Natural Convection of a Magnetic Fluid under the Magnetic Field

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Natural convection of a magnetic fluid was studied experimentally and numerically for three models which was a cubic cavity, a cubic cavity which had a horizontal cylinder and the coaxial cylinders. Magnetic fields were applied in various directions by permanent magnets. The thermosensitive liquid crystal sheet was utilized in order to visualize wall-temperature distributions. Several kinds of experiment were carried out in order to clarify the influence of direction and strength of magnetic fields on the natural convection. Numerical Simulations by finite element method were used to show velocity and temperature fields in the magnetic fluid. Boussininesq approximation was used and the induced magnetic field caused by a motion of magnetic particle was ignored in the calculation. Temperature distributions and velocity field in magnetic fluid were observed in detail by the calculation results. As these results it became known that the natural convection of a magnetic fluid was controlled … More by the intensity and direction of the magnetic fields.To investigate the thermal properties of magnetic fluids, we introduced a new way of determining constitutive equations of magnetic fluids. That is the method which is a combination of the theory of integrity bases and the principle of maximal dissipation rate based on the thermodynamical discussions. The basic equations, which derived by this method, satisfy the principle of material frame indifference. Furthermore, they express viscoelastic effect internal freedom, conducting effect, and nonlinear effect simultaneously Using this method, the basic equations of both nonconducting and conducting nonpolar magnetic fluids were given.Some dynamic behavior of a magnetic fluid in a container were experimentally examined. Experiments were carried out for rectangular, cylindrical and spherical containers respectively. These containers were laterally oscillated. The vertical non-uniform magnetic field was applied by permanent magnets which were fitted underneath the container. It was found that harmonic wave motion, swirling waves and flow pattern of surface waves were influenced by the magnetic fields. The resonant frequency of the fluid-container system moved toward high frequency region with the magnetic field intensity. This behavior was also studied by the linear approximate theory. Theoretical results were qualitatively in good agreement with experimental results. Less