Thermoelectric Energy Harvesting in Harsh Environments and Laser Additive Manufacturing for Thermoelectric and Electromagnetic Materials

This dissertation presents innovative research at the intersection of thermoelectric solutions, additive manufacturing, and nuclear safety technology, addressing critical challenges in sensor powering for extreme environments, energy harvesting, and materials fabrication. The research is divided into three key areas, each contributing to advancements in its respective domain. First, a self-powered wireless through-wall data communication system was developed for monitoring nuclear facilities, specifically spent fuel storage dry casks. These facilities require continuous monitoring of internal conditions, including temperature, pressure, radiation, and humidity, under harsh environments characterized by high temperatures and intense radiation without any penetration through their walls. The constructed system integrated four modules: an energy harvester with power management circuits, an ultrasound wireless communication system using high-temperature piezoelectric transducers, electronic circuits for sensing and data transmission, and radiation shielding for electronics. Experimental validation demonstrated that the system harvests over 40 mW of power from thermal flow, withstands gamma radiation exceeding 100 Mrad, and survives temperatures up to 195°C. The system, designed to operate stably for fifty years, enables data transmission every ten minutes, ensuring reliable long-term monitoring for nuclear safety and security. Second, the efficiency of thermoelectric generators (TEGs), unique solid-state devices for thermal-to-electrical energy conversion, was explored through a novel manufacturing approach using selective laser melting (SLM) and direct energy deposition (DED). Conventional TEG fabrication methods have limitations in achieving optimal efficiency due to design and material constraints. SLM-based additive manufacturing offers a scalable solution for creating geometry-flexible and functionally graded thermoelectric materials. This research developed a physical model to simulate the SLM and DED process for fabricating Mg2Si thermoelectric materials with Si doping. The model incorporates conservation equations and accounts for fluid flow driven by buoyancy forces and surface tension, enabling detailed analysis of process parameters such as laser scanning speed and power input. The results provided insights into temperature distribution, powder bed shrinkage, and molten pool dynamics, advancing the understanding and optimization of thermoelectric device fabrication using additive manufacturing. One step further, SLM and DED experiments were carried out to validate the simulation results and testify to the feasibility of applying laser powder bed fusion on semiconductor materials. Third, the research investigates the application of laser additive manufacturing to improve performance and reduce the production costs of magnetic materials. Soft magnetic materials, critical for various industrial applications, are fabricated using DED. The research optimizes DED printing parameters and processes through quality control experiments inspired by the Taguchi method and analysis of variance models. The resulting silicon-iron samples exhibit minimal defects and cracks, demonstrating the feasibility of the approach. Detailed optical and scanning electron microscopy, coupled with magnetic characterization, reveal that the rapid cooling process inherent to laser-based AM enables unique microstructures that enhance magnetic properties. Collectively, this work addresses pressing technological challenges in energy harvesting, materials fabrication, and extreme environment monitoring. The developed systems and methodologies have broad implications for nuclear safety, additive manufacturing, and the efficient utilization of advanced materials. By integrating interdisciplinary approaches and leveraging cutting-edge manufacturing technologies, this dissertation contributes to the advancement of sustainable and resilient solutions for modern engineering challenges.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Department dc:contributor.department

Mechanical Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2024

Author dc:creator

• Sun, Kan

Chair dc:contributor.committeechair

• Huxtable, Scott T.

Committee members dc:contributor.committeemember

• Yu, Hang
• Tafti, Danesh K.
• Raeymaekers, Bart

• Thermoelectric
• Energy Harvesting
• Laser Additive Manufacturing

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:42284

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/123789