This study was concerned with the most common reverse flow type of cyclones where
the flow enters the cyclone through a tangential inlet and leaves via an axial outlet
pipe at the top of the cyclone. Numerical computations of two different cyclones were
based on the so-called Stairmand cyclone. The difference in geometry between these
two cyclones was basically characterized by the geometrical swirl number Sg of 3.5
and 4.
Turbulent secondary flows inside a straight square channel have been studied numerically
by using Large Eddy Simulation (LES) in order to verify the implementation
process. Prandtl’s secondary motion calculated by LES shows satisfying agreement
with both, Direct Numerical Simulation (DNS) and experimental results.
Numerical calculations were carried out at various axial positions and at the apex
cone of a gas cyclone separator. Two different NS-solvers (a commercial one, and
a research code), based on a pressure correction algorithm of the SIMPLE method
have been applied to predict the flow behavior. The flow was assumed as unsteady,
incompressible and isothermal. A k − epsilon turbulence model has been applied first
using the commercial code to investigate the gas flow. Due to the nature of cyclone
flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced
turbulence models such as RSM (Reynolds Stress Model) and LES (Large
Eddy Simulation) have been used as well. The RSM simulation was performed using
the commercial package CFX4.4, while for the LES calculations the research code
MISTRAL/PartFlow-3D code developed in our multiphase research group has been
applied utilizing the Smagorinsky model. It was found that the k − epsilon model cannot
predict flow phenomena inside the cyclone properly due to the strong curvature of
the streamlines. The RSM results are comparable with LES results in the area of
the apex cone plane. However, the application of the LES reveals qualitative agreement
with the experimental data, but requires higher computer capacity and longer
running times than RSM.
These calculations of the continuous phase flow were the basis for modeling the
behavior of the solid particles in the cyclone separator. Particle trajectories, pressure
drop and the cyclone separation efficiency have been studied in some detail.
This thesis is organized into five chapters. After an introduction and overview,
chapter 2 deals with continuous phase flow turbulence modeling including the governing
equations. The emphasis will be based on LES modelling. Furthermore, the
disperse phase motion is treated in chapter 3. In chapter 4, the validation process
of LES implementation with channel flow is presented. Moreover, prediction profiles
of the gas flow are presented and discussed. In addition, disperse phase flow results
are presented and discussed such as particle trajectories; pressure drop and cyclone
separation efficiency are also discussed. Chapter 5 summarizes and concludes the
thesis.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:18659 |
| Date | 24 January 2007 |
| Creators | Hanafy Shalaby, Hemdan |
| Contributors | Wozniak, Günter, Platzer, Bernd, Thévenin, Dominique, Technische Universität Chemnitz |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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