Heart-like pumps can help save energy, shows Austrian study

Why current pumping isn't efficient

Researchers David Scarselli and Bjorn Hof at ISTA created several experimental setups where they pumped water through clear pipes of various diameters and lengths to see how water behaves inside them.

The water used in the experiments contained tiny reflective particles, and shining a laser through the clear pipes revealed the swirls and eddies as the water was pushed through the pipes. Referred to as turbulence, these swirls and eddies create friction between the liquid and the pipes, which requires more energy to be spent to overcome them.

Pumping like the heart

The researchers turned to the millions of years of evolutionary experience of the heart, which uses a pulsing motion to push blood to various parts of the body. The researchers used multiple ways of pulsated pumping in their experiments. Some would accelerate the water slowly and stop rapidly, while others accelerated it quickly, while the stoppage was slower.

These attempts increased the drag in the system and, therefore, the energy required for pumping, which was not the desired outcome of the experiments. However, when they introduced a short resting phase between the pulses, where no liquid is pumped, the results obtained were much better.

The resting phase between the pulses reduced the turbulence in the pipes, making it easier for the next acceleration to reduce friction. Using an action similar to that of the human heart, the researchers found a 27 percent reduction in mean friction and a nine percent reduction in energy demand.

"A reduction of friction and turbulent fluctuations is clearly advantageous in the biological context because it prevents damage to the cells sensitive to shear stress that make up the innermost layer of our blood vessels," said Hof in the press release.

Years of research have been put into making pumping fluids more efficient. However, these solutions are limited to the laboratory since they are too complex and, hence, expensive to be applied in the real world.

The ISTA research would also require that existing pumps be retrofitted to generate the pulsating motion. However, this would still be more cost-effective than modifications needed to pipe walls, the researchers added.

The findings were published in the journal Nature today.

Abstract:

Flows through pipes and channels are, in practice, almost always turbulent, and the multiscale eddying motion is responsible for a major part of the encountered friction losses and pumping costs1. Conversely, for pulsatile flows, in particular for aortic blood flow, turbulence levels remain low despite relatively large peak velocities. For aortic blood flow, high turbulence levels are intolerable as they would damage the shear-sensitive endothelial cell layer2–5. Here we show that turbulence in ordinary pipe flow is diminished if the flow is driven in a pulsatile mode that incorporates all the key features of the cardiac waveform. At Reynolds numbers comparable to those of aortic blood flow, turbulence is largely inhibited, whereas, at much higher speeds, the turbulent drag is reduced by more than 25%. This specific operation mode is more efficient when compared with steady driving, which is the present situation for virtually all fluid transport processes ranging from heating circuits to water, gas, and oil pipelines.