Smashing fluids... the physics of flow

Nov 29, 2010

(PhysOrg.com) -- Hit it hard and it will fracture like a solid... but tilt it slowly and it will flow like a fluid. This is the intriguing property of a type of ‘complex fluid’ which has revealed ‘new physics’ in research by scientists at The University of Nottingham.

The new findings will be highly useful to the manufacturing industry because the processing and dispensing of everyday products like toothpaste, cosmetics, pharmaceuticals and foodstuffs depends on an understanding of the physical properties and behaviors of these fluids.

The research just published in Nature Communications by Dr. Michael Smith from the School of Physics and Astronomy, with collaborators at the University of Edinburgh and Politecnico di Torino, has used new methods to try to understand the flow properties of these concentrated solutions of .

Previous research has tried to measure flow properties by pressing the fluid between two circular rotating plates, called a ‘shear rheometer’, but this has limited applications relating to industrial manufacturing processes.

The new experiments tested various complex fluids in a different way using an ‘extensional rheometer’. Instead of squashing the substance, this device stretches it out between two plates at varying speeds to measure the flow properties. The method and the results gathered have revealed new physics which will have much better applications in manufacturing, for example, in the packaging and dispensing designs of many household products.

This video is not supported by your browser at this time.

Dr. Smith said: “Our observation of the fluid with a high speed camera revealed some intriguing effects depending on the concentration of particles and the speed at which the plates were moved. At low velocities the fluid is observed to behave like a liquid but at higher velocities and concentrations of particles the fluid can actually fracture like a solid. This happens if you dissolve a large amount of cornflour in some water, for example. The high concentration of tiny particles inside the fluid jam into one another forming clusters which lock solid if disturbed at a high enough speed.

“It is a bit like trying to move through a street crowded with an enormous number of people. If you move slowly enough you can make progress and the crowd and you ‘flow’. However, if you try and sprint down the street you will just knock into so many people that you’ll never be able to move at the speed you want to and hence everything becomes grid locked.”

The research was able to show that whilst many features of this kind of system were independent of the geometry of the flow examined, some effects due to the exposed fluid surface were much more important than had previously been thought. In particular an effect known as ‘dilatancy’ in which some of the particles poke through the surface of the liquid was found to play a crucial role in the jamming of the particles.

Dr. Smith added: “The most incredible results were observed when the fluid was stretched at a velocity just below that required to form a jammed fluid. The fluid was found to form a thin filament which narrowed until it was about hundred particles in diameter. At this point the fluid was observed to recoil elastically, like a rubber band!

“This is particularly fascinating since the particles are specifically designed to behave like hard spheres with no attractive forces. Where does the elasticity come from? The liquid drains from the filament faster than the particles causing them to poke through the surface as before. The liquid surface forms a meniscus around the particles. It is this curved surface of the which the researchers believe stores the energy and results in the unusual behavior.

“We hope this research provides an important initial step in understanding how the physics in common industrial flows may differ from the carefully controlled set up found in conventional academic studies”

Explore further: Finding faster-than-light particles by weighing them

More information: The full research report can be found online at Nature Communications at: www.nature.com/ncomms/journal/… full/ncomms1119.html

Related Stories

Groundwater threat to rivers worse than suspected

Nov 02, 2010

Excessive groundwater development represents a greater threat to nearby rivers and streams during dry periods (low flows) than previously thought, according to research released today by CSIRO.

Redirection reduces impact of erosion

Oct 06, 2010

The life expectancy of cooling plates in heat exchangers at Rio Tinto Alcan’s Yarwun alumina refinery has increased from a few days to as long as 12 months with help from CSIRO’s slurry erosion researchers, ...

Recommended for you

Finding faster-than-light particles by weighing them

18 hours ago

In a new paper accepted by the journal Astroparticle Physics, Robert Ehrlich, a recently retired physicist from George Mason University, claims that the neutrino is very likely a tachyon or faster-than-light par ...

Controlling core switching in Pac-man disks

Dec 24, 2014

Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage ...

Atoms queue up for quantum computer networks

Dec 24, 2014

In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed ...

New video supports radiation dosimetry audits

Dec 23, 2014

The National Physical Laboratory (NPL), working with the National Radiotherapy Trials Quality Assurance Group, has produced a video guide to support physicists participating in radiation dosimetry audits.

Acoustic tweezers manipulate cell-to-cell contact

Dec 22, 2014

Sound waves can precisely position groups of cells for study without the danger of changing or damaging the cells, according to a team of Penn State researchers who are using surface acoustic waves to manipulate ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Yellowdart
not rated yet Nov 29, 2010
I'm not sure why that is "new" physics. Hit a body of water at high velocity (like freefall) and that liquid definately feels like slamming into a brick wall.

Wouldnt the elaticity just be a function of the velocity and tension?
zevkirsh
not rated yet Nov 29, 2010
whatever liquid is in that video, it looks delicious.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.