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Numerical Analysis of Magnetic Fluid Sealing Performance 1 IntroductionThere are many factors that can influencemagnetic fluid sealing performance[1–4]. The materialcharacteristics of magnetic fluid and the intensity ofthe magnetic field have a direct influence on themagnetic fluid seal. The main factors that influencethe sealing performance include the sealing gap, theshaft eccentricity, the shaft diameter and the centrifugalforce. Analyzing these factors is important forthe design and manufacture of the magnetic fluid.The design and production factors influencing themagnetic fluid sealing performance are analyzed bynumerical computations. 2 Theory of Magnetic Fluid SealIn general, the applied field intensity is highenough, so the magnetic fluid can be magnetizedwhile saturated[1]. The magnetization of the magneticfluid approximately equals the saturation magnetizations M . When the centrifugal force is neglected inthe rotating shaft seal, the pressure in the magneticfluid isp = MsB + ρ gh + C (1)where B is the flux density, ρ the density of themagnetic fluid, g the acceleration of gravity, h thevertical distance from this point to a reference pointand C an integral constant determined by the boundaryconditions.When the quantity of the magnetic fluid is bigenough, the magnetic flux density on the lower pressureside is almost zero. When gravity is neglected,the seal pressure difference max Δp of a single-stageseal ismax s max Δp ≈ M B (2)When the shaft rotates at a speed of 0 ω , the influenceof the centrifugal force on the magnetic fluidshould be considered. The pressure p at any pointin the magnetic fluid isp = M B + Ψ r + ρ gh + C (3)wherewhere 1 R is the outer radius of the shaft, 2 R theinner radius of the pole piece and r the radius ofany point in the magnetic fluid. Eq. 2 shows that the sealing performance is directlyproportional to magnetic field strength and tothe saturated magnetization of the magnetic fluid. Toimprove the magnetic fluid sealing performance, themagnetic field should be improved and a high saturationmagnetization magnetic fluid should be used.
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