Simulation Analysis of Materials Motion in Rice Whitening Machine
Based on Discrete Element Theory
Weiwei Wu
1
, Jinglan Ruan
2
and Shuang Zhang
2
1
Guangdong Science & Technology Cooperation Center, 171 Lianxin Road, Guangdong, China
2
Henan University of Technology, Henan, China
Keywords: Rice Whitening Machine, Particle, Discrete Element, EDEM.
Abstract: Based on the Discrete Element Theory, this paper explores the dynamic variation process of the group
particle material system in the rice whitening machine through simulation analysis of the motion trail,
velocity, pressure and distribution of the material particle group in the working process with the help of
EDEM. The results indicate that the simulation analysis allows the real time observation of brown rice
motion status in the whitening chamber, including the streamlines, velocity and pressure vector, etc.; it also
generates the rule of how the particle and particle group velocity vary with time, and how the average
resultant force of the particle and particle group vary with time.
1 INTRODUCTION
Rice, as the traditional grain for Chinese residents,
its yield, processing volume and consumption in
China rank first in the world. The rice processing
industry has significant influence on the national
economy and people’s livelihood. In the rice
processing process, whitening is regarded as the
most important procedure, and the processing
properties of the rice whitening machine directly
affect the process effect of rice production. Experts
from both home and abroad have already made
researches on the rice whitening theory; however,
the complete theoretical system of rice whitening is
not yet established due to the complexity of the
mechanical physical interaction in the whitening
process, as most researches are qualitative and
quantitative analysis are relatively few. The long-
term production practice and theoretical studies
proved that the kinematic velocity and the pressured
status of the group particle material in the whitening
chamber are the key factors that affect the process
effect, and also the essence of the whitening theory.
Besides, the critical component affecting the
working performance of the rice whitening machine
is the whitening chamber. This paper has built a
parameterized model for the whitening chamber, and
made numerical simulation analysis for the motion
of group particle material in the whitening chamber
with the help of the simulation software EDEM to
explore the motion trail, velocity, pressure and
distribution of the material flow in the whitening
process, in order to provide theoretical foundation
for the design of rice whitening machine.
2 WORKING PRINCIPLE
Rice whitening machine is the kernel equipment for
rice processing with the task of wiping off the
surface layer of brown rice. To be specific, the
mechanical component in the whitening chamber
will continuously act on the materials to realize the
function of wiping off the bran through abrasive
action, frictional action, impacting, rolling, and axial
pushing, etc. Figure 1 shows the structure of vertical
emery roll whitening machine: the materials are
conveyed from the feeding hopper to the whitening
chamber by the screw iron roll; then with the
continuously impaction, compression and abrasive,
frictional action of the emery rolls, screens and the
huller blade, the materials are rolled by the high-
speed revolution of the emery rolls and the particles
are uniformly whitened. The post-whitening bran
powder will be collected and discharged by the bran
discharging system (Jinglan and Wenbin, 2017).
Figure 1: Structural diagram of the vertical emery-roll rice
whitening machine.
1 Feeding mechanism 2 Screw iron roll 3 Emery roller 4
Screen frame 5 Pressure gate 6 Bearing bracket 7 Bran
discharge hose 8 Spindle pulley 9 Frame 10 Encloser 11
Electrical motor 12 Pedestal
3 MODELING AND
SIMULATION ANALYSIS
Discrete Element Method (DEM) is an effective
numerical method developed for dealing with the
non-continuum mechanics in the particle flow
analysis. EDEM is the first simulation software in
the world specialized in the particle mechanics based
on DEM technology to provide a solution for the
particle system simulation and analysis in the
engineering field. With the help of EDEM, a
parameterized model of the particle system can be
built easily to study and explore the mechanical
property, material property and other physical
properties of the particles, and further control and
manage the information of each particle (e.g.
quality, temperature, velocity, etc.) and the force
acted on it. In recent years, the application scope of
EDEM is expanding with the development of the
technology and theory (Jie and Wenjun, 2014).
Since grain particle group is a kind of granular
mixtures, it is suitable for EDEM to be applied in the
research of food machinery.
3.1 Build Calculation Model for
Whitening Chamber
For the convenience of simulation calculation, the
whitening roller and screen are simplified and then
on this basis, the 3D solid model of the whitening
chamber is built for EDEM numerical simulation
analysis as shown in Figure 2. Sliding mesh
technique is used to divide the computational
domain into two parts -- the inside and the outside.
Figure 3 shows the simplified fluid region of the
whitening machine built by EDEM.
Figure 2: DEM calculation model.
Figure 3: Fluid region of rice whitening machine.
3.2 Build Calculation Model for Brown
Rice Particle
The object for the whitening process is the brown
rice. The aim of whitening is achieved through the
crashing, scrolling and rubbing between the brown
rice particles and the emery roller, screen and the
particles around to wipe off the surface layer. The
brown rice in China can be mainly divided into 3
categories: Japonica brown rice (short and thick),
Indica brown rice (long and thin) and sticky brown
rice. The related parameters of volume-weight,
density and particle size can be seen in Table 1.
As the shape of brown rice particle is similar to
an oval, a parameterized model is built by a pre-
EDEM processing software through the
accumulation of multi-spheres, i.e. using the particle
bonding method to build the DEM model for the
brown rice particle (Favier and Kremmer, 1999).
Table 1: Related parameters of brown rice particles.
Figure 4: Effect picture of DEM model for brown rice
particle.
3.3 Simulation Analysis
3.3.1 Selection of Contact Model and
Parameters Setting
Contact model is the basis for DEM simulation
analysis. The common contact model for EDEM are
Hertz-Mindlin no-slip soft sphere model, Hertz-
Mindlin bonding contact model, linear cohesion
contact model, and moving plane contact model, etc.
which are built according to the simulation object
(Yongjun and Shuai, 2017). This paper selected
Hertz-Mindlin no-slip soft sphere model according
to the contact property of brown rice particles,
brown rice particles and the screen or the emery
roller in the whitening chamber. Table 2 shows the
contact properties of the brown rice particles and the
component material properties of the whitening
machine. Figure 5 shows the basic physical
parameters of the brown rice and the steel, including
the desity and the poission ratio, as the gravity is
ignored. Figure 6 is the setting for the contact
properties between different models according to the
information in Table 2.
Figure 5: Parameter-setting for brown rice and steel.
Table 2: Contact properties of materials.
c: Property setting for contact between brown rice and
brown rice. d: Property setting for contact between brown
rice and steel
Figure 6: Property setting for contact between models.
The whitening roller consists of emery, and other
components are steel. The motion form of the
whitening roller and the screw iron roll is linear
rotation around their axis with 900rpm. The brown
rice particles will be conveyed to the whitening
chamber continuously at 320000 particles/s with the
initial linear velocity of 1m/s. The setting of time
step is realized through the options of “rayleigh time
step” and “fixed time step” (Liying and Yuepeng,
2016).
3.3.2 Simulation Result and Analysis
When the simulation is running, the motion
simulation of brown rice particles in the whitening
chamber at 0.36s, 5s, 8s can be seen in Figure 7. The
particles in the whitening chamber will accumulated
with time and the brown rice particles will move
forward under pressure. As shown in the figure, the
high speed region is where the particles just left the
screw iron roll to the whitening roll, and at the
discharge hole.
Figure 7: Motion of brown rice particles in whitening
chamber at 0.36s, 5s, 8s.
In Figure 8, the brown rice particles are moving
spiral downward along the whitening roller in the
form of streamlines, which is corresponding with the
actual flowing direction. If it is showed in the form
of velocity vector, the flowing direction of the
brown rice flow is also in accordance with the
reality, moving spiral downward along the whitening
roller.
In the simulation of group particles, Figure 9a
refers to the time-vary situation of the average
velocity of all particles in 0s to 6.5s; Figure 9b refers
to the time-vary situation of the average velocity of
the specific particle labelled No.1. The velocity of
No.1 particle is stable between 3.5s to 5.6s, reached
the peak at 5.6s and then become stable again.
Figure 8: Motion of brown rice showed in streamlines.
a: Time-varying velocity of brown rice particle flow.
b: Time-varying velocity of brown rice particle No.1.
Figure 9: Time-varying velocity of brown rice particle.
Figure 10 indicates the time-vary situation of the
average resultant force of the brown rice particle
flow in the whitening chamber. The pressure
increases as the brown rice particles moving from
the feeding end to the discharging end, but the total
value of the resultant force is not big. That is
because emery roller whitening machine is a speed
type which wipes off the surface of brown rice by
the high speed abrasive action of the emery roller.
Therefore, to a great extent the effectiveness of the
abrasive action is depending on the velocity rather
than the stress of the particles.
Figure 10: Time-varying average resultant force of particle
flow.
4 CONCLUSIONS
In the DEM simulation analysis, a DEM model of
brown rice particle in the shape of oval is built
through the particle bonding method. And the Hertz-
Mindlin no-slip soft sphere model is chosen
according to the contact property between the brown
rice particles, brown rice and screen, brown rice and
whitening roller. After the numerical simulation
analysis, the motion status of the brown rice particle
group in the whiteing chamber (including the
streamlines, and the velocity vector direction) is
generated. It comes to a conclusion that the velocity
of the brown rice particle flow and its individual
particle varies with time; the average resultant force
of the particle flow varies regularly with time.
ACKNOWLEDGEMENTS
Foundation Program: National Key Technology
R&D Program for the 13th Five-year Plan (Project
Number: 2017YFD0401101-01).
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APPENDIX
Author: Weiwei Wu (1986- ), research assistant,
research direction: science & technology research.
Corresponding author: Jinglan Ruan, professor,
research direction: design of grain, oil & food
machine.