Multiphase Flow Heat Transfer in Fuel Assemblies

January 2014ASCOMP; ASCOMP Inc. USA, www.ascomp.ch transat@ascomp.ch

The Westinghouse 24-rod mock-up of SVEA-96 fuel bundle Caraghiaur & Anglart (NED, 2009)

The Westinghouse 24-rod mock-up

The Westinghouse 24-rod mock-up of SVEA-96 fuel bundle

• KTH Stockholm (CFX, 1.300.00 cells)

The Westinghouse 24-rod mock-up

• ASCOMP (TransAT, IST MESH). From CAD (left) to OST grid (right). Note that the very coarse mesh shown in right is for illustration only.

The Westinghouse 24-rod mock-up

• ASCOMP (TransAT, 1.400.00 cells)

The Westinghouse 24-rod mock-up

• KTH Stockholm (CFX) • ASCOMP (TransAT)

-30 -20 -10 0 10 20 3015000

20000

25000

30000

35000

40000

45000 0º E xp.-135º E xp.Trans at s harp IS T dy40mm m1Trans at s harp IS T dy200mm m2Trans at s tandard IS T dy40mm m1

Dis tance from the middle of s pacer, [mm]

Pre

ssur

e, [k

Pa]

The Westinghouse 24-rod mock-up

The OECD PSBT 5x5 Benchmark with 3 spacers (3 million cells, K-e model)

The OECD PSBT 5x5 Benchmark

The OECD PSBT 5x5 Benchmark

The OECD PSBT 5x5 Benchmark

Flow field and heat contours downstream the 1st simple spacer

The OECD PSBT 5x5 Benchmark

Flow field and heat contours downstream the 1st mixing vane

The OECD PSBT 5x5 Benchmark

The OECD PSBT 5x5 Benchmark

NUPEC PWR Test Facility

Problem Description (PSBT OECD)

Heat flux q”

Flow outletFuel Rod

L=1000 mm

flow cross section

r=5 mm

P=13.0 mm

Fig. 1. Computational domain: Dimensions & BC’s.

Benchmark definition within CASL: Lakehal & Buongiorno, 2011: main changes: length reduced to 1m from 3m, power to 1.6kW from 7 MW, and thus Re=GDe/ 4.8105 to 1.0104

Pressure 15.5 MPaSaturation

temperature344.6C

Inlet temperature 290CMass flux 3333 kg/m2sHeat Flux 581 kW/m2

Power 7. MW

Pressure 15.5 MPaSaturation

temperature344.6C

Inlet temperature 290CMass flux 74.1 kg/m2s (or Re=300)Heat Flux 50 kW/m2

Power 1.57 kWTable 2: Downscaled operating flow Cdts. for LES

Table 1: Reference operating Cdts. for PSBT OECD cases (Rubin et al., 2010).

Problem Description (PSBT OECD)

Ret=300

Number of nodes ResolutionGrid type

total number of cellsx-y z Dx+

--Dy+ N blocks

Grid Med

40-40

798 0.5-2.1 208 BFC1,317,40

0Grid Fine

60-60

1.600 0.4-1.5 832 BFC6,011,20

0

q=00

q=450

Figure 3. Medium (left) and fine (right) grids for LES (x-y). Arrows show 00 and 450 segments

Flow along a heated single rod at Re*=300

• SGS model: LES (Dynamic SGS model) • Schemes: Central 2nd order; RK 3rd order in time• Adaptive time-stepping ~ Dt = 0.0001s (CFL = 0.1-

0.3)• Days on the DOE Jaguar on 144 and 832 MPI // cores

Figure 4. Fine vs. medium resolutions (non-scaled domain): Instantaneous cross-sectional velocities and temperature contours.

Results

• Fine grid: instantaneous Fine grid: time average

• Medium grid: instantaneous Medium grid: time average

Results

• Fine grid: instantaneous Fine grid: time average

• Medium grid: instantaneous Medium grid: time average

Results

Medium grid Fine grid

Figure 7a. Mean velocity profiles across the subchannel (00 & 450) compared to the DNS of Eggels (1994).

Results (comparison with DNS of pipe flow)

Medium grid: 0 and 450 Fine grid: 0 & 450

Figure 7b. Time averaged normal-stresses profiles (<w’w’>)

Quantity Medium grid Fine grid Analytical/Exp.

Pressure drop DP [Pa]

10.223 10.52 ~ 10.0

Heat transfer coefficient (HTC) at XONB

[kW/m2K]

   

1.495

   1.535

1.62 (Colburn) 2.16 (Col-W*)

1.44 (Gnielinski) 1.99 (Gnlsk-W) 1.50 (Petukov)

2.00 (Ptkov-W)

Distance to XONB [m] Min-max0.49–0.57

Min-max0.49–0.6

~ 0.59 (Colburn)~ 0.79 (Col-W)

Thermal entry length [m]

Min-max0.21–0.28

Min-max0.21–0.29

 ~ 0.29–0.46

*W means with the Weisman (1959) correction factor

Global Results

=1.826p/D-1.043=1.33

Convective boiling phenomenon: The physical reality of turbulent confined bubbly flow is way more complex than the idealized conditions considered in two-phase flow studies (smooth or sinusoidal wavy films, spherical or elliptic droplets and bubbles, etc.). Turbulence-bubbles interactions is mysterious!

Bubble layer in high-subcooling, high-mass-flux, high-pressure, flow boiling of Freon near the point of DNB. The situation is qualitatively similar to the PWR hot channel during a transient overpower event.

Iso-contours of transport quantities, including liquid and vapour temperature. 2D Axisymmetric simulations TransAT.

Bubbly-flow boiling: Debora test case (CEA)

Test Case: DEBORA Experiments of Manon et al (2000, 2001)

Pipe Length: 5mPipe Diameter: 19.2 mm

Bubbly-flow boiling: Debora test case (CEA)

Void Fraction for Case 2 & 3: Tin = 58.4 C and 63.4 C

Void Fraction for Case 4 & 5: Tin = 67.9 C and 70.14 C

Void Fraction for Case 6 & 7: Tin = 72.6 C and 73.7 C

Bubbly-flow boiling: Debora test case (CEA)

There are differences between the 2-fluid & the N-phase homogeneous models. Same grid, same turbulence model, same comp. parameters.

All models fail near the wall for Tin=73.7 C

Test Case: Experiments of Lee, Park & Lee (2002) and Tu & Yeoh (2003)

Bubbly-flow boiling: Lee et al. & Tu & Yeoh (KAERI)

Heat flux mass flux Tinlet Tsat

MW/ m2 kg/m2/s K K

0.1523 474 371.5 383

a

Norm. Radial distance

• Pipe Length: 2.376m• q=152.3 kW/m2

• Gl=474 kg/(m2s)• P=0.14 Mpa• ΔTsub=11.5 K.

Bubbly-flow boiling: Bartolomei Test Case

Test Case: Experiments of Bartolomei et al (1982)

• Pipe Length: 1.4m• Heated Length = 1m• q =1.2 MW/m2

• Gl= 1500 kg/(m2s)• P = 6.89 Mpa• ΔTsub= 63 K.

Heat transfer in tube buddle in a steam generator 3D Setup (SNERDI)

Geometry of the flow field

Location and size of tube and supports

Hot water

Cold water

Cold water

Cross-Sectional view of support * * Coarse grid is shown to illustrate

the cross-section

Conjugate heat transfer through the tube to heat the cold water where phase change occurs.

Cold water• P2=5.8MPa• Tf=259 ℃• va=0.63 m/s• Tsat = 271 ℃

Hot Water • P1=15.5MPa • Ti= 322℃• vi=5.3m/s

Heat transfer in tube buddle in a steam generator 3D Results (SNERDI)

Testcase

Pressure

[MPa]

Inlet Tem

p[°C]

Power

[kW]

Mass Flux

[kg m-2s-1]

1.2211 15295.

490 11

1.2223 15319.

670 11

1.2237 15329.

660 11

1.4411 10238.

960 5

1.4325 10253.

860 2

1.4326 10268.

860 5Cell

Size (in mm)

No. of Cells

No. of

Processors

Wall Clock Time

(in days)

5.31 9216 1 0.332.655

73728 8 0.75

1.328

1280000

108 1.5

0.885

2880000

128 4

NUPEC PWR Test Facility: Phase average

a) ∆x = 2.65mm b) ∆x = 1.328mm ) ∆x = 0.885mm

Steady State void fraction profiles for different grids (Testcase: 1.2237).

NUPEC PWR Test Facility: Phase average