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Journal articles on the topic 'Magnetics of ferrofluids'
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1
Zhang, Jian Hui, and Hai Bo Sun. "Synthesis and Properties of Fe3O4 Ferrofluids with Narrow Particle Size Distribution." Materials Science Forum 694 (July 2011): 575–79. http://dx.doi.org/10.4028/www.scientific.net/msf.694.575.
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Fe3O4 ferrofluids with uniform magnetic particles were prepared via improved chemical coprecipation technique. A narrow distribution of 8.6-10.8 nm particle sizes was obtained from the magnetization curve using the free-form-model based on Bayesian inference theory. The mean particle diameter about 9.8 nm is consistent with the XRD and SEM results. The hydrodynamic properties of ferrofluids were investigated with different applied magnetic field and shear rate. The experimental results show that diluted ferrofluid and concentrated ferrofluid are Newtonian-fluid and Bingham-plastic fluid, respectively.
2
Hodenius, Michael A. J., Thoralf Niendorf, Gabriele A. Krombach, et al. "Synthesis, Physicochemical Characterization and MR Relaxometry of Aqueous Ferrofluids." Journal of Nanoscience and Nanotechnology 8, no. 5 (2008): 2399–409. http://dx.doi.org/10.1166/jnn.2008.18276.
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The synthesis and characterization of ferrofluid based MR contrast agents, which offer R2* versatility beyond that of ferucarbotran, is described. Ferrofluids were formed after stabilizing magnetite cores with dodecanoic acid (a), oleic acid (b), dodecylamine (c), citric acid (d) or tartaric acid (e). Core sizes were deduced from TEM micrographs. Magnetic properties were determined by SQUID magnetometry. Hydrodynamic particle diameters were determined by dynamic light scattering measurements. Zeta potentials were measured by combining laser Doppler velocimetry and phase analysis light scattering. Iron contents were evaluated colorimetrically. MR relaxometry including R1 and R2* was conducted in vitro using homogeneous ferrofluid samples. The average core diameters of ferrofluids a, b and c equaled 9.4±2.8 nm and approximately 2 nm for ferrofluids d and e. Magnetization measurements at 300 K revealed superparamagnetic behaviour for the dried 9 nm diameter cores and paramagnetic-like behaviour for the dried cores of ferrofluids d and e. Iron contents were between 32–75 mg Fe/mL, reflecting the ferrofluids' high particle concentrations. Hydrodynamic particle diameters equaled 100–120 nm (a, b and c). For the ferrofluids a, b, d and e coated with anions, strong negative zeta potential values between −27.5 mV and −54.0 mV were determined and a positive zeta potential value of +33.5 mV was found for ferrofluid c, covered with cationic dodecylammonium ions. MR relaxometry yielded R1-values of 1.9±0.3 (a), 4.0±0.8 (b), 5.2±1.0 (c), 0.124±0.002 (d) and 0.092±0.005 s−1 mM−1 (e), and R2*-values of 856±24 (a), 729±16 (b), 922±29 (c), 1.7±0.05 (d) and 0.49±0.05 s−1 mM−1 (e). Thus, the synthesized ferrofluids reveal a broad spectrum of R2* relaxivities. As a result, the various MR contrast agents have a great potential to be used in studies dealing with malignant tissue targeting or molecular imaging.
3
Nargund, Achala, and Asha C. S. "Analysis of flow of polar and non polar incompressible ferrofluids." JOURNAL OF ADVANCES IN PHYSICS 10, no. 2 (2015): 2733–40. http://dx.doi.org/10.24297/jap.v10i2.1333.
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In this paper, flow between two parallel plates is analyzed for both polar and non polar ferrofluids. Velocity is obtained without pressure gradient for polar fluid and with pressure gradient for non polar fluid. The solution of the spin velocity is found in terms of applied magnetic field and magnetic flux density for polar fluid. Shear stress is calculated for both polar and non polar ferrofluid.
4
Lavrova, Olga, Viktor Polevikov, and Sergei Polevikov. "NUMERICAL MODELLING OF MAGNETIC SHIELDING BY A CYLINDRICAL FERROFLUID LAYER." Mathematical Modelling and Analysis 24, no. 2 (2019): 155–70. http://dx.doi.org/10.3846/mma.2019.011.
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A coupled method of finite differences and boundary elements is applied to solve a nonlinear transmission problem of magnetostatics. The problem describes an interaction of a uniform magnetic field with a cylindrical ferrofluid layer. Ferrofluid magnetisations, based on expansions over the Langevin law, are considered to model ferrofluids with a different concentration of ferroparticles. The shielding effectiveness factor of the cylindrical thick-walled ferrofluid layer is calculated depending on intensities of the uniform magnetic field and on thickness of the ferrofluid layer.
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Frycz, Marcin. "Effect of Temperature and Deformation Rate on the Dynamic Viscosity of Ferrofluid." Solid State Phenomena 199 (March 2013): 137–42. http://dx.doi.org/10.4028/www.scientific.net/ssp.199.137.
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This paper presents the results of studies which characterize the dynamic viscosity changes of ferrofluid in terms of changes of selected physical conditions of its work. Knowledge of the variation of the ferrofluids density, lubricity, and especially viscosity depending on the concentration of Fe3O4 magnetic particles, temperature, deformation speed and impact direction, type and value of magnetic induction, it is necessary to analyze the changes of operating conditions of the slide journal bearing ferrofluids lubricated. This theme is the broader context of the authors interests and his research. In this article has been briefly characterized the viscous properties of the tested ferrofluid. There also has been shown an analysis of the impact of changes in temperature and velocity of deformation on the change of ferrofluids dynamic viscosity. The paper has been summarized the observations and conclusions reached on the basis of analysis results.
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Rosenthal, Adam D., Carlos Rinaldi, Thomas Franklin, and Markus Zahn. "Torque Measurements in Spin-Up Flow of Ferrofluids." Journal of Fluids Engineering 126, no. 2 (2004): 198–205. http://dx.doi.org/10.1115/1.1669030.
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Measurements of magnetic-field-induced torque in applied uniform rotating magnetic fields are presented and compared to theoretical analyses for water- and oil-based ferrofluids. These experiments measure the viscous torque on the inner wall of a stationary hollow polycarbonate spindle that is completely filled with ferrofluid and attached to a viscometer functioning as a torque meter. The spindle remains stationary and is centered inside a three-phase AC 2-pole motor stator winding, creating uniform time-varying rotating magnetic fields. The viscous torque is measured as a function of magnetic field amplitude, frequency, and direction of rotation. These measurements demonstrate that ferrofluid flow and torque are present even in the absence of free surfaces and agree with a recently derived analysis of the torque during spin-up flow of ferrofluids.
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Soleimani, Hassan, Noor Rasyada Ahmad Latiff, Noorhana Yahya, et al. "Magnetization of Ferrofluid and its Influence on Improving Oil Recovery." Defect and Diffusion Forum 390 (January 2019): 161–67. http://dx.doi.org/10.4028/www.scientific.net/ddf.390.161.
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Large amount of crude oil remains in the reservoir due to the poor sweep and displacement efficiency after displacing fluid injection. To remediate this effect, a thicker displacing fluid is used to reduce viscous fingering for a more stable flood front. A ferrofluid is a suitable candidate due to the tunable viscosity profile when subjected to a magnetic field [1]. In this work, the ability of cobalt substituted magnetite ferrofluid to improve incremental recovery after waterflooding has been investigated via sand pack flooding. Prior to sand pack flooding, structural and magnetic properties of cobalt substituted magnetite nanoparticles were characterized via XRD, FESEM and VSM. Viscosity tests with field strength variation from 0 to 66.88 mT have shown a significant dependency of the ferrofluid’s viscosity on the applied field strength. 6-fold increment of viscosity was recorded when magnetic field strength changes from 19.5 to 66.88 mT. During sand pack flooding, 7.20% of incremental oil was obtained with the ferrofluid injection, even without the presence of a magnetic field. When subjected to a magnetic field, 12.93% and 15.83% of the incremental oil was obtained at 19.5 and 66.88 mT, respectively. It is proven that increase of ferrofluid viscosity with magnetic field strength results in higher incremental recovery. Improved sweep and displacement efficiency has been achieved by injecting the ferrofluid into the oil reservoir.
8
SCHUMACHER, KRISTOPHER R., JAMES J. RILEY, and BRUCE A. FINLAYSON. "Homogeneous turbulence in ferrofluids with a steady magnetic field." Journal of Fluid Mechanics 599 (March 6, 2008): 1–28. http://dx.doi.org/10.1017/s0022112007009640.
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The general equations necessary for a basic theoretical interpretation of the physics of turbulence in ferrofluids are presented. The equations are examined and show multiple novel turbulence aspects that arise in ferrofluids. For example, two new modes of turbulent kinetic energy and turbulent kinetic energy dissipation rate occur, and unique modes of energy conversion (rotational to/from translational kinetic energy and magnetic energy to/from turbulent kinetic energy) are exhibited in turbulent ferrofluid flows. Furthermore, it is shown that potential models for turbulence in ferrofluids are complicated by additional closure requirements from the five additional nonlinear terms in the governing equations. The equations are applied to turbulence of a ferrofluid in the presence of a steady magnetic field (as well as the case of no magnetic field) in order to identify the importance of the new terms. Results are presented for the enhanced anisotropy in the presence of a magnetic field, and results show how turbulence properties (both classical ones and new ones) vary with the strength of the magnetic field. Three different equations for the magnetization are examined and lead to different results at large magnitudes of the applied magnetic field.
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Bognár, Gabriella, and Krisztián Hriczó. "Numerical Simulation of Water Based Ferrofluid Flows along Moving Surfaces." Processes 8, no. 7 (2020): 830. http://dx.doi.org/10.3390/pr8070830.
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The steady two-dimensional boundary layer flow past a stretching flat sheet in a water-based ferrofluid is investigated. The spatially varying magnetic field is created by two line currents. The similarity method is applied to transform the governing equations into a system of coupled ordinary differential equations. Numerical investigations are performed for ferrofluids, the suspensions of water, and three types of ferroparticles (magnetite, cobalt ferrite, and Mn-Zn ferrite). The impact of the solid volume fraction, the surface stretching parameter, and the ferromagnetic coefficient on the dimensionless velocity and temperature profiles, the skin friction coefficient, and the local Nusselt number are analysed for the three types of ferrofluid.
10
Doganay, Serkan, Alpaslan Turgut, and Levent Cetin. "Ferrofluid Plug Actuation for Micro Pumping Systems." Key Engineering Materials 750 (August 2017): 168–72. http://dx.doi.org/10.4028/www.scientific.net/kem.750.168.
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Ferrofluids are colloidal mixtures which consist of nanosized magnetic particles suspended in a base fluid. The typical magnetic particles could be maghemite, magnetite or cobalt ferrite etc. To keep a ferrofluid suspension in a stable state is possible by an electrical double layer or by adding surfactant. They have many applications on electrical, mechanical and optical systems. Recently, the ability of being manipulated by an external magnetic field made them considerable for microfluidic systems such as micro operations, pumping and mixing. Among them, micro scaled pumping systems have appeared as a critical research area due to its notable potential to be applied on many biological and electronic systems. Moreover, the development of lab on a chip and the micro total analysis systems for biological issues has revealed the necessity of liquid transport for micro quantities. Micropumps with ferrofluid plug actuation mechanisms are considered to have the ability to fulfill this requirement. Therefore, driving the working fluids with ferrofluid plugs in a micro-sized tube or channel has attracted researchers’ interest. In this study, ferrofluid plug actuated micro pumping systems have been reviewed from the available literature based on their design and their maximum generated flow rate.
11
Sehat, Ashkan, Hani Sadrhosseini, and M. Behshad Shafii. "Experimental Study of Internal Forced Convection of Ferrofluid Flow in Porous Media." Defect and Diffusion Forum 348 (January 2014): 139–46. http://dx.doi.org/10.4028/www.scientific.net/ddf.348.139.
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This work presents an experimental study of the effect of a magnetic field on laminar forced convection of a ferrofluid flowing in a tube filled with permeable material. The walls of the tube are subjected to a uniform heat flux and the permeable bed consists of uniform spheres of 3-mm diameter. The ferrofluid synthesis is based on reacting iron (II) and iron (III) in an aqueous ammonia solution to form magnetite, Fe3O4. The magnetite is mixed with aqueous tetra methyl ammonium hydroxide, (CH3)4NOH, solution. The dependency of the pressure drop on the volume fraction, and comparison of the pressure drop and the temperature distribution of the tube wall is studied. Also comparison of the wall temperature distribution, convection heat transfer coefficient and the Nusselt numbers of ferrofluids with different volume fractions is investigated for various Reynolds numbers (147 < Re < 205 ). It is observed that the heat transfer is enhanced by using a porous media, increasing the volume fraction had a similar effect. The pressure coefficient decreases for higher Reynolds number. The effect of magnetic field in four strategies, named modes, on ferrofluid flow through the porous media is presented.
12
Vorobiev, Alexei, Dmitry Chernyshov, Gennady Gordeev, and Diana Orlova. "Nondestructive characterization of ferrofluids by wide-angle synchrotron light diffraction: crystalline structure and size distribution of colloidal nanoparticles." Journal of Applied Crystallography 41, no. 5 (2008): 831–35. http://dx.doi.org/10.1107/s002188980802339x.
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The combination of magnetic and nonmagnetic interactions between the colloidal particles in ferrofluids results in various local inter-particle correlations that, in turn, change the macroscopic properties of the whole system. Therefore, characterization of the particle ensemble is a crucial point, allowing optimization of a ferrofluid for a particular application. Here it is shown how the crystal structure of the particles can be easily obtained in a fast synchrotron light diffraction experiment without any special treatment of the ferrofluid sample. Moreover, from the same diffraction patterns, such important parameters as particle mean size and dispersion are retrieved; these are compared with the corresponding parameters obtained from electron microscopy data. A particular problem of magnetite–maghemite transformation in nanoparticles stabilized by the surfactant shell is pointed out.
13
Rowghanian, P., C. D. Meinhart, and O. Campàs. "Dynamics of ferrofluid drop deformations under spatially uniform magnetic fields." Journal of Fluid Mechanics 802 (August 3, 2016): 245–62. http://dx.doi.org/10.1017/jfm.2016.447.
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We systematically study the shape and dynamics of a Newtonian ferrofluid drop immersed in an immiscible, Newtonian and non-magnetic viscous fluid under the action of a uniform external magnetic field. We obtain the exact equilibrium drop shapes for arbitrary ferrofluids, characterize the extent of deviations of the exact shape from the commonly assumed ellipsoidal shape, and analyse the smoothness of highly curved tips in elongated drops. We also present a comprehensive study of drop deformation for a Langevin ferrofluid. Using a computational scheme that allows fast and accurate simulations of ferrofluid drop dynamics, we show that the dynamics of drop deformation by an applied magnetic field is described up to a numerical factor by the same time scale as drop relaxation in the absence of any magnetic field. The numerical factor depends on the ratio of viscosities and the ratio of magnetic to capillary stresses, but is independent of the nature of the ferrofluid in most practical cases.
14
Suciu, Barenten. "Influence of the Drop Volume and Applied Magnetic Field on the Wetting Features of Water-based Ferrofluids." European Journal of Engineering Research and Science 5, no. 9 (2020): 1110–16. http://dx.doi.org/10.24018/ejers.2020.5.9.2158.
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In this work, the influence of the drop volume and applied magnetic field on the wetting features of water-based ferrofluids, is experimentally investigated. Firstly, water drops with volume in the range of 0.1–100 micro-liters are placed, by using micro-pipettes, on bare and coated acrylic plates, to gain reference data concerning the contact angle. Then, drops of water-based ferrofluid, with the volume ranging from 1 to 10 micro-liters, are set on bare acrylic plates, which are placed into the uniform magnetic field created, in normal direction to the plate, by using permanent magnets. Since the ferrofluid drops are elongated along the magnetic field, the contact angle increases at augmentation of the magnetic flux. Besides, when a critical magnetic flux is exceeded, ferrofluid drop loose contact with the plate and jumps towards the magnet. A heuristic equation to predict the fluctuation of the liquid surface tension versus the drop volume, and also versus the ratio of the applied magnetic field energy to the kinetic energy of the magnetic particles dispersed into the water-based ferrofluid, is suggested.
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Safarik, I., J. Prochazkova, E. Baldikova, et al. "Modification of Diamagnetic Materials Using Magnetic Fluids." Ukrainian Journal of Physics 65, no. 9 (2020): 751. http://dx.doi.org/10.15407/ujpe65.9.751.
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Magnetic fluids (ferrofluids) have found many important applications in various areas of biosciences, biotechnology, medicine, and environmental technology. In this review, we have summarized the relevant information dealing with a magnetic modification of diamagnetic materials using different types of ferrofluids. Special attention is focused on a magnetic modification of plant-derived biomaterials, microbial and microalgal cells, eukaryotic cells, biopolymers, inorganic materials, and organic polymers. Derivatization is usually caused by the presence of magnetic iron oxide nanoparticles within the pores of treated materials, on the materials surface or within the polymer gels. The obtained smart materials exhibit several types of responses to an external magnetic field, especially the possibility of the selective magnetic separation from difficult-to-handle environments by means of a magnetic separator. The ferrofluid-modified materials have been especially used as adsorbents, carriers, composite nanozymes or whole-cell biocatalysts.
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López-López, M. T., J. de Vicente, G. Bossis, F. González-Caballero, and J. D. G. Durán. "Preparation of stable magnetorheological fluids based on extremely bimodal iron–magnetite suspensions." Journal of Materials Research 20, no. 4 (2005): 874–81. http://dx.doi.org/10.1557/jmr.2005.0108.
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The high magneto-viscous response of magnetorheological fluids (MRFs) comes from the large size (≈1 μm) of the magnetic particles dispersed in the carrier liquid. Unfortunately, in the absence of a magnetic field, this large size constitutes the origin of some problems facing the technological applications of MRFs. These problems are (i) the instability of the suspensions caused by the fast settling of the high density magnetic particles used, and (ii) the poor redispersibility due to an irreversible aggregation. In this work, we used an electromagnetic induction method to study the stability of MRFs containing micron-sized iron particles dispersed in ferrofluids composed by oleate-covered magnetite nanoparticles dispersed in kerosene. Interestingly, we demonstrated that the sedimentation rate in iron/ferrofluid suspensions can be significantly lower than in iron/kerosene MRFs.
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Maqbool, Rukiya, M. Ijaz Khan, Sumaira Qayyum, and T. Hayat. "Numerical modeling and MHD stagnation point flow of ferrofluid (non-Newtonian) with Ohmic heating and viscous dissipation." International Journal of Modern Physics B 34, no. 28 (2020): 2050265. http://dx.doi.org/10.1142/s0217979220502653.
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Ferroliquids are made out of exceptionally tiny nanoscale particles (usually diameter 10 nanometers or less) of hematite, magnetite or some other compound comprising iron and a liquid. This is small enough for thermal agitation to scatter them equally inside a transporter liquid, and for them to contribute to general magnetic response of the liquid. The composition of the typical ferroliquid is about 5% magnetic solids, 10% surfactant and 85% carrier by volume. There are frequent applications of ferrofluids in mechanical and industrial engineering. Ferrofluids have innovative characteristics and their impact in magnetic fields prompts many fascinating applications. Albeit magnetic liquids are already utilized in certain devices they have not yet been abused to any level. It is trusted that this research communication may investigate the analyst to think of considering new uses for this entrancing material. Therefore, modeling is developed for the ferrofluid stagnation flow over a stretched surface with Ohmic heating and dissipation. The Tiwari–Das model is used for mathematical modeling of nanofluid. The nonlinear system of differential equations is first converted into first order and then tackled through the built-in-Shooting method. The impact of the different pertinent flow parameters is discussed on the velocity, temperature, Nusselt number and skin friction coefficient through the various plots and tables.
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Szczęch, Marcin. "Theoretical analysis and experimental studies on torque friction in magnetic fluid seals." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, no. 2 (2019): 274–81. http://dx.doi.org/10.1177/1350650119862399.
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Magnetic fluid seals are among the most common applications of ferrofluids. In such seals, the torque friction results only from the internal friction in the fluid and there is no direct contact between seal elements. Despite this, the heat generated during operation can be significant due to the low volume of the ferrofluid in the seal and high rotational speeds. The difficulty in calculating the torque friction is because the ferrofluid is a non-Newtonian fluid and changes its viscosity under the influence of a magnetic field. In order to measure torque friction in magnetic fluid seals, a special test stand was built. Tests were performed at different rotation speeds, different temperatures, and two seal stage geometries (rectangle and trapezoid). Numerical simulations were performed to determine the magnetic field distribution in the seal. Dynamic viscosity under the influence of the magnetic field was measured on a rotary rheometer. Mathematical models were compared with laboratory results. The results obtained from the calculations in some cases gave overstated values almost twice in value. An additional correction in the case of ferrofluid viscosity is proposed.
19
Qu, Xiu Rong, Shu Chen Lü, Shu Fang Fu, and Qing Yu Meng. "Synthesis and Magnetic Properties of Water-Based Fe3O4 Ferrofluid." Key Engineering Materials 428-429 (January 2010): 533–36. http://dx.doi.org/10.4028/www.scientific.net/kem.428-429.533.
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Stable water-based Fe3O4 ferrofluid was obtained by three steps. Fe3O4 nanoparticles with the size of about 10 nm were first prepared by chemical co-deposition method. In order to prevent Fe3O4 nanoparticles from agglomerating, they were coated by bilayer surfactants. Then, the coated Fe3O4 nanoparticles were dispersed well into water. Due to the actions of electrostatic force and hydrogen bond, the water-based Fe3O4 ferrofluids can keep stable for two years and no layered phenomenon occurred. The ferrofluid has high saturation magnetization, low remnant magnetization and coercive force.
20
Kim, Jae-Hee, Hyeon-Seok Seo, and Youn-Jea Kim. "Thermal-Flow Characteristics of Ferrofluids in a Rotating Eccentric Cylinder under External Magnetic Force." Micromachines 9, no. 9 (2018): 457. http://dx.doi.org/10.3390/mi9090457.
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Heat dissipation has become an important issue due to the miniaturization of various electronic devices. Various methods such as spray and nozzle coolers, heat sinks and so on are used for heat dissipation. However, the emergence of ferrofluids drastically improves the operating characteristics of electromagnetic systems and devices. A ferrofluid is a suspension containing 10-nm magnetic particles in a colloidal solution. This material exhibits paramagnetic behavior and is sensitive to magnetic field and temperature. In this study, heat transfer characteristics of ferrofluids in a rotating eccentric cylinder were investigated using the commercial code, COMSOL Multiphysics. Numerical results of the local Nusselt number, magnetophoretic force and velocity distributions were obtained from various eccentricities of the cylinder, and the results were graphically depicted with various flow conditions.
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Terentyev, Vladimir, Aleksei Bausov, and Mihail Toropov. "STUDY OF HERMETIC ABILITY OF A COMBINED FERROFLUIDIC SEALED OF BEARING ASSEMBLIES." Bulletin Samara State Agricultural Academy 6, no. 1 (2021): 25–31. http://dx.doi.org/10.12737/44167.
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The purpose of the research is to increase the efficiency of hermetic ability of bearing assemblies by using com-bined ferrofluidic sealed. The research objective is theoretic justification of the maximum concentration of ferro-magnetic particles in fluid, investigation of hermatic ability of a combined ferrofluidic seal under conditions of tem-perature changing and speed of a shaft rotation of packing bearing assembly. The study of hermetic ability of lip and ferro-fluidic sealed was carried out on a test bench, allowing to determine the packing ability of seals both in static and dynamic mode. On the basis of theoretical data, formulas were determined to find the maximum concen-tration of hard and magnetic phases in a ferrofluid, and its composition based on a polyethylsiloxane liquid PES-5 with a 40 kA/m saturation magnetization and a 1.2 Pas dynamic viscosity coefficient was developed. A mixture of magnetite with powdered iron was used as the ferromagnetic phase. Oleic acid was used as a surfactant. Studies to determine hermetic capacity have shown a higher efficiency of the combined ferrofluidic seal compared to the lip one. During static test within the temperature range between 20 to 600C, the critical pressure difference of the com-bined seal was 
 4-16% higher than that of the lip seal. Temperature increase of the bearing assembly from 20 to 1200C causes a decrease in critical pressure difference of up to 50%. This is due to a decrease in the sedimentative stability of the magnetic fluid as a result of an increase in temperature. Studies show that the combined ferrofluidic seal has a higher hermetic tightness at the starting torque than the standard lip seal. In contrast to the lip seal (which tends to lose its tightness at the starting torque), no leakage of pressure fluid from the sealed unit was observed of the com-bined ferrofluidic one with a pressure drop of 0.094 MPa. The results obtained allow reasonably select the concen-tration of magnetic particles in the ferrofluid, and also prove the prospects of replacing standard lip seals with com-bined ferrofluidic ones.
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Hong, Ting Fu, Jik Chang Leong, Long Kai Lin Liou, Chien Hsiung Tsai, and Lung Ming Fu. "Magnetic Microfluidic Mixer." Key Engineering Materials 483 (June 2011): 354–58. http://dx.doi.org/10.4028/www.scientific.net/kem.483.354.
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This paper presents a novel simple Y-type micromixer based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). An electromagnet driven by an AC power source is used to induce transient interactive flows between a ferrofluid and DI water. The alternative magnetic field causes the ferrofluid to expand significantly and uniformly toward DI water associated with a great number of extremely fine fingering structures on the interface in the microchannel. Different magnetic strengths of the electromagnet were applied by adjusting the magnitude of AC supplied power at frequency of 45 Hz. The results show, due to the magnetic fields, two fluids mix with each other efficiently (mixing ratio can be as high as 95%). When the magnetic field is high enough, the labyrinthine fingering instability take place. This phenomenon is favorable for the fluid mixing. In addition, the increasing magnetic field enhances the efficiency of the mixing apparently.
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Sunil and Amit Mahajan. "A nonlinear stability analysis in a double-diffusive magnetized ferrofluid with magnetic-field-dependent viscosity saturating a porous medium." Canadian Journal of Physics 87, no. 6 (2009): 659–73. http://dx.doi.org/10.1139/p09-016.
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A rigorous nonlinear stability result is derived by introducing a suitable generalized energy functional for a magnetized ferrofluid layer heated and soluted from below with magnetic-field-dependent (MFD) viscosity saturating a porous medium, in the stress-free boundary case. The mathematical emphasis is on how to control the nonlinear terms caused by the magnetic-body and inertia forces. For ferrofluids, we find that there is possibility of existence of subcritical instabilities, however, it is noted that, in case of a non-ferrofluid, the global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effect of the magnetic parameter, M3; solute gradient, Sf; Darcy number, Da; and MFD viscosity parameter, δ; on the subcritical instability region has also been analyzed.
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Karpets, M., M. Rajnak, O. Ivankov, et al. "Small-Angle Neutron Scattering Study of Transformer Oil-Based Ferrofluids." Ukrainian Journal of Physics 65, no. 8 (2020): 729. http://dx.doi.org/10.15407/ujpe65.8.729.
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It is known that ferrofluids typically respond to magnetic fields and can be manipulated by such external fields. The particle assembly in magnetic nanofluids can be induced even by a direct current (dc) electric field. An experimental study of magnetic colloidal particles and their changes induced by an external electric field in a ferrofluid based on 2 transformer oils with different concentrations of nanoparticles is presented. By small-angle neutron scattering (SANS), we show the influence of the electric field intensity and the concentration on magnetic nanoparticle aggregates.
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Lin, Jaw-Ren, and Li-Ming Chu. "Dynamic characteristics of exponential slider bearings lubricated with a ferrofluid – Shliomis model." Industrial Lubrication and Tribology 70, no. 4 (2018): 673–79. http://dx.doi.org/10.1108/ilt-03-2016-0063.
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Purpose The purpose of this paper is to investigate the dynamic characteristics of exponential slider bearings lubricated with a ferrofluid. Because of the development of modern engineering, the increasing use of ferrofluids in lubrication fields has shown great importance. Understanding the dynamic characteristics of exponential film bearings is helpful for engineers in bearing selection. Design/methodology/approach Applying the Shliomis ferrohydrodynamic flow model and considering the squeezing action of bearing pads, a dynamic Reynolds equation is obtained for an exponential film slider bearing lubricated with a ferrofluid in the presence of a transverse magnetic field. Analytical solutions of dynamic characteristics are obtained. Findings According to the results, the ferrofluid-lubricated exponential film bearing provides better dynamic stiffness and damping characteristics than the non-ferrofluid ones, especially the bearing operating at higher values of the volume concentration parameter and the magnetic Langevin parameter. Originality/value Numerical tables of stiffness and damping coefficients for different values of the volume concentration parameter and the Langevin parameter are also included for engineering references.
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Viviano, Antonino, Laura M. Stancanelli, Rosaria E. Musumeci, and Enrico Foti. "SHEAR STRESS MEASUREMENTS AT THE SEA BOTTOM BY MEANS OF FERROFLUIDS." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 88. http://dx.doi.org/10.9753/icce.v36.papers.88.
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An innovative measurement technique is proposed for investigating shear stress at sandy bottoms. This technique is based on the adoption of a ferrofluidic sensor and of an optical readout strategy. An experimental campaign is carried out for evaluating its performance. Experiments differ for the ferrofluidic sensor configuration (difference in the magnetic field) and for the bottom configurations (fixed bed or sandy bed). Calibration of the ferrofluidic sensor for the range of the investigated hydraulic condition and of the controlling magnetic field is presented. The ferrofluidic technique is promising when applied at sandy bottoms, as neither adhesion processes between sand grains and ferrofluid or influence of impacts of grains on the measurement are observed. In particular, the preliminary measure performed indicated that the ferrofluidic sensor is capable of sensing the different bed roughness.
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Salwiński, Józef, and Wojciech Horak. "Measurement of Normal Force in Magnetorheological and Ferrofluid Lubricated Bearings." Key Engineering Materials 490 (September 2011): 25–32. http://dx.doi.org/10.4028/www.scientific.net/kem.490.25.
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Preliminary analysis of magnetorheological fluid usability in fluid lubricated bearings has been described in the present study. Results of the study aimed at rheological properties of chosen fluids, which possess magnetic properties (both ferrofluids and magnetorheological fluids) with respect to their application in slide bearings have been presented Preliminary analysis of potential advantages related with the magnetic fluid bearing construction was carried out. Results of measurements of normal force developed within magnetorheological fluid and ferrofluid in result of magnetic field action at various shear rate values have been presented.
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Szczech, Marcin, and Wojciech Horak. "Tightness testing of rotary ferromagnetic fluid seal working in water environment." Industrial Lubrication and Tribology 67, no. 5 (2015): 455–59. http://dx.doi.org/10.1108/ilt-02-2015-0014.
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Purpose – The purpose of this publication is to determine the influence of selected factors on the durability and the tightness of ferrofluid seals working in water environments. Ferromagnetic fluid (FF) seals are one of the most common applications of magnetic fluid. New applications can be developed by extending the capabilities of these seals in fluid environments, especially in water. Design/methodology/approach – Tests were performed using ferrofluids with differing physical properties like density, dynamic viscosity and saturation magnetization. Working conditions, such as water pressure and peripheral speed, were taken into account. Findings – A mathematical description which allows the selection of an appropriate ferrofluid and the determination of the operating parameters of an FF seal was developed. Originality/value – This study concerns the influence of peripheral speed, water pressure and magnetic fluid properties on seal tightness.
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Rahman, Habibur, and Sergey A. Suslov. "Thermomagnetic convection in a layer of ferrofluid placed in a uniform oblique external magnetic field." Journal of Fluid Mechanics 764 (January 5, 2015): 316–48. http://dx.doi.org/10.1017/jfm.2014.709.
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AbstractLinear stability of magnetoconvection of a ferromagnetic fluid contained between two infinite differentially heated non-magnetic plates in the presence of an oblique uniform external magnetic field is studied in zero gravity conditions. The thermomagnetic convection that arises is caused by the spatial variation of magnetisation occurring due to its dependence on the temperature. The critical values of the governing parameters at which the transition between motionless and convective states is observed are determined for various field inclination angles and for fluid magnetic parameters that are consistently chosen from a realistic experimental range. It is shown that, similar to natural paramagnetic fluids, the most prominent convection patterns align with the in-layer component of the applied magnetic field but in contrast to such paramagnetic fluids the instability patterns detected in ferrofluids can be oscillatory. It is also found that, contrary to paramagnetic fluids, the stability characteristics of magnetoconvection in ferrofluids depend on the magnitude of the applied field which becomes an additional parameter of the problem. This is shown to be due to the nonlinearity of the magnetic field distribution within the ferrofluid.
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Haiza, H., I. I. Yaacob, and Ahmad Zahirani Ahmad Azhar. "Thermal Conductivity of Water Based Magnetite Ferrofluids at Different Temperature for Heat Transfer Applications." Solid State Phenomena 280 (August 2018): 36–42. http://dx.doi.org/10.4028/www.scientific.net/ssp.280.36.
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Magnetic magnetite, Fe3O4 nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe3O4 ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe3O4 nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe3O4 suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C.
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Usman, Muhammad, Muhammad Hamid, Syed Tauseef Mohyud Din, Asif Waheed, and Wei Wang. "Exploration of uniform heat flux on the flow and heat transportation of ferrofluids along a smooth plate: Comparative investigation." International Journal of Biomathematics 11, no. 04 (2018): 1850048. http://dx.doi.org/10.1142/s1793524518500481.
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The paper is devoted to a new extension in Gegenbauer wavelet method (GWM) to investigate the transfer of heat and MHD boundary-layer flow of ferrofluids beside a flat plate with velocity slip. A homogenous model study is conducted in which we assumed the heat transfer and forced convective flow of ferrofluids along a flat plate with a uniform wall heat flux. In the direction of transverse to plate, a magnetic field is imposed. Three various magnetic nanoparticle types including Mn–ZnFe2O4, CoFe2O4, Fe3O4are incorporated inside the base fluid. Two types of base fluids (water and kerosene) with bad thermal conductivity as compared to nanoparticles of solid magnetic have been assumed. The mathematical model is tackled via modified Gegenbauer wavelet method (MGWM). A simulation is accomplished for individual ferrofluid mixture by assuming the prevailing impacts of uniform and slip heat fluxes. The variation of heat transfers and skin friction were also observed at the surface of the plate and we analyzed the better heat transfer for every mixture. Kerosene-based magnetite (Fe3O4) delivers the better rate of heat transfer at wall due to its association with the kerosene-based Mn–Zn and cobalt ferrites. The slip velocity and magnetic field effects on the temperature, dimensionless velocity, rate of heat transfer and skin friction are examined for various magnetic nanoparticles inside the kerosene oil and water. We observed that the primary influence of magnetic field reduces the dimensionless surface temperature and accelerates the dimensionless velocity as compared to the hydrodynamic case, thus enhancing the rate of heat transfer and skin friction ferrofluids. Moreover, a detailed evaluation of outcomes obtained by MGWM, already published work and numerical RK-4 were found to be in excellent agreement. The error and convergence analysis are presented. Comparison of results, graphical plots, error and convergence analysis reveal the appropriateness of proposed method. The proposed algorithm can be extended for other nonlinear problems.
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Liu, Xubo, Noah Kent, Alejandro Ceballos, et al. "Reconfigurable ferromagnetic liquid droplets." Science 365, no. 6450 (2019): 264–67. http://dx.doi.org/10.1126/science.aaw8719.
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Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.
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Biedermann, Andrea R., Michele Pugnetti, and Yi Zhou. "Explaining the large variability in empirical relationships between magnetic pore fabrics and pore space properties." Geophysical Journal International 227, no. 1 (2021): 496–517. http://dx.doi.org/10.1093/gji/ggab230.
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SUMMARY The magnetic anisotropy exhibited by ferrofluid-impregnated samples serves as a proxy for their pore fabrics, and is therefore known as magnetic pore fabric (MPF). Empirically, the orientation of the maximum susceptibility indicates the average pore elongation direction, and predicts the preferred flow direction. Further, correlations exist between the degree and shape of magnetic anisotropy and the pores’ axial ratio and shape, and between the degrees of magnetic and permeability anisotropies. Despite its potential, the method has been rarely used, likely because the large variability in reported empirical relationships compromises interpretation. Recent work identified an additional contribution of distribution anisotropy, related to the arrangement of the pores, and a strong dependence of anisotropy parameters on the ferrofluid type and concentration, partly explaining the variability. Here, an additional effect is shown; the effective susceptibility of the ferrofluid depends on the measurement frequency, so that the resulting anisotropy depends on measurement conditions. Using synthetic samples with known void geometry and ferrofluids with known susceptibility (4.04 SI and 1.38 SI for EMG705 and EMG909, respectively), magnetic measurements at frequencies from 500 to 512 kHz are compared to numerical predictions. Measurements show a strong frequency-dependence, especially for EMG705, leading to large discrepancies between measured and calculated anisotropy degrees. We also observe artefacts related to the interaction of ferrofluid with its seal, and the aggregation of particles over time. The results presented here provide the basis for a robust and quantitative interpretation of MPFs in future studies, and allow for re-interpretation of previous results provided that the ferrofluid properties and measurement conditions are known. We recommend that experimental settings are selected to ensure a high intrinsic susceptibility of the fluid, and that the effective susceptibility of the fluid at measurement conditions is reported in future studies.
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Ilg, Patrick, and Siegfried Hess. "Nonequilibrium Dynamics and Magnetoviscosity of Moderately Concentrated Magnetic Liquids: A dynamic Mean-field Study." Zeitschrift für Naturforschung A 58, no. 11 (2003): 589–600. http://dx.doi.org/10.1515/zna-2003-1101.
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A mean-field Fokker-Planck equation approach to the dynamics of ferrofluids in the presence of a magnetic field and velocity gradients is proposed that incorporates magnetic dipole-dipole interactions of the colloidal particles. The model allows to study the combined effect of a magnetic field and dipolar interactions on the viscosity of the ferrofluid. It is found that dipolar interactions lead to additional non-Newtonian contributions to the stress tensor, which modify the behavior of the non-interacting system. The predictions of the present model are in qualitative agreement with experimental results, such as the enhancement as well as the different anisotropy of the magnetoviscous effect and the dependence on the symmetric velocity gradient.
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Lin, Jaw-Ren, Tzu-Chen Hung, and Shu-Ting Hu. "Effects of fluid inertia forces in ferrofluid lubricated circular stepped squeeze films – Shliomis model." Industrial Lubrication and Tribology 68, no. 6 (2016): 712–17. http://dx.doi.org/10.1108/ilt-09-2015-0122.
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Purpose This paper aims to study the inertia squeeze film characteristics between ferrofluid-lubricated circular stepped disks. Owing to the development of modern machine systems, the application of ferrofluids has received great attention. Because the circular disks are a special situation of circular stepped squeeze films, a further study of fluid inertia force effects on the ferrofluid-lubricated circular stepped squeezing mechanism is motivated. Design/methodology/approach On the basis of the ferrohydrodynamic flow model of Shliomis incorporating the momentum integral method, the effects of fluid inertia forces in ferrofluid-lubricated circular stepped squeeze films in the presence of external magnetic fields are investigated in this study. Analytical solutions of squeeze film performances are derived. Findings The fluid inertia force effects provide an increased load capacity and a longer squeeze film time for the ferrofluid-lubricated circular stepped squeeze film, especially for a larger value of the inertia parameter, the Langevin parameter and the volume concentration and a smaller value of the radius ratio and the step height ratio. Originality/value For engineering applications, numerical tables for squeeze film loads of circular stepped disks are also provided in this paper.
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Amirabadizadeh, Ahmad, Amir Zelati, and Zahra Lotfollahi. "Studying the Temperature Effect on the Magnetic Behavior of Fe3O4 Water Based Ferrofluid." Key Engineering Materials 744 (July 2017): 468–72. http://dx.doi.org/10.4028/www.scientific.net/kem.744.468.
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In this study, Iron Oxide (Fe3O4) nanoparticles water based ferrofluid, was synthesized by co-precipitation method. XRD was used to study the structural characterization of the sample and to measure the size of the crystallites (using Scherrer equation). TEM was utilized to examine the shape, the size distribution and the morphology of the nanoparticles. VSM was carried out to measure the magnetic properties (like Mr, Ms and Hc) of the Fe3O4 (magnetite) nanoparticle and magnetite ferrofluid at 80 and 300 K. The results indicate that the average size of the magnetite roughly spherical shape nanoparticles is 13nm. The VSM results show that the magnetite ferrofluid contains single domain magnetic nanoparticles with superparamagnetic behavior. In addition, the magnetic measurements demonstrate that with decreasing the temperature of the ferrofluid, its magnetic softness decreases while its anisotropy increases.
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Tsai, Chang Shu, Wei Chung Liu, and Hong Yi Chen. "Study on the Syntheses of Ferrofluids by Different Iron Compounds and their Specific Adsorption Rate of Magnetic Fluid Hyperthermia." Advanced Materials Research 647 (January 2013): 742–47. http://dx.doi.org/10.4028/www.scientific.net/amr.647.742.
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The highest SAR (specific adsorption rate) value of ferrofluid was found to be 28.5±1.9W/g, when prepared by using ferrous chloride tetrahydrate (FeCl2•4H2O) and iron(III)nitrate 9-hydrate(Fe(NO3)3• 9H2O) with the 1:1 ratio of iron compound’s molarity. The SAR values of ferrofluids were found to be 62.0±6.5, 59.4±10.3, and 66.0±5.0 W/g, respectively, when prepared by using ferrous sulfate 7-hydrate (FeSO4•7H2O) and ferric chloride hexahydrate (FeCl3•6H2O) with the 1：2.5, 2.5：1, and 3：1 ratio of iron compound’s molarity . The SAR values of ferrofluids were found to be 66.6±7.0 and 63.5±6.0 W/g respectively, when prepared by using ferrous sulfate 7-hydrate (FeSO4•7H2O) and iron(III)nitrate 9-hydrate (Fe(NO3)3•9H2O), with the 1：1, 1：1.5 and 1：2 ratio of iron compound’s molarity. The SAR values of ferrofluids were found to be 84.7±12.7, 93.4±14.2 and 89.2±6.4 W/g, respectively, when prepared by using ferrous chloride tetrahydrate (FeCl2•4H2O) and ferric chloride hexahydrate (FeCl3•6H2O), with the 1：1, 1：1.5 and 1：2 ratio of iron compound’s molarity .
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Raouf, Izaz, Piotr Gas, and Heung Soo Kim. "Numerical Investigation of Ferrofluid Preparation during In-Vitro Culture of Cancer Therapy for Magnetic Nanoparticle Hyperthermia." Sensors 21, no. 16 (2021): 5545. http://dx.doi.org/10.3390/s21165545.
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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.
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Volchkov, S. O., A. A. Chlenova, and V. N. Lepalovskij. "Modelling of thin film magnetoimpedance sensitive element designed for biodetection." EPJ Web of Conferences 185 (2018): 10005. http://dx.doi.org/10.1051/epjconf/201818510005.
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Magnetic soft matter (ferrofluids or ferrogels) is one of the rapidly growing areas of research and applications including magnetic biosensing. Giant magnetoimpedance is the effect with proven capacity to magnetic label detection. In this work, we describe a universal model to simulate conditions of magnetic biodetection and to check its validity with giant magnetoimpedance sensitive element based on magnetic multilayer. Finite element method allows calculations of high-frequency current distribution using the Maxwell's equations taking into account the magnetodynamics of iron oxide water-based ferrofluid in small channels similar to the blood vessels. The modelling was realized with the licensed software Comsol©. The calculations were performed on a specialized engineering server based on four processors Intel Xeon E5 and 124 Gb RAM, adapted for parallel computations and suitable for description of individual layers with nanometer dimensions for the number of elements in the mesh structure above 106 cells. The designed model allows calculations of the current density, the outside magnetic flux, resistivity, etc. for each one of the created cells and total values by integration of sub-domains. One can quantitatively describe concentration of ferrofluid, velocity and pressure in the blood vessel. These changes affecting on the giant magnetoimpedance of the FeNi-based multilayer were both calculated and measured.
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Ma, Rongchao, Yixin Zhou, and Jing Liu. "Floating and flying ferrofluid bridges induced by external magnetic fields." Modern Physics Letters B 29, no. 09 (2015): 1550029. http://dx.doi.org/10.1142/s0217984915500293.
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A ferrofluid is a mixture that exhibits both magnetism and fluidity. This merit enables the ferrofluid to be used in a wide variety of areas. Here we show that a floating ferrofluid bridge can be induced between two separated boards under a balanced external magnetic field generated by two magnets, while a flying ferrofluid bridge can be induced under an unbalanced external magnetic field generated by only one magnet. The mechanisms of the ferrofluid bridges were discussed and the corresponding mathematical equations were also established to describe the interacting magnetic force between the ferro particles inside the ferrofluid. This work answered a basic question that, except for the well-known floating water bridges that are related to electricity, one can also build up a liquid bridge that is related to magnetism.
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Madden, Aaron, Juan Fernandez de la Mora, Nirmesh Jain, Hadi Sabouri, and Brian Hawkett. "Effect of a homogeneous magnetic field on the electrospraying characteristics of sulfolane ferrofluids." Journal of Fluid Mechanics 833 (November 6, 2017): 430–44. http://dx.doi.org/10.1017/jfm.2017.589.
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We explore the effect of an applied homogeneous magnetic field on the electrospraying characteristics of a ferrofluid in the cone-jet mode. A sulfolane-based ferrofluid mixed with the ionic liquid ethyl ammonium nitrate has been synthesized. These mixtures have negligible volatility under ambient conditions and remain stable under a very wide range of electrical conductivities $K$. Magnetized Taylor cones spray with the same current emission characteristics as their non-magnetized counterparts in the shared voltage and flow rate parameter space. However, the magnetized Taylor cones studied remained stable at voltages 23 % lower than the non-magnetized spray; they also access flow rates 30 % and 40 % lower in ferrofluids with $K=0.3$ and $0.01~\text{S}~\text{m}^{-1}$. In the lower voltage ranges available only to magnetized tips, unusually long stable cones are observed. The magnetic stabilization mechanism responsible for these two effects remains unclear. It is noteworthy that these strong effects arise even when the tip curvature of the strictly magnetized liquid is orders of magnitude smaller than that for the strictly electrified liquid.
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S. A., Nesterov, Stradomskii Yu. I., and Belov V. S. "Study of Interconnected Physical Processes in the Magnetic Fluid Sealer." Problems of the Regional Energetics, no. 3(51) (August 2021): 1–9. http://dx.doi.org/10.52254/1857-0070.2021.3-51.01.
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The purpose of this work is creation of an interconnected numerical model of the magnetic and hydrodynamic fields of the ferrofluid sealer to analyze the effect of centrifugal forces during shaft rotation on the retained pressure drop. The set goal was achieved by selection of the necessary equations, boundary conditions, assumptions and properties concerning the ferrofluids when building a numerical model of the sealer gap in the Comsol Multiphysics simulation environment. The important results of the work were the obtained and analyzed distributions of the magnetic field and pressure field in the ferrofluid, the evaluation results of the of the effect of centrifugal forces arising during the shaft rotation, on the pressure drop held by the sealer. It was shown that with a shaft radius of up to 50 mm and speed up to 3000 rpm, the change in the retained pressure drop was insignificant, and it was up to 2 % of the values with a stationary shaft. Significant manifestation of centrifugal force for the investigated shaft radii began at 6000 rpm. It was shown that the decrease in the retained pressure drop with an increase in the working gap was associated with the decrease in the magnetic field gradient. The significance of the results consisted in the possibility of using the developed model for the study of the ferrofluid sealer gap processes. Comparison with the data obtained using the analytical formulas showed that the latter overestimated the retained pressure drop
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Dobroserdova, A., E. Minina, J. J. Cerdà, C. Holm, and S. Kantorovich. "Microstructure of Bidisperse Ferrofluids in a Monolayer." Solid State Phenomena 190 (June 2012): 625–28. http://dx.doi.org/10.4028/www.scientific.net/ssp.190.625.
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In the present study we briefly analyze the cluster structures observed in the model bidisperse ferrofluid constrained in quasi-2D (q2D) layer in the absence of an externally applied magnetic field. We use a combination of a DFT approach and molecular dynamic simulation to quantitatively describe various chain and ring structures and their equilibrium area fractions. We also show that to reach a good agreement between simulation data and theoretical predictions in q2D geometry in theory one needs to allow for more possible chain configurations than in the bulk system. We provide preliminary explanations why the microstructure of bulk bidisperse ferrofluids differs noticeably from the one in q2D layer.
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Servín-Hernández, E., Oliverio S. Rodríguez-Fernández, and L. A. García-Cerda. "Synthesis of Plasticizer-Based Ferrofluid and its Use in the Preparation of Magnetic PVC Nanocomposite." Materials Science Forum 644 (March 2010): 13–16. http://dx.doi.org/10.4028/www.scientific.net/msf.644.13.
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A magnetic polyvinylchloride (PVC) nanocomposite was prepared by static casting using a plasticizer-based ferrofluid. Two sets of nanocomposites were prepared: one under the influence of magnetic field and the other without magnetic field. The effects of ferrofluid content and the magnetic field on the magnetic and mechanical properties of the nanocomposite were studied in detail. Magnetite (Fe3O4) nanoparticles used for the ferrofluid preparation were prepared by the chemical co-precipitation method. Dioctyl phtalate (DOP)-based ferrofluid was prepared by the peptization technique. X-ray diffraction (XRD) was used to characterize the superparamagnetic behavior of the nanocomposite. A Universal tensometer was used to evaluate their mechanical properties. The results showed that the magnetization value of the nanocomposites increased as a function of ferrofluid concentration with all the samples showing superparamagnetic behavior. The mechanical studies showed that the tensile strength and elongation at break of the magnetic PVC nanocomposite were increased by the addition of ferrofluid and the applied magnetic field.
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Aristizábal-Fontal, Juan E., Farid B. Cortés, and Camilo A. Franco. "Viscosity reduction of extra heavy crude oil by magnetite nanoparticle-based ferrofluids." Adsorption Science & Technology 36, no. 1-2 (2017): 23–45. http://dx.doi.org/10.1177/0263617417704309.
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The main objective of this work is to synthesize and evaluate magnetite (Fe3O4) nanoparticle-based ferrofluids for reducing the viscosity of an extra heavy crude oil. The carrier fluid of the nanoparticles was synthesized using an engine lubricant recycled from the automotive industry and hexadecyltrimethylammonium bromide as a surfactant. Fe3O4 nanoparticles were synthesized by coprecipitation method. The effect of the concentration of nanoparticles in the viscosity reduction degree was determined for dosages between 0 and 50,000 mg/L. Different dosages of carrier fluid were evaluated between 0 and 10% v/v. The effects of the amount of brine emulsified, temperature, time, and shear rate were assessed. Overall, the results showed that viscosity and shear stress of extra heavy crude oil could be reduced up to 81 and 78% in the presence of ferrofluid, respectively. The rheological behavior of extra heavy crude oil in the presence and absence of ferrofluid was assessed by Cross, Ostwald-de Waele, and Herschel-Bulkley models.
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Petrenko, V. I., M. V. Avdeev, V. L. Aksenov, L. A. Bulavin, and L. Rosta. "Effect of Surfactant Excess in Non-Polar Ferrofluids Probed by Small-Angle Neutron Scattering." Solid State Phenomena 152-153 (April 2009): 198–201. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.198.
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The microstructure of ferrofluids (magnetite/oleic acid/benzene) with an excess of free oleic acid is investigated by small-angle neutron scattering (SANS). For such excess higher than 25 vol. % a sharp break in the stability of ferrofluids occurs followed by coagulation and precipitation. Below this value the influence of the surfactant excess on the stability of ferrofluids is insignificant; neither particle aggregation nor surfactant agglomeration is observed. The interaction of free acid molecules in the ferrofluids is compared with that in pure benzene solutions. A significant increase in the attraction is observed for acid molecules in the ferrofluids, which is related to the loss of magnetic fluids stability at high excess of acid.
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Ahmadi, R., and Madaah Hosseini. "A new approach for calculation of relaxation time and magnetic anisotropy of ferrofluids containing superparmagnetic nanoparticles." Journal of Mining and Metallurgy, Section B: Metallurgy 48, no. 1 (2012): 81–88. http://dx.doi.org/10.2298/jmmb110330004a.
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In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were characterized via TEM, XRD, VSM and PCS techniques and the results were used for the mentioned calculations.
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Shi, Di, Linlin Sun, Gujie Mi, Soumya Bhattacharya, Suprabha Nayar, and Thomas J. Webster. "Identifying Iron Oxide Based Materials that Can Either Pass or Not Pass through the in vitro Blood-Brain Barrier." MRS Proceedings 1621 (2014): 33–38. http://dx.doi.org/10.1557/opl.2014.198.
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ABSTRACTIn this study, an in vitro blood-brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). By comparing the permeability of FITC-Dextran at increasing exposure times in serum-free medium to such values in the literature, we confirm that the blood-brain barrier model was successfully established. After such confirmation, the permeability of five ferrofluid (FF) nanoparticle samples, GGB (ferrofluid synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this model. In addition, all the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen had better permeability to the blood-brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, magnetic nanomaterials, such as ferrofluids, that are less permeable to the blood brain barrier can be used to decrease neural tissue toxicity and magnetic nanomaterials with more permeable to the blood-brain barrier can be used for brain drug delivery.
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Mayer, Daniel. "An Approach to Measurment of Permeability/Permittivity Tensor of Ferrofluids." Journal of Electrical Engineering 66, no. 5 (2015): 292–96. http://dx.doi.org/10.2478/jee-2015-0048.
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Abstract The magnetic field acting on the ferrofluids causes microstructural conversions that result in a change of their permeability. For this physical phenomenon is referred to as field induced magnetism (FIMA). An experimental method is described for ferrofluids in this state to examine their permeability tensor. Also an analogous phenomenon is described also when there is a change of the ferrofluids permittivity. We call it field induced dielectric anisotropy (FIDA). The contribution describes the method of measuring of the permittivity tensor. It can be expected that the FIMA and FIDA of ferrofluids will find interesting applications in designing of various sensors, in measurement technology, in mechatronic and in other areas of practice.
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Amiri Roodan, Venoos, Jenifer Gómez-Pastora, Ioannis H. Karampelas, et al. "Formation and manipulation of ferrofluid droplets with magnetic fields in a microdevice: a numerical parametric study." Soft Matter 16, no. 41 (2020): 9506–18. http://dx.doi.org/10.1039/d0sm01426e.
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Integrated computational fluid dynamics and magnetics simulation is employed to analyze the effects of magnetic force on the formation and manipulation of ferrofluid droplets within a flowing non-magnetic continuous phase in a microfluidic device.