pressure drop and multi-scale flow structure measurements
TRANSCRIPT
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Pressure Drop and Multi-scale Flow Structure Measurements in a Pebble Bed
Reactor
Yassin A. Hassan
Elvis Domingue Ontiveros
Multiphase Flow Research Laboratory
Department of Nuclear Engineering
Texas A&M University
NRC/OSU Review Meeting
College Station
February 24, 2009
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Introduction
In the Advanced Gas Cooled Pebble Bed Reactors for nuclear power
generation, the fuel is presented in the form of spherical coated
particles.
The energy transfer phenomenon requires detailed understanding of
the flow and temperature fields around the spherical fuel pebbles.
Many of the macroscopic processes that affect material transport in
porous media are manifestations of the flow behavior of the system at
the microscopic scale ( at the scale of an individual pore volume)
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Dispersion, for example, is the result of the cumulative effects of a number
of micro-scale phenomena, including the mixing caused by solid obstructions
in the flow path, the incomplete connectivity of the medium, eddies in the
medium, and recirculation caused by regional pressure gradients.
Predictive macroscopic transport theory uses volume averages of micro-
scale flow.
Multipoint measurements with spatial resolution are necessary to permit
visualization of complex flow patterns and to provide data at high enough
spatial density to allow volume averaging
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Pebble bed Scales
System scale
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Particle Image Velocimetry (PIV)
Optical method ( Non-intrusive )
Velocity fields
Spatial resolution
Time resolution ( DPIV)
Capability of studying two-phase flows
Frame 1
Frame 2
Frame 1 Frame 2
T
Velocity field
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Air Water P-cymene
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Streamwise velocity component Re=50
Pore 1 Pore 2 Pore 3
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Streamwise velocity component Re=85
Pore 1 Pore 2 Pore 3
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Streamwise velocity component Re=221
Pore 1 Pore 2 Pore 3
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Streamwise velocity component Re=500
Pore 1 Pore 2 Pore 3
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New Packed Bed& Proposed Studies
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Scaling
Scale1:5 Length 1:4 DiameterD/d=10Annular configurationSimilar porosity
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Scaling
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Sphere packing type in packed bed
dp
dp
dp
In-line lattice packing
Cubic close packing
Wall region
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Wall influence
Annular core D/d=10 Cylindrical core D/d=28
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Multi-scale measurements
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Ergun
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Carman
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Etc. (From Re. Hayes paper)
Re. Hayes :
Where,
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Ex) Comparing correlations by using graph
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Ex) Comparing correlations by using graph
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Ex) Comparing correlations by using graph
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Lower plenum studies
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Heat transfer studies
An Induction furnace is an electrical furnace in which the heat is generated through electro-magnetic induction in an electrically conductive medium (usually a metal).
Convection and conduction studies
Induction furnace1.5-150 kHz
Metal beadPlastic beads
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*CFD Simulation of a Coolant Flow and a Heat Transfer in a Pebble Bed Reactor
Yassin A. Hassan*
Wang-Kee In
* This work was performed before-Presented here for information only
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Objective
• Examine a coolant (helium gas) flow structure in the Pebble Bed Reactor(PBR) core
• Estimate the temperature variation of a fuel pebble in the PBR core
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CFD-PBR (Track 7) 27
CFD Model 1 (Fluid+Solid)
Unstaggered 3x3 Pebble Array(Ball dia.=60mm, Porosity=0.46)
Pebble Size Number
Full 1
Half 6
Quarter 12
Octant 8
Total 8
UHe,in = 15 m/s
THe,in = 1000 K Qfuel,gen = 9.0 MW/m3
P=Const.
Cyclic Side B.C
11
9
- TRISO(~1mm Dia.)
- Fuel(UO2) core
- Graphite coating
- 450,000 fuel pebbles
in PBMR400 core
(core porosity 0.39)
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CFD-PBR (Track 7) 28
CFD Model 2 (Fluid Only)
Pebble Size Number
Full 14
Half 24
Quarter 24
Total 3220
1.6
201.6
128Cyclic B.C
Symmetric
Side B.C
Staggered Pebble Array(Ball dia.=60mm, Porosity=0.3)
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CFD-PBR (Track 7) 29
Computational Method
• Turbulence Model– Standard k-e(Epsilon) model
– SST k-w(Omega) model
• Convection Scheme: Second-order Upwind
• Reynolds Number (Dpebble, Vbulk,coolant)– 65000 for CFD model 1
– 46000, 290 for CFD model 2
• CFD Codes: STAR-CD(4.0), STAR-CCM+(V2.08)
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CFD-PBR (Track 7) 30
Velocity Vector around Pebble
Side View
Bottom View
Multiple vortices
Re=46000, Standard k-e
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CFD-PBR (Track 7) 31
Center Pebble Temperature
• Large temperature variation on pebble surface as well as
in pebble core(UO2 layer)
• Temperature variations are estimated as 180K in pebble core
and 15K on pebble surface
Pebble center
High temperature
behind pebble contact
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Pebble Array Temperature
• Higher surface temperature of the downstream pebbles than the upstream ones
• Significantly high temperature near the pebble contact region
Flowdirection
Pebble contact
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Central Pebble Surface Temp.
0 30 60 90 120 150 180730
740
750
760
770
Streamwise
Circumferential
Te
mp
era
ture
[oC
]Angle, [deg]
Side view Top view
Bottom view Hemispherical view
• Low temperature in the large flow region and high temp. in the narrow flow region
• Maximum variation of a pebble’s surface temperature is 25 oC
• The peak-to-peak variations are approx. 20 oC and 10 oC in the streamwise and
circumferential directions with a peak value near the bottom of a pebble, i.e., =160
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Summary
• Multiple vortices were predicted to occur at the bottom as well as at the side downstream of a pebble due to a flow separation.
• Temperature variation at a central pebble is approximately 340 oC and 25 oC in the pebble core and the pebble surface, respectively.
• The coolant flow structure in a PBR core appears to largely depend on the in-core distribution of the pebbles. In the future, a CFD model should be developed to more adequately represent the pebbles randomly stacked in the PBR core.
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Angelo FrisaniAkshay GandhirYassin Hassan
2/18/2009
Pebble Bed ReactorComputational Approach
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• Simple Cubic
– Symmetric
• Face Centered Cubic (FCC)
– Staggered
• Body Centered Cubic (BCC)
– Staggered
• Void Space
– Missing Sphere
Scenarios
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• Schematic
• Velocity Inlet– 1 m/s (Re =1890)
– 20 m/s (Re =37,800)
– 36 m/s (Re =68,040)
• Model– K-epsilon (current)
– K-omega
– Reynolds Stress Turbulence
– Spalart-Allmaras
Simple Cubic
Velocity Inlet
Symmetry Wall
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• Sphere Diameter=60mm
• Porosity=0.55
CFD Model – Fluid Region
Pebble Size Number Complete
Spheres
Octant 8 1
Quarter 36 9
Half 54 27
Full 27 27
Total 125 64
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Mesh
Name Number of Prism
Layers
Cell Number
No.1 2 563,283
No.2 2 737,735
No.3 2 1,068,483
No.4 2 2,583,764
No.5 5 4,536,619
No.6 2 10,272,720
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Prism Layers
5 Prism Layers
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Contact
with
other
sphere
Uin=1m/s
Pressure Distribution
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Bottom View
Contact with
other sphere
Velocity Around the Sphere
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Multiple Vortices Around
Sphere
Bottom View
Vortices
in the
contact
region
Vorticity
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Multiple
vortices in the
contact region
Uin=1m/s
Streamline around the cener block
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Future Computational Work
Simulation of other geometries
Body Centered Cubic
Face Centered Cubic
Void Space (Missing Sphere)
Data Analysis
Compare results with existing correlations.