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附录Ⅱ；Numericalstudyonparticle；headforastreetvacuumswee；BofuWu*,JinlaiMen,JieChe；SchoolofMechanicalEnglis；ABSTRACT；Thepurposeofthispaperist；Keywords:Pickuphead;Part；1.Introduction；Cu

附录Ⅱ Numerical study on particle removal performance of pickup head for a street vacuum sweeper Bofu Wu *, Jinlai Men, Jie Chen School of Mechanical English Shanghai Jiao TongUniversity，Shanghai,200240,China

ABSTRACT The purpose of this paper is to investigate the particle removal performance of pickup head for a street vacuum sweeper numerically. An integrated 3D numerical model was constructed based on particle suction process in computational fluid dynamics (CFD) software. The airflow through the pickup head was treated as a continuum, while particles were modeled as dispersed phase. The Reynolds stress model (RSM) and discrete particle model (DPM) were chosen in order to predict the air and particles flow accurately. The numerical simulation results show that the sweeper-traveling speed and the pressure drop across the pickup head have great effects on the particle removal performance. The removal efficiency of particles increases with the lower sweeper-traveling speed or the higher pressure drop, and small size particles have higher grade efficiency than that of large size particles under the same operating conditions. Moreover, the removal mass flow rate of particles increases with the higher sweeper-traveling speed. Therefore, a trade-off should be considered among high removal efficiency, low energy consumption, and high removal mass flow rate. Through the numerical simulation, the effectiveness of street vacuum sweeper for removing particles from road surface is evaluated, and an optimal operating condition is obtained. Besides, more information is generated to better understand the particle suction process of the pickup head.

Keywords: Pickup head; Particle removal performance ;CFD ;Sweeper-traveling speed Pressure drop

1.Introduction Currently, there is a widespread concern over the pollution of particle matter. Dust and silt are the major sources of particle matter pollution, the removal of which therefore attracts considerable attention [1]. Street sweeping is typically practiced to

remove the accumulation of dust and silt from road surface to improve aesthetics, public healthy, and storm water quality, so it is considered as an effective pollutant control practice for many local authorities [2,3]. Pickup head is the key component of street vacuum sweeper, which is designed to pick up particles efficiently from road surface and send them to dust collection hopper smoothly. The particle removal performance of the pickup head is the most important index for a street vacuum sweeper.

Many researches have been performed on estimating the particle removal performance of street sweeping. For example, a study by Chang et al. [4] evaluated the effectiveness of street sweeping and washing for controlling ambient total suspended particles by experiments, which indicated that the street sweeping and washing process was effective at removing dust and silt from urban roads. However, some researchers such as Vaze and Chiew [5] considered that the contribution of street sweeping to environmental quality was not very clear, and may have an adverse impact because street sweepers did not pick up smaller size particles effectively. Kang and Stenstorm [6] studied the street sweeping effectiveness as a stormwater management practice by using statistical power analysis. They pointed out that the effect of street sweeping should not be underestimated because some previous researches were based on insufficient data. Therefore, new methods were needed to evaluate the street sweeping effectiveness.

As the particle removal performance for street vacuum sweeper varies based on sweeping technology, operating conditions, sweeping frequency, street dirt loading and particle size distribution [7], it is necessary to develop a repeatable and reliable method to calculate the particle removal performance of pickup head for a street vacuum sweeper. In order to evaluate the particle removal performance of pickup head, engineers generally concentrate on two parameters, the sweeper-traveling speed and the pressure drop across the pickup head. Their influences on the particle removal efficiency and the particle removal mass flow rate directly relate to the performance of the street vacuum sweeper. Chen et al. [8] investigated the influence of sweeper structure and sweeper-traveling speed on the particle removal performance by experiments. They found that the wing plate of pickup head and the sweeper-traveling speed had great influence on the critical pickup velocity of particles. Meanwhile, they analyzed the relationship of the particle pickup velocities and the airflow rates.