Particle Dynamics in Fluidized Beds
The dynamics of particulate multiphase flows within fluidized beds is highly complex and directly affects the properties and quality of the powdery products in pharmaceutical, food and fertilizer industry. Estimating the particle velocity and associated solid mass fraction were in focus of the first funding period of NaWiTec research. Optical measurement devices, such as optical fiber probe technique and Particle Image Velocimetry have been applied in order to obtain information concerning the bed expansion, particle load or particle distribution within the bed, which can be used to derive further system parameters. Fig.1 shows the facilities which have been used for the experimental analysis. However, the investigations have been limited to mono-disperse particle systems. It has been shown, that insight concerning particle flow properties gained for a quasi 2D fluidized bed can be transferred to describe real particle behavior in 3D fluidized beds.

      (a)                                                                                         (b)
Figure 1: (a) flat, transparent fluidized bed with high speed camera system and (b) cylindrical fluidized bed with indications for measurement positions of the fiber optical probe

In continuation of the successful work of the first funding period, where parameters for macroscopic modeling of the granulation process have been obtained, we focus on three new subjects in the second funding period.
  1. Now, we investigate poly-disperse particle systems, where particles may vary in size, shape and viscous behavior. Analyzing the influence of these property variations on the particle dynamics, yields further insight and fosters the understanding of real phenomena, like inhomogeneous particle growth in granulation and agglomeration. Real particle size and shape distributions, which correspond to defined granulation progresses, are provided by the research topic „Formulation of structure particles in fluidized beds“. Considering variable viscous behavior of the particles, as found for example in the glass transition process, is a completely new aspect within the research of NaWiTec. Here, we want to provide experimental data for the particle dynamics, which are relevant for granulation processes in the food industry.
  2. Adaptions of the apparatus are inherently linked to changes within the particle systems. Real particle size and shape distributions may result in particle segregation, which has to be avoided by evaluating and applying innovative fluidization concepts. Moreover, improved geometrical configurations of the apparatuses or atomizer location can be considered in order to realize optimal process conditions (ideal particle dynamics with adjustable particle residence times in spray and drying zones). The effects attributed to glass transition are even more complex and may lead to total collapse of the bed in case of particle clumping. Obviously, this case has tremendous consequences in real application and has to be avoided. The viscous behavior can be influenced by humidity and temperature. Here, we evaluate the potential of control concepts in order to ensure best process conditions.
  3. The application of alternative measurement devices and the optimization of available techniques are also in focus of the research topic. In particular, optical measurement techniques like Particle Tracking Velocimetry (PTV) should be tested and applied for individual recognition of particles and their local properties in different fluidized bed configurations. Furthermore, the estimation of particle rotation, which is a more complex dynamic property, has to be realized. This directly leads to improved modeling approaches with more realistic description of particle motion and its effect on the product quality.
Complementary to the experimental work, coupled flow and particle simulations are carried out. They yield information for micro processes and provide data concerning the collision frequency and energy of particle-particle, particle-wall and particle-droplet contacts. This information is essential for the research topic “Modeling of particle formation”, which is concerned with macroscopic modeling approaches incorporating detailed descriptions of micro processes.
On the other hand, wetting and agglomeration efficiency can be derived from the simulations.
Particle and fluid flow are simulated using numerical tools, in order to approximate these system parameters. Beside commercial software, such as ANSYS Fluent (flow simulation) and EDEM (particle modeling), open source codes should be used in the second funding period of NaWiTec.
Open source codes enable almost unlimited parallel computation which is required for large scale processes with realistic particle numbers of several million particles. The flow and particle simulations are coupled using a two-fluid approach (Eulerian-Eulerian). Therefore, the two phases (gas and particles) may exchange momentum and energy. Fig. 2 shows simulation results for a fluidized bed in top-spray configuration, including the atomizer in the upper area. More information can be obtained from the video, which can be found at the end of this page. 

         (a)                                                                        (b)
Figure 2: Coupled CFD-DEM simulations of (a) fluidized bed top-spray process and (b) droplets distribution of the two component nozzle

The research project is funded by the German Federal Ministry of Science and Education (BMBF) as part of the InnoProfile-Transfer project "Unternehmen Region".


M.Sc. Zhaochen Jiang
University Course Drying 2020
30.03.2020 - 02.04.2020 in Magdeburg
University Course Fluidization Technology 2019
04.11.2019 - 07.11.2019 in Hamburg
Award for Maciej Jaskulski
Cluster WIGRATEC enters the next round
Arun S. Mujumdar Medal for Prof. E. Tsotsas
Award for best oral presentation
Award for best oral presentation for Christoph Neugebauer on Population Balance Modeling Conference 2018
Faculty Prize 2018
Award for Prof. E. Tsotsas
Honorary Professorship of UCTM, Sofia, for Prof. Tsotsas
University Course Drying 2018
19. March -- 22. March 2018 in Magdeburg
University Course Fluidization Technology 2017
6. - 9. November 2017 in Hamburg
Award on Conference
Best Research Award for Sayali Zarekar on IDS in Gifu, Japan
Award on Conference
Best Poster Award for Christian Rieck at PARTEC 2016 in Nuremberg, Germany
Award on Conference
Best poster award for Vesselin Idakiev at national conference
Award on Conference
Best Presentation Awards on Nordic Baltic Drying Conference 2015
ECCE 2015
27. September - 01. October 2015 in Nice, France
Granulation Workshop 2015
1st July - 3rd July 2015 in Sheffield, UK
University Course Drying 2016
29. March -- 01. April 2016 in Magdeburg
Extension of the Research Training Group 1554
Extension of the funding period for 4.5 years
Award on annual conference
Award for best poster presentation goes to Maryam Dadkhah
Modern Drying Technology Vol. 3
Prof. E. Tsotsas in CES Top 20 Reviewer 2010
Award on Asia Pacific Drying Conference
VDI Ehrenring für Jun.-Prof. Mirko Peglow
University Course Drying 2014
Fundamentals and Applications of Drying Technology