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A ferrofluid drop located on a horizontal plane and covering a vertical current-carrying conductor under the action of a magnetic field generated by the conductor and gravity is considered. The numerical study is based on a mathematical model of equilibrium states, consisting of equations for the free-surface shape of the ferrofluid drop and equations for the concentration of interacting magnetic nanoparticles inside the ferrofluid. The computational algorithm is organized as an iterative coupling between the finite-difference approximation of the free-surface and the Newton's method for the concentration equations formulated on an a-posteriori adaptive mesh, representing the discrete free-surface. Numerical results predict that the interactions between magnetic nanoparticles have little effect on the equilibrium free-surface shapes in weak magnetic fields but lead to a stronger shape elongation in moderate magnetic fields when compared to simulations with diffusion of non-interacting particles. Simulations have shown a sharp transition from drop-like shapes to sheath-like coverage of the conductor for a ferrofluid drop of large volume at different contact angles. [ABSTRACT FROM AUTHOR]

The paper deals with a theoretical study of the magnetoviscous effect in polydisperse ferrofluids. A two-fractional model of colloid consisting of relatively large and small particles is studied. The model is based on the idea that the magnetoviscous effect is determined by chain-like aggregates formed by large particles. The effect of the small particle fraction is determined by two factors: (i) the magnetic interaction between large and small particles, which leads to a reduction of the chain length and weakening of the fluid magnetoviscosity, (ii) the steric interaction between small and large particles, which enlarges the chain length, therefore, enhances this effect. The resulting effect is determined by the ratio of the sizes of large and small particles. [ABSTRACT FROM AUTHOR]

In industrial processes such as the paper production, reservoir engineering and thermal retrieval process, combined Soret and Dufour effects are involved. Also, the Soret-Dufour effect has been used in the chemical industry for detachment, purification, and radioactive nuclear waste material. Therefore, a mathematical model of Soret-Dufour effects in a Casson fluid flow caused by a shrinking sheet is presented in this paper. This model is subjected to an inclined magnetic field, along with the exponential variations of the variables at the sheet, i.e. velocity, temperature, and concentration. Ordinary differential equations for momentum, energy, and concentration are solved numerically using the bvp4c MATLAB program. At the end of the calculations, the profiles of velocity, temperature and concentration are displayed. In addition, the skin friction coefficient, the local Nusselt number and the local Sherwood number are also considered. Numerical results of velocity, temperature, and concentration profiles, together with the skin friction coefficient, local Nusselt number and local Sherwood number are shown in the form of tables and graphs. The numerical results show that the skin friction coefficient and the local Sherwood number decrease, whereas the temperature profile and the local Nusselt number for the first solution increase with the increment of the Soret number. Velocity and concentration profiles decrease with the increment of the Dufour number. [ABSTRACT FROM AUTHOR]

In this paper, processes of dissipation of disturbances of pressure and velocity in a magnetic fluid layer are experimentally studied. It is shown that the introduction of multi-layer carbon nanotubes (MCNT) up to 2wt.% into a magnetic fluid substantially increases the dissipation of disturbances due to increasing viscous friction and elastic properties of multilayer carbon nanotubes. [ABSTRACT FROM AUTHOR]

The present article describes a numerical strategy for the estimation of the shear coefficient of spin viscosity for a ferrofluid sample confined to a cylindrical container and exposed to the effect of an external rotating magnetic field with a low amplitude and frequency. As far as we know, there are no experimental measurements of such coefficient. Furthermore, the few analytical values reported differ in several orders of magnitude. First, we describe briefly the mathematical model of the system and its numerical solution. Then, the definition of the direct and inverse problems is given as a part of the methodology for estimating such coefficient. Finally, we solve the inverse problem using simulated measurements and two global optimization algorithms. We generate this type of measurements by adding white Gaussian noise signals to the numerical solution of the ferrohydrodynamic mathematical model. Several noise levels in the range of 10 to 40 dB were used to increase the number of scenarios for validation purpose. Results showed an excellent agreement between the estimated values and those used in the numerical solution of the mathematical model. A statistical analysis revealed a normal distribution that was dependent on the noise level. This variation did not affect the results, but showed instead the validity of the proposed method. Additionally, this strategy stands as a computational tool for validating experimental results of the future in situ measurements. [ABSTRACT FROM AUTHOR]

Experimental results on the absorption of ultrasound by a magnetic fluid in a rotating magnetic field have been obtained for the first time. It is shown that the lag of the angular dependence of the ultrasonic absorption coefficient by a magnetic fluid in the range of magnetic field rotation frequencies fH =0.056 - 280mHz at T =295K is not observed within the limits of observational errors. Similar results were observed for both low-viscosity and high-viscosity magnetic fluids. [ABSTRACT FROM AUTHOR]

Exact solutions of the Smirnov–Chukbar–Zaburdaev equation (ESCZ) have been obtained for the first time using the variable separation method. The solutions describe acoustic-type nonlinear movements in a lattice of electronic vortices in plasmas [ABSTRACT FROM AUTHOR]

The article presents results of an experimental study on damping an oscillatory system with incomplete sealing of the air cavity by a magnetic fluid. The sealing degree varies due to the process of gas pumping through capillaries of different radii. The proposed relaxation theory of a capillary oscillating gas flow predicts abnormally large values of the damping coefficient and almost complete damping of the oscillatory system with a magneto-fluid inertial element. The obtained data are of applied importance. [ABSTRACT FROM AUTHOR]

This article presents results of numerical simulations that describe the velocity profiles of the continuous circular motion of a ferrofluid in a cylindrical vessel generated by the presence of an external magnetic and rotating field of high strength and frequency. The partitioned solution of the ferrohydrodynamic equations was derived by the means of finite differences separately or the hydrodynamic problem and for the magnetic one. The results obtained show the saturation of velocity profiles from a particular value of the magnetic field strength, depending on the characteristics of ferrofluid samples. Potentially these results can be applied for the development of numerical tools related to the transportation processes of materials with intrinsic or created magnetic properties and in the presence of high strength rotating magnetic fields, where the Langevin parameter is much greater than unity. [ABSTRACT FROM AUTHOR]

In the "shallow water" approximation, the problem of propagation of non-linear ring waves with relatively small amplitudes in a thin layer of paramagnetic fluid with variable depth exposed to a non-uniform magnetic field is considered. The equations of motion that have a variational feature are derived. An exact method of solution for the problem with weak discontinuity has been developed. The problem with a weak shock wave is solved as an approximation to this solution. An example of wave propagation at the equilibrium initial state is considered. [ABSTRACT FROM AUTHOR]

Assuming the magnetic fluid a homogeneous dipole gas implies its magnetization description by the Langevin law derived for an ensemble of molecules of paramagnetic gas. In the paper, an approach used in the literature and aimed at finding the regularities of the magnetization process of paramagnets and of the possibilities of its routine application to characterize similar processes in magnetic colloids is critically analyzed. Basing on the results of experimental studies of the temperature and concentration dependences of magnetic susceptibility, effective fields in such media have been calculated and the conditions for applying models typical of molecular paramagnets have been found. [ABSTRACT FROM AUTHOR]

A study on the shape and stability of semi-bounded magnetic fluid drops on a horizontal plate exposed to an inclined magnetic field as well as the shape of an air bubble in a horizontal flat channel filled with a magnetic fluid is discussed. [ABSTRACT FROM AUTHOR]

Deformations of a variable volume of magnetic fluid around a spherical body with a magnetizable material exposed to a uniform applied magnetic field are studied experimentally and theoretically. The possibility to develop a device for dosing fluids using the lifting of the magnetic fluid surface along a ferromagnetic body in a uniform magnetic field is shown. [ABSTRACT FROM AUTHOR]

In this paper, a force acting on a non-magnetic body immersed into a magnetic fluid exposed to an external uniform magnetic field has been studied experimentally. We consider the case when the ponderomotive force is caused by the non-uniform demagnetizing field of the fluid. Analysis of the results has revealed that the ponderomotive force depends on the displacement of an aluminum cylinder relative to the cavity center and on the external field strength. The ponderomotive force increases with the field strength, reaches its maximum value near the borders of the cavity with a magnetic fluid, where the highest field non-uniformity is provided which is always equal to zero at the cavity center. [ABSTRACT FROM AUTHOR]

In this paper, structures and related mechanical properties of some tool steels subjected to quench-cooling in a magnetic fluid with a different concentration of the magnetic phase under a steady magnetic field of different intensity are studied. The goal of the research is to find out how the cooling modes of steel samples, found in previously published papers, in a magnetic fluid subject to magnetic fields of varying intensity affect the steel structure. The possibility of controlled quenching in a magnetic fluid is determined by the dependence of the cooling intensity on the fluid composition, on the magnitude and degree of the magnetic field uniformity near the cooled surface. Varying cooling intensity determines different mechanisms of phase transformations in steel in the quenching process. The possibility to obtain a significant variety of structural components in quenched steel samples has been experimentally proved. For the quenching process, only one magnetic fluid was used which varied the intensity of the applied external magnetic field. It is known that traditional quenching allows obtaining different structural components in hardening steels only by complex selection of different quenching media. [ABSTRACT FROM AUTHOR]

The paper gives an assessment of the viscosity increment (magnetoviscous effect) in a thin near-wall layer of a column of magnetic fluid which oscillates in a tube when applying a strong transverse magnetic field. The value of the magnetoviscous effect was calculated using a formula derived from two different theoretical approaches and applied to previously published experimental results of complex measurements of the oscillation frequency and saturation magnetization of a magnetic fluid under the assumption that there is no viscosity field dependence. [ABSTRACT FROM AUTHOR]

The article presents results of an experimental study of capturing, transporting and subsequent splitting of an air cavity into bubbles by a magnetic fluid in the zone of 'magnetic vacuum' of an annular magnet. The study was carried out using the acoustomagnetic method. The captured air cavity is characterized by a decreased elasticity coefficient, and the resulting bubbles are relatively large in size. [ABSTRACT FROM AUTHOR]

The influence of Brownian diffusion and magnetophoresis, which are followed by phase transition, on the characteristics of a stationary plane Couette flow of magnetic fluid in a non-uniform magnetic field is discussed. The phase transition conditions in magnetic fluids are assumed as a natural restriction to the particle concentration increase in a non-uniform magnetic field. Profiles of the particles' concentration are calculated, and dependences of the volume magnetic force and of the viscous force are established. [ABSTRACT FROM AUTHOR]

In this numerical study, we applied the linear stability theory to investigate the onset of penetrative convection due to purely internal heating in a thin magnetic nanofluid layer saturating a porous medium. A model that has the combined effect of Brownian diffusion, thermophoresis, magnetophoresis and Darcy's law is considered. The Chebyshev pseudospectral method and QZ algorithm are applied to solve the resulting eigenvalue problem. The numerical results are derived for various combinations of boundary conditions on impermeable, conducting, free and with constant heat flux surfaces for waterand ester-based magnetic nanofluids. The results show that the onset of penetrative convection is advanced with an increase in Lewis number (Le), concentration Rayleigh number (Re), modified diffusivity ratio (NA), but opposite is the case with an increase in value of the permeability (K), Langevin parameter (αL), porosity (∈), width of the magnetic nanofluid layer (d), modified diffusivity ratio (N'A). Moreover, it is also observed that the modified particle density increment (NB) does not significantly affect the stability of the system. [ABSTRACT FROM AUTHOR]

An experiment on the propagation of a plane-polarized SHF-ranged electromagnetic wave in magnetic colloids containing magnetite particles was performed. It is found that the action of the magnetic field aligned with the wave on such media results in turning (rotation) of the wave polarization plane (Faraday effect). Moreover, this effect is pronounced only at exceeding a certain critical volume concentration of magnetite. Some peculiarities of the phenomenon have been found in structurally ordered magnetic colloids which could be attributed to the alteration of their structure under the magnetic field action. [ABSTRACT FROM AUTHOR]

A method to produce magnetite from the precipitates of iron hydroxide extracted from groundwater at the iron removal stations is considered. It is shown that as a result of the reduction process, with the use of carbon black waste, it is possible to produce magnetite with parameters similar to those of natural magnetite. [ABSTRACT FROM AUTHOR]

A theoretical model has been developed to describe the weak-field growth of the magnetic susceptibility of inverse ferrofluid emulsion provided the interdroplet interaction is taken into account. The presented mean-field approach predicts a nonlinear dependence of the initial magnetic susceptibility on the droplet concentration and provides a good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The paper deals with an experimental study of the emulsion whose dispersion medium is a magnetic fluid, whereas the disperse phase is formed by water. It is demonstrated that chain aggregates are formed from the disperse phase drops under the action of an external magnetic field. The change of the emulsion microstructure affects its electrical properties. The emulsion specific electrical conductivity was measured. It was found that under relatively weak external magnetic fields the emulsion electrical conductivity may change several times. [ABSTRACT FROM AUTHOR]

Spectral dependences of the complex refractive index of kerosene-based magnetic fluids are measured by an ellipsometric method. The concentration dependence of the real part of the refractive index is characterized by an effective medium approximation. The influence of light absorption and scattering on the extinction spectra of magnetic fluids is discussed. [ABSTRACT FROM AUTHOR]

Small steady-state deformational oscillations of a drop of magnetic fluid in a nonstationary uniform magnetic field are theoretically investigated. The drop is suspended in a magnetic fluid immiscible with the drop fluid. The Reynolds number is so small that inertia can be neglected. The variation of the magnetic field is so slow that the approximation of quasi-stationary magnetic field and the approximation of quasi-steady flow may be used. [ABSTRACT FROM AUTHOR]

Boiling of a magnetic fluid is of interest in the hardening steel technology for nondeformation cooling with a given distribution of the current and stresses. The character of the heat transfer during boiling essentially depends on the formation, growth and detachment of the vapor bubbles. In this paper, we investigate mechanisms of the magnetic field influence on the kinetic parameters of the bubble boiling process in a magnetic fluid, in particular, on the formation frequency of vapor bubbles. [ABSTRACT FROM AUTHOR]

The paper describes the results on measuring the dependence of the acoustomagnetic effect on the angle between the magnetic field and the measuring inductive coil. We measured the sound speed in a magnetic fluid-glass tube system for two samples of nanodispersed magnetic fluid. The samples are disperse systems of single-domain magnetite particles in a hydrocarbon (kerosene, mineral oil) medium stabilized by oleic acid. The results are in good agreement with the previously published theory. One can use our experimental data to calculate physical (magnetic and geometric) parameters of magnetic nanoparticles applying acoustogranulometric technique. [ABSTRACT FROM AUTHOR]

Conditions of the operation of main ventilation fans and their impact on the reliability of the seal bearing fan assemblies are analyzed. The application of magnetic fluid sealing complexes instead of ordinary seals is proved. Research results are confirmed by experimental-industrial exploitation of the main ventilation fans with installed sealing complexes. [ABSTRACT FROM AUTHOR]

We investigate equilibrium morphologies of linear and ring-shaped magnetic filaments made from crosslinked ferromagnetic spherical or ellipsoidal colloidal particles. Using Langevin dynamics simulations, we calculate the radius of gyration and the total magnetic moment of a single filament at zero field and different temperatures, analyzing the influence of the particles shape, the strength of their magnetic moment and the filament length. Our results show that, among such parameters, the shape of the particles has the strongest qualitative impact on the equilibrium behavior of the filaments. [ABSTRACT FROM AUTHOR]

Static shapes of the magnetic fluid surface in non-uniform magnetic fields are studied theoretically. In particular, the case when the magnetic fluid volume can fill the space between non-magnetic surfaces is addressed. Two typical non-uniform field geometries with spherical and cylindrical symmetries are analyzed, i.e. the field of a magnetizable sphere exposed to a uniform magnetic field and the field of a straight current-carrying wire. [ABSTRACT FROM AUTHOR]

Results of the analysis of linear regression models are presented described in the experimental studies on the electrical capacity of a cell with a microlayer of magnetic nanofluid carried out with changed input parameters (factors), such as the polarizing voltage (0-20 V), the volume concentration of the disperse phase (2.3-14.4%), the interelectrode gap (100-200 µm), the layer temperature (293-368 K). Two-dimensional and three-dimensional graphical dependences of the electrical capacitance of the microlayer of magnetic nanofluid determined by the input parameters are presented. [ABSTRACT FROM AUTHOR]

The action of a DC electric field directed perpendicularly to an initially homogeneous magnetic fluid (MF) layer gives rise to a new, more concentrated phase, i.e. microdrop formations in the near-electrode layer at a threshold field. Despite of the thorough enough studies [2-8], the fundamental understanding of the structure formation and near-electrode layer properties is still the question of debate. [ABSTRACT FROM AUTHOR]

Magnetic response of a concentrated polydisperse ferrofluid to a strong linearly polarized applied field is investigated both experimentally and theoretically. It is shown that in a wide range of particle concentrations and field amplitudes the second-order modified mean-field theory by Ivanov and Kuznetsova [2] well describes the experimentally observed magnetization spectra if the field frequency is low enough and internal relaxation processes in ferrofluid can be neglected. [ABSTRACT FROM AUTHOR]

A magnetic fluid drop immersed in oil and exposed to a harmonic electric field is studied theoretically. All surface charge transportations are considered. It is shown that the surface conductivity can quantitatively change the deformation, but cannot change it qualitatively. [ABSTRACT FROM AUTHOR]

Investigations of temperature dependences of dynamic susceptibility for three ferrofluid samples with different size distributions are presented. These studies were performed at different sampling frequencies under the action of an external DC magnetic field. Analysis was done in terms of a Debye-like theory of complex susceptibility. It was also found that the temperature corresponding to maximum of the imaginary component of the complex magnetic susceptibility depends on the frequency of the probing field as a Vogel-Fulcher-like law. [ABSTRACT FROM AUTHOR]

The microstructure formation in a flat layer of magnetic fluid emulsion in water under the action of an in-plane rotating magnetic field has been studied. Several microstructure types have been found. The revealed microstructures were numerically investigated by Brownian dynamics simulations. The appearance of a macroscopic torque in a magnetic fluid emulsion sample associated with the microstructure dynamics in a rotating magnetic field was observed and studied. [ABSTRACT FROM AUTHOR]

An experimental investigation of the surface tension temperature dependence s(T) of the condensed phase (drop-like aggregates) in magnetic fluids undergoing magnetocontrollable phase transition of gas-liquid type was carried out. Accurate numerical processing of experimental data has revealed an anomalous (if compared to ordinary fluids) behavior of the s(T) function for all tested samples: it enhances with the growth of temperature due to the granulometric aspect of the first-order phase transition in magnetic fluids. [ABSTRACT FROM AUTHOR]

The motion of two horizontal layers of nonlinearly magnetizable inviscid ferrofluids which have a plane interface is considered. A criterion of such motion stability is found. [ABSTRACT FROM AUTHOR]

Our experimental study has shown that whereas the application of a uniform magnetic field can significantly intensify heat transfer in ferrofluids, in general, it is a nonmonotonic function of the strength of the applied magnetic field. [ABSTRACT FROM AUTHOR]

The paper presents the results of an experimental study of the deformation of a ferrofluid layer located on a liquid substrate exposed to a uniform vertically-oriented magnetic field, the amplitude of which varies in time according to a harmonic law. We restrict our study to the case of small amplitudes and frequencies, at which no ferrofluid layer disintegration takes place. [ABSTRACT FROM AUTHOR]

Investigations of the properties and application possibilities of magnetic fluids (MF) are an extremely dynamic research field nowadays. Many researchers, working in the field of MF physics and application, studied unique properties of magnetic fluids. Different physical phenomena determined by the MF application have been investigated. The growing interest caused by the use of magnetic fluids in instrumentation is determined by the MF interaction with electric and magnetic fields [1]. Studying a certain property of MF makes it impossible to eliminate the effect of more or fewer factors. On the one hand, it has some advantages since it allows to judge about the phenomenon from different points of view and, on the other hand, causes some difficulties when comparing results. As to the electrical properties (electrical conductivity, dielectric permittivity), it should be taken into account that they can be characterized by different methods using samples with different structures and produced by various methods. MFs have a more complex and diverse structure than most colloidal systems, because their structure is affected both by electric and magnetic fields. [ABSTRACT FROM AUTHOR]

Simulations of Brownian dynamics in dipolar hard spheres are used to investigate the concentration range, in which theoretical models of the weak-field dynamic magnetic response are valid, taking into account interparticle magnetic dipole-dipole correlations. [ABSTRACT FROM AUTHOR]

The problem of propagation of non-linear waves with a small amplitude in a thin layer of paramagnetic fluid with variable thickness in magnetic field is considered in shallow water theory. The equations of motion are derived and the method of solving the problem with weak discontinuity is developed. With the help of this method the problem with a weak shock wave is solved. An example of equilibrium initial state is considered. [ABSTRACT FROM AUTHOR]

The paper presents results of the investigation of magnetization features of thin layers of differently based magnetic colloids with a well-developed system of magnetized aggregates, exposed to magnetic and electric fields. It has been found that the magnetization processes of volumetric samples and of thin layers differ. For thin layers of the investigated magnetic fluid, a dependence of the magnetization relaxation time on the layer thickness and also on the mutual orientation of the layer plane and external constant magnetic field is found. It is shown that an alternating electric field also affects the magnetic properties of a thin layer of magnetic colloid with magnetized aggregates. [ABSTRACT FROM AUTHOR]

Autowaves arise in various media of chemical, physical, biological origin. An important example of an excitable active medium in which autowave processes occur are biological tissues, including myocardium. The spreading of the nerve impulse in the cardiac muscle is autowave by nature and obeys the universal laws of autowave spreading. Violation of the autowave spreading modes leads to serious pathologies. Control of the arising wave with the help of external influences makes it possible to eliminate such pathology. These considerations determine the importance of autowave process investigations. In this paper, we investigate the modes of autowave excitation spreading which were observed in the near-electrode layer of magnetic fluid. [ABSTRACT FROM AUTHOR]

Extinction and scattering of light by aqueous magnetic emulsions with different concentrations of magnetic fluid were studied. Particles size distribution in magnetic emulsions by dynamic light scattering was measured. Peculiarities of light extinction under the action of a magnetic field are discussed. [ABSTRACT FROM AUTHOR]

Measurements and theoretical analysis of the processes of static shear and oscillations of a magnetic fluid column confined by magnetic levitation in a strong magnetic field in a horizontally placed tube are made. Calculations of saturation magnetization made with reference to the obtained results on shear and oscillation frequency for a sample of the magnetic fluid under study are in good agreement with experimental data. The described technique is of interest when studying saturation magnetization, magnetophoresis, aggregation of nanoparticles and their temporal dependence in magnetic colloids. [ABSTRACT FROM AUTHOR]

Results of theoretical investigation on the influence of the non-linear magnetic vortex interaction in a magnetic colloid rotating in a transverse field with its axial (along the axis of rotation) dynamic susceptibility are presented. The mechanism of the magnetic vortex resonance observed during experiments is described, which suggests the occurrence of a peak dependence of the axial susceptibility on the rotation frequency close to the frequency of the probe field. [ABSTRACT FROM AUTHOR]

Excitation waves are one of the main mechanisms of signal transmission in living organisms. Excitation waves in chemical, mechanical, social environments are well-known. The spreading of waves in an excitable medium differs from the spreading of mechanical and electromagnetic waves. The excitable medium has a special ability to accumulate energy in individual elements and then to exchange it (by transmitting the excitation pulse) from one element to another. One of the main properties of the excitable medium is the possibility to recover after the wave passage. This makes possible the appearance of the so-called autowave processes (AWP) which are similar to self-oscillatory processes in concentrated systems. The study of such processes is important for understanding active media of very diverse nature: biological, physical, chemical. [ABSTRACT FROM AUTHOR]

Transformer oil-based magnetic fluids are of great scientific interest due to their enhanced thermal properties and evident higher breakdown voltage if compared with pure transformer oil. To understand the paradoxical and peculiar dielectric properties of such magnetic fluids, one needs to reveal and identify all polarization processes contributing to the total polarization of the material. Even though power transformers exploiting transformer oil operate at 50 or 60Hz frequency, it is desirable to investigate the oils dielectric properties in a broader frequency range, too. In this study, we show some selected dielectric spectra of a magnetic fluid consisting of transformer oil and magnetite nanoparticles stabilized by oleic acid. Complex dielectric permittivity spectra of the studied sample exhibit two pronounced dielectric dispersions associated with the space charge migration and interface relaxation phenomena. [ABSTRACT FROM AUTHOR]