ELECTROMAGNETIC STIRRING
ELECTROMAGNETIC STIRRING
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DOI：
10.1063/1.858062
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发表时间：
1991-05-01
期刊：
影响因子：
--
通讯作者：
MOFFATT, HK
中科院分区：
文献类型：
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作者：
MOFFATT, HK
众所周知，在固体或流体导体上施加交变磁场（单相或多相），会在导体中产生电流，从而产生洛伦兹力分布。这个洛伦兹力通常是旋转的，如果导体是流体，它就会运动。因此，磁场作为一种非侵入式搅拌装置，原则上，它可以被设计成提供任何所需的搅拌模式。搅拌也可以通过流体驱动的稳定电流分布和相关磁场的相互作用来实现。当磁场频率高时，洛伦兹力被限制在一个薄的电磁边界层内，磁场的净效应是在边界层内诱导一个切向速度或切向应力。速度或应力的分布与外加场的结构有关。对称结构可能导致流线位于环形表面的搅拌模式；然而，更普遍的是，流线模式是混乱的。给出了这两种类型的例子，并讨论了应用。如果导电微粒悬浮在不导电的流体中，整个微粒受到相同类型的交变磁场的作用，就会出现一个有点相关的问题。电流现在在粒子中产生，每个粒子都受到一个力和一对电偶。当几个粒子处于悬浮状态时，每个粒子的运动都会受到其他粒子的影响，这就产生了一个有点类似于相互作用的点涡问题的问题。对于导电粒子的悬浮液，电场的不均匀性导致粒子浓度的不均匀性，通常会引起整体流动。简要总结了这种行为背后的一般原则。
It is well known that an alternating magnetic field (either single phase or multiphase) applied to a conductor, whether solid or fluid, will induce electric currents in the conductor, and hence a Lorentz force distribution. This Lorentz force is in general rotational, and if the conductor is fluid, it is set in motion. Thus the magnetic field acts as a nonintrusive stirring device and it can, in principle, be engineered to provide any desired pattern of stirring. Stirring may also be effected through the interaction of a steady current distribution driven through a fluid and the associated magnetic field. When the field frequency is high, the Lorentz force is confined to a thin electromagnetic boundary layer, and the net effect of the magnetic field is to induce either a tangential velocity or a tangential stress just inside the boundary layer. The distribution of velocity or stress is related to the structure of the applied field. Symmetric configurations may lead to patterns of stirring in which the streamlines lie on toroidal surfaces; more generally, however, the streamline pattern is chaotic. Examples of both types are presented, and applications are discussed. A somewhat related problem arises if electrically conducting particles are suspended in a nonconducting fluid, the whole being subjected to the same type of alternating magnetic field. Currents are now induced in the particles, and each particle experiences a force and a couple. When several particles are in suspension, the movement of each is influenced by the presence of the others, and a problem somewhat analogous to the problem of interacting point vortices arises. For a suspension of conducting particles, inhomogeneity of the field leads to inhomogeneity of the concentration of particles, and a bulk flow is, in general, induced. The general principles underlying this behavior are briefly summarized.