Kinetics of fine particle aggregation in turbulence

Abstract

The kinetics of particle aggregation, including coagulation and hydrophobic flocculation, in turbulent flow has been studied. It is discovered by both theoretical analysis and experimental results that the macroscopic kinetic model of particle aggregation is closely correlated with the microscopic particle–particle interaction. The energy barrier U max between the approaching particles determines whether a particle collision can result in effective aggregation or not. While the adhesive strength J of aggregated particles determines whether the formed aggregates are disrupted by the surface erosion in the viscous subrange of turbulence or by the fragmentation in the inertial subrange of turbulence. The maximum aggregate size d max depends on the ratio of the aggregate strength and the disruption stress of turbulent flow. Due to the apparently distinguished natures of particle–particle interaction in coagulation and hydrophobic flocculation, the aggregation kinetics of the two are different. Experimental results has proven that the coagulation process is generally accompanied with the surface erosion of aggregates in the viscous subrange of turbulence, whilst the hydrophobic flocculation process is mainly affected by the fragmentation mechanism of aggregate disruption in the inertial subrange of turbulence due to the much stronger strength of the flocs. Based on the theoretic analysis and the experimental results a general kinetic model of particle aggregation has been proposed.