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Model Based Development of The Enhanced
Multi-Mission Radioisotope Thermoelectric
Generator and Effect of Thermoelectric
Element Length on eMMRTG
Swapnil Magdum
APRIL 2019
Western Michigan University
Mechanical and Aerospace Engineering
1
Outline
Introduction
Literature Review
Project Scope
Dimensional Investigation
3-D Modelling
Analytical Model
Numerical Modelling and Simulation
Results
Conclusion
Future Scope
2
Introduction - MMRTG3
Images taken from http://www.space.com/12004-nasa-mars-
rover-curiosity-photos-mars-science-laboratory.html
Figure 1- Conceptual image of the Curiosity Mars Rover Figure 2- The Curiosity Mars Rover at JPL during the final testing
Launched -11/2011, Landed - 07/2012
Introduction - eMMRTG
Figure 3- Cutaway of eMMRTG Figure 4- CAD model of eMMRTG and its component
Image taken from Woerner D. (2016). Image taken from Holgate et al. (2016).
4
General Purpose Heat Source (GPHS)5
Figure 5 - GPHS used in eMMRTG Figure 6- Pu 238 as a fuel for GPHS
Image taken from Hammel et al. (2016)
Thermoelectric Couple
Same cross-sectional area for
both legs.
Both use Skutterudite.
This reduces overall
complexity and analysis.
This leads to an overall 25%
power increase from the
MMRTG.
Images taken from Woerner D.(2016).
Figure 7 - MMRTG and eMMRTG thermoelectric couples
6
Introduction - MMRTG vs eMMRTG7
Holgate T., et al (2015).
Note: The only difference between the MMRTG and eMMRTG is the TE material used. Otherwise the two designs are identical.
Project Scope
Future Mars Rover
Modification in the design of eMMRTG to obtain more output power
Assumptions
Constant Heat Generation
Simplified Model and Estimated dimensions
Material properties are independent of temperature
8
ANSYS - Dimensional Investigation9
Images taken from Woerner D.(2016)Figure 7 - Cutaway of eMMRTG
10
11
Exploded view of the reproduced eMMRTG
12
Fin shell and fin
Module bar
Mica
Heat distribution
block
TEG module
Liner
Aerogel insulation
General Purpose
Heat Source
Figure 8 - Exploded view of the reproduced eMMRTG
14
Analytical Modelling
15
A Simple Analytical Model16
Lee, H.(2017).
Figure 9 - A system with only heat sink
Numerical Modelling and Simulation
17
18
Heat flux Input
Symmetry
Setting up the model with
different input parameters
Figure 10 – Setting up the model
19
Figure 11- Static temperature contour of all domains Figure 12- Static temperature contour of P-type thermoelement
20
Temperature distribution in the
thermoelectric element
Figure 13- Static temperature contour of thermoelectric couple
Temperature (K) ANSYS Result JPL Result
Hot Side 818.1 873
Cold Side 408.3 373-473
Table 2 - comparison of ANSYS result and JPL result
300
400
500
600
700
800
900
0 2 4 6 8 10 12 14
Tem
pra
ture
(K
)
Leg Length (mm)
21
Figure 14- Heat transfer from fin to atmosphere (XZ plane) Figure 15- Heat transfer from fin shell to atmosphere (YZ plane)
22
Figure 16 - Velocity streamlines (YZ plane) Figure 17 - Temperature profile along the fin
23Thermal Boundary Layer Thickness
Image taken from Bardy, E. (2008).
Figure 18 - Theoretical velocity and
thermal profile in natural convection
along a vertical wall Figure 19 - Thermal boundary layer thickness
290
300
310
320
330
340
350
0 5 10 15 20 25 30 35
Tem
pe
ratu
re (
K)
Length of the fin (mm)
on the Mars on the Earth
24
Image taken from Bardy, E. (2008).
Velocity Boundary Layer Thickness
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 5 10 15 20 25 30 35
Ve
loc
ity
(m
/s)
Length of the fin (mm)
on the Mars on the EarthFigure 20 - Theoretical velocity and
thermal profile in natural convection
along a vertical wall Figure 21 - Velocity boundary layer thickness
25
Average Convention Heat Transfer Coefficient (h) for
Vertical Natural Convection
𝑅𝑎 =𝑔. β. 𝑇𝑠 − 𝑇𝑖𝑛𝑓 . 𝐿3
α. υ
𝑁𝑢 = 0.6 +0.387. 𝑅𝑎
16
1 +0.559𝑃𝑟
916
827
2
ℎ =𝑁𝑢. 𝑘𝑎𝐿
𝑔 = 9.807𝑚
𝑠2𝑘𝑎 = 27.1𝑒 − 3
𝑊
𝑚2𝐾α = 26.3𝑒−6
𝑚2
𝑠υ = 18𝑒−6
𝑚2
𝑠β =
1
𝑇𝑓Pr = 0.72
𝐿 = 0.465 𝑚
26
Local Heat transfer coefficient along the vertical wall of
the fin shell
ℎ𝐴𝑖𝑟 = 2.64 W/m2K
ℎ𝐶𝑂2 = 1.12 W/m2K
Analytical Average
heat transfer
coefficient on the
Earth and on the
Mars
27
Figure 22 – Thermal-Electric Analysis
• Power calculations-
I = 1.62A𝑅𝑙𝑒𝑔𝑠 = 0.03605 Ω
Total 𝑅𝑙𝑒𝑔𝑠 = 6.9234 Ω
𝑅𝑙𝑜𝑎𝑑 = 6.9234 Ω
𝑃𝑢𝑛𝑖𝑡 = 𝐼2𝑅𝑙𝑜𝑎𝑑𝑃𝑢𝑛𝑖𝑡 = 18.17 W𝑃𝑡𝑜𝑡𝑎𝑙 = 145.36 W
28
Table 3 - Comparison of the numerical and the analytical results with the literature
Numerical and Analytical results comparison with the literature
ParametersLiterature Results
[JPL Results]Numerical Results Analytical Results
The hot junction
temperature (K)873 818.1 922.38
The cold junction
temperature (K)373-473 408.3 325.13
Current induced in the
circuit (A)- 1.62 1.64
The output power of the
1/8th unit (W)- 18.17 18.62
The total output power of
the unit (W)145-170 145.36 148.92
Effect of ceramic material on the power
output
29
30
Table 4 – Effect of the ceramic material on the power output
Effect of the ceramic material on the power output
MaterialThermal Conductivity
(W/mK)
Hot Side
(K)
Cold side
(K)
Current
(A)
Power of the 1/8th unit
(W)
Total power output
(W)
Alumina 22 818.1 408.3 1.62 18.17 145.36
Aluminum nitride
140 862.2 442.72 1.71 20.23 161.87
Effect of thermoelectric element leg length on
the power output
31
32
Figure 24 - Effect of the thermoelectric leg length on the power output
Effect of the thermoelectric element leg length on the power output
Figure 23 - Thermoelectric couple
Image taken from Hammel et al. (2016)
155
165
175
185
195
205
215
225
235
0 2 4 6 8 10 12 14
Ou
tpu
t p
ow
er
(W)
Thermoelectric element leg length (mm)
Power
33
Table 5 – Thermoelectric element leg length effect on the power output
Effect of the thermoelectric element leg length on the power output
Leg
length
(mm)
Load resistance
(Ω)
Current
(A)
Power of the 1/8th unit
(W)
Total power output
(W)
Rise in the total power output
(%)
1 0.55 7.03 27.18 217.45 49.59 %
3 1.64 3.80 23.68 189.44 30.32 %
6 3.27 2.59 21.93 175.44 20.69 %
9 4.91 2.04 20.45 163.60 12.55 %
12.7 6.92 1.71 20.23 161.87 11.35 %
Conclusion
Effect of ceramic material – 11.35% power improvement
Effect of Thermoelectric element leg length – 49.59% power improvement
Up to 6 mm- a little bit improvement in the power output
At 3 mm and 1 mm – drastic improvement
Enable to reduce weight (for the Spacecraft)
Future Scope
ZT value improvement
Investigation of the optimum load resistance to internal resistance ratio
34
35Questions
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