López-Alcaraz P, Catherall A T, Hill R J A, Leaper M C, Swift Michael R, King P J
School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
Eur Phys J E Soft Matter. 2007 Oct;24(2):145-56. doi: 10.1140/epje/i2007-10225-1. Epub 2007 Oct 31.
A fluid-immersed granular mixture may spontaneously separate when subjected to vertical vibration, separation occurring when the ratio of particle inertia to fluid drag is sufficiently different between the component species of the mixture. Here, we describe how fluid-driven separation is influenced by magneto-Archimedes buoyancy, the additional buoyancy force experienced by a body immersed in a paramagnetic fluid when a strong inhomogeneous magnetic field is applied. In our experiments glass and bronze mixtures immersed in paramagnetic aqueous solutions of MnCl2 have been subjected to sinusoidal vertical vibration. In the absence of a magnetic field the separation is similar to that observed when the interstitial fluid is water. However, at modest applied magnetic fields, magneto-Archimedes buoyancy may balance the inertia/fluid-drag separation mechanism, or it may dominate the separation process. We identify the vibratory and magnetic conditions for four granular configurations, each having distinctive granular convection. Abrupt transitions between these states occur at well-defined values of the magnetic and vibrational parameters. In order to gain insight into the dynamics of the separation process we use computer simulations based on solutions of the Navier-Stokes' equations. The simulations reproduce the experimental results revealing the important role of convection and gap formation in the stability of the different states.
当受到垂直振动时，沉浸在流体中的颗粒混合物可能会自发分离，当混合物的组分颗粒的惯性与流体阻力之比存在足够差异时，就会发生分离。在此，我们描述了磁阿基米德浮力对流体驱动分离的影响，磁阿基米德浮力是指当施加强非均匀磁场时，沉浸在顺磁性流体中的物体所经历的额外浮力。在我们的实验中，将玻璃和青铜混合物沉浸在MnCl₂的顺磁性水溶液中，并使其受到正弦垂直振动。在没有磁场的情况下，分离情况与间隙流体为水时观察到的情况相似。然而，在适度施加磁场时，磁阿基米德浮力可能会平衡惯性/流体阻力分离机制，或者它可能主导分离过程。我们确定了四种颗粒构型的振动和磁条件，每种构型都有独特的颗粒对流。这些状态之间的突然转变发生在明确的磁参数和振动参数值处。为了深入了解分离过程的动力学，我们基于纳维-斯托克斯方程的解进行了计算机模拟。模拟结果再现了实验结果，揭示了对流和间隙形成在不同状态稳定性中的重要作用。
