University of Wollongong Research Online University of Wollongong Thesis Collection 1954-2016 University of Wollongong Thesis Collections 2015 Design and construction of high temperature thermoelectric power generator module characterisation system Tomas Katkus University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/theses University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. 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Recommended Citation Katkus, Tomas, Design and construction of high temperature thermoelectric power generator module characterisation system, thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2015. https://ro.uow.edu.au/theses/4499 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] Institute for Superconducting and Electronic Materials Design and Construction of High Temperature Thermoelectric Power Generator Module Characterisation System Tomas Katkus This thesis is presented as part of the requirement for the Award of the Degree of Doctor of Philosophy of the University of Wollongong March 2015 ABSTRACT Thermoelectric (TE) power generators (TEGs) are used to convert thermal energy directly into electrical energy. Therefore, thermoelectric power generation is believed to be among key technologies that will allow harnessing of large amounts of waste heat produced in steel and automotive industries. Currently used TEGs have limited conversion efficiency and don’t have capacity to penetrate these highly important industry sectors. Nevertheless, thermoelectric power generators are already successfully used for waste heat energy recovery or for pure power generation in some of the niche fields, such as space applications, scientific equipment and facilities, and lasers. With increasing demand on clean energy sources and advancing thermoelectric technology/materials, the use of thermoelectric devices is becoming more prominent owing to their long lifetime, high reliability, and silent operation. Currently, the efficiency of a typical low temperature TEG is approximately 5 %. Thus, in order to make thermoelectric power generation more attractive as an alternative energy harnessing technology, the overall efficiency of a TEG has to be significantly improved. The most of the research efforts concentrate on the development of novel TE materials, which would have higher Figure of Merit (zT), a value that indicates how good/bad thermoelectric material is. It is a widely accepted fact that for practical considerations the Figure of Merit for any given thermoelectric material, p- or n-type, has to exceed unity. Recent studies on nanostructuring and chemical modifications of well-known semiconducting thermoelectric materials have shown peak ZT values as high as 2.4 in the vicinity of 300 K for Bi2Te3 and 1.8 at 850 K for PbTe. The concentration of research efforts in the field of TE materials can be explained by the fact that thermoelectric properties of materials can be readily characterised using off-the-shelf measurement systems. However, knowing fundamental characteristics of a given thermoelectric material cannot be directly related to the conversion efficiency of a TEG. 2 The manufacturing of a thermoelectric power module includes selection of TE materials, electrodes, insulating plates, adhesives, and module architecture. The complexity of this task is easily illustrated by a very small number of research papers describing characterisation of thermoelectric modules. Furthermore, in contrast to the thermoelectric material characterisation systems, there are no commercial systems available that would allow accurate characterisation of fabricated TEGs. The lack of such systems tremendously hinders the capacity to effectively characterise “lab- built” thermoelectric generators. Although few TEG measurement systems have been reported in the literature, they all lack one or more key features of a comprehensive TEG measurement system: high temperature capability, adaptability to modules of various sizes, ability to operate in an inert atmosphere, sufficient module clamping force, and/or accurate and seamless electrical characterisation ability. The main aim of this thesis was to design and construct a comprehensive computer controlled characterisation system, which would allow efficient characterisation of in-house built TEG modules. This system incorporates all of the above mentioned features in a bench-top engineering solution integrating high power heating, liquid cooling, hydraulic compression, force and temperature sensing – all in a controllable atmosphere. The measurement system has been specifically designed to accommodate wide range of TEG modules suited for low to high temperature applications. The system accurately reproduces application conditions the module may be subjected to in a real world environment. Moreover, it measures electrical and thermal performance properties of TEG modules. The main advantages of the built TEG module characterisation system are: Capability to measure TEG modules of various sizes; Simultaneous characterisation of multiple TEG modules; Maximum hot side temperature – 1000 °C; Variable atmosphere including air, argon, and/or vacuum; 20 kN module compression force can be applied during measurements; 3 A sophisticated custom built computer based interface for accurate data collection; Custom designed electronic load for seamless TEG electrical characterisation; Direct heat flux measurements using reference materials. Bismuth telluride based Thermonamic TEHP-12656-0.3 and Everredtronics TEG 127-50D TEG modules were characterised. Their performance data was analysed and compared to the available manufacturer data. The measured data correlated well with anticipated values, however, some discrepancies were observed due to the commonly overlooked inaccuracies in the conventional module resistance measurements. Further development of the system will ensure its suitability for accurate evaluation of TEG module performance. 4 ACKNOWLEDGEMENTS I would like to thank my supervisors Dr. G. Peleckis, Prof. X. L. Wang, and Prof. S. X. Dou for giving me an opportunity to work at the Institute for Superconducting and Electronic Materials and sharing their knowledge and expertise with me. I am grateful to the University of Wollongong for providing me with the scholarships for the PhD studies. Without those this work would have been impossible. Special thanks go to the AIIM workshop personnel, Mr. R. Morgan, Mr. P. Hammersley, Mr. J. Wilton, and Mr. M. Davies. Their knowledge, skills and expertise in the field help me to design this measurement system and achieve proficiency in mechanical and electrical engineering. Their major input in the selection of materials and design of certain components have reflected in the system being highly efficient. I would also like to express my gratitude to all of the friends in and outside of Australia. Their support meant a lot to me and helped me to concentrate on the tasks ahead. Lastly, I would like to thank my family and relatives for trusting me in accomplishing this major step in my life. 5 TABLE OF CONTENTS ABSTRACT ................................................................................................................. 2 ACKNOWLEDGEMENTS ......................................................................................... 5 TABLE OF CONTENTS ............................................................................................. 6 LIST OF TABLES ..................................................................................................... 10 LIST OF FIGURES ................................................................................................... 10 LIST OF TECHNICAL DRAWINGS ....................................................................... 16 LIST OF ABREVIATIONS ....................................................................................... 17 1 INTRODUCTION .................................................................................................. 21 2 THERMOELECTRIC DEVICE FUNDAMENTALS AND LITERATURE REVIEW .................................................................................................................... 25 2.1 Seebeck Effect ...........................................................................................