m. yoda, s. i. abdel-khalik, d. l. sadowski and m. d. hageman woodruff school of mechanical...

M. Yoda, S. I. Abdel-Khalik, D. L. Sadowski and M. D. Hageman

Woodruff School of Mechanical Engineering

Update on Thermal Performance of the Gas-

Cooled Plate-Type Divertor

ARIES-Pathways (8/09) 2

Objective / MotivationObjective• Experimentally evaluate and validate thermal performance of

gas-cooled divertor designs in support of the ARIES team

Motivation• Leading divertor designs rely on jet impingement cooling to

achieve desired performance• Accommodate heat fluxes up to 10 MW/m2 • Performance is “robust” with respect to manufacturing

tolerances and variations in flow distribution• Extremely high heat transfer coefficients (~50 kW/(m2K))

predicted by commercial CFD codes used for the design• Experimentally validate such numerical predictions


Approach• Design and instrument test modules that closely

match divertor geometries• Conduct experiments at conditions matching and

spanning expected non-dimensional parameters for prototypical operating conditions– Reynolds number Re– Use air instead of He

• Measure temperature distributions and pressure drop• Compare experimental data with predictions from

CFD software for test geometry and conditions– Nu(Re), P*(Re)


Investigated leading gas-cooled divertor designs• FZK Helium-Cooled Multi-Jet (HEMJ) “Finger”

[Norajitra et al. 2005]

– Ihli et al. 2007; Crosatti et al. 2009• ARIES-CS T-Tube [Ihli et al. 2007; Raffray et al. 2008]

– Crosatti et al. 2007; Abdel-Khalik et al. 2008; Crosatti et al. 2009

• ARIES-Pathways Plate-Type Design[Malang; Wang et al. 2009]

– Variant with metal open-cell foam: Gayton et al. 2009

[Sharafat et al. 2007]

– Variant with pin-fin array: In progress

Some History


Outcomes• Enhanced confidence in predicted performance by

commercial CFD codes at prototypical and off-normal operating conditions– FLUENT®

• Use validated CFD codes to optimize/modify divertor designs

• Predict sensitivity to changes in geometry and operating conditions to define and establish manufacturing tolerances


Plate-Type Divertor Design• Covers large area (2000 cm2 = 0.2 m2): divertor area

O(100 m2)

100 cmCastellated

W armor0.5 cm thick

20– HEMJ, T-tube

cool 2.5, 13 cm2

– Accommodates

up to 10 MW/m2

without exceeding

Tmax 1300 °C, max 400 MPa

– 9 individual manifold units with ~3 mm thick W-alloy side walls brazed together


GT Test ModuleArmor

In

Out

• Jet issues from 0.5 mm slot, then impinges on and cools underside of W-alloy pressure boundary– Coolant flows along 2 mm gap,

exits via outlet manifold– Original design

[Malang 2007]

– Use air as coolant– Reynolds number Re = 1.1104–

6.8104 (vs. 3.3104 at nominal operating conditions)

– Nominal heat flux qnom = 0.2– 0.75 MW/m2

In

Out

Heated brass shell

Al inner cartridge


Al Inner Cartridge

InOut

• Inlet, outlet manifolds embedded inside Al cartridge– Manifolds 19 mm 15 mm 76.2 mm – 2 mm 76.2 mm slot– Coolant enters outlet

manifold via holes – Side wall bolted on


Brass Outer Shell• Models pressure boundary

– 5 TC in shell to measure cooled surface temperature distribution: 2 in center; (1,5) and (3,4) at same depth 0.5 mm from surface

– Brass shell heated by heater block

– k for brass similar to that of W-alloy


Pin-Fin Array• Can thermal performance of leading divertor

designs be further improved?– Mo open-cell foam in 2 mm gap increased HTC by

40–50%, but also increased P* by similar fraction[Gayton et al. 2009]

– In HEMP, a variant of HEMJ, coolant impinges on pin-fin array [Diegele et al. 2003]

• Combine plate with pin-fin array– 808 1.0 mm 2.0 mm pin fins (nearly) contacting

Al cartridge on 1.2 mm pitch

– 2 mm “clear” area for impinging jet

– Pin fins EDM’ed into inside of brass shell


Heated Test Section

Copper heater block

Graphite shim

Brass outer shell

Aluminum cartridge

Gasket


GT Air Flow Loop

Inlet P, T measurement

Outlet P, T measurement

Cu heater block• 3 cartridge heaters• 6 TC in neck measure q• 2 TC at top monitor max.

Cu temperature


• Nu from TC data – Nearly uniform T along

slot– Nu based on gap width, k

at 300K and effective HTC (for pin fins)

• qnom = 0.2–0.75 MW/m2

Effect of Pin Fins

Re (/104)

Pin finsBare surface

TC 1 TC 4 TC 2 TC 5 TC 3

Nominal operating condition

Nu


• Ratio of Nu and P for cooled surface with, without pin-fins

• Pin-fins with ~260% more surface area improve cooling performance by ~150%–200% while increasing pressure drop by ~40–70%

Comparison: Pins vs. Bare

Re (/104)

Nu

p /

Nu

Mass flow rate [g/s]

P

p* /

P *

Nominal operating condition


Summary• Designed and studied experimental test modules

modeling leading He-cooled divertor designs– T-tube, HEMJ “finger,” plate– Conducted dynamically similar thermal-hydraulics

experiments matching and spanning expected prototypical operating conditions

• Used commercial CFD software to predict performance of experimental test modules– Good agreement between experimental data and model

predictions (including those from other groups)– Use validated codes to predict performance of gas-cooled

components with complex geometries


Conclusions• Plate-type divertor + pin-fin array promising design

– Smaller number of divertor modules required reduced cost, complexity

– Two- to three-fold enhancement by pin fins can accommodate heat fluxes much higher than 10 MW/m2

• Initial results for un-optimized configuration: use CFD to suggest improvements to current experimental design– Effect of pin pitch, diameter– Effect of slot width


Next Steps

To complete ARIES-Pathways study:• Validate CFD codes (e.g. FLUENT) and plate models

with experimental data– Model pin-fin array

• Use validated CFD codes to optimize/modify pin-fin layout – Predict maximum heat flux that can be accommodated by

optimized pin-fin/plate-type divertor– Predict pressure drop across optimized pin-fin array

m. yoda, s. i. abdel-khalik, d. l. sadowski and m. d. hageman woodruff school of mechanical...

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