Integrated Stave Mechanics/Cooling Backup

1
Integrated StaveMechanics/CoolingBackup

• ATLAS Upgrade Workshop
• Valencia
• December 2007
• M. Cepeda, S. Dardin, M. Gilchriese, C. Haber and
  R. Post
• LBNL
• W.Miller and W. Miller
• iTi

2
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/cooling
• http//phyweb.lbl.gov/atlaswiki/index.php?titleAT
  LAS_Upgrade_RandD_-_Mechanical_Studies

3
Prototypes
4
Reminder of Prototype Concept
Link to drawings is here
71.5mm

• For prototypes..fixed gt 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
5
Prototype Stave Core Assembly
Length (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
6
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 foamsmaller tube

7
Thermal Measurements

• Measurements before and after thermal cycle 50
  times to -35C are summarized below
• Delta T calculated from average of inletoutlet
  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

8
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

9
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

10
Thermal FEA
11
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?titleAT
LAS_Upgrade_RandD_-_Mechanical_Studies
12
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

13
Thermal Runaway Model Parameters
14
Surface Heating Curve
New curve based on 1mW/mm2 at 0ºC (Nobu-MIWG Nov.
2007) and exponential temperature dependence
15
Thermal Runaway Solutions
Plot of peak detector temperature leading up to
runaway (as function of tube surface wall
temperature)
Surface heating 1mW/mm2 _at_ 0C Exponential
temperature dependency
(Nobu-MIWG Mtg. Nov. 2007)
16
Thermal Runaway-Variable Surface Heating
Comparing effect of surface heating using
0.25W/chip as baseline
Surface Heating
0
1mW/mm2
2mW/mm2
17
Detector Surface Heating
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
18
Thermal Runaway-Typical Thermal Plot
Chip 0.5W Coolant Tube Surface -16.8ºC Peak
chip 6.18ºC Peak detector edge 5.17ºC
Throughout solutions peak chip and peak detector
differential temperature stays near 1.0 to 1.1ºC
With 0.25W/chip the temp difference is nominally
0.5ºC
Nearly thermal runaway point
19
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 _at_ 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 _at_ 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

20
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 ?T from chip and detector surface to
  tube surface
• Peak chip temperature
• Middle hybrid region -20.5ºC
• Peak Detector
• Middle hybrid region -21.5ºC
• ?T in region of max gradient 6.5ºC

21
10 CM Wide Stave-No Bridge

• Solution
• Replaced honeycomb core with Allcomp carbon foam
  (lt0.2g/cm3 45W/mK)
• Also, replaced POCO foam tube support with same
  foam
• Peak Chip Temp -22.7ºC
• Peak Detector -24ºC
• ?T (referenced to tube wall)
• 4ºC

22
10 CM Wide Stave-No Bridge

• Solution Simulate outer long strip detector
• One upper and power hybrid for 10cm detector
• 20 chips _at_ 0.25W/chip
• Coolant tube inner surface -28ºC
• Materials, see slide (2)
• Detector
• Peak temp beneath hybrid -24.8ºC
• ?T in region of max gradient 3.2ºC
• Chip Peak Temp -24.1ºC

23
Thermal Bridge Model (1/2 of 10cm)
1mm air gap for bridge
10cm
Wire bonds, simulated as thin solid, reduced K to
97W/mK
Al Cooling tube 0.21mm ID
Chips 0.38mm thick (148W/mK)
Separation between facings 4.95mm
Foam bridge support
24
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
25
Model Parameters
Cable and adjacent adhesive layers modeled as
single layer 0.227mm and K0.31W/mK
26
Solution with -30ºC Tube 8000 W/m2K 0.5W/chip Q
(Si)0
Slight asymmetry caused by variance in interior
coolant wall temperature
Chip peak-16.5ºC
Detector max-21.4ºC
27
Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q
(Si)0
Slight asymmetry caused by variance in interior
coolant wall temperature
Chip peak-23.3ºC
Detector max-25.8ºC
28
Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q
(Si)0
Sandwich foam core 3W/mK, density 0.06 g/cm3
Bridge foam and tube foam 45W/mk, density 0.2
g/cm3 (no POCO foam)
Peak chip-21.8ºC
Peak detector temp -24.2ºC
Wire bonds 97W/mK
29
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

30
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

31
Carbon Foam to Aluminum Tube Joint

• 100C temperature differential
• Cure temp to -25C
• Foam thickness8mm, G690MPa, a4ppm/C
• Aluminum wall thickness 0.305mm, E10Msi,
  a12ppmC
• Adhesive thickness0.10mm, Compliant G40MPa
  (5862psi), Rigid G1 GPa
• Max shear stress, t1062psi, compliant t 42psi

32
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