Boundary interface condition of magnetic fluid determines the magnetic levitation force experienced by a permanent magnet suspended in the magnetic fluid

Abstract

The buoyancy experienced by a permanent magnet suspended in magnetic fluid is studied, and the expression for calculating the magnetic fluid buoyancy is derived. The magnetic fluid buoyancy or magnetic fluid levitation force, which can be obtained by calculating the sum of Archimedes levitation force and magnetic levitation force, depends on the boundary interface condition of magnetic fluid. The type of the boundary interface and the pressure over it determine the boundary interface condition, and the dependence of boundary interface condition of magnetic fluid and magnetic fluid levitation force is studied. If the boundary interface of the magnetic fluid is a liquid-gas interface in contact with air, the magnetic fluid levitation force will be equal to the gravity of the magnetic fluid. A sudden change in magnetic fluid levitation force can be seen when the liquid-gas boundary interface of magnetic fluid is broken by the wall of a container. Or, in other words, the emergence of a solid-liquid boundary interface will influence the magnetic fluid levitation force, and the magnitude of the change is proportional to magnetic field intensity over the solid-liquid boundary interface. Once the liquid-gas boundary interface is close to a horizontal plane, the magnitude of magnetic fluid levitation force will reach a relatively stable value. In the experiments, the volume of magnetic fluid, the location of the magnet, and the magnetic particle concentration in magnetic fluid are used to control and change the boundary interface condition of magnetic fluid.