Influence of carbon nanotubes on the dissipation of disturbances in a magnetic fluid layer

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. Figs 9, Refs 9.

Experimental research of viscoelastic properties and stress relaxation of magnetizable elastomers

Torsional deformations of cylindrical bodies with magnetizable elastomers in a uniform magnetic field are considered. During theoretical research, different models of viscoelastic materials are used. Experimental studies of stress relaxation in a magnetic field are carried out, and the models that consider stress relaxation are used to describe the experiment. Dependences of the shear moduli and viscosity coefficients of magnetizable elastomers on the magnetic field strength are found experimentally. Tables 1, Figs 10, Refs 9.

A simple scenario of the laminar breakdown in liquid metal flows

In the article, authors present a numerical method for modelling a laminar-turbulent transition in magnetohydrodynamic flows. The small magnetic Reynolds number approach is considered. Velocity, pressure and electrical potential are decomposed to the sum of state values and finite amplitude perturbations. A solver based on the Nektar++ framework is described. The authors suggest using small-length local perturbations as a transition trigger. They can be imposed by blowing or by electrical enforcing. The stability of the Hartmann flow and the flow in the bend are considered as examples. Tables 4, Figs 19, Refs 28.

Flat liquid metal jet affected by a transverse magnetic field

A liquid metal flat jet immersed in a square duct under the influence of a transverse magnetic field is studied experimentally. Two cases are considered: when the applied magnetic field is oriented parallel (coplanar field) or perpendicularly (transverse field) to the initial plane of the jet. The main goal of the study is to investigate the mean flow characteristics and the stages of the jet's transformation. Signals of streamwise velocity at different locations are measured, which allows us to determine average velocity profiles and spatial-temporal characteristics of the velocity field. The two considered configurations are directly compared under the same flow regimes, with the same equipment. Figs 8, Refs 11.

Electrically driven cylindrical free shear flows under an axial uniform magnetic field

We consider a mathematical model of two-dimensional electrically driven laminar axisymmetric circular free shear flows in a cylindrical vessel under the action of an applied axial uniform magnetic field. The mathematical approach is based on the studies by J.C.R. Hunt and W.E. Williams (J. Fluid. Mech., 31, 705, 1968). We solve a system of stationary partial differential equations with two unknown functions of velocity and induced magnetic field. The flows are generated as a result of the interaction of the electric current injected into the liquid and the applied field using one or two pairs of concentric annular electrodes located apart on the end walls. Two lateral free shear layers and two Hartmann layers on the end walls and a quasi-potential flow core between them emerge when the Hartmann number Ha >> 1. As a result, almost all injected current passes through these layers. Depending on the direction of the current injection, coinciding or two counter flows between the end walls are realized. The Hartmann number varies in a range from 2 to 300. When a moderate magnetic field (Ha = 50) is reached, the flow rate and the induced magnetic field flux cease to depend on the magnitude of the applied field but depend on the injected electric current value. Increasing magnetic field leads only to inner restructuring of the flows. Redistributions of velocities and induced magnetic fields, electric current density versus Hartmann number are analyzed. Figs 18, Refs 21.

Experimental observation of metal-electrolyte interface stability in a model of liquid metal battery

An electric current is passed through the interface of liquid gallium and aqueous electrolyte in a square cross-section cell under a background vertical magnetic field. The oscillation increment of surface waves is calculated from potential measurements at variable current strengths. The surface is also visually observed through transparent side walls. No growing surface waves occur for the Sele parameter as high as 1.5. Instead, a quasi-static surface deformation is caused by the rotation of the metal and electrolyte. The maximum height of this surface deformation increases approximately in proportion to the current. Figs 7, Refs 15.

Absorption of ultrasound by a magnetic fluid in a rotating magnetic field

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 - 280 mHz at T = 295 K is not observed within the limits of observational errors. Similar results were observed for both low-viscosity and high-viscosity magnetic fluids. Tables 1, Figs 6, Refs 39.

Experimental investigation of the MHD pump with inclined partitions in a flat straight channel

We present the results of an experimental study of an MHD pump model with a flat straight channel containing a few inclined partitions. The partitions are not joint to the narrow walls of the channel and are shifted to one of these walls. The channel is embraced from the outside by Π-shaped ferromagnetic cores arranged along the channel in a staggered manner. P-Q characteristics of the MHD pump model under study were obtained for the partitions of different lengths. The locations of the partitions with respect to the narrow walls of the channel and the inclination angle of the partitions were varied as well. Figs 5, Refs 4.

Magnetohydrodynamic system -- a need for a sustainable power generation source

The magnetohydrodynamic generator is one of the renewable energy generation methods which is primarily based on the Faraday’s law of electromagnetic induction. This paper presents a detailed review about MHD -- its introduction and further advancement in its technology subsequently. An attempt has been made to make the reader understand the details about its operating principle. The MHD systems, being static, are much more efficient compared to conventional fossil fuel based generating systems. Also, these are more environment friendly as there are no emissions from the MHD generator. This paper also presents different types of MHD generators. The MHD generator can be considered to be a newest, efficient and reliable alternative to the conventional energy conversion system which would help to make a step forward towards the totally sustainable society. Figs 8, Refs 73.

Shear coefficient of spin viscosity estimation through velocity profiles of a ferrofluid under the effect of an external rotating magnetic field of low amplitude and frequency

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. Tables 7, Figs 11, Refs 17.