Research On Simulation Of Aggregate Particles In Shear Flow

Water resource is experiencing a severe shortage. For one hand, available water inChina is much lower than the world’s degree. For another, water is severelycontaminated. As a result, little water can be used as drinking water. So bothconventional technology and advanced processes are needed when water treatmentprocess is designed. Coagulation and sedimentation, which play key roles in removalof colloidal particles, are important parts in water treatment.During coagulation process, there are3kind of removing particles: compressingthe electric double layer, charge neutralization and adsorption volume sweep netting.Then small particles became cluster. However, model just focused on particles’collide,neglecting the formation style. After that, it was study that cluster’s physical properties,including clusters of radius of gyration, fractal dimension and porosity etc., andsettling properties.From the model, with the increasing of cluster size, the radius of gyration wasgrowing, so did fractal dimension and porosity. In addition, the floc settlingperformance was getting better. During the period of model running, stirring intensitywas bigger and bigger. In the meanwhile, more clusters were broken and the clusterbecame into more parts. It could be seen that large-size and medium-size clusters wereeasy to break. But the number of small-sized clusters become less and less. Inconclusion, breaking leaded to less small-size cluster.In the experimental study of the precipitation process, intake water keptunchanged. The result of several comprehensive online testing showed that more than5um floc were mostly been removed and less than5um floc basically could not beremoved after sedimentation tank. The reason was that sedimentation could removefloc rather than small-size cluster. Moreover sedimentation tank’s mechanical actionand shear force of the flow brought more floc breakage.From experimental and model curve, it could be seen that floc settling mainlywere determined by mutual collisions between particles. And stir could improve flocsettling performance. Because weak flocs broke and restructured. Meanwhile morecollision leaded to more medium-size and large-size clusters. In short, after breaking,fewer small-size clusters resulted in better sedimentation effect. In order to discuss quantity of reagent, we changed simulation conditions. It couldbe fould that increasing dosage brought prone to more collusion between particles andbetter coagulation effect. In addition, with the augment of NTU, more time wereneeded to achieve the same coagulation result.