振动颗粒混合物中的三明治式分离

Sandwich-like segregation in vertically vibrated binary granular mixtures

在竖直振动两种颗粒的混合物的实验中 ,观察到了一种新的分离现象———“三明治”式分离 ,即大而重的颗粒被夹在两层小的轻颗粒之间 .这不同于“巴西果”效应导致的大而重的颗粒在上的两层有序结构 .实验表明当振动加速度大于某个临界值时这种三层有序将取代两层结构 ,而且是稳定的 .实验中观察到导致“三明治”式分离的两种不同的分离过程 .对这两种过程的物理机理及其与振动加速度、振动频率及颗粒尺寸等因素的关系做了研究 。

In a vertically vibrated binary granular mixture, sandwich-like segregation pattern is observed; a layer of large heavy particles is sandwiched in between two layers of small particles. This pattern is different from the double-layer structure, known as the 'Brazil nut' effect, where the large heavy particles populate on the top. Our experiments show that such a three-layer structure is a stable pattern. It occurs when the vibration acceleration is beyond a critical threshold. Two different segregation processes are observed. The mechanisms for these two segregation processes are discussed. The dependence of the segregation processes on the driving frequency f and acceleration Gamma, and the size ratio and volume ratio of the particles are also experimentally studied.