Simulation Analysis of Materials Motion in Rice Whitening Machine

Based on Discrete Element Theory

Weiwei Wu

, Jinglan Ruan

and Shuang Zhang

Guangdong Science & Technology Cooperation Center, 171 Lianxin Road, Guangdong, China

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.