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The need for clean air has probably never been greater. Many industrial employees need to avoid exposure to airborne particulates, while certain industrial processes demand clean air of exceptional quality. Medical and biological fields rely on sterile air, while filtration can improve air quality in offices, homes and all types of transport.
Filters act in a variety of complex and subtle ways. Each chapter introduces its subject matter simply, before tackling the problem in greater depth. The book therefore provides an excellent basis for detailed study, but is also invaluable to anyone needing an overview of the subject.
Chapter headings and main section headings: Introduction. Symbolic notation. Macroscopic Description of Filter Behaviour. Surface filtration and depth filtration. Types of filter. Method of filtration and assessment of efficiency. Layer efficiency. Single fibre efficiency. Filter Structure. Introduction. Paper filters. Carded filters. Porous foam. Model filters. Flow Patterns and Pressure Drop. Nature of airflow through a filter. General fluid dynamics theory. Microscopic airflow patterns in filters. Filters of irregular or imperfect structure. Flow in conditions other than simple Stokes flow. Macroscopic flow patterns. Flow through filters of non-uniform structure. Particle Capture by Mechanical Means. Introduction. Generalized theory of single fibre efficiency. Particle capture by direct interception. Particle capture by inertial impaction. Capture of particles by gravity. Capture of particles by diffusional deposition. Capture of non-spherical particles by fibrous filters. Combined effect of two or more capture mechanisms. Variation of deposition site with capture process. Effect of leakage on filter performance. Potential problems with model filters. Electrically Charged Filter Material. Introduction. Basic mechanisms of action. Classification of material. The importance of electric charge configuration. Measurement of filter charge. Charge stability and the effect of storage on filter performance. Particle Capture by Electric Forces. Introduction. Capture by permanently charged fibres. Capture by image forces. Experimental observation of electrostatic capture. Augmentation of filtration efficiency by external electric fields. Augmentation of filtration efficiency by charging of particles. Particle Adhesion and Particle Bounce. Introduction. Adhesion forces between particles and fibres. Dynamics of impact. Effects of Loading. Introduction. Qualitative description of filter clogging. The influence of aerosol properties on clogging rate. Macroscopic theory of filter clogging. Airflow pattern and drag force acting on particle complexes. Theoretical description of clogging. Experimental observation of dendrite structure on a single fibre. Experimental observations on model and real fibrous filters. Fractal structure of particle deposits. Effect of loading with liquid aerosols. Time-dependent effects in filter clogging. The effect of dust loading on the performance of electrically charged filters. Filter Testing. Introduction. Pressure drop measurement. Area weight measurement. General problems of aerosol penetration measurement. Aerosol detectors. Testing with monodisperse aerosols. Size-selective testing with polydisperse aerosols. Non size selective testing with polydisperse aerosols. Testing of high efficiency filters. Tests with electrically charged aerosols. Worst possible case testing. Realistic prediction of filter performance. Standard filters. Conclusion. Index. 150 illus. approx.