## 5 Results and Discussion
### Effect on the Efficiency of the Suction of the Recirculated Secondary Airflow in the System  
As the recirculating airflow in the inlet duct of the system moves through the pickup head, the path of movement may change owing to an increase in the airflow velocity. During the erratic movement of the particles around the suction port, a certain part of the flow that passes through the inlet duct of the pickup head collides with the road surface, whereas the rest moves toward the suction mouth. The collision of the particle stream in the system with the particle stream on the road surface results in a change in the trajectory of the particles owing to the effect on the motion. Figure 15 shows the effect of the amount of flow re-entering the system on suction efficiency. The assimilation efficiency of light particles was 0.93 \(\eta\) when 10% of the airflow from the system was directed into the inlet duct of the pickup head, whereas the suction efficiency for metal particles was 0.71 \(\eta\). The highest particle assimilation efficiency was obtained when 60-70% of the airflow in the system was returned through the inlet ducts of the pickup head. When the airflow in the system was fully recirculated, the particle suction efficiency was relatively low. The results of the experiment showed that the airflow in the system did not recirculate by 100% in any case. A certain amount of airflow is released into the environment. There are many reasons for this: change in the trajectory of airflow moving through the inlet duct owing to collision with the road surface, increase in the speed of movement of the sweeper, and negative pressure around the suction mouth, among other reasons. The amount of secondary airflow returned to the system to achieve greater efficiency is important for a regenerative air vacuum sweeper. In regenerative air vacuum sweepers, it is usually very difficult to ensure that the full airflow is returned to the system because of the speed of movement of the sweeper and the pressure around the suction port. Airflow does not circulate in the complete system, owing to changes in road conditions and changes in the trajectory of the secondary airflow as a result of a collision with the road surface. Figure 16 shows how the secondary airflow affects the suction efficiency of the particles when they are recirculated in the system. When 70% of the secondary airflow was recirculated in the system, the conveyor belt speed achieved a particle suction efficiency of 0.97 \(\eta\) at 4 km/h. It can be observed that the suction efficiency of the particles decreases when the speed of the conveyor belt movement increases. The particle collection efficiency was relatively low when the secondary airflow was fully circulated in the system. The efficiency of particle suction during the period of 100% recirculation of air intake was 0.93 \(\eta\) at a conveyor speed of 4 km/h, and the efficiency of particle collection was 0.75 \(\eta\) at a speed of 16 km/h. The  
Figure 14: Calculation results of particle removal starting velocity on different particle shape and diameter. efficiency of particle reception when the secondary air intake in the system was recirculated by 40% was 0.95 \(\eta\) per conveyor belt at 4 km/h, while the efficiency at 16 km/h was 0.78 \(\eta\). This means that the complete or partial circulation of the secondary airflow in the system may have a significant effect on the particle acceptance efficiency. Figure 17 shows the effect of the secondary airflow in the pickup head inlet ducts on the efficiency of the individual recirculation in the system. Although the high efficiency of airflow introduced through the inlet duct D2 was achieved when 70% of the airflow was recirculated in the system, the airflow introduced through the two input channels was 14% lower than when it was recirculated in the system.