Transcript Title of Presentation - C&R Technologies, Inc.

JWST Testing Issues – Thermal &
Structural
William Bell, Frank Kudirka, &
Paul-W. Young
Topsfield Engineering Service, Inc.
Topsfield Engineering Service, Inc.
Purpose
This study explores JWST thermal and
structural testing issues and possible
solutions, as presented to NASA in June 2004
Topsfield Engineering Service, Inc.
Slide 2
Summary

Facility Goals

Thermal Design

Helium Refrigeration

Structural Design

Vibration Isolation

Clean Room Considerations
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Slide 3
Testing Facility Goals

Provide for controlled cool-down, soak, and warm-up

Be capable of taking the Test Assembly from 300 K to
35 K and steady state within 10 days

Hold to a set point temperature, within ± 1 K, during
steady state conditions

Vibration isolation
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Slide 4
Proposed Test
Facility
Vacuum Chamber
20 K Shroud
or Dewar
Test Article
80 K Shroud
Thermal
Desktop
Model
Ties
Helium Refrigerator Flow Paths
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Slide 5
Proposed Test Facility – Weights - lbs
Chamber
740,000
N2 Shroud
101,000
He Shroud
45,000
Outer Structure
60,000
Inner Structure
190,000
Test Article
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8,000
Slide 6
Thermal Control Considerations

Evaluate different options for Cool down


Radiative Heat Transfer
Natural Convective Heat Transfer
Sealed 20 K Shroud (dewar) at 1 torr
 Unsealed 20 K Shroud with operation at 0.01 torr


Forced Convection Heat Transfer
In shroud tubing
 Tracing tubing on structure


Mass Flow Heat Transfer
Within Shroud and Tracing tubing
 Direct contact spraying


Evaluate options for thermal insulation


MLI Blankets
Minimize temperature difference Topsfield Engineering Service, Inc.
< 2 C across structure
Slide 7
Cool down Methods

Method 1 - Radiation only

Method 2 - Radiation and natural convection in the 20
K Dewar at a pressure above the Chamber Pressure
Method 4 - Radiation and natural convection in the
entire Chamber
For each above Method, the 80 K shroud is cooled down at
a rate consistent with the 20 K shroud (dewar)
The Test Support structure and the 20 K shroud (dewar)
are cooled by forced convection flow of Helium gas from
the 5 kW refrigerator

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Slide 8
Thermal Model Cases
Method
No
Vacuum - torr
Description
Test Article
Chamber
1A
He Shroud & N2 Shroud - no MLI
1e-5
1e-5
1B
He Shroud & MLI only - 2” blanket
1e-5
1e-5
1C
He Shroud & MLI only - 2” blanket
0.01
0.01
2A
He Dewar & N2 Shroud - no MLI
0.10
1e-5
2B
He Dewar & N2 Shroud - no MLI
1.00
1e-5
4A
He Shroud & N2 Shroud - 1” MLI both Shrouds
0.01
0.01
4B
He Shroud & N2 Shroud - 2” MLI both Shrouds
1.00
1.00
Test Article Heat Load Distribution
MLI Model thermal conductivity vs. pressure
Pressure - torr
k - watts/in K
1e-5
8.382e-7
0.01
6.604e-6
1
0.000127
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Case
Radiative
Load - watts
Conductive
Load - watts
1
1000
0
4
200
800
6
50
950
7
25
975
9
5
995
Slide 9
Thermal Analysis Cases
CHAMBER
CHAMBER
20K He
SHROUD
20K Helium
SHROUD
80K GN2
SHROUD
TA
10-5 Torr
CHAMBER
TA
2” MLI
BLANKET
METHOD 1A
CHAMBER
10-5 Torr
TA
2” MLI
BLANKET
10-2 Torr
METHOD 1B
2A 0.1 Torr
2B 1.0 Torr
20K Helium
dewar pressure tight
80K GN2
SHROUD
20K He
SHROUD
CHAMBER
METHOD 1C
MLI BLANKETS
4A: 1” thick
4B: 2” thick
20K He
SHROUD
TA
80K GN2
SHROUD
TA
4A 0.01 Torr
4B 1.0 Torr
10-5 Torr
METHODS 4A & 4B
METHODS 2A & 2B
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Note: Both shrouds as tight as possible
Slide 10
Thermal Model Construction
Nodes:
33
 Linear Conductors:
46
 Radiation Conductors: 58
 Lumps:
3
 Paths:
2
 Ties:
7

Topsfield Engineering Service, Inc.
Slide 11
Thermal Model Surface Finish/Emissivity
LN2 Shroud
Chamber
Wall
He Shroud
Item
7
2
3
6
1
4 5
Description
Surface
Emissivity i/o
1. SPF Chamber Inner
Bare Aluminum
0.10
2. LN2 Shroud Outer
Bare Aluminum
0.10
3. LN2 Shroud Inner
Z307
0.87
4. He Shroud Outer
Bare Aluminum
0.10
5. He Shroud Inner
Z307
0.87
6. Test Article/Structure
SS304L/Z307
0.15/.7
7. SPF Chamber Outer
Bare Aluminum
0.10
Test Structure
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Slide 12
Flow Regime Definition
Knudsen Number
Kn = /p, where  is the mean free path and p is the
characteristic dimension.
Continuum flow – Kn < 0.01
Transition flow – 0.01 < Kn < 0.3
Molecular flow – Kn > 0.3
Topsfield Engineering Service, Inc.
Slide 13
Chamber Flow Regimes
Pressure
Temperature

inches
torr
K
-
-
-
1
30
0.0004
3.6e-5
Continuum
0.1
30
0.004
0.00036
Continuum
0.01
30
0.04
0.0036
Continuum
10-6
30
426
35.5
Molecular
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Kn
Flow Regime
Slide 14
Thermal Desktop Capability
Molecular Conduction
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Slide 15
Thermal Desktop Capability
Natural Convection
Caution
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Slide 16
Method 1 Results
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Slide 17
Method 2 Results
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Slide 18
Method 4 Results
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Slide 19
Thermal Analysis Results
Method
Case
Time to reach
Steady State days
1A
1A
1A
1B
1B
1B
1C
1C
1C
2A
2A
2A
2B
2B
2B
4A
4A
4A
4B
4B
4B
1
4
9
1
4
9
1
4
9
1
4
9
1
4
9
1
4
9
1
4
9
8.3
8.3
8.3
8.3
8.3
8.3
10.8
10.0
10.0
7.9
7.9
7.9
7.9
7.9
7.9
8.3
8.3
8.3
5
5
5
Meets Test Article Cool Cold Steady State
Test Article Steady State
down Temperature and Helium Gas flow
Temperature - K
Time goals
rate grams/sec
72
NO
40
49
NO
40
29
YES
40
73
NO
44
47
NO
44
29
YES
44
58
NO
109
35
YES
109
25
YES
109
40
NO
62
26
YES
62
22
YES
62
29
YES
62
24
YES
62
22
YES
62
88
NO
137
50
NO
137
25
YES
137
33
YES
194
28
YES
194
24
YES
194
Topsfield Engineering Service, Inc.
Cold Steady State
Heat Rate to
Helium gas watts
1167
1167
1167
1293
1293
1293
3256
3256
3256
1787
1787
1787
1787
1787
1787
3987
3987
3987
5625
5625
5625
Slide 20
Helium Refrigeration
Helium Plant PFD
He Plant
Size is based
on analysis
results
shown on
LN
Slide 18
2
COMPRESSOR
GAS STORAGE
80K – 300K
Supply
< 80K
EXPANDERS
TO SHROUD/STRUCTURE
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FROM SHROUD/STRUCTURE
Slide 21
Structural Design Considerations

80 K and 20 K shroud support






6 stainless steel columns in corners
Must allow for 1” of radial shrinkage
Not connected to test structure
Columns could bend if long enough or
could be placed on rollers
A thermal break is required - G-10 block
sandwiched between flanges
20 K shroud hung off 80 K shroud
Topsfield Engineering Service, Inc.
Slide 22
Structural Design Considerations

20 K Dewar




Clamshell design
3 stainless steel columns in corners
Rollers at base to move unit around and
allow radial shrinkage
80 K shroud hung off 20 K Dewar
Topsfield Engineering Service, Inc.
Slide 23
20 K Shroud Design

20 K Shroud to be “Pressure Tight”
 Design

Pressure inside shroud 1 to 10 torr
20 K Shroud to be “Flow Tight”
 Pressure
in entire chamber 1x 10-2 torr
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Slide 24
Structural Design Considerations

Test Support Material Selection
 Differential
material strain - Al and SS are virtually the same below 25 K
 Al shrinks 37% more than SS from ambient to about 20 K
 Al can be made as stiff as SS by making the beams deeper, the equivalent beam in Al
will weigh 41% as much as SS
 Al must be heat treated after welding to recover its strength
 Welded Al or Welded SS may have different properties than un-welded, small differences
below 20 K
 Different alloying materials in different heats of either Al or SS could result in slightly
different properties. Again small effect below 20 K
 Micro-yield stress in Al is lower than SS, but so is the modulus. Allowable temperature
rise in a restrained beam is almost equal between the 2 materials
 Al is 10 times more conductive than SS, therefore, easier to isolate thermally SS columns
than Al columns. Both, however, need thermal breaks
 Because of structure size consideration and the heat treat requirement of Al, SS is
recommended over Al
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Slide 25
Support Concept
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Slide 26
Vibration Design Considerations



Minimize, or eliminate, any vibration transmission
to the Test Assembly
To avoid subjecting the test assembly to random or
non-repeating load (s), of a magnitude that would
affect optical test stability
Support of Test Fixture on “hard points” until after
cool-down
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Slide 27
Test Support & Article
Access Platform
20 K Shroud
w/plenum
Clean Air Flow In
Clean Air Flow Out
Class 10,000
Clean Room
80 K Shroud
Note that top shroud panels are
removed for visibility
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Slide 28
Acknowledgements
The Study that led to the development of
this presentation was accomplished under
a contract with Crawford Consulting
Services, Inc. for the NASA Plumbrook
Facility Team
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Slide 29