Passive heat switching using temperature-dependent magnetic forces
Geoff Wehmeyer, Rice University
Friday, February 26, 2021
Heat switches are currently used to regulate the temperature (T) of batteries, electronic devices, car engines, and water heaters. The goal for all of these applications is to passively hold the system at a desired setpoint under variable external thermal conditions and/or energy generation rates, enabling improved efficiency and reliability. The most popular room-T heat switches make and break solid-solid contact using actuation mechanisms ranging from paraffin expansion to coefficient of thermal expansion mismatch or shape-memory alloy contraction. Although these switches have demonstrated thermal conductance turndown ratios >100:1, desired improvements in size, weight, and turndown motivates research into different mechanisms for next-generation heat switching.
Here, I will present our early results developing a compact passive magnetic heat switch (PMHS) for spacecraft thermal management applications. This PMHS uses T-dependent forces between ferromagnetic materials to bring surfaces in and out of contact, offering the potential for high conductance turndown (>400:1 estimated in a vacuum environment) with <1 cm switch thickness. We used finite-element thermal and magnetostatic calculations to design a PMHS with a switching T near 0oC, minimal hysteresis, and on-state contact pressures >10 kPa. Our preliminary experimental data shows that gadolinium and neodymium magnets can be used to achieve reversible T-dependent magnetic actuation near room T with <1oC hysteresis. I will conclude by sharing our future plans to demonstrate high PMHS turndown, and to apply these heat switches for improved spacecraft thermal control and next-generation solid-state refrigeration.
Meeting ID: 963 7926 0028