Cyclone separators have existed since the 1800s and are still widely used in many industries to separate particles from gases. Although cyclones are geometrically simple, the physics describing the flow and separation processes which occur in them is complex. Over the decades many researchers have studied these devices and have developed a number of theories and empirical models for design purposes. In practice, most cyclones are designed using some type of empirical information. Physical prototypes are then built, tested and tuned until an acceptable level of performance is obtained. Recent advancements in numerical methods and in the performance capabilities of moderately priced computers have opened the possibility of developing computer-based methods, which are not primarily based on empirical models that can be effectively used for cyclone design. Cyclone flows are characterized by high swirl and stream wise curvature. This paper presents a description of the numerical models that can be used to calculate the performance of cyclones including the gas flow and the particle tracking processes.
A commercially available computational fluid dynamics (CFD) computer program using these numerical models was used to calculate the performance of a cyclone at several operating points. The calculated performance was then compared to experimental data. One of the characteristics of the separation process which was observed was the short circuiting of particles. This short circuiting allowed some particles to leave the system shortly after they were injected. The phenomenon of particle re-entrainment from the dust bin, which reduces the effectiveness of the cyclone, was also observed in the calculated results.
As a result of the work done in this study, a computer-based cyclone separator design methodology is presented. The methodology is believed to be unique in that it takes advantage of the cyclone design knowledge which has been gained over the years of research by others as well as current state-of-the-art numerical methods. The existing knowledge is used to provide quick starting geometry at the beginning of a new design process when no other information is available. This knowledge is presented in the form of cyclone performance and sizing correlations. Also, to aid in the design process, guidelines have been assembled from the literature, which help the designer decide which types of geometry changes should be considered to affect the performance characteristics with which he is most concerned. The heart of the methodology is a CFD-based approach that provides detailed cyclone performance calculations. This methodology provides the potential to produce cyclone designs with the required performance characteristics more quickly and more economically than older methods which use empirical and experimental design approaches exclusively.