ИСТИНА

In this work, the deformation of a magnetic fluid with variable volume around the spherical magnetizable body in a vertical uniform applied magnetic field (prototype of a pumping or dosing device) is studied experimentally and theoretically. In experiment a fixed volume of a non-magnetic immiscible fluid (polymethylsiloxane) is placed above the water-based magnetic fluid. Fluids are placed in the cylindrical tube. The spherical magnetizable body is on the tube bottom. The volume of the magnetic fluid can change due to source of fluid (a magnetic fluid flows from a large reservoir with a constant fluid level). In experiments, a stepwise vertical uniform applied magnetic field is created by pare of Helmholtz coils. The magnetic fluid surface rises when magnetic field increases, and the non-magnetic fluid rises. Thus, it is possible to dose the fluid if the outflow hole is in the tube wall above the initial level of the non-magnetic fluid and the non-magnetic fluid reaches a hole at some field value, so part of it flows out. In the experiment, the change of the non-magnetic fluid level on magnetic field was measured. The shape of the magnetic fluid with increasing and decreasing magnetic field was recorded. The hysteresis of the contact angle of a magnetic fluid is found. A small difference between the fluids lifting in the increasing and decreasing magnetic field, caused by the hysteresis of the contact angle, is obtained. A calculation method to obtain the equilibrium of magnetic fluid surface shapes, taking into account the surface tension, gravity, and the nonlinear dependence of the magnetization on the magnetic field, is developed. Calculations for the experimental parameters considering the hysteresis of the wetting angle were made. The dependencies of the fluids lifting above the initial level on the applied magnetic field are plotted experimentally and numerically. A good agreement of the numerical and experimental results is obtained.