Thesis supervisor: Attila Egedy
co-supervisor: Zsolt Ulbert
Location of studies (in Hungarian): University of Pannonia Abbreviation of location of studies: FMIT
Description of the research topic:
The gas-solid two-phase flow is widely used process in many industrial applications. Its main feature that the interaction between the solid particles and gas phase can provide an extensive mass and heat transfer, good mixing of solids and ideal environment for gas-solid chemical reactions. The solid particles driven by fluid drag force and the inter-particle forces from their neighbor particles exhibit a complex flow patterns. The experimental studies of these systems require extensive work, the results obtained from experiments are usually incomplete due to the limitation of measurement technique and the difficulties of placement of scientific measurement inside the two-phase flow without changing its hydro-dynamical characteristics. The experiments, however, can be made easier by means of computer simulation.
The dynamical processes inside the two-phase flow are described as a branch of transport phenomena based on the well-known principles of conservation of mass, momentum and energy for each phase. The mathematical models proposed by authors apply mainly three theories classified by the treatment of the particulate phase. In the first theory both gas and particulate phase are assumed to form a continuum and we can define a finite volume into which some quantity such as mass, momentum or energy, is flowing in and out. These numerical methods are referred as Eulerian methods in the chemical engineering literature. In the Eulerian methods the gas and solid phase are described as interpenetrating continuum media. These models are also referred as two fluid models (TFM). They have been widely used for simulating the hydrodynamic of two-phase flows however they are unable to model the discrete particle dynamics and flow characteristics of individual particles.
The direct simulation methods (DSM) use CFD and moving unstructured mesh generated around the particles to calculate fluid flow field between the moving particles. The length scale of irregular meshes is significantly smaller than the particle size. The fluid exerts forces and torques on the particles and the motion of particles induces flow in the fluid by changing the positions of boundaries and the fluid velocity values at the boundaries. The forces acting on the particles are directly determined by the Navier-Stokes equations where the positions and velocities of particles act as the boundary conditions. The geometry of computation domain occupied by the fluid changes continuously due to particle motion. At each time step the finite element mesh is updated accordingly to the particle positions and the mesh velocities projected for the new mesh.
In the third type of models the gas phase also forms continuum, however, the discrete particles are considered as individual systems moving with their own velocity and constant mass. These approaches are usually called Eulerian-Lagrangian or Eulerian-discrete element methods. After the quick development in computer technology and parallel computing the discrete element method have become an important tool in modeling granular systems in the last decides and made it also possible to calculate gas-solid flows by Eulerian-Lagrangian type simulations which are accurate approach in the dynamic simulation of complex gas-solid flow problems. In discrete element method the motion of individual particles is described directly by Newton’s second law of motion accounting for interaction with other particles and gas phase. A number of attempts have been made to apply the DEM to particle system involving fluid-particle interactions. In these simulations the gas-solid flow is modeled by the coupled approach of discrete element method and calculation fluid dynamics (CFD). The gas flow is determined by solving the locally averaged form of Navier-Stokes equations which provides information for the calculation of fluid drag force acting on individual particles.
The goal of the PhD is to achieve new scientific results. The main tasks of the students are:
• literature overview about novel techniques, and multiphase flow modeling,
• model development in gas-solid two-phase flow modelling,
• model development in discrete element modelling of particulate phase (treatment of non-spherical particle collision, development of collision detection algorithm),
• development of numeric algorithm and computer programs for solving of mathematical models.
• application CFD theory and tools in modelling and simulation,
• development of programs for parallel computing,
• design of measuring system for model validation, carry out experiments,
• participation in scientific conferences, publication of research results in academic journals.
The supervisors have research experience in the field of computational fluid dynamic simulation in chemical engineering application. Gas-solid two phase flows have multiple application in the field, for example: VOC removing, fluidization etc. The Department of Process Engineering have multiple laboratory scale devices for the development of modeling techniques for these devices, with recently developed experimental methods and video processing validation techniques. The main task of the student to develop DEM and CFD models capable of desciring the processes of gas-fluid two phase flows.
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