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NSF-DOE Thermoelectrics Partnership:
Automotive Thermoelectric Modules with Scalable Thermo- and Electro-Mechanical Interfaces
Prof. Ken GoodsonDepartment of Mechanical EngineeringStanford University
Dr. Boris KozinskyEnergy Modeling, Control, & ComputationR. Bosch LLC
Prof. George NolasDepartment of PhysicsUniversity of South Florida
Automotive Thermoelectric Modules with Scalable Thermo-and Electro-Mechanical Interfaces
Project LeadershipProf. Ken Goodson, Stanford Mechanical EngineeringProf. George Nolas, USF Department of PhysicsDr. Boris Kozinsky, Energy Comp. & Modeling, BoschProf. Mehdi Asheghi, Stanford Mechanical EngineeringDr. Winnie Wong-Ng, NIST Functional Properties Group
StaffDr. Yongkwan Dong, USF Department of PhysicsDr. Matt Panzer, Stanford Mechanical Engineering
Students:Yuan Gao, Lewis Hom, Saniya Leblanc, Amy Marconnet
Leveraged Support:Northrop Grumman, AMD/SRC, ONR, AFOSRFellowships from NSF, Sandia National Labs, Stanford DARE
Program Managers: John Fairbanks, Tom Avedisian (DOE). Arvind Atreya (NSF)
Key Challenges for Thermoelectricsin Combustion Systems
…Low-thermal-resistance interfaces with tailored electrical properties, which are stable under thermal cycling.
…High-temperature TE materials that are stable and promise low-cost scaleup.
…Characterization methods that include interfaces and correlate better with system performance.
hot side / heat exchanger
insulation / e.g. ceramic plate
conductor/ e.g. copper
insulation / e.g. ceramic plate
cold side / heat exchanger
conductor/ e.g. copper conductor/ e.g. copper
n p
thermalthermal
electrical& thermal
electrical& thermalthermalthermal
diffusion barrier
joining technology
contact resistanceHeat
Cooling
hot side / heat exchanger
insulation / e.g. ceramic plate
conductor/ e.g. copper
insulation / e.g. ceramic plate
cold side / heat exchanger
conductor/ e.g. copper conductor/ e.g. copper
n p
thermalthermal
electrical& thermal
electrical& thermalthermalthermal
diffusion barrier
joining technology
contact resistanceHeat
Cooling
600 °C
90 °C
Improvements in the intrinsic ZT of TE materials are proving to be very difficult to translate into efficient, reliable TEG systems.
Major needs include…
Thermal Interface Challenges for Thermoelectrics
• Combustion systems experience enormous stresses at interfaces due to large temperature differences.
• Interfaces must offer low thermal resistance, targeted electrical performance, mechanical compliance.
Thermoelectric Interface Challenge
200 µm
Connecting metal
Solder
Hatzikraniotis et al., Proc. Mater. Res. Soc. Symp., 2009.
Clin et al., J. Electronic Materials, 2009
“Nanostructured Interfaces for Thermoelectrics,”Gao, Marconnet, Leblanc, Shakouri, Goodson et al., Proc ICT 2009, J. Electronic Materials, 2010
Pettes, Hodes, Goodson, Trans. Advanced Packaging, 2009
0 2 4 6 8 10 12 14 16 18 200
20
40
60
80
100
120
140
160
180
200
TEM thickness (mm)
Pow
er (W
)
No interfaceThermal greaseSolderCNT array
LeBlanc, Gao, Goodson,Proc. IMECE 2008
Thermal Interface Challenges for Thermoelectrics
Thermoelectric Interface Challenge
200 µm
Connecting metal
Solder
Hatzikraniotis et al., Proc. Mater. Res. Soc. Symp., 2009.
Clin et al., J. Electronic Materials, 2009
TEG (combustion)
“Nanostructured Interfaces for Thermoelectrics,”Gao, Marconnet, Leblanc, Shakouri, Goodson et al., Proc ICT 2009, J. Electronic Materials, 2010
Pettes, Hodes, Goodson, Trans. Advanced Packaging, 2009
• Combustion systems experience enormous stresses at interfaces due to large temperature differences.
• Interfaces must offer low thermal resistance, targeted electrical performance, mechanical compliance.
Automotive Thermoelectric Modules with Scalable Thermo- and Electro-Mechanical Interfaces
GOALSDevelop, and assess the impact of, novel interface and material solutions for TEG systems of interest for Bosch.
Explore and integrate promising technologies including nanostructured interfaces, filled skutterudites, cold-side microfluidics.
Practical TE characterization including interface effects and thermal cycling. METHODS
Multiphysics simulations ranging from ab-initio (band structure) to system scale.
Photothermal metrology including Pico/nanosecond TDTR, cross-sectional IR. MEMS-based mechanical characterization.
System impact assessment considering the interplay of thermal, fluidic, mechanical, electrical, and thermoelectric phenomena.
Removable backer
Nanostructured Film
Mid-temperature binderAdhesion layer
Panzer, Dai, Goodson, et al., Patent Pending (2007)
BoschPrototype TEG in exhaust system
Hu, Fisher, Goodson, et al., J. Heat Transfer (2006)
Area(emphasis)
Specifics Source
Interfaces100%
Nanostructured films & composites, metallic bondingAb initio simulations and optimization
StanfordBosch
Metrology100%
(ZT)eff with independent k&cp, thermal cyclingHigh temperature ZT
StanfordUSF/NIST
Materials100%
Filled skutterudites and half Heusler intermetallicsAb initio simulations for high-T optimization
USFBosch
Durability50%
In-situ thermal cycling tests, propertiesInterface analysis through SEM, XRD, EDS
StanfordBosch
Heat sink50%
Gas/liquid simulations using ANSYS-FluentNovel cold HX using microfluidics, vapor venting
BoschStanford
System50%
System specification, multiphysics codeEvaluation of research impacts
BoschStanford
Outreach TE for vehicles competition, UG Lab, K-12 outreach Stan&USF
Research Overview
Heavy-ion Filling Yields Lower Thermal Conductivity. Low Valence Filling Facilitates Optimization of Power Factor and ZT.
Nolas et al., MRS Bulletin (2006).Nolas, Kaeser, Littleton, Tritt, APL 77, 1855 (2000), Nolas, JAP 79, 4002 (1996)
Lamberton, G.S. Nolas, et al. APL 80, 598 (2001). Nolas, Cohn, and Slack, PRB (1998)
Bulk TE Materials for Automotive Applications
•Skutterudites with partial filling using heavy, low valence “guest” atoms
George S. NolasDepartment of Physics,
University of South Florida
Heavy-ion Filling Yields Lower Thermal Conductivity.
Partial Filling – Optimization of mobility & thermal conductivity
Bulk TE Materials for Automotive Applications
George S. NolasDepartment of Physics,
University of South Florida
•Half-Heusler alloys: from small grain size towards the disordered state
x= 0.3 ; y = 1.5
x= 0.05 ; y=0
x= 0.6 ; y = 2.4
x= 0.23 ; y=0
x= 0.75 ; y = 2.6
x=y=0
x= 0.9 ; y = 2.4
LaxCo4Sb12-ySny
x= 0.3 ; y = 1.5
x= 0.05 ; y=0
x= 0.6 ; y = 2.4
x= 0.23 ; y=0
x= 0.75 ; y = 2.6
x=y=0
x= 0.9 ; y = 2.4
LaxCo4Sb12-ySny
Nolas et al., MRS Bulletin (2006).Nolas, Kaeser, Littleton, Tritt, APL 77, 1855 (2000), Nolas, JAP 79, 4002 (1996)
Lamberton, G.S. Nolas, et al. APL 80, 598 (2001). Nolas, Cohn, and Slack, PRB (1998)
•Skutterudites with partial filling using heavy, low valence “guest” atoms
Ab-initio/BTE computations will assist the optimization of TE material stoichiometry.
Past work at Bosch predicted the effect of Ba filling on CoSb3 skutterudites using DFPT.
Collaborative optimization with Nolas group will focus on filled skutterudites, mobility, seebeck, and interfaces with metallics.
Functional Simulation & Optimization of Materials
Seebeck coefficient
experiment*ab-initio
ab-initio τ(E)
Resistivity
experiment
CoSb
ab-initio
Boris Kozinsky (CR/RTC2-NA) | 12/14/2010 | © Robert Bosch GmbH 2010. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.
Research and Technology Center North America
Dr. Boris Kozinsky, Energy Modeling, Control, and Computation, Bosch LLCWee, Kozinsky et al, Phys. Rev. B 81 (2010)
Interface Modeling & OptimizationKozinsky, Physical Review Letters (2006). Panzer, Goodson et al. JAP (2008)
CTE of TiNiSn Half-Heusler Alloys
(Bosch) exp
ab-initio
Unfilled CoSb3 (stable)
OrthorhombicCoSb2 (Unstable)
MonoclinicCoSb2(Stable)
Co-Sb phase diagramEn
ergy
Diff
eren
ce p
er A
tom
(eV)
Simulations examine thermodynamic stability of TE material phases and assess potential for interdiffusion.
Simulations examine interface electrical conduction and optimize resistance considering band structure.
Mechanical & thermal simulations will focus on the expansion coefficients and transport through low-dimensional contacts.
Panzer, GoodsonJ. Appl. Phys (2008)
Low-dimensional contact resistance
Conduction Physics in CNT Films
SubstrateSubstrateSubstrateSubstrate
Individual CNT conductance
Inter-tube contact
Nanoscale metal-CNT interface resistance (phonons)
Partial nanotube engagement
Spatially varying aligment
Growth interface resistance
Pop,Dai,Goodson et al. Physical Review Letters (2005)Pop,Dai,Goodson et al. Nano Letters (2006)Hu,Fisher,Goodson et al. Journal of Heat Transfer (2006,07)Panzer,Dai,Goodson et al. Journal of Heat Transfer (2008)Panzer,Goodson Journal of Applied Physics (2008)Gao,Shakouri,Goodson et al. Journal of Electronic Materials (2010)Panzer,Murayama,Goodson et al. Nano Letters (2010)
Nanosecond Thermoreflectance Picosecond Thermoreflectance
Cross-sectional IR MicroscopyMechanical Characterization
Sample Film
Heat Sink (Si or metal substrate)
Metal CoatingPulsed Laser
Heating
Probe laser for thermometry
Transparent Substrate (e.g. quartz)
Metal CoatingCNT Catalyst
CNT
Laser Doppler Velocimeter
Vibrometer, ω
Polysilicon CNT
Si substrateOxide
Heater
growth substrate
CNT Film
CNT
kdxdT 1
∝
BRTdxdTk
→∆
∝
−1
500 μm
Distance (μm)
Thermal and MechanicalCharacterization of Aligned CNT Films
010203040506070
0.005 0.006 0.007 0.008 0.009
Metallization and CNT Thermal Resistanceusing Nanosecond Thermoreflectance
RCNT-Sub + RCNT
Rtot
RCNT-Metal
φ= Ceff/Cv,individual
Ther
mal
Res
ista
nce
(m2 K
/MW
)
Ti
Pt Pd
Al
Ni
║0.10
PotentialPerformance
Panzer, Murayama, Wardle, Goodson, et al., Nano Letters (2010)
CNT Engagement Factor
Mechanical Behavior of CNT Films
Maruyama Lab Samples (SWNT), 95 kg/m3
MonanoSamples (MWNT), ~30 kg/m3
Wardle Lab Samples/MIT(MWNT), 45 kg/m3
Students: Yoonjin Won, Yuan Gao, Matt Panzer. Collaborators: Prof. Wei Cai, Stanford ME
Zipping/Velcro Model
Thickness (μm)
Modulus (MPa)
Density (kg/m3)
CNTTop 0.4 140 >29CNTMiddle 0-150 7 29Si 8.7 155e3 2330
Crust Model
Thermal & Mechanical Requirements at Interfaces
Thermal Resistivity (m K / W)1.00.1
Elas
tic M
odul
us (M
Pa)
Greases & Gels
Organic Phase Change
Metallic Alloys
Adhesives
0.01
Nano-gels
Lifetimethermal cycling
104
103
102
101
Thermal & Mechanical Requirements at Interfaces
Thermal Resistivity (m K / W)1.00.1
Elas
tic M
odul
us (M
Pa)
Greases & Gels
Organic Phase Change
Metallic Alloys
Adhesives
0.01
Nano-gels
Lifetimethermal cycling
104
103
102
101
Our Latest CNT Data
Thermal Cycling of CNT-SiGe Composite
0
2
4
6
8
10
12
1 10 100
R" (
m2
K M
W-1
)
N Cycles
R" TotalR" CNT-SubR" CNT-Pt
R”Total R”CNT-Sub + R”CNTR”CNT-Metal
Resistances for 1.5, 2.5, and 40 micron thick CNT films varied between 0.035 and 0.055 cm2 oC/W, with evidence of decreasing engagement with increasing film thickness.
Gao, Leblanc, Marconnet, Shakouri, Goodson et al., “Nanostructured Interfaces for Thermoelectrics,“Proc. ICT 2009. J. Electronic Materials (2010).
Cycles (30 to 200 C, 6min)
(ZT)eff Characterization with Electrical Heating & Cross-Sectional IR Thermometry
p-type
Pellet
Ceramic plate
Ceramic plate
Connecting metal
Cold Side
Cross-sectional IR Microscopy
Th = 300-700 K
AC current source
Rv
Rref
Resistive Heater
Lock-inAmp.
n-type
PelletVSource
RSense
1
2
3
4
10-3 10-2 10-1 1 10 102 103
6.0
5.0
3.5
3.0
Phase (deg)
Frequency (Hz)
Nor
mal
ized
tem
p. A
mpl
itude
0.0
45
90
Thermal
Sapp
hire
IR T
rans
pare
nt w
indo
w
Heater
growth substrate
CNT Film
CNT
kdxdT 1
∝
QFI
Spatial resolution ~ 2 mmTemp. range 300-700 K
IR microscope systemHeating/thermometrySetup
Connecting metal
Boris Kozinsky (CR/RTC2-NA) | 12/14/2010 | © Robert Bosch GmbH 2010. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.
Research and Technology Center North America
HX and System-Level Simulations Bosch-lead system
simulations explore impact of improved parameters on system efficiency
Multiphysics simulations of thermal/thermoelectric transport in TE material, and interface transport incorporating ab initio results.
HX design and optimization accounts for novel pressure drop designs including Stanford Vapor Escape technology
Educational EngagementThermoelectrics for Vehicles Challenge: Multi-University Competition
Undergraduate Thermoelectrics Lab
K-12 Educational Outreach
Long-term vision: Teams of undergraduates work with commercial TE components and heat sinks to extract waste heat from demo vehicle exhaust.
Stanford’s heat transfer course (ME131A) will include a thermoelectrics laboratory experience. Connects theory and practical applications. Recruits undergraduates for research experiences
in thermoelectrics with graduate student mentoring.
High school students and teachers will conduct energy-conversion research in Stanford’s Microscale Heat Transfer Laboratory.
Connects classroom education and research & development.Links students with industry, graduate & faculty advisors.
Interactions and Flow ofSamples & Information
Stanford• Prepares CNTs samples on TE materials• Transport property measurements of CNT-TE pellet combination, thermomechanical reliability tests on interface (300-800 K)• Process development for CNT TIM tape
Bosch• Ab-initio simulations of transport properties of TE materials and interfaces.•System-level simulation and optimization
USF• Develops high-T, high efficiency TE materials• Transport properties (ρ, S and κ) and Hall measurements (10 - 300K)• Structural, morphological and thermal (DTA/TGA) analyses
NIST• Transport properties (ρ, S and κ) and Hall measure- ments (1.8-390K)•Specific heat, Power Factor measurement at 300 K.• Custom-designed precision TE properties measurement system (300 – 1200 K)
1- Interface2- System-level3- Durability4- Materials5- Heat sink6- Metrology
1, 3, 4, 6
4, 6
1, 2, 3, 5
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