Multiphase Flow Heat Transfer in Fuel Assemblies January 2014 ASCOMP; ASCOMP Inc. USA, www.ascomp.ch transat@ascomp.ch

The Westinghouse 24-rod mock-up 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)

The OECD PSBT 5x5 Benchmark 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

NUPEC PWR Test Facility

Problem Description (PSBT OECD) P=13.0 mm Flow outlet Fuel Rod r=5 mm L=1000 mm flow cross section Heat flux q” 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/  4.8105 to  1.0104

Saturation temperature Saturation temperature Problem Description (PSBT OECD) Pressure 15.5 MPa Saturation temperature 344.6C Inlet temperature 290C Mass flux 3333 kg/m2s Heat Flux 581 kW/m2 Power MW Table 1: Reference operating Cdts. for PSBT OECD cases (Rubin et al., 2010). Pressure 15.5 MPa Saturation temperature 344.6C Inlet temperature 290C Mass flux 74.1 kg/m2s (or Re=300) Heat Flux 50 kW/m2 Power 1.57 kW Table 2: Downscaled operating flow Cdts. for LES

Flow along a heated single rod at Re*=300 Ret=300 Number of nodes Resolution Grid type total number of cells x-y z Dx+--Dy+ N blocks Grid Med 40-40 798 0.5-2.1 208 BFC 1,317,400 Grid Fine 60-60 1.600 0.4-1.5 832 6,011,200 Figure 3. Medium (left) and fine (right) grids for LES (x-y). Arrows show 00 and 450 segments q=450 q=00 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

Results 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 (comparison with DNS of pipe flow) Medium grid Fine grid Figure 7a. Mean velocity profiles across the subchannel (00 & 450) compared to the DNS of Eggels (1994). Medium grid: 0 and 450 Fine grid: 0 & 450 Figure 7b. Time averaged normal-stresses profiles (<w’w’>)

Global Results =1.826p/D-1.043=1.33 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-max 0.49–0.57 0.49–0.6 ~ 0.59 (Colburn) ~ 0.79 (Col-W) Thermal entry length [m] 0.21–0.28 0.21–0.29 ~ 0.29–0.46 =1.826p/D-1.043=1.33 *W means with the Weisman (1959) correction factor

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.

Bubbly-flow boiling: Debora test case (CEA) 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: 5m Pipe Diameter: 19.2 mm

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 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: Lee et al. & Tu & Yeoh (KAERI) Test Case: Experiments of Lee, Park & Lee (2002) and Tu & Yeoh (2003) Pipe Length: 2.376m q=152.3 kW/m2 Gl=474 kg/(m2s) P=0.14 Mpa ΔTsub=11.5 K. a Norm. Radial distance Heat flux mass flux Tinlet Tsat MW/ m2 kg/m2/s K 0.1523 474 371.5 383

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) Cold water P2=5.8MPa Tf=259 ℃ va=0.63 m/s Tsat = 271 ℃ Location and size of tube and supports Geometry of the flow field Cold water Hot Water P1=15.5MPa Ti= 322℃ vi=5.3m/s Hot water Cold water Conjugate heat transfer through the tube to heat the cold water where phase change occurs. Cross-Sectional view of support * * Coarse grid is shown to illustrate the cross-section

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

NUPEC PWR Test Facility: Phase average Testcase Pressure [MPa] Inlet Temp [°C] Power [kW] Mass Flux [kg m-2s-1] 1.2211 15 295.4 90 11 1.2223 319.6 70 1.2237 329.6 60 1.4411 10 238.9 5 1.4325 253.8 2 1.4326 268.8 Cell Size (in mm) No. of Cells No. of Processors Wall Clock Time (in days) 5.31 9216 1 0.33 2.655 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).