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Multiphase systems---Some current projects


 
 

Computational fluid dynamic (CFD) modelling of dense particle clouds and strands

Many important processes depend on the behaviour of dense particle clouds and strands. Such dense clouds and strands will behave quite differently to the way individual particles would in the same fluid. Numerical simulation of this is very difficult, demanding proper modelling of two-way coupling between fluid and particles, and of the particle-particle and particle-wall interaction.


We study this at different levels of detail:

  • Eulerian-Eulerian modelling, where the particles are treated as a pseudo fluid, interpenetrating and interacting with the carrier fluid. This is suitable for simulations of larger systems.
  • Eulerian-Lagrangian modelling, where each particle is treated as a point, and tracked in the flow field, using models for their interaction with the fluid and with other particles and containing walls
  • Direct numerical simulation, where the particles are large relative to the computational grid, so that the fluid flow equations can be solved around them, giving the forces acting on them directly.
In recent work we have extended the classical hard-sphere model to include adhesion and cohesion so that a collision may result in deposition on a wall or agglomeration of particles. This makes it possible to study a wealth of industrially relevant processes, e.g. for flow assurance, directly by Eulerian-Lagrangian simulations. Two articles about this are in print, one in Phys. Rev. E and one in Chem. Eng. Sci.
 

Animation of a particle collision using a standard hard-sphere collision model
 

Animation of the same particle collision using the modified hard-sphere collision model with cohesion, the Hamaker constant is high enough in this example to cause agglomeration

 

Contact information:
E-mail: Pawel Kosinski
E-mail: Alex Hoffmann


 
 

Fuel cells

In our fuel cell activities, sponsored by the NFR and carried out in collaboration with CMR Prototech AS, we are looking at the production and characterization of nano-particle-based raw materials for oxide fuel cell (SOFC) components and the formation and testing of cells from these raw materials.


Specifically we are

  • producing and characterizing a wide variety of nanoparticles by a new, patented, variant of the sol-gel process for use as precursor powders for SOFC components.
  • Producing and testing thin layers of controlled porosity from the nanoparticles to produce solid oxide fuel cells with improved efficiency, e.g. with electrophoretical deposition


 


Nanoparticles of yttrium-stabilized zirconia


 


SEM image of complete cell produced during the project


 

Contact information:
E-mail: Crina Suciu


 

 

Stochastic models for particle transport in fluidized beds

Most mathematical models in chemical engineering are deterministic, based on conservation equations. For a complex system such as the transport of particles in fluidized beds, this approach, however, often does not lead directly to a solvable model. In this study a new modeling approach, more consistent with the inherently random particle transport, based on Markov chains is used. There are many attractive features of this approach, for instance the models are easy to formulate based on physical ideas about the motion of a single particle, and they are computationally easy to handle with a matrix oriented package.


Although there is no project running in this field right now, this is a continuing interest in the group. Some of the things we have been looking at are:

  • Slugging fluidized beds, modeling the displacement of particles in the system as a result of the formation and rise of slugs.
  • Formulating models for the gas and particle flow in the regeneration vessel of the FCC process, investigating the effect on the performance of the unit of changing different operational and geometrical parameters.
  • Residence time distributions for particles or fluid elements in processes

Contact information:
E-mail: Alex C. Hoffmann


 
 

Cohesive particles and the buildup of plugs and deposits in process equipment and pipelines

Understanding the build-up of solid-particle deposits is crucial for the processing industry to avoid deposition and plugging by knowledge-based design. This study aims to observe and model the build-up of particle deposits in transport and processing equipment. Experimentally the build-up on solid surfaces is studied by micro-imaging of a surface exposed to a particle-laden flow. Theoretically CFD simulations, making use of the above-mentioned collision model, are carried out.


 


Particles deposited on a surface in a flow system


 

Contact information:
E-mail: Maryam Ghaffari

E-mail: Boris Balakin

E-mail: Alex Hoffmann


 

In another activity we look at the surface properties of hydrate particles in various environments using classical molecular dynamics (MD) simulations, and determine the forces between to opposing surfaces, to determine the cohesivity of the particles, and the most important factors influencing cohesivity.


 


Unit cell of type II hydrate containing propane


 

Contact information:
E-mail: Bjørn Sæthre


 
 

CFD simulation of particles for process safety applications

Some of our activities are carried out in collaboration with the group Process Safety. In the field of dust explosions the behaviour of dense particle clouds and strands needs to be modelled precisely to assess the danger of formation of explosive clouds and to model the progression of an explosions once it has been initiated.

In spite of the fast integration of CFD into academia and industry, many fundamental problems still need to be resolved, particularly in relation to multiphase systems. Simulations, that at first glance look plausible, may, in fact, have little to do with reality if the interaction between the phases is not properly modelled, and this may be critical when assessing the danger of accidents taking place.


 


Comparison of dust lifting from a smooth (top) and a rough (bottom) wall behind a passing shockwave


 

Contact information:
E-mail: Pawel Kosinski


 
 

Solid Separation from Highly Viscous Liquids by Cyclone Technology (CLEANSAND)

The aim of this project is to design innovative hydrocyclones to extend the use of hydrocyclone technology within the oil and gas exploration industries.

Two experimental techniques are being used, one is to test the separation efficiency of liquid cyclones on new types of particles and fluids and relate the results to know models for cyclone efficiency with the aim of designing cyclone-based separators for new and exotic applications. The other is the study the actual separation using the technique referred to as PEPT (positron emission particle tracking), where a radioactive particle is followed as it flows through the separator in a PET (positron emission tomography) camera.


 


Grade-efficiency curves obtained in a dedicated experimental rig, the size analyses required to generate these curves were carried out using a sedimentation-based technique, eliminating a number of potential errors arising when other sizing techniques are used.


 


Animation of tracer particle moving through a hydrocyclone measured using the PEPT technique. The size of the particle is exaggerated.


 

Contact information:
E-mail: Yu-Fen Chang

E-mail: Alex Hoffmann


 
 

Pneumatic conveying studied by PEPT

This is a large project carried out in collaboration with the University Hospital in Bergen and sponsored by the NFR to study the behaviour of particles in pneumatic conveying using PEPT.

The speed and quality of the newest PET technology installed in Bergen makes a very high spatial and temporal resolution possible in PEPT, such that fast processes can be studied.

In this project the behaviour of particles in pneumatic conveying tubes is studied using PEPT for the first time.


 


 
Particle tracer going through the test section of a pneumatic conveying model system. In this case the particle spirals through the test section, a variety of behaviours have been observed.


 

Contact information:
E-mail: Pawel Kosinski

E-mail: Boris Balakin

E-mail: Prachi Chhabra

E-mail: Alex Hoffmann


 
 

Numerical modelling of Pelton turbines

The project is carried out in collaboration with BKK. The aim is to model the working of Pelton turbines economically and precisely, gleaning on the information that is relevant to determine the efficiency of the turbine. The task is challenging, mainly due to the free jets impacting on solid surfaces in such turbines


 


 
Pelton turbine


 

Contact information:
E-mail: Jesper Tveit


 
 

Diffusion in micro- and nanopores

The project is in its start-up phase. The aim will be to investigate diffusion of gaseous species in networks of micro-and nanopores experimentally and theoretically. Applications are solid-catalysed reactions of gaseous species, e.g. in fuel cells.


 

Contact information:
E-mail: Stamatina Karakitsiou

E-mail: Crina Ilea

E-mail: Bodil Holst

E-mail: Alex Hoffmann


 
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