Smashing fluids... the physics of flow

November 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: Videos Extract Mechanical Properties of Liquid-Gel Interfaces

More information: The full research report can be found online at Nature Communications at: www.nature.com/ncomms/journal/v1/n8/full/ncomms1119.html

Related Stories

Videos Extract Mechanical Properties of Liquid-Gel Interfaces

January 23, 2008

Blood coursing through vessels, lubricated cartilage sliding against joints, ink jets splashing on paper—living and nonliving things abound with fluids meeting solids. However important these liquid/solid boundaries may ...

Redirection reduces impact of erosion

October 6, 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, according ...

Groundwater threat to rivers worse than suspected

November 2, 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.

Recommended for you

Study calculates the speed of ice formation

August 3, 2015

Researchers at Princeton University have for the first time directly calculated the rate at which water crystallizes into ice in a realistic computer model of water molecules. The simulations, which were carried out on supercomputers, ...

Small tilt in magnets makes them viable memory chips

August 3, 2015

University of California, Berkeley, researchers have discovered a new way to switch the polarization of nanomagnets, paving the way for high-density storage to move from hard disks onto integrated circuits.

Scientists bring order, and color, to microparticles

August 3, 2015

A team of New York University scientists has developed a technique that prompts microparticles to form ordered structures in a variety of materials. The advance, which appears in the Journal of the American Chemical Society ...

Rogue wave theory to save ships

July 29, 2015

Physicists have found an explanation for rogue waves in the ocean and hope their theory will lead to devices to warn ships and save lives.

2 comments

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.