Eric Brown Lab

Mechanical Engineering
& Materials Science
Yale University

Dynamos

Droplet of iron powder suspended in Gallium Indium alloy. Left: no magnetic field. Right: with magnetic field
Fluid dynamos occur for example in the Earth and Sun where large masses of conducting fluid swirl around to generate a magnetic field. Demonstration of such an effect in a laboratory experiment remains a major scientific challenge. To meet this challenge, our group plans to develop suspensions of magnetic particles in liquid-metals with the necessary material properties to generate a dynamo in the laboratory. These materials will allow us to build the universe's smallest dynamo with the ability to tune magnetic and mechanical properties far beyond what has previously been available with pure materials, opening up new opportunities to experimentally investigate magnetohydrodynamics.

To develop these materials, we started with characterization of the surface properties and mechanical behavior of liquid metals [Xu et al., Phys. Fluids (2012), Xu et al., PRE (2013)], Xu et al., JoVE (2014)]. We also learned how to measure magnetic susceptibility of suspensions [Bai et al. (2017)]. These advances led to a suspending process in which an acid is used to clean and prevent oxidation of the liquid metal and suspended metal particles so that they can wet and suspend [Carle et al. (2017)]. With magnetic suspended particles we can reach a magnetic permeability up to 5 times larger than a pure liquid metal, which would allow stronger MHD effects than sodium, the current standard. The addition of nonmagnetic particles allows us to tune the viscosity independently by a factor of 160 to control turbulent effects separately. We anticipate these material properties are at or near the thresholds required to observe several MHD effects. For example, to create a spontaneous dynamo in a flow on the scale of about 20 cm, or reach a magnetic reynolds number of 1 (enough to see weak magnetohydrodynamic effects) in a laminar flow, or to observe Lorentz forces where the generated magnetic field could affect the flow in a feedback loop. Only further investigation will tell if these phenomena can be produced, but if they can be produced in small-scale laboratory experiments it opens up many possibilities for the use of MHD phenomena in device-scale applications.


Funding: NSF CBET 1255541 (Fluid Dynamics)