In 2024, Yan Li, Assistant Professor of Engineering, received an Irving Institute Faculty Seed Grant to advance her research in thermoelectric engineering in partnership with Oak Ridge National Laboratory. Building on this work, she, her PhD student Ya Tang, and her ORNL collaborator Xianhui Zhao, recently published a paper titled A Novel Thermoelectric System for Enhancing Power Generation from Waste Heat in Energy Conversion and Management.
Their innovative system maximizes power output by as much as 130% through modeling realistic temperature variations, unlike previous static approaches. This breakthrough has significant implications for energy conservation. By optimizing heat recovery and improving energy conversion efficiency, this technology could substantially reduce energy demand and carbon emissions. To learn more, I've interviewed Professor Yan Li about the research.
Question: What inspired you to focus on thermoelectric generators (TEGs) for waste heat recovery, and what potential do you see for this technology in addressing global energy challenges?
Professor Yan Li: Thank you for raising this important question. My interest in this research stems from the fact that many engineering systems, particularly in industrial processes and transportation, release a substantial amount of heat as a byproduct. Recovering this otherwise wasted thermal energy and converting it into electricity offers tremendous potential for advancing a more sustainable and energy-efficient future.
Traditional energy recovery systems, such as steam turbines, are heavy, bulky, and rely on multiple moving parts. Their size, complexity, and high maintenance requirements make them unsuitable for compact or distributed applications. In contrast, TEGs are compact solid-state devices without moving parts. Therefore, the maintenance cost is much lower. Another promising aspect of TEGs is that they are scalable both up and down. For example, they can be miniaturized to power wearable electronics or scaled up for deployment in geothermal wells. Because of these advantages, I do believe TEG technology holds tremendous potential for advancing global energy sustainability.
Question: Your research highlights a significant increase in power output using a novel system. Could you break down, in simple terms, the key innovations – the metastructure heat sink and turbulator – and explain how they synergistically achieve this improvement?
Professor Yan Li: Sure. TEGs exhibit optimal performance when a large temperature gradient is maintained between their hot and cold sides. However, due to heat transfer, this temperature gradient gradually decreases, leading to a reduction in the power output and overall efficiency of the device over time. To address this challenge, our work focuses on maintaining the temperature gradient as much as possible. We found that a metastructure heat sink can effectively dissipate heat from the hot side of the TEGs, while the turbulator can enhance the interaction between the cooling water and the heat sink. Both mechanisms promote more effective heat removal from the hot side of TEGs and therefore leading to more effective energy harvesting.
Question: The paper mentions limitations of existing models for TEG performance prediction. How does your model, using both computational fluid dynamics (CFD) and finite elements methods (FEM), overcome these limitations, and what advantages does it offer in designing and optimizing TEG systems?
Professor Yan Li: Previous simulation models often assume constant cold-side temperature that neglect the real-time thermal interactions in the TEG system. This simplification can lead to an overestimation of power output, as the temperature of the cooling water tends to rise over time, even in a steady-state environment. When a turbulator is included to enhance convective heat transfer between the cooling water and the heat sink, the system becomes more complex and these models are not applicable.
Our coupled CFD-FEM model accounts for transient heat flow, fluid dynamics, and material properties simultaneously. This model enables more accurate predictions of TEG performance under realistic conditions and allows us to optimize both geometry and placement of system components with greater confidence.
Question: The study considers a range of metastructure designs. What were the most surprising findings regarding the impact of heat sink geometry on overall system performance, and what general design principles emerged from this analysis?
Professor Yan Li: Great question. Our surprising finding was that an effective metastructure heat sink should have both a large cross-sectional area and a large surface area. The large cross-sectional area facilitates efficient heat transfer from the cold side of the TEG to the heat sink, while a large surface area promotes heat dissipation to the cooling water.
However, these requirements are geometrically contradictory. For example, increasing porosity is an intuitive way to increase the surface area, but it often comes at the cost of reducing the cross-sectional area available for heat conduction. It is indeed a trade-off in design. I think an AI-assisted tool will help us optimize the geometry without trial-and-error. This is an exciting direction we plan to explore in our next phase of research.
Question: How might this technology be most effectively applied in real-world scenarios?
Professor Yan Li: I think the TEG technology can be most effectively applied in real-world scenarios where waste heat is abundant, space is limited, and maintenance needs to be minimal. These are their biggest advantages compared to traditional energy recovery approaches. For example, in next-generation transportation vehicles, such as electric vertical take-off and landing (eVTOL) aircraft, TEGs can be integrated to harvest heat to supplement power from batteries without adding significant weight or requiring complex maintenance. TEGs can also reduce or eliminate the need for frequent charging in wearable devices used in military or medical applications. These are all exciting real applications where TEGs can really make a difference.
Question: The paper notes the limitations of current TE materials regarding temperature tolerance. What are the most promising avenues for materials research to overcome this challenge, and what impact would this have on the broader applicability of TEG technology?
Professor Yan Li: The narrow temperature tolerance of current TE materials remains a significant barrier to broader TEG adoption. Most commercial TE materials, such as bismuth telluride, perform well only in limited temperature ranges (typically below 300°C), which limits their use in high-temperature industrial or automotive environments. I think significant research efforts from the materials science community are underway to address this challenge. These efforts include the discovery of new high-temperature TE materials, as well as the nanostructuring and band engineering of existing compounds to improve their thermal stability and performance across a wider temperature range.
Question: For students looking to get involved in this field, what skills or knowledge would be most valuable, and what specific research areas offer the most potential for innovation?
Professor Yan Li: I believe thermoelectric materials research is inherently interdisciplinary and offers many exciting opportunities. From a materials science perspective, pushing the current temperature limits through the synthesis of novel material systems remains a highly promising area. Additionally, additive manufacturing of thermoelectric materials is still in its early stages, with significant challenges to overcome in establishing a robust design-to-manufacturing workflow. Moreover, the integration of AI for materials discovery, manufacturing optimization, and inverse design holds great potential to accelerate innovation and enable customized, high-performance thermoelectric devices.
For students interested in this area, a solid foundation in materials sciences, mechanics, thermal and chemical engineering is important. Specific skills, such as computational modeling (e.g, CFD and FEM modeling), material characterization (e.g., SEM, XRD, Seebeck and conductivity measurements) and 3D printing are highly valuable. Dartmouth offers programs and research opportunities to help students develop these skills.
Question: How does the cost-effectiveness of your proposed system compare to existing waste heat recovery technologies, and what steps are needed to make it economically viable for widespread adoption?
Professor Yan Li: Compared to existing waste heat recovery technologies, our proposed system does not require lubrication or mechanical upkeep. It can also harvest low-to-medium grade heat that is typically unusable by conventional systems. I think these are the primary cost advantages of our system and TEG systems in general. Currently the cost-effectiveness of TEGs is still constrained by the high cost of thermoelectric materials and relatively low energy conversion efficiency. At this point, the upfront cost may not be low, but they can be more cost-effective over the system's lifetime in applications.
Question: The research points to the importance of tailoring TEG system design to specific applications. What are some key considerations for adapting your design to different waste heat sources, such as those found in industrial processes, automotive exhaust, or solar-thermal setups?
Professor Yan Li: There are several key considerations for adapting TEG systems to specific applications. First, the operating temperature range and heat flow characteristics are critical for selecting appropriate thermoelectric materials, as each material has an optimal temperature range for maximum performance. For example, high-temperature materials are better suited for industrial furnaces, while low-temperature materials are appropriate for solar-thermal or automotive exhaust systems. Second, the mechanical operating conditions must be considered. Applications involving strong vibrations, such as automotive exhaust, require mechanically robust and vibration-tolerant system designs to ensure long-term stability. Finally, physical constraints and environmental exposure, such as space limitations, dust, moisture, or corrosive gases/liquids, must be accounted for when selecting materials and designing the system architecture.
Question: What are the next steps in your research? What specific aspects of the TEG system are you planning to further investigate or optimize?
Professor Yan Li: In the next phase of my research, we are focusing on two main thrusts. The first involves 3D printing thermoelectric materials with geometries that can conform to diverse application environments, such as the complex structures found in geothermal wells. The second explores thermoelectrocatalysis (TECatal), a hybrid approach that leverages the unique properties of thermoelectric materials to enhance both energy conversion and catalytic reaction efficiency. We are very excited about expanding the scope of our previous work into these emerging areas and finding new pathways for multifunctional energy systems and advanced materials integration.