Our Simulation Insights for Engineers series shows the many ways Rocky helps engineers and product designers. This blog post highlights examples of Rocky DEM simulations of coating processes, used to develop insight needed to improve efficiency and product quality.

Did you know the flavors on potato chips or colors on Skittles candies are produced with a layer of coating? Simulation of the coating process has historically used mechanistic models, and today, Discrete Element Method (DEM) complements experimental methods. In addition, Integrating Rocky DEM with other simulation software, including a CFD-DEM optimization, has created a platform to simulate many aspects of coating processes.

By providing enhanced process understanding and detailed insight into the micro-environments of coating equipment, Rocky DEM simulation is helping engineers improve their manufacturing equipment and processes in many ways. Determining how homogenous the coating is on each piece of the product, assessing coating differences among pieces, preventing erosion, reducing breakage, ensuring product quality and uniformity, and improving equipment performance: all these design and engineering tasks are easier and faster with help from Rocky DEM.

It turns out that there are a few capabilities that can help simulate particle coating processes:

• Represent the real shape of the particle.
• Include a large number of particles to represent the real process at the right scale as much as possible.
• Run any simulation and model the engineering problem within reasonable computational efficiency.

Pharmaceutical applications

Developing new medicine is expensive and time consuming, so pharmaceutical companies need to optimize their time and resources. Also, with today’s strong regulation on the part of national governments, the product approval process in the pharmaceutical industry presents additional challenges.

Rocky DEM simulations are also helpful in the drug manufacturing process by capturing dynamic interactions among processes, geometry, and materials. With Rocky’s help, pharmaceutical companies can make quick decisions on certain formulations and process parameters. Engineers can evaluate scale-up issues and equipment design changes, and they can troubleshoot problems that may arise in their coating equipment and processes.

For example, to learn how tablet mixing affects spray coating, a research team at Purdue used Rocky’s polyhedral elements to model tablets in different-sized coating pans. The exposure time of each tablet’s surface area was determined via a simulated spray. Powerful GPU processing reduced the time needed to perform the simulation. Researchers learned that agitating the tablets before the spray zone could improve the coverage of the coating.

Rocky DEM was our tool of choice, with its capability to model tablet shapes using polyhedral elements that accurately predict real-world particle behavior. Traditional DEM software uses bonded-sphere elements, which can produce artificial roughness that significantly affects the accuracy of tablet dynamics simulation.

Carl Wassgren, Professor, School of Mechanical Engineering and Department of Industrial and Physical Pharmacy / Director, Center for Particulate Products and Processes – Purdue University

With Rocky’s polyhedral shape representation, designers can import custom shapes to accurately represent the tablets they’re modeling. In the video below, approximately 250,000 polyhedral particles with 222 vertices are simulated in a commercial-scale tablet coater. In addition, Rocky’s postprocessing capabilities allow engineers to look at critical process output parameters to help with risk mitigation.

Rocky can also be coupled with Ansys Fluent to study the drying process in a tablet coater. In the example below, the coating was heated and allowed to dry via convection from a hot air stream, and the solute in the coating liquid was deposited onto the tablet surface. Afterward, the particle temperature was increased again until thermal equilibrium with the hot air was achieved. Finally, by measuring the final particle mass variability, coating homogeneity was assessed.

The ability of Rocky DEM to handle true particle shape, combined with the native support for multi-GPU, has enabled Bayer to model full-scale equipment and processes, providing details from particle level through innovative intra-particle collision statistics functionality, up to the whole system. This allows Bayer to simultaneously optimize both its coating-process efficiency and product quality.

Dr. Rakulan Sivanesapillai, Modeling Formation Processes Expert – Bayer AG

Food applications

In the food processing industry, insights are needed to ensure that products such as potato chips, nuts, and candy can be coated uniformly and effectively while minimizing product breakage and loss. By modeling real-scale equipment, engineers can accurately predict dynamic bulk and particle behavior.

Rocky DEM can model liquid-film-spray injection and drying to evaluate coating variability and predict breakage, all while accounting for liquid-bridge adhesion forces. Simulations can be done using custom polyhedral particles that model coating processes while eliminating artificially bumpy surfaces that can significantly affect particle dynamics. Equipment can then be designed to reduce breakage and waste and to improve the homogeneity of the coating coverage.

For example, Rocky DEM coupled with Ansys Fluent can use liquid film and bridge models and heat and mass transfer to accurately simulate the coating of candy pieces. This model considers the effects of liquid on particles’ surfaces and the liquid’s impact on particle interaction, such as collision damping and shear forces and adhesion. Rheological behavior and percolation phenomena can also be simulated.

For information on how Rocky DEM can help improve your coating processes, contact us today.