## 5 Results and Discussion
### Particle Removal Efficiency
The effect of the change in the diameters of the suction head and suction tube on the suction efficiency of the particles is shown in Figure 10. We measured the efficiency of particle suction using three different suction tubes during the experiment when the absorption efficiency of leaf particles smaller than 15 mm in size was determined. When the tube diameter was 90 mm, the sweeping surface area was 3.6 m\({}^{2}\), the inclination angle was 30\({}^{\circ}\), the conveyor belt speed was 6 km/h, and the suction efficiency was 0.95 \(\eta\). The diameter of the tube was 110 mm and the suction efficiency was 0.96 \(\eta\), while the efficiency at a tube diameter of 130 mm was greater than 0.98 \(\eta\). An increase in the conveyor belt speed and a relative decrease in the particle suction efficiency were observed owing to the increase in residence time. When the conveyor speed was increased to 16 km/h, the particle suction efficiency was 0.84 \(\eta\) for a tube diameter of 90 mm. The highest efficiency was achieved with a pipe diameter of 130 mm. During the measurement of particle suction efficiency, it was observed that a tube with a size of 130 mm was more efficient when the suction port airflow rate was 35 m/s. The inclination angle of the pickup head suction is an important part of a good collection of particles. It was necessary to ensure that the suction mouth was at the optimal inclination angle to ensure that the particles were fully absorbed. Figure 11 shows how the suction mouth of the pickup head affects the absorption efficiency of the particles when the inclination angle is different. The efficiency was 0.74 \(\eta\) at 20 m/s when the angle of inclination of the suction mouth was 75\({}^{\circ}\), and the efficiency was 0.93 \(\eta\) at 35 m/s. The inclination angle of the suction mouth was 0.94 \(\eta\) at 60\({}^{\circ}\) airflow at 35 m/s, whereas the inclination angle at 30\({}^{\circ}\) particle suction efficiency was 0.96 \(\eta\). The experimental results showed that the collection head was highly efficient when the inclination angle of the suction mouth was 30\({}^{\circ}\). A change in the velocity of the airflow moving through the suction port causes a change in the air pressure in the suction port. In the pickup head chamber, the secondary airflow collision with the atmospheric airflow affects the pressure change during recirculation in the system. The higher the pressure drop in the pickup head chamber, the higher the dust removal efficiency. An increase in the speed of the airflow through the intake port caused an increase in the pressure drop in the inlet chamber of the system. Figure 10: The experimental result of the effect of change of suction port tube diameter on the efficiency of suction of particles. The effect of particle removal on the pressure drop was measured, and several experiments were carried out with pressure drop values of 1200-2400 Pa across the pickup head when the conveyer belt speed was 8 km/h [17; 19]. Figure 12 shows an increase in the overall removal efficiency with increasing inlet pressure drop. This effect can be expected because as the pressure drop at the pickup head increases, more kinetic energy can be obtained through the connection between the particles and the airflow; therefore, more particles can be obtained by the airflow. The clay particle removal efficiency was 0.68 \(\eta\) when the pressure drop was 1200 Pa. Removal efficiency in wood particles was 0.82 \(\eta\). When the pressure drop was 2400 Pa, the removal efficiency of wood particles was 0.98 \(\eta\), that of removal of sand particles was 0.95 \(\eta\), and that of clay particles was less than 0.9 \(\eta\). For small particles, the grade efficiency decreases slightly with the pressure drop, but it increases significantly for large particles. There is a strong relationship between the velocity slip ratio and inlet pressure drop. Low-pressure drops result in lower velocity slip ratios because the velocity slip ratio is highly dependent on the drag force acting on the particles.