Prediction of Turbo Air Classifier Cut Size Based on Particle Trajectory

Abstract

As a mainstream dynamic dry classifer, the turbo air classifier is widely used in powder preparation industries for its adjustable cut size, controllable product granularity and high classification performance. As an important indicator for evaluating the classification performance of a turbo air classifier, cut size is often predicted in advance to evaluate classification effect so that the operation parameters can be adjusted suitably according to the production requirement. There are two common ways to obtain cut size of turbo air classifiers. One is based on a theoretical formula; another is based on an experimentally derived formula. There are a few problems with the aforementioned ways of predicting cut size. The theoretical analysis often has some large deviations from the actual values. Analysis based on empirical formula can obtain an accurate predicted cut size at the cost of a large number of training samples. In this paper, a new strategy is introduced to determine the cut size based on numerical simulation of gas-solid two-phase flow in the turbo air classifier using ANSYS® CFX, Release 15.0. The three-dimensional Reynolds-averaged Navier-Stokes equations along with the k-ε turbulence model are adopted to describe the gas flow, and the Lagrangian particle tracking technique is used to calculate the particle trajectory. According to its definition, cut size can be obtained by means of analyzing the particle trajectory. The effects of rotor cage rotational speed and particle density on cut size are also obtained based on analysis of the change of cut size. The simulation results are validated against the experimental data. Numerical simulation provides a new way to obtain the cut size of a turbo air classifier and serves as a method to regulate the operating parameters for classification. It also provides a reference method to study the cut size of various types of classifier.