Update: HEMJ Experiments in the

GT Helium Loop

M. Yoda, S. I. Abdel-Khalik, D. L. Sadowski, B. H. MillsSeptember 18, 2013

Objectives •Evaluate thermal performance of leading helium-cooled divertor designs at prototypical conditions •Determine design correlations from experimental data at near-prototypical conditions and numerical simulations•Use correlations to estimate how changes in operating conditions affect divertor thermal performanceCurrent Approach•Test a single helium-cooled divertor with multi-jet cooling (HEMJ) module in helium loop at prototypical pressures, near-prototypical temperatures •Estimate maximum heat flux and He pumping power requirements from cooled surface temperature and pressure drop data

Gas-Cooled Divertors

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HEMJ Design

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W-alloy

18 mmW Tile

Steel

15 mm

18 mm

• Divertor design proposed for DEMO– Jet impingement cooling: He at 600 °C

(increased to 650-700 °C), 10 MPa exits from 25 (24 each 0.6 mm dia. + one 1.0 mm dia.) holes

– He mass flow rate 6.8 g/s

– KIT/Efremov experiments of 9-module unit at prototypical conditions show HEMJ can accommodate heat fluxes q > 10 MW/m2

– Cools very small area: need ~5105 modules to cool O(100 m2) divertor

m

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Background• Previous work: Dynamically similar studies of various divertor

designs extrapolated to prototypical conditions– Study HEMJ, finger-type divertor with single impinging jet, He-cooled

flat-plate (HCFP) and T-tube divertors– Cool with air, He and Ar at near-ambient temperatures– Match coolant mass flow rate (Re) and fraction of heat removed by

convection, vs. conduction (Biot number Bi Nu / , where thermal

conductivity ratio ks / k)

– Determine correlations for Nusselt number Nu = f (Re, ) [neglecting

Prandtl number effects] and loss coefficient KL = g (Re)

• Test at near-prototypical conditions in helium test loop– 10 g/s, inlet temperature Ti 400 °C, inlet pressure pi 10 MPa

– Can accommodate test sections with pressure drops 0.7 MPam

Average Nu and KL

• Reynolds number from mass flow rate– Dj = 1 mm

• Calculate average heat transfer coefficient – Heat flux from energy balance for He (Te exit

temperature)– Avg. cooled surface temperature extrapolated from embedded TCs– Ac = 131.5 mm2 = area of cooled surface

• Average Nusselt number from– coolant thermal conductivity

• Loss coefficient from pressure drop p– average speed

j

4mRe

D

p e in

c in c

( )

( )

mc T Th

T T A

cT

jhDNu

kh

m

k

L 2ρ 2

pK

V

V

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Helium Loop Schematic

• Evacuate loop, then charge to 10 MPa with He from 41.3 MPa source tanks

• Two buffer tanks increase He inventory and reduce flow pulsation

• Mass flow rate adjusted using bypass • He supplied to test module is heated

with recuperator and electric heater• Inline filters remove particulates

larger than 7 μm

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He source tanks

Reciprocating compressor

Vacuum pump

Recuperator

CoolerTest section

Electric heaterBuffer tanks

Bypass

Reciprocating Compressor

Reciprocating Compressor

Test Section (in fume

hood)

Test Section (in fume

hood)

Buffer TanksBuffer Tanks

Recuperator/Preheater

Recuperator/Preheater

GT Helium Loop

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HEMJ Experiments• HEMJ test section: J-1c design– D185 W-alloy (97% W + 2.1% Ni

+ 0.9% Fe) outer shell + brass C360 inner jets cartridge

– Heat with oxy-acetylene torch: incident heat fluxes q 2.7 MW/m2

– Flow argon over flame impingement location to minimize oxidation (D185 “oxidation-resistant” up to 600 °C): maximum measured temperatures ~950 °C

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Current Status• HEMJ experiments in GT helium loop– Inlet temperatures Ti = 43 – 295 °C (pi = 10 MPa)

– Mass flow rates = 2.9 – 6.9 g/s (fluctuations <3%): Re 1.4104 4.1104 (vs. 2.14104 at prototypical conditions)

– Incident heat fluxes q = 0.7 2.7 MW/m2

– Minor oxidation + stress-induced fracture (at TC port 0.25 mm from heated surface) observed on outer shell

– Based on pressure drop data loss coefficients KL = 2.4 – 2.5 over all

measurements– Inconsistent results for Nu due to variations in gap between inner

cartridge, outer shell (0.9 mm): machining tolerance (0.1 mm) + seating of cartridge inside shell

m

Relaminarization• Focus of US-Japan collaboration

PHENIX (Kyoto U., TUS)– Relaminarization/“Deteriorated turbulent heat

transfer” reduction in Nu due to variations in coolant properties

– Based on available data (in simpler geometries), only occurs at low Re: potential issue for off-normal events

– Use He loop to see if anomalous heat transfer behavior observed at low Re ( 0.6 g/s with 6% fluctuation), smaller gaps

– Hosting visitors in Aug., Sept.

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Reynolds number

mMcEligot & Jackson 2004

Flow regime map: Square ducts

Next Steps• HEMJ experiments– New test section: WL10 outer cartridge + stainless steel inner jets cartridge with

adjustable gap– Measurements by ORNL ks (T) for D185, brass

– Increase Ti to ~400 °C and q above 5 MW/m2 using 10 kW RF induction heater

(loan from INL): avoid oxidation• Relaminarization experiments– Continue experiments at low mass flow rates– Vary gap width

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