Investigation and simulation of a cross-flow air classifier

Extensive experimental tests and a computational study of the performance i n a cross-flow air classifier have been carried out. A computational fluid dynamics (CFD) package-Fluent-is used to first understand and explain why t he cuts or the sharpness of cut of this classifier are not as sharp as they ought to be, and then to optimize the geometry and operational conditions. Flow fields of the classifier under various set-up conditions and geometry were measured by using laser Doppler anemometry (LDA). Using sieve analyses and the HELOS-laser method, the patterns of behaviour of separation parame ters such as cut size and sharpness of cut have been investigated at differ ent boundary conditions. Using the Fluent package, a two-dimensional computational fluid dynamics mo del has been developed. The model is based on the Euler-Lagrangian approach . Different turbulence models have been tested. Both Fluent 4.5, with a str uctured grid, and Fluent 5.1, with structured and unstructured grids, have been used. Discussions and analyses of the experimental, as well as the computational results, are presented. The simulation with a structured grid shows good ag reement with experimental data, except for the sharpness of cut. The reason s of poor performance of the classifier have been found. The geometry is op timized and other conditions were also improved. The performance of the cla ssifier is improved. The experimental observations together with the comput ed results should increase the depth of understanding of the underlying mec hanisms. (C) 2001 Elsevier Science B.V. All rights reserved.