Dynamics of Droplets

Abstract

1R36. Dynamics of Droplets. - A Frohn and N Roth (Inst fur Thermodynamik, Univ of Stuttgart, Pfaffenwaldring 31, Stuttgart, 70550, Germany). Springer-Verlag, Berlin. 2000. 292 pp. ISBN 3- 540-65887-4. $82.00.Reviewed by Y Chisti (Inst of Tech and Eng, Massey Univ, Private Bag 11 222, Palmerston N, New Zealand).Many natural and technical processes depend on generation of droplets and interaction among droplets and other phases. Droplet dynamics influence processes as diverse as cloud formation, rain, spray painting, and dispersal of aerosols. Because of its wide-ranging significance, substantial research literature has accumulated on droplet dynamics, but not many books treat this subject. This book provides a useful discussion of droplet dynamics in a compact volume. Some of the theoretical aspects relevant to drop dynamics are covered in an extensive first chapter. The major topics discussed include surface tension and internal pressure; liquid-liquid and solid-liquid interfaces; charged droplets; small-amplitude droplet oscillations; internal circulation; instability of droplets; instability of jets; relaxation phenomena; thermodynamics; phase transition processes; droplet evaporation; and interaction of light with droplets. Topics, such as internal circulation and how it is affected by droplet dimensions and the presence of surfactants, are addressed quite poorly despite the importance of these topics in many processing scenarios. A chapter is devoted to droplet generation. This subject is discussed in less depth than some of the other topics in the book. Much practical information exists on design, selection, and operation of spray nozzles and other droplet generation devices, but the book does not reflect this knowledge. Pressure atomizers, rotary atomizers, and ultrasonic atomizers are barely mentioned. A chapter entitled “Droplet systems” addresses topics such as sprays, streams and arrays of droplets, and single droplets suspended by various means. An extensive chapter deals with the relevant measurement techniques such as the photographic methods, techniques of measuring velocity and size, measurement of optical properties, temperature, and surface tension. Not all available methods are discussed sufficiently or thoroughly. In most practical droplet systems, droplets interact among themselves with the suspending gas and with the suspended solids. Methods for the study of such physical interactions in flow systems are devoted a chapter. Many droplet-related processes involve phase transitions. Examples are condensation of water vapor into clouds, evaporation of fuel droplets during combustion, and spray-drying of droplets to powders. Some of the experimental methods for study of phase transition in droplet systems are discussed in an extensive chapter devoted entirely to this subject. Combustion related phase transition phenomena are discussed in particular depth. Some of the applications of droplet dynamics are outlined briefly, perhaps superficially, in a chapter entitled “Miscellaneous applications.” The applications mentioned include everything from ink jet printing to gaining an understanding of development of condensation trails of high-flying aircraft. The book covers many topics, but also leaves out a great deal. Nevertheless, this book should prove useful to anyone working on droplet dynamics and related fields such as spray technology and aerosol science. The book’s emphasis on experimental methods is one of its strong points. The book cites more than 500 references and is illustrated with more than 200 figures of generally good quality. On the negative side, the writing is needlessly verbose and sometime irritatingly so. The book’s short index is not especially useful, but this shortcoming is partly compensated for by a detailed table of contents. The text is hardbound, of good quality, and is reasonably priced ($82.00) for a specialist monograph. Dynamics of Droplets is a recommended acquisition for research libraries and individuals working on droplet dynamics.