FRACTAL AGGREGATES EVOLUTION DURING FLOCCULATION

ABSTRACT A temporal analysis of fractal aggregates during water flocculation is presented. Water was prepared using kaolin solution and a non-intrusive image-based analysis method was used for two-dimensional fractal dimension assessment (dF). The dF values were determined for aggregates larger than 270 µm from 100 images taken in each combination of velocity gradients (Gf) and flocculation times (Tf). The Gf values of 20, 30, 40, 50 and 60 s-1 and Tf values of 2 to 180 minutes were studied, with a ΔTf of 1 minute for 2 ≤ Tf ≤ 10 minutes and a ΔTf of 5 minutes for 10 ≤ Tf ≤ 180 minutes. Results showed that dF tends toward stability from a Tf of 40 minutes, with distinct levels in each Gf. Further, dF values decrease from 1.80 to 1.35 for Gf from 20 to 60 s-1.

摘要 本研究针对水体絮凝过程中的分形聚集体开展了时序分析。实验采用高岭土溶液配制水样，并通过非侵入式图像分析法开展二维分形维数（dF）的测定。针对每一速度梯度（Gf）与絮凝时间（Tf）的组合工况，从拍摄的100幅图像中选取粒径大于270 μm的聚集体，测定其分形维数值。本研究设置的速度梯度（Gf）取值为20、30、40、50、60 s⁻¹，絮凝时间（Tf）范围为2至180分钟；其中当2 ≤ Tf ≤10分钟时，时间步长ΔTf为1分钟，当10 ≤ Tf ≤180分钟时，时间步长ΔTf为5分钟。结果表明，当絮凝时间达到40分钟后，分形维数（dF）趋于稳定，且不同速度梯度下的分形维数存在显著差异。此外，当速度梯度从20 s⁻¹升高至60 s⁻¹时，分形维数（dF）由1.80降至1.35。