Particle residence time is an extremely important variable in a cyclonic dryer project. With the goal of obtaining a device that conduces to a long particle residence time, the influence of cyclone dimensions on particle residence time and on the type of flow is discussed here. The research was based on a device with a very high ratio of cyclone diameter to other dimensions. Simulations were developed with computational fluid dynamics techniques by the use of the commercial code CFX 4.4® of AEA Technology. Particles were treated individually. The fit of a turbulence model was also discussed. Theoretical and experimental results showed that the dimensions of the conical part of the cyclone had a very important influence on flow and consequently on particle residence time. The influences of volumetric concentration and particle diameter on particle residence time were also observed.