Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 151735

151735 - Preventing Efficiency Degradation in Thermoelectric Generators With Advanced Metamaterial Designs for Waste Heat Recovery 

Introduction

Thermoelectric generators (TEGs) have garnered much attention from research and industrial fields for their ability to convert low-grade heat directly into electricity when a temperature gradient is applied to them. The advantages of TEGs include zero emissions, minimal mechanical parts, fast response, high reliability, and scalability to different applications. These advantages have attracted increasing attention from diverse fields including waste heat recovery, wearable devices, and solar energy utilization in response to growing energy demands.

However, TEGs also face multiple challenges, such as low energy conversion efficiency and efficiency degradation. This degradation is evidenced by the decreased thermal gradient over time due to thermal conduction, resulting in a 70-80% drop in output voltage/power after stabilization. While active cooling is an effective method to prevent this degradation, it requires efficient active cooling systems. Nonetheless, the energy cost of this cooling typically exceeds the power gain. This leads us to the objective of this study: how to prevent the degradation of efficiency and thereby enhance the voltage and power output.

Contributions

In this work, a honeycomb metamaterial heat sink is integrated with a TEG to serve as a passive cooling system. Without additional energy costs, this system can effectively prevent efficiency degradation. Moreover, an experimentally validated finite element model has been developed, capable of predicting the performance of any TEG integrated with metastructure designs. After a systematic study of metamaterial heat sinks, it is found that TEGs equipped with honeycomb metamaterial heat sinks can prevent efficiency degradation and contribute to higher output power. Compared to TEGs with conventional heat sinks, the output power of our optimal design can be improved by 30.51%.

Methods

In this study, a TEG performance testing platform has been built.  It comprises three main modules: computer analysis, measurement, and data acquisition. In the computer analysis module, a voltmeter is used to control the sampling rate and create real-time data collection of measured voltage. The measurement module includes a hot plate, a digital thermometer, a copper plate, and an iron stand with a clamp. Data acquisition involves attaching two electrodes, one positive and one negative, to the top of the sample and the copper plate, respectively. After positioning the sample on the copper plate, data acquisition begins efficiently on the testing platform. Two important performance parameters, open-circuit voltage (V_oc) and the current-voltage (IV) curves under various loads are measured. This data will be utilized to refine the finite element model.

The finite element model is then developed and validated by the experimental data. This model can predict the output power of TEGs with systematically-varied metamaterial designs—named square honeycomb, triangular honeycomb, re-entrant honeycomb, hexagonal honeycomb, and irregular design—each having dimensions of 40mm(L)×40mm(W)×40mm(H). Key design factors of unit cell number are also examined to quantify their effects.

Results

Introducing a honeycomb metamaterial design into heat sinks can effectively prevent thermal gradient loss in TEGs. Specifically, compared to TEGs with conventional heat sinks, output power can be increased by 9.25-18.28% in all TEGs with honeycomb-based heat sinks. Additionally, increasing the unit cell number of triangular and re-entrant honeycomb metamaterials from 4×4×4 to 7×7×7 can further boost output power by 10.07-11.82%.

Conclusion

This research introduces a new approach in applying metamaterial design concepts to enhance passive heat sink performance in TEG systems. The study considers various metastructure heat sink designs and evaluates their performance through an experimentally validated FEA model. The results indicate that honeycomb metamaterial heat sinks are more effective than the traditional heat sink in preventing efficiency degradation of TEGs. Specifically, a TEG with triangular honeycomb design can increase the open-circuit voltage and output power by 8.15% and 18.28%, respectively, compared to TEGs with conventional heat sinks. Conclusions from this study can serve as useful design guidelines for future TEGs, and provide valuable insights into optimizing efficiency, durability, and overall performance.

Presenting Author: Bo Huang Dartmouth College

Presenting Author Biography: I am an undergraduate student researcher at Dartmouth College intending on pursuing a degree in engineering science and a BA in electrical or mechanical engineering. I am currently affiliated with the Yan Li Lab under the Thayer School of Engineering.

Authors:

Bo Huang Dartmouth College
Ya Tang Dartmouth College
Yan Li Dartmouth College