Dr Bjornar Sandnes at the Energy Safety Research Institute at Swansea University’s College of Engineering said: “It is true that sand moves in mysterious ways and can act as a solid support when you walk on the beach, but grab a handful, and the sand flows like a liquid between your fingers.  Cereal grains, sugar, soil, coal and pharmaceutical powders are other examples of granular materials that show similar complex behaviour.”

The researchers reported in Physical Review Letters that they found that such granular material separates into plugs when pushed along by a moving air-water meniscus.  Now the teamsay that this tendency for sand and other granular materials to jam up in tight spaces could be exploited to scrub off biofilms in hard to reach placesand could help solve a world-wide problem by preventing contamination and transmission of infectious diseases via medical and food processing equipment.

‌The new results also shed light on conveying of powders and grains through pipes and tubes, which is commonly used to transport materials from one place to another.

Dr Sandnes said: “It has been estimated that as much as 10% of the world’s energy consumption is related to processing of granular materials, yet it is surprising how much we still have to learn about granular flows.” 

The experiments carried out by lead author Dr Guillaume Dumazer at the University of Oslo demonstrate the problems that can arise when processing mixtures of gases, liquids and granular materials. A tube filled with a mixture of water and grains is slowly drained such that a moving air-water meniscus bulldozes up the grains. The grains eventually jam up, forcing the air to penetrate through the material, leaving behind a static granular plug. The process repeats until the whole tube is clogged full of plugs that choke the flow through the tube.

Watch the process

Read the study  

Dr Dumazer said: “Our system is an ideal case where it is relatively easy to observe the competing viscous and frictional forces acting on the granular material. The same forces are at play in oil-gas-sand transport, and in conveying of particulates in the chemical and pharmaceutical industries, and clogging causes problems in these applications.”

There are not only problems though. “We can now control how we make the plugs.” says Dr Sandnes. “We then push them back and forth with air pressure to scrub the inside surface of the tube clean. And when we’re done, we fluidize and flush the grains out.”

Synopsis on physics.aps.org http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.117.028002