Nikola Tesla has gone from overlooked genius to folk hero and the inventor modern engineers want to be associated with. Nevertheless his ideas were so diverse many are not well known, including what he called a “valvular conduit”. A study of this device to use vibrations to pump fuel or other fluids has found it has unrealized potential 101 years after its patenting.
Just as angled barbs allow a solid object to move one way, but obstruct its removal, the device now known as the Tesla Valve uses a series of loops to let fluid flow in one direction while hindering counter-flow. Having no moving parts, Tesla Valves are much more resilient than standard check valves. The original design has inspired many imitations, efforts at improvement, and Youtube videos explaining how it works, but it seems these may have not grasped the full extent of the apparently simple patent.
"It's remarkable that this 100-year-old invention is still not completely understood and may be useful in modern technologies in ways not yet considered," Dr Leif Ristorph of New York University said in a statement.
Ristorph led a series of experiments on a prototype built to match Tesla's original design as closely as possible, attempting to pass liquids in both directions at different speeds and liquid viscosities. In Nature Communications Ristorph and co-authors report at low flow rates fluids move through the Valve equally easily each way. However, reverse flow above a certain speed is almost impossible, while flow rates can go much higher in the forward direction if the pressure is right.
"Crucially, this turn-on comes with the generation of turbulent flows in the reverse direction, which 'plug' the pipe with vortices and disrupting currents," Ristroph explained. "Moreover, the turbulence appears at far lower flow rates than have ever previously been observed for pipes of more standard shapes - up to 20 times lower speed than conventional turbulence in a cylindrical pipe or tube.”
Many technologies operate well in steady flow environments, but fail in the face of oscillating forces, part of the reason so many innovative ideas for harvesting wind or wave energy fail in the real world. The Tesla Valve is the reverse, actually working better when the fluid entering it comes in pulses, converting varying inputs to a steady output.
"We think this is what Tesla had in mind for the device, since he was thinking about analogous operations with electrical currents," Ristroph said. "He in fact is most famous for inventing the AC motor as well as an AC-DC converter."
Fluid physics operate very differently for small volumes and high viscosities, such as are used in diagnostic equipment, compared to the faster movements Tesla was seeking to facilitate. The authors think this could be part of the reason the Valve's potential has been missed for so long.
Ironically, Ristroph's validation of the Valve could come just as some of the uses he sees for it decline, displaced by the company named after its inventor. Ristorph thinks the valve could; “Harness the vibrations in engines and machinery to pump fuel, coolant, lubricant, or other gases and liquids.” No doubt such opportunities will still exist, but with the most widespread applications of engines running on fuel on the verge of being displaced by electric motors, the Valve might have missed its optimum moment.