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Seventh International Conference on CFD in the Minerals and Process Industries
CSIRO, Melbourne, Australia
9-11 December 2009

SCREW CONVEYOR PERFORMANCE: COMPARISON OF
DISCRETE ELEMENT MODELLING WITH LABORATORY EXPERIMENTS
Philip J. OWEN and Paul W. CLEARY
CSIRO Mathematics, Informatics and Statistics, Clayton, Victoria 3168, AUSTRALIA
was first reported by Shimizu and Cundall (2001).They
examined the performance of horizontal and vertical
screw conveyors and compared their results with previous
work and empirical equations. Owen et al. (2003)
introduced the use of a periodic slice model to explore the
performance of a long screw conveyor. Cleary (2004)
used DEM to study draw down patterns from a hopper by
a 45° inclined screw conveyor. This work was extended
by Cleary(2007) to examine the effect of particle shape
on the draw down flow from the hopper and on the
transport characteristics of the screw conveyor.

ABSTRACT
Screw conveyors are used extensively in agriculture and
processing industries for elevating and/or transporting
bulk materials over short to medium distances. They are
very effective for conveying dry particulate solids, giving
goodcontrol over the throughput. Despite their apparent
simplicity, the transportation action is very complex and
designers have tended to rely heavily on empirical
performance data. In our previous work, we explored how
screw conveyor performance is affected by its operating
conditions (such as: the rotational speed of the screw, the
inclination of the screw conveyor, and its volumetric filllevel). In that work, the predicted mass flow rate was in
excellent agreement with experimentally measured values
for the horizontal and vertical configurations across the
full range of screw rotation rates. Although the throughput
predictions for the screw conveyor inclined at 30° and 60°
followed the same qualitative trend, there were moderate
differences between the DEM and experimentalresults. In
this paper, we use the Discrete Element Method (DEM) to
examine how variations of particle properties (such as:
particle shape, particle-particle and particle-wall friction)
influence the performance of the screw conveyor. The
primary focus of our study is comparing predicted mass
flow rates with experimentally measured values. The
secondary focus is to study how other performancemeasures (such as: particle speeds and power
consumption) vary due to changes in the properties of the
particles.

In our previous work, Owen and Cleary (2009), the
predicted mass flow rates for vertically and horizontally
inclined screw conveyors were in excellent agreement
with experimentally measured values. Although the
throughput predictions for the screw conveyor inclined at
30° and60° followed the correct qualitative trend, the
DEM and experimental mass flow rates differ by 16% and
24% respectively for these two inclinations. In this paper
we will use the Discrete Element Method (DEM) to
explore these differences by looking at variations of:
particle shape, particle–particle and particle–wall friction.
We will also study how other performance measures (such
as:particle speeds and power consumption) vary due to
changes in the properties of the particles.
MODEL DESCRIPTION
DEM simulation involves following the motion of every
particle and modelling each collision: inter-particle and
between the particles and their environment (e.g. the
internal surface of the screw casing and the surface of the
rotating screw). The boundary geometry is built using a
CADpackage and imported as a triangular surface mesh
into the DEM package. This provides unlimited flexibility
in specifying the three dimensional geometries with which
the particles interact. Here the particles are modelled as
spheres and super-quadrics. The DEM code used here is
described in more detail in Cleary (1998a&b, 2004).

INTRODUCTION
Screw conveyors are widely used for...