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Thermoelectric Technology forThermoelectric Technology for Automotive Waste Heat RecoveryAutomotive Waste Heat Recovery
Jihui YangGM Research & Development Center2007 DEER Conference, Detroit, MI
August 15, 2007 Outline � Introduction � Engineering Highlights � Materials Research Highlights � Automotive TE cooling?
- environmental impact of R134a Sponsored by � Summary
US Department of Energy Energy Efficiency Renewable Energy (EERE)
Waste Heat Recovery and Utilization Research and Development for Passenger Vehicle and Light/Heavy Duty Truck Applications
DE-FC26-04NT42278
Thermoelectric Power Generation fromThermoelectric Power Generation from Automotive Waste Heat RecoveryAutomotive Waste Heat Recovery
• Target : 10% fuel economy improvement without increasing emissions
• Partnering: – GM – materials research, subsystem design, integration, modeling, and
validation – GE – TE module, subsystem design and manufacturing – Oak Ridge National Lab – high temperature material property
measurement and validation – RTI – superlattice-based thin film materials and modules – University of Michigan – bulk materials : filled skutterudites, nano-
composites,… – University of South Florida – bulk materials: clathrates, nano-grain
PbTe, … – Michigan State University – bulk PbTe-based materials …
DOE Program High-Level ProcessDOE Program High-Level Process
Science: GM, RTI, UM, MSU & USF
Engineering: GE, GM, & RTI
Target: Cost-effective 10% FE Improvement
Material Data Validation: ORNL
Techno
logy D
evelop
ment
Microstructural
From Science, Engineering, toFrom Science, Engineering, to TechnologyTechnology 0.12 Wout0.0.1212 Wout
A Candidate TEA Candidate TE MaterialMaterial 1818
0.1 234.80.0.11 234.8451.45 61.6
0.08 668.40.0.0808 668.4885.88 25.2
0.06 11020.0.0606 110213191319153615360.040.0.04041752175219691969
0.020.0.020221862186
000350 400 450 500 550 600 65035350 400 450 500 550 600 6500 400 450 500 550 600 650
Exhaust Flow Input Temperature [C]Exhaust Flow Input Temperature [C]Continuum
Exha
ust M
ass
Flow
[kg
/s]
Exha
ustM
ass
Flow
[kg/
s]
Competency
Engineering
Cold-side heat exchanger Exhaust
outlet to muffler
TEm odules
Materials Science Exhaust heat
exchanger Cold-side heatAtomistic exchanger
Hot exhaust inlet
Chemistry Electronic
log(Length scale) Physics
nm μm mm m
Standby/Idle 17.2 (3.6)%
Engine Losses 62.4 (69.2)%
Accessories 2.2 (1.5)%
Driveline Losses 5.6 (5.4)%
Aero 2.6 (10.9)%
Rolling 4.2 (7.1)%
Kinetic
Braking 5.8 (2.2)%
Engine 100% 18.2%
(25.6%) D/L 12.6% (20.2%)
Standby/Idle17.2 (3.6)%
Engine Losses62.4 (69.2)%
Engine Losses62.4 (69.2)%
Accessories2.2 (1.5)%
Accessories2.2 (1.5)%
Driveline Losses5.6 (5.4)%
Driveline Losses5.6 (5.4)%
Aero2.6 (10.9)%
Aero2.6 (10.9)%
Rolling4.2 (7.1)%Rolling4.2 (7.1)%
KineticKinetic
Braking5.8 (2.2)%Braking5.8 (2.2)%
EngineEngine100% 18.2%
(25.6%) D/LD/L 12.6%(20.2%)
PNGV source
• Today’s ICE-based vehicles: < 20% of fuel energy is used for propulsion
• > 60% of gasoline energy (waste heat) is not utilized
Energy Distribution - Typical Mid-Size Vehicle on the Federal Test Procedure (FTP) Schedule Urban (Highway) % energy use
Energy Distribution - Typical Mid-Size Vehicle on the Federal Test Procedure (FTP) Schedule Urban (Highway) % energy use
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0 500 1000 1500 2000 2500 3000
TIME (SEC)
EXH
AUS
T G
AS F
LOW
RAT
E (k
g/s)
0
200
400
600
800
1000
1200
TEM
PER
ATUR
E (K
)
EXHAUST MASS FLOW
EXHAUST GAS TEMPERATURE
COOLANT TEMPERATURE
LD9 ENGINE --EPA FTP CYCLE
Exhaust Flow and Temperatures for a 4 Cylinder Engine Exhaust Flow and Temperatures for a 4 Cylinder Engine
IC Engine
Electrical Storage Transmission
Electric Power
Controls
Powertrain Control
Electronics
Catalytic Converter Heat Collector
Thermoelectric Device
Cooling
Exhaust
Vehicle Electrical System
Alternator
• Engine coolant is also a possible heat source, but smaller ΔT
Thermoelectric Energy Recovery Augmented Electrical System Thermoelectric Energy Recovery Augmented Electrical System
Nano-derived materials give additional controlNano-derived materials give additional control� Enhanced density of states due to quantum confinement effects
⇒Increase S (sharp edge of electron D.O.S. near Fermi surface EF) ⇒without reducing σ ( very high electron D.O.S. near Fermi surface EF)
� Boundary scattering at interfaces reduces κL more than σ � Possibility of materials engineering to further improve ZT
3D E 2D E
EF 1D E 0D E
Bulk semiconductor Quantum well Quantum wire Quantum dot
conductor thermopower temperature electrical conductivityinsulator
2
κ ρ κ κ electronic
L e thermal
TE Figure S T S 2σT of Merit ZT = =
+electronelectron phonon T conductivity
total thermal conductivity electrical resistivity lattice thermal conductivity
D. O
. S.
D. O
. S.
D. O
. S.
D. O
. S.
Thermoelectric Waste Heat RecoveryThermoelectric Waste Heat RecoveryEfficiency:
T − T 1 + ZT − 1ε = H C
TT H 1 + ZT + C
HT
Year 1940 1950 1960 1970 1980 1990 2000 2010
ZT
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
ZnSb PbTe
Bi2Te3 Zn4Sb3
filled skutterudites
Bi2Te3/Sb2Te3 superlattices
PbSeTe/PbTe quantum dots
AgPb18SbTe20
• Many recent material advances are nano-based
$ / W – a Program Metric$ / W – a Program Metric� $/W (not only ZT) is used for balancing various material, module, and subsystem options
� $/W can be readily converted to $/Δmpg, and $/Δmpg < Savings/Δmpg is necessary to provide consumer value
FE (mpg) 0 10 20 30 40 50 60 70
3 Y
ear F
uel S
avin
g pe
r 1m
pg F
E im
prov
emen
t
0
200
400
600
800
1000
1200
1400
1600
1800
2000
$2/gallon $3/gallon $4/gallon
Consumer Fuel Savings/Δmpg ≈ $300-400/Δmpg (15000 mile/yr., 3yrs., 18-20 mpg)
� plenty of space for accommodating TE subsystem � a lot of waste heat: exhaust and radiator � current muffler: 610 x 310 x235 (mm) � available envelope: 840 x 360 x 255 (mm)
Vehicle Selection – Full Size TruckVehicle Selection – Full Size Truck
Typical Exhaust Heat -Ci ty Driving Cycle
0
10
20
30
40
50
60
70
80
0 500 1000 1500 2000 2500
Test Time (s)
kW
Fuel Economy Analysis - OFuel Economy Analysis - verdriveOverdriveThrottle PositionThrottle Position Cycle Vehicle SpeedCycle Vehicle Speed 19.6
EngineEngine DrivDri erver19.4
Midsize TruckFuel &Fuel &Fuel & Throttle Transmission BrakingThThrottlerottle Transmission BrakingControlContControlrol BodyBodBodyy 19.2
VehicleVehicle19.0
Intake ShiftIntaIntakeke ShiftShift Wheel SlipWhWheel Slipeel SlipManifold ControlMaManifoldnifold ControlControl & Rolling& R& Rollingolling
FE (m
pg)
18.8
4167 lbs18.6
CyliCylindernder TorquTorquTorqueee GeaGeaGearrr Fore/AFore/AFore/Afffttt 18.4 BlBlockock ConvertConvertConvertererer CaCaCassseee DynaDynaDynammmicsicsics 4417 lbs
18.2 4667 lbs
SpinSpinSpin AeroAeroAero18.0
LossesLossesLosses DraDraDraggg 17.8 0 200 400 600
EL (W)
10% fuel economy improvement for a full size truck would require (for a hybrid full size truck): � 1.65 kW – city � 2.5 kW – Highway
350 W is the minimum requirement � equal to the base electrical load of today's generator on FTP, and would improve its composite
Urban/Highway fuel economy by ~ 3%
Subsystem Model SchematicSubsystem Model Schematic
Subsystem ModelingSubsystem Modeling
Exhaust: TH, TC, flow & fluid properties
Radiator: TH, TC, flow & fluid properties
Elec. Load: Effective R, Vreq,
GM’s Inputs GE’s System Model
Device config. • Structure / design Heat transfer • Hot & cold exchangers • Interfaces Power conditioning • DC/DCc onverter
Requirements: Cost, Power, Life
GM’s MPG modelOutput
cost
Δmass, ΔP, power
% FESavings
GM’s FETo ols
Materials Dev. • α(T),ρ(T),λ(T) •Cost & mass •Geom. req.
Subsystem Modeling – 2 D Thermoelectric Network Model Subsystem Modeling – 2 D Thermoelectric Network Model
n p
metal
metalmetal
metal
conductor
Cont act Resist ances
conductor conductor
insulator
insulator
Hot side heat exchanger
Cold side heat exchanger
thermal
thermal
Electrical & thermal
thermal
thermal
volume resistivity
Electrical & thermal
Thermal shunt path
Joule & Peltier terms
Joule heating from all electrical contacts are accounted for.
n p
metal
metalmetal
metal
conductor
ContactResistan
n p
meta
ces
conductor conductor
insulator
insulator
Hot side heat exchanger
Cold side heat exchanger
thermal
thermal
Electrical &thermal
thermal
thermal
volumeresistivity
Electrical &thermal
Thermalshuntpath
Joule & Peltier terms
l
metalmetal
metal
conductor
ContactResistances
conductor conductor
insulator
insulator
Hot side heat exchanger
Cold side heat exchanger
thermal
thermal
Electrical &thermal
thermal
thermal
volumeresistivity
Electrical &thermal
Thermalshuntpath
Joule & Peltier terms
Joule heating from all electrical contacts are accounted for.
2007 Year End Module and Subsystem Goals2007 Year End Module and Subsystem Goals
• Thermoelectric Module Design – TE material manufacturing – Thermomechanically robust materials & module design
– Initial module characterization
• Subsystem Design and Optimization – Heat exchanger optimization – Thermal and mechanical integration strategy – Exhaust flow testing facility complete
TE Module Conceptual DesignTE Module Conceptual Design
Identifying and modeling candidate module designs for cost, thermoelectric performance and thermo-mechanical durability • Minimize thermal stresses
pn
• High operating temperature • Good ohmic contact & high thermal conductivity (diffusion barriers, solders/brazes, electrodes)
pn
• Minimize shunt path • No thermo-chemical degradation
common header
pn
Independent hot-side
egg crate
In-line stack
n pn p
Module Design OptimizationModule Design Optimization
Initial Design Study:
• Identify primary module design variables
• Examine effect on primary output variables 1. Power output 2. Cost 3. Thermo-mechanical
durability
Design Space OptimizationDesign Space OptimizationRun Optimized
Training
Scaled Cost
Scaled Power Output
Scal
ed D
urab
ility
) )
Better
Evaluate sensitivities of designs on Pareto frontier
Overlay of TE System Efficiency andOverlay of TE System Efficiency and Expected Exhaust ConditionsExpected Exhaust Conditions
0.12 WoutA Candidate TE Material 18
0.1 234.8 451.6
0.08 668.4 885.2
0.06 1102
1319
15360.041752
19690.02
2186
0350 400 450 500 550 600 650
Exhaust Flow Input Temperature [C]
Exh
aust
Mas
s F l
ow [
kg/s
]
Phase I SummaryPhase I Summary
� quantified electric power requirements for 10% FE improvement
� established $/W as a program metric – automotive and consumer focus; and determined cost target for both exhaust and radiator TE waste heat recovery (materials, modules, subsystems)
� completed the initial exhaust and radiator subsystems design, performance analysis, and cost modeling
� assessed manufacturability of bulk and thin-film modules and subsystems
� validated many known materials’ performance, and enhanced the design of thin-film modules
� explored routes toward higher ZT and low material cost
� exhaust recovery can meet the 350 W requirement with existing materials with high starting purities but at high cost
� radiator recovery alone will not meet the 350 W requirement and is cost prohibitive
Dual-frequency Resonant Phonon Scattering in Skutterudites Dual-frequency Resonant Phonon Scattering in Skutterudites
δ
Filling atom cage
δ
Filling atomcage
Small displacement δ of the filler from it equilibrium x will lead to an increase of the total energy of the system.
Smal
2 31 1( ) ( ) ( ) ( )2 6
E x E x E x E xδ δ δ+ = + + +�� ��� "2
harmonic termharm anharmonic term
In a harmonic approximation, is the spring constant.( )E x��
l displacement δ of the filler from itequilibrium x will lead to an increase of the total energy of the system.
31 1( ) ( ) ( ) ( )2 6
E x E x E x E xδ δ δ+ = + + +�� ��� "
onic term anharmonic term
In a harmonic approximation, is the spring constant.( )E x��
0 ( )E x
m ω =
��
Phonon DOS
ω
P
ωDω
Quasi-localized modes due to void fillingQuasi-localized mhonon DOS
ωD
odes due to void filling
Thermoelectric Enhancement in NanocompositesThermoelectric Enhancement in Nanocomposites
PbTe (room temperature)
J. Martin, G.S. Nolas, W. Zang & L. Chen, APL 90, 222112 (2007)
• Non-conglomerated nanocrystals within the bulk matrix • Power Factor enhancement of 30% at room temperature • Three weeks at 600 K with preservation of nanostructure
Filled Skutterudite NanocompositesFilled Skutterudite Nanocomposites
T (K) 200 300 400 500 600 700 800 900
Pow
er fa
ctor
(μW
/cm
-K2 )
10
15
20
25
30
35
40
45
50
x=0 x=0.05 x=0.1 x=0.2 x=0.3 x=0.4
Yb0.2BaxCo4Sb12
T (K) 200 300 400 500 600 700 800 900
ZT
0.0
.2
.4
.6
.8
1.0
1.2
1.4
1.6 x=0 x=0.05 x=0.1 x=0.2 x=0.3 x=0.4
ZT = 1.36 for x=0.05
HTML at Oak Ridge Natioanl LabHTML at Oak Ridge Natioanl LabORNL efforts will focus on the following areas:
– High temperature transport properties testing – Utilizing ORNL capabilities to continue the search for
high ZT materials – Start mechanical properties testing on selected
materials
– Continue to develop and expand measurement capabilities for TE materials
Environmental Impact of R134a Containing Automobile AC: Global Warming Environmental Impact of R134a Containing Automobile AC: Global Warming� Direct and Indirect Global Warming Impact of R-134a
Direct leakage R-134a: 345 gm/yr * 1,400 = 483 kg/yr
Indirect increase in emissions due to AC R-134a: 23.5 gallons/yr * 8.9 kg CO2/gal = 209 kg/yr
� Total Global Warming Impact of R-134a, and Entire Gas-Powered Vehicle
R-134a: 483 + 209 = 692 kg/yr
Entire Vehicle: avg. 696 gal/yr * 8.9 kgCO2/gal = 6194 kg/yr
* M. S. Bhatti, “A critical look at R-744 and R-134a mobile air-conditioning systems”, SAE SAE-970527
SummarySummary
� Automotive TE waste heat recovery is promising for FE improvement
� $/W or $/Δmpg needs to used to assess its commercial feasibility
� Major challenges in materials and engineering
� Automotive TE cooling needs to be evaluated