Journal articles: 'Ferrofluids'

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Hodenius, Michael A. J., Thoralf Niendorf, Gabriele A. Krombach, Walter Richtering, Thomas Eckert, Heiko Lueken, Manfred Speldrich, et al. "Synthesis, Physicochemical Characterization and MR Relaxometry of Aqueous Ferrofluids." Journal of Nanoscience and Nanotechnology 8, no. 5 (May 1, 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.

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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.

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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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Ganachari, Sharanabasava V., Veerabhadragouda B. Patil, Nagaraj R. Banapurmath, Manzoore Elahi M. Soudagar, Kiran Shahapurkar, Ashraf Elfasakhany, Mishal Alsehli, et al. "The Investigation of Mixed Ferrofluids Containing Iron Oxide nanoparticles and Microspheres." Advances in Materials Science and Engineering 2021 (December 9, 2021): 1–11. http://dx.doi.org/10.1155/2021/7616666.

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The aim of the present work is the synthesis and characterization of iron oxide (Fe3O4) nanoparticles. These nanoparticles are coated with oleic acid and polyvinyl butyral and mixed with microspheres and further developed ferrofluids with silicon oil. Studies of the performance of the nanoparticles in these ferrofluids with and without coating agents were carried out. The nanoparticles were synthesized using the chemical co-precipitation technique and coated with oleic acid and polyvinyl butyral, and it further mixed with microsphere ferrofluids and developed using silicon oil. The prepared Fe3O4 nanoparticles and their coated forms of oleic acid and polyvinyl butyral were mixed with microspheres; furthermore, ferrofluids were developed with silicon oil. All forms of these ferrofluids are characterized for morphology and phase purity (SEM, XRD, and FTIR). The iron oxide (Fe3O4) nanoparticles have shown different magnetic properties, differentiating macroscopic iron oxide in suspended particles. The ratio of surface to volume increases along with the decrease in atomic size, essential for assessing the surface morphological properties. The magneto-rheological (MR) fluids were determined, and shear stress of Expancel microsphere mixed iron oxide nanoparticle with and without them was found almost equal. However, the ferrofluid with PVB coated nanoparticles and microspheres emerged as a stable rheological ferrofluid, sustaining high shear stress and low viscosity with increasing shear rate. Also, shear rates up to 650 s−1 have been observed, showing very high shear stress withstanding capacity. The stability and performance of the magnetic colloidal ferrofluids depend on the thermal contribution and the balance between attractive/repulsive interactions.

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Li, Wangxu, Zhenggui Li, Wei Han, Yibin Li, Shengnan Yan, Qin Zhao, and Fang Chen. "Measured viscosity characteristics of Fe₃O₄ ferrofluid in magnetic and thermal fields." Physics of Fluids 35, no. 1 (January 2023): 012002. http://dx.doi.org/10.1063/5.0131551.

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The rheological mechanisms governing the viscosity characteristics of nano-ferrofluids are very complicated; there is no universal theoretical treatment that explains the dependence of the ferrofluid viscosity on the flow, magnetic, and temperature fields. Thus, determining the viscosity characteristics of ferrofluids in various physical fields is of great theoretical and practical significance. This study explores experimentally the relationship between the ferrofluid viscosity and temperature, magnetic-field strength, and magnetic-field inclination. A special experimental bench on which the magnetic field and temperature can be precisely controlled is designed and constructed. It is found that the ferrofluid viscosity is negatively correlated with temperature. Increasing the percentage of the magnetic particles in the ferrofluid increases the viscosity at any given temperature. Ferrofluids are shown to exhibit the magnetic–viscosity phenomenon: under the action of a magnetic field, the viscosity increases until a magnetic viscosity saturation value is reached. Increasing the magnetic field inclination can aggravate the magnetic–viscosity phenomenon but does not change the saturation value. Contrary to the naïve Hall theory but in agreement with earlier phenomenological studies, the magneto-viscous effect is greater with horizontal than with vertical magnetic fields. Simultaneous exposure to temperature and magnetic fields is investigated; the two fields appear to act independently on the viscosity. The magnetic viscosity saturation value is not affected by temperatures in the range of 30–60 °C.

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Zuhroh, Sayyidati, Ahmad Taufiq, Arif Hidayat, and Nasikhudin. "Exploration of the Antifungal Activity of Zn0.2Fe2.8O4/ Ag Ferrofluids with Double Surfactants and Sunflower Seed Oil as Dispersion Medium." Key Engineering Materials 940 (January 30, 2023): 65–71. http://dx.doi.org/10.4028/p-bmrq2p.

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Candidiasis is an infection caused by the fungus C. albicans. Ferrofluid Zn0.2Fe2.8O4/Ag is the best candidate to overcome the problem of infection caused by this fungus. In addition to the safe ingredients used, its ability to create ROS and maintain stability has the potential to be an excellent antifungal agent. The purpose of this study was to create a new ferrofluid with double surfactants for the antifungal C. albicans. Zn0.2Fe2.8O4/Ag ferrofluids were synthesized using a bottom-up method, starting from the synthesis of Zn0.2Fe2.8O4 nanoparticles, Zn0.2Fe2.8O4/Ag nanocomposites, to the synthesis of Zn0.2Fe2.8O4/Ag ferrofluids. Zn0.2Fe2.8O4/Ag powder was characterized using XRD and SEM to determine the particle structure and morphology. Meanwhile, Zn0.2Fe2.8O4/Ag ferrofluids were characterized using FTIR and antifungal activity tests to determine the functional group and zone of inhibition against the growth of the fungus C. albicans. The results of the characterization analysis showed that Zn0.2Fe2.8O4/Ag nanoparticles had good crystallinity, with a crystallite size of Zn0.2Fe2.8O4/Ag of 11.32 nm and an Ag crystallite size of 7.00 nm. SEM characterization showed that Zn0.2Fe2.8O4/Ag nanoparticles had agglomeration with the average particle size distribution of 443 nm. The functional groups detected by FTIR confirmed the success of the ferrofluid synthesis Zn0.2Fe2.8O4/Ag where spinel functional groups, olefin groups, and functional groups S=O were formed. The results of the antifungal activity test showed that Zn0.2Fe2.8O4/Ag ferrofluids were relatively active as an antifungal agent, with a diameter of the C. albicans growth inhibition zone of 9.63 mm.

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Saputro, Rosy Eko, Ahmad Taufiq, Sunaryono, Nurul Hidayat, and Arif Hidayat. "Effects of DMSO Content on the Optical Properties, Liquid Stability, and Antimicrobial Activity of Fe3O4/OA/DMSO Ferrofluids." Nano 15, no. 05 (May 2020): 2050067. http://dx.doi.org/10.1142/s1793292020500678.

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Fe3O4 nanoparticles were synthesized through a sonochemical method and were subsequently investigated by X-ray diffraction (XRD), which showed that the phase obtained was Fe3O4 with the most intense peak at 2[Formula: see text] of 35.5∘. The particle size of the Fe3O4 nanoparticles was 11.4[Formula: see text]nm. The dried ferrofluids containing Fe3O4 as a filler, oleic acid (OA) and dimethyl sulfoxide (DMSO) as surfactants tended to be amorphous. Scanning electron microscopy (SEM) observation of the Fe3O4 nanoparticles revealed agglomeration, and the dried ferrofluids morphology showed excellent dispersion. The constituent elements of both the Fe3O4 nanoparticles and the Fe3O4/OA/DMSO ferrofluids were identified through energy-dispersive X-ray spectroscopy to be Fe, O and C. Fourier transform infrared (FTIR) investigation revealed functional groups of the Fe3O4/OA/DMSO ferrofluids constituent Fe3O4 as the filler, OA and DMSO as surfactants, and olive oil as a dispersant. The absorbance of the samples was characterized by UV–Vis spectrophotometry, and the results were used to calculate the energy gap of the Fe3O4/OA/DMSO ferrofluids ranged from 2.20[Formula: see text]eV to 2.45[Formula: see text]eV. Through the absorbance measurements, the optical properties of Fe3O4/OA/DMSO ferrofluids were evaluated on the basis of their refractive indices, which ranged from 2.86 to 3.02. The stability of the Fe3O4/OA/DMSO ferrofluids was characterized by transmittance data collected for 12[Formula: see text]h, and excellent stability was obtained, as indicated by a relatively stable transmittance. Last, the antimicrobial activity of the Fe3O4/OA/DMSO ferrofluids was assessed through the diffusion method; the results showed that increasing DMSO volume resulted in greater ferrofluid antimicrobial activity.

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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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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 (March 1, 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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Lavrova, Olga, Viktor Polevikov, and Sergei Polevikov. "NUMERICAL MODELLING OF MAGNETIC SHIELDING BY A CYLINDRICAL FERROFLUID LAYER." Mathematical Modelling and Analysis 24, no. 2 (February 5, 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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Chandrashekara, N. P., and S. Rajashree. "Effect of synchronized and unsynchronized boundary temperature modulation on the regulation of heat transfer in a ferrofluid with Fe₃O₄ nanoparticles." Journal of Physics: Conference Series 2748, no. 1 (April 1, 2024): 012018. http://dx.doi.org/10.1088/1742-6596/2748/1/012018.

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Abstract Linear and non-linear analysis was carried out for a temperature modulated Rayleigh-Bénard ferroconvection (RBF) problem using Lorenz and Ginzburg-Landau models. The parallel and horizontal plates of infinite extension enclosing the ferrofluid (with nanosized Fe3O4 - magnetite), is cooled from the top and heated from the bottom and is exposed to an exterior static magnetic field which manipulates the flow of a ferrofluid. The Lorenz model in its linear form manifests the stationary Rayleigh number expression, whereas the nonlinear form of the model leads to Ginzburg-Landau equation determining the amplitude, which aids to quantify the amount of heat transfer in ferrofluids with the effect of temperature modulation. The influence of various parameters like Lewis number, concentration Rayleigh number, ferromagnetic parameters on the onset of ferroconvection has been discussed in detail using marginal stability curves. On the other hand, the effect of different parameters like ferro-nanoparticle volume fraction, modulation frequency, phase angle, temperature modulation on heat transfer in ferrofluids has been analyzed and represented graphically.

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ZĄBEK, Daniel, Andrzej GRZEBIELEC, Luca CMOK, Patricija HRIBAR BOŠTJANČIČ, and Alenka MERTELJ. "Experimental analysis of the stability of ferrofluids based on Iron Oxide powder." Inżynieria Bezpieczeństwa Obiektów Antropogenicznych, no. 2 (June 30, 2021): 1–6. http://dx.doi.org/10.37105/iboa.108.

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Ferrofluids most often consist of three components, they are: solid particles, the liquid in which they are dissolved and a substance that is supposed to prevent sedimentation - called surfacant. The biggest problem with ferrofluids is their stability. Mixtures in which one of the phases is a solid phase have a natural tendency to sedimentation. As a result, physical properties change during the use of such materials. As part of the research, it was decided to check which ferrofluid composition would be most resistant to continuous evaporation and condensation processes. Three different mixtures were analyzed. As a result of the experiment it was found that the best behavior was mixture of: iron-oxide with n-heptane and fatty acid as surfacant.

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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 (September 12, 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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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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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.

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Nargund, Achala, and Asha C. S. "Analysis of flow of polar and non polar incompressible ferrofluids." JOURNAL OF ADVANCES IN PHYSICS 10, no. 2 (August 30, 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 polarÂ ferrofluids. Velocity is obtained without pressure gradient for polar fluid and with pressure gradient forÂ non polar fluid. The solution of the spin velocity is found in terms of applied magnetic field and magneticÂ flux density for polar fluid. Shear stress is calculated for both polar and non polar ferrofluid.

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Safarik, I., J. Prochazkova, E. Baldikova, M. Timko, P. Kopcansky, M. Rajnak, N. Torma, and K. Pospiskova. "Modification of Diamagnetic Materials Using Magnetic Fluids." Ukrainian Journal of Physics 65, no. 9 (August 26, 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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Zabek, Daniel, Andrzej Grzebielec, Luca Cmok, Patricija Hribar Boštjančič, and Alenka Mertelj. "Two-Phase Ferrofluid Systems: Surfactants and Thermal Properties of Iron Oxide Nanofluids for Condensation." E3S Web of Conferences 137 (2019): 01015. http://dx.doi.org/10.1051/e3sconf/201913701015.

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Evaporation heat transfer with ferrofluids has the potential to improve heat and mass transfer compared to conventional two-phase systems. The ferromagnetic nanoparticles which control the rheology and heat transfer properties of the ferrofluid, must be coated with a dispersing agent, also referred to as a surfactant, to prevent particle agglomeration. This paper compares ferromagnetic iron-oxide particles coated with fatty acid, polymeric and hydrophobic surfactants after undergoing evaporation and condensation. The outcome was measured by assessing the dispersion of the ferrofluid after condensation. The fatty acid surfactants demonstrated the best dispersion after condensation proving temperature stability.

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Altmeyer, Sebastian. "Ferrofluids." Scholarpedia 15, no. 11 (2020): 55163. http://dx.doi.org/10.4249/scholarpedia.55163.

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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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Ajith, K., Archana Sumohan Pillai, I. V. Muthu Vijayan Enoch, and A. Brusly Solomon. "Thermal Conductivity Analysis of Ethylene Glycol/H2O- Based MgFe2O4 Ferrofluid." Materials Science Forum 1048 (January 4, 2022): 83–88. http://dx.doi.org/10.4028/www.scientific.net/msf.1048.83.

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The current investigation aims to synthesize MgFe2O4 magnetic nanoparticle and measure the thermal conductivity of MgFe2O4 ferrofluid. Prepared MgFe2O4 nanoparticle's structural characterization, the concentration of constituents, and surface morphology were analyzed using XRD, EDAX, and TEM respectively. This study also analyses the influence of magnetic flux on the thermal conductivity of MgFe2O4/ EG: H2O (60:40) based ferrofluids formed by the two-step method. Thermal conductivity of ferrofluid measured at different volume fractions (ranging from 0.01% to 0.20%) show that thermal conductivity augmented with an escalation in volume fraction and the highest enhancement of 10.32% was reached at 0.20% volume fraction. Results indicate that the applied magnetic flux improves the thermal conductivity of ferrofluid from 10.32% to 14.75% at 0.20% volume fraction and 350 Gauss Magnetic flux.

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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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Bognár, Gabriella, and Krisztián Hriczó. "Numerical Simulation of Water Based Ferrofluid Flows along Moving Surfaces." Processes 8, no. 7 (July 13, 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.

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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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Karpets, M., M. Rajnak, O. Ivankov, K. Paulovicova, M. Timko, P. Kopcansky, and L. Bulavin. "Small-Angle Neutron Scattering Study of Transformer Oil-Based Ferrofluids." Ukrainian Journal of Physics 65, no. 8 (July 30, 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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Lavrova, Olga, and Viktor Polevikov. "NUMERICAL STUDY OF THE SHIELDING PROPERTIES OF A FERROFLUID TAKING INTO ACCOUNT MAGNITOPHORESIS AND PARTICLE INTERACTION." Mathematical Modelling and Analysis 27, no. 1 (February 7, 2022): 161–78. http://dx.doi.org/10.3846/mma.2022.14660.

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Shielding properties of a cylindrical thick-walled ferrofluid layer that protects against externally applied uniform magnetic fields are numerically investigated. We take into account the diffusion of magnetic nanoparticles in the ferrofluid with magnetic dipole-dipole, steric and hydrodynamic interactions between particles. Permeability of the ferrofluid is considered to be dependent on the magnetic-field strength and the particle concentration. A combined method of finite differences and boundary elements is applied to solve a nonlinear transmission problem of magnetostatics in the whole space, augmented by nonlinear algebraic equations based on the mass transfer equation for magnetic nanoparticles in ferrofluids. Numerical experiments revealed that the diffusion of particles has negligible influence on the shielding properties at weak and strong intensities of the applied magnetic field when comparing with the results of computations for a uniform particle distribution.

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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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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.

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29

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 (August 16, 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.

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Chen, Fang, Xiaobing Liu, Zhenggui Li, Shengnan Yan, Hao Fu, and Zhaoqiang Yan. "Investigation of the Rheological Properties of Zn-Ferrite/Perfluoropolyether Oil-Based Ferrofluids." Nanomaterials 11, no. 10 (October 9, 2021): 2653. http://dx.doi.org/10.3390/nano11102653.

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The rheological properties of ferrofluids are related to various applications, such as sealing and loudspeakers, and have therefore attracted widespread attention. However, the rheological properties and their influence on the mechanisms of perfluoropolyether oil (PFPE oil)-based ferrofluids are complicated and not clear. Here, a series of PFPE oil-based ferrofluids were synthesized via a chemical co-precipitation method, and their rheological properties were revealed, systematically. The results indicate that the prepared Zn-ferrite particles have an average size of 12.1 nm, within a range of 4–18 nm, and that the ferrofluids have excellent dispersion stability. The activity of the ferrofluids changes from Newtonian to non-Newtonian, then to solid-like with increasing w from 10 wt% to 45.5 wt%, owing to their variation in microstructures. The viscosity of the ferrofluids increases with increasing Mw (the molecular weight of base liquid PFPE oil polymer), attributed to the increase in entanglements between PFPE oil molecules. The magnetization temperature variation of Zn-ferrite nanoparticles and viscosity temperature variation of PFPE oil together contribute to the viscosity temperature change in ferrofluids. The viscosity of the ferrofluids basically remains unchanged when shear rate is above 50 s−1, with increasing magnetic field strength; however, it first increases and then levels off when the rate is under 10 s−1, revealing that the shear rate and magnetic field strength together affect viscosity. The viscosity and its alteration in Zn-ferrite/PFPE oil-based ferrofluids could be deduced through our work, which will be greatly significant in basic theoretical research and in various applications.

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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 (September 28, 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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32

Suciu, Barenten. "Influence of the Drop Volume and Applied Magnetic Field on the Wetting Features of Water-based Ferrofluids." European Journal of Engineering and Technology Research 5, no. 9 (September 28, 2020): 1110–16. http://dx.doi.org/10.24018/ejeng.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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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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34

Clark, Noel A. "Ferromagnetic ferrofluids." Nature 504, no. 7479 (December 2013): 229–30. http://dx.doi.org/10.1038/504229a.

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35

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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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 (April 27, 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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37

Szczech, Marcin, and Wojciech Horak. "Tightness testing of rotary ferromagnetic fluid seal working in water environment." Industrial Lubrication and Tribology 67, no. 5 (August 10, 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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38

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 (May 8, 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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BORIN, DMITRY, and STEFAN ODENBACH. "RHEOLOGY OF NOVEL FERROFLUIDS." International Journal of Modern Physics B 25, no. 07 (March 20, 2011): 963–69. http://dx.doi.org/10.1142/s0217979211058511.

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The progress in the synthesis of new magnetic nanoparticles and agglomerates stimulates the development of novel ferrofluids with enhanced rheological properties. In the current work ferrofluids based on Co-nanoplatelets and clustered iron oxide nanoparticles have been considered. Steady-shear experiments and yield stress measurements of these ferrofluids have been performed using rotational rheometry.

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Rezaeian, Masoud, Moein Nouri, Mojtaba Hassani-Gangaraj, Amir Shamloo, and Rohollah Nasiri. "The Effect of Non-Uniform Magnetic Field on the Efficiency of Mixing in Droplet-Based Microfluidics: A Numerical Investigation." Micromachines 13, no. 10 (October 2, 2022): 1661. http://dx.doi.org/10.3390/mi13101661.

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Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics on the efficiency of the mixing process inside droplets. When different concentrations of ferrofluids are affected by a constant magnetic field, there is no significant change in mixing efficiency. As the magnetic field intensifies, the magnetic force makes the circulation flow inside the droplet asymmetric, leading to chaotic advection, which creates a flow that increases the mixing efficiency. The results show that the use of magnetic fields is an effective method to enhance the mixing efficiency within droplets, and the efficiency of mixing increases from 65.4 to 86.1% by increasing the magnetic field intensity from 0 to 90 mT. Besides that, the effect of ferrofluid’s concentration on the mixing efficiency is studied. It is shown that when the concentration of the ferrofluid changes from 0 to 0.6 mol/m3, the mixing efficiency increases considerably. It is also shown that by changing the intensity of the magnetic field, the mixing efficiency increases by about 11%.

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Ryapolov, Petr A., and Eugene B. Postnikov. "Mittag–Leffler Function as an Approximant to the Concentrated Ferrofluid’s Magnetization Curve." Fractal and Fractional 5, no. 4 (September 30, 2021): 147. http://dx.doi.org/10.3390/fractalfract5040147.

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In this work, we show that the static magnetization curve of high-concentrated ferrofluids can be accurately approximated by the Mittag–Leffler function of the inverse external magnetic field. The dependence of the Mittag–Leffler function’s fractional index on physical characteristics of samples is analysed and its growth with the growing degree of system’s dilution is revealed. These results provide a certain background for revealing mechanisms of hindered fluctuations in concentrated solutions of strongly interacting of the magnetic nanoparticles as well as a simple tool for an explicit specification of macroscopic force fields in ferrofluid-based technical systems.

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Sammaiah, Arukali, Qingwen Dai, Wei Huang, and Xiaolei Wang. "Synthesis of GO-Fe3O4-based ferrofluid and its lubrication performances." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, no. 7 (October 10, 2019): 1160–67. http://dx.doi.org/10.1177/1350650119882198.

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As a thin material with a lamellar structure, graphene oxide (GO) may extend the already superior tribological properties of ferrofluids. For this purpose, magnetic Fe3O4 nanoparticles were fabricated on the GO surface with different compositions by the co-precipitation method. Then, the GO-Fe3O4 nanohybrids coated with a surfactant were dispersed in paraffin oil to achieve stable ferrofluids. The tribological results demonstrated that compared with paraffin oil, friction coefficient reduced by 19.4% and 25.8–35.5% when lubricated with ferrofluids containing 0.5 wt% of Fe3O4 nanoparticle and GO-Fe3O4 nanohybrids, respectively. The results also indicated that nanohybrids with the higher content of GO exhibited better lubrication behaviors. It can be concluded that the introduction of GO helps to further promote the lubricity of traditional Fe3O4-based ferrofluids. The excellent tribological behaviors of GO-Fe3O4-based ferrofluids were ascribed to the triboflim and the synergistic effects of GO and Fe3O4.

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Socoliuc, V., M. V. Avdeev, V. Kuncser, Rodica Turcu, Etelka Tombácz, and L. Vékás. "Ferrofluids and bio-ferrofluids: looking back and stepping forward." Nanoscale 14, no. 13 (2022): 4786–886. http://dx.doi.org/10.1039/d1nr05841j.

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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 (June 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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45

García-Ortiz, José Hermenegildo, and Francisco José Galindo-Rosales. "Extensional Magnetorheology as a Tool for Optimizing the Formulation of Ferrofluids in Oil-Spill Clean-Up Processes." Processes 8, no. 5 (May 17, 2020): 597. http://dx.doi.org/10.3390/pr8050597.

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In this study, we propose a new way of optimising the formulation of ferrofluids for oil-spill clean-up processes, based on the rheological behaviour under extensional flow and magnetic fields. Different commercial ferrofluids (FFs), consisting of a set of six ferrofluids with different magnetic saturation and particle concentration, were characterised in a Capillary Break-Up Extensional Rheometer (CaBER) equipped with two magnetorheological cells that allow imposing a homogeneous and tunable magnetic field either parallel or perpendicular to the flow direction. The filament thinning process with different intensities and orientation of the magnetic field with respect to the flow direction was analysed, and the results showed that the perpendicular configuration did not have a significant effect on the behaviour of the ferrofluids, as in shear magnetorheometry. However, the parallel configuration allowed to determine that the formulation of ferrofluids for oil-spill cleaning processes should consist of a 4% vol concentration of magnetic nanoparticles with a magnetic saturation of M s > 20 mT.

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46

Mayer, Daniel. "An Approach to Measurment of Permeability/Permittivity Tensor of Ferrofluids." Journal of Electrical Engineering 66, no. 5 (September 1, 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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Che Rosli, Ahmad Najmi Naqiuddin, Muhamad Alias Md. Jedi, Wan Mohd Faizal Wan Mahmood, and Mostafa S. Shadloo. "Thermodynamic Properties of Ferrofluid: Preparation, Stability and Statistical Mechanics." Jurnal Kejuruteraan 36, no. 3 (May 30, 2024): 957–64. http://dx.doi.org/10.17576/jkukm-2024-36(3)-10.

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Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. For such fluids, the problem arises in calculating thermal conductivity, viscosity, and thermodynamic properties on nanoparticles and ferrofluids. Thus, the main objective is to determine thermal conductivity and viscosity for ferro-nanoparticles and ferrofluids. For this study, the ZnO and Fe3O4 are checked for mechanical properties such as SEM, TEM and XRD. Then, being suspended into the diesel engine oil SAE-50 as base fluid and surfactant, Triton-100, in preparation of two-step method. Ferrofluids are prepared for 0.1%, 0.4% & 0.7% w/v and stability of nanofluids are being observed for 5 days. From the results obtained experimentally, the nanoparticles were found to be in good stability as no coagulate occur. This is because the EDLRF acts as the opposite to Van der Waals attractive force which separates the particles from each other. Finally, the thermal conductivity and viscosity for ferro-nanoparticles and ferrofluids were successfully obtained and demonstrated. Statistical mechanics are then discussed to calculate the properties of ferrofluids. The analytical results from statistical mechanics are potentially be used to compare with the experiment data.

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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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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 (October 6, 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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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.

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Journal articles on the topic 'Ferrofluids'

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