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

Synopsis: Teaching Fish How to Swim
Fluid Dynamics

Synopsis: Teaching Fish How to Swim

A new model of swimming fish and cetaceans pinpoints the parameters that matter most for efficient motion. Read More »

Viewpoint: Porous Materials Exhibit Granular-Like Stress Chains
Materials Science

Viewpoint: Porous Materials Exhibit Granular-Like Stress Chains

Simulations of porous materials exhibit internal stress patterns like those in granular materials, despite the fact that these two systems are practically “negative images” of each other. Read More »

Focus: Bacteria Form Waveguides
Biological Physics

Focus: Bacteria Form Waveguides

A laser beam sent through a suspension of marine bacteria pulls the organisms into the beam, which focuses the light. Read More »

More Articles