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Topsfield Engineering Service, Inc. JWST Testing Issues – Thermal & Structural William Bell, Frank Kudirka, & Paul-W. Young Topsfield Engineering Service,

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Presentation on theme: "Topsfield Engineering Service, Inc. JWST Testing Issues – Thermal & Structural William Bell, Frank Kudirka, & Paul-W. Young Topsfield Engineering Service,"— Presentation transcript:

1 Topsfield Engineering Service, Inc. JWST Testing Issues – Thermal & Structural William Bell, Frank Kudirka, & Paul-W. Young Topsfield Engineering Service, Inc.

2 Slide 2 Purpose This study explores JWST thermal and structural testing issues and possible solutions, as presented to NASA in June 2004

3 Topsfield Engineering Service, Inc. Slide 3 Summary n Facility Goals n Thermal Design n Helium Refrigeration n Structural Design n Vibration Isolation n Clean Room Considerations

4 Topsfield Engineering Service, Inc. Slide 4 Testing Facility Goals n Provide for controlled cool-down, soak, and warm-up n Be capable of taking the Test Assembly from 300 K to 35 K and steady state within 10 days n Hold to a set point temperature, within ± 1 K, during steady state conditions n Vibration isolation

5 Topsfield Engineering Service, Inc. Slide 5 Proposed Test Facility Vacuum Chamber 80 K Shroud 20 K Shroud or Dewar Test Article Ties Helium Refrigerator Flow Paths Thermal Desktop Model

6 Topsfield Engineering Service, Inc. Slide 6 Proposed Test Facility – Weights - lbs Chamber740,000 N2 Shroud 101,000 He Shroud 45,000 Outer Structure60,000 Inner Structure190,000 Test Article8,000

7 Topsfield Engineering Service, Inc. Slide 7 Thermal Control Considerations n 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 n Evaluate options for thermal insulation MLI Blankets n Minimize temperature difference - < 2 C across structure

8 Topsfield Engineering Service, Inc. Slide 8 Cool down Methods n Method 1 - Radiation only n Method 2 - Radiation and natural convection in the 20 K Dewar at a pressure above the Chamber Pressure n 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

9 Topsfield Engineering Service, Inc. Slide 9 Test Article Heat Load Distribution CaseRadiative Load - watts Conductive Load - watts 110000 4200800 650950 725975 95995 Thermal Model Cases Method No Description Vacuum - torr Test ArticleChamber 1AHe Shroud & N2 Shroud - no MLI1e-5 1BHe Shroud & MLI only - 2 blanket1e-5 1CHe Shroud & MLI only - 2 blanket0.01 2AHe Dewar & N2 Shroud - no MLI0.101e-5 2BHe Dewar & N2 Shroud - no MLI1.001e-5 4AHe Shroud & N2 Shroud - 1 MLI both Shrouds0.01 4BHe Shroud & N2 Shroud - 2 MLI both Shrouds1.00 MLI Model thermal conductivity vs. pressure Pressure - torrk - watts/in K 1e-58.382e-7 0.016.604e-6 10.000127

10 Topsfield Engineering Service, Inc. Slide 10 Thermal Analysis Cases CHAMBER METHOD 1A 80K GN 2 SHROUD 20K Helium SHROUD TA 10 -5 Torr TA CHAMBER METHODS 2A & 2B 80K GN 2 SHROUD 20K Helium dewar - pressure tight 10 -5 Torr 2A 0.1 Torr 2B 1.0 Torr CHAMBER Note: Both shrouds as tight as possible 80K GN 2 SHROUD 20K He SHROUD TA 4A 0.01 Torr 4B 1.0 Torr MLI BLANKETS 4A: 1 thick 4B: 2 thick METHODS 4A & 4B CHAMBER METHOD 1B 20K He SHROUD TA 10 -5 Torr 2 MLI BLANKET CHAMBER METHOD 1C 20K He SHROUD TA 10 -2 Torr 2 MLI BLANKET

11 Topsfield Engineering Service, Inc. Slide 11 Thermal Model Construction n Nodes:33 n Linear Conductors: 46 n Radiation Conductors: 58 n Lumps:3 n Paths:2 n Ties: 7

12 Topsfield Engineering Service, Inc. Slide 12 Thermal Model Surface Finish/Emissivity LN 2 Shroud He Shroud Chamber Wall Test Structure Item 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 1 7 2 3 54 6

13 Topsfield Engineering Service, Inc. Slide 13 Flow Regime Definition Knudsen Number K n = /p, where is the mean free path and p is the characteristic dimension. Continuum flow – K n < 0.01 Transition flow – 0.01 < K n < 0.3 Molecular flow – K n > 0.3

14 Topsfield Engineering Service, Inc. Slide 14 Chamber Flow Regimes PressureTemperature inches KnKn Flow Regime torrK--- 1300.00043.6e-5Continuum 0.1300.0040.00036Continuum 0.01300.040.0036Continuum 10-63042635.5Molecular

15 Topsfield Engineering Service, Inc. Slide 15 Thermal Desktop Capability Molecular Conduction

16 Topsfield Engineering Service, Inc. Slide 16 Thermal Desktop Capability Natural Convection Caution

17 Topsfield Engineering Service, Inc. Slide 17 Method 1 Results

18 Topsfield Engineering Service, Inc. Slide 18 Method 2 Results

19 Topsfield Engineering Service, Inc. Slide 19 Method 4 Results

20 Topsfield Engineering Service, Inc. Slide 20 Thermal Analysis Results MethodCase Time to reach Steady State days Test Article Steady State Temperature - K Meets Test Article Cool down Temperature and Time goals Cold Steady State Helium Gas flow rate grams/sec Cold Steady State Heat Rate to Helium gas watts 1A18.372NO401167 1A48.349NO401167 1A98.329YES401167 1B18.373NO441293 1B48.347NO441293 1B98.329YES441293 1C110.858NO1093256 1C410.035YES109 3256 1C910.025YES109 3256 2A17.940NO621787 2A47.926YES621787 2A97.922YES621787 2B17.929YES621787 2B47.924YES621787 2B97.922YES621787 4A18.388NO1373987 4A48.350NO1373987 4A98.325YES1373987 4B1533YES1945625 4B4528YES1945625 4B9524YES1945625

21 Topsfield Engineering Service, Inc. Slide 21 Helium Refrigeration Helium Plant PFD COMPRESSOR LN 2 Supply GAS STORAGE FROM SHROUD/STRUCTURETO SHROUD/STRUCTURE 80K – 300K < 80K EXPANDERS He Plant Size is based on analysis results shown on Slide 18

22 Topsfield Engineering Service, Inc. Slide 22 Structural Design Considerations n 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

23 Topsfield Engineering Service, Inc. Slide 23 Structural Design Considerations n 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

24 Topsfield Engineering Service, Inc. Slide 24 20 K Shroud Design n 20 K Shroud to be Pressure Tight Design Pressure inside shroud 1 to 10 torr n 20 K Shroud to be Flow Tight Pressure in entire chamber 1x 10-2 torr

25 Topsfield Engineering Service, Inc. Slide 25 Structural Design Considerations n 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

26 Topsfield Engineering Service, Inc. Slide 26 Support Concept

27 Topsfield Engineering Service, Inc. Slide 27 Vibration Design Considerations n Minimize, or eliminate, any vibration transmission to the Test Assembly n To avoid subjecting the test assembly to random or non-repeating load (s), of a magnitude that would affect optical test stability n Support of Test Fixture on hard points until after cool-down

28 Topsfield Engineering Service, Inc. Slide 28 Class 10,000 Clean Room 20 K Shroud w/plenum 80 K Shroud Access Platform Test Support & Article Note that top shroud panels are removed for visibility Clean Air Flow In Clean Air Flow Out

29 Topsfield Engineering Service, Inc. Slide 29 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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