Henry Moseley X-ray Imaging Facility, Department of Materials Science, The University of Manchester, Manchester, M13 9PL, UK.
Department of Mathematics, The University of Manchester, Manchester, M13 9PL, UK.
Sci Rep. 2021 Apr 19;11(1):8352. doi: 10.1038/s41598-021-87280-1.
When opening a box of mixed nuts, a common experience is to find the largest nuts at the top. This well-known effect is the result of size-segregation where differently sized 'particles' sort themselves into distinct layers when shaken, vibrated or sheared. Colloquially this is known as the 'Brazil-nut effect'. While there have been many studies into the phenomena, difficulties observing granular materials mean that we still know relatively little about the process by which irregular larger particles (the Brazil nuts) reach the top. Here, for the first time, we capture the complex dynamics of Brazil nut motion within a sheared nut mixture through time-lapse X-ray Computed Tomography (CT). We have found that the Brazil nuts do not start to rise until they have first rotated sufficiently towards the vertical axis and then ultimately return to a flat orientation when they reach the surface. We also consider why certain Brazil nuts do not rise through the pack. This study highlights the important role of particle shape and orientation in segregation. Further, this ability to track the motion in 3D will pave the way for new experimental studies of segregating mixtures and will open the door to even more realistic simulations and powerful predictive models. Understanding the effect of size and shape on segregation has implications far beyond food products including various anti-mixing behaviors critical to many industries such as pharmaceuticals and mining.
当打开一盒混合坚果时，常见的体验是在顶部找到最大的坚果。这种众所周知的效果是尺寸分离的结果，当摇动、振动或剪切时，不同大小的“颗粒”会自行分层。通俗地说，这被称为“巴西坚果效应”。尽管已经有很多关于这种现象的研究，但由于难以观察到颗粒材料，我们仍然对不规则较大颗粒（巴西坚果）如何到达顶部的过程知之甚少。在这里，我们首次通过时移 X 射线计算机断层扫描 (CT) 捕捉到剪切坚果混合物中巴西坚果运动的复杂动态。我们发现，巴西坚果在开始上升之前，首先必须充分向垂直轴旋转，然后当它们到达表面时最终恢复到平坦的方向。我们还考虑了为什么某些巴西坚果不会通过包装上升。这项研究强调了颗粒形状和方向在分离中的重要作用。此外，这种在 3D 中跟踪运动的能力将为分离混合物的新实验研究铺平道路，并为更现实的模拟和强大的预测模型打开大门。了解尺寸和形状对分离的影响不仅限于食品产品，还包括制药和采矿等许多行业中至关重要的各种防混合行为。
