Industrial Moisture and Humidity Measurement: A Practical Guide by Jan Wernecke and Roland Wernecke

9:51 PM
Industrial Moisture and Humidity Measurement: A Practical Guide
by Jan Wernecke and Roland Wernecke
Industrial Moisture and Humidity Measurement: A Practical Guide

Contents
Preface XIX
1 Water – Substance of Life 1
1.1 Water as a Natural Resource 1
1.2 Physical and Chemical Properties of Water 2
1.2.1 The Water Molecule 2
1.2.2 Physical Properties 3
1.2.3 Chemical Properties 5
1.3 Significance of Water for Energy Conversion 6
1.4 General Terminology 7
Further Reading 8

2 Thermodynamic Terms and Definitions 9
2.1 Terms in Humidity Measurement 9
2.1.1 Description of the Gas Water Vapor Pressure 10
2.1.2 Gas Temperature Definitions 12
2.1.3 The Psychrometric Equation 14
2.1.4 Definitions of Parameters Expressed in Amounts of Substance,
Concentrations, and Ratios 16
2.1.5 Additional Terms and Definitions 21
2.2 Terms in Moisture Measurement in Solid and Liquid Materials 25
2.2.1 Types of Water Bonds in Solids and Liquids 25
2.2.1.1 Water in Solids 25
2.2.1.2 Water in Liquids 26
2.2.1.3 Surface Pores, Gradation, and Capillaries 27
2.2.2 Terms and Definitions of Moisture Measurement Parameters
in Solids 27
2.2.3 Gas Humidity and Moisture in Solids 30
2.2.4 Terms and Definitions of Drying Process Parameters 33
2.2.5 Additional Terms and Definitions 34
2.3 Terms and Definitions in Measurement and Controlling
Technology 35
2.3.1 Description of Sensors in Monitoring and Control Technology 36
2.3.2 Terms used in Control 41
2.3.3 Sensor Parameters 43
2.3.4 Measurement Uncertainty 44
References 46
Further Reading 46

3 Water in Solid, Liquid, and Gaseous Materials 47
3.1 Specialties of Solid and Liquid Materials 48
3.2 Contact and Noncontact Measurement Methods 50
3.3 Bonding Types of Water in Solid and Liquid Materials 52
3.4 Analogy Models 53
References 55
Further Reading 55
4 Moisture and Humidity Measurement Methods in Solid, Liquid,
and Gaseous Substances 57
4.1 Introduction 57
4.2 Measurement of Electrical and Magnetic Properties 58
4.2.1 Measurement Principle 60
4.2.2 Low-Frequency Method 62
4.2.2.1 Measurement Principle 62
4.2.2.2 Technical Implementation 62
4.2.3 High-Frequency Method 64
4.2.3.1 Measurement Principle 64
4.2.3.2 Technical Implementation 66
4.2.4 Microwave Method 70
4.2.4.1 Measurement Principle 70
4.2.4.2 Technical Implementation 70
4.2.5 Radar Method 72
4.2.5.1 Measurement Principle 72
4.2.5.2 Technical Implementation 72
4.2.5.3 Specialties 73
4.3 Measurement of Water Vapor Pressure in Gases 73
4.3.1 Metal Oxide Sensors 73
4.3.1.1 Physical Principle 73
4.3.1.2 Technical Implementation 74
4.3.1.3 Principal Application 75
4.3.2 Quartz Microbalance 75
4.3.2.1 Physical Principle 75
4.3.2.2 Technical Implementation 75
4.3.2.3 Principal Application 76
4.3.3 Psychrometer 76
4.3.3.1 Physical Principle 77
4.3.3.2 Technical Implementation 77
4.3.3.3 Mathematical Description of Psychrometers 80
4.3.4 Capacitive Polymer Sensors 80
4.3.4.1 Physical Principle 80
4.3.4.2 Technical Implementation 81
4.3.4.3 Specialties 84
4.3.5 Dew Point Mirror 86
4.3.5.1 Physical Principle 86
4.3.5.2 Technical Implementation 86
4.3.6 Zirconium Oxide Devices 92
4.3.6.1 Technical Implementation 94
4.3.7 Measurements Based on Geometric Changes of Natural
and Artificial Materials 95
4.3.7.1 Physical Principle 95
4.3.7.2 Technical Implementation 95
4.3.7.3 Technical Implementation of Hygrometers with Size-Varying
Material 97
4.3.8 Resistive Sensors 98
4.3.8.1 Physical Principle 98
4.3.8.2 Technical Implementation 99
4.4 Water Content Measurements Using Chemical Methods 101
4.4.1 Coulometric Measurement 101
4.4.1.1 Measurement Principle 101
4.4.1.2 Technical Implementation 102
4.4.1.3 Specialties 104
4.4.2 Calcium Carbide 106
4.4.2.1 Measurement Principle 106
4.4.2.2 Technical Implementation 106
4.4.3 Calcium Hydride 108
4.4.3.1 Measurement Principle 108
4.4.3.2 Technical Implementation 109
4.4.4 Karl Fischer Titration 109
4.4.4.1 Principle 109
4.4.4.2 Technical Implementation 110
4.4.4.3 Applications 110
4.4.5 Humidity Indicator 112
4.4.5.1 Principle 112
4.4.5.2 Technical Realization 112
4.4.5.3 Applications 114
4.5 Measurement of the Optical Properties of Water and Water Vapor 114
4.5.1 Measurements in the Infrared Spectral Range 116
4.5.1.1 Physical Principle 116
4.5.1.2 Technical Implementation 117
4.5.1.3 Measurement in Liquids 123
4.5.1.4 Measurement in Opaque Materials 123
4.5.2 Measurement in the UV Range 124
4.5.2.1 Technical Implementation 125
4.5.3 Measurement with Optical Fibers 127
4.5.3.1 Physical Principle 127
4.5.3.2 Technical Implementation 127
4.5.4 Measurement of Mie Scattering by Water Droplets 129
4.5.4.1 Physical Principle 129
4.5.4.2 Technical Implementation 131
4.5.5 Holographic Measurement of Water Droplets 131
4.5.5.1 Physical Principle 131
4.5.5.2 Digital Holography 132
4.5.5.3 Technical Implementation 133
4.6 Measurement of Acoustic Properties of Water Vapor 134
4.6.1 Physical Principle 134
4.6.2 Technical Implementation 134
4.7 Measurement of Suction Pressure in Solid Materials 136
4.7.1 Tensiometry 136
4.7.1.1 Physical Principle 136
4.7.1.2 Technical Implementation 137
4.7.2 Gypsum Block Method 139
4.7.2.1 Physical Principle 139
4.7.2.2 Technical Implementation 139
4.7.2.3 Special Designs 140
4.8 Measurement of Nuclear Properties of Water 141
4.8.1 Neutron Measurement 141
4.8.1.1 Physical Principle 141
4.8.1.2 Technical Implementation 141
4.8.2 Devices Based on Gamma Radiation 142
4.8.2.1 Physical Principle 142
4.8.2.2 Technical Implementation 142
4.9 Nuclear Magnetic Resonance Spectroscopy 143
4.9.1 Physical Principle 143
4.9.2 Technical Implementation 144
4.10 Thermogravimetry 145
4.10.1 Physical Principle 145
4.10.2 Technical Implementation 146
4.10.2.1 Heat Sources 147
4.10.2.2 Drying with Desiccants 148
4.10.2.3 Oven Drying Method 149
4.11 Measurement of the Thermal Properties of Solids 150
4.11.1 Physical Principle 150
4.11.2 Technical Implementation 151
4.11.3 Measurement of Water Movement 151
4.11.4 Moisture Measurement in Insulating Materials 153
4.12 Nanostructured Measurement Devices 154
4.12.1 Contact Methods 154
4.12.2 Noncontact Methods 155
4.12.3 Nanometrology 156
References 156
Further Reading 158

5 Selection of a Measurement Method 161
5.1 Assessment of the Measurement Task 161
5.1.1 Defining the Goal of a Measurement 161
5.1.2 Conditions at the Measurement Location 163
5.2 Evaluation of Different Measurement Methods 164
5.2.1 Selection Strategies 164
5.2.2 Evaluation According to the Application 165
5.2.2.1 Other Moisture and Humidity Measurement Methods 167
5.3 Selection of Hardware 168
5.3.1 Comparison of Measurement Equipment 168
5.3.2 Cost Calculation 168
5.3.3 Determining Material-Specific Parameters 169
5.3.3.1 Laboratory Measurements 169
5.3.3.2 Measurement Under Real Production Conditions 170
Further Reading 171
6 Reliability and Traceability of Measurements 173
6.1 Metrological Terminology 174
6.1.1 Measurand 174
6.1.2 Accuracy 175
6.1.3 Precision 175
6.1.4 Reproducibility 175
6.1.5 Repeatability 176
6.1.6 Systematic Error 176
6.1.7 Random Error 176
6.1.8 Measurement Uncertainty 176
6.1.9 Calibration 177
6.1.10 Adjustment 178
6.1.11 Measurement Standard (Etalon) 178
6.1.12 Reference Standard 178
6.1.13 Reference Material 178
6.1.14 Industrial Standard 178
6.2 Moisture and Humidity Metrology 179
6.2.1 Calibration Case Studies 179
6.3 Typical Terms in Industrial Applications 180
References 181
7 Moisture Measurement in Meteorology, Agriculture,
and the Environment 183
7.1 Agriculture and Horticulture 183
7.1.1 Water Content in Soil and Agricultural Substrates 183
Contents jIX
7.1.1.1 Bonding of Water in Soil Substrate 183
7.1.1.2 Measurement of Soil Moisture 184
7.1.2 Moisture in Agricultural Products 188
7.1.2.1 Grain 188
7.1.3 Climate Control Equipment in Agriculture and Horticulture 190
7.1.4 Wetting and Dewing of Fruits and Leaves 190
7.1.4.1 Wetting of Plantations 191
7.1.4.2 Wetting Measurement Directly at the Plant 195
7.1.5 Measurement of Product Freshness 196
7.2 Waste Management 199
7.2.1 Measurement in Recycling Products 199
7.2.1.1 Moisture in Biofilters 199
7.2.1.2 Moisture in Compost 200
7.2.2 Moisture Measurement in Incinerator Flue Gas 202
7.2.2.1 Techniques for Dew Point Measurement in Acids 203
7.3 Measurement of Weather Conditions 207
7.3.1 Electronic Recording Devices for Outdoor Climate Measurements 208
7.3.1.1 Measurement of Snow Moisture 208
7.3.2 Meteorological Stations for Specialized Applications 209
7.3.3 Evaluation of Road Conditions 210
7.3.3.1 Road Conditions in Winter 212
7.3.3.2 Measurement of Relevant Road Condition Parameters 213
7.3.4 Humidity Measurement at High Altitude 216
7.3.4.1 Airplane Equipment for Humidity Measurement 216
7.3.4.2 High-Altitude Humidity Measurement from the Ground 217
References 217
Further Reading 217
8 Applications in the Food and Beverage Industry 219
8.1 Water Activity Measurement 219
8.1.1 Water Activity as a Parameter in the Food Industry 219
8.1.2 Water Activity Measurement 221
8.1.2.1 Static Water Activity Measurement 222
8.1.2.2 Dynamic Water Activity Measurement 224
8.1.2.3 Cryostatic aw Measurement 225
8.1.3 Sorption Isotherms 226
8.1.3.1 Measurement of Sorption Isotherms 229
8.1.3.2 Surface Water 230
8.1.4 Reference Methods 231
8.2 Food Processing 232
8.2.1 Moisture Measurement in Meat and Sausage Products 232
8.2.1.1 Evaluation of Measurement Methods 233
8.2.1.2 Product Monitoring 233
8.2.2 Production Control 235
8.2.2.1 Inspection of Incoming Goods 235
8.2.2.2 Influence of the Ambient Climate 236
8.2.2.3 Moisture Measurement During Particular Stages of Processing 238
8.3 Monitoring and Control of Production Stages in the Food
Industry 242
8.3.1 Moisture Measurement and Control During Coffee Production 243
8.3.1.1 Coffee Roasting 243
8.3.1.2 Interim Storage in a Silo 244
8.3.1.3 Milling Process 245
8.3.1.4 Packaging Process 246
8.3.2 Moisture Measurement During Smoking and Baking Processes 248
8.3.2.1 Specialties 248
8.3.2.2 Monitoring of Baking Parameters 249
8.4 Storage and Transport of Food 251
8.4.1 Storage Conditions 251
8.4.1.1 Characterization of Storage Conditions for Different Food
Products 251
8.4.1.2 Large Warehouses 252
8.4.1.3 Energy-Efficient Storage 252
8.4.2 Special Climate Conditions 254
8.4.2.1 Maturation of Cheese and Meat 254
8.4.2.2 Controlled and Modified Atmosphere 255
8.4.2.3 Controlling Humidity during Sea and Land Transport 256
8.4.2.4 Humidity Measurement in Packaging 257
References 259
Further Reading 259
9 Moisture and Humidity Measurement in Industrial Plants 261
9.1 Humidity Measurement Under Extreme Conditions 261
9.1.1 Measurement at High Temperatures 261
9.1.1.1 Humidity Measurement at High Temperatures (Up to 200_C) 262
9.1.1.2 Humidity Measurement at Extremely High Temperatures
(Above 300_C) 263
9.1.1.3 Sensor Installation and Sampling 266
9.1.2 Aggressive Components in the Gas Flow 270
9.1.2.1 Systems with Self-Monitoring and Sensor Checks for Inline Trace
Humidity Measurement 270
9.1.2.2 Measurement in Corrosive or Highly Contaminated
Environments 272
9.1.2.3 Detection of Leakages in Cooling Systems 273
9.1.3 Measurement at High Pressure 276
9.2 Moisture Measurement During Running Production Processes 277
9.2.1 Continuous Measurement in Silos, Pipes, and on Conveyor Belts 277
9.2.1.1 Guidelines for the Selection of a Measurement Method 277
9.2.1.2 Cross-Sensitivities and Compensation During Measurement 279
9.2.1.3 Measurement in Pipes 282
9.2.2 Determination of Residual Moisture at the Inner Walls of Hoses and
Tubes 284
9.2.2.1 Measurement Methods 284
9.2.2.2 Measurement Station for the Determination of Residual Water in
Tubes 288
9.2.3 Water Content Measurement in Coarse Materials 291
9.2.3.1 Sample Extraction Systems for Bulk Materials 291
9.2.3.2 Moisture Measurement in Coal and Ore 292
9.2.3.3 Control of Mixing Processes 293
9.3 Moisture Measurement in the Automotive and Aircraft Construction
Industries 294
9.3.1 Measurement in Oil and Fuel Systems 294
9.3.2 Automotive Components Made from Renewable Raw Materials and
Plastics 295
9.3.3 Measurement in Fast-Moving Gases During Injection and Ignition
Processes 297
9.3.3.1 Calibration of the Measurement Setup 299
9.3.4 Detection of Moisture in Insulation Layers 301
9.3.4.1 Tightness Tests 301
9.4 Moisture and Humidity Measurement in Electrical Engineering,
Electronics, and Optics 302
9.4.1 Trace Humidity Measurement in Electronic Components 302
9.4.2 Monitoring of Transformers and Switching Stations 304
9.4.3 Switch Stations 305
9.4.3.1 Suppression of Condensation Inside Switch Stations 305
Reference 306
Further Reading 306
10 Applications in the Chemical, Pharmaceutical, and Plastics
Industries 307
10.1 Moisture Measurement in Plastic Granules and Powders 307
10.1.1 Detection of Low Water Content in the Laboratory 307
10.1.1.1 Karl Fischer Titrator 307
10.1.1.2 Gas Chromatography 307
10.1.1.3 Thermogravimetry 308
10.1.1.4 Combined Methods 308
10.1.1.5 Calcium Hydride Method 309
10.1.2 Inline Measurement of Powders and Granules with Low Moisture
Content 310
10.1.2.1 Equilibrium Relative Humidity (ERH) 310
10.1.2.2 Quasi-Continuous Measurement 310
10.1.3 Inline Measurement of Powders and Granules in the High Moisture
Range 311
10.1.3.1 Selection of a Measurement Method 311
10.1.3.2 Determination of Cross-Sensitivities 316
10.2 Drying of Solid Materials 318
10.2.1 Goals of Drying 318
10.2.2 Principles of Drying 318
10.2.2.1 Thermal Drying 320
10.2.2.2 Vacuum Drying 321
10.2.2.3 Freeze-Drying 321
10.2.2.4 Chemical Drying 321
10.2.2.5 Selection of a Drying Principle 322
10.2.3 Monitoring and Control of Drying Processes 322
10.3 Storage of Moisture-Sensitive Products 324
10.3.1 Monitoring of Warehouses and Manufacturing Facilities 324
10.3.2 Storage of Samples in a Dry Environment 325
10.3.2.1 Desiccants 325
10.3.2.2 Membrane Dryers 328
10.4 Inline Measurement in Nonaqueous Fluids 330
10.4.1 Sensor Modifications 330
10.4.2 Moisture Measurement in Oil and Fuel 335
References 336
Further Reading 336
11 Applications in the Manufacture and Processing of Paper and
Textiles 337
11.1 Random Test Measurements and Inspection of Goods 337
11.1.1 Paper Properties and the Climate of the Surrounding
Environment 337
11.1.2 Influence of Moisture on Paper Properties 339
11.1.3 Quality Control by Random Test Measurements 341
11.1.3.1 Nonmoving Goods 341
11.1.3.2 Moving Goods 343
11.1.3.3 Laboratory Measurements 344
11.2 Continuous Measurement of Paper and Fabric Webs 346
11.2.1 Moving Cardboard 346
11.2.2 Moisture Measurement on Moving Filaments 350
11.2.3 Film Thickness Measurements of Water–Color Mixture Layers 354
11.3 Storage and Transport of Paper and Textiles 356
11.3.1 Climate Control of Production Facilities and Storerooms 356
11.3.2 Transport of Hygroscopic Materials 357
References 358
Further Reading 359
12 Moisture Measurement in the Building Industry 361
12.1 Moisture Measurement in Aggregates 361
12.1.1 Measurement in Silos and on Conveyor Belts 362
12.1.1.1 Measurement Using Neutrons 362
12.1.1.2 Optical Measurement 363
12.1.1.3 High-Frequency Measurement 364
12.1.2 Manufacture of Prefabricated Elements 365
12.1.2.1 Furniture Boards 365
12.1.2.2 Drying and Firing of Building Material 365
12.2 Measurement on Buildings and Brickwork 366
12.2.1 Calcium Carbide Method 368
12.2.2 Thermogravimetry 369
12.2.3 Neutron Measurement 369
12.2.4 Electromagnetic Methods 369
12.2.5 Equilibrium Relative Humidity 371
12.2.6 Measurement of Thermal Properties 373
12.2.6.1 Infrared Thermography 373
12.2.6.2 Measurement of Thermal Conductivity 374
12.2.6.3 Temperature Measurement Using Optical Fibers 374
12.2.7 Other Methods 375
12.2.7.1 Radar Measurement 375
12.2.7.2 Infrared Reflectometry 375
12.2.7.3 Nuclear Magnetic Resonance 375
12.3 Climate Control in Rooms and Buildings 376
12.3.1 Apartments and Workplaces 376
12.3.1.1 Humidity Measurement 376
12.3.2 Museums and Exhibition Showrooms 378
12.3.3 Climate Control in Closed Chambers and Small Rooms 380
12.3.3.1 Air Humidifying 380
12.3.3.2 Dehumidifying of Air 382
12.3.4 Rooms Containing Electrical Systems 382
Further Reading 384
13 Laboratory-Based Moisture Measurement 385
13.1 Laboratory Measurement Stations for Humidity and Moisture
Measurement 385
13.1.1 Climate Chambers 386
13.1.2 Gas Mixing Systems for Trace Humidity Measurement 388
13.1.3 Laboratory Measurement Station for Moisture Measurement 390
13.1.3.1 Measurement Station for Liquid and Solid Materials 390
13.1.3.2 Measurement of Trace Moisture in Solid Materials 393
13.1.4 Measurement Station to Determine the Water Vapor Permeability
of Foils 395
13.2 Generation of Gases with a Defined Humidity 396
13.2.1 Humidification and Drying of Gas Flows 396
13.2.1.1 Complete Humidification of a Gas Flow 397
13.2.1.2 Gas Humidification by Permeation 398
13.2.1.3 Humidification by Capillary Diffusion 399
13.2.1.4 Humidification by Continuous Injection 400
13.2.2 Humidity Generators 400
13.2.2.1 Two-Pressure Humidity Generator 401
13.2.2.2 Two-Temperature Humidity Generator 402
13.2.2.3 Gas Mixing Humidity Generator 403
13.2.2.4 Coulometric Humidity Generator 404
13.2.3 Saturated and Unsaturated Solutions 405
13.2.3.1 Saturated Solutions 405
13.2.3.2 Unsaturated Salt Solutions 406
13.2.3.3 Other Solutions 409
13.3 Humidity Measurement in Medical Applications 409
13.3.1 Specialties of Clinical Applications 409
13.3.2 Humidity Measurement in Respiratory Air 410
13.3.2.1 The Respiration Process in Humans 410
13.3.2.2 Self-Regulating Systems for the Humidification of Respiratory Air 412
13.3.2.3 Humidity Measurement in Respiratory Air 413
13.3.3 Humidity Measurement on the Skin 416
13.3.4 Applications in Medical Supply Technology 417
13.3.4.1 Incubator 417
13.3.4.2 Gas Supply System 417
13.3.4.3 Room Climate Control 417
13.3.4.4 Sterilization 418
References 418
Further Reading 418

14 Moisture and Humidity Measurement in Space 421
14.1 Model Representations of the Formation and Distribution
of Water 421
14.1.1 Interactions between the Surface and the Atmosphere 422
14.1.1.1 Water at Low Temperatures 423
14.1.1.2 Soil Water 425
14.1.1.3 Formation of a Water Cycle 425
14.1.2 Simulation of a Planetary Atmosphere 427
14.2 Measurement Methods in Aerospace 430
14.2.1 Remote Sensing 430
14.2.2 Measurements on Planetary Surfaces 430
14.2.3 Ground-Based Measurement Methods 431
14.2.4 Testing and Calibration of Aerospace Technology
in the Laboratory 434
14.3 Requirements for Measurement Equipment in the Aerospace
Industry 436
14.3.1 General Climatic Conditions during Operation 436
14.3.2 Technical Requirements of Measurement Equipment 437
14.3.2.1 Integration into the Overall System 437
14.3.2.2 Requirements for Operation 438
14.3.3 Technical Specifications of Selected Sensors for Spaceflight
Applications 438
14.3.4 Concept of a Combined Measurement Sensor 443
14.3.4.1 Variation of Measurement Techniques 443
14.3.4.2 Combined Probe for Extraterrestrial Soil Moisture Measurements 445
14.3.5 Combined Probe for Extraterrestrial Atmospheric Humidity
Measurements 447
References 451
Further Reading 452
Appendix A: Relevant Units of Thermodynamics 455
A.1 Basic Units of the International System of Units (SI System) 455
A.2 Conversion of Units 456
A.3 Conversion of Units (Material Properties) 457
A.4 Conversion of Units (Thermodynamic) 459
Appendix B: Tables and Diagrams of Thermodynamics 463
B.1 Mollier Diagram 463
B.2 Details of Mollier Diagram 464
B.3 Calculation of Pressure Dew Point 464
B.4 Water Vapor Over Water 465
B.5 Water Vapor Over Ice 465
B.6 Psychrometer Charts 466
B.7 Correlation Between Relative Humidity, Dew Point and
Temperature 467
Appendix C: Constants and Parameters 469
C.1 Relevant Constants 469
C.2 Parameters of Dry Air 469
C.3 Parameters of Water, Water Vapor, Ice 470
C.4 Parameter of Carbon Dioxide 471
C.5 Other Parameters 471
Appendix D: Material Parameters 473
D.1 Specific Electric Resistance of Different Materials 473
D.2 Relative Permittivity of Different Insulators 474
D.3 Spectral Lines of Different Chemical Elements 475
D.4 Density of Various Solid Materials 476
D.5 Heat of Evaporation of Different Gases 476
D.6 Cooling Temperature of Common Coolants 477
Appendix E: Water Adsorption in Products 479
E.1 Sorption Isotherm of Wood Fiber 479
E.2 Sorption Isotherm of Grinded Natural Stone 479
E.3 Sorption Isotherm of Soot 480
E.4 Sorption Isotherm of Flour 480
E.5 Sorption Isotherm of Freeze-Dried Coffee Powder 480
E.6 Sorption Isotherm of Milled Coffee Beans 481
E.7 Sorption Isotherm of Paper 481
E.8 Storing Conditions of Fruit and Vegetables 482
E.9 Storing Conditions of Fruit and Vegetables Under Controlled
Atmosphere 482
Index 483

It is US$10. To get this book send email: textileebooks@gmail.com

Share This

Related Posts

Previous
Next Post »