Simulating the effect of external liquid agents in granular materials with EDEM API

Granular materials are found in many industrial processes such as mineral processing, powder metallurgy, pharmaceutical and chemical manufacturing. It is well known that the Discrete Element Method (DEM) can help understand and optimize these processes with simulation software, but what happens when there are other agents besides the granular material influencing the behavior of the particles?

In this blog post I would like to briefly explain and show how EDEM, through its Application Programming Interface (API), can model advanced interparticle phenomena coming from the appearance of a liquid or active ingredient. Two models are used to illustrate this capability:

WET COATING MODEL

The Wet Coating model is able to capture the transfer of volume from a coating agent to particles while updating the size of the coated particles to reflect the volume gained. The existence of liquid in the particle interactions is taken care of by a liquid bridge contact model. Essentially, the liquid content of the particles derived from the coating will have a direct effect on the liquid bridge forces during contacts. This means that the coating will not only modify the particle weight but also its interaction with other particles.

Applications that could benefit from such model would be tablet coating, seed coating or any process where a liquid is dropped into a granular material and absorbed. This model is not meant to handle scenarios where the particles are suspended in liquid; however, further modifications could be done to account for this complex phenomenon.

In this example video of a conical mixer there is a granular material and a coating agent being sprayed. It can be observed how the particles grow in size due to the volume transferred in the coating process. Furthermore, the coated particles tend to stick against each other due to the existence of a liquid bridge, a phenomena which can be seen in the animation: As the mixing process progresses, coated particles move inside the conical mixer but tend to maintain the contacts against each other.

AGGLOMERATION MODEL

The objective of this model is the formation of a cluster of certain particle types during an industrial process. Usually, applications like granulation in pharma, general mixing or some processes in the steel making plants could benefit from this code.

In this case, the model does not include the continuous addition of liquid or active ingredient to the simulation as in the previous one. Here, the user would need to assign “liquid” or active ingredient” as a starting particle property and place the different particle materials in the simulation as required. This API code also allows to set a material to be “responsive” to agglomeration. This means that there can be a total of 3 material types: material with active ingredient to form the agglomerate, a material whose particles can stick to the “active ingredient” to also help create the cluster and finally one or more which are not responsive to any of aforementioned.

The main part of this contact model comes when there is an interaction between any combination of “active ingredient” materials or “responsive” materials with the exception of “responsive” vs “responsive”: The existence of “active ingredient” in the contacted particles creates an agglomeration force, which grows as the amount of “active ingredient” and “responsive” particles on the agglomerated cluster increases. To summarize, the user defines the amount of existing active ingredient as a starting condition which, together with the regular material flow, would determine how big the cluster can potentially be.

In this example there are 2 powder-like materials and one of them responds to agglomeration behavior. The user can specify the amount of liquid content in the agglomeration material which will affect the formation of clumps. The higher the liquid content, the easier it will be to create clumps. Furthermore, the bigger the clump, the bigger the attractive forces will be towards the agglomeration material particles.

As seen above, EDEM is capable of reproducing sticky particle behavior coming from advanced phenomenon found in real industrial processes. This allows our users to understand which parameters are affecting their applications related to wetting, coating or agglomeration – and how. These models are available to all EDEM users in the User Forum and can either be used straight away or be modified further to capture a wider range of behaviors related to particles with liquid components.

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