The break in the rhythm would do it for him. Pumping a fluid through a pipe in a pulsating fashion, in the rhythm of the heart pumping blood through the aorta, reduces turbulence and can therefore yield considerable energy savings. That write researchers of the Institute of Science and Technology Austria Wednesday in the scientific journal Nature.
That sounds great, but when asked, experts are skeptical about the application of the idea. The pause in pumping also creates a pressure wave, and an elastic aorta can absorb it better than a rigid pipeline.
Pumping and circulating liquids and gases takes a lot of energy. An estimated 10 percent of global electricity production is used for pumping. This ranges from a large scale – industrial oil and gas pipelines – to a small scale – the heating pipes in the home. It takes so much energy because friction in the pipelines creates vortices in the fluid (turbulence), with forces going in all directions instead of just forwards, as desired.
Another strategy
This is a known issue. Solutions are sought in pipe design or fluid composition. However, the human body uses a different strategy. Thanks to the rhythm of the heart, there is little turbulence in the bloodstream.
The idea of pulsating pumping is not new. The underlying idea is that an acceleration, which arises when a pump applies more force, slows down the generation of turbulent kinetic energy and reduces the shear stress with the wall of the pipe. Delay also affects resistance. Taking a break from pumping, as a heart does, had not been studied before.
The researchers experimented with a tube that was 1.2 meters long and had an inner diameter of one centimetre. A piston drove the water through an arrangement. At continuous speed, turbulence was seen throughout the tube. This is also the case with a uniformly changing speed. If the rhythm of the human heart was maintained, including a pause after the delay, no turbulence could be seen. The waves in the graph belonging to this variant resemble those of a cardiogram.
New energy in the wave
The explanation for this, according to the researchers, is that the pause in pumping decouples the acceleration from the preceding deceleration. This gives the turbulence the chance to dissipate before new energy enters the wave.
The researchers calculate the energy savings that this can yield at 9 percent, compared to pumps with continuous speed.
“The idea is nice and I think the measured effects on a laboratory scale are correct,” says Jerry Westerweel, professor of fluid dynamics at TU Delft. “But the phenomenon cannot be scaled up.”
Close the tap quickly
That’s because of the pressure wave caused by the delay. “There is a ‘water hammer’,” says Westerweel. “You can experience this at home if you turn off a tap quickly, then you hear a bang and the pipes vibrate. In the experiment of the Austrians, the degree of deceleration in combination with the short length of the tube does not result in significant pressure differences. But if you look at the dynamics of a pipe system on a scale used in the oil and gas industry, the pressure wave is significant.”
He calculates: “At a diameter of 20 centimeters, a pipe length of 10 kilometers and an oil velocity of 3 meters per second, a pressure wave of 30 bar can arise with the same variation of pulsating flow as in the article.” For comparison: the pressure in a water pipe is 2 to 4 bar.
The comparison with the bloodstream is flawed in more places. “The vein wall is elastic, which means that part of the energy goes into stretching the wall in a pulsating flow,” says Westerweel. “Also, the vasculature accommodates variations in blood flow by increasing the diameter of the blood vessel, which slows down the velocity of the flow. None of this is possible in a rigid tube, as in the article.”