# Presentation: 270956

## Upgrade Stave Study Topics

- Current Analysis Tasks
_*Stave Stiffness*_, ability to resist gravity sag, critical at upper and lower Φ
_*Stave thermal/mechanical*_ aspects
- Heat transfer to evaporative cooling tubes
- Thermal strains from thermal gradient from chips to tubes
- Thermal strains from cool-down, room temperature to initial state (minus 25oC)
_*Coolant tube sizing*_ within confines of stave structure
- Analysis guided by realistic constraints on radiation length
- Attempt to make analytical model representative at all times

- Radiation length driven design as always, issues focus on:
- Composite material properties
- High modulus, optimized fiber orientation for maximum axial stiffness
- High conductivity fiber system for heat transport
- Issue to be addressed is CTE mismatch in the assembly
-  Al cooling tube or possibly PEEK
- Stave length, gravity sag, bounded between fixed end and simple supports
- Estimate range to be ~60μm fixed to ~320 μm simple for present composite sandwich geometry
- Desire limit of ~50-75microns

## Stave Stiffness Structural Model for Gravity Sag

## Full Length (96cm) Model w/o Pins

- Sandwich model composed of solid elements
- NASTRAN solver, FEMAP mesh generator
- Model Properties
- K13D2U with 4/1 fiber orientation for facings
- Carbon foam core
- Side ribs from same material as facing
- Aluminum End Cap with receiver holes for pins
- Simple support conditions imposed in interior of holes
- Silicon modules and hybrids coupled to facing without compliance of dielectric cable
- Cable mass included with facing mass

- Sag 69 μm, but pin deflection not included

## Sag with Pin End Supports

- End Cap Material: Aluminum
- Steel 0.125in pins
- Kinematical BC on pins

- Max central sag 92.6 μm

## Small Distortion Evident in Pins

- Steel Pin Deflection: 0.8microns
-          0.125in diameter

## Pin Deflection Increased Sag to 92.6μm

- End of Pin: 0.8microns

- 3.3microns in stave

## End Cap Distortion

**End Cap Distortion**

- Pin engagement: 0.236”
- Side support: 0.394”
- Stave Ledge: 0.12”

- Ledge

- Side support

- pin

## Model Variations

- Model without pins versus model with pins
- Al end cap, Facing K13D2U 4/1, no pins: 67microns
- Same configuration with 0.125in dia steel pins: 92.6microns
- End Cap Material
- Aluminum versus Composite, radiation length penalty
- Stave gravity sag _*with Al*_: 92.6microns
- Stave gravity sag _*with K13D2U 4/1*_: 101.5microns (this was not expected)
- Matches stave facing CTE
- Stave gravity sag with K13D2U balanced
- Sag essentially same as the 4/1 fiber orientation
*Uncouple Silicon Wafer and BeO*
- By reducing tensile modulus to nearly zero
- Al End Cap, steel pins, facing K13D2U 4/1
- _Sag increase from 92.6 to 104microns_

## Revised Stave Model

- Why new model?
- Attempt to reduce sag back down from ~100 μm
- Continued assessment of contribution to stiffness from silicon modules and BeO hybrid
- Correct mesh of sandwich core (one foam piece did not mesh), improve contact with stave facing
- Modifications
- Increased pin diameter from 0.125in dia. to 0.173in dia
- Added mass of hybrid and silicon wafer to facing mass (total decoupling of stiffness from detectors)
- Mass of cable added to composite facing as before
- First Solution
- End Cap Al
- Support pins solid steel
- Next
- evaluate hollow pins
- different end cap material

## Gravity Solution

- Central deflection 90.5microns
-    (as compared to 104 μm )

- 674122 solid elements

- Stiffness of modules and hybrid not included

- 96cm long by 6.4cm wide composite stave

## Results continued

- Pin deflection
- 0.36microns

- Stave support
- 1.8microns

- XYZ restraint
- Opposite pin Y and Z

- Pin deflection reduced by half

## Results continued

- X and Y

- Y only

## Stave Thermal Mechanical FEA of Thermal Strain

## Distortion from Cool-Down

- Geometry
- 96cm long stave, with kinematic support at two end caps (no pins)
- End caps, Al material
- Stave facings, K13D2U with 4 to fiber orientation, maximizes axial stiffness
- Al cooling tubes
- Alternating pattern of silicon modules and BeO hybrids on upper and lower stave surface
- Shift in pattern providing detector hermeticity
- Thermal solution
- 50oC temperature change, RM Temp to -25oC
- Thermal strain, wave pattern with nominally 10.6micron variation

## Cooling Thermal Gradient

- FEA solution for both Al and Carbon-Fiber Filled PEEK tubes
- 6 chips for each hybrid, 0.5W each: heat zone shifts top to bottom
- Film coefficient 3000W/m2K, typical of Pixel stave for C3F8, two parallel tubes
- Lower peak chip temperature favors Al cooling tube

## Stave Cooling Tube Size Two-Phase Flow

## Coolant Considerations

- Coolant
- C3F8, evaporative coolant
- Enters at -25oC through throttling process, with a quality of 0.3 (30% vapor)
- Exit, near all vapor (assume quality ~0.8 to 0.88 for calculating require mass flow)
- Tube
- Hydraulic diameter, 8mm, elongated providing 2mm of flat contact with stave composite facings
- Tube length (2-pass) ~192cm (entrance and exit at same stave end)
- Capacity
- For dissipated chip power 108W, need 2.2gm/sec
- Pressure drop
- <25mbar in two pass two, without elbow
- [will calculate for elbow next, along with heat transfer coefficient]