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1
Hall A Tungsten Calorimeter
Preliminary Mechanical Designand
Thermal Analysis
May 14, 2004
2
Contents
• Objective & Requirements• Location• Mechanical Design• Thermal Analysis• Silver/Tungsten Comparisons• Assembly, Test & Installation• Cost Estimate• Schedule• Open Questions
3
Objective & Requirements
• OBJECTIVE:– Produce a calorimeter for beam current
measurements in Hall A that meets or exceeds design specifications on schedule and within budget
• REQUIREMENTS:– Design must
• minimize heat leaks• support thermometry• contain heater(s) for calibration• have method of cooling for repeat measurements• be insertable due to invasive nature of calorimetric
measurement• fit in available Hall A beamline real estate• survive in high radiation environment
4
257.22”
BCM
• Hall A Layout
• Super Harp Girder
- Locate Calorimeter between BCMs on girder
Location
5
15”12.75”
• Real Estate Constraints– Plenty of room above the
girder– Primarily constrained by
distance from beamline to girder
Super harp girder cross-section
Hall A Beamline 1.5” Dia
Mechanical Design
6
• The Slug
Volume = 3131.32 cm^3
BEAM
Mechanical Design
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– Desire a fully dense, machinable part with good thermal properties
– Pure tungsten shapes typically produced by powder met process (pressing and sintering followed by a extrusion or swaging operation to reduce porosity). Subsequent operations to reduce porosity are not practical for a part a large as ours.
– Density and machinability can be improved by adding small amounts of Ni and Cu (W,Ni,Cu 95:3.5:1.5) but thermal properties are less desirable.
– OSRAM/Sylvania produces a W,Cu 95:5 powder that will produce a very dense(~99%), homogenous, machinable part that has higher thermal conductivity than the above materials and still retains a high density. This is a unique process for making W:Cu composites that does not require infiltrating the Cu into a tungsten framework. Infiltrating would not be an option for a part as large as ours. This is the material of choice and has been used for the thermal analyses presented here.
* Thermal properties detailed later in the thermal analysis section
• The Slug (Con’t)
Mechanical Design
8
• Three Position Actuation Scheme– Advances in compliant thermal interfaces that
improve contact conductance in vacuum at low contact pressures offer an opportunity to cool the slug by conduction rather than convection. The scheme proposed eliminates the need to embed or otherwise attach cooling tubes that could increase the heat loss from the slug and would complicate the thermal response due to non-homogeneous diffusion properties.
The three positions:• 1. Charging• 2. Equilibrating• 3. Cooling
Mechanical Design
9
Mechanical Design
22.1”
40.2” Ø16.5”
11.8”
BEAM
Approximate Weight
450 Lbs
10
• Mechanism
Mechanical Design
3 Position Pneumatic Cylinder
Guided Support & Feedthru Cross
Welded Bellows
Support & Guide Rod
Ball Bushing
Instrumentation & Power
Feedthrus
Turnbuckle
Slug Vertical Support Tube
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• Slug Support & Cooling Plate
Mechanical Design
Oversized ebeam/ horizontal support tube allows beam ops to continue when slug is equilibrating or cooling (i.e., position 2 or 3)
Socket set screws to support & align slug (contains ceramic insert to provide thermal and electrical isolation)
3 point mount to base of vessel to align cooling plate to slug flat
Cu Cooling plate covered with compliant thermal interface material
Cooling plate alignment base
Cooling plate thermal isolation
Slug support arms
Coupling to attach to vertical support tube
Opening in base of tube to route wires to slug
12
• Compliant Thermal Interface– Consists of an array of aligned
7µm diameter carbon fibers– Each fiber spans the gap
between mating surfaces resulting in improved thermal performance over conventional particle filled pads
– High aspect ratio provides mechanical compliance (~.006” displacement at 15psi for .020” thk pad)
– Fibers can be directly attached to cooling plate using a thermally conductive epoxy or encapsulated in a polymeric base.
Mechanical Design
13
• Vacuum Vessel
Mechanical Design
3 point mount to super harp girder
Ø 8” CF access port
Ø 10” CF port provides access to cooling plate
Ø 2.75” CF Chill water feedthru (jacketed to minimize heat transfer to vessel)
Ø 2.75” CF beamline port
Ø 16.5” CF
Ø 4.5” CF port for instrumentation feedthru
Vessel baseplate
14
• Calorimeter on super harp girder looking downbeam
Mechanical Design
15
Beam
Mechanical Design
• Calorimeter on super harp girder
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Thermal Analysis
• Design Considerations– Heat Loads
• Power I*E <= 5kW
– Need to understand…• Thermal Response Time • Heat Leaks
– Conductive through mounts and wires (TC’s, Faraday, and heater(s))
– Radiation exchange with surroundings• Cooldown Time
– Require ability to repeat measurements in ~ 30 minutes• Effect of heater(s) on the thermal response of the device
– Correlate calibration vs. ebeam run
17
Thermal Analysis
• Thermal Modeling– For initial modeling, a 2d transient axis-symmetric implicit
finite difference (FD) model was written using Visual Basic for Applications in Excel
– Lumped mass model used for initial cooldown estimates – IDEAS TMG transient solver now available at Jlab was
used to check results from FD code and conduct more detailed analyses that more accurately capture the transient heat flow out of (and into) the slug. Future refinements will include radiation exchange and a heater model for comparisons between simulated calibration and ebeam runs. Analyses presented here use the FD code to capture the radiation losses.
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Thermal Analysis
• Material Properties
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• Finite Difference Thermal Model
– Decreased radius to match volume of actual slug to account for flat and entrance hole
– Conduction losses calculated at each time step. Heat flow based on assumption that T is linear thru the mounts.
– Radiation losses assume a two surface enclosure for each face of the slug (e.g., slug upbeam face only views Area1 of idealized chamber)
Thermal Analysis
20
• Finite Difference Thermal Model Input Panel
*
* Kmount very small here to capture only rad losses
Thermal Analysis
21
Upbeam Mounting Pins
(spaced 90° apart)
Downbeam Mounting Pins
(spaced 90° apart)
Faraday Wire
Downbeam TC Wires
(spaced 120° apart)
Upbeam TC Wires
(spaced 120° apart)
• IDEAS/TMG Model
– Took advantage of symmetry and modeled only half of the slug
– Mounting pins and wires modeled using beam elements
– Slug modeled using solid elements
– Wires are 8”Lg, mounts are 1”Lg
Thermal Analysis
22
Thermal Analysis
• Initial and boundary conditions used for the simulations presented in the next several slides– Uniform initial temperature distribution of 0°C– The ends of the wires and mounts are fixed at 0°C– From time t=0s to t=48s 5kW of beam power is deposited
uniformly in a cylindrical volume 5mm in diameter that begins one radiation length into the slug at the base of the entrance hole and extends five radiation lengths into the slug
– At t=350s the slug is brought in contact with the cooling plate. Overall contact conductance of 1250W/m^2/K to a fixed -15°C (corresponds to a chill water temp of ~12°C)
– At t=1050s the slug is lifted from the cooling plate
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RTD Temperatures
-10.000
0.000
10.000
20.000
30.000
40.000
50.000
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
Time [s]
Tem
p [K
]
Up Beam Upper RTD Up Beam Lower RTD Down Beam Lower RTD Down Beam Upper RTD
• IDEAS/TMG Thermal Model Results
Thermal Analysis
Beam off (t=48s)
Lift off cooling plate (t=1050s)
Measurement over/ begin cooldown (t=350s)
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• IDEAS/TMG Thermal Model Results
Thermal Analysis
Estimated Conductive Loss from RTD & Faraday Wires
-0.050
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
Time [s]
Hea
t L
oss
[W
]
Up Beam Down Beam Faraday Total
25
• IDEAS/TMG Thermal Model Results
Estimated Conductive Heat Loss from Mounts
-0.250
-0.150
-0.050
0.050
0.150
0.250
0.350
0.450
0.550
0.650
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
Time [s]
Hea
t L
oss
[W
]
Up Beam Down Beam Total
Thermal Analysis
26
• IDEAS/TMG Thermal Model Results
Estimated Conductive Heat Loss from Wires & Mounts
-0.400
-0.200
0.000
0.200
0.400
0.600
0.800
1.000
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
Time [s]
Hea
t Lo
ss [W
]
Thermal Analysis
27
• IDEAS/TMG Thermal Model Results
Estimated Integrated Heat Loss from Wires & Mounts
-25
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
Time [s]
Hea
t Lo
ss [J
]
Thermal Analysis
28
• Finite Difference Thermal Model Results
Estimated Radiation Heat Loss
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Time [s]
Hea
t Lo
ss [W
]
Up Beam Face Down Beam Face Outer Face Total
Thermal Analysis
29
• IDEAS/TMG & Finite Difference Thermal Model Results
Estimated TOTAL Heat Loss
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
2.000
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375
Time [s]
Hea
t Lo
ss [W
]
Thermal Analysis
30
• IDEAS/TMG & Finite Difference Thermal Model Results
Estimated TOTAL Integrated Heat Loss
0
50
100
150
200
250
300
350
400
450
500
550
600
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350
Time [s]
Hea
t Lo
ss [J
]
Thermal Analysis
31
• IDEAS/TMG Thermal Model Results Summary
Thermal Analysis
– Total energy deposited 48sec*5kW=240kJ– Total energy lost before taking measurement
=531J– This represents a loss of only ~.2%
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Silver/Tungsten Comparisons
• Time constants (using FD model):– Silver ~ 35sec (for 14cm diameter x 24cm Lg slug)– Tungsten ~ 39sec
Temperature Response Comparisons
0
5
10
15
20
25
30
35
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350
Time [s]
Do
wn
bea
m R
TD
Tem
p [K
]
Silver Tungsten
33
Assembly, Test & Installation
• Plan to obtain samples of thermal
interface candidates and conduct outgassing, particulate, and thermal testing ASAP
• Will assemble and test the device outside of the Hall
• Expect minimal modifications to super harp girder to accommodate device
34
Cost Estimate
• MECHANICAL Portion of Device– Mechanism………………………..$10k– Slug……..…………………………..$9.5k– Cooling Plate……………………..$5.6k– Vacuum Vessel…..................$11.3k
TOTAL = $36.4k
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Schedule
36
Open Questions
• Will the thermal interface material perform as modeled?
• What effect does the heater(s) have on the thermal response and losses?
• What can be done to increase the heat transfer from the heater cartridge to the slug?