CFD studies and design iterations for the n TOF Spallation ... · CFD studies and design iterations for the n_TOF Spallation Target #3 cooling circuit - Students' Coffee n_TOF Facility

CFD studies and design iterations for the n_TOF Spallation Target #3 cooling circuitStudents' Coffee - 59th meeting

Rui XimenesEN-STI-TCD

29/01/201

91

Outline

29/01/2019

CFD studies and design iterations for the n_TOF Spallation Target #3 cooling circuit - Students' Coffee

n_TOF Facility | Target Consolidation | Computational Fluid Dynamics | Brief design overview | CFD design iterations | Final design

cooling performance2

• n_TOF Facility

• Target Consolidation

• Computational Fluid Dynamics

• Brief design overview

• CFD design iterations

• Final design cooling performance

n_TOF Facility

• Located in CERN-Meyrin

• Beam from PS: 26 GeV/c; 1.66e12p+/s(6x1013p+/super cycle)

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cooling performance

n-TOF

Target

n_TOF Facility

• Facility, designed to study neutron-nucleus interactions for a wide energy range and high-intensity

neutron beams.

• Two experimental areas:

• EAR1 horizontal 183m downstream the target;

• EAR2 vertical 18m above target.

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cooling performance

• Current target(#2):

• Single core of pure Lead;

• Water cooled;

• Presents issues regarding corrosion/contamination.

• Upgrade target design

• +operation reliability

• no corrosion/contamination

• Avoid cladding solutions

• Solution: N2(gas) cooled design with sliced core.

• +new cooling station

Target Consolidation

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n_TOF Target #2

n_TOF Target #3 core

Target Consolidation

Constrains & Requirements for the N2(gas) cooled design:

• Key requirements

• Identical or better physics performance (1.66e12p+/s, 15mm σ);

• Average(Steady-state) temperature in the Lead below 100Cº;

• Cooling circuit compatible with some sort of anti-creep structure;

• Integration: Target is confined to a very limited space/”pool”.

• Cooling specs/constrains:

• Gas cooled (N2), to avoid corrosion/contamination risks;

• Supply at 20Cº, to avoid external condensation;

• ~Atmospheric pressure;

• Flow 700-1000Nm3/h.

• Pressure Drop as low as possible.

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cooling performance

Beam

direction

Limited due to re-use of existing pipes to

the pit & to comply with target vessel

CFD domains | CAD Model

Numerical method to analyze fluid flows

• Short summary of the process:

• Define our Fluid Geometry/volume & solid Domains(if CHT);

• Discretized the domain(mesh);

• Setup physics: Properties, models, boundary conditions, flow

conditions;

• Run simulation;

• Analyze and post process results.

• CFD gives us the possibility to explore and comprehensively

understand fluid flows.

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Essential if we want to optimize it!

(Re)Design

Mesh

Setup

Simulate

Analyze

Optimization process

Computational Fluid Dynamics

Brief design overview

• Lead core

• 6 lead slices

• Spaced 10mm

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cooling performance

600 mm

Channel

50 mm

150 mm


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cooling performance

• Cradle(Al)

• Has two inlets for the

cooling

• Distributes the N2

through the channels

between lead slices.

Cradle


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cooling performance

• Stiffeners(Al)

• To hold the lead in place

together with the cradle

• No fluid passage on the sides

Stiffeners

Cradle


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cooling performance

N2

• N2 passes in between each lead

slice and on the downstream face

(6 channels with forced

convection)

Cradle

Stiffeners


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cooling performance

• Anti-creep plates(Al)

• Provide anti-creep structure

• & shape of the cooling channels

• One per channel and on the

upstream and downstream faces

Anti-creep

plates

Cradle

Stiffeners

N2


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cooling performance

• Tie rods and screws to hold lead

slices, anti-creep plates, stiffeners

and cradle together.

Anti-creep

plates

Tie rods

Cradle

Stiffeners

N2


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cooling performance

• Vessel (INOX)

• Cradle fixed to the vessel with tie rods

• 2 inlets & 2 outlets

N2


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cooling performance

Moderators

cooling circuit

N2 Pipes

CFD design iterations: outlets/inlets position

• Iterations to define inlets/outlets:

• Minimize pressure drop

• Distribute homogeneously flow amongst cooling channels.

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cooling performance

Flow

separation

Where? how many?

Dimensions?

Less 30% pressure drop with

optimized configuration

CFD design iterations: Align flow with beam axis

• Iterations to direct the N2 flow into the beam axis:

• Enhance cooling

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cooling performance

Face view of downstream channel velocity. (No anti-creep).

Max mass Flow/Velocity not aligned

with beam/hottest surface locations.

Top view of channels velocity at beam height. (No anti-creep).Beam

Top view temperature

distribution at beam height.

Obstruction of the moderator + tilted beam



• Enhance cooling

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cooling performance

Upstream face view of channel 2 velocity. (With baseline anti-creep).Top view of channels velocity at beam height. (Baseline anti-creep).Beam

Flow still not aligned after introduction

of a multi channel anti-creep plate.

Meanwhile, Vertical

moderator enlarged and

outlets readjusted

Baseline anti-

creep concept



• Enhance cooling

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cooling performance

Upstream face view of channel 2 velocity. (With baseline anti-creep).Top view of the cradle with deflector and improved shape.Beam

Increased space for flow at the end of

the channels

Deflector aligned with beam direction

Maximum temperature reduced by 13%

Obstruction ribCFD design iterations: Anti-creep optimization

• Iterations to optimize flow through anti-

creep plates:

• Enhance cooling

• Obstruction ribs to direct the flow to the

beam axis

• Defining gaps with ribs

• Vertical position in the channels

• Shape

• Length

• Width

• Gaps

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cooling performance

Aim to increase the cooling

in beam region

Top view scheme

Rib

Rib

N2

Gap

Gap

Anti-creep plate Lead

N2 in Gaps is not connected

N2 in Gaps is connected

10

mm

• Final optimized geometry results

Final design cooling performance

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cooling performance

Stea

dy

stat

e R

esu

lts

sum

mar

y1.

66e1

2p

+/s

Temperature N2 Inlets 20 C

Pressure N2 Outlet 7654.3 Pa

Reference pressure 1 atm

Volume Flow 787 Nm3/h

Max Velocity N2 76.4 m/s

Max Velocity N2(channels) 60.0 m/s

Pressure Drop -3.9 kPa

Temperature Max lb1 75.9 C






Energy balance 2653 W

Temperature across

lead at beam height.

N2 Velocity in

channel 2.1

6 5 4 3 2 1

0.0

50.0

100.0

150.0

200.0

1 3 5 7 9 11 13 15 17 19 21

HTC

[W

m^-

2 K

^-1

]

Gap nr

HTC per gap at Channel 2.1

Analytical HTC

CFD HTC

Analytical HTCs estimated with the PKN

correlation for smooth ducts

Thank you!

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CFD studies and design iterations for the n TOF Spallation ... · CFD studies and design iterations for the n_TOF Spallation Target #3 cooling circuit - Students' Coffee n_TOF Facility

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