Characterization And Measurement Of The Flow Field During The Coagulation Process

Particle image velocimetry(PIV) and numerical simulation(CFD) was applied to measure the Taylor-Couette flow and obtain the information of the vortex flow at different rotation speed. The measurement results obtained by PIV and CFD were compared carefully under the same condition, and the Taylor- Couette was used in flocculation experiment to analyze the relationship between the characteristics of flow field and flocculation effect quantitatively. Through the PIV measurement, numerical simulation and flocculation experiment, the following conclusions can be drawn :1. When the rotation speed was less than 7 r/min, the adjacent vortex was relatively independent and the size of vortex was essentially equal, the velocity was stable and smaller than others; When the rotation speed was within 7~40 r/min, the size and form of vortex varied periodically with the rotation speed and time, and the velocity also varied; When the rotation speed was within 40~63 r/min, the size and form of adjacent vortex was the same, and there were slight fluctuations in the vortex flow field, the transmission between adjacent vortices has attenuated, the velocity varied slightly with rotation speed and time; When the rotation speed was more than63 r/min, the degree of disorder of vortex form and the fluctuation of velocity was more violent.So the Taylor- Couette flow field can be divided into four region: less than 7 r/min, 7 ~ 40 r/min, 40 ~ 63 r/min and more than 63 r/min..2. Through the comparison and thorough quantitative analysis of the results of PIV measurement and the numerical simulation obtained under the same conditions, it can be seen that there were several ranges of the rotation speed according to the different vortex forms and features corresponding different inner rotation speed; The velocity characteristics of each partition were similar, but the velocity characteristics of different partitions were different. The vortices showed four forms in the vortex flow with the change of the inner speed ranges(less than 7 r/min, 7 r/min ~ 40 r/min,40 r/min to 63 r/min, and more than 63 r/min).3. Through the comparison and thorough quantitative analysis of the coagulation effect obtained under the different coagulant dosages, when the rotation speed was less than 7 r/min, the size distribution of floc was pockety and the removal rate was low; When the rotation speed was within 7 r/min~40 r/min, the number of large floc increased with the the increase of rotation speed, the size distribution of floc was uniform, and the removal rate was high; When the rotation speed was within 40r/min~63 r/min, the floc size and the removal rate was decreased; When the rotationspeed was more than 63 r/min, the number of small floc was increased and the removal rate was low. So the coagulation effect was significantly different with different dosage of coagulant and the different ranges of the rotation speed. Therefore,the rationality of the vortex flow partition was testified.4. In order to further testify the rationality of the vortex flow field partition,Through the comparison and thorough quantitative analysis of the coagulation effect obtained under the different coagulant aid dosages, when the rotation speed was less than 7 r/min, the large floc can be generated at different coagulant aid dosages, but the size distribution of floc was pockety and the removal rate was low; When the rotation speed was within 7 r/min~40 r/min, the number of large floc was significantly increased, the size distribution of floc was uniform and the removal rate was high;When the rotation speed was within 40 r/min~63 r/min, the floc size was decreased,but the large floc can be generated with the increase of coagulant aid dosage and the removal rate increased with the increase of coagulant aid dosage; When the rotation speed was more than 63 r/min, the removal rate was basically unchanged with the increase of coagulant aid dosage, when the coagulant aid dosage was high, the removal rate was significantly increased. The coagulation effect was significantly different with different dosage of coagulant aid and the different ranges of the rotation speed. Therefore, the rationality of the vortex flow partition was further testified.