Granular Materials - Application and Project Examples

Granular materials and the associated processing processes are highly signifi cant to the economy and, at the same time, they are an exciting area of research in the simulation of complex fluids. In joint development projects with industry partners, it has been shown that besides the challenges already mentioned, the characterization of the granular materials is an essential component of predictive simulations. In the following you will find project examples for the most diverse applications:

 

Design of Granular Products and Processes with GRAIN

Simulation of Mixing Processes and Devices

The simulation of mixers represents the unique challenge of combining granular flows and rapidly moving mixing units, which produce enormous shear forces in a solid.

The GRAIN software module is able to simulate such processes, using realistic rotational speeds and material properties.

 

Project Example with EIRICH

Project partner: Maschinenfabrik Gustav Eirich GmbH & Co KG

 

Services:

  • Spatially resolved information for local
    • density
    • velocity
    • shear rate
    • pressure
    • strain
  • Virtual tests for
    • the design of the mixing machine
    • high scaling of the mixer
    • process conditions
Simulation von Mischvorgängen und -geräten
© ITWM

Simulation of a mixing process.

Simulation of Agitator Bead Mills

Mills play a critical role in the manufacturing processes of granular materials. After several years of joint research in the simulation of granular media single phase granular flow processes – or those that can be considered as a simplified single phase – are now manageable as a simulation. The next challenge is the simulation of multi-phase flows with at least one granular or powdery phase.

Of these, the simulation of the flow in bead mills presents a special challenge. The calculation of complex flows within a simulation links several areas of current research:

  • Two-phase suspension flows of powder and water, modeled as a non-Newtonian fluid
  • a third phase modeled as granular beads, fast moving components
  • and a fourth phase of the surrounding air.

The modeling and numerical difficulties that this presents are huge. The interaction of four, full resolution, spatial and temporal phases must be modeled, not only among themselves but also with the fast moving components. The resulting phase-specific requirements for the numerical simulation process are met with an extended time-step control.

The FLUID component, a multiphase, non-Newtonian model together with a third Newtonian phase, was combined here for the first time with the GRAIN component – for the simulation of the mixing beads in such a complex problem. In collaboration with the project partners, subsequent simulation results were successfully compared with available measurements.

 

Project example with KRONOS:

Project partner: KRONOS INTERNATIONAL, INC.

Task: Simulation of the flow of a TiO2 suspension by granular agitator balls in a vertically rotating disk mill.

 

Services

  • Dynamic calculation of local variables
    • density distribution of the suspension and agitator balls
    • velocity fields
    • pressure distribution
    • shear forces and power loss in all phases
  • Virtual tests of the performance of the mill in relation to:
    • local load and local power loss to characterize the grinding performance
    • local shear forces on the plates and cylinder walls to show the abrasive wear
Simulation Mühle
© ITWM

The real mill is fully resolved both in space and time. The plots allow a view and evaluation of the flow behavior of all phases in the whole mill and locally.

Zoom Simulation Mühle
© ITWM

The arrows show the flow of TiO2 suspension, while the pseudocolor plots shows the density of beads simulated as a granular material.

KRONOS-Rührwerkskugelmühle
© KRONOS

KRONOS bead mill

Simulation of Silos

Based on our unique model for the flow of granular filling materials, we are able to simulate the influence of the material, the installations, the fixtures and the silodesign itself on the flow field in a silo within our GRAIN software.

In particular, GRAIN is able to simulate silo-specific behavior such as core shooting and to calculate the residence time of a silo.

In contrast to DEM simulations, we are able to take into account silos with industrial size and realistic particle size, thereby obtaining calculation times that are comparable to complex CFD simulations.

 

Project Examples with the University of Kaiserslautern

Project partner: Chair of Mechanical Process Engineering (MVT)

Task: Simulation of the residence time of a recycling process in a silo with conical installation.

 

Services:

  • 3d simulation with spatial resolution of streams in silo and silo mixers with local information about:
    • density
    • velocity
    • pressure
    • strain
  • Virtual tests and evaluation of
    • residence time distribution
    • flow pattern
    • flow path for arbitrarily placed viewers and markers

 

Strömungsbild innerhalb eines Silos
© ITWM

Flow image inside a silo.

Verweilzeit
© ITWM

Distribution of the residence time.

Lufteinlassgeschwindigkeit
© ITWM

Time profile of the granules in the pipe cross-section in a simulation with CoRheoS GRAIN.

Pneumatic transport - the transport of granular material through a pipe by a gas flow - is a commonly used and product gentle way of transporting granular materials. However, it requires a careful and materialspecific process design because under certain circumstances bad flow conditions or - even worse - a blockade of the pipe occur.

With the software module GRAIN a complete tool for the process design support is in development. It helps the engineer to consider material and system specific  conditions for the adjustment of the flow boundary conditions (material and gas flow).

 

Project Example TU Munich, Department of Process Engineering of Disperse Systems:

Results:
Spatially resolved information of

  • local gas and granular velocity
  • pressure drop of gas phase
  • local porosity of the granular material
  • mass flow of granular material