Optimal design of large gap magnetic fluid sealing device in a liquid environment

Magnetic fluid seals (MFSs) have been widely used as a gas seal because of its advantages such as low wear, zero leakage, and long service life. However, the MFS is generally unstable due to structural- and material-related challenges in a liquid environment. To improve the pressure resistance and durability of the sealing liquid, we proposed an improved structure, where the annular pole component is designed as a radially magnetized annular permanent magnet. Furthermore, the structural parameters are optimized to maximize the magnetic induction intensity in the sealing gap. An MFS test device was simultaneously designed, according to the optimized results, to test the pressure resistance and durability under static and dynamic conditions. The results show that the pressure resistance and durability of the improved MFS structure is better than those of the traditional structures, specifically for a large gap structure. Furthermore, in a static seal, the sealing performance depends on the magnetic fluid magnetic saturation rather than other physical parameters, while in dynamic sealing, although magnetic saturation is a primary factor, the viscosity of the magnetic fluid also affects the sealing performance. Furthermore, the high-viscosity magnetic fluid had a higher critical pressure, while the low-viscosity magnetic fluid improved the durability of the seal. This result provides a reference for designing a magnetic fluid sealing device in a liquid environment.