THERMAL ANALYSIS SUMMARY FOR LBNE-BLIP IRRADIATION TESTS

P. Hurh2/19/2010

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). .

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)

Sample Capsule Layout

33 gpm per “box” Flow areas matched

to balance flow Thermal analysis on

capsules only

Capsule Schematic (NTS)

Sample Volume0.005” Gap0.01” SS

Window

Graphite FillerSS Capsule

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

ANSYS model

Z. Tang Model with input from 1st MARS analysis (sigma=4.23 mm)

1st Pass MARS analysis

Vacuum, no contact

Z. Tang Model with input from 1st MARS analysis (sx=sy=4.23 mm, 90 µA)

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)

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

Vacuum Contact Conductance Values

Above indicates range of 400-1600 (W/m2/K) for SS surfaces

Incropera & DeWitt, Fundamentals of heat transfer

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.

Vacuum, contact everywhere

Conductance = 200 W/m2/K

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

Thermal/Contact Model (Simos)

Window deformation modeled

Contact conductance only in contact areas

Samples modeled as full width plates

Thermal/Contact Model (Simos)

Roughly matches Tang analysis

Almost uniform temperature profile

Conductance = 200 W/m2/K

Beam spot used? 400 W/g

Thermal/Contact Model (Simos)

Does not match Tang analysis

Almost uniform temperature profile

Conductance = 1000 W/m2/K

Beam spot used? 400 W/g

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)

Helium gas filled, no contact

Helium gas filled, no contact

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?

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)

Simplistic Model

For rings within contact area, contact conductance calculated with Song & Yovanovich method for low pressure contact:

Simplistic Model

Good Agreement with measurements in our regime!

Simplistic Model

For gap distances GTE 25 µm, conductance modeled as simple conduction through gas (thermal conductivity, kg)

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

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

Simplistic Model: Helium Results

Simplistic Model: Argon Results

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

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

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