MODELING AND SIMULATION OF A SEGMENTED THERMOELECTRIC GENERATOR _______________________________________ A Thesis presented to the Faculty of the Graduate School at the University of Missouri-Columbia _______________________________________________________ In Partial Fulfillment of the Requirements for the Degree Master of Science _____________________________________________________ by Qiuyi Su Dr. Thomas G Engel, Thesis Supervisor DECEMBER 2017 The undersigned, appointed by the dean of the Graduate School, have examined the thesis entitled MODELING AND SIMULATION OF A SEGMENTED THERMOELECTRIC GENERATOR presented by Qiuyi Su, a candidate for the degree of master of science, and hereby certify that, in their opinion, it is worthy of acceptance. Professor Thomas G. Engel Professor Mark Prelas Professor Yuyi Lin ACKNOWLEDGEMENTS I feel much indebted to many people who have instructed and favored me in the course of writing this paper. First and foremost, I would want to show my deepest gratitude to my supervisor, Professor Thomas G. Engel, a respectable and responsible teacher. He taught me three courses during my study in Mizzou. His patient, kindness and enlightening instruction help me to complete my study. Additionally, I would like to thank Professor Mark Prelas and Professor Yuyi Lin for their advice and willingness to serve on my master advisory committee. I shall also express my gratitude to all my teachers helped me to develop the fundamental and essential academic competence. Last but not least, I wish to thank all my friends, especially my three wonderful roommates, for their encouragement and support. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................... ii LIST OF FIGURES ....................................................................................... iv LIST OF TABLES ....................................................................................... vii LIST OF NOMENCLATURE .................................................................... viii ABSTRACT .................................................................................................. ix Chapter 1. INTRODUCTION ..................................................................................1 1.1 Background ...........................................................................................................1 1.2 Physics of Thermoelectric Generators ...................................................................2 1.3 Objective................................................................................................................5 1.4 Thesis Outline ........................................................................................................5 2. LITERAUTURE REVIEW ....................................................................7 2.1 Low Temperature TEGS .......................................................................................7 2.2 Medium and High Temperature TEGs ..................................................................8 2.3 Segmented Compatibility ......................................................................................9 2.4 Summary................................................................................................................9 3. MODEL BUILDING AND TESTING .................................................11 3.1 Geometry Structure .............................................................................................12 3.2 Properties of Materials ........................................................................................14 3.3 Computation and Results .....................................................................................14 4. MODEL OPTIZATION .......................................................................19 4.1 Raising Temperature Difference .........................................................................19 4.2 Reselecting Thermoelectric Materials .................................................................20 4.3 Rebuilding TEG’s Geometry ...............................................................................22 5. SUMMARY & CONCLUSION ...........................................................25 iii 5.1 Overview of the Project .......................................................................................25 5.2 General Process to Design a Segmented TEG ....................................................26 APPENDIX I ..........................................................................................28 APPENDIX II .........................................................................................32 REFERENCE ..........................................................................................33 iv LIST OF FIGURES Figure Page Fig. 1.1 Pie chart of 2014 US net generation by energy source .......................................................1 Fig. 1.2 Example of a basic TE battery ............................................................................................3 Fig. 1.3 Example of a paralleled TE battery ....................................................................................4 Fig. 1.4 Example of a paralleled and segmented TE battery ...........................................................4 Fig. 3.1 Fabrication process of a physical segmented TEGs.Source from [20].........................11 Fig. 3.2 COMSOL model of the segmented TEGs with the top plate unseen(a) Illustration of bottom plate (b) Illustration of segmented couples (c) Illustration of Cu electrodes (d) Illustration of external circuit .................................................................................................12,13 Fig. 3.3 Temperature distribution diagram with the top plate unseen .......................................15 Fig. 3.4 Equivalent electrical model of the TEG ........................................................................15 Fig. 3.5 Potential distribution diagram of open-circuit circuit with the top plate unseen .......15 Fig. 3.6 Potential distribution diagram of close-circuit circuit with Rload=0.95 and the top plate unseen ...................................................................................................................................17 Fig. 4.1 Temperature dependence of the TEG (a) Open-circuit voltage (b) Inherent resistance (c) Output power(d) Conversion efficiency................................................................................20 Fig. 4.2 Resistance distribution along n-type segmented TE legs. Source from [20] ...................23 Fig. 4.3 Flow-chart of the process of selecting segments materials .........................................23 Fig. 6.1 Temperature dependence of (a) Thermal conductivity (b) Seebeck coefficient (c) Electrical conductivity of Bi2Te3 .................................................................................................26 Fig. 6.2 Temperature dependence of (a) Thermal conductivity (b) Seebeck coefficient (c) Electrical conductivity of Bi0.3Sb1.7Te3 .......................................................................................27 Fig. 6.3 Temperature dependence of (a) Thermal conductivity (b) Seebeck coefficient (c) Electrical conductivity of PbSe0.5Te0.5 ........................................................................................28 Fig. 6.4 Temperature dependence of (a) Thermal conductivity (b) Seebeck coefficient (c) Electrical conductivity of Zn4Sb3 ................................................................................................29 Fig. 6.5 Temperature dependence of (a) Thermal conductivity (b) Seebeck coefficient (c) Electrical conductivity of 75% Bi2Te3, 25% Bi2Se3 ...................................................................30 v LIST OF TABLES TABLE ....................................................................................................................................... Page Table 1 Test results of the simulation model .................................................................................18 Table 2 Test results after raising temperature ................................................................................20 Table 3 Thermoelectric properties of thermoelectric materials .....................................................21 Table 4 Comparison of several electrical materials (T=450K) ......................................................22 Table 5 Thermoelectric properties of thermoelectric materials after replacement (T=450K) .......23 Table 6 Test results after replacing thermoelectric material ..........................................................23 Table 7 Test results after rebuilding TEG’s geometry...................................................................24 vi LIST OF NOMENCLATURE A cross section area m2 Es Seebeck field V/m I Output current A l length of the leg m T Absolute Temperature K Tc Cold side temperature K Th Hot side temperature K T Temperature difference K Rload load resistance Rin inherent resistance u Relative current density A/m2 Vo Open circuit voltage V Vload Output Voltage V P (Pmax) (max) Output power W QH Input power (Hot side) W s Compatibility factor 1/V z Figure of merit 1/K Seebeck coefficient V/K Thermal conductivity W/m/K t Efficiency of the TEG % Electrical Resistance /m Electrical conductivity S/m max Maximum efficiency by Carnot laws % vii Abstract Interest in thermoelectric generators for waste heat recovery has flourished in recent years. Typically, the efficiency