水力紊动条件对泥沙絮体分形结构的影响

Effects of hydrodynamic turbulent conditions on aggregate fractal structures

在含沙量为85 kg/m3的悬浊液中投加阳型高分子聚合物,改变水力紊动条件:剪切速率(r)或速度梯度(G)与剪切时间(t),借助沉降技术、图像分析技术及分形特性定量表征参数“分维”探讨了架桥絮体结构的演变规律,得出分形结构达最佳状态时的水力紊动强度(Gt)值存在两个临界值:快速絮凝阶段和慢速絮凝阶段。实验发现,不同含沙量架桥絮体分形结构致密度最高时所需的最佳Gt值相近。含沙量越低,r或G值应降低,t值增加,分维值降低。另外,相同含沙量无机混凝剂絮体与高分子架桥絮体分形结构达最佳时,前者所需Gt值高,对应的G值低,t需延长,絮体平均质量分维(D3)值高,但絮体结构脆弱。

Based on adding the cation high molecular weight polymer into the turbid suspended liquor containing 85 kg/m^3 of sediments, this paper discusses the changing hydrodynamic turbulent conditions in the process of flocculation, such as shearing rate r （or velocity gradient G） and shearing time t,and the use of the settlement and the image analysis technology, the factor ＂fractal dimension D＂ which can characterize the fractal properties in quantity and the evolution regularities of the fractal structures of the bridging-flocculated aggregates.The results show that there are two critical values about hydrodynamic turbulent strength C,t （ G1 t1 = 2350 ± 100 at rapid flocculation stage and G2t2 = 12400±100 at slow flocculation stage）when fractal structures reach the optimum state. It is found in experiment that the optimum Gt value is nearly the same when the compactness of the fractal structures of the bridging-flocculated aggregates reaches the highest point of the different raw silt content.When raw silt content is low, r or G value should be reduced and t value increased. However, the value of the fractal dimension D decreases. Furthermore, when the fractal structures of floes formed by the addition inorganic coagulant and the bridging-floeculation aggregates formed by the additional high molecular flocculant reach the optimum state with the same raw silt content, the former needs the higher Gt value, corresponding to the lower G value and the longer t value and the average mass fractal dimension D3 value of floe is higher, but the fractal structure of floe appears frangible.