ADVANCES IN HEAT TRANSFER

VOLUME 33 , 1999

CONTENTS

Heat and Mass Transfer in Microwave Processing

CRAIG SALTIEL AND ASHIM K. DATTA

I. Introduction...................................... 1

A. Historical Perspective and Current Microwave Applications ............ 3

II. Microwave Oven Components. ......................... 6

A. Microwave Frequencies ............................... 6

B. Microwave Generators. ............................... 8

C. Waveguides ...............,,,,..,........,..,.,, 12

D. Applicators. ..................................... 13

III. Microwave-Material Interactions: Dielectric Properties ..... 14

A. Microwave-Material Interaction Mechanisms ................... 15

B. Dielectric Properties ............,,.,.........,...,.,, 16

IV. Electromagnetic Fields in a Microwave Enclosure ............ 20

A. Maxwell's Equations. ................................ 20

B. Particular Solutions of Maxwell's Equations .................... 25

V. Heat Transport during Microwave Processing ............... 41

A. Microwave Power Absorption and the Energy Equation .............. 41

B. Lumped Systems .................................. 43

C. Minimal Diffusion.................................. 44

D. Temperature Profiles for Plane Waves ....................... 45

E. Heat Transfer in Resonant-Cavity Applicators ................... 48

F. Thermal Runaway and Phase Change Heating ,,..,,,,,,,,,,.,.,, 58

G. Hybrid Heating and the Use of Susceptors. .................... 61

H. Heating Uniformity and Variable-Frequency Microwaves ......... 63

1. Microwave-Induced Plasma ............................. 67

J. Batch (Natural Convection) Microwave Heating of Liquids ........ 69

K. Continuous Microwave Heating of Liquids..,...,,.........,.,, 70

L. Inhibition of Boiling in Microwave Heating .................... 70

M. Measurement of Temperature and Heating Uniformity in a Microwave

Heating Environment .,,,,.....,,,,,.......,,........ 71

VI. Mass Transport in Porous Media under Microwave Heating. . . . . 72

A. Microwave Power Absorption in a Wet Material .................. 72

B. Multiphase Transport Models for Microwave Heating of Porous Media 73

C. Multiphase Moisture Transport in Wet Porous Media under

Intensive Microwave Heating ............................ 75

D. Microwave Drying. ,.,,,...,,.,,.,.......,,......... 82

E. Moisture Transport during Microwave Freeze Drying ,,,,,,.....,., 83

VII. Closing Remarks. . 86

Acknowledgments. 87

Key to Symbols . . 87

References...... 88

Enhancement of Heat Transfer and Mass Transport in Single-Phase and

Two-Phase Flows with Electrohydrodynamics

J. SEYED-YAGOOBI AND J. E. BRYAN

Abstract........................................ 95

I. Introduction ..................................... 95

II. Theoretical Background ............................. 96

A. Electric Body Force Density............................ 96

B. Maxwell Stress Tensor ............................... 100

III. EHD Enhancement of Boiling Heat Transfer ............... 101

A. Nucleate Boiling .................................. 101

B. Internal Convective Boiling ............................ 121

IV EHD Enhancement of Condensation Heat Transfer ........... 140

A. External Condensation ,,,........,,,,.........,,..... 141

B. Internal Convective Condensation ......................... 147

V EHD Pumping ................................... 147

A. lon-Drag Pumping ................................. 147

B. Induction Pumping. ..,.,,.........,,,,,..........,, 156

C. Selected Applications ............................... 170

VI. Enhancement of Heat Transfer with Corona Wind. ........... 172

VII. Conclusions..................................... 177

Acknowledgments................................. 178

Nomenclature.................................... 178

References...................................... 180

Microscale Aspects of Thermal Radiation Transport and Laser Applications

SUNIL KUMAR AND KUMAL MITRA

Abstract........................................ 187

I. Introduction ..................................... 188

A. Importance of Physical Dimensions: Applications of Fabricated

Microstructures. .................................. 189

B. Importance of Temporal Pulse Widths: Applications of Short-Pulse Lasers and

X-rays ....................................... 191

C. Importance of Intensity: Applications of High-Intensity Pulsed Lasers ..... 202

II. Fundamentals.................................... 202

A. Phonons ...................................... 202

B. Electrons ...................................... 207

C. Photons. ...................................... 214

III. Length Scales and Related Radiation Regimes. .............. 219

A. Macroscopic and Microscopic Length Scales. ................... 220

B. Microscale Regimes ................................. 227

IV Time Scales and Related Regimes ....................... 235

A. Process and Intrinsic Time Scales. ......................... 235

B. Temporal Radiation Regimes ............................ 238

V Electromagnetic Wave Interference and Related Models ........ 243

A. Dependent and Independent Scattering and Absorption in Particulate Systems. . 243

B. Rectangular Microgrooves. ............................. 250

VI. Models for Thin Metallic Films. ........................ 252

VII. Short-Pulse Radiation Transport through Scattering Absorbing Media......................... 258

A. Modeling. ...................................... 258

B. Source Pulse and Boundary Conditions ...................... 264

C. Optical Properties Used ............................... 265

D. Results........................................ 265

VIII. Laser-Metal Interaction .............................. 271

A. Modeling. ...................................... 271

B. Results. ....................................... 275

IX. Interaction of High-Intensity Short-Pulse Lasers with Liquids and Organic Materials.....277

A. Saturable Absorption in Liquids .......................... 278

B. Ablation of Organic Polymers. ........................... 280

X. Summary........................................ 283

XI. Acknowledgments.................................. 283

Nomenclature..................................... 283

References....................................... 285

Gas IR Radiative Properties: From Spectroscopic Data to Approximate Models

JEAN TAINE AND ANOUAR SOUFIANI

Abstract ............................. 295

I. Introduction........................... 296

II. Characterization of an Isolated Line........... 302

A. Properties of the Molecular States of CO2 and H2O. . . . . 304

B. The Three Fundamental Radiative Interaction Phenomena. . 313

C. Line, Broadening Effects ................... 316

D. Absorption Coefficient of an Isolated Line.......... 322

III. Gas Molecular Spectra. ................... 325

A. Classification of Molecular Transitions ............ 325

B. Gas IR Spectra ........................ 327

IV Statistical Narrowband (SNB) Models ......... 341

A. Uniform Media ........................ 342

B. Nonuniform Media ...................... 350

C. Mixtures of Absorbing Species ................ 354

D. Statistical Narrowband Model Parameters................... 355

E. Radiative Transfer Equation and Statistical Narrowband Models. ...... 357

F. Accuracy of Statistical Narrowband Models ................. 359

V The Correlated-^ (CK) and Correlated-A-Fictitious-Gas (CKFG) Methods...............369

A. Uniform Media, ^-Distribution Method .................... 369

B. Nonuniform Media, CK. Method ....................... 371

C. Nonuniform Media, CKFG Method ...................... 377

D. Accuracy of CK: and CKFG Models ..................... 380

VI. Models Based on Global Absorption Distribution Functions.... 384

A. Media with Uniform Radiative Properties................... 384

B. Common Version of the WSGG Model .................... 385

C. The Spectral-Line-Based WSGG Model (SLW). ............... 386

D. The ADF and ADFFG Formulations ..................... 389

E. Treatment of Mixtures of Absorbing Gases .................. 391

VII. Accuracy of the Models Applied to Radiative Transfer in

Planar Media .................................. 392

VIII. Concluding Remarks............................. 399

Acknowledgments................................ 402

Appendix A. Mean Equivalent Black-Line Width for Lorentz Lines................................402

A. Random Uniform Model............................ 402

B. Exponential Distribution Function........................ 404

C. Inverse-Exponential Tailed Distribution Function ................ 405

List of Symbols ................................. 407

References..................................... 409

Cooling-Water Fouling in Heat Exchangers

HANS MULLER-STEINHAGEN

Abstract...................................... 415

I. Introduction................................... 416

A. Description of Problem ............................ 416

B. Design Practice. ................................ 416

C. Cost of Fouling. ................................ 419

II. Fouling Mechanisms during Heat Transfer to Water ........ 421

III. Sequential Events of Fouling........................ 422

IV General Approach to the Modeling of Heat-Exchanger Fouling. 424

V Crystallization Fouling............................ 425

A. Indices for the Scaling Tendency of Water .................. 425

B. Models for Scale Formation in Fleat Exchangers ............... 428

VI. Particulate Fouling............................... 449

A. Effect of Flow Velocity ............................ 449

B. Effect of Particle Concentration ........................ 452

C. Effect of Surface Temperature ......................... 453

D. Effect of Heat Flux. .............................. 454

E. Effect of Particle Size ............................... 455

F. Effect of Suspension pH .,.....,,..........,,.....,,. 455

VII. Biological Fouling ................................. 457

VIII. Industrial Cooling-Water Fouling........................ 460

A. Sheil-and-Tube Heat Exchangers .......................... 460

B. Plate-and-Frame Heat Exchangers ......................... 463

C. Approximate Influence of Process Parameters on Industrial Heat-Exchanger

Fouling. ....................................... 467

IX. Mitigation of Cooling-Water Fouling ..................... 472

A. Chemical Methods. ................................. 472

B. Mechanical Methods ................................ 477

X. Conclusions...................................... 489

Symbols ........................................ 490

References....................................... 491