Sandia’s Jim Martin and Kyle Solis (both in the Nanoscale Sciences Dept.) have discovered how to harness magnetic fields to create vigorous, organized fluid flows in particle suspensions. The magnetically stimulated flows offer an alternative when heat transfer is difficult because they overcome natural convection limits. Martin and Solis even demonstrated a heat-transfer valve that could potentially control computer processor temperature.
“Just because an effect is easy to generate doesn’t mean that it’s going to be easy to understand,” Martin said. He and Solis know that the observed mysterious flow patterns are a result of complex behavior stemming from fundamental phenomena—that they believe that they can come to understand and explain. It is also a tough problem to simulate because of the very large scale of the flow patterns when compared to the tiny particle size.
It’s not necessary to use very strong magnetic fields for the fluid flows. The researchers generate a uniform multiaxial alternating current magnetic field with a specially constructed magnet consisting of three nested pairs of coils arranged to create three mutually perpendicular magnetic fields. Imagine a rectangular box with a wire coil glued to each of the six sides. Coils on opposite sides are wired together and produce a field directed along their cylindrical axis. The arrangement enables researchers to create magnetic fields with independent frequencies along the north-south, east-west and up-down directions simultaneously. The net effect is a magnetic field whose direction and magnitude vary wildly and rapidly with time.
Martin and Solis found the patterns occur only for magnetic particles shaped like plates, essentially magnetic confetti. Spherical and rod-like particles don’t produce the effects. The pair used the phenomenon to create a heat valve they can control to transfer or block heat. They made flow cells a few inches long with blocks on the outside walls through which water flows to keep the blocks cold. The water blocks flank a chamber divided by a razor-blade-size heater made of plastic embedded with wire. To test thermal-transfer properties, the researchers run current through the heater and measure how hot it gets. Because the temperature depends on the heat-transfer properties of the chamber’s magnetically structured fluid, they control the temperature by controlling the flow created by platelets in the magnetic field.
Because a uniform magnetic field can be easily scaled to any size, he said, the technology could be practical in problems ranging from reactor cooling to microfluidics, a multidisciplinary field used, for example, in designing systems that handle minute volumes of fluids, such as blood samples.
The pair’s research, funded by the DOE Office of Science, is concentrating on extending fundamental understanding of novel heat transport in liquids, evaluating the effectiveness of various flows and exploring what happens when researchers modify experimental parameters.
Read the Sandia news release.
View a brief video of Jim Martin and Kyle Solis explaining their research on the effects of magnetic fields on fluid flows and how they stimulate vigorous flows.