Title:

Thermomagnetic devices for thermal switching, amplification, and rectification

Speaker:

Prof. Geoff Wehmeyer

Affiliation:

Rice University, Mechanical Engineering

When:

Friday, October 4, 2024 at 11:00:00 AM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Akanksha Menon
amenon84@gatech.edu
4048945737

Abstract

Advanced thermal control devices such as heat switches allow electronics, batteries, and buildings to be regulated at a constant temperature over a range of external thermal conditions, leading to improved energy efficiency and durability. However, existing passive heat switches based on paraffin wax expansion are inconveniently bulky and suffer from large thermal hysteresis. In this talk, I will discuss our group’s centimeter-scale thermal devices that use temperature-dependent magnetic forces to passively make/break thermal contact between surfaces. First, I will introduce our thermomagnetic switch that achieves relatively large (~30x) thermal ON/OFF ratios in compact geometries with small (<5 oC) thermal hysteresis, near-room-temperature switching, and durability over >1,000 cycles. This device was developed for applications in spacecraft thermal management. Second, I will show a thermomagnetic three-terminal thermal transistor that can switch, amplify, and modulate heat flows from the thermal source to thermal drain by using the temperature at the thermal gate as a trigger. We have explored applications of these thermal transistors for thermal logic operations or waste heat scavenging. Lastly, I will explain how steady-periodic thermal oscillations due to temperature-dependent magnetic forces can be used to rectify heat flows in a thermal diode device. We built a thermal circuit using two anti-parallel thermal diodes to passively regulate buildings in both warm weather and cold weather environments. Thus, our device and circuit demonstrations show how advanced thermal control elements have the potential to improve system energy efficiency via passive thermal regulation.

Biography

Geoff Wehmeyer is an assistant professor in Mechanical Engineering at Rice University. He received his B.S. in Mechanical Engineering from the University of Texas at Austin in 2013 and his Ph.D. in Mechanical Engineering from the University of California, Berkeley in 2018 before joining the faculty at Rice. His research interests include thermal property measurements of nanomaterials and switchable/nonlinear thermal devices for advanced thermal management. Dr. Wehmeyer is the current Vice-Chair of the ASME Heat Transfer Division K-9 Committee on Nanoscale Thermal Transport. He is the recipient of Rice Engineering’s Research + Teaching Award for Tenure-Track Faculty and Rice’s Sophia Meyer Farb Prize for Teaching. His group’s research has been recognized with a NSF CAREER award and a NASA Early Career Faculty award.