ME6750 Thermoelectrcs Desgn and Materals HoSung Lee, PhD Professor of Mechancal and Aerospace Engneerng Western Mchgan Unversty July, 017 1
Outlne Part I Desgn of Thermoelectrc Generators and Coolers Part II Thermoelectrc Materals
PART I Desgn 3
Thermoelectrc Phenomena Materal Room temperature - - - - - - - - - Room temperature - Free electrons E I Cold - - - - - - - - - V Hot Coulomb force Dffuson 4
Wre A Seebeck effect (181) V = α AB T Tc Wre B _ + I T h Wre B Pelter effect (1834) ሶ Q Pelter = π AB I. Q Thomson,A Wre A Thomson effect (1854) ሶ Q Thomson = τ AB I T. Q Pelter,AB T L _ Wre B + I. Q Thomson,B T H Wre B. Q Pelter,AB 5
Thomson Effect ሶ Q Thomson = τ AB I T 6
T j E T k Tj q Electrc Feld Heat Flow 0 T j dt d T j T k dt d T :Thomson coeffcent Gov. equaton 7
Ideal (Standard) Equaton Q h n T h I 1 I R K T h T c Thermoelectrc effect Joule heatng Thermal conducton Assumptons Thomson effect s neglgble Contact Resstances are neglgble Heat losses are neglgble Load resstance 8
Thermoelectrc Module Heat Absorbed p n n-type Semconductor p-type Semconcuctor p n p p n p n Postve (+) Electrcal Insulator (Ceramc) Heat Rejected Negatve (-) Electrcal Conductor (copper) 9
Converson Effcency max T c 1 T h 1 1 ZT 1 Tc ZT T h Z = α ρk = α σ k :Fgure of mert (1/K) where = Seebeck coeffcent, mv/ K; = electrcal resstvty, Wcm s = 1/ = electrcal conductvty (Wcm) -1 k = thermal conductvty, W/mK :Dmensonless fgure of mert 10
Maxmum Coeffcent of Performance COP max T T h c T c 1 ZT 1 T T h 1 1 ZT 1 c 3.7.4.1 1.8 0. DT/DT max = 0 0.1 DT/DT max = 0 0.1 0. 0.3 0.4 1 0.9 0.8 0.7 0.6 COP 1.5 0.3 0.5 0.5 Q c /Q cmax 1. 0.6 0.4 0.9 0.4 0.3 0.6 0.5 0.8 0. 0.6 0.3 0.8 0.1 0 0 0.1 0. 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 1 I/I max 11
Materals (Lee,016) 1
Exhaust Waste Heat Recovery Applcatons (TEG) Low Grade Waste Energy Recovery Mcro robots or devces Medcne (Wearable Electroncs) Solar Thermoelectrc Generator Radosotope Thermoelectrc Generator (RTG) on Mars Rover 13
Applcatons (TEC) Telecom Laser for Optc Fbers Medcal Instrument Automotve Ar Condtoner (Zonal Coolng) Car Seat Clmate Control Mcroprocessor Coolng 14
Mcro and Macro Analytcal Modelng Includng Ceramc and Electrcal Contact Resstance Q 1 = na ek c l c T 1 T 1c Q 1 = n αit 1c 1 I ρl o A e + ρ c A e A ek l o T c T 1c Q = n αit c + 1 I ρl o A e + ρ c A e A ek l o T c T 1c Electrcal contact resstance Q = na ek c l c T c T Ceramc thermal resstance I = α T 1c T c R L n + ρl o A + ρ c e A e Lee (016)-book Electrcal contact resstance 15
Mcro TEG (4. mm x 4. mm) Macro TEG (38 mm x 38 mm) Power Output (W) 3.5 1.5 1 Theory wth l = 1.14 mm Theory wth l = 1.5 mm Theory wth l =.54 mm CP1.4-17-045L, l = 1.14 mm CP1.4-17-06L, l = 1.5 mm CP1.4-17-10L, l =.54 mm 0.5 Lee (016)-book 0 0 0 40 60 80 100 Temperature Dfference (K) 16
Mcro TEG (4. mm x 4. mm) Macro TEG (38 mm x 38 mm) Lee (016)-book 17
ANSYS Numercal Smulatons (TEG)-Ths work 18
GM DOE Projects (005-016,$6 mllon) JPL, ORNL Purdue, U OF M, MSU, Marlow, Delph, Fraunhofer, etc. Skuttarudte Max. Power Output (W) 1 10 8 6 4 Predcton Experment, Salvador et al. (013) DT= 450 K 0 0 100 00 300 400 500 T (K) Marlow fabrcated module GM Suburban Descrpton Value Descrpton Value Seebeck coeffcent α n = 160 μvτk Seebeck coeffcent α p = 160 μvτk Electrcal resstvty ρ n = 0.45 10 3 Ωcm Electrcal resstvty ρ p = 1.7 10 3 Ωcm TE thermal conductvty k n = 3.7 WΤmK TE thermal k p =.75 WΤmK conductvty Ceramc thermal k AlN = 180 WΤmK Ceramc thermal k Al O 3 = 5 WΤmK conductvty for AlN conductvty for Al O 3 Electrcal contact ρ c = 1.6 10 6 Ωcm Cross-sectonal area A e = = 4 mm resstance Thckness of ceramc plate l c = 1.5 mm of TE element Leg length of TE l o = 4 mm Lee (016)-book (assumed) Number of thermocouples n = 3 element 19
010s 1950s Suggested Desgn wth Ceramc of Alumnum Ntrde (AlN) 0
PART II Materals 1
Fgure of Mert ZT = α σ k T = α σ k e +kl T :Dmensonless fgure of mert (1/K) where = Seebeck coeffcent, mv/ K; s = electrcal conductvty (Wcm) -1 k e = electronc thermal conductvty, W/mK k l = lattce thermal conductvty, W/mK Electrons: α σ (power factor), k e Lattce (Phonons): k l 3e s L o ke st k B 3 E g T n ne nem m Mott formula k e 1 m m E Wedemann-Franz law: B E E F Dffcultes
Effect of Nanostructured Materals Electron Relaxaton tme = constant Hcks and Dresselhaus (1993) Electron Relaxaton tme = functon of energy Lee (016)-book 4
Energy Envron. Sc. 014, 7, 51-68 5
Two approaches to mprove ZT 1. Electrons Not satsfactory-the present work tres to mprove usng ansotropy of materals. Phonons (Lattce) Nanocomposte materals Nanostructures quantum wells, nanowres, quantum dot superlattces (QDSL) etc. 6
Nanocomposte materals Scence, 008, 30, 634-638 (Poudel et al.)
Nanostructured materals nanowres Nature, 008, 451,163-167 (Hochbaum et al.)
Quantum Dot Superlattces (QDSL)-mpractcal Nature (001) Growth rate s so slow (1.4 mm/h) ZT =.6 at 300 K (B Te 3 /Sb Te 3 QDSL)(record) 9
Theoretcal Approaches for Thermoelectrc Transport Propertes 1. Classcal and Sem-classcal Theores Parabolc Sngle Band Model Nonparabolc Two-Band Kane Model. Frst-Prncples (ab nto) Calculatons Molecular Dynamcs (MD) Smulatons Densty Functonal Theory (DFT) 3. Monte Carlo Smulatons 30
E Valance electrons Conducton Band E C Band gap Eg 0 k Dopng level E V Valence Band 31
3 Nonparabolc Two-Band Kane Model (Lee, 016) : Densty of States 3 1 z y x d m m m m where : Densty-of-states effectve mass : Ferm ntegral g g B d v E E E E E T k m N g 1 1 3 1 3,, 0 3 0,, 1 de E E E E E E E f F m g g n l m l n
33 H H n e A e n R,, 1 :Hall coeffcent 1 1, 0 1 0, 1 0, 0 1) ( ) ( 3,, K d F F F F K K K A A n T E A :Hall factor where t m l m K A k s the ansotropy factor 1 1, 0 3, 3,, 3 c B d v F m T k m e N s : electrcal conductvty 1 31 t l c m m m 3 1 t l d m m m where F B E F F e k 1 1,1 0 1 1,1 1 1 F g B E E F F e k 1 1, 0 1 1, 1 s s s 1 1 : Seebeck coeffcents : total Seebeck coeffcent :conductvty effectve mass : densty-of-state effectve mass
Ansotropy Factor A K A magnetc feld H z n the z-drecton appled perpendcularly to an electrc current x n the x- drecton, wll produce an electrc feld defned by Ey n the y-drecton. Then the Hall coeffcent R H s R H E x y H z A K m m c d 3 3K K 1 K m l mt Ansotropy factor N s v, e 3 md, kbt 0 1 3 m c, 3 F 1, : electrcal conductvty Lee (016) 34
Comparson of the Present Model wth Measurements of PbTe (Lee,016) 35
Comparson of the Present Model wth Measurements of BTe3 (Lee, 016) 36
Tn Selende (SnSe) ZT =.6 at 900 K (record) ZT = 0.3 at 600 K Nature (014) 37
Comparson of the Present Model wth Measurements of SnSe (Lee, 016) 38
Tn Selende (SnSe) ZT =. at 733 K ZT = 1.5 at 600 K Nature Communcaton (016) 39
Fabrcaton of Sngle Crystal Czochralsk Technque Planetary Ball mllng 40
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Thermoelectrc Materals
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