M. Gilchriese

Integrated StaveMechanics/Cooling

June 5, 2008CERN

M. Gilchriese

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

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M. Gilchriese

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)

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Bus cable

Hybrids Coolant tube structure

Carbon honeycomb or foam

Carbon fiberfacing

Readout IC’s

Silicon sensors

M. Gilchriese

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

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PrototypeNumber 

Facing Length (m)

Facing Material # of Plies per Facing

Tube Type Purpose

1 0.343 CN60 10 Flattened Assembly trial

2 0.343 K13D2U 10 Flattened Thermal prototype

3 1.07 K13D2U 10 Flattened For modules

4 0.343 K13D2U 3 4.8 mm round/ POCO foam

Thermalprototype

5 0.343 K13D2U 3 2.8 mm round/ POCO foam

Thermal prototype

M. Gilchriese

Prototype Construction

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Honeycomb core

Prototype #4

Prototype #3

Facing

Carbon foam

Carbon foam

Prototype #5

Honeycomb 5 mm thick for all prototypes

M. Gilchriese

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

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Bus cableAlumina

Heaters 0.3mm silicon

Thermal measurements of prototypes

Dummy detector removal

M. Gilchriese

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)

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Models of Thermal Performance

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Item Thickness Thermal Conductivity

(W/mK)

X/Y/Z

Solid Elements

Tube OD: 2.8mm, ID: 2.1mm 200

Composite Facing Thickness 0.21mm 148/1.3/294

Cable 0.125 0.12

Detector 0.28mm 148

BeO 0.38mm 210

Dielectric Hybrid 0.23mm 5

Chips 0.38mm 148

POCO Foam (0.9mm min) varies 50/125/50

Adhesives

Foam to Tube (CGL) 0.1 mm 1

Foam to Composite Facing (CGL) 0.1 mm 1

Facing to Cable 0.05 mm 0.8

Cable to Detector 0.05 mm 0.8

Detector to BeO 0.05 mm 0.8

BeO to Dielectric hybrid 0.05 mm 1.55

Dielectric to chip 0.05 mm 1.55

Shown for 10 x 10 cm2 detectors¼-model, primarily for thermal runawayAgrees with multi-hybrid model T

Multi-hybrid model. More elements. Vary composition of stave. Assess T change

M. Gilchriese

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

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M. Gilchriese

Modified Structure Performance

• Relevant for C3F8 with Tmin =-25C

• Add more cooling – triple U-tube

• Or replace honeycomb with thermally conducting foam

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-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

-35 -30 -25 -20 -15 -10 -5 0 5

Pe

ak

De

tec

tor

Te

mp

era

ture

oC

Tube Inner Wall Temperature oC

Triple U, 0.3W/chip, 1mW/mm2 @0C

Triple U, 0.5W/chip, 2mW/mm2 @ C

Single U-tube, foam, 0.3W/chip, 1mW/mm2 @0C

Single U-tube, 0.3W/chip, 1 mW/mm2 @0C

M. Gilchriese

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.

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Facing Properties

Fiber K is given (Z/X/Y)

Thickness

(mm)

Lay-up Chip Peak T

(ºC)

Detector Peak T

(ºC)

Cooling Tube

K13D2U(294/148/1.3) 0.21 0/90/0 8.61 7.96 Single U-Tube

K13D2U(221/221/1.3) 0.42 0/60/-60/s 7.31 6.61 Single U-Tube

K13D2U(294/148/1.3) 0.42 90/0/0/s 7.93 7.24 Single U-Tube

K13D2U(352/89/1.3) 0.70 90/0/0/0/0/s 8.30 7.62 Single U-Tube

Carbon-Carbon(314/183/25) 0.42 90/0/0/s 6.88 6.19 Single U-Tube

K1100(367/185/2) 0.21 0/90/0 8.05 7.39 Single U-Tube

K13D2U(386/97/1.44) 0.21 0/90/0 4.34 3.69 Triple U-Tube

K13D2U(352/89/1.3) 0.70 90/0/0/0/0/s 5.25 4.55 Triple U-Tube

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.

M. Gilchriese

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

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Description Chip Peak Temperature

(ºC)

Bridge Gradient

(ºC)

Sensor Max/Min

( ºC)

a. No air, no wire bonds 4.53 10.2 -17.7/-26.5

b. No air, with wire bonds -2.12 7.81 -19.2/-25.7

c. No wire bonds, with air -1.52 8.2 -15.6/-25.4

d. With air, with wire bonds -5.84 6.58 -20.0/-24.4

M. Gilchriese

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

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Model IC Peak

Temp(C)

Bridge

Gradient(C)

Sensor

Tmax(C)

¼ bridge model(baseline foam conductivity) -5.8 6.6 -20

¼ bridge model (bridge foam reduced to 10W/mK) +2.4 5.0 -17.8

Multi-Hybrid bridge model (baseline foam conductivity)

With 0.01m/s air flow @ -15ºC

-6.2 n/a -19.9

Multi-Hybrid bridge model (sandwich foam 1W/mK)

With 0.01m/s air flow @ -15ºC, 1W per Detector

-5.74 n/a -19.4

M. Gilchriese

Two-phase Flow Calculations

• Two-phase flow estimates for CO2 (-35C) and C3F8 (-25C)

• Thermal runaway estimated at entrance (worst case)

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Entrance( 0)

Exit ( 1)Tfluid -35oC

CO2 Heat Transfer 2.8mm OD tube

-35C Fluid Temperature

0

5000

10000

15000

0 0.2 0.4 0.6 0.8 1

Vapor Quality

He

at

Tra

ns

fer

Co

eff

icie

nt-

W/m

2 K

Combined

Boiling

CO2 Coolant Tube 2.8mm OD -35oC

0

1

2

3

0 0.2 0.4 0.6 0.8 1

Vapor QualityT

em

pe

ratu

re -

oC

Film TemperatureDrop

240 W heat load2 m tube, 2.2 mm ID

Vapor quality ()

Complex calculations!

TP 1oCTwall -35+1.75 -33C

Twall -35+1+2.5 -31C CO2

M. Gilchriese

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 OK15

M. Gilchriese

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!

16 -20

-15

-10

-5

0

5

10

15

0 1 2 3 4 5

Pea

k D

etec

tor

Tem

per

atu

re C

mW/mm2 @ 0C

Single U-tube, honeycomb core, 0.3W/chip, h=1436

Single U-tube, honeycomb core, 0.3W/chip, h=3000

Single U-tube, foam core, 0.3W/chip, h=1436

Single U-tube, foam core, 0.3W/chip,h=3000

Triple U-tube, honeycomb core, 0.3W/chip, h=1206

Triple U-tube, honeycomb core, 0.5W/chip, h=1206

M. Gilchriese

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)

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M. Gilchriese

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 needed18

M. Gilchriese

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

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Description X0 (%) Single Al U-tube (3mm OD, 2.2mm ID), honeycomb core 0.30-0.35

Single Al U-tube (6mm OD, 5.3mm ID), foam core ( = 0.2 g/cc) 0.45-0.50

Triple Al U-tube (6mm OD, 5.3mm ID), honeycomb core 0.65-0.70

Single Al U-tube (3mm OD, 2.2 mm ID), foam core ( = 0.2 g/cc) 0.35-0.40

C3F8 CO2

M. Gilchriese

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

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M. Gilchriese

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

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M. Gilchriese

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!

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M. Gilchriese23

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 $