Showing papers in "Magnetohydrodynamics in 2009"

Thermoelectric MHD in dendritic solidification

Abstract: The effects of a constant uniform magnetic field on dendritic solidification were investigated using an enthalpy based numerical model. The interaction between thermoelectric currents on a growing crystal and the magnetic field generates a Lorentz force that creates flow. The need for very high resolution at the liquid-solid boundary where the thermoelectric source originates plus the need to accommodate multiple grains for a realistic simulation, make this a very demanding computational problem. For practical simulations, a quasi 3-dimensional approximation is proposed which nevertheless retains essential elements of transport in the third dimension. A magnetic field normal to the plane of growth leads to general flow circulation around an equiaxed dendrite, with secondary recirculations between the arms. The heat/solute advection by the flow is shown to cause a change in the morphology of the dendrite; secondary growth is promoted preferentially on one side of the dendrite arm and the tip velocity of the primary arm is increased. The degree of approximation introduced is quantified by extending the model into 3-dimensions, where the full Navier-Stokes equation is solved, and compared against the 2-dimensional solution.

Experimental study of mhd flows in a prototypic inlet manifold section of the dcll test blanket module

Abstract: This paper presents preliminary results on a magnetohydrodynamic (MHD) flow in a prototypic distribution and collection manifold relevant to the Dual Coolant Lead Lithium (DCLL) blanket concept. A series of experiments has been carried out in order to understand the mechanisms that determine the division of flow from a single supply channel to three parallel channels stacked in the direction the magnetic field lines. First flow rate data show that for a relatively high interaction parameter ( N> 90), a uniform flow distribution is achieved with less than 5% flow unbalance. For lower values of N , the ratio between the outer to the central channels flow rates is found to follow a N m type scaling law, with m =1 /4 for 60

Experimental study of a hybrid ferrohydrodynamic instability in miscible ferrofluids: droplet size effects

Abstract: Ching-Yao Chen1†, W.-K.Tsai, Jose A.Miranda3‡ 1 Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China †E-mail:chingyao@mail.nctu.edu.tw 2 Department of Mechanical Engineering, National Yunlin University of Science and Technology, Yunlin, Taiwan, Republic of China 3 Departamento de Fisica, LFTC, Universidade Federal de Pernambuco, Recife, Pernambuco 50670-901 Brazil ‡E-mail:jme@df.ufpe.br

Model experiments on macroscopic thermoelectromagnetic convection

Abstract: Thermoelectromagnetic convection (TEMC) in a shallow square layer of liquid metal was investigated experimentally. The most prominent features of the setup were an as homogeneous as possible temperature gradient, a strongly inhomogeneous magnetic field, and a large value of the Seebeck coefficient. Ultrasound Doppler measurements of the flow field showed that, even at relatively small temperature gradients, a quite distinct TEMC is accomplishable if the setup is optimised with respect to the Lorentz force.

Magnetohydrodynamics of insulating spheres

Abstract: The effect of electric and magnetic fields on a conducting fluid surrounding an insulating object plays a role in various industrial, biomedical and micro-fluidic applications. Computational simulations of the magnetohydrodynamic flow around an insulating sphere, with crossed magnetic and electric fields perpendicular to the main flow, are performed for Rm << 1 in the ranges 0.1 ? Re ? 100, 1 ? Ha ? 20 and 0.01 ? N ? 1000. Careful examination of this fundamental three-dimensional flow reveals a rich physical structure with surface charge on the sphere neighbouring volume charge of opposite sign. Hartmann layers, circulating current and asymmetric velocity and current profiles appear as a result of the applied magnetic and electric field. A parametric study on the magnetic field’s influence on the drag coefficient is performed computationally. The obtained results bridge a gap between various analytical solutions of limiting cases and show good correspondence to earlier work. Correlations for the drag coefficient are proposed that can be valuable for the description of insulating inclusions in various flow applications with magnetic fields.

Numerical simulation of unsteady MHD flows and applications

Abstract: We present a robust numerical method for solving the compressible Ideal Magneto-Hydrodynamic equations. It is based on the Residual Distribution (RD) algorithms already successfully tested in many problems. We adapted the scheme to the multi-dimensional unsteady MHD model. The constraint ∇ · B = 0 is enforced by the use a Generalized Lagrange Multiplier (GLM) technique. First, we present this complete system and the keys to get its eigensystem, as we may need it in the algorithm. Next, we introduce the numerical scheme built in order to get a compressible, unsteady and implicit solver which has good shock-capturing properties and is second-order accurate at the converged state. To show the efficiency of our method, we will then comment some 2D results. We will end by pointing out some issues and the extensions we plan for this solver.

The structural transitions in a nematic liquid crystals doped with magneticaly labeled carbon nanotubes

Abstract: Z. Mitróová, N. Tomašovičová, M. Koneracká, V. Závǐsová, M. Timko, J. Kováč, P. Kopčanský, L. Tomčo, N. Éber, K. Fodor-Csorba, T. Tóth-Katona, A. Vajda, J. Jadzyn, E. Beaugnon, X. Chaud 1 Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia 2 Faculty of Aeronautics, Technical University, Rampova 7, 041 21 Košice, Slovakia 3 Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary 4 Institute of Molecular Physics, Polish Academy of Sciences, Smoluchovskiego 17, 60179 Poznan, Poland 5 Grenoble High Magnetic Field Laboratory, Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, Grenoble, France

Characterization of MHD convection in thin cell electrodeposition

Abstract: We are studying the effect of a magnetic field normal to the cell in electrodeposition of zinc arborescences. When the cell thickness is reduced, the MHD convection, responsible for morphology changes, spiraling, etc. is suppressed, but in a high magnetic field there is still an effect maybe due to small-scale hydrodynamic convection or to the Lorentz force on the growing metallic branches, the "Laplace" force.

Modelling of levitation melting using a fixed mesh method

Abstract: Numerical modelling is indispensable in the design of levitation melting equipment. The shape and the position of the levitated molten metal are very important for the power transfer from the coil towards the molten metal. This paper verifies whether the shape and position of this molten metal can be determined using the level set method.