Fibrous Filter Media | Philip J. Brown and Christopher L. Cox


Fibrous Filter Media
Edited by Philip J. Brown and Christopher L. Cox

Fibrous Filter Media


List of contributors ix
Preface xi 

Part I Principles of Fibrous Filtration 1
1 Gas filtration 3
Thad J. Ptak
1.1 Introduction 3
1.2 History of air filters 4
1.3 Principles of gas filtration 6
1.4 Filters for solid_gas separation 19
1.5 Conclusions 25
References 26
2 Industrial liquid filtration equipment 27
Nicholas P. Cheremisinoff
2.1 Introduction 27
2.2 Defining solids 27
2.3 Glossary of filtration terms 28
2.4 Filter presses 30
2.5 Belt filter presses 40
2.6 Rotary drum filters 45
Further reading 49
3 Fibrous filtration of liquid aerosols 51
Ryan Mead-Hunter, Andrew J.C. King and Benjamin J. Mullins
3.1 Introduction 51
3.2 Experimental studies of whole filters 53
3.3 Particle (droplet) capture and single fiber efficiency 61
3.4 Filter efficiency and penetration 64
3.5 Pressure drop and saturation models 66
3.6 Iterative models 74
3.7 Fiber wetting and single fiber studies 75
3.8 Capillarity 81
3.9 Colloid aerosols 83
3.10 Visualization 85
3.11 Simulation 85
3.12 Conclusion 87
References 88
4 The charging and stability of electret filters 95
Ali Kilic, Stephen Russell, Eunkyoung Shim and
Behnam Pourdeyhimi
4.1 Introduction 95
4.2 Electrets 96
4.3 Electret filters 97
4.4 Basic electret characteristics 102
4.5 Methods for producing electret filters 109
References 117
Further reading 121 

Part II Types of Fibrous Filters 123
5 Knitted fibrous filter media 125
Benjamin J. Mullins, Andrew J.C. King, Ryan Mead-Hunter
and Wolfgang Heikamp
5.1 Introduction 125
5.2 Structure and application 126
5.3 Pressure drop and efficiency 128
5.4 Mist eliminator-specific research 129
5.5 Summary and conclusion 132
References 132
6 Nonwoven fabric filters 133
Ningtao Mao
6.1 Introduction 133
6.2 Fiber types and processing for nonwoven fabric filters 134
6.3 Filtration mechanism of nonwoven fabrics and
their filter efficiency 144
6.4 Applications of nonwoven fabric filters 156
6.5 Future trends 162
6.6 Sources of further information 163
References 164
7 Simulation of filtration in shaped fiber media 173
Christopher L. Cox, Patrick Buckingham, Philip J. Brown,
Elizabeth K. Skomra and John Larzelere
7.1 Introduction 173
7.2 Solution methodology 175
7.3 Results and discussion 182
7.4 Conclusions and continuing work 187
Acknowledgment 188
References 188
8 Plasma textiles as fibrous filter media 191
Warren J. Jasper and Srinivasan C. Rasipuram
8.1 Introduction 191
8.2 Single fiber theory 192
8.3 Single fiber efficiency 194
8.4 Two infinitely long parallel cylinders 195
8.5 Filtration testing of a plasma textile 198
8.6 Filtration efficiency results 199
8.7 Conclusions 207
References 207

Part III Applications of Fibrous Filters 211
9 Nanofibers for coalescing filter media for
water_diesel separation 213
Xi Yang and George Chase
9.1 Brief review of coalescing filter media 213
9.2 Brief review of electrospinning 216
9.3 Experimental description 220
9.4 Conclusions 225
References 225
10 Air filtration in aero engines 229
Nicholas Bojdo and Antonio Filippone
10.1 Introduction 229
10.2 History of the Engine Inlet Barrier Filter 230
10.3 EIBF design 232
10.4 EIBF applications 234
10.5 EIBF performance 234
10.6 EIBF performance modeling 236
10.7 EIBF case study 240
References 242
11 Filtration of drinking water 245
Darren Radcliffe-Oatley
11.1 Introduction 245
11.2 Types of water filter 250
11.3 Materials 255
11.4 Applications 258
11.5 Future trends 267
11.6 Conclusion 271
References 272
12 Application of nanofibrous membranes and their suitability for
membrane bioreactor processes in wastewater treatment 275
Petr Mikula´ˇsek and Ji ˇ rı´Cuhorka
12.1 Introduction 275
12.2 Membrane bioreactors 276
12.3 Nanofibrous membrane 282
12.4 Future directions 287
12.5 Conclusions 288
References 288
Index 291

The histories of mankind, fibers, and textiles are so intricately woven that their separation is indistinguishable. It is well established that approximately 7000 years ago man developed the ability to produce yarn, and subsequently fabric, from cellulosebased plants such as flax and cotton, followed in subsequent centuries by the evolution of silk and woolen fabrics. However, the laborious method of hand production still prevailed as recently as 200 years ago, which only changed with the onset of the industrial revolution in the late 1700s and the rise of the textile factory system that allowed the production of massive quantities of goods.

On a human level the need to create textiles for filtration can be traced to the early days of mining. In this instance to reduce mine dust inhalation and for darker more insidious reasons such as the primitive powdered chemical warfare agents previously proposed by Leonardo da Vinci for enemy asphyxiation. Leonardo’s counter measure (or at least a partial solution) was to protect people with what is essentially a wet woven cloth mask, i.e., a filter, an all too frequently utilized familiar counter measure today.

In the last 150 years, great scientific advances have been made. Specifically, the fields of polymer and fiber science, chemistry and engineering have forged the way for new fibers and textiles. Systematic approaches to understanding have enabled us to address the potentially vast requirements that modern filters must meet.

In his book Anticipations of the Reaction of Mechanical and Scientific Progress Upon Human Life and Thought (1902), Herbert George “H.G.” Wells speculates and forecasts the future of the next century in a frank and sincere manner. We cannot presume to predict what the next 100 years will hold for humanity, especially given the advances witnessed in the last 20 years. However, we can perceive what future benefits fiber-based filtration will have for humanity. We can safely say that fibrous filter media will continue to improve human life by enabling (among other things) cars to drive, planes to fly, higher water quality, cleaner air, houses to be built, and overall a healthier global environment to live in. These benefits will be achieved by scientific and engineering advances in the subject area.

Currently, fibrous filter media comprise a myriad of materials for use in both gas and liquid applications. The subject is multifaceted in many ways: highly interdisciplinary, significantly diverse with respect to materials, products, and applications, and is still ripe for further innovation. The need for filters is unquestionable and the demand is untiring. The disciplines represented by the contributors to Fibrous

Filter Media include textile science, mathematics, physics, chemistry, and at least four engineering branches. These authors come from academia, industry, and government laboratories, and are scattered over four continents.

Part I introduces the principles and methodology of gas and liquid fibrous filtration. The first chapter, Gas filtration, begins with a history of fibrous air filters, then a theoretical background is provided, including governing equations used in modeling fibrous filtration of gases. An overview of liquid filtration from an industry perspective is the focus of Chapter 2, Industrial liquid filtration equipment, along with a detailed description of three types of equipment used in solid_liquid separation. The theory underlying fibrous filtration of liquid aerosols is elucidated in Chapter 3, Fibrous filtration of liquid aerosols. Experimentally validated modeling is also presented, along with many references for further reading. A methodical exposition of the theory behind charged electret filters is provided in Chapter 4, The charging and stability of electret filters, plus a discussion of production methods and an extensive literature background on the subject.

In Part II, an overview of types of fibrous filters is provided, including details of fiber types, fabric construction and applications. Chapter 5, Knitted fibrous filter media, focuses on knitted fibrous filter media, with a discussion of theory and experiment underlying a subject that until now has not received the attention it deserves. The theory, production methods, and applications of nonwoven fabric filters are featured in Chapter 6, Nonwoven fabric filters, along with many supporting references. Shaped fiber filtration for airborne particulates is the subject of Chapter 7, Simulation of filtration in shaped fiber media, with the presentation of a modeling approach adaptable for fibers of any cross-sectional shape. Both theoretical and experimental aspects of plasma textile fibrous filters, in which electrostatic charging and electret filtration are combined to form a “tunable” nanoparticle filter, are discussed in Chapter 8, Plasma textiles as fibrous filter media.

Part III covers a variety of filtration applications in which fibrous assemblies are used. The separation of water and diesel fuel using electrospun nanofiber filters is described in Chapter 9, Nanofibers for coalescing filter media for water_diesel separation, through an introduction to the process along with a discussion of experiments and experimental results. Chapter 10, Air filtration in aero engines, presents the critical role played by an engine inlet barrier filter for aeronautical applications and includes a discussion of simulations used in the design of these filters. An informative treatment of drinking water filtration is provided in Chapter 11, Filtration of drinking water, including materials used, a description of the RO process, economic factors, and future trends. Chapter 12, Application of nanofibrous membranes and their suitability for membrane bioreactor processes in wastewater treatment, presents nanofibrous membrane bioreactors for wastewater treatment and includes a discussion of performance, production, applications, and future directions for the technology.

Altogether, this book is designed to provide the reader with an overview of fibrous filtration principles, materials, and applications. The vastness of the subject precludes any claim of an all-encompassing treatment of the topic. As noted above, several of the chapters include a thorough literature search and suggestions for further research. Our hope is that this book will help to spur on new discoveries in fibrous filtration that will improve the quality of life for many people. We gratefully acknowledge the authors who contributed their expertise in the compilation of this book.

Philip J. Brown and Christopher L. Cox

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