Cryogenic Cooling with a Single Crystal Bismuth Nernst-Ettingshausen Cooler
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Mechanical and Aerospace Engineering Undergraduate Research Theses; 2018
Conventional active cooling systems such as air conditioning and water heat pumps are cumbersome and involve moving parts, which can lead to wear over time. Alternatively, active cooling can be performed using thermomagnetic materials, providing a small form factor without any moving parts. Some semimetals, such as bismuth, can become a heat pump by using the Hall Effect; this is called a Nernst-Ettingshausen cooler. Under the influence of an electric current and a transverse magnetic field, electrons are forced to one side of the sample. The travel of electrons acts as a heat pump and creates a temperature gradient across the sample. The colder side could be used to draw heat from a desired surface to be cooled, without any moving parts. A drawback to Nernst-Ettingshausen coolers is that they are relatively inefficient as a heat pump, thus requiring more input energy to transfer a set amount of heat. Research is required to find semimetal alloys that can achieve a greater efficiency. This research seeks to create a bismuth single crystal to test its cooling characteristics. These results could provide insight into the feasibility of bismuth as a material for Nernst-Ettingshausen cooling and other solid-state cooling applications. The sample is placed in a chamber with a controlled ambient temperature. Electric current is passed through the sample in a transverse magnetic field. The resulting temperature gradient in the sample is then measured. This experiment is repeated by procedurally varying current and ambient temperature, while magnetic field is maintained constant. We found that the sample achieves a higher temperature gradient and exhibits greater cooling potential with higher applied current. The sample performs better at lower ambient temperatures. With improved mounting methods and strategically applied current, bismuth single crystal presents itself as a viable solution for Ettingshausen cooling.
Academic Major: Mechanical Engineering
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