磁性液体一阶磁浮力原理实验研究

Experimental study of first-order magnetic buoyancy for ferrofluid

基于伯努利方程推导了磁性液体的一阶磁浮力,实验研究了不同轴线上一阶磁浮力的变化规律,便于学生理解一阶磁浮力变化的本质原因.磁性液体一阶磁浮力受磁场强度、磁场梯度,以及磁性液体的饱和磁化强度和磁化率影响.沿z轴方向随磁场强度和磁场梯度减弱,一阶磁浮力逐渐变小并趋于零,磁性液体悬浮能力变弱.MFP-1磁性液体的饱和磁化强度和磁化率大于MFP-2磁性液体,其一阶磁浮力较大;电流为3.00 A时,MFP-1磁性液体将玻璃、铝、黄铜、紫铜和铅球悬浮,并出现Rosensweig尖峰,而MFP-2磁性液体仅将玻璃、铝和黄铜球悬浮.沿r轴方向不同高度处磁场强度和磁场梯度变化规律不同,随高度增加,磁场梯度逐渐趋于零,此时一阶磁浮力主要受磁场强度影响,测试杯壁处一阶磁浮力最小,出现了非磁性测试球上升过程中向测试杯壁移动现象.

The formula for first-order magnetic buoyancy is derived based on the Bernoulli＇s equation of ferrofluid. The distribution of first-order magnetic buoyancy is studied at various axes by the experimental method in order to understand the basic reason of first-order magnetic buoyancy. The first-order magnetic buoyancy is influenced by magnetic field intensity, magnetic field gradient, saturation magnetization and susceptibility of ferrofluid. With decreasing magnetic field intensity and magnetic field gradient along z direction, the first-order magnetic buoyancy grows smaller gradually and goes to zero at the end; therefore suspending power of ferrofluid weakens. Saturation magnetization and susceptibility of MFP-1 ferrofluid are bigger than MFP-2 ferrofluid and first-order magnetic buoyancy of MFP-1 ferrofluid is bigger. When the current is 3.00A, glass, aluminum, brass, red copper and lead bails have been suspended and Rosensweig peaks appeared in the MFP-1 ferrofluid, but glass, aluminum and brass balls were only suspended in the MFP-2 ferrofluid. The distributions of magnetic field intensity and mag- netic field gradient are different along r direction at various heights. Magnetic field gradient goes to zero gradually with increasing the height and is the primary affecting factor for first-order magnetic buoyancy. Nonmagnetic balls are moved to the sidewall of glass beaker where the first-order magnetic buoyancy is smaller.