3R37. Gas Cyclones and Swirl Tubes: Principles, Design and Operation. - AC Hoffmann (Dept of Phys, Univ of Bergen, Allegaten 55, Bergen, 5007, Norway) and LE Stein (Process Eng Consultant, Mechanical Separations, 5818 Autumn Forest Dr, Houston TX 77092). Springer-Verlag, Berlin. 2002. 334 pp. ISBN 3-540-43326-0. $139.00
Reviewed by P Bradshaw (Dept of Mech Eng, Stanford Univ, 488 Escondido Mall, Bldg 500/Room 501C, Stanford CA 94305).
Cyclones, in this context, are devices for separating two phases in a fluid flow. These are the familiar inverted cones seen in dust-extraction systems, without which many a flour mill or carpenters’ shop would be wrecked by a dust explosion. They appear in many other places, such as the catalytic cracking units that are at the heart of an oil refinery. Their design is not trivial.
At the start of Chapter 15, the authors endearingly confess, “The modeling equations in the previous chapters are not enough to design a cyclone or swirl tube from scratch.” They proceed to review practical details, “To give a feel for the range of ‘viable’ designs.” This is an engineer’s book, but not an old-fashioned handbook. Nearly half the eighty-odd references are less than ten years old, and only eight are from 1960 or before—mainly classical papers or books cited out of piety rather than as recommended reading. The authors’ aim, stated in the Preface, is “to present a long-overdue overview,” and they seem to have achieved it very well.
The book is, clearly, intended for design engineers in industry, though college engineering departments could do worse than to make this book required reading as an introduction to real life.
The book begins with three chapters on basic ideas, including some of the mathematics of probability density functions for particle size. Then follow three chapters on modeling of the flow in a cyclone and its efficiency, and the inclusion of special effects such as wall roughness (eg, collected solids), the influence of mass-loading, and the spatial variation of particle-size pdf within the body of the cyclone. Here modeling means algebraic equations, based, of course, on the equations of motion for fluid and particles. There are, of course, unknowns in the equations, such as the skin-friction coefficient—and “wall friction has a profound effect on the flow in cyclones.” However, there are remarkably few data correlations or design charts.
The 13-page Chapter 7 is a respite from cyclone modeling. It is called Computational Fluid Dynamics, but is actually an excellent introduction to turbulence modeling, numerical simulations, and methods of calculating particle-laden flows. This reviewer fears it may be the cause of numerous violations of the Copyright Act by instructors seeking handouts. Current turbulence models are not very good at predicting swirling flows, so it will be some time before the simpler algebraic formulas of the first six chapters go out of use. The authors’ attitude is unbiased, and in earlier chapters, CFD results are compared with experimental data and the predictions of the simple formulas.
Chapter 8 is also tutorial, covering dimensional analysis and scaling laws. Most academic authors would have put it earlier, but although the formulas of the first six chapters have to be dimensionally correct, they do not for the most part contain dimensionless parameters.
Chapter 9 on Other Factors Influencing Performance (effect of solids loading and of the position near the narrow end where the vortex rolls up) is followed by a chapter on measurement techniques - as Chapters 11–16 deal with practical and specialized matters, this is the right place to discuss testing techniques. Incidentally, it was not until the advent of the laser Doppler anemometer that worthwhile measurements could be made within a cyclone, so a real understanding of the flow was only achieved fairly recently.
Most chapters have worked examples (not problems! this is not a textbook), which are very helpful in illuminating the formulas.
Gas Cyclones and Swirl Tubes: Principles, Design and Operation should be invaluable to designers and even operators of cyclones, and cyclones are so ubiquitous that its influence will be felt in many branches of industry. At $139.00, it is likely to be bought more by libraries and by design groups than by individuals, but anyone involved with cyclones in any way should read it.