Experimental and Numerical Studies of Fine Quartz Single-Particle Sedimentation Based on Particle Morphology

The sedimentation characteristics of quartz particles affect their separation and settling dehydration processes. Particle morphology determines the sedimentation equilibrium velocity. In this paper, the sedimentation of a single quartz particle is characterized by employing experimental and CFD-DEM approaches. SEM served to examine quartz particles measuring 30–500 μm, and they exhibited flaky–blocky morphologies with an average long–middle axis ratio of 1.6. Consistent with the SEM-detected morphological features of the quartz particles, suggested here is a simpler drag coefficient model, followed by verification of the model with experimental data. The results show that the velocity of a quartz particle in the non-settling direction had a fluctuation of ±0.2 mm/s. The fluctuation reached 0.4 mm/s at varying settlement release angles. The order in which the particles reached sedimentation equilibrium velocity during the settlement process was double-cone, single-cone, and square when the initial velocity was greater than sedimentation equilibrium velocity. Furthermore, the long–middle axis ratio of quartz particles diminished as their equilibrium sedimentation velocities rose. Given that the quartz particles ranged from 30 to 50 μm in size, the long–middle axis ratio wielded no discernible effect on the sedimentation equilibrium velocity.

A New Method for Predicting Erosion Damage of Suddenly Contracted Pipe Impacted by Particle Cluster via CFD-DEM

A numerical study on the erosion of particle clusters in an abrupt pipe was conducted by means of the combined computational fluid dynamics (CFD) and discrete element methods (DEM). Furthermore, a particle-wall extrusion model and a criterion for judging particle collision interference were developed to classify and calculate the erosion rate caused by different interparticle collision mechanisms in a cluster. Meanwhile, a full-scale pipe flow experiment was conducted to confirm the effect of a particle cluster on the erosion rate and to verify the calculated results. The reducing wall was made of super 13Cr stainless steel materials and the round ceramsite as an impact particle was 0.65 mm in diameter and 1850 kg/m³ in density. The results included an erosion depth, particle-wall contact parameters, and a velocity decay rate of colliding particles along the radial direction at the target surface. Subsequently, the effect of interparticle collision mechanisms on particle cluster erosion was discussed. The calculated results demonstrate that collision interference between particles during one cluster impact was more likely to appear on the surface with large particle impact angles. This collision process between the rebounded particles and the following particles not only consumed the kinetic energy but also changed the impact angle of the following particles.