Research On Dynamic Interface Stability In Magnetic Fluid Sealing Liquid

In this paper, the main factors influencing the interfacial stability are probed. The criterion of the interfacial stability between the magnetic fluid and sealed liquid is given. The related property of the magnetic fluid seal is described. The present situation and the developmental trend of the study on the magnetic fluid technology are systematically summarized and reviewed. The research on the technology of sealing liquid with the magnetic fluid is attached more and more to importance. If the magnetic fluid seal ability and lifetime can be improved, especially solving the problems of sealing liquid with the magnetic fluid, the magnetic fluid applications in seals will be expanded greatly. There are many methods of preparing the magnetic fluid which are related to the type of the magnetic particles. The different methods correspond to different technology by which the various kinds of the magnetic fluids are produced according to the different applications. By using chemical co-deposition method, research on practically preparing the magnetic fluid is performed in the paper. The physics performances of the magnetic fluid such as dispersion stability and magnetization property are related to its valid applications. Hence the magnetization performance and dispersion stability are discussed further. There are many factors influencing the dispersion stability, for example, the chain molecule length of the surfactant, the material and size of the magnetic solid particle and carrier liquid etc. The results of the simulation computation of the dispersion stability and magnetization performance are given. The fundamental of the magnetic fluid seal and the method of the magnetic field in the seal gap are introduced. Solving the magnetic field in the seal gap by an analytical method is emphasized. The magnetic fluid seal is composed of the magnetic fluid, a permanent magnet, the magnetic pole pieces and a shaft. The magnetic fluid in the seal gap forms an"O"-shape liquid seal ring. The seal device design of the magnetic fluid should be on the basis of the magnetic field analysis. The mechanic property and analytical method of the magnetic fluid seal are described. The hydrostatic characteristic of the magnetic fluid seal is discussed. Then the establishment and solution of dynamic motion model of the magnetic fluid are described. The speed distribution, pressure distribution and seal ability of the magnetic fluid in the seal gap with the angle-shaped magnetic pole pieces are derived. For the dynamic seal, its seal ability is determined by the effect of the magnetic field and the motion state of the magnetic fluid. For simplifying the analysis of the magnetic fluid motion, theoretically the magnetic fluid is considered as the Newtonian fluid. If it is taken as the non-Newtonian fluid, there are many the forms of the constructive equation for describing its rheological characteristics. The basic model used in the paper is power-law model. The general analytical method of interfacial stability between common liquids is introduced. The analytical method of dynamic interface stability in sealing liquid with the magnetic fluid is emphasized. The interface stability criterion is deduced. In general condition, the interfacial tension of magnetic fluid and the gravity are stabilization effect on the interface. This is same as the Kelvin-Helmholtz interfacial stability phenomenon of the common liquid. Thus when the liquid is sealed by the magnetic fluid, the high rotating speed is harmful to the seal. Increasing the difference between the magnetic fluid density and the sealed liquid density and decreasing their speed difference, their interfacial stability may be improved. The design of an experimental project and device is introduced. And then the other tests and parameters measurement related to interfacial stability are described, including the measurement of magnetic field distribution and the experiment of mutual insolubility between magnetic fluid and sealed liquid and so on, by which the proof is provided for experimental analysis of interfacial stability. Finally, the experiment of dynamic interface stability between the magnetic fluid and the sealed liquid is carried out, by which a forming process of the instability phenomenon is observed and analyzed.