# Improving Cleaning Performance of Rice Combine Harvesters by DEM–CFD Coupling Technology

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Terminal Velocity Test-Bed for Each Threshing Output Component

_{1}in the test port (2) was measured with a hot-wire digital anemometer (VT100, KIMO, Paris, France) with a measurement range from 0.15 to 30 m/s and a resolution of 0.01 m/s. Finally, the terminal velocity V

_{i}(m/s) was calculated by substituting the minimum and maximum values of L (m) into the following equation:

_{1}is the diameter of the convergence cylinder (m) and φ = 5.5° is the taper angle of the conical tube (°).

#### 2.2. Test Materials and Their Basic Physical Characteristics

^{3}, 0.19 g/cm

^{3}, and 0.16 g/cm

^{3}, respectively. The moisture content measurement results and 1000-grain weight of each variety are shown in Table 1.

#### 2.3. Analyzing the Motion Law of the Threshing Output in the Existing Cleaning Shoe Based on EDEM-CFD Simulation

#### 2.3.1. EDEM-CFD Coupling Theory

#### 2.3.2. Governing Equations of the Fluid System

_{f}is the fluid density, t is time,

**u**

_{f}is the fluid velocity, p is the air pressure, μ

_{f}denotes the viscosity,

**g**is the gravity force vector, and

**S**is the momentum sink.

**S**is calculated by:

_{i}Felice drag model adds a porosity correction term to the free-stream drag model to take into account the effects of neighboring particles on the drag. In this paper, we adopt the D

_{i}Felice drag model to calculate F

_{D,i}, which can be expressed as:

_{p}is the diameter of the considered particle. C

_{D}is the particle–fluid drag coefficient that depends on the Reynolds number R

_{e}of the particle, and ε−χ denotes a corrective function accounting for the presence of other particles in the system on the drag force of the particle under consideration. A standard k−ε turbulence model and wall function are applied to calculate the airflow.

#### 2.3.3. Governing Equations of DEM Simulation

^{®}2.7, DEM Solutions, Troy, MI, USA) was used in this work. The process is a cycle with a repeated calculation of the equation of motion for all the particles individually using the forces evaluated by using contact models to obtain the acceleration, velocity, and displacement.

_{n}is:

^{*}is the equivalent Young’s modulus of the two interacting particles, δ

_{n}is the normal overlap, R* is the equivalent radius, m

^{*}is the equivalent mass, e is the coefficient of restitution, and v

_{n}

^{rel}is the normal relative velocity.

_{t}is:

^{*}is the equivalent shear modulus of the two interacting particles, δ

_{τ}is the tangential overlap, and v

_{τ}

^{rel}is the tangential relative velocity. E

^{*}, R

^{*}, and m

^{*}are given by:

_{r}is the coefficient of the rolling friction, R

_{i}is the distance of the contact point from the center of the particle i, and ω

_{i}is the unit angular velocity of the particle i at the contact point.

#### 2.3.4. Simulation Settings in the EDEM-FLUENT Simulation

#### 2.3.5. Measurement of Airflow Distribution Inside the Newly Designed Cleaning Shoe

^{−1}. The average grain to MOG (material other than grain) ratio was 2.9:1 and the average moisture content of the straw and the grains was 66% and 24%, respectively. The header width of the combine harvester was 2.2 m and the forward velocity was 1–1.2 m/s. A

**tarpaulin**was utilized to collect all of the sieve outputs, and then the full grains were filtered out from the material other than grain (MOG) using a stationary re-cleaner (Agriculex ASC-3 Seed Cleaner, Guelph, ON, Canada), weighed, and the grain sieve losses were calculated. Each test length was 50 m.

## 3. Results and Discussion

#### 3.1. Basic Physical Characteristics of the Test Samples

#### 3.2. Terminal Velocity for Each Component’s Analysis

^{−1}, and its terminal velocity was distributed within the range of 9.05–12.15 m/s when the big branch is in the vertical position. The influence of the moisture content on the terminal velocity should be fully considered when designing a cleaning device.

#### 3.3. Analyzing Velocity Variation of Grains and Short Straws in Longitudinal Direction

^{−6}s. Different colors represent different materials. It can be concluded from Figure 11 that the materials generated by the particle factory reach the upper sieve surface when t = 0.172 s. At t = 0.27 s, the materials reach the lower screen surface, and some grains penetrate the sieve directly. At t = 0.313 s, owing to the suspension speed of the short straws distributed from 3.12 to 5.21 m/s, some short straws are blown out of the calculation domain directly. At t = 1.351 s, the total number of grains penetrating the screen has increased. At the same time, some grains are blown out because of the interaction between short straws and grains. The variation in the grain and short straw longitude velocity with time in different regions is shown in Figure 11.

**longitudinal velocity**was increased with a smaller growth acceleration rate. When the grains entered the middle section of the sieve, the grains’

**longitudinal**velocity increased dramatically, from 0.18 m/s to 0.3 m/s in about 20 ms, then changed to 0.8 m/s owing to the airflow velocity becoming gradually larger in this region. For the grains which collected at the middle of the sieve, the grains’

**longitudinal velocity**increased with a relative high growth acceleration rate, and when they entered the end section of the sieve, the grains’

**longitudinal velocity**jumped from 0.2 m/s to about 0.5 m/s. Then, the grains’

**longitudinal velocity**continued growing, owing to the airflow velocity recovering. For the grains which collected at the end section of the sieve, the grains’

**longitudinal velocity**increased quickly, from 0 to 0.5 m/s in about 100 ms, and then they were blown out of the calculation domain directly. The

**longitudinal velocity**of short straws was increased with a different growth acceleration rate in a different region of the sieve. Owing to the impediment of the lower grain pan, a mandatory change in airflow direction occurred, leading to a smaller value of airflow velocity in the front of sieve, and resulted in the smallest growth acceleration rate in this area. In the following backward moving process, their

**longitudinal velocity**increased gradually, whereas at the end section of the sieve, some short straws were blown out swiftly.

**indicates**that the airflow velocity was smaller at the front of the upper sieve, which was not beneficial for grain stratification and penetration. Since there was an accumulation of a large amount of threshing mixture, most of the short straws cannot be effectively separated. Most of them pass through the sieve with the grains, which leads to a larger grain impurity ratio. On the other hand, at the end of the upper sieve, the airflow velocity was relatively high in places closer to the wall, and some full grains also were blown out and caused a grain loss. To solve this problem, a kind of efficient cleaning device with the major structural improvements as follows was put forward: (1) The length of the lower grain pan was shortened to make it into a streamline arc plate, as the experiment results indicated that there was a slightly mandatory change in the air flow direction, which can help to develop an upward airflow at the end of streamline arc plate and also can prevent vortex generation. (2) A centrifugal fan with double outlets was designed to increase airflow velocity at the front of the sieve. (3) A return conveying plate was adhered under the longitudinal axial flow threshing cylinder to upgrade the processing capacity of the cleaning device. A diagram of the newly developed cleaning device is shown in Figure 12.

**seen**that the ideal airflow velocity in different sections is: about 9 m/s in the upper outlet, 4–6 m/s in the middle section, and 3–4 m/s in the tail section. Combined with the terminal velocity of the threshing outputs, it can be understood that there is a good airflow velocity distribution inside the newly designed cleaning shoe, which can be expected to have a better cleaning performance when harvesting rice.

## 4. Conclusions

**With the increase in the moisture content, the mass of each component of the threshing outputs increased accordingly**, and the terminal velocity increased accordingly. The terminal velocity of grains with stripes and branches with grains was close to that of the full grains, as it is difficult to separate out those with airflow, resulting in a higher grain impurity ratio. The distribution range of the terminal velocity for leaves and short straws has no overlap with that of the full grains; thus, it is convenient to separate them by selecting an appropriate airflow velocity. There is a terminal velocity overlap of short straws from the bottom of the stem, and for a branch in the horizontal state and with full grains, it is difficult to separate the short stems from the bottom of the stem and branch in the horizontal state by airflow. It can be concluded that an airflow velocity around 6 m s

^{−1}would provide good separation of the grains and MOG. Under this condition, a large branch (vertical posture) falls into the tailing auger for re-threshing and re-cleaning, and most of the leaves are blown out of the cleaning shoe instantly.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Setup for terminal velocity measurement of threshing outputs; 1—conical tubes, 2—airflow velocity test port, 3—material inlet, 4—convergence cylinder, 5—regulator tube, 6—stand frame, 7—throttle, 8—fan.

**Figure 2.**Illustrations of the different components in the threshing outputs for which the terminal velocity was measured.

**Figure 3.**Three-dimensional model of the existing

**cleaning shoe**: 1. shake plate, 2. airflow inlet, 3. vibrating and cleaning upper sieve, 4. vibrating and cleaning lower sieve, 5. outlet, 6. lower grain pan.

**Figure 4.**Developed grain particle model and short straw particle model. (

**a**) Grain model, (

**b**) Cross-section of a short straw model.

**Figure 5.**Distribution diagram of measuring points in the newly designed cleaning shoe. No. 1–7 are the airflow velocity measuring points.

**Figure 6.**Terminal velocity distribution for full rice grains, blight grains, grains with short handles, short branches with grains, and long branches with grains, (

**a**) full rice grains, (

**b**) grains with short handles, (

**c**) short branches with grains, (

**d**) blight grains, (

**e**) long branches with grains. No. 1–3: rice variety 1: 24.3%, 25.4%, 26.1%; No. 4–6: rice variety 2: 23.6%, 24.8%, 25.9%; No. 7–9: rice variety 3: 23.2%, 25.3%, 25.9%.

**Figure 7.**Terminal velocity of rice straws with different lengths from different parts of the stem. T-MC1—short straw from the top stem with a moisture content of 62.5%; M-MC1—short straw from the middle stem with a moisture content of 62.5%; B-MC1—short straw from the bottom stem with a moisture content of 62.5%; T-MC2—short straw from the top stem with a moisture content of 65.4%; M-MC2—short straw from the middle stem with a moisture content of 65.4%; B-MC2—short straw from the bottom stem with a moisture content of 65.4%; T-MC3—short straw from the top stem with a moisture content of 69.2%; M-MC3—short straw from the middle stem with a moisture content of 69.2%; B-MC3—short straw from the bottom stem with a moisture content of 69.2%.

**Figure 8.**Terminal velocity of leaves with different varieties and lengths. No. 1–9 are the leave lengths of 15, 25, and 30 mm with a moisture content of 62.5%, 65.4%, and 69.2%, respectively.

**Figure 9.**Terminal velocity contrast between different components. No. 1: full grains, No. 2: blighted grains, No. 3: grains with short handles, No. 4: large branches (horizontal posture), No. 5: large branches (vertical posture), No. 6: small branches with grains, No. 7–9: short straws from the bottom stems, No. 10–12: short straws from the middle stems, No. 13–15: short straws from upper stems, No. 16–18: leaves.

**Figure 10.**Simulation of the sieve working process, (

**a**) t = 0.172 s, (

**b**) t = 0.27 s, (

**c**) t = 0.313 s, (

**d**) t = 1.351 s.

**Figure 11.**Variation in grain and short straw longitude velocity with time. (

**a**) grains, (

**b**) short straws.

**Figure 12.**Diagram of the multi-cleaning system and its main working parts. 1—tangential threshing rotor, 2—longitudinal threshing rotor, 3—tails return duct, 4—return conveying plate, 5—vibrating sieve, 6—tailings auger, 7—grain auger, 8—centrifugal fan.

Items | Measuring Result | ||||||||
---|---|---|---|---|---|---|---|---|---|

Rice Variety 1 | Rice Variety 2 | Rice Variety 3 | |||||||

Three-dimensional size of full grains, mm | 3.48 × 2.71 × 7.72 | 3.22 × 2.38 × 8.13 | 2.37 × 3.49 × 8.14 | ||||||

Moisture content of full grains, % | 26.1 | 25.4 | 24.3 | 25.9 | 24.8 | 23.6 | 25.9 | 25.3 | 23.2 |

1000-grain weight of full grains, g | 30.2 | 31.2 | 33.6 | 28.6 | 30.1 | 31.7 | 29.4 | 31.4 | 33.6 |

Three-dimensional size of blight grains, mm | 1.06 × 2.40 × 7.12 | 1.20 × 3.35 × 7.18 | 3.21 × 1.04 × 7.87 | ||||||

Moisture content of short straws, % | 69.2 | 65.4 | 62.5 | 65.8 | 64.2 | 61.5 | 67.8 | 64.0 | 62.1 |

Length of the long branches with grains, mm | 74–83 (with 10–16 grains) | 78–83 (with 10–13 grains) | 65–77 (with 8–15 grains) | ||||||

Length of small branches with grains, mm | 14–21 (with 3–5 grains) | 12–15 (with 3–5 grains) | 12–15 (with 3–5 grains) | ||||||

Length of grains with small handles, mm | 11–13 | 10–12 | 10–13 | ||||||

Length of short straws, mm | 10, 20, 30 | ||||||||

Length of leaves, mm | 15, 25, 30 |

Material Properties | Grain | Short Straw | Plate | |
---|---|---|---|---|

Density (kg/m^{3}) | 1350 | 160 | 7850 | |

Poisson’s ratio | 0.25 | 0.45 | 0.29 | |

Shear modulus (Pa) | 2.0 × 108 | 4.4 × 106 | 8.0 × 1010 | |

Collision properties | Grain–grain | Grain–plate | Short straw –plate | Short straw –grain |

Coefficient of restitution | 0.43 | 0.5 | 0.26 | 0.2 |

Coefficient of static friction | 0.75 | 0.56 | 0.8 | 0.8 |

Coefficient of rolling friction | 0.01 | 0.01 | 0.01 | 0.01 |

Vibrating sieve | Motion form | Amplitude | Frequency vibrating direction angle | |

Sinusoidal translation | 20 mm | 6 Hz 20° |

Test No. | Fan Speed /rpm | Guide Plate I Angle /° | Guide Plate II Angle /° | Sieve Opening /mm | Grain Sieve Loss /% | Grain Impurity Ratio /% |
---|---|---|---|---|---|---|

1 | 1100 | 8 | 13 | 20 | 0.26 | 1.03 |

2 | 1100 | 27 | 29 | 25 | 0.42 | 1.22 |

3 | 1100 | 45 | 45 | 30 | 0.16 | 2.01 |

4 | 1300 | 8 | 29 | 30 | 0.39 | 0.76 |

5 | 1300 | 27 | 45 | 20 | 0.69 | 0.63 |

6 | 1300 | 45 | 13 | 25 | 0.53 | 1.22 |

7 | 1500 | 8 | 45 | 25 | 1.28 | 0.94 |

8 | 1500 | 27 | 13 | 30 | 1.80 | 0.75 |

9 | 1500 | 45 | 29 | 20 | 0.78 | 0.46 |

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## Share and Cite

**MDPI and ACS Style**

Ding, B.; Liang, Z.; Qi, Y.; Ye, Z.; Zhou, J.
Improving Cleaning Performance of Rice Combine Harvesters by DEM–CFD Coupling Technology. *Agriculture* **2022**, *12*, 1457.
https://doi.org/10.3390/agriculture12091457

**AMA Style**

Ding B, Liang Z, Qi Y, Ye Z, Zhou J.
Improving Cleaning Performance of Rice Combine Harvesters by DEM–CFD Coupling Technology. *Agriculture*. 2022; 12(9):1457.
https://doi.org/10.3390/agriculture12091457

**Chicago/Turabian Style**

Ding, Bochuan, Zhenwei Liang, Yongqi Qi, Zhikang Ye, and Jiahao Zhou.
2022. "Improving Cleaning Performance of Rice Combine Harvesters by DEM–CFD Coupling Technology" *Agriculture* 12, no. 9: 1457.
https://doi.org/10.3390/agriculture12091457