical solutions for the desired ordinary system are contracted via built-in shooting method. The flow parameters are discussed graphically.

Discussion: “Effect of Porous Medium in Stagnation Point Flow of Ferrofluid Due to a Variable Convected Thicked Sheet” [ASME J. Heat Transfer, 2019, 141 (11), p. 112602

Abstract The current discussion is presented to increase the awareness among the readers of ASME Journal of Heat Transfer. Comments are presented on the paper by Imtiaz et al. [1], where the authors investigated the influences of porous medium and stagnation point flow on ferrofluid flow past a variable-thicked sheet. Correction for the definition of the stream function (ψ) is given. These correct relations of the stream function (ψ) satisfies the continuity equation. In addition, correction for the first boundary condition is given.

Comparative analysis for partial slip flow of ferrofluid [formula omitted] nanoparticles in a semi-porous channel

The present study develops the equations that govern a steady flow of ferrofluid in a semi-porous channel (SPC) under the effects of Lorentz force. Three different base fluids namely water, kerosene and blood and magnetite as ferroparticles are used in the analysis. These equations are modeled by using the Cartesian coordinate system with the help of Berman’s similarity transformation. The partial slip condition is also considered at the lower plate of the channel. Three different methods of solution, namely the method of homotopy analysis (HAM) (analytical technique), the method of differential transformation (DTM) (semi-numerical technique) and the method of Runge-Kutta (numerical technique), are used to achieve the solution of non-dimensional, non-linear ordinary differential equations. For HAM solution, the auxiliary parameter ħ delivers an effective way to regulate the convergence range of solution series whereas in DTM an approximation to the solution is obtained without any auxiliary parameter. The impact of Hartman and Reynolds number on the flow velocity are shown graphically and discussed. Finally, the comparison between the solution methods is given and found in very good agreement.

Effect of Magnetic Field Dependent Viscosity on the Unsteady Ferrofluid Flow Due to a Rotating Disk

The effect of magnetic field dependent viscosity on ferrofluid flow due to a rotating disk is studied in the presence of a stationary magnetic field. The results for velocity profiles for various values of MFD viscosity parameter are shown graphically. These results are compared with the ordinary case when the applied magnetic field is absent. Besides, the shear stress on the wall of the disk and its surface is calculated numerically.

Investigation of micropolar hybrid ferrofluid flow over a vertical plate by considering various base fluid and nanoparticle shape factor

PurposeThe purpose of this paper is to investigate micropolar magnetohydrodynamics (MHD) fluid flow passing over a vertical plate. Three different base fluids have been used that include water, ethylene glycol and ethylene glycol/water (50%–50%). Also, a nanoparticle was used in all of the base fluids. The effects of natural convection heat transfer and magnetic field have been taken into account.Design/methodology/approachThe main purpose of solving the governing equations is to scrutinize the effects of the magnetic parameter, the nanoparticle volume fraction, micropolar parameter and nanoparticles shape factor on velocity, temperature and microrotation profiles, the skin friction coefficient and the Nusselt number. These surveys have been considered for three base fluids simultaneously.FindingsThe results indicate that for water-based fluids, the temperature profile of lamina-shaped nanoparticles is 38.09% higher than brick-shaped nanoparticles.Originality/valueThis paper provides micropolar MHD fluid flow analysis considering natural convection heat transfer and magnetic field in three different base fluids. The aim of assessments is the diagnosis of some parameter effects, such as magnetic parameter and nanoparticle volume fraction, on velocity, temperature and microrotation profiles and components. Also, the use of mixed base fluids presented as a novelty in this paper.

Lie Group Analysis of Unsteady Flow of Kerosene/Cobalt Ferrofluid Past A Radiated Stretching Surface with Navier Slip and Convective Heating

In this work, we identified the characteristics of unsteady magnetohydrodynamic (MHD) flow of ferrofluid past a radiated stretching surface. Cobalt–kerosene ferrofluid is considered and the impacts of Navier slip and convective heating are additionally considered. The mathematical model which describes the problem was built from some partial differential equations and then converted to self-similar equations with the assistance of the Lie group method; after that, the mathematical model was solved numerically with the aid of Runge–Kutta–Fehlberg method. Graphical representations were used to exemplify the impact of influential parameters on dimensionless velocity and temperature profiles; the obtained results for the skin friction coefficient and Nusselt number were also examined graphically. It was demonstrated that the magnetic field, Navier slip, and solid volume fraction of ferroparticles tended to reduce the dimensionless velocity, while the radiation parameter and Biot number had no effects on the dimensionless velocity. Moreover, the magnetic field and solid volume fraction increase skin friction whereas Navier slip reduces the skin friction. Furthermore, the Navier slip and magnetic field reduce the Nusselt number, whereas solid volume fraction of ferroparticles, convective heating, and radiation parameters help in increasing the Nusselt number.

Effect of asymmetrical heat rise/fall on the film flow of magnetohydrodynamic hybrid ferrofluid

The movement of the ferrous nanoparticles is random in the base fluid, and it will be homogeneous under the enforced magnetic field. This phenomenon shows a significant impact on the energy transmission process. In view of this, we inspected the stream and energy transport in magnetohydrodynamic dissipative ferro and hybrid ferrofluids by considering an uneven heat rise/fall and radiation effects. We studied the Fe3O4 (magnetic oxide) and CoFe2O4 (cobalt iron oxide) ferrous particles embedded in H2O-EG (ethylene glycol) (50–50%) mixture. The flow model is converted as ODEs with suitable similarities and resolved them using the 4th order Runge-Kutta scheme. The influence of related constraints on transport phenomena examined through graphical illustrations. Simultaneous solutions explored for both ferro and hybrid ferrofluid cases. It is found that the magnetic oxide and cobalt iron oxide suspended in H2O-EG (ethylene glycol) (50–50%) mixture effectively reduces the heat transfer rate under specific conditions.

Modeling and experiments of capillary flow of non-symmetric magnetic fluids under uniform field

The present work aims to investigate the flow of a non-symmetric ferrofluid undergoing a uniform magnetic field in axial symmetry through both theoretical and experimental approaches. The magneto viscous effect is investigated for a fully developed laminar flow. The governing equations are made non-dimensional in order to identify the physical non-dimensional numbers such as the Péclet number, the particle volume fraction and the parameter of effective applied magnetic field. A regular perturbation method is used to obtain new asymptotic solutions on the limits of very low and very high Péclet numbers. Additionally, numerical integration of the equations system provides a solution for the entire range of Péclet. The magnetization profiles and more global quantities like wall viscosity and the relative viscosity are determined. The numerical and asymptotic solutions present an excellent agreement in the application range of the asymptotic solution. Finally, the magneto viscous effect in capillary flow is also determined through an experimental investigation, showing a very good agreement with the asymptotic solution corresponding to the limit of a low Péclet number.

Optimization of heat transfer properties on ferrofluid flow over a stretching sheet in the presence of static magnetic field

The main emphasis of the present research is to investigate the composite effects of magnetization force and rotational viscosity on two-dimensional ferrohydrodynamic non-conducting nanofluid flow over a stretching sheet under the influence of the stationary magnetic field. Microrotation of magnetic fluid and rotation of nanoparticles are also considered. Shliomis model is used in the problem formulation, and then the similarity transformation is applied to transform partial differential equations into a set of nonlinear-coupled ordinary differential equations in dimensionless form. Transformed nonlinear-coupled differential equations are solved through the finite element method using COMSOL Multiphysics under the mathematical modeling. Results for velocity distribution, temperature distribution, concentration distribution and angular velocity distribution are obtained after considering the effects of Maxwell parameter, ferromagnetic interaction number, thermal Grashof number, solutal Grashof number, Brownian motion parameter, thermophoresis number, chemical reaction parameter, radiation absorption coefficient, heat generation/absorption parameter, Prandtl number and Schmidt number in the flow. It has been observed that magnetic energy transforms into kinetic energy, thermal boundary layer and concentration boundary layer in the presence of considered physical parameters.

Effect of non-uniform magnetic fields on the characteristics of ferrofluid flow in a square enclosure

The importance of heat management has been emphasized in various industrial fields and cooling technology of efficiently removing heat is required. The natural convection of a fluid-filled enclosure is being applied in applications such as heat exchangers, solar energy collection, and electronics cooling. In this study, when the same heat source was applied, velocity, temperature, magnetic Rayleigh number, and local Nusselt number in the enclosure were analyzed according to the magnetic field strength and obstacles. The highest heat transfer performance was obtained at 2000 kA/m of rhombus and magnetic field strength. Finally, the optimum point that has a higher heat transfer rate than the reference model was derived by modifying the strength of the magnetic field.

Numerical study of magnetic field effect on the ferrofluid forced convection and entropy generation in a curved pipe

This paper presents the effect of a magnetic field on the ferrofluid flow pattern, heat transfer and entropy generation in a curved pipe. A non-uniform magnetic field is applied to ferrofluid (water + 2% vol. Fe3O4 nanoparticles) flow and under the constant heat flux boundary condition. Governing equations are solved by the finite volume method and based on the SIMPLE algorithm. The major objective of this work is to illustrate the effects of circumferential angle $$\left( {0^\circ \le \phi \le 180^\circ } \right)$$ and strengths of a magnetic field $$\left( {0 \le {\text{Mn}} \le 3 \times 10^{6} } \right)$$ on the hydro-thermal behavior and entropy production rate. It is found that circumferential angle of the magnetic source plays an important role in hydro-thermal performance of a curved pipe. At low magnetic numbers, the optimal circumferential location of the magnetic source is $$\phi_{\text{opt}} = 180^\circ$$ which leads to the maximum heat transfer enhancement and hydro-thermal performance and the minimal entropy generation rate. For high magnetic numbers, the optimal operating condition occurs at $$\phi = 0^\circ$$ and $$\phi = 60^\circ$$ depending on the magnetic number. Second law analysis reveals that the major source of entropy generation comes from heat transfer irreversibility which reduces significantly by applying a magnetic field. In the range of studied parameters, the maximum heat transfer enhancement is about 29% which occurs at $$\phi = 0^\circ$$ and $${\text{Mn}} = 3 \times 10^{6}$$.

Mathematical Solution on MHD Stagnation Point Flow of Ferrofluid

This study presents a numerical investigation on the magnetohydrodynamic (MHD) stagnation point flow of a ferrofluid with Newtonian heating. The black oxide of iron, magnetite (Fe3O4) which acts as magnetic materials and water as a base fluid are considered. The two dimensional stagnation point flow of cold ferrofluid against a hot wall under the influence of the uniform magnetic field of strength is located some distance behind the stagnation point. The effect of magnetic and volume fraction on the velocity and temperature boundary layer profiles are obtained through the formulated governing equations. The governing equations which are in the form of dimensional non-linear partial differential equations are reduced to dimensionless non-linear ordinary differential equations by using appropriate similarity transformation. Then, they are solved numerically by using the Keller-box method which is programmed in the Matlab software. It is found that the cold fluid moves towards the magnetic source that is close to the hot wall. Hence, leads to the better cooling rate and enhances the heat transfer rate. Meanwhile, an increase of the magnetite nanoparticles volume fraction, increases the ferrofluid capabilities in thermal conductivity and consequently enhances the heat transfer.

A numerical study on heat transfer of a ferrofluid flow in a square cavity under simultaneous gravitational and magnetic convection

Thermomagnetic convection is based on the use of external magnetic fields to better control heat transfer fluxes in ferrofluids, finding important applications in engineering and many related areas. The improvement of such methods relies on fundamentally understanding the flow of ferrofluids under temperature gradients and external magnetic fields. However, the underlying physics of this phenomenon is very complex and not yet well characterized. The problem we analyze in this paper consists of a ferrofluid confined in a square cavity heated from the top and subjected to an external magnetic field applied in the horizontal direction. Differently from earlier investigations, this scenario leads to a clear competition between stabilizing gravitational forces and destabilizing magnetic forces; the unbalance between them drives the flow and dictates the mechanisms of heat transfer in the system. The problem is described by the equations of conservation of mass, momentum, and energy; both gravitational and magnetic effects are accounted for through the definition of the body force following the well-known Boussinesq approximation to express the ferrofluid’s density and magnetization as functions of temperature. The resulting set of fully coupled, nonlinear equations of the model is solved with a fully implicit finite element method. The results show that thermomagnetic convection increases convective heat transfer fluxes in the flow, but its net effects essentially depend on a complex balance among viscous, magnetic, and gravitational forces which determines the pattern of recirculation regions inside the cavity. There are two critical values associated with the external field’s intensity: the first marks the onset of thermomagnetic convection when the destabilizing magnetic effects become comparable to the stabilizing gravitational ones and the second corresponds to the external field’s strength that suffices to make the effects of gravity nearly negligible in the flow dynamics. The latter regime is dictated by a balance between viscous and magnetic forces only, and the corresponding numerical predictions agree notoriously well with a scaling analysis which suggests that $${\overline{\mathrm{Nu}}} \sim \mathrm{Ra}_\mathrm{m}^{1/4}$$, where $${\overline{\mathrm{Nu}}}$$ is the average Nusselt number at the isothermal walls and $$\mathrm{Ra}_\mathrm{m}$$ is the magnetic Rayleigh number, a dimensionless parameter associated with the intensity of the external field.

Numerical Examination of Thermophysical Properties of Cobalt Ferroparticles over a Wavy Surface Saturated in Non-Darcian Porous Medium

Abstract In this study, the effect of magnetic field on an incompressible ferrofluid flow along a vertical wavy surface saturated in a porous medium is investigated. Ferrofluid is made by incorporating magnetic particles, in this case cobalt, at the nanoscale level into a base fluid. For the study of porous medium two well-known models, namely, Darcy and non-Darcy, are used. The mathematical model in terms of governing partial differential equations which are based on conservation laws in mechanics according to the assumption is developed, and this model is converted into a dimensionless form by suitable transformations. Due to the complex non-linear partial differential equations, the numerical solution is calculated by using an implicit finite difference scheme. The impact of involved parameters, namely, magnetic parameter, nanoparticle volume fraction parameter, the amplitude of the wavy surface, and the Grashof number, on Nusselt and average Nusselt numbers are studied through graphs and tables. The results show that for large values of the magnetic parameter, both the Nusselt number and the average Nusselt number decrease in ferrofluid flow. The value of the Nusselt number in the Darcy model is higher than the value of the Nusselt number in the non-Darcy model.

Thermal Radiation and MHD Effects in the Mixed Convection Flow of Fe3O4–Water Ferrofluid towards a Nonlinearly Moving Surface

This paper investigated the magnetohydrodynamic (MHD) mixed convection flow of Fe3O4-water ferrofluid over a nonlinearly moving surface. The present work focused on how the state of suction on the surface of the moving sheet and the effects of thermal radiation influence the fluid flow and heat transfer characteristics within the stagnation region. As such, a similarity solution is engaged to transform the governing partial differential equations to the ordinary differential equations. A collocation method, namely the bvp4c function in the MATLAB software solves the reduced system, numerically. Two different numerical solutions were identified for the cases of assisting and opposing flows. The stability analysis was conducted to test the stability of the non-uniqueness solutions. The increment of the thermal radiation effect affects the rate of heat transfer to decrease. The stability analysis conveyed that the upper branch solution is stable and vice versa for the other solution.

Hybrid nanoparticles migration due to MHD free convection considering radiation effect

Hybrid ferrofluid flow pattern was analyzed in this article and Lorentz force has been applied to regulate the efficiency. Besides, radiation impact was added and permeability of region was considered in equations. Results show that an increase of Ha suppresses the nanomaterial flow and cooling performance of heat surface reduces It is determined that greater surface temperature of bottom wall can be obtained with impose of magnetic field. In addition, Nuave decays with reduce of permeability due to lower temperature gradient. An increase of buoyancy force characterizes a decrease of bottom wall temperature which indicates higher Nuave.

Rapid Microfluidic Mixer Based on Ferrofluid and Integrated Microscale NdFeB-PDMS Magnet.

Ferrofluid-based micromixers have been widely used for a myriad of microfluidic industrial applications in biochemical engineering, food processing, and detection/analytical processes. However, complete mixing in micromixers is extremely time-consuming and requires very long microchannels due to laminar flow. In this paper, we developed an effective and low-cost microfluidic device integrated with microscale magnets manufactured with neodymium (NdFeB) powders and polydimethylsiloxane (PDMS) to achieve rapid micromixing between ferrofluid and buffer flow. Experiments were conducted systematically to investigate the effect of flow rate, concentration of the ferrofluid, and micromagnet NdFeB:PDMS mass ratio on the mixing performance. It was found that mixing is more efficient with lower total flow rates and higher ferrofluid concentration, which generate greater magnetic forces acting on both streamwise and lateral directions to increase the intermixing of the fluids within a longer residence time. Numerical models were also developed to simulate the mixing process in the microchannel under the same conditions and the simulation results indicated excellent agreements with the experimental data on mixing performance. Combining experimental measurements and numerical simulations, this study demonstrates a simple yet effective method to realize rapid mixing for lab-on-chip systems.