The effect of a magnetic field on free convection heat transfer (original) (raw)
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Some aspects of heat and mass transfer in magnetic fluids
IEEE Transactions on Magnetics, 1980
The present paper deals with the problem of investigating free convection concerning body flow of axial symmetry and showing the activity of gravitation and magnetic forces. The application of boundary layer approximation for solving the problem of thermomagnetic convection near horizontal cylinder has been discussed. Basing upon the solution of Stokes flow of magnetic sphere the analysis of mass transfer in magnetic suspension has been carried out to show the origin of thermophoresis under non-isothermal conditions. The direction of particle transfer depends on mutual orientation of the magnetic field and temperature gradient. Basing upon the experimental results of magnetophoresis in colloid solution of magnetite it was suggested to solve the probl e m of mass transfer for consideration of the kinetics of particle sedimentation on the walls. Magnetic field is known to influence transfer processes in biological suspensions. Magnetophoresis of lymphocytes in physiological solution has been displayed.
Heat and mass transfer phenomena in magnetic fluids
GAMM-Mitteilungen, 2007
In this article the influence of a magnetic field on heat and mass transport phenomena in magnetic fluids (ferrofluids) will be discussed. The first section is dealing with a magnetically driven convection, the so called thermomagnetic convection while in the second section the influence of a temperature gradient on the mass transport, the Soret effect in ferrofluids, is reviewed.
This paper present research result of the behavior of unsteady free convection flow of a visco-elastic fluid past an infinite porous plate with constant suction under the action of the time depend plate temperature. A uniform magnetic field is applied transversely to the porous plate and the magnetic lines of forced are taken to be fixed relative to the fluid. It is assumed that the plate temperate fluctuates about a constant mean, in the magnitude but not in direction. The numerical results of the real part M r and imaginary part M i of the fluctuating part of the velocity are tabulated. It is determined that the velocity distribution inside the boundary layer lags behind the wall fluctuation by the constant angle . The results obtained in the paper are useful in analyzing the effect of the magnetic field on free convection flows in liquid metals, electrolytes, and ionized gases.
Natural Convection of Liquid Metals in an Inclined Enclosure in the Presence of a Magnetic Field
The problem of steady, laminar, natural convective flow of electrically-conducting liquid metals such as gallium and germanium in an inclined rectangular enclosure in the presence of a uniform magnetic field is considered. Transverse gradient of heat is applied on two opposing walls of the inclined enclosure while the other two walls are adiabatic. A magnetic field is applied normal to the non-insulated walls. The problem is formulated in terms of the vorticity – stream function procedure. A numerical solution based on the finite-difference method is obtained. Representative results illustrating the effects of the enclosure inclination angle and the Hartmann number for two different Rayleigh numbers on the contour maps of the streamlines and temperature as well as the profiles of velocity components and temperature at mid-section of the enclosure are reported. In addition, results for the average Nusselt number are presented and discussed for various parametric conditions.
Investigation of Magneto Hydrodynamic Natural Convection Flows in a 3-D Rectangular Enclosure
Journal of Applied Fluid Mechanics, 2016
The article deals with magnetic field of free convective flows in cavities similar to those used in artificial growth of single crystals from melts (horizontal Bridgman configurations) and having aspect ratios an equal to "4". The combined effect of wall electrical conductivity and vertical direction of the magnetic field on the buoyancy induced flow of mercury was investigated numerically. The validation of the numerical method was achieved by comparison with both experimental and analytical data found in the literature. The plotted results for variation of velocity, temperature and Nusselt number in terms of the Hartmann number Ha and Rayleigh number "Ra" showed a considerable decrease in convection intensity as the magnetic field is increased, especially for values of "Gr" situated around 10 7. The calculations also showed that the vertically directed magnetic field (perpendicular to the x-z plane) is the most effective in controlling the flow and hence the speed of growth of the crystal. Also, wall electrical conductivity enhances damping by changing the distribution of the induced electric current to one which augments the magnitude of the Lorentz force.
Laminar Pipe Flow with Mixed Convection under the Influence of Magnetic Field
Nanomaterials
Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120–1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from the...
Effect of external magnetic fields on various free-surface flows
Progress in Computational Fluid Dynamics, An International Journal, 2008
Liquid-gas free-surface flows in the presence of gravity, surface tension and magnetic field are numerically studied. Two phases (both liquid and gas) are assumed to be an incompressible, immiscible, Newtonian fluid and both viscous dissipation and Joule heating are neglected. Thermal convection due to buoyancy and thermo-capillary effects is not taken into account. The numerical results reveal significant difference in the free-surface flows depending on the applied magnetic field not only for the electric conducting fluids such as mercury and gallium but also for ordinary non-conducting fluids such as water and air.
Buoyancy-driven convection in liquid metals subjected to transverse magnetic fields
Journal of Indian Institute of …, 2005
This study presents the numerical simulation of Navier-Stokes, energy and hydromagnetic equations to analyse two-dimensional natural convection of liquid metals subjected to transverse magnetic field. The spatio-temporal study shows that the oscillatory flow changes to steady fluid flow pattern with increase in intensity of applied magnetic field for a range of Rayleigh number (Ra) between 10 5 and 10 8 . The strength of magnetic field governs the pattern formation as well as the amplitude of the velocities for any particular Rayleigh number in the above range. The amplitude of aperiodic oscillations of any dynamical variable at higher Ra gets significantly damped out, especially removal of low-power harmonics with increase in the strength of magnetic field through variation of Chandrasekhar number.
Thermodiffusion in magnetic fluids
Journal of Magnetism and Magnetic Materials, 2005
Investigations were made to determine the Soret coefficient of magnetic particles in a ferrofluid under the influence of a magnetic field. This so-called magnetic Soret effect was theoretically predicted to be two to three orders of magnitude smaller than the conventional Soret effect. In contrast, former experiments have qualitatively shown that the magnetic Soret effect is much higher than the theoretical predictions. However, in those experiments the influence of buoyancy and magnetic driven convection disturbed the measurement significantly. Thus, it is still an open question how strong the magnetic Soret effect can be. Therefore, an experimental setup was developed which minimizes parasitic effects, simplifying the analysis of the experimental results. These results provide quantitative measures of the magnetic field dependence of the Soret effect in suspensions of magnetic nanoparticles. It is shown that the magnetic Soret effect can even be higher than the conventional one and that its strength as well as its direction depend on the magnetic field strength and its relative alignment to the temperature gradient in the fluid.