*3.4. Parameter Optimization and Comparison Experiments*

In order to obtain the optimal parameters for each factor, the established three-factor orthogonal test was optimized by using Design-Expert 8.0 software. In order to obtain the optimal parameters for each factor, a three-factor orthogonal test was established using Design-Expert numerical analysis software for parameter optimization. Based on the analysis of the test results and the optimization of the influencing factors, the optimal combination of factors was obtained: the angle of the sieve plate angle was 55.7◦, the air flow velocity was 14.1 m·s−1, and the distance of the sieve plate was 33.2 mm, which resulted in a prediction of 95.12% of the net fruit yield of hazelnuts.

Based on the optimal parameters obtained, five replicate tests were performed, and the test result was 94.25%. The error rate was 3.4%. It can be seen that under the optimal parameters, the field prototype test results are similar to the simulation test results and can meet the requirements of hazelnut picking operation.

#### **4. Discussion**

Hazelnuts and leaves were selected from the particle mixture for the study through statistics and analysis of the mixture. The critical value of particle suspension velocity was obtained by the experiment, and it is an important parameter to measure to know whether the material could be separated. A coupled CFD-DEM method was used to simulate the effect of a pneumatic hazelnut harvester on the net fruit rate of hazelnuts under different combinations of operating parameters. The coupled CFD-DEM simulation was verified to describe the motion of the particle mixture in the sorting device well through a field experiment. Through analyzing the fluid dynamics inside the hazelnut harvester, the study proved that the optimization of air flow velocity, sieve plate angle, and distance of the sieve plate could improve the working performance of the hazelnut harvester. The working principle of the hazelnut harvester was analyzed from the point of the movement of the sorting mixture. The results of the comparison experiment show that the hazelnut harvester with the optimized combination of operating parameters can effectively sort the particle mixture and reduce the impurity rate and energy consumption. Working performance experiments show that the optimized hazelnut harvester could pick and sort the particle mixture well under real field conditions.

In the follow-up research, the combination of various devices should be considered in order to further improve the net fruit rate. For example, HASATSAN researched and designed a high horsepower tractor-driven hazelnut harvester and used a precision-improving interchangeable vibrating screen set to work simultaneously with three harvesting hoses. The harvester was constructed to harvest a particle mixture in any geographic condition with a vacuuming system; TURBO-VAC has designed an integrated hazelnut harvester that used a diesel engine to drive a fan that rotates at high speed to pick and sort particles in a single pass. By refining the functions of each component and the components combining and cooperating with each other, we will be able to further improve the performance of the hazelnut harvester. In this paper only one hazelnut variety was used as the experimental material, and the actual suspension speed of different varieties of hazelnuts varied greatly; hence, further research is needed in terms of applicability. In addition, the vibration of the whole machine and the environment of the actual workplace will have some influence on the cleaning situation; these are influences which need to be considered in future experimental research.
