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Integrated Stave Mechanics/Cooling

Integrated Stave Mechanics/Cooling. June 5, 2008 CERN. Outline. Additional information at http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/StaveReview/stave_draft_note.pdf Concept Prototype construction/test Thermal performance Structural studies Material Questions What if…..

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Integrated Stave Mechanics/Cooling

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  1. Integrated StaveMechanics/Cooling June 5, 2008 CERN

  2. Outline • Additional information at • http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/StaveReview/stave_draft_note.pdf • Concept • Prototype construction/test • Thermal performance • Structural studies • Material • Questions • What if….. • Development plan • Production cost/schedule

  3. Silicon sensors Carbon honeycomb or foam Carbon fiber facing Bus cable Coolant tube structure Hybrids Readout IC’s Concept • Approximate dimensions of mechanical/cooling core • Short-strips: length about 1 m + end-of-stave card (2 m possible) • Long-strips: about 2 m long + end-of-stave card • About 11 cm wide • Thickness  3-3.5 mm (CO2) or  5.5-6.5 mm(C3F8)

  4. Prototypes • Prototype stave structures were fabricated and tested (thermal/mechanical) starting Fall ‘06 up to about one year ago. • The design of the prototypes was fixed before choice of  10 x 10 cm2 detectors and the prototypes are therefore  7 cm wide. • Goals: gain experience with fabrication, thermal performance, simple mechanical properties and build 1 m object for modules

  5. Prototype Construction Carbon foam Honeycomb  5 mm thick for all prototypes Honeycomb core Prototype #3 Facing Prototype #4 Carbon foam Prototype #5

  6. Prototype Testing • Thermal performance • Simulated heat loads(e.g. 3.3 W/”hybrid”) • IR imaging. Water coolant. Compare to FEA • Before & after T cycling -35 to 20C • As built-accuracy (CMM scans) • Deflection measurements • Compare to expected properties • “Module” removal trials • Attach dummy silicon with adhesive, cure, remove, replace • Detailed weights -> material estimates Bus cable Alumina Heaters 0.3mm silicon Thermal measurements of prototypes Dummy detector removal

  7. Prototype Lessons • Fabrication straightforward • Obviously some learning but no surprises • Thermal performance (T/Watt) similar for all three tube types, 4.8 mm tube+foam being best, flattened tube or small tube about the same • Thermal performance in good agreement with FEA within errors of measurement based on expected materials properties (and their errors). • No change in thermal performance after 50 cycles from -35C to 20C • Deflection measurements in reasonable agreement with expectations (within  20%) but small sample (two prototypes) • As-built accuracy (planarity of facing plane) somewhat worse than we hoped (1 m prototype). • Deviation from average (rms) 30-60 . All points within  ± 100  window • Why? Non-uniformities in honeycomb as provided by vendor. Can be reduced • Dummy module removal, clean-up and replacement easy with SE4445 (adhesive used to attach current pixel modules)

  8. Models of Thermal Performance Shown for  10 x 10 cm2 detectors ¼-model, primarily for thermal runaway Agrees with multi-hybrid model T Multi-hybrid model. More elements. Vary composition of stave. Assess T change

  9. Nominal Structure Thermal Performance • Honeycomb core • ¼ model run as function of tube wall temperature • Take into account detector heating • Can already tell from this that C3F8 with Tmin =-25C is problematic

  10. Modified Structure Performance • Relevant for C3F8 with Tmin =-25C • Add more cooling – triple U-tube • Or replace honeycomb with thermally conducting foam

  11. More Improvements to Structure? • Vary facing thermal properties. Practically gain  1C in T • Improve K of bus-cable? Assumed K=0.12. If K=0.38 (estimated from average metal content), gain 1.5C in T. Effects on thermal performance from variations in the facing properties assuming a 0oC temperature for the coolant tube inner wall, 0.3 W/chip and no detector heating.

  12. Bridged-Hybrid Models • Some studies but not full thermal runaway estimates • See backup note for materials • Concept uses foam in addition to facings to carry heat from foot of bridge back to cooling tube • 0.25 W/chip, -28C wall temperature, no detector heating for these results

  13. Bridged-Hybrid Thermal Results • Effect of air flow studied (not significant at T and flow studied) • Nominal stave design (not bridge) at 0.25 W/chip, -28C wall and no detector heating has Tmax  -22C • Bridge -20 to -18C depending on foam K • Optimization of tube position (closer to bridge foot) not studied, expect would reduce Tmax

  14. Two-phase Flow Calculations • Two-phase flow estimates for CO2 (-35C) and C3F8 (-25C) • Thermal runaway estimated at entrance (worst case) Entrance(  0) Twall  -35+1+2.5  -31C TP  1oC CO2 Twall  -35+1.75  -33C Tfluid  -35oC Exit (  1) 240 W heat load 2 m tube, 2.2 mm ID Vapor quality () Complex calculations!

  15. Thermal Runaway – CO2 • Bulk fluid temperature -34C (entrance) • Fixed heat transfer (film) coefficient 6833 (calculated at entrance) for 240 W • Note film coefficient is heat dependent(goes up with more heat), not taken into account by us here • Headroom OK

  16. Thermal Runaway – C3F8(Tmin -25C) • Heat transfer coefficient either calculated at entrance for 240 W(different for single and triple U-tube) or taken as 3000. • Note that we would calculate value to be 3000 for 500 W (about at thermal runaway) • Triple U – OK • Foam(K=15 W/mK) instead of honeycomb OK • If C3F8(Tmin -25C)+foam, need measurement!

  17. Thermal Performance Conclusions • The baseline design with a honeycomb core and a single U-tube does not have acceptable headroom for Tmin = -25oC, representative of current cooling performance with C3F8 • The baseline design with a triple U-tube and a honeycomb core has acceptable headroom for Tmin = -25oC, representative of current cooling performance with C3F8 • A modified design with thermally conducting carbon foam instead of honeycomb and a single U-tube may have acceptable headroom for C3F8 with Tmin = -25oC (and colder fluids) • The baseline design has acceptable headroom for a single U-tube and honeycomb core for Tmin-35oC, which could be applicable to CO2 or perhaps mixtures of C3F8 with other fluorocarbons. • The headroom could be increased by small amounts from optimization of the carbon-fiber facings (gain  1oC) and from improved thermal conductivity of the bus-cable (gain  1- 3oC). These possible gains would be most important to realize if C3F8 with Tmin about -25OC were used. • The headroom for a bridged-hybrid design with Tmin-35oC is likely to be sufficient (but more precise calculations remain to be done)

  18. Structural Studies • Preferred support concept is stave-on-shell • Stave sag, vibrational modes, etc coupled with number of supports along length, shell design (minimize overall X0) – not studied in detail. • Simple calculation of sag (< 75 in horizontal position, worst) with support every  50 cm • Stave distortions upon cool-down from 25C to operating temperature • Quick look taking artificially bad case of alternating modules top and bottom. Result is  11 microns out of plane for 50C temperature change • Should be less with balanced structure • Shear stress between Al tube and foam estimated and looks OK – see ATLAS note • Clearly much more structural analysis needed

  19. Material • Material estimates for simple stave only. Does not include coolant, bus-cable, modules, end-of-stave cards, support points, strain relief… • Based partly on prototype weights (scaled) and from calculation • Uncertainty in facing thickness/density, adhesive choices, tube diameters => plausible range below for different configurations • Top three for nominal design (modules glued to bus-cable). Bottom estimate for bridged-hybrid C3F8 CO2

  20. Questions • Is it credible to assume the use of conducting carbon foam around the tube in the baseline design (with honeycomb core)? • Yes. Foam of density  0.5 g/cc (as used in prototypes) is available from at least two vendors. Production (batch size) is 150,000-200,000 cc, far more than we would need • One of the design alternatives uses low density carbon foam ( ≤ 0.2 g/cc). Is this credible? • We think so. We are actively working with three vendors (for pixel staves) on conducting foam with the appropriate properties and have samples in hand from all three. The production rate is claimed to not be driven by . • Are there any other “non-standard” materials proposed for use? • No. • Could you make a 4 m stave for the long-strip layers? • Not in my opinion

  21. What If…. • What if the short-strips staves were 2 m long instead of 1 m? • Fabrication of 2 m stave cores would not be significantly more challenging than 1 m stave cores. Could be cheaper (less labor) since fewer parts. • CO2 cooling at about -35C would work with a  4 m single U-tube but probably would increase tube ID by small amount (tenths of mm) • Structurally would be same as 1 m since supported along length (e.g. every 50 cm) except possibly for fixation scheme that accounts for CTE difference between stave and shell support but even this goes away if 2 m is fixed at center and 1 m fixed at an end. • Good experience handling 1 m prototype, including wire bonding. 2 m harder, but not by much • Survey of modules on 2 m stave harder, may require cross reference at 1 m scale, depends on survey capability. Not showstopper. • What if stainless steel pipes were used? • Impact on thermal performance small (< 1C) • Bending (for larger diameter for C3F8) – not sure • Radiation length increase CO2 (C3F8) 0.3(0.5)% x ratio of wall thickness to Al

  22. Development Plan • These four principal activities would occur largely in parallel • Thermal ( 1 yr once coolant testing available) • Selection of coolant essential to make progress (or need to carry multiple design options) • Small-scale prototypes likely to be needed • Design, fabricate and test full-length prototype(s) • Structural ( 1.5 yrs) • Also coolant dependent. Once coolant selected….. • Combined design of stave and supporting structure (obviously also coupled with thermal design) => baseline design that meets thermal and structural requirements. • Build prototypes and test (in addition to thermal prototypes) • Module interface ( 2 yrs) • Define and prototype module mounting requirements: temporary holding for module mounting, survey, testing (boxes, how to cool), shipping (boxes), etc… • Production planning interface ( 2 yrs) • Tooling, procedures, who builds what, etc.. • Durations shown ignore resource constraints!

  23. Production • A preliminary estimate of production cost and duration made earlier this year: http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/StaveReview/Cost%20Estimate%20for%20Integrated%20Stave%20Mechanics.doc • Covers barrel and simple extrapolation to disks. All staves/petals. • Material and equipment costs in U.S. $. • Cost and manpower range estimated. • Includes contingency (but not escalation) • Materials and equipment: $2-4M • Engineering labor: 8-12 FTE years • Technical labor: 28-48 FTE years • Rough schedule •  2 years design/prototype •  1 year pre-production •  2 years production • Resource constraints not included! Costs in U.S. ‘08 $

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