Micro-Scale CFD Modeling of Packed-Beds Daniel P. Combest and Dr. P.A. Ramachandran and Dr. M.P. Dudukovic Chemical Reaction Engineering Laboratory (CREL) Department of Energy, Environmental, and Chemical Engineering. Washington University, St. Louis, MO. Heat and Mass Transfer Session. 6 th OpenFOAM Workshop Penn State University. June 14 th 2011 1
Motivation For Research The geometry influences phenomena within a packed bed across multiple length scales. Macro/Reactor-Scale Meso-Scale Micro-Scale Particle-Scale Pore-Scale Decreasing Length Scales In Packed-Bed Reactors 2
Objectives Objective Improve the understanding of micro-scale processes in packed bed reactors Topics Geometry and mesh generation Steady-state results Passive scalar transport Conjugate solver 3
Geometry and Mesh Generation Domain Generation 1000 cylinders 4
Geometry and Mesh Generation Domain Generation Removed a quarter section 20.5 cm bed radius 20.5 cm section height 3 cm particle diameter 3 cm particle length 1000 cylinders 5
Geometry and Mesh Generation Face and Volume Meshing Create face meshes on each particle surface Create volume mesh from the particle faces. 6
Geometry and Mesh Generation Face and Volume Meshing Issue with transition region meshes 7
Geometry and Mesh Generation Pure Tet Mesh 9,695,976 Cells 19,759,649 Faces Mesh Conversion Diverging turbulence model Issues with convergence Long simulation time 8
Geometry and Mesh Generation Pure Tet Mesh 9,695,976 Cells 19,759,649 Faces Mesh Conversion Hex-Poly Mesh 2,074,208 Cells 13,324,232 Faces 9
potentialfoam 2 U p 0 0 Steady-State Results Solution Strategy simplefoam (with S-A model) ( U U ) 1 st order discretization p eff 2 2nd order discretization U t Model k- RSM Models or Post-Processing Velocity-pressure field (E 1, E 2, k m, h) Transient passive scalar (Dispersion Coefficient) Steady state with boundary flux ( -R A ) Conjugate mass transfer (and variants) 10
Steady-State Results (1,-1,0) plane Velocity Field y + = 2.7 Max(y + ) = 6 Min (y + ) = 0.002 11
Steady-State Results (1,-1,0) plane Velocity Field Key Points Many boundary layers Stagnant zones behind particles issues with inlet/outlet? y + = 2.7 Max(y + ) = 6 Min (y + ) = 0.002 12
Steady-State Results Turbulent Viscosity nu t (1,-1,0) plane 13
Steady-State Results Turbulent Viscosity nu t (1,-1,0) plane Key Points Inlet nutilda overestimate must be compared to other models turbintensity = 0.05 mixing length 0.03 m 14
Steady-State Results Turbulent Viscosity nu t (1,-1,0) plane 15
Steady-State Results Turbulent Viscosity nu t (1,-1,0) plane Key Points D t will be near scale of D 16
Passive Scalar Modeling Model Equation C t Model and Code ( U C ) D C u' c' 17
Passive Scalar Modeling Model Equation C t Model and Code ( U C ) D C u' c' Coded Equation solve ( fvm::ddt(c) + fvm::div(phi, C) + fvm::susp(-fvc::div(phi), C) - fvm::laplacian(d, C) - fvm::laplacian(dturbulent, C) ); 18
Passive Scalar Modeling Model Equation C t Model and Code ( U C ) D C u' c' Coded Equation solve ( fvm::ddt(c) + fvm::div(phi, C) + fvm::susp(-fvc::div(phi), C) - fvm::laplacian(d, C) - fvm::laplacian(dturbulent, C) ); Key Points Monitor outlet concentration Use bounded schemes 19
F [unitless] Passive Scalar Modeling F-Curve F-Curve for Re p =1000 1 0.9 0.8 0.7 F C 0.6 C max 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 Time [sec] Uses patchmassflowaverage from simplefunctionobjects library 20
F [unitless] Passive Scalar Modeling F-Curve F-Curve for Re p =1000 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 F C C max Key Points Agrees with proper behavior Within bounds Used in lower order CRE models 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 Time [sec] Uses patchmassflowaverage from simplefunctionobjects library 21
Passive Scalar Modeling Time Dependent C 22
Passive Scalar Modeling Time Dependent C Boundary layer effects Recirculation regions 23
Passive Scalar Modeling Time Dependent C 24
Passive Scalar Modeling Time Dependent C High Dt 25
Conjugate Mass Solver Model Equations ( U D s C ) D C s R Boundary condition at the interface D C D s C s s C Model and Observations u' c' 26
Conjugate Mass Solver Model Equations ( U D s C ) D C s R Boundary condition at the interface D C D s C s s C Model and Observations u' c' Keys to Steady State Solver Use conjugateheatfoam Resolve turbulent affects with gradient diffusion hypothesis Drop time-derrivative Store previous iterations individually (C and Cs) Relax fields individually (C and Cs) 27
Current State Conjugate Mass Solver Sticking Points Simple solutions on square domains work fine and are fast Issues with matching solid faces with fluid patches (user error?) Need a tool/process to automatically couple patches between multiple regions 28
Closure simplefoam #TODO: Lower turbulent intensity on inlet #TODO: Different turbulence models Tracer experiments #TIP: Bounded schemes and fvm::susp(-fvc::div(phi), C) #TIP: Monitor outlet C for negative concentrations Conjugate Problems #IMPROVEMENT?: Map patches between regions automatically #TODO: Fix and post pyfoam-bash scripts to decompose parallel cases 29
Acknowledgements Funding Chemical Reaction Engineering Laboratory (CREL) MRE Fund (http://crelonweb.eec.wustl.edu/) OpenFOAM Developers Community Advisors Dr. Ramachandran Dr. Dudukovic 30
Thanks for your attention! Questions? Dan Combest dcombest@seas.wustl.edu 31
Steady-State Velocity Field 32
simplefoam Settings Boundary Conditions Probe points Patch averages Residuals 33
Passive Scalar Settings Boundary Conditions Probe points Patch averages Residuals 34
Porosity [-] Geometry and Mesh Generation 1.1 Step 0 Step 5 Step 21 Step 50 Step 100 Step 200 Step 245 1 0.9 Increasing Packing Cycles 0.8 0.7 0.6 0.5 0 1 2 3 4 5 6 Distance From Wall in Particle Diameters [-] 35
Geometry and Mesh Generation 1000 cylinders L b /D p = 16.18 = 0.63 L p /D p = 1, D b /D p = 13.4 41 cm bed diameter 500 trilobes L b /D p = 19.4 = 0.68 36
Steady-State Results Velocity Field (0,0,1) plane Key Points Highly variable Evidence of interacting BLs Transition regime? Far from structured packing 37