Background
Thermal switches have applications in the temperature regulation of cryogenic devices and in thermal storage in power generation. Several technologies are used for thermal switches, but the switching ratio (ratio of the effective thermal conductance between the on and off mode) is usually less than 5. According to theory, a thermal switch constructed with thermoelectric materials could provide significantly higher switching ratios. Additionally, a thermal switch made with thermoelectric materials could have its switching ratio adjusted by varying the electrical current supplied to the switch. It was the goal of this study to investigate the performance of common thermoelectric materials for use in a solid-state thermal switch
During this project, I assisted a fellow graduate student in the construction, testing, and analysis of a solid-state thermal switch utilizing common thermoelectric materials. Additionally, I developed a computer simulation to compare its theoretical performance to its experimentally observed behavior.
Device Construction & Testing
Common thermoelectric materials, bismuth telluride-based n- and p-type semiconductor materials, were chosen for the device. These materials were soldered to copper strips for current flow and placed on an alumina baseplate. The device was mounted in a cryostat and tested between 80 K and 400 K. Effective thermal conductance in the on and off mode, switching ratio, and transient response of the switch were measured during testing.
Outcomes
Testing demonstrated that a thermal switch constructed of bismuth telluride-based materials exhibits switching ratios of around 100 at small temperature differentials. It was also found that there was little variation in performance between -20 C and 140 C. The performance of the device aligned well with simulations, demonstrating that such devices could be engineered for different applications with a high degree of accuracy. This study was published in the International Journal of Heat and Mass Transfer, and I presented the research during the MRS Conference in 2019.
This project taught me how to develop tests for thermal devices, construct semiconductor devices, and apply complex academic concepts to novel situations.
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Reflection
In addition to the study I performed with a fellow graduate student, I would have liked to construct a test with control logic to see how well the switch could regulate temperature.