Volume Of Magnetic Fluid Research Articles

Experimental study of sealing mechanism and sealing performance of symmetric magnetic fluid seal with occlusal pole teeth

To investigate the sealing mechanism and performance of the symmetric magnetic fluid seal (SMFS) with occlusal pole teeth (OPT), an experimental device was designed. The impact of magnetic fluid volumes and groove widths on the sealing mechanism and performance of the SMFS-OPT was investigated under different environments. Combining experimental results and numerical analyses, the applicability of the magnetic fluid sealing theoretical pressure resistance formula to SMFS-OPT is verified. The results show that low magnetic fluid volume and a large groove width prolong the differential pressure reduction process, thereby reducing the pressure resistance of the sealing device. Increasing the volume of the magnetic fluid increases the sealing device's self-healing rate but does not change the trend of the number of ruptures' impact on the pressure resistance.

Optimization of Performance Characteristics of Magnetofluidic Seals for Wind Power Plants

The use of magnetofluidic seals are a promising direction in sealing rotating shafts of wind power plants. Magnetofluidic seals are characterized by high tightness, simplicity of the design, low losses by friction. Magnetic fluid seal of the rotating shaft consists of a ring magnet and two concentrators of magnetic field, forming with the shaft a narrow ring gap in which the magnetic fluid retained by magnetic field is a hermetic seal. Magnetic forces provide balance of volume of magnetic fluid under the impact of pressure drop and centrifugal forces. With an increase in the speed of rotation of the shaft up to 10 m/s, deformation of the free surface of the magnetic fluid at the surface of the shaft in the form of a funnel is visually observed, which causes a decrease in the retained pressure drop. As the rotation speed increases, the funnel increases, part of the magnetic fluid is ejected from the working area, the retained pressure drop decreases, and at 50 m/s there is a complete release of the magnetic fluid and depressurization of the seal. In order to increase the stability of the free surface of the magnetic fluid in the field of centrifugal forces, multilayer carbon nanotubes were introduced into it. They are characterized by a high specific surface area and, accordingly, a strong Van der Waals attraction. In a magnetic fluid, multilayer carbon nanotubes form structures which are oriented along the magnetic field lines. The following increase in the static load retained by a layer of magnetic fluid has been experimentally determined with the introduction of nanocarbon structures: when coinciding with the axis of the structures the increase was by 100 %, for the normal direction of the load to the axis of the structure – by 50 %. In the seal, with an increase in the shaft rotation speed, deformation of the free surface of a magnetic fluid with nanocarbon structures was observed at 18 m/s at a distance of 3 mm from the shaft surface. The pressure drop retained by the seal increased in the speed range of 10–40 m/s, the maximum effect of 50 % was obtained at a speed of 40 m/s. Thus, the introduction of nanocarbon structures into the magnetic fluid made it possible to reduce the influence of centrifugal forces on the retained pressure drop and increase the efficiency of the magnetofluidic seal at high speeds of rotation of the shaft of wind power plants.

Dynamics of Magnetic Fluids and Bidisperse Magnetic Systems under Oscillatory Shear

This article presents the results of a study on the dynamics of a volume of magnetic fluid levitating in a uniform magnetic field of an electromagnet experiencing an oscillatory shift. Samples with different physical parameters were considered, and the dependence of the magnetoviscous effect was studied. It showed that the greatest influence on the dynamics of a magnetic fluid that experiences vibrational-shear and magnetic-viscosity effects is exerted by the sample microstructure and the presence of large magnetic particles. The results of this work can be used in the development of a technique for magnetic fluid samples express testing, as well as in the development of acceleration and vibration sensors based on magnetic fluids

Features of the Behavior of a Plane Axisymmetric Mag-netic Fluid Drop in a Nonmagnetic Solvent and a Uni-form Magnetic Field

The work is devoted to an experimental study of the process of dissolution of a magnetic fluid in a nonmagnetic solvent under the action of a uniform magnetic field. It is experimentally established that in a volume of magnetic fluid surrounded by a miscible solvent fluid, under the action of a uniform magnetic field, a mechanical movement arises, triggering deformation of this volume. Initially, the axisymmetric volume of the fluid takes an ellipsoidal shape, lengthening along the magnetic field direction. The main reason for this movement is the pressure differences in the magnetic fluid, caused by jumps and nonuniformities of the magnetic field at the interface between magnetic and nonmagnetic media. Simultaneously with the mechanical motion, the diffusion dissolution of the magnetic fluid occurs, which is also accompanied by the motion of the diffusion front at the interface between the fluids. The concentration gradients of magnetic particles that arise in this case cause gradients of the magnetization of the fluid and, as a consequence, gradients of the magnetic field intensity. Together, this triggers the appearance of a bulk magnetic force in the magnetic fluid, and the pressure gradients associated with it. The main regularities of this process have been established, viz. the dependence of change of the geometric characteristics of the volume and its deformation rate on time. It is shown that at the initial stage of the process, the rates of mechanical movement of the boundaries of the magnetic fluid volume are much higher than the rates of movement of the diffusion front. Thus, the initial rate of mechanical elongation of the droplet under the experimental conditions is 0.25 mm/min, and the diffusion front rate is 0.08 mm/min. Over time, these processes slow down and stop when the volume of the magnetic fluid is completely dissolved. Herewith, the mechanical elongation of the drop is the first to stop and, in the case under consideration, takes about ten minutes.

Viscometer for investigating the viscosity of magnetic fluid media

The rational application of magnetic fluids in various technical systems requires their stability analysis, hydrodynamic particle size, dissipative processes in the colloid control. The existing viscometers do not fully meet all requirements, in particular, they do not allow research in a magnetic field of given magnitude and certain topography. It is proposed to determine rheological properties of magnetic fluids using rotary viscometer, in which two measuring gaps are structurally designed and filled with studied fluid, which is important for calculating characteristics of low viscosity magnetic media. The device design implements practically homogeneous magnetic field, varying within wide range and directed perpendicular to liquid shear stress. The device allows to steadily maintain shear rate in medium under study, and to determine viscosity with a sufficiently large change. A small magnetic fluid volume is required to estimate rheological characteristics. The accuracy of measurements of the internal friction force, device heating temperature, coaxial cylinders rotation speed and magnetic field inside investigated medium meet the requirements of international standards. Laminar fluid flow process in the device gap is described mathematically. This made it possible to justify the construction geometrical dimensions in order to increase the measurements and determine rheological properties of low-viscosity magnetic materials. The formulas for calculation of Newtonian fluid viscosity coefficient, shear stress and shear rate based on experimental data were obtained.

Design and Experimental Study on Divergent Magnetic Fluid Seal with Large Clearance and Dual Magnetic Sources

In order to solve the leakage problem of rotating machinery under the condition of large clearance, a new type of divergent magnetic fluid sealing device with secondary magnetic source was designed. The magnetic field distribution in the clearance of the magnetic fluid seal was simulated by the finite element method of magnetic field, and the theoretical value of the sealing pressure resistance was calculated according to the pressure resistance theory of the divergent magnetic fluid seal. The influences of the volume of magnetic fluid injection, the number of teeth, the clearance, and the eccentricity of the rotating shaft on the pressure resistance abilities of divergent magnetic fluid seal were studied by experimental method and compared with the pressure resistance experimental value of ordinary magnetic fluid seal. The results showed that when the injection volume of magnetic fluid is more than 3 ml, the sealing pressure resistance ability of the magnetic fluid does increase greatly and tends to be stable gradually. The saturated magnetic fluid injection volume of divergent magnetic fluid seal with large clearance is 3 ml. With the increase of radial teeth, the pressure resistance ability of magnetic fluid seal first increases and then decreases. With the increase of axial teeth, the pressure resistance ability of magnetic fluid seal also increases. With the increase of radial clearance, the pressure resistance value of magnetic fluid seal first increases and then decreases. With the increase of axial clearance, the pressure resistance value of magnetic fluid seal decreases. The pressure resistance ability of divergent magnetic fluid seal is significantly higher than that of ordinary magnetic fluid seal.

The dynamics analysis of a magnetic fluid shock absorber with different inner surface materials

Suffering low frequency and small amplitude shaking, energy dissipation of long overhanding structures on the spacecraft under weightless environment is a key research topic for the safety of such spacecraft. The paper presented a novel magnetic fluid shock absorber to reduce the vibration of low frequency and small amplitude. The proposed shock absorber had the composite magnet structure including three magnets in the working element and it was attached with different inner surface materials. To the best of our knowledge, this was the first time to consider the relationship between inner surface materials and damping performance of the shock absorber. First, the damping performance of the shock absorber with various magnetic fluid volume percentage and gap size was investigated by reducing the free oscillations of the brass plate. Meanwhile, the magnetic restoring force between the working element and the repulsion magnet was measured. The experimental results showed that the magnetic restoring force versus the distance was almost linear, under small amplitude. When the distance was greater than 20 mm, the approximate calculation formula of the equivalent stiffness could be obtained. We analyzed the influence of the different internal surface materials of the shock absorber on the damping performance by calculating the fluid resistance which was determined by both the viscous shear force and the capillary force. Experimental results verified that the capillary force had a significant influence on fluid resistance and couldn’t be ignored. In terms of the vibration decay time, the damping efficiency of chemigum was 61.39% and 57.87% better than that of fluororubber for the gap of 2 mm and 3 mm respectively. According to the logarithmic decay rate, the damping efficiency of chemigum was 2.965 times that of fluororubber under the gap of 2 mm and was 2.515 times under the gap of 3 mm. For the reason that the shock absorber was used in aerospace, weight was an important factor. Our experiments proved that we must take into account both the densities of materials and the damping performance when selecting inner surface materials.

Optimization of Design Parameters Affecting the Performance of a Magnetic Fluid Rotary Seal

Three different design parameters of magnetic fluid seal are optimized for the maximum pressure differential capacity of the seal. The program finite element method magnetics (FEMM) based on finite element method is used to find the magnetic flux inside the gap for all the combinations of the design parameters. The data are analyzed using the MINITAB statistical analysis software. The multivariable regression analysis technique is used to find the percentage effect of different parameters and also the optimized dimensions. The effect of magnetic fluid volume on maximum pressure differential capacity of a seal is observed, and the optimized volume is found. The results provide enough data to design and fabricate the seal. This seal can be used in positive as well as negative pressure applications. For example, as vacuum rotary shaft seal in low-pressure chemical vapor deposition machines, pressure seal for stirrer shaft in chemical process chambers to seal toxic gases. This seal can also be used as an exclusion seal, such as a bearing protection seals in robotic arms used in manufacturing plants.

Influence of local particle concentration gradient forces on the flow-mediated mass transport in a numerical model of magnetic drug targeting

Magnetic nanoparticles have been widely applied in the nanomedicine field: therapies based on magnetic drug targeting have shown promising results towards the improvement of the current state of the art of medical treatments. Particles interaction with their carrying flow or the surrounding tissues still needs to be completely understood, as well as the mechanisms underlying interparticle interactions. These interactions can potentially promote particles aggregation in the fluid doman and therefore influence the therapy outcome. This study presents a numerical model to describe particles magnetohydrodynamics in a realistic setup for magnetic drug targeting. The focus is a quantitative analysis of the contribution of the local ferrofluid concentration gradients to the magnetic fluid volume force, as well as an investigation on the dependence of the magnetic fluid volume force on particles diameter and ferrofluid concentration. The results show that the main contribution to the magnetic fluid volume force is the magnetic field gradients term. However, the concentration gradients term ranges in the same order of magnitude and therefore cannot be neglected in the force formulation. In addition, the molar concentration distribution has been found to change with different force formulations and with different values of the molar influx too. The model outlines that the magnetic fluid volume force increases with the particle diameter and the ferrofluid concentration. However, both relationships are not linear, but more complex. The described approach proves to be versatile and further applicable to more complex geometries and scenarios. In addition, the outcome and the achievements of the presented numerical model provide for the first time insights into the role of the local ferrofluid concentration gradients in the determination of the magnetic fluid volume force and represent a starting point for further investigations of the mechanisms underlying the flow-mediated ferrofluid mass transport.

Magnetic fluid seal critical pressure calculation based on numerical simulations

Magnetic fluid seals are among the most common ferrofluid applications. One interesting area is the use of numerical simulations to determine the critical pressure, which is a basic parameter determining the possible range of seal operating pressures. The purpose of this study is to present the method of critical pressure calculations in magnetic fluid seals based on magnetic field numerical simulations, which will provide better results than the methods used previously. It is a relatively simple method and can help to reduce the difference between simulations and experiments. Different seal stage shapes, such as symmetric trapezoidal, asymmetric trapezoidal, and rectangular, were taken into account. The research shows that an increase in the magnetic fluid volume applied at the seal stage and a magnetic saturation increase in the seal gap allow the manufacturing inaccuracy influence to be reduced, meaning that the difference between the simulation and experiment results is smaller. In addition, in this paper, the pressure transfer mechanism between liquid rings of the multistage seal is analyzed to show its influence on the critical pressure value calculated based on simulations.

Theoretical Analysis for Wireless Magnetothermal Deep Brain Stimulation Using Commercial Nanoparticles.

A wireless magnetothermal stimulation (WMS) is suggested as a fast, tetherless, and implanted device-free stimulation method using low-radio frequency (100 kHz to 1 MHz) alternating magnetic fields (AMF). As magnetic nanoparticles (MNPs) can transduce alternating magnetic fields into heat, they are targeted to a region of the brain expressing the temperature-sensitive ion channel (TRPV1). The local temperature of the targeted area is increased up to 44 °C to open the TRPV1 channels and cause an influx of Ca2+ sensitive promoter, which can activate individual neurons inside the brain. The WMS has initially succeeded in showing the potential of thermomagnetics for the remote control of neural cell activity with MNPs that are internally targeted to the brain. In this paper, by using the steady-state temperature rise defined by Fourier’s law, the bio-heat equation, and COMSOL Multiphysics software, we investigate most of the basic parameters such as the specific loss power (SLP) of MNPs, the injection volume of magnetic fluid, stimulation and cooling times, and cytotoxic effects at high temperatures (43–44 °C) to provide a realizable design guideline for WMS.

Boundary interface condition of magnetic fluid determines the magnetic levitation force experienced by a permanent magnet suspended in the magnetic fluid

The buoyancy experienced by a permanent magnet suspended in magnetic fluid is studied, and the expression for calculating the magnetic fluid buoyancy is derived. The magnetic fluid buoyancy or magnetic fluid levitation force, which can be obtained by calculating the sum of Archimedes levitation force and magnetic levitation force, depends on the boundary interface condition of magnetic fluid. The type of the boundary interface and the pressure over it determine the boundary interface condition, and the dependence of boundary interface condition of magnetic fluid and magnetic fluid levitation force is studied. If the boundary interface of the magnetic fluid is a liquid-gas interface in contact with air, the magnetic fluid levitation force will be equal to the gravity of the magnetic fluid. A sudden change in magnetic fluid levitation force can be seen when the liquid-gas boundary interface of magnetic fluid is broken by the wall of a container. Or, in other words, the emergence of a solid-liquid boundary interface will influence the magnetic fluid levitation force, and the magnitude of the change is proportional to magnetic field intensity over the solid-liquid boundary interface. Once the liquid-gas boundary interface is close to a horizontal plane, the magnitude of magnetic fluid levitation force will reach a relatively stable value. In the experiments, the volume of magnetic fluid, the location of the magnet, and the magnetic particle concentration in magnetic fluid are used to control and change the boundary interface condition of magnetic fluid.

Numerical Analysis and Experiment Study of Magnetic Fluid Boundary in Seals

Magnetic fluid seals are widely used technical applications of magnetic fluid. This paper presents a numerical simulation model to obtain the boundary of magnetic fluid in seals. The magnetic field in the seal is solved by finite element method, and the boundary is calculated by using Navier-Stokes equations in magnetic fluid. In order to observe the surface and obtain the seal capacity, the plane magnetic fluid seal experiment is carried out. The relationship between the seal capacity and the magnetic fluid volume is presented. The seal capacity which is obtained by the theoretical analysis has well congruence with the result of the experiment. The displacement of boundary with the pressure difference is quantitatively depicted.

Levitation and motion of a magnet partially immersed into a magnetic fluid

The levitation of a permanent disc magnet partially immersed into a magnetic fluid volume on a horizontal plane is studied theoretically and experimentally. Motion of the magnet along a thin magnetic fluid layer is investigated experimentally. A mathematical model of the magnet dynamics is proposed.

Surface shape stability analysis of a magnetic fluid in the field of an electromagnet

Static surface shapes of a magnetic fluid volume between two plates in a non-uniform magnetic field are investigated theoretically and experimentally. Abrupt changes and hysteresis of the magnetic fluid surface shape are observed in the experiments when the current in the coil increases and decreases quasi-statically. The necessary and sufficient conditions for a local minimum of the energy functional are derived theoretically. A method to find stable/unstable surface shapes is developed. The ambiguity in the determination of the magnetic fluid surface shape at the same value of the current is shown. It is found that the experimentally observed surface shapes of the given magnetic fluid volume coincide with the shapes obtained numerically, and practically all of them satisfy the derived necessary and sufficient conditions of the minimum energy. The stability curves of the magnetic fluid bridge between the plates are determined experimentally and theoretically.

Non-uniform Distribution of Magnetic Fluid in Multistage Magnetic Fluid Seals

Magnetic fluid, a new type of magnetic material, is a colloidal liquid constituted of nano-scale ferromagnetic particles suspended in carrier fluid. Magnetic fluid sealing is one of the most successful applications of magnetic fluid. As a new type of seal offering the advantages of no leakage, long life and high reliability, the magnetic fluid seal has been widely utilized under vacuum- and low-pressure-differential conditions. In practical applications, for improved pressure capacity, a multistage sealing structure is always used. However, in engineering applications, a uniform distribution of magnetic fluid under each tooth often cannot be achieved, which problem weakens the overall pressure capacity of the seals. In order to improve the pressure capacity of magnetic fluid seals and broaden their applications, the present study theoretically and experimentally analyzed the degree of non-uniform distribution of multistage magnetic fluid seals. A mathematical model reflecting the relationship between the pressure capacity and the distribution of magnetic fluid under a single tooth was constructed, and a formula showing the relationship between the volume of magnetic fluid and its contact width with the shaft was derived. Furthermore, the relationship of magnetic fluid volume to capacity was analyzed. Thereby, the causes of non-uniform distribution could be verified: injection of magnetic fluid; the assembly of magnetic fluid seals; the change of magnetic fluid silhouette under pressure loading; the magnetic fluid sealing mechanism of pressure transmission, and seal failure. In consideration of these causes, methods to improve the pressure capacity of magnetic fluid seals was devised (and is herein proposed).

Energy dissipation in a finite volume of magnetic fluid

This study is devoted to investigation of energy dissipation processes which happen in a magnetic fluid drop with compound magnet during its motion in cylindrical non magnetic container. The possibility of energy dissipation control by means of electromagnetic field is examined. It's found that a change of magnetic field of compound magnet can lead to both increase and decrease of oscillation decay time and relative damping factor can be varied in a range of ±35%.

Instability of the magnetic fluid shape in the field of a line conductor with current

The static shape of the surface of a finite magnetic fluid volume between horizontal plates is investigated theoretically. The nonuniform magnetic field is generated by a horizontal line conductor with current, which is placed above the upper plate. The variational problem of minimum energy relative to plane surface perturbations is considered for a simply connected magnetic fluid volume. The problem is solved for arbitrary magnetic fields in the noninductive approximation with account for the gravity force and surface tension. Unstable solutions are found. The possibility of stepwise behavior in response to quasi-static changes of the current in the conductor is investigated for the surface shape of a finite magnetic fluid volume.

Magnetic fluid volume between horizontal plates in the field of an electromagnetic coil

Magnetic fluid volume between horizontal plates in the field of an electromagnetic coil

Investigations on a Branched Tube Model in Magnetic Drug Targeting—Systematic Measurements and Simulation

Due to its high targeting efficiency magnetic drug targeting has been proposed as a promising technique for tumor treatment. Since drug-loaded nanoparticles are concentrated within a target region due to the influence of a magnetic field unwanted side effects are considerably reduced. In a first step to contribute to the understanding of basic phenomena experiments on a half-Y-branched glass tube model as a model-system for a blood vessel supplying a tumor were performed. The results of those systematic quantitative measurements were summarized in novel drug-targeting maps. Based on the considered setup and artery-model the current focus is a theoretical approach with a finite-element simulation. The fluid flow is described by the Navier-Stokes equations, the mass flux is given by the advection-diffusion equation and the magnetic field is derived from Maxwell's equations. The magnetic volume force acting on a volume of magnetic fluid combines the magnet and the ferrofluid data and is proportional to the field dependent magnetisation and the gradient of the field strength. The diffusion equation additionally allows the implementation of a concentration-dependent magnetic volume force. Our experimental investigations have shown that the miscibility of even the water-based ferrofluid and water is low. Since in medical applications the ferrofluid will be injected close to an appropriate junction one cannot necessarily assume a homogeneous mixture approaching the branch-region. Therefore, the characteristic focus of the presented simulation is a model where at the point of injection the ferrofluid and the carrier-fluid are initially separated and further mixture occurs due to the velocity field, diffusion, volume forces and magnetophoresis.