Copyright 2018 Robert Clark
In the blog post Pumping pressurized fluids to high altitude for the space tower and for fighting forest fires, Page 2: high volume, high head, single pump solution, I speculated that we might be able to send water streams long distances, kilometers long, without piping by using laminar flow. As shown in the videos, on that page laminar flows displays surprising cohesiveness in the water streams, and extends the distances possibile over standard streams.
Studies on the flow distance of non-laminar water streams show their distance is dependent on where the break-up distance occurs, . This is known to be dependent of turbulence within the piping. Laminar flow achieves longer distance because of reduced turbulence. Then the natural question to ask is how much we can reduce turbulence.
Certainly, a rough surface within a pipe induces high turbulences. Then the best we could do to reduce that is to use an atomically flat surface. A report shows at least in helium gases shows atomically flat surfaces can reduce drag by orders of magnitude:
Date: June 20, 2018
Source: University of Manchester
Published in Nature, this new research shows that the channels allow gas through them at rates that are orders of magnitude faster than expected from theory. This will not only be important for fundamental studies on molecular flows at nanoscale but also for applications such as desalination and filtration.
The reported anomalously-high flow is due to a phenomenon called 'specular surface scattering', which allows a gas to pass through the channel as if it were not there at all.
Note this would be important not just for inducing low turbulence and laminar flow for a pipe-free approach but also for the approach using piping to reduce drag and pressure loss.
Actually, there are two effects involved in this report that need to be investigated separately. One, is that the surface is atomically flat, the other is that the channels are at nanoscopic widths.
The flatness at atomic scales would likely reduce drag and turbulence for macroscale pipes, and therefore also improve the laminar flow effect on exiting the pipe.
But an aspect of how laminar flow streams are produced suggests the nanoscale piping in itself would also improve laminar flow. In the case of laminar flows in amateur experimenters, they were produced by using multiple small straws placed within the pipe to produce multiple small streams. The experimenters noted the effect is much better for small straws as for example coffee stirrers compared to larger straws as used for example sodas. Then the natural question that needs to be investigated is how much better would the effect be for microscale and nanoscale piping.
In extending the results of the published report on helium gases to water another effect needs to be taken into account, the stickiness of water on surfaces. Materials low in this measure are called hydrophobic. Recent research has been on materials extremely low on this measure called superhydrophobic. In this case simulations and experiments show the drag can be reduced 50%, .
1.)Theoretical Range and Trajectory of a Water Jet.
2.)An analysis of superhydrophobic turbulent drag reduction mechanisms using direct numerical simulation.
Physics of Fluids 22, 065102 (2010);
Michael B. Martell, Jonathan P. Rothstein, and J. Blair Perota