February 12th, 2018
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A simple definition of a granular material is a conglomeration of distinct macroscopic solid particles, such as sand, nuts, coal, rice, coffee, grain, or corn.
With a multitude of industrial applications, a granular analysis is important because it is rooted in classical analysis methods. However, granular materials are considered as a new material form, different from solids, liquids, and gases. The motion of the particle follows Newton’s equations, where repulsive forces between particles are non-zero only when there is a contact between particles. 
The granular material must be large enough to avoid thermal motion fluctuations. Conventionally, the lower size limit of the granular material is about 1 µm. Powders are a special class of granular material due to their small particle size, which makes them more cohesive and more easily suspended in a gas.
Particle modeling considers the static and dynamic behavior of different types of granular materials. Depending on the industrial process that is to be analyzed, one can simulate the transport of a discrete phase within an incompressible fluid flow or the simple moving and separating process, like in a screw conveyor or a mill. Particle analyses can help engineers to design the particle equipment profile, as well as accelerate and drive the particle process efficiently.
Generally, two modeling methods for particle flow can be applied: the discrete element method (DEM) for industrial bulk solids systems and the discrete phase model (DPM) for the transport of a discrete phase within an incompressible fluid flow simulation.
Both DEM and DFM are used in a wide range of industries, including mining, metals processing, pharmaceuticals, construction and agricultural machinery, food and consumer goods, and chemical processing. Both methods are used to simulate and analyze the performance of bulk particle handling and processing equipment—from powders and granules to ore, grains, tablets, fibers, and more.
Process modeling of industrial bulk solids systems presents a challenging opportunity with regards to understanding the underlying physics, scaling lab-scale models, obtaining detailed large-scale data and balancing computational simplicity with the required rigor to accurately predict the actual behavior.
Moreover, due to market globalization and related efficiency reasons, the design and development process of bulk material handling equipment is often characterized by a fast construction phase, where the major risk is an improper design. Furthermore, the process of designing special production equipment like large conveyor plants cannot be standardized.
The use of discrete element simulation in the field of bulk solids handling equipment provides many possibilities for the optimization of the design and the operating conditions, as well as insights into the wear characteristics. 
In the vast majority of natural or industrial processes concerning granular materials, a secondary fluid phase—such as air —is present, and its effects, like fluidization (aeration of particles by gas injection), play an important role. 
The main benefit particle analyses offer engineers is related to improving the understanding the system and enabling virtual prototypes of bulk solids handling and processing equipment. Virtual prototypes can help optimize material usage and troubleshoot difficult particle processes.
You can find several particle analyses in the SimScale Public Projects Library that can be used as free templates for any community member.
One of the most recent simulations created in the Public Projects Library is a “particle analysis of a mill profile”.
The objective of this project was to find a better profile for the mill, in order to produce specific acceleration characteristics for the particles. The CAD model contains the geometry of the mixing mill (solid part) and the volume where the particles are inserted by the filling algorithm. A mesh is not needed for this analysis type. The outer shape of the mill geometry is extracted automatically and used as a boundary for the particles.
The filling is done at the beginning of the computation. In this case, half of a cylinder geometry is used. At the beginning of the simulation, the particles fall to the ground because of the gravitational load. The mill does not move at that time (t<0.5s). After the particles come to a rest, the acceleration process is started. The mill is accelerated constantly so that the angular velocity (rad) is proportional to the time. The angular velocity can be adjusted either via a formula or a table value. For industrial applications, it is important that the particles inside the mill slide from the top to the bottom part during the mill rotational movement and do not fly around causing damage or fracture. This particle simulation can help the engineers to design the mill profile, as well as accelerate and drive the mill efficiently.
The main purpose of this analysis was to study the impact of the blade shapes for different mixing mills. 
Another very interesting project from SimScale shows how to simulate a particle fluid flow through a cyclone separator .
To discover all the simulation features provided by SimScale, download the document below.
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