THERMAL ANALYSIS SUMMARY FOR LBNE-BLIP IRRADIATION TESTS P. Hurh 2/19/2010.
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Transcript of THERMAL ANALYSIS SUMMARY FOR LBNE-BLIP IRRADIATION TESTS P. Hurh 2/19/2010.
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THERMAL ANALYSIS SUMMARY FOR LBNE-BLIP IRRADIATION TESTS
P. Hurh2/19/2010
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Irradiation Temperature is Important
Material Property changes are dependent upon irradiation temperature
Annealing while being irradiated
Changes in thermal conductivity with neutron dose (dpa) at different irradiation temperatures (Bonal et al 2009).
Effects of neutron irradiation on the Young’s modulus of pitch coke graphite (Bonal et al 2009). .
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What irradiation temperature range is desired for LBNE-BLIP testing? NOvA 700 KW graphite target
temperature range is predicted to be 700-900 ºC (1000-1200 ºK).
IHEP 2 MW graphite max target temperature range is predicted to be 380-430 ºC (650-700 ºK).
To see larger changes in material properties, lower irradiation temperatures desired.
Goal temperature range: 300-800 ºC ??(600-1100 ºK)
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Sample Capsule Layout
33 gpm per “box” Flow areas matched
to balance flow Thermal analysis on
capsules only
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Capsule Schematic (NTS)
Sample Volume0.005” Gap0.01” SS
Window
Graphite FillerSS Capsule
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Capsule under pressure
Contact Area, r0Gap Volume
With gas in gap volume, contact area and gap volumes change as pressure differential changes (and vice versa)
Under vacuum, conduction only in contact area with radiative heat transfer in gap volume
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ANSYS model
Z. Tang Model with input from 1st MARS analysis (sigma=4.23 mm)
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1st Pass MARS analysis
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Vacuum, no contact
Z. Tang Model with input from 1st MARS analysis (sx=sy=4.23 mm, 90 µA)
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Contact Conductance
Many variables (pressure, interstitial fluid, elasticity, plasticity, surface roughness, maximum asperity, temperature, thermal conductance…)
Many different measured values (most studies focus on relative differences rather than absolute values)
For higher contact pressures and/or for vacuum environment, no reliable predictive method unless all variables are controlled (and known)
Perhaps a more reliable predictive method for low contact pressure with gas environment (more later)
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Vacuum Contact Conductance Values
In air environment In vacuum environment
Varying values in both vacuum and air (curves 1 and 3 in left graph, curves 4 and 6 in right graph)
100 kN/m2 is pressure range of interest
This survey indicates a range of 200 to 1000 W/m2/K for vacuum
G. P. Peterson, Texas A&M
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Vacuum Contact Conductance Values
Above indicates range of 400-1600 (W/m2/K) for SS surfaces
Incropera & DeWitt, Fundamentals of heat transfer
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Vacuum Contact Conductance Values
Above indicates 241 and 452 (W/m2/K) for SS surfaces in vacuum
Song et al, Thermal Gap Conductance of Conforming Surfaces in Contact, Journal of Heat Transfer, Vol. 115, pg 538.
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Vacuum, contact everywhere
Conductance = 200 W/m2/K
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Vacuum, contact everywhere
Conductance = 1000 W/m2/K
Note reduction in temperature is only ~200 K
Gaps between samples impeding heat flow
This was actually done to mimic contact in air which varies from 1000 to 3000 W/m2/K
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Thermal/Contact Model (Simos)
Window deformation modeled
Contact conductance only in contact areas
Samples modeled as full width plates
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Thermal/Contact Model (Simos)
Roughly matches Tang analysis
Almost uniform temperature profile
Conductance = 200 W/m2/K
Beam spot used? 400 W/g
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Thermal/Contact Model (Simos)
Does not match Tang analysis
Almost uniform temperature profile
Conductance = 1000 W/m2/K
Beam spot used? 400 W/g
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Gas Environment
Provides larger contact conductance values
Provides GTE gap conductance values (compared to radiation)
Provides interstitial conductive fluid in areas where contact is questionable (uneven sample/window surfaces)
Adds the variable of capsule internal pressure to the thermal problem (as temperature varies, internal pressure varies, changing contact area)
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Helium gas filled, no contact
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Helium gas filled, no contact
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Helium, no contact, sensitivity So, Tang’s sensitivity analysis showed
some sensitivity to thermal conductivity of sample material (spreading of heat transversely)
For factor of 5 reduction in k, less than a factor of 2 increase in temperature delta across gap
Contact may decrease temperatures further
Helium may keep samples too cold?
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Simplistic Model
In order to better understand the effects of gas in the sample capsule, a spreadsheet model was created
1-dimensional heat transfer model (no transverse heat transfer)
Treated as 1 mm wide annular rings Each ring has a gap conductance value
calculated Contact area determined by deflection
and volume/pressure calculations (manual iteration)
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Simplistic Model
For rings within contact area, contact conductance calculated with Song & Yovanovich method for low pressure contact:
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Simplistic Model
Good Agreement with measurements in our regime!
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Simplistic Model
For gap distances GTE 25 µm, conductance modeled as simple conduction through gas (thermal conductivity, kg)
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Simplistic Model
Model assumes atmospheric pressure inside capsule when welding complete (cool)
Model uses an average beam sigma based on latest BLIP phosphor image (7.855 mm)
Model uses peak energy deposition scaled from first MARS analysis and adjusted for higher current (136 W/g)
Model accounts for changes in volume due to window deflection and sample expansion
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Simplistic Model
Calculates new window to fluid heat transfer coefficient using expected flows and hydraulic diameter correlations (6170 W/m2/K)
Does not account for temperature rise through SS window foil or through sample thickness (predicts only sample surface temperature next to window)
Assumes 30 feet of water head (13 psi) when installed at BLIP
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Simplistic Model: Helium Results
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Simplistic Model: Argon Results
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Simplistic Model: Summary
Condition Del T Gap
Del Fluid Temp Fluid Total
Helium, contact
33 59 300 392
Helium, 25 µm gap
68 59 300 427
Argon, contact 182 59 300 541
Argon, 25 µm gap
419 59 300 778 Helium is least sensitive to contact issues (35 K range)
Argon is not bad (240 K range) Temperature range for Argon is good match for
desired range (500K – 800 K) Actual temperatures may be lower due to
transverse heat flow (especially for Argon) and boiling
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Compare with vacuum
Condition Del T Gap
Del Fluid Temp Fluid
Total
Helium, contact 33 59 300 392
Helium, 25 µm gap
68 59 300 427
Argon, contact 182 59 300 541
Argon, 25 µm gap
419 59 300 778
Vacuum, contact 102 59 300 461
Vacuum, 25 µm gap
1290 59 300 1649 Vacuum contact scaled from Simos best case model
Vacuum gap from Tang worst case model (not scaled yet)
Vacuum has largest range and sensitivity to contact (>1000 K) and can get very hot
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Future Work
Z. Tang’s model can be used with the simplistic model’s contact area prediction to more accurately model the Argon gas case (and use new energy deposition results)
Recommend using Argon environment Temperature Range matches desired OK range in extremes Relatively easy to weld in argon purged glove-box
Temperature Monitoring via annealing threshold Need to work with Simos to see evidence of
threshold in past runs