Convection Of Magnetic Fluid Research Articles

Thermomagnetic convection in a porous enclosure in the presence of outer uniform magnetic field

Present study pays attention to the influence of porous media and uniform magnetic field on thermal convection in magnetic fluid. It is shown that in porous square cavity the competition between gravity convection and thermomagnetic convection mechanisms can lead to a complicated dependence of the heat flux through the cavity on magnetic field: increasing of magnetic field could both enhance and depress heat transfer. Hence, the dependences of Nu ( Ra ) and Nu ( Ra m ) can be very complicated with hysteresis in some cases.

Thermodiffusive magneto convection in ferrofluids with two-frequency gravity modulation

Thermosolutal convection in magnetic fluids is considered in the presence of vertical magnetic field and bifrequency vertical vibrations. Using the Floquet theory, the regions of parametric instability have been obtained for different values of parameters and threshold acceleration necessary for instability has been found numerically. With two-frequency forcing, bicritical point has been observed where subharmonic instability and harmonic instability simultaneously occur with distinct values of the wave numbers. The change in concentration of magnetic particles in the magnetic fluids has been found to affect the instability behavior and the threshold acceleration.

Advanced Fluid Information. Gravity Simulation of Natural Convection in Magnetic Fluid.

Transition phenomena for the natural convection of a magnetic fluid in a square cavity was studied numerically for an externally imposed magnetic field. In the present study, particular attention was focused to verify heat transfer characteristics for non-gravity situation when the magnetic field was imposed. By applying magnetic fields the convection state many be largely affected improving heat transfer characteristics followed by various flow transitions in the non-gravity simulation. It was revealed that magnetic field could enhance the convection and consequently improves heat transfer characteristics, indicating that the magnetic field would be used as a substitute for the gravity in the zero-gravity situation of space.

Thermal convection in a rotating layer of a magnetic fluid

Thermal convection in magnetic fluids can be driven by buoyancy or by magnetic forces (due to the thermomagnetic effect). Depending on the direction of the applied temperature gradient, buoyancy effects can be stabilizing (heating from above) or destabilizing (heating from below), whereas the magnetic forces always play a destabilizing role for magnetic fields perpendicular to the interface. We investigate the influence of rotations using both linear and weakly non-linear analyses of the governing hydrodynamic equations in the Boussinesq approximation. With a linear stability analysis we determine the values of the wavelength and the temperature gradient at the onset of convection (critical values). These are calculated analytically in the case of stress free boundaries and numerically for rigid boundaries. We discuss the validity of the assumptions entering the calculations for stress free boundaries. In the case of free boundary conditions, asymptotic expressions of the critical values for high rotation rates are derived. When the system is heated from above and the magnetic forces only slightly exceed the buoyancy forces, linear results show that both the critical wavelength and the critical temperature gradient diverge. Again, this behavior is described by asymptotic expressions. We derive envelope equations for convection patterns characterized by both: one wave vector and two competing wave vectors of equal length but different directions. These equations show that the system always exhibits a forward bifurcation. The well-known Kuppers-Lortz instability is also present in magnetic fluids. This instability sets in at critical values for a sufficiently high rotation rate. In simple fluids the angle $$\alpha $$ depends only on the Prandtl number of the fluid. We show that for magnetic fluids this angle can be changed by changing the ratio of the buoyancy forces to the magnetic forces (i.e. by changing the magnetic field). There is also a weak dependence on the other magnetic parameters of the system. For a commercially available magnetic fluid this angle can be increased by approximately $$10^\circ $$ - $$15^\circ $$ compared to the simple fluid case.

Microgravity experiments on thermomagnetic convection in magnetic fluids

We have investigated the onset and the flow profile of thermomagnetic convection in a cylindrical fluid layer. Under microgravity conditions provided by the use of sounding rockets and at the drop tower ‘Bremen’ (ZARM, University of Bremen, Germany) the experiments could be carried out with periodic boundary conditions in which the vertical force of gravity, that normally produces three-dimensional flow, is made negligible, thus permitting the establishment of counter-rotating vortices.

Sounding rocket and drop tower experiments on thermomagnetic convection in magnetic fluids

In our experiments a magnetic fluid is enclosed in a hollow-cylindrical container heated from the center and cooled at the outer surface. It is under the influence of an azimuthal magnetic field with radial gradient. The flow profile has been investigated by small thermistors placed at the inner surface of the outer wall of the container. The experiments were carried out with sounding rockets and at the drop tower “Bremen” (ZARM, University of Bremen). The flow profile of the convective flow, and the critical magnetic Rayleigh number obtained in these experiments agree well with theoretical predictions.

Convection in Magnetic Fluids With Internal Heat Generation

The effect of a uniform distribution of heat source on the onset of stationary convection in a horizontal Boussinesq magnetic fluid layer bounded by isothermal nonmagnetic boundaries is investigated. Solutions are obtained using a higher order Galerkin expansion technique, considering different isothermal boundary combinations (rigid-rigid, rigid-free, and free-free). It is found that the effect of internal magnetic number, due to a heat source, is to make the system more unstable. The results obtained, in the limiting cases, compare well with the existing literature.