Influence of Vortex-Finder Diameter on Axial Gas Flow in Simple Cyclone

Several types of flow patterns in cyclones were found in recent publications. As a means for structuring the findings the publications were split up into two classes. Each class represented a certain feature of the axial velocity profile of the gas flow inside the cyclone. Class V represents cyclones with a maximum of the axial velocity at the vortex core of the cyclone, whereas Class W represents cyclones with an axial velocity profile that resembles an upside down W. This class has a local minimum of axial velocity at the vortex core or even displays backflow. The geometries of the cyclones belonging either to Class V or to Class W showed only small relative differences. It was assumed that the diameter of the vortex finder had a great influence on the class membership. This influence was simulated and measured for different basic geometries. The goal of this work was to develop the basics for reliable simulation results using the preprocessor GAMBIT and the finite volume CFD code FLUENT (which also serves as a postprocessor). Laser Doppler Anemometry (LDA) experiments were carried out on a laboratory scale cyclone to verify simulation results. In addition the results of cyclones which were investigated in previously published papers were used as a basis for developing a method of simulation, to validate numerical results and class membership. The prediction of pressure drop over the cyclone is overestimated by FLUENT (regarding the test cases). It was proven experimentally that downstream geometry (pipes etc.) has a great influence on flow profiles inside the cyclone. The axial flow profile can change dramatically if the pipes downstream the vortex finder are removed. A Class V cyclone displaying a maximum of axial velocity at the vortex core can change to a Class W cyclone with a minimum of axial velocity at the vortex core.