Detailed numerical investigations of two-phase flow and transport. narrow channels. Dr.-Ing. Martin Wörner. Institut für Kern- und Energietechnik

Transcription

1 Detailed numerical investigations of two-phase flow and transport INSTITUT phenomena FÜR KERN- UND ENERGIETECHNIK in narrow channels Dr.-Ing. Martin Wörner Opening Workshop Helmholtz Research School Energy-Related Catalysis Karlsruhe Institute of Technology November 17, 2010 Movie KIT Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der Helmholtz-Gemeinschaft

2 Outline Introduction Multiphase micro reactors Interaction between flow, transport and reaction Numerical simulation method Results Hydrodynamics Mass transfer Chemical reaction Conclusions and outlook 2

3 Multiphase micro reactors Hessel et al. (IMM Mainz) Moulijn, Kreutzer et al. (TU Delft) Ismagilov et al. (Univ. Chicago) Dr. Martin Wörner

4 Advantages of Taylor flow Good mixing of species within the bubble Large interfacial area per unit volume and thin liquid film between bubble and wall efficient heat and mass transfer Axial segmentation of liquid reduced axial dispersion Recirculation in liquid slug good mixing in liquid slug and wall-normal convective transport in laminar flow Channel cross section: 400 µm 280 µm Movie of Günther et al. Langmuir 21 (2005)

5 Outline Introduction Multiphase micro reactors Interaction between flow, transport and reaction Numerical simulation method Results Hydrodynamics Mass transfer Chemical reaction Conclusions and outlook 5

6 Hydrodynamics Q & G Q & L A ch y U B A ( y) L J = ( Q& + Q& )/ A J total total G L ch ρ, µ L σ L ρ, µ G G U ( y) L,film Bubble velocity U B is a priori unknown It depends on viscous, capillary, inertial and gravitational forces and is determined by the momentum equations of the two phases The thickness and velocity of the liquid film as well as the volumetric gas content ε G are closely related to U B AL ( y) A ch = U UB J U B tot L,film ( y) V Q& G G ε G = VG + VL U B Ach Dr. Martin Wörner

7 Hydrodynamics (cont.) Sketch of streamlines in moving frame of reference U L,max = C Jt ota l ( C = 2; C = 2.096) Condition for bypass flow is U C J B ttal o Condition for recirculation flow is U < C J B ttal o Dr. Martin Wörner

8 Mass transfer and reaction Educt Product Complex non-linear coupling between flow, transport and reaction. Goal: Understand and quantify phenomena by detailed numerical simulation. r 0 B total R = 2 U 2 / R J G-L r 0 r 1 G-S Heat chemical reaction S-L Heat L-S washcoat r 1 R = Ca 2 µ U L σ U J B B total 8

9 Outline Introduction Multiphase micro reactors Interaction between flow, transport and reaction Numerical simulation method Results Hydrodynamics Mass transfer Chemical reaction Conclusions and outlook 9

10 Simulation method* In-house computer code *Öztaskin et al. Phys. Fluids 21 (2009) Navier-Stokes equation in single field formulation with surface tension term for two incompressible immiscible Newtonian fluids with constant physical properties Volume-of-fluid method with piecewise linear interface reconstruction 10

11 Simulation method* (cont.) Solution of single-field concentration equation for an arbitrary number of chemical species No feedback of species on hydrodynamics (yet) *Onea et al. Chem. Eng. Sci. 64 (2009)

12 Outline Introduction Multiphase micro reactors Interaction between flow, transport and reaction Numerical simulation method Results Hydrodynamics Mass transfer Chemical reaction Conclusions and outlook 12

13 Computed bubble shapes 1mm 1mm L ε uc G Re Ca = 6mm = 0.4 σρ D = µ L 2 L h La = Ca Re µ LU σ B ρ D U µ L h B L Ca = Re =

14 Experimental validation* * Experiments by T. Bauer and R. Lange Keskin et al. AIChE J. 56 (2010)

15 Transition to annular flow time 15 L uc = 4 mm, ε G = 0.4

16 Outline Introduction Multiphase micro reactors Interaction between flow, transport and reaction Numerical simulation method Results Hydrodynamics Mass transfer Chemical reaction Conclusions and outlook 16

17 Gas-liquid mass transfer Transient simulations ( qualitative ) Sc L =0.8, H=0.03 Onea et al. Chem. Eng. Sci. 64 (2009) c% c ref c% c ref 17

18 Mass transfer and chemical reaction Without chemical reaction Fast heterog. reaction (1 st o.) c% c ref c% c ref short bubbles are more efficient long bubbles are more efficient 18

19 Disparity of length scales Scale of the smallest structures in the bulk phase 3 Velocity field: Kolmogorov micro-scale λu = ν / ε 2 Concentration field: Batchelor scale λc = νd / ε λc 1 v Sc λ (Schmidt number) Sc D u Boundary layer thickness at the moving interface Velocity field: Concentration field: δ δ c u 1 Sc δu L/ Re δ L / Pe = L / ScRe c ( ) 1/4 ( ) 1/4 19

20 Disparity of length scales (cont.) Typical values of the Schmidt number Gases Sc = O(1) Liquids Sc = O(1000) λ λ The smallest length scales in the concentration field are about a factor of 30 smaller than those in the velocity field c u c = The grid required for resolving all scales in the concentration field is 30 times finer than required for the velocity field (in 3D this corresponds to a factor of 30 3 = ) This makes numerical methods that use the same grid for the velocity and concentration field very inefficient use of hierarchical grids, i.e. a finer grid for the concentration field than for the velocity field (ongoing PhD) δ δ u Dr. Martin Wörner

21 Conclusions High potential of Taylor flow for intensification of heterogeneously catalyzed gas-liquid processes in micro reactors Complicate interaction between two-phase flow, transport (heat and mass) and reaction Understanding and quantification of this non-linear interaction (which involves various length and time scales) is a key issue toward the design and optimization of multi-phase micro reactors Detailed numerical investigations provide a promising tool Current status of numerical methods Hydrodynamics of two-phase flow including bubble and drop formation Coalescence phenomena Mass transfer (realistic Schmidt numbers) Interfacial transport of soluble and insoluble surfactants Coupling of two-phase flow and transport with detailed chemical kinetics 21

22 Outlook DETCHEM Detailed chemical kinetics Gas phase processes (e.g. catalytic converter) Coupling FLUENT Hydrodynamics 22

23 Outlook DETCHEM Detailed chemical kinetics at channel walls Kinetics for FTS Coupling Two-phase processes in monolith reactors (e.g. Fischer-Tropsch synthesis) TURBIT-VOF Detailed simulation of two-phase flow and transport within channel 23

24 Thanks PhD students Winfried Sabisch (2000) Bradut Ghidersa (2004) Milica Ilić (2005) Alexandru Onea (2007) Carlos Falconi Erasmus students from Sakarya University (Turkey) Furkan Özkan Özge Keskin Murat Öztaskin Semih Kececi Sercan Erdogan 24