Magnetically-stimulated fluid flow patterns may offer a new method for handling difficult heat transfer problems by overcoming natural convection limits, according to new research from scientists at Sandia National Laboratories.
Convection cooling, which refers to the transfer of heat between two places by the movement of fluids, is often forced in many modern cooling systems using pumps and fans with associated seals and valves placed in contact with the fluid. However, these moving components can eventually corrode and break, rendering the system unusable. In addition, convection cooling does not work in outer space where gravity does not exist or in a liquid beneath a hot object, placing limits on its use in certain situations.
Now, Sandia researchers Jim Martin and Kyle Solis say they have discovered a new technique that could be useful for cooling in microgravity or for transferring heat in circumstances that prevent convection. Known as isothermal magnetic advection, the new technique makes fluids move without mechanical assistance through the addition of a small amount of magnetic platelets to the liquid and the application of modest, uniform alternating current (AC) magnetic fields.
According to the researchers, the platelets are initially dispersed randomly throughout the liquid, but quickly form into patterns when a magnetic field is applied. The structure of the patterns, known as advection lattices, is dependent on the magnetic field that is used. Using this phenomenon, Martin and Solis created a heat valve with which they can control to transfer or block heat.
“The patterns are pretty remarkable because it’s not easy to understand why the fluid should flow in the first place because a uniform magnetic field does not exert a force on a particle, just a torque,” Martin said. Comparing the flow lattices to the patterns formed by flocks of birds, he added, “every bird [obeys] some simple rules like avoiding crashing into neighboring birds. There’s no leader. These patterns just spontaneously emerge from these simple rules. That’s more or less the same thing here. Each particle is obeying simple rules but collectively there’s this emergent behavior that’s quite surprising.”
The research is funded by the Department of Energy’s Office of Science.
