Investigation on fine particle agglomeration and separation promoted by different bluff bodies

Abstract

Using particle agglomeration to help separate fine particles receives increasing attention in air purification processes. Recent studies suggested that enhanced turbulence using bluff bodies can significantly improve the agglomeration of fine particles. However, since micron-sized particles are difficult to measure, the current exploration of flow fields and particles is mainly based on simulations and lacks experimental validation. This paper innovatively used a phase doppler particle analyzer to measure the flow field in terms of velocity, streamline and turbulence intensity, as well as particle size and number concentration in an agglomeration chamber with a bluff body located at the center. Different shaped bluff bodies were also considered. It was found that low-velocity recirculation region with different shapes appeared in the wake, and vortex flow with special structures were observed. From the perspective of particles, the development of the flow field generated by a single bluff body effectively caused an increase in particle size and a decrease in particle number, which is because that the flow field promotes collisional agglomeration. More specifically, for V-structure bluff body, the particle size improved from 6 μm to a maximum of 13 μm and the particle number concentration decreased by 8 times. The agglomeration efficiency for PM2.5 and PM10 reached 89.06% and 87.38% respectively. Furthermore, by analyzing the velocity of different sized particles, it was reasonable to assume that different sized particles appeared to have velocity differences due to recirculating vortex flow, while the overlapping trajectories of positive and negative moving particles was mainly responsible for the collision probability enhancement. This paper presents new insights into particle agglomeration separation for this environment-friendly and low-cost technology.