Synopsis: Magnetized plumbing
Developed in the 1960s by NASA scientists seeking a nonmechanical method for moving liquid fuels in outer space, ferrofluids are comprised of magnetic nanoparticles suspended in carrier liquids. Although ferrofluids have found other uses, the original goal—to pump liquids—has remained elusive. Now, in an article in Physical Review B, Leidong Mao at the University of Georgia, Athens, and his colleagues report closed-loop ferrofluid pumping with simple electric coils.
In traditional approaches, a drop of ferrofluid placed in a thin tube can act like a piston when pulled by a permanent magnet moving along the tube’s exterior. But the maximum flow rate in a simple pump like this is only about one microliter per second. Several years ago, Mao’s coauthor Hur Koser and his colleagues proposed an alternative approach—using a set of electric coils to generate a traveling magnetic field that pumps ferrofluids directly without requiring any moving parts.
The authors have now realized this design with simple, inexpensive components. A closed loop of PVC pipe was wrapped with separate coils of copper tape and filled with a commercial ferrofluid consisting of magnetite nanoparticles suspended in mineral oil. When electric current runs through the coils, a wave of magnetic field (peaking at millitesla) passes down the pipe, drawing the fluid with it at a rate of around milliliter per second. Simulations showed that the field creates this propulsion by rotating the nanoparticles at varying speeds. The authors claim the same design could be scaled up in size for industrial systems, or down for microfluidic applications. – Michael Schirber