Around the world, energy equivalent to 10% of global electricity production is expended just keeping liquids moving through pipes.
Until now, this extraordinary outlay was considered unavoidable, the cost of doing business in the face of physics, but a team of researchers from the the Institute of Science and Technology Austria (IST Austria) has found a way to reduce energy input potentially by as much as 95%.
Left to its own devices, liquid such as water or oil flowing through a pipe is an unruly phenomenon. The liquid flowing through the centre of the pipe moves faster, because it experiences less drag, than the liquid touching the sides.
The result of this inequality, inevitably, is turbulence, with the liquid crashing into itself chaotically, forming vortices, generating still more friction and therefore requiring the input of still more energy to keep it moving.
What’s more, turbulence, once begun, becomes self-sustaining. Until now, engineering solutions have focussed on reducing its severity, elimination being considered impossible.
Enter Björn Hof and colleagues from IST Austria, who tackled the problem from a new angle: instead of trying to dampen the turbulence, they tried instead to destabilise it.
The theory was uncontroversial. If you remove turbulence from a flowing liquid it will become laminar. That is, it will form into layers, which move smoothly in lockstep, never colliding with each other.
The problem in the real world, however, is that the differential drag experienced by liquid in contact with pipe walls compared to liquid flowing freely means turbulence is inevitable.
Hof’s team realised that this is because friction influences speed: if the liquid at the pipe-boundaries moved at the same velocity as the stuff in the middle, then turbulence would be avoided, laminar flow would establish, and everything would move along much more efficiently.
To achieve this, the researchers installed rotors at various points along a pipe. The turning blades reduced the velocity difference between fluid in different areas. The eddies that initiate the onset of turbulence were quickly dissolved, resulting in the creation of laminar flow.
Better still, the researchers found that the laminar state, once induced, was self-sustaining, remaining constant – at least in experimental set-ups – until the liquid completed its transit.
“Nobody knew that it was possible to get rid of turbulence in practice,” explains team member Jakob Kuhnen. “We have now proven that it can be done. This opens up new possibilities to develop applications for pipelines.”
The research is published in the journal Nature Physics.
Hof and colleagues concede that there is still substantial development work to be done in order to scale up the proof-of-concept to full industrial roll-out. However, the team has already taken out two patents on their designs – which was probably a very smart move indeed.