Department of Physics, Emory University, Atlanta, Georgia 30322, USA.
Phys Rev E. 2017 Dec;96(6-1):062605. doi: 10.1103/PhysRevE.96.062605. Epub 2017 Dec 7.
Using experiments and simulations, we study the flow of soft particles through quasi-two-dimensional hoppers. The first experiment uses oil-in-water emulsion droplets in a thin sample chamber. Due to surfactants coating the droplets, they easily slide past each other, approximating soft frictionless disks. For these droplets, clogging at the hopper exit requires a narrow hopper opening only slightly larger than the droplet diameter. The second experiment uses soft hydrogel particles in a thin sample chamber, where we vary gravity by changing the tilt angle of the chamber. For reduced gravity, clogging becomes easier and can occur for larger hopper openings. Our simulations mimic the emulsion experiments and demonstrate that softness is a key factor controlling clogging: with stiffer particles or a weaker gravitational force, clogging is easier. The fractional amount a single particle is deformed under its own weight is a useful parameter measuring particle softness. Data from the simulation and hydrogel experiments collapse when compared using this parameter. Our results suggest that prior studies using hard particles were in a limit where the role of softness is negligible, which causes clogging to occur with significantly larger openings.
我们通过实验和模拟研究了软颗粒在准二维料斗中的流动。第一个实验使用薄样品室内的油包水乳状液液滴。由于表面活性剂覆盖在液滴上，它们很容易相互滑动，近似于软无摩擦的圆盘。对于这些液滴，在料斗出口处堵塞仅需要比液滴直径略大的狭窄料斗开口。第二个实验使用薄样品室内的软水凝胶颗粒，我们通过改变腔室的倾斜角度来改变重力。对于较小的重力，堵塞变得更容易，并且可以在较大的料斗开口处发生。我们的模拟模拟了乳液实验，并表明柔软度是控制堵塞的关键因素：颗粒越硬或重力越弱，堵塞就越容易。单个颗粒在自身重量下的变形分数是衡量颗粒柔软度的有用参数。使用该参数比较模拟和水凝胶实验的数据时，它们会重合。我们的结果表明，之前使用硬颗粒的研究处于柔软度可以忽略不计的极限，这导致堵塞发生时需要更大的开口。
