Pumps like the heart
According to an international study, nearly 20 percent of global electricity consumption is used for pumping liquids – from industrial applications that transport oil and gas to heating systems that pump hot water in private homes. A research team led by Davide Scarselli and Björn Hof from the Institute of Science and Technology Austria (ISTA) sought a way to reduce this energy demand and drew inspiration from nature. In a new study published in the journal Nature, they demonstrated that pulsating the pumping of liquids through a pipe, similar to how the human heart pumps blood, can reduce friction within the pipe – and thus also energy consumption.
Turbulent friction
“Over the years, researchers and engineers have tried to make pumping liquids more efficient,” says Davide Scarselli, lead author of the study. “While many solutions have been simulated or tested in laboratories, they are often too complex and therefore too expensive to be used in real-world industrial applications. We were looking for an approach that wouldn't require complicated structural changes to the infrastructure, such as sensors and motors.”
Instead of modifying the properties of the pipes to reduce friction between the flowing liquid and the pipe walls, the scientists tried a different approach. “Like every part of our body, the human heart has been shaped by millions of years of evolution,” explains Björn Hof, professor at ISTA. “Unlike conventional mechanical pumps, which generate a steady flow of fluid, the heart pulsates. We were curious to see if this unique form of propulsion offered any advantage.”
Instead of modifying the properties of the pipes to reduce friction between the flowing liquid and the pipe walls, the scientists tried a different approach. To this end, Scarselli and his colleague Atul Varshney created several experimental setups with transparent tubes of varying lengths and diameters through which they pumped water. "The starting point for our experiments was a steady flow of water in which eddies moved chaotically as they were forced through the tube," explains Scarselli. These eddies are called turbulence and cause much of the friction between the fluid and the tube walls. Overcoming this friction requires energy.
The researchers visualized the turbulence by adding tiny reflective particles to the water and shining a laser through the transparent tube. Scarselli adds: "The laser shoots light in a horizontal arc through the tube, which is reflected by the particles. We took images of this, which allowed us to determine whether the flow was turbulent or laminar, the latter meaning there were no eddies."
Reduced Friction Through Rest Periods
Next, the researchers experimented with different types of pulsating pumps. In some pulse patterns, the water was first accelerated slowly and then quickly stopped; in others, it was the other way around. Hof explains the results: “Normally, pulsating pumps increase resistance and the energy required, which wasn’t what we were looking for. However, when we inserted a short rest period between pulses, during which the pump didn’t drive the water—just like the human heart—we achieved much better results.”
For an optimized pulsating pumping motion similar to that of the human heart, the researchers found a 27 percent reduction in mean friction and a 9 percent reduction in energy consumption. “A reduction in friction and turbulent fluctuations is clearly advantageous in a biological context, as it prevents damage to the cells in the innermost layer of our blood vessels, which are sensitive to shear stress. We could potentially learn from this and use it in future applications,” explains Hof.
Scarselli adds: “While we have shown promising results in the lab, applying our research in the real world is less straightforward. To generate these pulsating motions, the pumps would need to be modified. However, this would still be much less expensive than modifying the pipe walls or installing motors. We hope that other scientists will build on our findings to explore these nature-inspired solutions for industrial applications.”