Synopsis: Capillary Effect in Grains Explained

Numerical simulations show that a previously observed capillary-like action in vibrating grain systems is due to convective motion of the grains.  
Synopsis figure
F. Fan et al., Phys. Rev. Lett. (2017)

When a narrow tube is inserted into a bed of vibrating grains, the granular material rises up inside the tube, much like a liquid climbs through a thin straw. For liquids, this capillary, or wicking, action results from attractive interactions between the liquid molecules and the tube walls. But that explanation does not apply to grains—they do not stick to walls with enough force to defy gravity. New computer simulations show that the effect instead relies on friction-induced convective motion in the vibrating grains.

Fengxian Fan, from the University of Shanghai for Science and Technology, and colleagues simulated a rectangular container partly filled with spherical grains (0.6 mm diameter). In the center of the container, a cylindrical tube (8 mm diameter) descended into the grains. When the tube was vibrated up and down, the simulated grains rose up the tube to a height of around 50 mm. But the effect disappeared when the team made the container walls frictionless. Wall friction causes a well-known convective motion in shaken grain systems (called the Brazil nut effect) in which grains at the walls are pushed downward, while grains in the center move up. The team showed that when the inserted tube vibrates, the resulting grain convection produces a pressure in the bottom of the tube that pushes material upwards. This understanding might help in the design and development of a grain pump that could transport grains along pipes for industrial processes.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Soft MatterFluid Dynamics

Previous Synopsis

Quantum Information

A Dark Side for Qubits

Read More »

Next Synopsis

Related Articles

Focus: <i>Video</i>—Fluid Video Contest Winners
Fluid Dynamics

Focus: Video—Fluid Video Contest Winners

Swimming starfish larvae, dripping paint, and swirling gas jets are featured in the APS Division of Fluid Dynamics’ winning videos. Read More »

Synopsis: How to Make Superhydrophobicity Last
Fluid Dynamics

Synopsis: How to Make Superhydrophobicity Last

Researchers find tricks to prolong the typically short-lived water repellency of a superhydrophobic surface. Read More »

Focus: Drops Falling in Clouds Make More Drops
Fluid Dynamics

Focus: Drops Falling in Clouds Make More Drops

Experiments with a simplified version of the atmosphere show that falling drops seed many smaller droplets in their wake. Read More »

More Articles