Drying Phenomena

Ibrahim Dincer is a full professor of Mechanical Engineering in the Faculty of Engineering and Applied Science at UOIT. He is Vice President for Strategy in International Association for Hydrogen Energy (IAHE) and Vice-President for World Society of Sustainable Energy Technologies (WSSET). Renowned for his pioneering works in the area of sustainable energy technologies he has authored and co-authored numerous books and book chapters, more than 1000 refereed journal and conference papers, and many technical reports. He has chaired many national and international conferences, symposia, workshops and technical meetings. He has delivered more than 350 keynote and invited lectures. He is an active member of various international scientific organizations and societies, and serves as editor-in-chief, associate editor, regional editor, and editorial board member on various prestigious international journals. He is a recipient of several research, teaching and service awards, including the Premier's research excellence award in Ontario, Canada in 2004. He has made innovative contributions to the understanding and development of sustainable energy technologies, including drying systems and applications, and his group has developed various novel technologies/methods/models/etc. He has recently been identified as one of the 2014's Most Influential Scientific Minds in Engineering. This honour, presented by Thomson Reuters, is given to researchers who rank among the top 1% most cited for their subject field and year of publication, earning the mark of exceptional impact. Calin Zamfirescu is a senior researcher in Dr. Dincer's group at UOIT where he has been working since 2007. His research falls in the field of clean energy technology and process engineering. He was a tenure-track assistant professor of mechanical engineering for four years at Technical University of Civil Engineering of Bucharest, Romania, where he received his PhD in 1999. He was awarded with six research fellowships during five years at the Universities of Delft (in the Netherlands), Duke (in North Carolina, USA) and Henri Poincare (in Nancy, France). He has co-authored some books and more that 50 peer-reviewed papers in well-recognized journals.

Preface xi

Nomenclature xv

1 Fundamental Aspects 1

1.1 Introduction 1

1.2 Fundamental Properties and Quantities 2

1.3 Ideal Gas and Real Gas 13

1.4 The Laws of Thermodynamics 19

1.5 Thermodynamic Analysis Through Energy and Exergy 24

1.5.1 Exergy 24

1.5.2 Balance Equations 27

1.6 Psychometrics 36

1.7 Heat Transfer 45

1.7.1 General Aspects 45

1.7.2 Heat Transfer Modes 48

1.7.3 Transient Heat Transfer 54

1.8 Mass Transfer 58

1.9 Concluding Remarks 63

1.10 Study Problems 63

References 65

2 Basics of Drying 67

2.1 Introduction 67

2.2 Drying Phases 68

2.3 Basic Heat and Moisture Transfer Analysis 69

2.4 Moist Material 76

2.5 Types of Moisture Diffusion 81

2.6 Shrinkage 82

2.7 Modeling of Packed-Bed Drying 86

2.8 Diffusion in Porous Media with Low Moisture Content 88

2.9 Modeling of Heterogeneous Diffusion in Moist Solids 90

2.10 Conclusions 97

2.11 Study Problems 97

References 98

3 Drying Processes and Systems 99

3.1 Introduction 99

3.2 Drying Systems Classification 100

3.3 Main Types of Drying Devices and Systems 105

3.3.1 Batch Tray Dryers 105

3.3.2 Batch Through-Circulation Dryers 106

3.3.3 Continuous Tunnel Dryers 108

3.3.4 Rotary Dryers 110

3.3.5 Agitated Dryers 114

3.3.6 Direct-Heat Vibrating-Conveyor Dryers 116

3.3.7 Gravity Dryers 117

3.3.8 Dispersion Dryers 119

3.3.9 Fluidized Bed Dryers 128

3.3.10 Drum Dryers 130

3.3.11 Solar Drying Systems 132

3.4 Processes in Drying Systems 137

3.4.1 Natural Drying 137

3.4.2 Forced Drying 145

3.5 Conclusions 151

3.6 Study Problems 151

References 152

4 Energy and Exergy Analyses of Drying Processes and Systems 153

4.1 Introduction 153

4.2 Balance Equations for a Drying Process 154

4.3 Performance Assessment of Drying Systems 159

4.3.1 Energy and Exergy Efficiencies 159

4.3.2 Other Assessment Parameters 161

4.4 Case Study 1: Analysis of Continuous-Flow Direct Combustion Dryers 162

4.5 Analysis of Heat Pump Dryers 169

4.6 Analysis of Fluidized Bed Dryers 178

4.6.1 Hydrodynamics of Fluidized Beds 179

4.6.2 Balance Equations 181

4.6.3 Efficiency Formulations 183

4.7 Conclusions 187

4.8 Study Problems 187

References 188

5 Heat and Moisture Transfer 189

5.1 Introduction 189

5.2 Transient Moisture Transfer During Drying of Regularly Shaped Materials 190

5.2.1 Transient Diffusion in Infinite Slab 191

5.2.2 Drying Time of an Infinite Slab Material 200

5.2.3 Transient Diffusion in an Infinite Cylinder 202

5.2.4 Transient Diffusion in Spherical-Shape Material 205

5.2.5 Compact Analytical Solution or Time-Dependent Diffusion in Basic Shapes 208

5.3 Shape Factors for Drying Time 209

5.3.1 Infinite Rectangular Rod of Size 2L × 2β1L 210

5.3.2 Rectangular Rod of Size 2L × 2β1L×2β2L 210

5.3.3 Long Cylinder of Diameter 2L and Length 2β1L 212

5.3.4 Short Cylinder of Diameter 2β1L and Length 2L 213

5.3.5 Infinite Elliptical Cylinder of Minor Axis 2L and Major Axis 2β1L 213

5.3.6 Ellipsoid Having the Axes 2L, 2β1L, and 2β2L 213

5.4 Moisture Transfer Coefficient and Diffusivity Estimation from Drying Curve 216

5.5 Simultaneous Heat and Moisture Transfer 219

5.6 Models for Heat and Moisture Transfer in Drying 225

5.6.1 Theoretical Models 226

5.6.2 Semitheoretical and Empirical Models for Drying 231

5.7 Conclusions 232

5.8 Study Problems 233

References 234

6 Numerical Heat and Moisture Transfer 237

6.1 Introduction 237

6.2 Numerical Methods for PDEs 239

6.2.1 The Finite Difference Method 240

6.2.2 Weighted Residuals Methods: Finite Element, Finite Volume, Boundary Element 246

6.3 One-Dimensional Problems 249

6.3.1 Decoupled Equations with Nonuniform Initial Conditions and Variable Boundary Conditions 249

6.3.2 Partially Coupled Equations 253

6.3.3 Fully Coupled Equations 256

6.4 Two-Dimensional Problems 261

6.4.1 Cartesian Coordinates 261

6.4.2 Cylindrical Coordinates with Axial Symmetry 271

6.4.3 Polar Coordinates 276

6.4.4 Spherical Coordinates 280

6.5 Three-Dimensional Problems 284

6.6 Influence of the External Flow Field on Heat and Moisture Transfer 288

6.7 Conclusions 291

6.8 Study Problems 291

References 292

7 Drying Parameters and Correlations 295

7.1 Introduction 295

7.2 Drying Parameters 296

7.2.1 Moisture Transfer Parameters 296

7.2.2 Drying Time Parameters 299

7.3 Drying Correlations 301

7.3.1 Moisture Diffusivity Correlation with Temperature and Moisture Content 301

7.3.2 Correlation for the Shrinkage Ratio 304

7.3.3 Biot Number–Reynolds Number Correlations 305

7.3.4 Sherwood Number–Reynolds Number Correlations 307

7.3.5 Biot Number–Dincer Number Correlation 310

7.3.6 Regression Correlations for μ1 Eigenvalues versus Lag Factor 312

7.3.7 Biot Number–Drying Coefficient Correlation 313

7.3.8 Moisture Diffusivity–Drying Coefficient Correlation 315

7.3.9 Biot Number–Lag Factor Correlation 316

7.3.10 Graphical Determination of Moisture Transfer Parameters in Drying 317

7.3.11 Moisture Transfer Coefficient 318

7.4 Conclusions 320

7.5 Study Problems 320

References 321

8 Exergoeconomic and Exergoenvironmental Analyses of Drying Processes and Systems 323

8.1 Introduction 323

8.2 The Economic Value of Exergy 326

8.3 EXCEM Method 329

8.4 SPECO Method 337

8.5 Exergoenvironmental Analysis 340

8.6 Conclusions 345

8.7 Study Problems 345

References 346

9 Optimization of Drying Processes and Systems 349

9.1 Introduction 349

9.2 Objective Functions for Drying Systems Optimization 351

9.2.1 Technical Objective Functions 351

9.2.2 Environmental Objective Functions 359

9.2.3 Economic Objective Functions 362

9.3 Single-Objective Optimization 363

9.3.1 Trade-off Problems in Drying Systems 363

9.3.2 Mathematical Formulation and Optimization Methods 366

9.3.3 Parametric Single-Objective Optimization 371

9.4 Multiobjective Optimization 375

9.5 Conclusions 379

9.6 Study Problems 379

References 380

10 Sustainability and Environmental Impact Assessment of Drying Systems 381

10.1 Introduction 381

10.2 Sustainability 383

10.2.1 Sustainability Assessment Indicators 383

10.2.2 Exergy-Based Sustainability Assessment 391

10.3 Environmental Impact 397

10.3.1 Reference Environment Models 399

10.3.2 Anthropogenic Impact on the Environment 401

10.3.3 Exergy Destruction and Environmental Impact of Drying Systems 411

10.4 Case Study: Exergo-Sustainability Assessment of a Heat Pump Dryer 419

10.4.1 Reference Dryer Description 419

10.4.2 Exergo-Sustainability Assessment for the Reference Drying System 421

10.4.3 Improved Dryer Description 425

10.4.4 Exergo-Sustainability Assessment for the Improved Drying System 428

10.4.5 Concluding Remarks 430

10.5 Conclusions 430

10.6 Study Problems 430

References 431

11 Novel Drying Systems and Applications 433

11.1 Introduction 433

11.2 Drying with Superheated Steam 436

11.3 Chemical Heat Pump Dryers 438

11.4 Advances on Spray Drying Systems 441

11.4.1 Spray Drying of CuCl2(aq) 441

11.4.2 Spray Drying of Nanoparticles 445

11.4.3 Microencapsulation through Spray Drying 446

11.5 Membrane Air Drying for Enhanced Evaporative Cooling 448

11.6 Ultrasound-Assisted Drying 449

11.7 Conclusions 451

11.8 Study Problems 451

References 452

Appendix A: Conversion Factors 455

Appendix B: Thermophysical Properties of Water 457

Appendix C: Thermophysical Properties of Some Foods and Solid Materials 461

Appendix D: Psychometric Properties of Humid Air 463

Index 469