Vybrané aplikace modelování procesů mísení pomocí DEM simulací

Abstract

The dissertation presents a methodology of numerical modelling in field of homogenization processes. The topic of homogenization of particulate materials is focused to description of blending equipment, mixing mechanisms, methods of mixture homogeneity evaluation and characterization of powders. In addition, the discrete element method which is frequently used in R&D and industry is described within the overview of the present state of the art. Two points of view are linked in the thesis: 1) blending of bulk solids which mankind has been dealing with it since time immemorial and 2) a modern simulation method which has been outgrow in recent decades, thanks to the computer technologies development. After the introduction, the second chapter summarizes the field of blending of particulates by mechanical principles and all its troubles that can occur in this complex process. An important part of this chapter is a description of mixture quality. Many ways of homogeneity determination exist in the literature and therefore it is appropriate to summarize and evaluate the usability of the most commonly used ones. There are also discussed methods of sampling which can have a major influence on the perception of the degree of homogeneity of the mixture. The third chapter deals with a general description of the discrete element method. It contains a brief history, the basic principles of the method, the possibilities of utilization, advantages, current limits as well as description of using in the design and optimization of equipment. There are also defined basic contact models based on algorithms of calculations in simulation of particle systems including a description of basic mathematical relations. The chapter ends with a summary of the current limits of the discrete element method. In the practical and experimental part of the dissertation thesis the general way of calibration of virtual particle materials is described. Different particulates have been selected and defined for use in a subsequent study of blending in a rotary drum. In the fifth chapter a set of calibration experiments are performed and described which lead to the determination and optimization of input parameter values for DEM. The experimental study examines the effects of particle size, shape and density, drum filling percentage, rotational drum speed and drum filling pattern. 126 different operating conditions have been defined by a combination of materials, filling percentage, rotational speed and filling pattern. The study of the industrial blender presents the usability of DEM in industrial processes, including the approach and methodology. Generally procedures as in the experimental part of the dissertation have been applied but they have been adapted to the solved industrial application of homogenization of fine cohesive powders in a volume of 300 litres. The main contribution of the dissertation thesis is a comprehensive description of the process of making DEM simulations for different types of materials in application to homogenization equipment. Different ways of calibration and validation experimental methods are discussed, which lead to the understanding of individual processes and the reliability of simulation models that have become very complex in recent years.