Pulsating instead of continuous fluid transport: A study shows that there is technical energy-saving potential in the pumping concept of the cardiovascular system. The experiments show that rhythmic bursts with rest phases, which are similar to the functional principle of the heart, can significantly reduce fluid friction in pipes. This in turn can reduce the energy requirement for pumping by up to nine percent, the researchers report.
Countless pumps are constantly running in industry and in private households around the world. They transport various liquids or gases through pipe systems - and do so with a gigantic amount of energy: according to estimates, pump systems are responsible for almost twenty percent of global electricity consumption. Opportunities for saving energy are therefore in great demand from an economic and ecological perspective. Scientists from the Institute of Science and Technology Austria (ISTA) in Klosterneuburg are also dedicated to researching optimization potential in the transport of liquids and gases.
“We have been trying for a long time to make the pumping of liquids more efficient. However, the optimization options revealed through simulations or laboratory tests are often too complex and therefore too expensive to be used in real applications. “We were therefore looking for an approach that did not require complicated structural changes to the infrastructure, such as sensors and motors,” says lead author Davide Scarselli from ISTA. Instead of changing the nature of pipes to reduce friction between the flowing fluid and the pipe walls, Scarselli and his colleagues focused on the pumps.
Exemplary cardiovascular system
The team looked to nature for inspiration: the cardiovascular system came into focus. “Like every part of our body, the human heart has been shaped by evolution over millions of years,” says senior author Björn Hof from ISTA. “Unlike conventional mechanical pumps, which generate a steady flow of fluid, the heart is known to pulsate. We were curious as to whether this particular type of drive offered an advantage,” says the scientist.
To explore this, the researchers carried out pumping experiments in experimental setups with transparent pipes of different lengths and diameters. They made the fluid dynamics visible by adding tiny reflective particles to the water. The team was then able to record their movements precisely: “A laser shoots light in a horizontal arc through the transparent tube and is reflected by the particles. “We took pictures of it that allowed us to see whether the flow was turbulent or laminar, the latter meaning that there were no vortices,” explains Scarselli.
The starting point was investigations into the flow effects of a uniform water flow, as generated by conventional pump systems. “This caused vortices to form that moved chaotically as they were pushed through the pipe,” says Scarselli. This turbulence causes much of the friction between the liquid and the walls of the pipe, the researchers explain. Overcoming precisely this friction has to be done by a pump and therefore costs energy.
Pulsating pumping calms turbulence
After collecting the basic data, the researchers then examined what happens if pulsating pumping is used to transport liquid instead of continuous pumping. They tested different forms of acceleration and rest breaks. As they found, certain pulsating pumping concepts increase the resistance and therefore the energy required. “However, when we added short rest periods between pulses, during which the pump does not drive the water at all – like the human heart does – this was not the case. During the rest phase, the turbulence decreases and in the subsequent acceleration phase, the friction is effectively reduced,” explains Scarselli.
The experimental data and calculations ultimately showed: With the optimal pulse pumping movement, which is similar to that of the human heart, there is a significant reduction in turbulence and thus in average friction by 27 percent. This now also illustrates why the cardiovascular system works this way: “In a biological context, a reduction in friction and turbulent fluctuations is clearly beneficial as it prevents damage to the cells in the innermost layer of our blood vessels, which are sensitive respond to shear stress,” says Hof. For the technology, however, the savings potential that comes with it is particularly relevant. Because compared to continuous pumping systems, the energy requirement is reduced by nine percent, according to the calculations. "So we could potentially use this in future applications," says Hof.
However, further research is needed until then, the researchers emphasize. “While we have shown promising results in the lab, translating our research into real-world applications is less straightforward,” says Scarselli. It remains to be seen to what extent it makes sense to adapt pump systems so that they can generate pulsating fluid flows. But the researchers see considerable potential. “We hope that other scientists will build on our findings to explore these nature-inspired solutions for applications,” concludes Scarselli.
Source: Institutes of Science and Technology Austria, specialist article: Nature, doi: 10.1038/s41586-023-06399-5