Oil-based Magnetic Fluid Research Articles

The Influence of Viscosity on Heat Dissipation under Conditions of the High-Frequency Oscillating Magnetic Field

High-frequency components such as microprocessors, transistors, antennas, voltage-controlled oscillators, and many others generate a large amount of heat. In the absence of satisfactory cooling, these components may suffer damage or even destruction. Therefore, it is important to find effective ways to cool these components. A possible solution is to use oil-based magnetic fluids. Magnetic fluids contain magnetic particles dispersed in oil, and their properties, including viscosity, affect their cooling capabilities. Viscosity can be changed by adding various additives or by adjusting the concentration of magnetic particles. The advantage of using oil-based magnetic fluids for cooling is that they allow for precise dosing and control of the amount of fluid applied to the component, reducing thermal losses and increasing cooling efficiency. In addition, oil-based magnetic fluids can also act as a dielectric, reducing electrical noise and increasing electromagnetic compatibility with the components. Analyzing the heating rate of magnetic fluids consisting of mineral oils in an alternating magnetic field with a frequency of 500 kHz, we have shown the capability of controlling thermal losses by adjusting the viscosity of the carrier liquid.

Influence of High Viscosity and Magnetoviscous Effect on the Washout Resistance of Magnetic Fluid

Magnetic fluid seals have long been thought to be a successful sealing form while sealing liquids are always a challenge. The instability of the liquid–liquid interface under the washout has become the key technical problem that hinders the realization of sealing liquid. This work mainly presents an experimental study about the influence of high viscosity and magnetoviscous effects on washout resistance. Three engine oil-based magnetic fluids of different viscosities were prepared with two kinds of surfactants. The magnetoviscous effects of the prepared magnetic fluids under different working conditions were found through rheological experiments. The viscosity of the three samples decreased at most by about 100 times with the shear rate increasing. An experimental platform was designed and built for the washout tests. The entire process of magnetic fluids being washed away was obtained experimentally. The magnetic fluid of higher viscosity can remain stationary with lower magnetic force. The quantitative results show that the viscosity of the magnetic fluid has a significant influence on washout resistance under a magnetic field.

Development of a Model and Experimental Study of Thermal Processes in a Ferrofluid Sealer

The aim of the work is to create an interconnected numerical model of the magnetic, hydrodynamic and temperature fields of a ferrofluid sealer and to analyze thermal processes occurring in highspeed seals. This goal is achieved by selecting the necessary equations, boundary conditions, assumptions and physical properties of the magnetic fluid when building the numerical model of the sealer’s working gap, verification of the developed model by the results of the physical experiment. The important results of the work are the obtained and analyzed data on the influence both of physical properties and the geometry of the working gap of the ferrofluid sealer on the heating of the ferrofluid. With a shaft radius of 140 mm and a linear velocity at the shaft surface of 25 m/s due to viscous heating the ferrofluid temperature exceeding the ambient temperature can reach values up to 80 degrees and higher, it has been shown. The use of the equation proposed by V.E. Fertman to determine the thermal conductivity of ferrofluid and the mixing rule to determine its heat capacity allows us to describe with sufficient accuracy for engineering calculations the thermophysical properties of concentrated ferrofluids, it was shown. The significance of the results consists in the possibility of using the developed numerical model in the study of interrelated physical processes in the working gap of the ferrofluid sealer of rotating shafts. The physical and concentration parameters of the synthetic oil-based magnetic fluid given in the paper and the results of its test operation as part of a ferrofluid seal can be used to verify the results of newly developed models of ferrofluid devices.

Oil-based magnetic fluids. Synthesis, properties, and application prospects

In this work, magnetite crude oil-based magnetic fluids have been synthesized and studied. Their physicochemical parameters (density, viscosity, magnetic phase particle size) have been determined. IR spectroscopy and thermogravimetric analysis have been performed. The magnetocaloric properties (magnetocaloric effect and heat capacity) of magnetic fluids have been determined by the microcalorimetric method in the temperature range of 278-350 K in the magnetic field changing its value from 0 to 1.0 T. The maximum value of the magnetocaloric effect of a magnetic fluid with a magnetic phase volume concentration of 0.08 is 0.0035 K at 310 K and at the magnetic induction to 1.0 T. The obtained samples of magnetic fluids have low production costs because crude oil is used as the carrier fluid and can be recommended for various applications of the petroleum and gas industry, for example, for well killing.

Temperature-compensated optical fiber magnetic field sensor with cascaded femtosecond laser micromachining hollow core fiber and fiber loop

A fiber magnetic field sensor with temperature compensation is put forward and experimentally verified by utilizing Fabry-Perot interferometer (FPI) and multimode interferometer (MI). The FPI with ultra-short cavity (about 20 μm), which is proposed to improve the spectrum contrast after being filled with oil-based magnetic fluids (MF) and achieve the sensing of magnetic field, is drilled through by femtosecond laser. The FPI is composed of two sections of single mode fiber and a hollow core fiber, which is named as single mode fiber-hollow core fiber-single mode fiber (SHS). The MI composed of the coated-fiber-loop, which is only sensitive to temperature, is proposed to compensate the temperature on the sensing of magnetic field. The fiber loop is fabricated by only bending a section of coated single mode fiber (SMF). According to the experiment results, the spectrum visibility of magnetic field sensing part can be improved by 3.1 times by shortening the Fabry-Perot (FP) cavity length. The interference wavelength increases nonlinearly from 0 to 69.1 Gs while linearly from 69.1 to 137.7 Gs. In addition, its temperature sensitivity is −0.20 nm/℃ from 23.0 to 42.9 ℃. Moreover, the sensitivity of MI is −2.31 nm/℃ from 23.0 to 42.9 ℃. It could be used to compensate the temperature influence effectively. The structure boasts characteristics of simple manufacture, low cost and highly-sensitive, which can be applied in the fields of magnetic field sensing.

Flow-State Identification of Oil-Based Magnetic Fluid Seal Based on Acoustic Emission Technology

At present, most research studies on the changing process of the magnetic fluid seal are analyzed with the pressure signal of each chamber or the magnetic fluid flow photos taken by a camera, which need to change the seal structure. Based on nondestructive acoustic emission technology, a flow-state identification model of the oil-based magnetic fluid seal using the grey wolf optimizer and random forest is proposed in this study. The acoustic emission signal and pressure signal are collected at the same time under static conditions in the two-stage pole shoes oil-based magnetic fluid seal experiment. Through power spectrum analysis of the acoustic emission signal with the aid of pressure signal, the changing process before seal failure is divided into three states: no magnetic fluid flow, the first pole shoe magnetic fluid flow, and two pole shoes magnetic fluid flow together. Then, the time- and frequency-domain features of acoustic emission signal samples are extracted to form feature vectors as inputs, and the flow-state identification model is established based on the grey wolf optimizer and random forest. The experimental results show that the testing accuracy and F1 scores (the index representing the precision and recall at the same weight) of three states are close to or higher than 90%. The effectiveness of oil-based magnetic fluid seal flow-state identification model based on non-destructive acoustic emission technology is proved.

The simulation of a new high frequency transformer

Core losses of transformers motivate many engineers and scientists to design and implement different transformers for their specific aims. Since there exists a growing interest on high frequency applications in today’s world, design and optimization studies of a magnetic fluid core transformer (MFCT), having an easy and cheap production approach in high frequency applications, are considered in the present paper. The desired design should operate in a more efficient way within a wide frequency band. The MFCT considered here can be a solution to the eddy currents and core losses encountered in the conventional transformers with its low conductivity, oil-based magnetic fluid and super paramagnetic characteristic. The magnetic fluid in the proposed work consists of a combination of ferromagnetic particles made by iron in an averaged diameter of 70 µm with an adjustable magnetism compared to the traditional magnetic fluids and an engine oil, thereby the magnetic permeability of the overall fluid core can be fully adjustable by the variation of mass proportion between the oil and iron powder as an easy process without any chemical process. A COMSOL Multi-Physics design is performed via a finite element package in three dimensions. It is proven that the iron particles exhibit a complicated pattern inside the engine oil and produce a well-defined high frequency output at the secondary windings in a wide range of frequency.

Neutron Reflectometry Study of Transformer Oil-Based Magnetic Fluid Under Electric Field

Abstract This paper is focused on characterization of magnetic fluids (MFs) and experimental investigation of interfacial structural changes in transformer oil-based magnetic fluids (TOMFs) under the influence of electric field. Recently, such nanodielectric fluids have been proposed to be used as transformer liquid insulation as the addition of particles seeks to improve the dielectric and thermal properties of the base liquids. Ferrofluids typically respond to electric and magnetic fields and can be easy manipulated by such external fields. By mean of neutron reflectometry (NR), we show impact of the electric field intensity on magnetic nanoparticle aggregates in a dilute (1.8 vol %.) classical ferrofluid.

Monitoring of Pickering emulsion stability during magnetic heating using ultrasound measurements

Magnetic heating of colloidal systems is becoming a more and more common route for inducing temperature rise, especially in applications where very local temperature elevation is desired. Although the calorimetric properties of magnetic colloids are extensively investigated, the influence of the alternating magnetic field on their structure has rarely been reported. Meanwhile, potential permanent structural changes such as the formation of agglomerates can affect the stability of magnetic dispersions or magnetic Pickering emulsions. In the present work, we propose to use ultrasound as a technique to determine if such changes occur during magnetic heating. Oil-in-oil emulsions with magnetite particle shells around the droplets and oil-based magnetic fluids were exposed to alternating magnetic fields, and the changes in ultrasonic attenuation and the speed of ultrasound were determined. Finally, changes in acoustic properties were investigated in dispersions of magnetic and polystyrene particles after heating to the melting temperature of the soft particles.

Investigation of structural changes in oil-based magnetic fluids by surface acoustic waves

Surface acoustic waves (SAWs) are used for the first time to investigate structural changes in transformer oil-based magnetic fluids under magnetic field. The measurement of the attenuation of SAW propagating along the interface between magnetic fluid and the piezoelectric substrate is showed as an effective tool to study such processes in the case of magnetic fluids when the obviously utilized longitudinal acoustic waves due to the higher viscosity are not available. The magnetic particles FeO.Fe2O3 in several different volume concentrations, from 0.05% to 3.5%, were added to the transformer oil MOL. Both linear increasing and jumped changed magnetic field were applied to study structural changes. The interaction between the magnetic field and magnetic moments of nanoparticles can lead to the aggregation of magnetic nanoparticles and following chain or cluster formations that have an influence on the SAW attenuation. The concentration of magnetic nanoparticles and temperature of magnetic fluid have a decisive influence on structural changes due to the changes of viscosity and thermal motion with the increasing temperature that both affect the process of cluster formation. The measurement of the acoustic anisotropy and applying the theoretical predictions gives additional useful information about the structure of nanoparticles formations in investigated magnetic fluids. Obtained results are compared and discussed.

Rheological properties of silicon oil-based magnetic fluid with magnetic nanoparticles (MNPs)-multiwalled carbon nanotube (MWNT)

In order to research the influence of multiwalled carbon nanotube (MWNT) on the rheological properties of magnetic fluid, silicon oil-based magnetic fluid with or without MWNT was prepared in the present investigation. Magnetic nanoparticles (MNPs) were synthesized by chemical coprecipitation with a certain amount of MWNT (0, 0.5 wt%). Then, Siliane coupling agents N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was used to modify the MNPs. The morphologies, microstructures and magnetic properties of the particles were characterized by transmission electron microscopy, fourier transform infrared spectroscopy and vibrating sample magnetometer. The effect of MWNT on rheological properties was investigated by the rotational rheometer, such as viscosity-temperature, viscosity-magnetism. Therefore, the results showed that the addition of MWNT significantly increases the viscosity of the magnetic fluid, and the viscosity increases with the magnetic field strength and decreases with increasing temperature. In addition, the shear stress increases with increasing shear rate, while the viscosity decreases with increasing shear rate. The rheological properties of magnetic fluid with or without MWNT are consistent.

The Effect of Magnetic Field on the Structure Formation in an Oil-Based Magnetic Fluid with Multicore Iron Oxide Nanoparticles

The Effect of Magnetic Field on the Structure Formation in an Oil-Based Magnetic Fluid with Multicore Iron Oxide Nanoparticles

Dielectric relaxations in a transformer oil-based magnetic fluid

Dielectric relaxations in a transformer oil-based magnetic fluid

Magnetic field actuated manipulation and transfer of oil droplets on a stable underwater superoleophobic surface.

The transport of fluids at functional interfaces, driven by the external stimuli, is well established. The lossless transport of oil-based fluids under water remains a challenge, however, due to their high stickiness towards the surface. Here, a superhydrophilic and underwater superoleophobic tri-phase water/oil/solid nanoarray surface has been designed and prepared. The unique tri-phase surface exhibits underwater superoleophobic properties with an extremely low stickiness towards oil-based fluids. The magnetic-field-driven manipulation and transport of oil-based magnetic fluids are demonstrated under water, which opens up a new pathway to design flexible and smart devices for the control and transfer of liquid droplets by using tri-phase systems.

Structure of nanoparticles in transformer oil-based magnetic fluids, anisotropy of acoustic attenuation

The anisotropy of acoustic attenuation in transformer oil-based magnetic fluids upon the external magnetic field was studied to discover the structure of nanoparticles. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles leads to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids and the concentration of nanoparticles also have very important influence on the structural changes. The measurement of the dependence of the acoustic attenuation on the angle between the magnetic field direction and acoustic wave vector (anisotropy) can give the useful information about the structure of magnetic nanoparticles formations. In the present, the results of anisotropy measurements of the transformer oil-based magnetic fluids are described and using appropriate theory the basic parameters of clusters are calculated. On the basis of the performed calculations, the proportion of the acoustic wave energy used for excitation of the translational and rotational degrees of freedom was also established.

Simplified unified model for estimating the motion of magnetic nanoparticles within electrohydrodynamic field.

In previous research, we studied the electrical breakdown characteristics of a transformer oil-based magnetic fluid; mailnly, those were carried out by the experimental measurements. The first study was aimed at enhancing the dielectric breakdown voltage of transformer oil by adding magnetic nanoparticles experimentally under the official testing condition of dielectric liquids. The next study was focused on explaining the reason why the dielectric characterisitics of the fluids were changed through optically visualizing the particles motion in a microchannel using an optical microscopic measurement and numerically calculating the dielectrophoretic force induced in the fluids with considering only the properties of magnetic nanoparticles. In this study, we developed a simplified unified model for calculating further the motion of magnetic nanoparticles suspended in the presence of electrohydrodynamic field using the COMSOL multiphysics finite element simulation suite and investigated the effects of magnetic nanoparticle dielectrophoretic activity aimed at enhancing the electrical breakdown characteristics of transformer oil.

Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase.

We present dual-mode, on-demand droplet routing in a multiple-outlet microfluidic device using an oil-based magnetic fluid. Magnetite (Fe3O4) nanoparticle-contained oleic acid (MNOA) was used as a carrier phase for droplet generation and manipulation. The water-in-MNOA droplets were selectively distributed in a curved microchannel with three branches by utilizing both a hydrodynamic laminar flow pattern and an external magnetic field. Without the applied magnetic field, the droplets travelled along a hydrodynamic centerline that was displaced at each bifurcating junction. However, in the presence of a permanent magnet, they were repelled from the centerline and diverted into the desired channel when the repelled distance exceeded the minimum offset allocated to the channel. The repelled distance, which is proportional to the magnetic field gradient, was manipulated by controlling the magnet's distance from the device. To evaluate routing performance, three different sizes of droplets with diameters of 63, 88, and 102 μm were directed into designated outlets with the magnet positioned at varying distances. The result demonstrated that the 102-μm droplets were sorted with an accuracy of ∼93%. Our technique enables on-demand droplet routing in multiple outlet channels by simply manipulating magnet positions (active mode) as well as size-based droplet separation with a fixed magnet position (passive mode).

Effect of Different pH on Characterization of Oil-Based Magnetic Fluid

In this paper, the oil-based magnetic fluid was prepared by chemical co-precipitation method and sodium oleate was the surfactant. The effect of different pH on the characterization of magnetic fluid was studied. The characterization was detected by Fourier Transform Infrared spectroscopy (FT-IR), Transmission Electron Microscope (TEM) and Vibrating Sample Magnetometer (VSM). The results show that the nanoparticles were coated successfully by sodium oleate at pH=5. And the saturation magnetization of Fe3O4 magnetic nanoparticles is 58.0 emu/g, the saturation magnetization of magnetic fluid prepared is 20.2 emu/g, and the Fe3O4 particles are dispersed well. Although the Fe3O4 magnetic particles coated by sodium oleate at pH = 10.5 has a higher saturation magnetization (67.8 emu/g), but the magnetic fluid is less stable and has an obvious settlement phenomenon.

Signature of cluster disruption within magnetic fluid samples: The key information provided by low frequency alternating current susceptibility measurements

This paper is focused on the signature of thermal-assisted cluster disruption while analyzing the inverse alternating current (AC) susceptibility (1/χ) versus temperature (T) curves recorded at lower AC frequencies (f), below 300 Hz. A commercial oil-based magnetic fluid (MF) sample was used in the experiments to investigate the critical temperature (T*) that characterizes the thermal disruption of aggregates suspended within the MF sample. T* was found to reduce as f increased within the frequency range of our investigation (63–263 Hz). Furthermore, T* was found to scale with the square of the applied AC frequency. Both theoretical and experimental evidences support that the excitation field frequency (f) dependence of the critical temperature (T*) is well described by T*(f)=T*(0)−Af21+Bf2. The model is based on energy absorption of magnetic nanoparticles in an AC magnetic field.

Numerical simulation of particle concentration in dielectrophoretic flow for high voltage applications

A numerical simulation of magnetic nanoparticles in a liquid dielectric was developed to model dielectrophoretic flows for high voltage applications, e.g. transformers, capacitors, high voltage cables, and switchgears. From previous research, we found that the dielectric breakdown voltage of a transformer oil-based magnetic fluid was affected positively or negatively according to the amount of magnetic nanoparticles under the official testing condition of dielectric fluids. In order to understand these phenomena for enhancing the dielectric characteristics of the fluid, the magnetic particles were finally visualized experimentally and numerically in a fluidic chip consisting of a microchannel and electrodes. In this study, we calculated the dielectrophoretic flow and the particle concentration in the microfluidic system with different applied voltage and investigated the virtual images of magnetic nanoparticles for explaining the dielectric characteristics changes of a liquid dielectric with adding the particles.