Numerical study of a stirred coffee roaster...Fast camera particle flow e. Power source Rice...

transcript

Innovations for a better world.

Numerical study of the flow

of rice grains in a whitenerMaster project in industry

Wenyi SONG, EPFL

Innovations for a better world.

Who is Bühler?

Rice whitener project | Wenyi SONG | 2019-06-19

06:30 07:15

07:00 07:30

The rice whitening process

Typically 12% is the bran composition by weight in brown rice

https://www.chowhound.com/food-news/176585/whats-

the-difference-between-white-rice-and-brown-rice/

The rice whitener

• Capacity = 3500 to 8000 kg/h

• Tip-speed = 10.5 to 15 m/s (~700 rpm)

• Milling gap = 80% grain length (~10 mm)

Project roadmap

Experimental study

1. Spherical particles

2. Rice grains

Numerical study

1. Spherical particles

2. Polyhedron particles

Validation of model

1. Comparison of data:

• Global motion

• Particle velocity

• Bulk angle

• Torque

2. Determination of

simulation parameters:

• Friction coefficients

Model applied to

industrial machine

Useful information on

process:

• Flow behavior

• Stress distribution

• Correlation between

process result and

simulated stress

distribution

Effective bran removal &

decreased breakage rate

Experimental setup

a. Light source

b. Photo diode rotation speed

c. Couette cell

d. Fast camera particle flow

e. Power source

Numerical Setup

Feature Setting

Number of particles 3531 spherical or

4733 rice-shaped

Weight of particles 71 g

Height of gap 5.4, 8.1, 8.4 cm

Number of corners 50

Rotational speed 210, 375, 425 rpm

Normal Force Hysteretic Linear Spring

Tangential Force Linear Spring Coulomb Limit

Hardware resources 16 cores & Quadro GV100

Polyhedron

5.4, 8.1, 8.4 cm

Particle properties

Particle Density

[kg/m3]

Young’s modulus

Poisson ratio

POM* 1420 3.2 0.44

Rice grain** 1500 1 0.25

Interaction Particle - Particle Particle - Boundary

Static friction coef.** 0.28 0.3/0.5

Restitution coef.** 0.5 0.5

POM particles (d=3 mm)

Rice grains (l=6.7 mm, w=1.8 mm)

*Values from http://www.dmh.at/materials/product/42_pom400/ and Polymer Properties Database

**Values obtained from http://doi.org/10.1016/j.apt.2018.02.021

Results for POM particles

Global motion of POM particles

Experiment, 375 rpm

Flow pattern of POM particles

Experiment, 375 rpm

Particle trajectories

Experiment, 375 rpm

Mean particle velocity at outer layer of the gap

SimulationExperiment

Results for rice grains

Global motion of rice grains

Experiment, 205 rpm

Profile of rice grains

Slope: -0.73

Experiment, 205 rpm

Slope: -0.78

Simulation, 210 rpm

POM vs. rice grains

Normal and tangential contact forces from DEM

Rice grainsSpherical POM

Normal and tangential collision velocity and stress from DEM

Collision stressCollision velocity

Conclusion

• Several flow features of spherical particles and rice grains have been

successfully extracted and analysed, i.e.:

o Global flow patterns;

o Particle trajectories and velocities;

o Global particle-particle collision statistics.

• Experiment with simplified geometry acts as a calibration/validation

method for the DEM numerical model.

Tangential stress

Outlook

• With desktop experiment:

o Determine suitable parameters for the numerical simulation.

o Analyse the motion of rice grains.

o Analyse the contact force distribution of rice grains.

• With industrial machine:

o Study global flow behaviour of rice grains.

o Correlate simulated stress distributions with bran removal

efficiency observed in industry.

o Enable breakage model in the simulation.

o Propose suitable improvements of the process.

Maximum Tangential Force

Thank you for your attention.

Numerical study of a stirred coffee roaster...Fast camera particle flow e. Power source Rice...

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