Efficient Therm
oelectric Power Conversion from W
aste
Heat for Deployed Forces
Project SI-1651
Chris Caylor and Rama Venkatasubramanian, Center for Solid-State Energetics,
RTI International, Research Triangle Park, NC 27709;
Paul Dev, D-STAR Engineering Corporation, Shelton, CT 06484;
Selma Matthews, U.S. Arm
y CERDEC, Arm
y Power Division, Fort Belvoir, VA 22060
This work was enabled by the DARPA DTEC Program funded through the Office of Naval Research
Perform
ers
Dr. Chris Caylor
RTI International
Specialist in thin film
and bulk m
aterials for therm
oelectric applications.
Dr. Rama Venkatasubramanian
RTI International
Director of Center for Solid-State Energetics, original work on high
perform
ance thin-film
superlattice therm
oelectric m
aterials and devices
Dr. Paul Dev
D-STAR Engineering Corporation
Project manager and president of D-Star Engineering, providing expertise
in heat exchangers for therm
oelectric devices with diesel engines.
Ms. Selm
a Matthews
US Arm
y CERDEC, Arm
y Power Division
Senior Research Engineer in the CERDEC Arm
y Power Divisions Power
Technology Branch and responsible for the identification, research and development
of emerging and advanced power technologies that will support future DoD
platform
s.
Problem Statement
•The DoD and the m
obile forces of its branches m
ust deal with thelarge carbon
footprintof its operations by increasing fuel efficiencyand lowering fuel use.
•Fuel efficiency in m
obile electric power generationis one area where improvements
can be m
ade.
•Furtherm
ore, fuel use, as well as personnel risk, could be lowered by m
ore efficient
power generationby requiring fewer fuel deliveries, which m
ust be accomplished via
manned convoys.
Technical Objective: Develop waste heat recovery systems with power levels up to 500 Watts integrated with mobile diesel generators.
Therm
oelectric Power Generation
�Therm
oelectric (TE) materials joined in
couples (p-type and n-type) can be used
for cooling or power generation
�Power generation uses a temperature
difference (∆T) to drive electric current.
�TE conversion efficiency is based on
materials properties and achievable ∆T in
the application (heat exchangers).
�ZT is TE figure-of-merit, higher ZT m
eans
more efficient power generation
TE Technology for Different Temperature Ranges
Bi-Polar Couple Assembled Module
(BCAM) Device Technology
Traditional
BCAM
Low stress; Scalable; Withstands 16 G’s
RMS acceleration at device level
RTI TE devices can be used independently or can be
combined in cascades
3-4
3-4
9-10
Mid-Temp
Stage
350
500
4-5
4-5
16-18
High/Mid/Low
Cascade
775
800
2-3
3-4
13-14
Mid/High
Cascade
650
800
4-5
4-5
13-14
Mid/Low
Cascade
475
500
Incinerator /
Engine Exhaust
8-11
4-5
5-6
Low-Temp
Stage
150-175
200
Engine Jacket
1-2
0.5-1
2-3
Low-Temp
Stage
50-75
90-100
Hot Water
Specific
Power
(W/gram)
Power
Density
(W/cm
2)
Eff.
(%)
TE Device
Structure
∆ ∆∆∆T (K)
Avail.
Thot
(oC)
Field Application
Scaling of Low-Temperature TE Arrays
4x4 m
odule
P ~ 1 W
6x6 m
odule
P ~ 2.1 W
16x16module
8x8 m
odule
P ~ 3.4 W
Multi-Module-Arrays
1 p-n
couple
P ~ 0.16 W
512-couple
P ~ 15 W
2048-couple
P ~ 19 W
Mid-Temperature Bulk
Device Scale Up Progress
1 Bulk Couple
0.2 W
atts
8 Bulk Couples
1.5 W
atts
15 Bulk Couples
3 W
atts
31 Bulk Couples
6 W
atts
60 Bulk Couples
12 W
atts
124 Bulk Couples
25 W
atts
504 Bulk Couples
40 W
atts
63 Bulk Couples
Technical Approach
Estimated Perform
ance of 2-Stages vs1-Stage Based On
Measured Individual Stage Efficiencies
η~5%
Low-Tem
perature
Single Stage
150°C 450°C 750°C
η~10-13%
Mid-Tem
perature
Single Stage and
2-Stage Devices
η~15-18%
High-Tem
perature
3-Stage Devices
65.8
81.0
92.4
101.9
117.6
129.7
Power/cpl
(mW)
THot~ 500 °C 8.5
9.1
9.8
10.2
11.0
11.6
Eff
(%)
7.6
56.3
6.4
39.6
125
BCA-337
6.9
47.1
5.8
33.1
150
BCA-338
8.3
66.7
6.9
46.7
100
BCA-335
8.6
73.6
7.1
51.0
75
BCA-336
9.5
88.7
8.3
67.5
50
BCA-330
10.0
97.8
8.7
73.9
25
BCA-332
Eff
(%)
Power/cpl
(mW)
Eff
(%)
Power/cpl
(mW)
THot~ 450 °C
THot~ 400 °C
TCold
(°C)
Device
Entrance Cap of Muffler Back of Muffler Muffler Front of Muffler
DRS 3kw gen-set
Generator Engine Engine Cooling Fan Hsg.
DRS Fermont 3 kW Gen-set
Muffler
Possible location of Header Pipe
Thermoelectric Device
Possible Location of Thermoelectric Device
Thermoelectric Device 5cm x 5cm
Rough Guide to Potential Thermoelectric
System
Perform
ance
Phase 2 and Phase 3 will need to see increased therm
al
and converter efficiencies to reach 10% fuel
efficiency increase go
Perform
ance for phase 1 will be based on full loadoperation and using single-stage
thermoelectric devices
CERDEC data on 3kW TQG shows that it is ~24% fuel efficient at full load (12.5kW
heat input and 9.5kW waste heat, of which ½, roughly, makes it into the exhaust)
Thermal efficiency = converting available waste heat to that of heat into
thermoelectric device
Converter efficiency = converting heat into TE device to electricity
52%
36%
14%
Required Therm
al Efficiency
300W
150W
50W
TE Output Power Target
10%
5.0%
1.7%
Fuel Efficiency Increase
12%
9.0%
7.5%
TE Converter EfficiencyTarget
Phase 3
Phase 2
Phase 1
New
Q-m
eter System
at RTI for Larger Power
Device Efficiency M
easurements
5-10 W
atts heat flow (much larger than
earlier Q-m
eter m
easurements)
Used to m
easure single-stage and
multi-stage devices for efficiency
comparison
Comparison of Q-m
eter and Calculated Heat Flows
456789
10
11
12
13
250
350
450
550
Hot-Side Temperature (C)
Thermoelectric
Conversion Efficiency (%)
Calculated Heat Flow
Q-Stick Measured Heat Flow
11.1
2.9
8.5
25
150
500
2-stage PbTe/TAGS//SL
11.3
3.1
8.5
25
150
500
2-stage PbTe/TAGS//SL
11.6
2.9
9.0
25
130
500
2-stage PbTe/TAGS//SL
11.6
11.6
25
500
Single stage PbTe/TAGS
Total η
(%)
Low-Temp
Stage
η(%
)
PbTe/TAGS
Stage η
(%)
TCold
(°C)
TMid
(°C)
THot
(°C)
Device
Single-Stage PbTe/TAGS Efficiency M
atrix
*SL = RTI’s Superlattice Thin Film
Device
�12-13% 2-stage conversion efficiency is the target for phase 2/phase 3 demonstration
for SERDP
�Steady development of superlattice devices has shown improved perform
ance and is
poised to pass the perform
ance of the single-stage device
Entrance End Cap M
uffler Characterization
0
50
100
150
200
250
300
350
400
450
500
00.5
11.5
22.5
3
Generator Load (kW)
Temperature (°C)
Cooling Air
Muffler Metal
Exhaust Gas