Preface ........................................................ XV
About the Editors ............................................ XVII
List of Contributors .......................................... XIX
Part I Fluid Dynamics in Microchannels ......................... 1
1 Multiphase Flow .............................................. 3
Axel Günther and Michiel T. Kreutzer
1.1 Introduction ............................................... 3
1.2 Fundamentals of Multiphase Flow ............................ 4
1.2.1 Properties of Fluids and Interfaces ................. 5
1.2.1.1 MicroChannel Surface Characteristics and
Wetting .................................... 6
1.2.1.2 Scaling of Forces .......................... 7
1.2.1.3 Surface Tension Variations ................. 8
1.2.1.4 Particles and Fluid Interfaces ............. 8
1.2.2 Classification of Phase Distributions ............... 9
1.3 Dynamic Behavior of Multiphase Microflows .................. 9
1.3.1 Flow Instabilities ................................. 10
1.3.1.1 Capillary Instability ..................... 10
1.3.1.2 Deformation of Stratified Liquid Layers ... 12
1.3.2 Multiphase Flow Regimes ............................ 12
1.3.3 Formation of Multiphase Flow ....................... 15
1.3.4 Susceptibility of Multiphase Flow to Pressure
Fluctuations
1.3.5 Separation of Phases ............................... 16
1.4 Role of Channel Geometries ................................ 17
1.5 Experimental and Numerical Techniques ..................... 20
1.5.1 Numerical .......................................... 20
1.5.2 Experimental ....................................... 20
1.5.2.1 Brightfield Microscopy .................... 21
1.5.2.2 Fluorescence Microscopy ................... 21
1.5.2.3 Particle Tracking and Particle Image
Velocimetry ............................... 23
1.5.2.4 Confocal Microscopy ....................... 24
1.5.2.5 Flow Sensors .............................. 24
1.5.2.6 Magnetic Resonance Imaging ................ 24
1.5.2.7 X-ray Tomography .......................... 25
1.6 Annular and Stratified Two-phase Flows .................... 25
1.7 Droplet and Bubble Flows .................................. 26
1.7.1 Lubrication Analysis ............................... 26
1.7.2 Pressure Drop in Segmented-flow Microfluidic
Networks ........................................... 28
1.8 Practical Aspects of Microfluidic Networks ................ 28
1.8.1 Parallel Scaling ................................... 28
1.8.2 Using Multiphase Flows for Controlling Fluid
Paths .............................................. 30
References ..................................................... 32
2 Microfluidic Networks ....................................... 41
Norbert Kockmann
2.1 Introduction .............................................. 41
2.2 Fluid Mechanics ........................................... 41
2.3 Basic Channel Structures .................................. 44
2.4 Network Design ............................................ 46
2.5 Lumped Element Modeling ................................... 48
2.6 Parallel Channel Devices .................................. 52
2.7 Headers and Manifold for Plate Stacks ..................... 54
2.8 Conclusion ................................................ 56
References ..................................................... 58
3 Boiling and Two-phase Flow in Microchannels ................. 61
John R. Thome and Cherhardt Ribatski
3.1 Introduction .............................................. 61
3.2 Macro-to-Microscale Transition ............................ 62
3.3 Flow Patterns in Microscale Channels ...................... 63
3.4 Pressure Drop ............................................. 66
3.5 Boiling Heat Transfer ..................................... 67
3.6 Critical Heat Flux ........................................ 70
3.7 Two-phase Flow Instabilities .............................. 72
3.8 Prediction Methods ........................................ 76
3.8.1 Frictional Pressure Drop ........................... 76
3.8.2 Heat Transfer ...................................... 78
3.8.3 Critical Heat Flux ................................. 82
References ..................................................... 87
4 Microscale Flow Visualization ............................... 93
Marko Hoffmann, Michael Schlüter, and Norbert Räbiger
4.1 Introduction .............................................. 93
4.2 Fundamentals .............................................. 94
4.3 Visualization of Flow Fields in Micro-and Minichannels .... 95
4.3.1 Microparticle Image Velocimetry (μ-PiV) ............ 95
4.3.1.1 Correlation Averaging Method .............. 96
4.3.1.2 3D Reconstruction ......................... 98
4.3.1.3 Accuracy of μ-PIV Measurements ............ 99
4.3.1.4 Depth of Correlation ..................... 100
4.3.1.5 Brownian Motion .......................... 101
4.3.2 Extension of Common μ-PIV for Enhancement of
Spatial and Temporal Resolution ................... 102
4.3.2.1 Multiphase Flow .......................... 102
4.3.3 Confocal Microparticle Image Velocimetry .......... 103
4.3.4 Stereoscopic Microparticle Image Velocimetry ...... 104
4.3.5 3D Particle Tracking Velocimetry .................. 105
4.4 Visualization of Concentration and Temperature Fields
in Micro- and Minichannels ............................... 106
4.4.1 Analysis of Concentration Fields .................. 107
4.4.2 Analysis of Temperature Fields .................... 109
4.4.3 Visualization of Mixing Processes Without
Chemical Reactions ................................ 110
4.4.4 Visualization of Reactive Mixing .................. 110
4.5 Conclusion .......................................... 113
References ............................................... 113
5 Modeling of Microfluidic Devices ........................... 117
David F. Fletcher, Brian S. Haynes, Joëlle Aubin, and
Catherine Xuereb
5.1 Introduction ............................................. 117
5.2 Characteristics of Microsystems .......................... 117
5.2.1 Non-continuum Effects ............................. 118
5.2.2 Laminar Flow ...................................... 118
5.2.3 Surface Roughness ................................. 119
5.2.4 Viscous Energy Dissipation ........................ 120
5.2.5 Gravitational Effects ............................. 120
5.2.6 Electric Effects .................................. 121
5.2.7 Surface Tension Effects ........................... 122
5.2.8 WaU Slip Effects .................................. 123
5.3 The Importance of Appropriate Solution Methods ........... 124
5.3.1 Conventional Navier-Stokes Solvers ................ 124
5.3.1.1 Numerical Diffusion ...................... 124
5.3.1.2 Interfacial Surface Location and
Parasitic Currents ....................... 125
5.3.1.3 Heat Transfer Simulations ................ 126
5.3.2 Advanced Solution Methods ......................... 126
5.4 Single-phase Simulations ................................. 127
5.4.1 Heat Transfer Enhancement ......................... 127
5.4.2 Mixing ............................................ 129
5.4.3 Modeling of Mass Transfer and Chemical Reaction ... 133
5.5 Multi-phase Simulations .................................. 134
5.5.1 Taylor Bubble Simulations ......................... 134
5.5.2 Droplet Simulations ............................... 136
5.6 Summary and Perspective .................................. 138
References .................................................... 139
Part II Mixing in Microsystems ............................... 145
6 Characterization of Mixing and Segregation in Homogeneous
Flow Systems ............................................... 147
Laurent Falk and Jean-Marc Commenge
6.1 Introduction ............................................. 147
6.2 Mixing Principles and Features of Microsystems ........... 148
6.2.1 Molecular Diffusion ............................... 149
6.2.2 Mixing in a Shear Field ........................... 150
6.2.3 Application to Mixing in Microchannels ............ 151
6.2.4 Chaotic Mixers .................................... 154
6.2.4.1 Additional Readings: Chaotic Mixing
Model in Microchannels ................... 156
6.2.5 Mixing Efficiency ................................. 158
6.3 Experimental Mixing Characterization ..................... 159
6.3.1 Physical Methods .................................. 159
6.3.2 Chemical Methods .................................. 161
6.3.3 Villermaux-Dushman Reaction ....................... 162
6.3.4 Mixing Time ....................................... 165
6.4 Comparison of Performances of Micromixers ................ 166
6.5 Conclusions .............................................. 170
References .................................................... 170
7 Passive and Active Micromixers ............................. 175
Zhigang Wu and Nam-Trung Nguyen
7.1 Introduction ............................................. 175
7.2 Passive Micromixers ...................................... 177
7.2.1 Parallel Lamination Micromixers ................... 177
7.2.2 Serial Lamination Micromixers ..................... 183
7.2.3 Micromixers Based on Chaotic Advection ............ 184
7.2.3.1 Chaotic Advection at High Reynolds
Numbers .................................. 184
7.2.3.2 Chaotic Advection at Intermediate
Reynolds Numbers ......................... 185
7.2.3.3 Chaotic Advection at Low Reynolds
Numbers .................................. 186
7.2.4 Droplet Micromixers ............................... 188
7.3 Active Micromixers ....................................... 190
7.3.1 Pressure-induced Disturbance ...................... 190
7.3.2 Electrohydrodynamic Disturbance ................... 191
7.3.3 Magnetohydrodynamic Disturbance ................... 292
7.3.4 Acoustic Disturbance .............................. 192
7.3.5 Thermal Disturbance ............................... 193
7.4 Fabrication Methods ...................................... 194
7.5 Conclusion ............................................... 295
References .................................................... 197
8 Mixing and Contacting of Heterogeneous Systems ............. 205
Asterios Gavriilidis and Panagiota Angeli
8.1 Gas-Liquid Systems ....................................... 207
8.1.1 Segmented Flow Contactors ......................... 208
8.1.1.1 Bubble Formation and Length .............. 209
8.1.1.2 Hydrodynamics ............................ 210
8.1.1.3 Bubble Shape and Film Thickness .......... 210
8.1.1.4 Pressure Drop ............................ 211
8.1.1.5 Mixing and Mass Transfer ................. 212
8.1.1.6 Phase Separation ......................... 213
8.1.1.7 Multichannel Systems ..................... 214
8.1.2 Packed MicroChannel Contactors .................... 214
8.1.3 Foam and Bubble Suspension Microcontactors ........ 216
8.1.3.1 T-type Mixing Section Geometries ......... 216
8.1.3.2 Flow Focusing Mixing Section Geometries .. 217
8.1.3.3 Multichannel Systems ..................... 220
8.1.3.4 Dispersion Effects ....................... 220
8.1.4 Overlapping MicroChannel and Micromesh
Contactors ........................................ 221
8.1.5 Falling Film MicroChannel Contactor ............... 223
8.2 Non-miscible Liquid-Liquid Systems ....................... 226
8.2.1 Segmented Flow Contactors ......................... 228
8.2.1.1 Slug/Plug Formation ...................... 228
8.2.1.2 Hydrodynamics and Mixing ................. 230
8.2.1.3 Pressure Drop ............................ 230
8.2.2 Liquid-Liquid Dispersion Microcontactors .......... 231
8.2.2.1 T-type and Co-flow Mixing Section
Geometries ............................... 231
8.2.2.2 Flow Focusing Geometries ................. 234
8.2.2.3 Multichannel Systems ..................... 235
8.2.3 Overlapping MicroChannel and Micromesh
Contactors ........................................ 240
References ............................................... 243
Part III Heat/Mass Transfer .................................. 253
9 Heat Transfer in Homogeneous Systems ....................... 255
Franz Trachsel and Philipp Rudolf von Rohr
9.1 Introduction ............................................. 255
9.2 Continuum Assumption ..................................... 256
9.2.1 Gases ............................................. 257
9.2.2 Liquids ........................................... 257
9.3 Heat Transfer in Homogeneous Microfluidic Systems ........ 259
9.4 Pronounced Effects in MicroChannel Heat Transfer ......... 261
9.4.1 Axial Heat Conduction in the Fluid ................ 261
9.4.2 Conjugate Heat Transfer ........................... 265
9.4.3 Surface Roughness ................................. 266
9.4.4 Viscous Dissipation ............................... 267
9.4.5 Variation of Thermophysical Properties ............ 268
9.4.6 Electric Double Layer ............................. 269
9.4.7 Entrance Region ................................... 269
9.4.8 Measurement Accuracy .............................. 270
9.5 Conventional Heat Transfer Correlations for Macroscale
Tubes and Channels ....................................... 270
9.5.1 Developing Hydrodynamic Regions of Laminar Flow ... 271
9.5.2 Developing Thermal Flow ........................... 271
9.5.3 Fully Developed Laminar Flow ...................... 271
9.5.3.1 Constant Wall Temperature ................ 271
9.5.3.2 Constant Heat Flux ....................... 272
9.5.4 Turbulent Flow .................................... 272
9.5.4.1 Transition Regime 2300 < Re < 104 ........ 274
9.6 Conclusion ............................................... 274
References .................................................... 279
10 Transport Phenomena in Microscale Reacting Flows ........... 283
Niket S. Kaisare, Ceorgios D. Stefanidis, and Dionisios
C. Vlachos
10.1 Introduction ............................................. 283
10.2 Spatial Gradients in Microchannels ....................... 284
10.2.1 Axial Thermal Gradients ........................... 285
10.2.2 Transverse External Thermal Gradients ............. 287
10.2.3 Transverse External Mass Transfer ................. 287
10.2.4 Internal Heat and Mass Transfer ................... 288
10.3 Thermal Radiation in Microchannels ....................... 289
10.4 Transverse Heat and Mass Transfer Correlations ........... 292
10.5 Homogeneous Microburners ................................. 293
10.5.1 Effect of Transverse Transport on Flame
Stability ......................................... 293
10.5.2 Transverse Heat Transfer and Nusselt Number ....... 295
10.6 Catalytic Microreactors .................................. 296
10.7 Conclusions .............................................. 300
References .................................................... 301
11 Fluid-Fluid and Fluid-Solid Mass Transfer .................. 303
Michiel T. Kreutzer and Axel Günther
11.1 Introduction ............................................. 303
11.1.1 Relevance ......................................... 303
11.1.2 Basics, Relevant Time Scales ...................... 304
11.2 Stable Fluid Interfaces: Annular Flows and Falling
Films .................................................... 307
11.3 Droplet/Bubble Segmented Flows ........................... 309
11.3.1 Fluid-Fluid Mass Transfer Without Reaction at the
Wall .............................................. 311
11.3.2 Continuous Phase to Wall Mass Transfer ............ 313
11.3.3 Disperse Phase to Wall Mass Transfer .............. 314
11.4 Complex Geometries - Packed Beds and Foams ............... 317
References .................................................... 319
Part IV Microstructured Devices for Purification and
Separation Processes .......................................... 323
12 Extraction ................................................. 325
Nobuaki Aoki and Kazuhiro Mae
12.1 Introduction ............................................. 325
12.2 Parallel Flow of Two Immiscible Phases ................... 325
12.2.1 Instances of Extraction Systems and Devices
Using Parallel Flow ............................... 326
12.2.2 Surface Modification of Channel Geometry for
Stabilizing Parallel Flow ......................... 329
12.2.3 Application in Organic Synthesis .................. 330
12.3 Droplet Manipulation ..................................... 331
12.3.1 Devices for Continuous Generation of Dispersed
Droplets .......................................... 332
12.3.2 Coalescence of Droplets in Dispersions ............ 333
12.3.3 Precise Operation of Individual Droplets .......... 334
12.4 Liquid-Liquid Slug Flow .................................. 336
12.4.1 Extraction Process Based on Slug Flow ............. 337
12.4.2 Quantitative Study of Mass Transfer in Slug
Flow .............................................. 339
12.4.3 Application of Mass Transfer in Slug Flow to
Organic Synthesis ................................. 339
12.5 Conclusion ............................................... 341
References .................................................... 342
13 Capillary Electrochromatography ............................ 347
Hans-Joerg Bart
13.1 Introduction ............................................. 347
13.2 Theory ................................................... 348
13.3 Stationary Phases ........................................ 353
13.3.1 o-CEC Phases ...................................... 354
13.3.2 Granular Packed Columns ........................... 354
13.3.3 Monolithic Phases ................................. 355
13.4 Chip Electrochromatography ............................... 356
13.5 Conclusions and Perspectives ............................. 358
References .................................................... 358
Part V Microstructured Reactors .............................. 365
14 Homogeneous Reactions ...................................... 367
Volker Hessel and Patrick Löb
14.1 Benefits ................................................. 367
14.1.1 Reaction Engineering Benefits ..................... 367
14.1.2 Process Engineering Benefits ...................... 368
14.2 Reactor Concepts - the Tools for Process
Intensification .......................................... 369
14.2.1 Micromixers, Micro Heat Exchangers and
Minitubes/Capillaries ............................. 369
14.2.2 Integrated Reactors ............................... 370
14.3 Reaction Optimization .................................... 371
14.3.1 Process Parameters with Impact on Reactor
Performance ....................................... 372
14.3.2 Residence Time Distribution ....................... 372
14.3.2.1 RTD Studies on Liquid-phase Flows ........ 372
14.3.2.2 RTD Studies on Gas-phase Flows ........... 374
14.3.3 Impact of Mixing .................................. 375
14.3.4 Impact of Heat Exchange ........................... 379
14.3.5 Impact of Electromagnetic Waves and Alternative
Energies .......................................... 380
14.4 Process Design ........................................... 380
14.4.1 Combined Reaction-Separation ...................... 380
14.4.2 Multi-step Reactions .............................. 381
14.5 Novel Process Windows .................................... 383
14.5.1 High Temperatures - Rate Acceleration ............. 384
14.5.2 High Pressures - Transition State Volume Effects .. 385
14.5.3 Solventless and Solvent-free Operation ............ 385
14.5.4 Exploration into Explosive and Thermal Runaway
Regimes ........................................... 386
14.6 From Laboratory to Production Scale - Scale-out .......... 387
14.6.1 Numbering-up ...................................... 387
14.6.2 Internal Numbering-up or Equaling-up .............. 387
14.6.3 External Numbering-up: Device Parallelization ..... 389
14.6.4 Smart Scale-up .................................... 389
14.6.5 Multi-scale Architecture .......................... 390
References .................................................... 390
15 Heterogeneous Multiphase Reactions ......................... 395
Madhvanand N. Kashid, David W. Agar, Albert Renken, and
Lioubov Kiwi-Minsker
15.1 Introduction ............................................. 395
15.2 General Criteria for Reactor Choice and Design ........... 397
15.3 Fluid-Solid Reactors ..................................... 398
15.3.1 Pressure Drop ..................................... 399
15.3.2 Residence Time Distribution ....................... 400
15.3.3 Mass Transfer and Chemical Reaction ............... 404
15.4 Fluid-Fluid Reactors ..................................... 407
15.4.1 Gas-Liquid Systems ................................ 407
15.4.1.1 Pressure Drop ............................ 420
15.4.1.2 Residence Time Distribution .............. 423
15.4.1.3 Mass Transfer and Film Saturation ........ 426
15.4.2 Liquid-Liquid Systems ............................. 428
15.4.2.1 Pressure Drop ............................ 419
15.4.2.2 Residence Time Distribution .............. 421
15.4.2.3 Chemical Reaction in Liquid-Liquid
Systems .................................. 422
15.5 Three-phase Reactions .................................... 424
15.5.1 Gas-Liquid-Solid .................................. 424
15.5.1.1 Continuous-phase Microstructured
Reactors ................................. 427
15.5.1.2 Dispersed-phase Microstructured
Reactors ................................. 428
15.5.2 Gas-Liquid-Liquid Systems ......................... 430
15.6 Conclusion ............................................... 431
References .................................................... 435
16 Photoreactors .............................................. 441
Roger Gorges and Andreas Kirsch
16.1 Photochemical Reactions .................................. 441
16.2 Single-phase Photochemical Reactions ..................... 442
16.3 Multi-phase Photochemical Reactions ...................... 447
16.4 Immobilized Photocatalysts ............................... 451
16.5 Conclusion ............................................... 455
References .................................................... 456
17 Microstructured Reactors for Electrochemical Synthesis ..... 459
Sabine Rode and François Lapicque
17.1 Fundamentals of Electrochemical Processes ................ 459
17.1.1 Electrode Reaction Stoichiometries and Faraday's
Law ............................................... 460
17.1.2 Electrode Potentials and Gibbs Free Energy
Change of the Overall Reaction .................... 461
17.1.3 Kinetics and Mass Transfer Limitations of the
Electrode Reaction ................................ 461
17.1.4 Process Performance Criteria ...................... 462
17.1.5 Specific Energy Consumption and Cell Voltage ...... 463
17.1.6 Ohmic Drop and Heat Generation .................... 463
17.2 Electrochemical Equipment and Process Flow Schemes ....... 464
17.2.1 Some Overall Process Options ...................... 464
17.2.1.1 Divided and Undivided Cells .............. 464
17.2.1.2 Direct and Indirect Electrosynthesis ..... 465
17.2.1.3 Simple and Paired Electrosynthesis ....... 465
17.2.2 Typical Commercial Cells .......................... 465
17.2.2.1 Tank Cells ............................... 465
17.2.2.2 Filterpress-type Flow Cells .............. 466
17.2.2.3 Cells with Parallel Electrodes and
a Millimeter or Submillimeter
Inter-electrode Gap ...................... 466
17.2.2.4 Cells with Non-parallel Dissymmetric
Electrodes ............................... 467
17.2.3 Process Flow Schemes .............................. 467
17.3 Microreactors in Electrochemical Synthesis ............... 468
17.3.1 Process Intensification Mechanisms ................ 469
17.3.1.1 Enhancement of the Mass Transfer Rates ... 469
17.3.1.2 Coupling of the Electrode Processes ...... 469
17.3.1.3 Reduction of the Ohmic Drop .............. 469
17.3.1.4 Operation in Single-pass
High-conversion Mode ..................... 469
17.3.2 Coplanar Interdigitated Microband Electrodes ...... 470
17.3.3 Plate and Channel Microreactors ................... 472
17.3.3.1 Reagent Flux and Applied Current ......... 471
17.3.3.2 Mass Transfer Limitations and Reagent
Conversion ............................... 471
17.3.3.3 Liquid-Solid Mass Transfer Coefficient
and Coupling of the Electrode Processes .. 472
17.3.3.4 Increase in the Space-Time Yield at a
Constant Ohmic Penalty ................... 473
17.3.3.5 Experimental Investigations Reported in
the Literature ........................... 473
17.3.3.6 Reactor Model ............................ 476
17.4 Conclusion and Outlook ................................... 477
References .................................................... 479
Index ......................................................... 481
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