Flow Characteristics of Magnetic Fluid on Yoke Surface of Magnetic Fluid Seal

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The magnetic force distribution on the yoke surface of a magnetic fluid seal is clarified using finite element analysis. Calculations are performed for two kinds of typical magnetic fluid shape, that is, film shape and spike shape. It is interesting to note that magnetic force direction switches halfway the yoke length. The region wherein magnetic fluid flows to the yoke top direction is found to be wider for a thicker magnet,thicker yoke and the case with a spindle. This leads to a new concept of magnetic fluid seal having self injection action.The critical rotational speed at which splashing of the magnetic fluid is initiated is found to be uniquely determined by the spread of the meniscus under a fixed magnetic flux condition. It should be noted that, with increasing flux density from 0.2 to 0.4T, the critical speed is considerable increased nearly two times.Calculation procedure to determine the surface shape of the meniscus formed around the seal gap is established through the extension of the SMAC method to the case involving surface tension and magnetic force. The calculation is justified being compared with the experimental meniscus shape.