21-Sep-2010

Model solution for powder tests

Abstract

Despite their widespread use, powders have complex and variable characteristics that are not well understood. New and improved computerised models are changing this, says DEM Solutions

Despite their widespread use, powders have complex and variable characteristics that are not well understood. New and improved computerised models are changing this, says DEM Solutions

Powder handling and processing have always presented unique challenges to industry because of the variable physical characteristics and flow properties of powders. This is particularly true in the pharmaceutical sector, where powders play a major role in r&d and in production operations.

A greater understanding of powder characteristics was recently acquired following work using a rheometer alongside predictive modelling software at the research-based multi-national, Pfizer.

Dr Rahul Bharadwaj, a senior scientist with Pfizer at the r&d facility in Groton, Connecticut, is part of the company’s predictive drug product design group and is responsible for the design and implementation of computational tools for predicting material characteristics. His group routinely uses DEM Solutions’ EDEM software to model and predict the behaviour and flow properties of powders used in Pfizer products.

EDEM allows users to visualise and analyse particle kinematics as they design, test, and optimise their equipment and processes. Dr Bharadwaj’s group has found it to be a helpful tool in predicting powder performance and uses it in various studies to simulate the behaviour of powder and tablets during various processing and transport operations.

A thorough, physics-based understanding of the material testing tools commonly employed in powder characterisation can improve the company’s ability to meet challenges it faces in predicting and controlling powder handling and processing operations during pharmaceutical manufacture.

Dr Bharadwaj undertook an evaluation of a powder rheometer used to characterise powder flowability.

The rheometer is a small, self-contained, rotational shear device that forces a twisted blade along a helical path through a powder sample, while recording physical data related to the sample flow rate and flow pattern.

Dr Bharadwaj needed a better understanding of the principles behind the operation of the powder rheometer. The software was able to simulate the operation of the rheometer and the resulting particle flow provided the ideal tool to study the dynamics of powder flow inside it.

EDEM simulations were carried out to model particle flow in the virtual powder rheometer and to examine the effects of various model input para-meters, such as particle shape, size and size distribution, on the force and torque exerted on the rheometer blade. The model output was compared with the values recorded during operation of the actual rheometer as it evaluated a material of known properties under similar conditions.

By comparing the results of the physical experiment with the EDEM simulation, Dr Bharadwaj was able to gain insight into the physical interactions of particles as they flowed in the rheometer.

‘EDEM has improved our understanding in the working of the rheo-meter, which helps us understand its utility as a tool in powder characterisation,’ says Dr Bharadwaj.

Pfizer is also using the software to study the flow of powders in shear cells and hoppers, and has plans to use the programme to model other pharma-ceutical related processes such as tablet compaction, powder mixing and blending, and the functionality of solid dose delivery methods, such as dry powder inhalers.

EDEM software upgrade

DEM Solutions has released EDEM 2.1, the latest version of its software used to simulate and optimise bulk material handling and processing operations. The upgraded version is supplied with many new integrated contact models and the flexibility to customise advanced physics and particle properties.
The software now includes an improved user interface and an optimised fluid dynamics coupling module for Fluent, a new dynamics coupling option.
For users working in manufacturing where tablets can be damaged during mixing and transportation, EDEM 2.1 integrates load-limited particle bonding and has the ability to visualise intact and broken bonds, post process and export bond data.
For users looking to expand into new areas with more complex particle properties, the EDEM extended API enables customisation of particle contact and body force models and provides full data-save and post-processing of user-defined particle attributes. In processes such as coating, for example, cohesion can be applied to each particle and set to change over time or due to interactions with other materials. These custom properties could then show regions of non-
uniform coating or variable cohesion between particles within the coating drum.
EDEM is said to be the first commercial DEM application to couple directly with CFD software, allowing users to simulate particle-fluid systems in applications such as dense-phase conveying, filtration, drying, particle agglomeration and clumping, fluidised flow, solid-liquid mixing, and spray coating.
The software uses a surface mesh to represent the geometric boundary, which enables a one-to-one coupling with the boundary surface elements of the Fluent fluid volume.

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