Theory analysis and experimental study on magnetic fluid injection of multi-stage magnetic fluid seal

Magnetic fluid seal (MFS) is one of the most mature applications of magnetic fluid (MF) and is widely used in numerous fields. But challenges arise in maintaining the volume of MF within the sealing gap, particularly under conditions of elevated seal pressure, high rotational speeds, and long-term usage. Injecting MF in multi-stage MFS post-installation poses a notable challenge. The conventional approach of injecting the entire optimal volume into pole teeth faces difficulties, as a portion of the MF tends to adhere to the surface of shaft and pole shoes during installation due to the uneven magnetic field. This study aimed to explore MF injection and devise a method for precisely controlling the MF volume in the sealing gap. To achieve this, a novel concept of multi-stage MFS with larger sealing gaps in specific stages was introduced. The injection and movement of MF were scrutinized through a combination of Computational Fluid Dynamics (CFD) simulations and experimental investigations. The findings from both CFD and experiments unequivocally establish the feasibility of injecting MF in multi-stage MFS. Effective injection is achieved when the inlet pressure increment is maintained below 20 kPa each time. Furthermore, experimental results highlight that the sealing capacity achieved through the injection method surpasses that of the common injection method, particularly for optimal volume MFS.