M. Gilchriese

Update on Pixel Prototype Mechanics/Cooling Structures at

LBNLFebruary 1, 2008

M. Cepeda, S. Dardin, M. Garcia-Sciveres, M. Gilchriese and R. PostLBNL

W. Miller and W. MilleriTi

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What Are We Doing?

• R&D on module supports using low-density, thermally conducting carbon foam + carbon fiber structures

• Goal is to investigate both stave-like(or sector-like) structures and monolithic ie. half-shell(or half-disk) structures

• Build and test prototypes and do FEA to compare to measurements and predict performance.

• Note all barrel concepts assume active edge modules!! Flat surfaces..

• Today– Update of thermal measurements on stave structure

– Comparison of these measurements to FEA

– Monolithic structure mockup made

– Next steps and conclusions

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Foam

• Currently working with foam made by proprietary chemical-vapor-deposition (CVD) process using reticulated vitreous carbon (RVC) foam as a precursor

• The RVC has density ~ 0.05 g/cc and is poor thermal conductor with a K ~ 0.07 W/m-K

• The CVD-deposited carbon coats the ligaments in the RVC foam, has a very high K and thus raises the effective K by factor ~ 100 but the density only by factor 2-4.

• Note this foam (and RVC foam) is straightforward to machine, including moderately complex shapes and has reasonable mechanical properties eg. CTE similar to silicon

• So far we have worked with samples (free) of density 0.18 g/cc• Made simple rectangular prototype – foam with tube in middle

– to test concept

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Pixel Stave Prototype - I

Foam with groove for tube. Three pieces joined. One side

Foam with groove for tube. Three pieces joined. One side

YSH-70 cloth 140 microns thick

K13D2U laminate 300 microns thick

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Pixel Stave Prototype - II

Tube with CGL7018

YSH-70 and K13D2U glued to foam

Tube in foam with CGL7018

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Pixel Stave Prototype - III

• Final assembly(foam+fiber halves glued together around tube)

• Tube is sized for CO2 coolant ie. about 2.2mm ID

• Platinum-on-silicon heater in middle to simulate pixel module and copper-kapton heaters on either side to minimize end effects.

6.9 mm

24 mm

Foam

260mg/cm2

(exc. Pipe)=> 130mg/cm2 for

Tube is 2.8mm OD

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Thermal Performance

• IR camera used

• Water coolant at 1.0 l/min at 20C.

• Vary power level in silicon heater

• And separately in copper-kapton

Label Emis BG Ave SD Max Min UnitA1 0.95 19.0 27.41 0.65 28.4 25.9 CA2 0.95 19.0 27.36 0.80 28.4 23.8 C

T in boxes

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Results

0

2

4

6

8

10

12

14

16

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

P/A(W/cm^2)

De

lta

T a

ve

rag

e

YSH-70 only

K13D2U only

YSH-70 sideHeat both

K13D2U sideHeat both

Note if CO2 used as coolantthen reference temperature could be about -30C. Thusdelta T of 10 => T of -20C.

FE

-I4

goal

FE

-I3

norm

al

Max

. sp

ecIncludes sensors & power conv. But not cables.

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FEA of Prototype

• Single-module in length, corresponding to silicon heater

• Heat from both sides

• Neglect kapton heaters on either side of silicon heater

• Instead have measured effect of additional heaters on the prototype

• Figure at right and summarized on next page

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FEA Comparison• Measured T for about 0.65W/cm2 on both sides of stave is about 14.5C for either

sided(very small difference between side with YSH-70 and K13D2U).• Correction for kapton heaters is about -1C. So value to compare with FEA is about

13.5C• FEA predicts 11-15C, taking into account errors in K and thickness of materials –

see below. Biggest unknown is foam K.

ItemAverageSurface T

TemperatureDifferential Thickness(mm) K

% Error DT Up

ErrorDifferential

T UpTop 30.902 10.652 4.33

Silicon Heater 30.835 0.067 0.28 148 30% 0.02SE4445 29.759 1.076 0.1 0.6 17% 0.18YSH70 Facing 28.501 1.258 0.165 0.6 17% 0.21YSH70 Adhesive 28.318 0.183 0.05 1.55 35% 0.06Foam 22.072 6.246 n/a 10 50% 3.12CGL 21 1.072 0.1 1.55 48% 0.52Al Tube 20.937 0.063 0.3 200 20% 0.01Film 20.25 0.687 n/a 30% 0.21Film 20.945 0.695 n/a 30% 0.21Al Tube 20.99 0.045 0.3 200 20% 0.01CGL 22.111 1.121 0.1 1.55 48% 0.54Foam 28.304 6.193 n/a 10 50% 3.10K13D2U Adhesive 28.487 0.183 0.05 1.55 35% 0.06K13D2U facing 30.008 1.521 0.32 1 20% 0.30SE4445 31.085 1.077 0.1 0.6 17% 0.18Silicon Heater 31.133 0.048 0.28 148 30% 0.01

Bottom 31.181 10.931 4.42

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Improvements?

• We were conservative in the amount of foam (2mm) between the facing and tube. Subsequent machining trials show that we can reduce this to 0.5-1mm. Reducing to 1mm would reduce the T by 1.5-2C (from calculation).

• The facing on the module side is there to (a) provide a surface to mount the module and (b) possibly for stiffness.

• We realized that at least (a) can be met with glue alone and this would also likely improve T

• See samples with good surface quality that consist of Hysol 9396 + 30% boron-nitride(for thermal conductivity) about 125 microns thick. No facing on front side. See pictures next page.

• Would tune thickness and shape of backside carbon-fiber facing to provide required stiffness, if this technique were used.

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Glue Surface Samples

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Monolithic Concepts for B-Layer

• Single half-barrel structure

• Modules inside

• Drawings show concepts for CO2 cooling, but would just use bigger pipe for CnFm cooling

• Concept is simple– Conducting foam

– Aluminum tube glued into foam

– Tune carbon-fiber outer shell to minimize material but meet stiffness and other mechanical requirements

– End-rings (not shown) for additional stiffness(glued to shell) and for inevitable cable and pipe strain relief

Carbon high K foam

Faces for module mounting

Round aluminum tube

Carbon fiber shell glued to foam

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Monolithic Mockup

• We have built a mockup of a monolithic foam-fiber structure(for SLHC B-layer with CO2 cooling) to understand how to do this.

• Used low-density RVC foam(not conducting foam) for convenience

• See next page for some pictures of details• As built, about 1.7 g/cm for half-barrel(foam,

tubes, adhesives, shell) => maybe 4 g/cm for real foam, real shell? Eg. 320 gm + end rings for 80 cm half-barrel

• Can easily see how to make mechanical/cooling structure to meet thermal/mechanical requirements.

• But mount and remove modules and connections? Needs considerable study – this is the hard part of this design

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Monolithic Construction

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Monolithic Options to Study

• Will do quick FEA look at alternative monolithic option proposed by Maurice

• One-module long model shown here.

• Mounting and connection access easier in this concept

• What K needed for foam to make this work with fewer tubes per module?

• Could keep one-tube per module, however

• Note in this case likely to need carbon fiber facings both sides for overall stiffness.

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Next Steps and Conclusions• Foam

– Measure thermal conductivity. Commercial firm, laser diffusivity– Anyone else interested and capable to test by other means? Have samples...– Have submitted proposal to develop foam and characterize it with company but wont

know for a few months if approved.– Module removal trials on samples with glue surface + foam. Is this a problem? If yes, go

back to thin laminate on surface, works for both stave and monolithic• Stave/sector

– Proof-of-concept complete…..could proceed to real design with existing materials. Note this would also work for disk sectors. Important to have unified concept for barrel and disks, in my opinion

– Would like to test with CO2 if we can find someone interested with this capability….• Monolithic structure

– Simple analysis of design variants to be done. What can work.– Would clearly work as is for flat half-disks….don’t have to worry about module mounting

issues• Need basic structural analysis(sag, stability…) to size carbon fiber aspects. • But possible another step would be to model overall layout for both barrel and disks

based on foam/fiber concept, mixing monolithic and stave approaches eg. B-layer and monolithic disks, remainder of barrel layers based on staves

• Would welcome collaboration with interested groups

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Backup

• Weight of monolithic mockup, roughly, without end rings– RVC foam+adhesives: 6.1 gms

– Tubes: 3.6 gms

– Shell: 3 gms

– This gives only about 1.7 gm/cm per half-shell length

• Extrapolate to higher density foam– Foam x 3 or about 18 gms

– Tubes same

– Shell. Don’t know guess at least x 2 or 6 gms

– About 4 gm/cm of half-shell length or roughly 320 gm for 80 cm length, not including end rings

– Of course, really need full structural analysis….