A Study On The Simulation Of Fractal Floc Structure

In the flocculation process of water treatment, the mutual particles collision, coagulation, the breaking up, and re-coagulation is a random process, and the outcoming floculus has a fractal structure characteristic. The study on the fioc growing process and its inner structure is of importance to enhance the solid/liquid separation efficiency. The paper adopted the Metlab tool, with the help of DLA model, DLCA model and DLA-DLCA two stages model, the coagulating process is studied through computer simulation. The simulation results have a certain significance both theoretically and practically to study the floc structure.The study shows: the fractal dimension of the floc in the 2-dimensional space decreases as the floc size augmented;at the same time, the floc density reduces with a power exponent regularity;and the void ratio increases with a exponent regularity. In the 3-dimensional space, the fractal dimension of the result floc increases as its size augmented, with density increases and void ratio reduces. The structural difference of 2-dimensional simulated floc and 3-dimensional one is mainly attributed to that the shielding effect in 3-dimensional space is lower than that in 2-dimensional space, and particles in 3-dimensional space have a relatively degree of freedom. The resulting floc based on the DLCA model has a more slack structure, and higher degree randomness, with a fractal dimension 1.80 or so. The DLA-DLCA two stages model results are related to the proportion with respect to the two growing stages.With the help of density function method, radius of gyration method and image analyzing method, the fractal dimensions of the 2-dimensional DLA simulated floc were compared and all the fractal dimension reduce as the sizes augmented. The first two methods got similar fractal dimensions, while the third method got a relatively smaller fractal dimension.Using image resolution method analyze image projection fractal dimension, compared to the 3-dimensional. The result shows that DLA model have no obvious linear relationship;as to DLCA and DLA-DLCA models, well linear relationship is found, which is of importance in the study of the 3-dimensional fractal dimension of real floes.