You probably don’t give much thought to the water running through your pipes, but it takes a surprisingly high amount of energy to get that water into your glass.
Pipe flows and hydraulic networks are responsible for approximately 10 per cent of the world’s electric energy consumption, and the main culprit is turbulence within the pipes themselves.
But a team of researchers from the Institute of Science and Technology Austria (IST) has developed a way to bring pipe turbulence down by as much as 90 per cent – saving almost 95 per cent of the energy costs in the process.
Order from chaos
Liquids such as water and oil flowing through pipes can best be described as organised chaos. The liquid flowing through the centre of the pipe moves much faster and more smoothly than the liquid flowing near the surface of the pipes, which experiences more drag and disturbances.
The result is turbulence, and consequently much more energy is needed to keep liquids pumping through pipes at high velocities. To make matters more difficult, turbulence, once begun, becomes self-sustaining, which makes mitigation hard and elimination downright impossible – until now.
IST Professor Bjorn Hof and a team of colleagues have developed a method to destabilise the turbulence so that liquids became laminar, or form into parallel layers that flow synchronously. What’s more, they observed that once this was achieved, the liquids remained in a non-turbulent state unless disturbed again.
The Hof group investigated the factors acting on liquids as they move through a pipe. They found that friction has immense influence on flow speed: liquids flowing closer to the walls of the pipe moved at a slower rate than the liquid flowing through the middle. This difference meant turbulence was inevitable.
But what would happen if liquid flowing near the walls moved at the same pace as liquid at the centre? If you could get liquid to flow at a consistent rate regardless of its position in the pipe, then the team theorised laminar flow would ensue and turbulence would cease.
In order to test this theory, the team conducted a few experiments to destabilise turbulence.
One involved a series of rotors placed along a pipe to reduce the speed difference between the fluid in the centre and that which was closer to the walls. As the highly turbulent flow proceeded further downstream from the rotor, the level of turbulence decreased until the entire flow was laminar.
Another experiment that achieved the same results was injecting liquid through small holes in the pipe wall, both perpendicular to the wall and parallel. Still another was swiftly moving a section of the pipe wall for a short distance.
“Nobody knew that it was possible to get rid of turbulence in practice. We have now proven that it can be done. This opens up new possibilities to develop applications for pipelines,” said team member Jakon Kuhnen.
Hof and his team have applied for patents for their discovery, but they admit it still has a ways to go before the proof of concept can be applied to pipes around the world. One issue to tackle is adjusting the method to account for larger velocities, but Hof stated that computer simulations look promising.
“In computer simulations, we have tested the impact of the flat velocity profile for Reynolds numbers up to 100,000, and it worked absolutely everywhere. The next step is now to make it work also for high speeds in the experiments,” Hof said.
These efforts could one day reduce the amount of energy it takes to keep water, gas and oil flowing through the roughly 3.5 million kilometres of pipes around the world, and thus reduce the cost and environmental impact of quenching our thirst, heating our homes and fuelling our cars.
