M. Gilchriese

Integrated StaveMechanics/Cooling

BackupATLAS Upgrade Workshop

ValenciaDecember 2007

M. Cepeda, S. Dardin, M. Gilchriese, C. Haber and R. PostLBNL

W.Miller and W. MilleriTi

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Introduction

• We collect here some backup information for the presentation on integrated stave mechanics/cooling.

• A few notes– Work on the integrated stave began in the Fall of 2006– The dimensions of prototypes, and a number of FEA calculations, were

set then when detectors were assumed to be about 6cm in width.– Thus prototypes were built assuming about 6 cm wide detector

dimensions rather than the current 10cm “baseline”. Thus a principal goal of the “6 cm” prototypes is to validate FEA estimates of the thermal performance, and then use the FEA to calculate for 10 cm

– In addition, the properties assumed for materials, particularly for thermal FEA calculations have evolved somewhat with time as have assumptions for detector power after irradiation.

• Link to information on integrated stave mechanics/coolinghttp://phyweb.lbl.gov/atlaswiki/index.php?title=ATLAS_Upgrade_RandD_-_Mechanical_Studies

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Prototypes

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Reminder of Prototype Concept

71.5mm

• For prototypes……..fixed > 1 year ago

• K13D2U, high-modulus facings

• Adjust facing thickness(layers) to achieve stiffness desired

• Carbon-fiber honeycomb in-between facing, fixed thickness

• Three types of tubes– Flattened(C3F8)

– Big round with POCO foam(C3F8/C2F6)

– Small round with POCO foam(CO2)

POCO foam: about 0.5 g/cc thermally conducting carbon foam

Link to drawings is here

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Prototype Stave Core AssemblyLength

(m)Facing Material

# of Plys Facing

Tube Type

Purpose Status

1 0.35 CN60 10 Flattened Assembly trial

Complete

2 0.35 K13D2U 10 Flattened Short, thermal

prototype

Complete

3 1.0 K13D2U 10 Flattened For modules

Complete

4 0.35 K13D2U 3 4.8 mm round/ POCO foam

Foam bonding, thermal

prototype

Complete

5 0.35 K13D2U 3 2.8 mm round/ POCO foam

CO2 thermal

prototype

Complete

6 ? K13D2U ? ? ? TBD in 2008

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Weight and Material

• Measured weights for 1m prototype(10 ply facings) and extrapolation to thinner facings(3 ply) and width for 10cm detectors given below. Note assumes minimal side closeouts

• Tube is flattened. Would get similar numbers for POCO foam+smaller tube 1 meter

10 ply, 7 cm % RL

1 meter3 ply, 10cm % RL

Facings 160.44 0.50% 73 0.15%Honeycomb 15.6236 0.05% 24 0.05%Bare tube 35.49 0.19% 35 0.13%Thermal adhesive 10.56 0.03% 11 0.02%Side closeouts 27.3011 0.09% 5 0.01%Epoxy 15.7236 0.05% 18 0.04%Subtotal 265.1383 0.91% 165 0.40%End closeouts 24.4317 0.13% 37 0.13%Total 289.57 202

Measured Extrapolated

Length(cm) 106.4 106.4Width(cm) 7.15 10.8Area(cm2) 760.76 1149.12Interior height(cm) 0.5 0.5

Ratio 1.51048951

Carbon 42Adhesive 42Aluminum 24

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Thermal Measurements• Measurements before and after thermal cycle 50 times to -35C are summarized below

– Delta T calculated from average of inlet+outlet water T for convenience. Max and min given to nearest 0.5C. Delta T rounded to nearest degree.

– No difference between before and after thermal cycle within errors– Note tube(4.8) with foam compared to flattened is better as is smaller tube with foam. We attribute this

to better coupling to tube• FEA results are given(for fixed fluid temperature everywhere). Agreement within 20% or

roughly 1.5C. Writeup of FEA is at link here

Item Conditions Max T Min T Inlet T Outlet T Delta T max Delta T min Delta T AvePrototypes

Flattened tube3.3W/heater, heat both sidesbefore thermal cycle 29 25.5 20.1 20.8 9 5 7

Flattened tube3.3W/heater, heat both sidesafter thermal cycle 28 25 20.1 20.5 8 5 6

Flattened tube3.3W/heater, heat one sidebefore thermal cycle 28.5 25 20.1 20.4 8 5 7

4.8mm tube3.3W/heater, heat one sidebefore thermal cycle 26.4 23.5 20.1 20.3 6 3 5

4.8mm tube3.3W/heater, heat one sideafter thermal cycle 27 24 20.1 20.3 7 4 5

2.9mm tube3.3W/heater, heat both sidesafter thermal cycle 28 24.5 20.3 21.1 7 4 6

2.9mm tube3.3W/heater, heat both sidesbefore thermal cycle 27 24 20.2 21 6 3 5

FEAFlattened tube 3.3W, heat both sides 27.5 20 20 8Flattened tube 3.3W/heater, one side 25.9 20 20 64.8mm tube 3.3W/heater, one side 25.5 23.5 20.3 20.3 5 3 4

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Remove/Replace

• We have completed a number of trials of gluing glass and silicon with SE4445 adhesive that was used to attach all pixel modules to local supports in the current pixel detector. Has decent thermal properties and already tested to 50 MRad for pixels.

• Attach, let cure(both week long and about 2 month long tested), remove, clean and replace.

• Straightforward mechanically, only need simple tooling for close-together detectors – promising (no surprise since did this already for pixels)

• Pictures on next pages, although hard to see

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Removal Pictures

• Glass slide after removal(slide at bottom of picture)

• Starting to peel SE4445

• Silicon detector after removal and before cleanup

• After about 2 month cure.• Done with two detectors, same

result

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Thermal FEA

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Comments

• Some of the most recent results are included here

• Many previous studies with somewhat different parameters.

• See the wiki

http://phyweb.lbl.gov/atlaswiki/index.php?title=ATLAS_Upgrade_RandD_-_Mechanical_Studies

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Thermal Runaway in 10cm Module • Thermal Runaway Issue: Based on new detector heating curve- (revised

by Nobu-MIWG meeting November 2007)– Quarter section from 10cm wide stave, single U-Tube– Spacing of U-Tube divides heat load collected by each symmetrically– Chip heat load and surface heating treated as variables

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Thermal Runaway Model Parameters

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Surface Heating Curve

New curve based on 1mW/mm2 at 0ºC (Nobu-MIWG Nov. 2007) and exponential temperature dependence

0.001

0.01

0.1

1

10

100

-40 -30 -20 -10 0 10 20 30 40

Detector Surface Temperature-(C)

Sur

face

Hea

ting

-(m

W/m

m2 )Nobu-MIWG Mtg. Nov. 2007

Previous

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Thermal Runaway Solutions

Plot of peak detector temperature leading up to runaway (as function of tube surface wall temperature)

Surface heating 1mW/mm2 @ 0CExponential temperature dependency

(Nobu-MIWG Mtg. Nov. 2007)

1mW/mm2 @ 0C

-30

-25

-20

-15

-10

-5

0

5

10

-30 -25 -20 -15 -10 -5

Tube Inner Wall Temperature-(C)

Max

Det

ecto

r S

urf

ace

Tem

per

atu

re-(

C)

0.5W/chip

0.25W/chip

0.125W/chip

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Thermal Runaway-Variable Surface Heating

Comparing effect of surface heating using 0.25W/chip as baseline

0.25W/chip

-30

-25

-20

-15

-10

-5

0

5

10

15

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

Tube Inner Wall Temperature-(C)

Max

Det

ecto

r S

urf

ace

Tem

per

atu

re-(

C)

Surface Heating01mW/

mm2

2mW/mm2

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Detector Surface Heating

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

-30 -25 -20 -15 -10 -5

Tube Inner Wall Temperature- (C)

De

tec

tor

He

atin

g-(

mW

/mm

2 )

0.5W/chip 1W/mm2 @ 0C

0.25W/chip 1mW/mm2 @ 0C

0.001

0.01

0.1

1

10

-40 -30 -20 -10 0 10 20 30

Peak Detector Temperature-(C)S

urf

ace

Hea

tin

g-(

mW

/mm

2 )

Nobu-MIWG Mtg. Nov. 2007

FEA: Heating with 0.5W/chip

FEA: Heating with 0.25W/chip

Curve at right shows slight deviation of solution convergence

Deviation caused by using peak silicon nodal temperature whereas solution is based on the detector outer surface edge average

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Thermal Runaway-Typical Thermal Plot

Chip: 0.5WCoolant Tube Surface -16.8ºCPeak chip: 6.18ºCPeak detector edge: 5.17ºCThroughout solutions peak chip and peak detector differential temperature stays near 1.0 to 1.1ºCWith 0.25W/chip the temp difference is nominally 0.5ºC

Nearly thermal runaway point

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Bridge Thermal Model• Salient Features

– High conductivity (700W/mK, 0.5mm thick) CC bridge material support for 0.28mm thick hybrid(1W/mK)

– 40 chips @ 0.25W/chip– Detector 0.28mm thick, 148W/mK– Allcomp carbon foam for bridge support (isotropic 45W/mK)– Carbon Foam for tube support (45/45/45 W/mK)

• Reduced density over POCO foam (0.2g/cc versus 0.5 g/cc)

– Sandwich foam• Allcomp foam option, ~0.1g/cc @ 3W/mK

• Comparison with Hybrid on 10cm Detector– Thermal solution with both with inner tube wall at -28ºC

• Simulates -30ºC with 8000W/m2K

• No change made to material properties in 10cm detector with integrated hybrid

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10cm Detector-No Bridge• Material Properties

– See previous slide (#2)

• 40 chips per detector, 80 total– 0.25W/chip Q (Si)=0W

– Tube inner surface -28ºC, no convection coefficient

• Interest in ΔT from chip and detector surface to tube surface

• Peak chip temperature– Middle hybrid region: -20.5ºC

• Peak Detector– Middle hybrid region: -21.5ºC

– ΔT in region of max gradient: 6.5ºC

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10 CM Wide Stave-No Bridge• Solution

– Replaced honeycomb core with Allcomp carbon foam (<0.2g/cm3: 45W/mK)

– Also, replaced POCO foam tube support with same foam

• Peak Chip Temp: -22.7ºC

• Peak Detector: -24ºC– ΔT (referenced to tube

wall)• 4ºC

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10 CM Wide Stave-No Bridge• Solution: Simulate “outer” long

strip detector– One upper and power hybrid for

10cm detector

– 20 chips @ 0.25W/chip

– Coolant tube inner surface: -28ºC

– Materials, see slide (#2)

• Detector– Peak temp beneath hybrid: -24.8ºC

– ΔT in region of max gradient: 3.2ºC

• Chip Peak Temp: -24.1ºC

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Thermal Bridge Model (1/2 of 10cm)

Wire bonds, simulated as thin solid, reduced K to 97W/mK

Chips 0.38mm thick (148W/mK)

Al Cooling tube 0.21mm ID

Separation between facings 4.95mm

10cm

Foam bridge support

1mm air gap for bridge

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Bridge Thermal Model

Enclosed bridge model in an air box. Air participates only through pure conduction. Air fills all cavities not occupied by a solid

Air box

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Model Parameters

Cable and adjacent adhesive layers modeled as single layer 0.227mm and K=0.31W/mK

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Solution with -30ºC Tube 8000 W/m2K 0.5W/chip Q (Si)=0

Slight asymmetry caused by variance in interior coolant wall temperature

Detector max=-21.4ºC

Chip peak=-16.5ºC

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Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q (Si)=0

Slight asymmetry caused by variance in interior coolant wall temperature

Detector max=-25.8ºC

Chip peak=-23.3ºC

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Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q (Si)=0

Bridge foam and tube foam 45W/mk, density ~0.2 g/cm3(no POCO foam) Peak detector temp -24.2ºC

Sandwich foam core 3W/mK, density ~0.06 g/cm3

Peak chip=-21.8ºC

Wire bonds 97W/mK

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Fluid Calculations• C3F8 calculations are here for flattened tube and here for round tube

• CO2 calculations are here and here.

• Summary from main talk reproduced below

• Note T(film) is an average around the loop T(loop) follows from the P vs T curves for the fluids and is rounded

to the nearest 0.5C

• These calculations are complex and need validation by measurements

Based on 240W, 1 meter length (2 m cooling tube). See Backup for references to more details.

Fluid Tube OD (mm)

Tube ID (mm)

Hydraulic Diameter (mm)

ΔP (mbar)

Coolant (ºC)

ΔT(film) (ºC)

ΔT(loop) (ºC)

C3F8 4.9 4.29 4.29 333 -25 3.5 5 C3F8 4.9(oval) n/a 5.27 121 -25 3.5 2 CO2 2.8 2.19 2.19 638 -35 2.0 1.5

ΔT(film) is drop from “bulk” to wall. ΔT(loop) follows from ΔP.

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Adhesive Joint Considerations• There are numerous analytic solutions for adhesive joint shear stress

caused by thermal expansion of dissimilar materials– General theme is that the shear stress is a maximum at the ends of joint,

and essentially zero at the center

– Maximum shear stress at the end is independent of the length of the joint• Key factors are:

– modulus of elasticity, CTE, and thickness of joined materials

– thickness and shear modulus of the adhesive

– Temperature differential

• A useful reference to bound the problem: Thermal Stresses in Bonded Joints, W.T. Chen and C.W. Nelson– Suggests for carbon foam joined to aluminum tube with CGL7018 (very

compliant adhesive) or EG7658 (semi-rigid) that shear stresses remain within material limits for a 100C temperature change

– Prototype testing will confirm our expectations

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Carbon Foam to Aluminum Tube Joint

• 100C temperature differential– Cure temp to -25C

– Foam thickness=8mm, G=690MPa, α=4ppm/C– Aluminum wall thickness 0.305mm, E=10Msi, α=12ppmC

– Adhesive thickness=0.10mm, Compliant G=40MPa (5862psi), Rigid G=1 GPa

• Max shear stress, τ=1062psi, compliant τ= 42psi

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Computer-Based Solutions• Structural Problems

– NASTRAN FE solver• Recent solutions with NE NASTRAN with FEMAP interface

• Prior work with MSC NASTRAN, but MSC no longer can bundle the NASTRAN solver with FEMAP pre-processor

– Choose not to use PATRAN pre-processor

• Fluid/Thermal Problems– Use CFDesign computational fluids dynamics code

• Very versatile

• Allows use of shell elements for describing interface resistances

• HEP Silicon-Based Tracking Detectors– Issue with very, very thin solids mixed in with larger solids

• In reasonable sized geometry, some solids may have only surface nodes, and no internal nodes;

– possible consequence is reduction of solution accuracy