CAREER: Nonlinear Solid-State Thermal to Electrical Power Generators

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

Abstract Nontechnical: Solid-state thermal-to-electrical conversion devices such as thermoelectric, thermionic and Nernst power generators are proposed for industrial waste heat recovery and solar-thermal-electrical conversion modules. They provide a clean, noise-free, reliable and green energy solution. Most of these devices are of low efficiency, which limits their applications in the market. They are mostly studied and designed to operate in the linear regime under small temperature differences. Like any other heat engine, the efficiency increases as the temperature difference increases. Therefore, in real applications, it is desired to impose large temperature differences to obtain higher output powers and higher efficiencies. When large temperature differences are applied, electrons are out of equilibrium with lattice and under highly non-equilibrium conditions, responses can be nonlinear. Here, the PI will study the highly non-equilibrium and nonlinear regime numerically using a comprehensive Monte Carlo method for electron transport. The PI will use thermo-reflectance technique to study the device operation experimentally. The experimental and numerical results will be used to design solid-state power generators suitable to work under large temperature differences. The results serve as a step toward wide commercialization of solid-state power generators. The PI will partner with different local programs to arrange for workshops throughout the year, in which the PI will design different hands-on activities and will introduce students to computer programing, thermal imaging, and renewable energies. Technical: In solid-state power generators, it is desired to transport heat from cathode to anode via electrons while restricting heat transport via lattice. Therefore, it is advantageous to have highly non-equilibrium electrons and operate in the nonlinear regime. Most theoretical tools developed so far are valid only in the linear transport regime where the output powers are small. In the linear transport, materials figure of merit, ZT, determines the efficiency. In the nonlinear regime, ZT is not the only relevant parameter and other parameters such as convective heat transfer coefficient, strength of electron-phonon coupling; applied field and geometry of the device play important roles. To study the nonlinear regime, the PI will develop a Monte Carlo code for electron-phonon transport, enabling investigation of charge, spin and heat transport under large applied fields and for different device geometries. The inputs of the code including interfacial transmission will be calculated using first principles. In addition to the capability of this tool, such numerical codes will help developing a fundamental understanding of transport and insights for developing analytical models for device analysis. The full solution of heat transfer problem including convection/radiation will address more practical but equally important aspect of the efficiency optimization problem. Finally, the PI will use thermo-reflectance imaging and thermomagnetic characterization to study nonlinear transport experimentally. These experiments provide a method for validation of the numerical predictions and additional insights to the device operation.