Simulating powders in EDEM with the Powders Starter Pack
Altair EmployeeOriginally published on the EDEM website July 19, 2018
Powders are at the core of numerous applications in the pharmaceutical, additive manufacturing, chemicals and other process manufacturing industries.
The Discrete Element Method (DEM) has proven to be a great predictive tool for simulating processes in the powder handling industry such as mixing, coating, drying and granulation. Powders have complex and variable characteristics and choosing the right parameters, appropriate DEM physics model and the appropriate experimental validation can be a challenge and a genuine barrier for researchers and engineers looking to simulate such material.
Left – Mixing free flowing powder. Right – Mixing cohesive poor flowing powder.
To help users overcome this obstacle we have developed the ‘Powders Starter Pack’, first introduced in EDEM 2018.2. The Powders Starter Pack is designed to be a useful starting point for anyone needing to simulate the complex nature of powders. It consists of a selection of 9 example material models focusing on small particle sizes and representing a range of materials with different flow properties and compressibility.
These models use the Edinburgh Elasto-Plastic Adhesion (EEPA) contact model which is particularly suited for complex cohesive materials such as fine dry powders.
How the models were developed
Firstly the Untapped Bulk Density and Static Angle of Repose (AOR) were calibrated. Using this test data the materials were categorised into free-flowing, fair flowing and poor flowing materials based on the AOR results.
Following this, the materials were subjected to a repeating tap test for tapped Bulk Density. Every 60 s the motion was paused for 2 s to allow the material to settle and the bulk density measurement was taken. When the Bulk Density variation between measurements was negligible the tapped density was recorded.
Compressibility of the material in the EEPA model is set via the Contact Plasticity Ratio. This was highlighted in a custom compression test where the material was compressed under a pressure of 3 MPa and the final material height recorded. In the images below the material from the untapped bulk density test is shown in its original state and after compression (left and right images respectively). Cases 1, 4 and 7 show the lowest change in sample height and this corresponds to the lowest Contact Plasticity Ratio. Samples 3, 6 and 8 show the highest levels of compression and have the highest contact plasticity ratios. Case 7 shows higher levels of compressibility than Case 1 due to the cohesive nature of the material restricting the initial packing.
The aim of the Powders Starter Pack is as an initial starter material for powder applications, the same tests can be run with varying material parameters for specific cases and material types, alternatively the same material can be fitted to different experimental tests for further calibration.
In this video you can visualize the difference in mixing free flowing powder and cohesive poor flowing powder. The video shows the differences in velocities and compressive forces on particles. It also shows the bottom view of both cases where particles are colored by position along Z direction so that you can see and compare the voids in material developed during mixing.
The Powders Starter Pack is a great resource for users simulating powder-related applications. Our objective is make DEM simulation more accessible to engineers and providing them with material models they can use immediately plays a key role in this. This is a great addition to our other popular resources, the GEMM database and the Soils Starter pack.