Advanced Radioisotope Thermoelectric Generator (ARTG

Transcription

Advanced Radioisotope Thermoelectric Generator (ARTG)
Leverages Segmented Thermoelectric Technology
NETS 2015
William Otting – Aerojet Rocketdyne
Tom Hammel – Teledyne Energy Systems
David Woerner – Jet Propulsion Laboratory
Jean-Pierre Fleurial – Jet Propulsion Laboratory
National Aeronautics and
Space Administration
Abstract 5079
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Agenda
 Background
 Design Study Objectives
 Advanced Thermoelectric Materials
 System Parametric Model
 Select Results
 Summary
Background
 Advanced thermoelectric materials and couple technologies are being successfully
developed at JPL under the NASA sponsored Radioisotope Power Systems’
Thermoelectric Technology Development Project (TTDP)
 Advanced Thermoelectric Materials
– Skutterudite (SKD) materials for temperatures up to ~600°C (873 K)
– La3-xTe4/Yb14MnSb11 Zintl materials extend temperature range to 1000°C (1273 K)
when segmented with the SKD materials
 Technology Status:
– SKD technology is now developed and is being
transferred to industry (Teledyne Energy
Systems) for production under the TTDP’s
Advanced Thermoelectric Couple (ATEC) Task
 Near Term Technology Infusion
– Implementing SKD couples results in an
enhanced MMRTG (eMMRTG) providing a
sizable 25% power boost at Beginning of Life
and > 50% at End of Design Life
– Technology insertion into the existing MMRTG
platform provides a low risk path to a high
performing multi-mission generator
eMMRTG
MMRTG:
PbTe &
TAGS
eMMRTG:
Skutterudite
(SKD)
Background
 Next Steps: Segmented Thermoelectric Technology insertion into a GPHS-RTG
like platform
– Transition the n-type La3-xTe4 and p-type Yb14MnSb11 Zintl technologies to
production
– Segmenting with the SKDs results in a high temperature couple suitable for
deep space vacuum generators
– The segmented couples have demonstrated more than 15% thermal-toelectric efficiency across a 1000°C to 200°C ∆T
– Current ATEC technology work focuses on achieving low power degradation
rates over the targeted design life (17 years)
The present design study was performed to evaluate options
for implementing advanced segmented thermoelectric
technology into a deep space generator
ARTG Design Study
Objective:
• Understand the first order design tradeoffs between mass, power, and efficiency
for a deep space generator implementing the segmented thermoelectric materials
Approach:
• Integrate generator sizing and thermoelectric sizing into a single model to allow
parametric evaluation of the system considering a range of hot and cold junction
temperatures.
– Use ATEC-ARTG deep space generator concept as a point of departure
– Use measured thermoelectric material properties for thermoelectric sizing
and layout
• Evaluate point design vacuum systems and a modular system
– Case 1: 18-GPHS modules, Thj = 1000°C
– Case 2: 8-GPHS modules, Thj = 1000°C
– Case 3: 8- GPHS modules, Thj = 850°C
– Case 4: Modular; 4-to-16 GPHS modules, Thj =1000°C
Point of Departure Design: ATEC - ARTG
Advanced RTG
• Advanced RTG – deep
space (vacuum only)
• Incorporates Step-2
GPHS
• Designed to withstand
EELV loads
• Cantilevered ATEC
thermoelectric couples
• Incorporates MFI/aerogel
insulation
• Based on 12-GPHS
modules
• Thj - 1273 K (1000°C)
• Tcj - 569 K (296°C)
• Mass – 38 kg
Advanced Thermoelectric Couple Technology
x2 Efficiency of Heritage
RTG Couples
Segmented Couple
15% Conversion
Efficiency at
Beginning of Life
(BOL)
Higher Performance Materials
2x increase in ZTave over SOA Si-Ge alloys (1275 to 475 K DT)
when combined through segmentation
Trade Study Overview
1.6
LTP6‐3
LTP6‐4
LTP12‐3
LTP13‐3
LTP18‐2
1.4
1.2
1.60
AZH05-1
1.0
AZH06-1
1.40
ZT
AZH07-1
AZH08-1
1.20
ZT
TE Sizing
Model
0.6
1.00
1.6
0.8
100 g Baseline
0.80
Average Yb14MnSb11 ball-milled
0.4
YMS233 after 720hrs at 1273K
1.4
YMS234 after 720 hrs at 1273K
0.60
1.2
0.2
0.40
YMS998-3 after 6 months at 1273K
1.0
0.20
0.0
200
ZT
YMS1660 after 6 months at 1273K
1.4
1.2
0.00
ALT16-1 1500hr at 1273K
YMS1666
months at
1323K 500
200 after 12
300
400
ALT16-1 after 6 monthsYMS
at 1273K
1660 after 24 months at 1273K
0.8
300
400
500
600
700
800
900
1000
1100
600
700
800
900
1000
1100
1200
1300
1400
T(K)
YMS1666
after 24 months at 1323K
ALT16-1 after 12 months
at 1273K
0.4
1.0
ALT22 BOL
ALT22 1500hr at 1323K
0.2
ALT22 after 6month at 1323K
0.8
ZT
ALT22 after 12 months at 1323K
ALT35 after 1500hrs at 1273K
0.0
0.6
ALT35 after 1500hrs at 1323K
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
T(K)
0.4
0.2
0.0
200
300
400
500
600
700
800
900
1000
1200
1300
T (K)
0.6
1100
1200
1300
1400
T(K)




Series/parallel circuit
3% Electrical losses
Square cross-section legs
Optimum shape factor
TE properties
Generator Sizing
Model
Leg Height
TE Height
TE Height
TE Gap
Key input variables
 # GPHS: Q input
 Tsink
 THJ/TCJ
 Load voltage (32.8 Vdc)
 T/E length
System Parametric
Performance Model
Key Outputs:
 Power output
 Number of T/E couples
 N and P leg: bit widths
 N and P leg: segment lengths
 T/E efficiency
 Open circuit voltage
 Generator efficiency
 Heat rejection sizing
 Generator dimensions/weight
Point of Departure
Generator Design
ARTG
Case 1: 18-GPHS Modules, Thj=1000°C
Select System Plots
Case 1: Fin Root Temperature Design Parametric
Thj=1000°C, 18-GPHS Modules
10.0
Specific Power near
Maximum at Tcj=250°C
9.5
9.0
481.4 W
8.5
Specific Power, We/kg
Case 1:
Power Target – 500 W
T hot junction – 1000°C (1273 K)
TE length – 1.27 cm
461.9 W
442.3 W
499.1 W
8.0
7.5
516.8 W
7.0
6.5
6.0
5.5
535.8 W
5.0
Q inv = 244 W/GPHS
Power @ 32.8 V
Power includes 3% lead loss
4.5
T cold
junction
(deg C)
Mass
(kg)
175
200
225
250
275
300
101.7
71.7
60.3
55.7
54.0
53.5
Power
Output
(W)
Specific
Power
(W/kg)
12.2%
11.8%
11.4%
11.0%
10.5%
10.1%
535.8
516.8
499.1
481.4
461.9
442.3
5.27
7.20
8.28
8.64
8.56
8.27
300
325
Number of Generator
Couples efficiency
394
404
415
427
441
456
4.0
100
125
150
175
200
225
250
Cold Junction Temperature, deg C
275
Case 1 – TE Height Design Parametric
482.1 W
9.0
481.4 W
Case 1:
T cold junction – 250°C (523 K)
Number of couples - 427
480.8 W
8.5
480.3 W
ARTG
479.8 W
8.0
479.3 W
478.8 W
7.5
GPHS RTG
Insulation Thickness
7.0
6.5
T fin root Generator
(deg C) efficiency
6.0
217
226
230
233
235
237
238
5.5
5.0
Q inv = 244 W/GPHS
Power @ 32.8 V
4.5
11.0%
11.0%
10.9%
10.9%
10.9%
10.9%
10.9%
Mass
(kg)
Power
Output
(W)
Specific
Power
(W/kg)
55.0
55.7
57.0
58.7
60.7
63.0
65.7
482.1
481.4
480.8
480.3
479.8
479.3
478.8
8.76
8.64
8.44
8.19
7.90
7.60
7.29
4.0
0.00
0.25
0.50
0.75
1.00
1.25
1.50
TE Length, cm
1.75
2.00
2.25
2.50
2.75
ARTG
Select System Plots
9.0
Case 2:
8.5
Specific Power near
Maximum at Tcj = 240°C
8.0
203.9 W
7.5
195.8 W
211.4 W
187.6 W
7.0
219.1 W
6.5
T cold
Number of
junction
Couples
(deg C)
6.0
5.5
5.0
226.8 W
Q inv = 244 W/GPHS
Power @ 32.8 V
4.5
175
200
225
250
275
300
394
404
415
427
441
456
Mass
(kg)
Generator
efficiency
Power
Output
(W)
Specific
Power
(W/kg)
45.3
33.6
29.2
27.6
27.0
26.9
11.6%
11.2%
10.8%
10.4%
10.0%
9.6%
226.8
219.1
211.4
203.9
195.8
187.6
5.01
6.52
7.23
7.39
7.25
6.97
4.0
100
125
150
175
200
225
250
275
300
325
9.0
Case 2:
8.5
8.0
7.5
211.4 W
212.1 W
211.2 W
211.0 W
7.0
210.6 W
210.2 W
209.8 W
6.5
(deg C) efficiency
6.0
5.5
5.0
Q inv = 244 W/GPHS
Power @ 32.8 V
4.5
4.0
0.00
0.25
0.50
0.75
189
199
203
206
208
210
212
1.00
10.9%
10.8%
10.8%
10.8%
10.8%
10.8%
10.7%
1.25
1.50
TE Length, cm
Mass
(kg)
Power
Output
(W)
Specific
Power
(W/kg)
29.7
29.2
29.5
30.0
30.8
31.7
32.7
212.1
211.4
211.2
211.0
210.6
210.2
209.8
7.13
7.23
7.16
7.03
6.84
6.63
6.41
1.75
2.00
2.25
2.50
2.75
ARTG
System Plots
9.0
Case 3:
8.5
8.0
7.5
Specific Power near
Maximum at Tcj = 235°C
7.0
183.2 W
191.3 W
6.5
173.6 W
164.9 W
200.2 W
6.0
T cold
junction
(deg C)
5.5
5.0
207.9 W
Q inv = 244 W/GPHS
Power @ 32.8 V
4.5
4.0
100
125
150
175
200
225
250
275
300
Number of Couples
502
516
535
554
579
604
175
200
225
250
Mass
(kg)
Generator
efficiency
Power
Output
(W)
Specific
Power
(W/kg)
43.7
33.4
29.5
28.0
27.5
27.4
10.7%
10.3%
9.8%
9.4%
8.9%
8.4%
207.9
200.2
191.3
183.2
173.6
164.9
4.8
6.0
6.5
6.6
6.3
6.0
275
300
325
9.0
(deg C) efficiency
8.5
194
202
206
209
211
212
213
8.0
7.5
7.0
191.5 W
6.5
191.3 W
9.8%
9.8%
9.8%
9.8%
9.8%
9.8%
9.8%
191.1 W
190.9 W
Mass
(kg)
Power
Output
(W)
Specific
Power
(W/kg)
29.6
29.5
29.9
30.6
31.5
32.6
33.7
191.5
191.3
191.1
190.9
190.7
190.5
190.3
6.47
6.49
6.39
6.23
6.05
5.85
5.64
190.7 W
6.0
190.5 W
190.3 W
5.5
Case 3:
5.0
Q inv = 244 W/GPHS
Power @ 32.8 V
4.5
4.0
0.00
0.25
0.50
0.75
1.00
1.25
1.50
TE Length, cm
1.75
2.00
2.25
2.50
2.75
Case 1-3 Summary Results and Observations
• The 18-GPHS ARTG provides 60-70% higher performance when compared to the
previous SiGe GPHS RTG (300 W and 5.3 W/kg)
• The 8-GPHS ARTG shows a modest penalty for scaling down from 18-to-8 GPHS
modules: about 12% lower on specific power and 5% lower on efficiency
• Design and operation at Thj = 850°C vs 1000°C reduces power and specific power
by about 10% and reduces efficiency by about 8%
Case 1:
Case 2:
Case 3:
18‐GPHS (Step‐2) 8‐GPHS (Step‐2) 8‐GPHS (Step‐2)
Thj = 1000°C
Thj = 1000°C
Thj = 850°C
Power @ 32.8 V
480 ‐ 515 W
205 ‐ 220 W
187 ‐ 200 W
Specific Power
7.2 ‐ 8.6 W/kg
6.5 ‐ 7.4 W/kg
6.0 ‐ 6.5 W/kg
11.0 ‐ 11.8%
10.4 ‐ 11.2%
9.6 ‐ 10.3%
Generator Efficiency
The ARTG has the potential to provide power levels and specific power levels
60-70% above the SiGe GPHS RTG
Case 1-3 Summary
Couple Comparisons: TE height = 1.27 cm
JPL Test Couple:
1000°C/200°C
Case 1:
18-GPHS Modules
1000°C/225°C
Case 2:
8-GPHS Modules
1000°C/225°C
Case 3:
8-GPHS Modules
850°C/225°C
Thermoelectric couple sizes required are within the
range of those already fabricated at JPL
Concept 4 - Modular
Design Concept 4 – Modular
ARTG in 4-GPHS Building Block
Module 4
4-GPHSs
Module 1
4-GPHSs
-
VL
+
Module 3
4-GPHSs
Module 3
4-GPHSs
Module 2
4-GPHSs
Module 2
4-GPHSs
Module 2
4-GPHSs
Module 1
4-GPHSs
Module 1
4-GPHSs
Module 1
4-GPHSs
-
VL
+
32.8 V
32.8 V
4-GPHS Modules
8-GPHS Modules
-
VL
+
32.8 V
12-GPHS Modules
-
VL
+
32.8 V
16-GPHS Modules
Design Concept 4 – Modular
ARTG in 4-GPHS Building Block
 All systems utilize the same thermoelectric
module as a common building block
 The 32.8 V is generated in a 4-GPHS
module array
Segmented Module
•
•
•
•
Q inv = 244 W/GPHS
Thj = 1000°C
Tcj = 250°C
Vload = 32.8 V
4‐GPHS Modules
8‐GPHS Modules
12‐GPHS Modules
16‐GPHS Modules
Power @32.8 V
93.2 W
204.8 W
313.6 W
425.2 W
Specific Power
5.7 W/kg
7.3 W/kg
7.7 W/kg
8.1 W/kg
9.5%
10.5%
10.7%
10.9%
Generator Efficiency
Summary and Conclusions
• Study findings:
– Advanced segmented thermoelectric technology has the potential to provide
a significant performance boost for deep space generators … about 60-70%
over SiGe deep space generator
– Advanced segmented thermoelectric couples operate over the same
temperature range as SiGe deep space generators … pushing the generator
technology is not required
• Benefits of a modular generator:
– A modular RTG based on a common multi-couple thermoelectric module
design has broad application for future missions while leveraging
nonrecurring engineering and development costs
– Provides missions the flexibility to select the optimum power system size for
their mission and helps NASA best manage its fuel inventory
An ARTG based on the segmented thermoelectric couples has the potential to provide
power levels and specific power levels much higher than ever before making missions
more capable, cost effective, and potentially enabling new classes of missions

Advanced Radioisotope Thermoelectric Generator (ARTG

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