Experimental Reseach And Numerical Simulation Study On Flow Field Of The Reciprocating Baffled Flocculation Tank

The reciprocating baffled flocculation tank is a kind of flocculation process that has been widely used. If the change of the amount of water is not big, it has the advantages that the flocculation result is good; the structure of tank is simple and it is convenient to manage. So it is mostly applied by the large and medium water plants.However, the reciprocating baffled flocculation tank also has big disadvantages. The hydraulic condition is not ideal. The percentage of invalid energy consumption is too much. These cause the huge body of the tank, long time of the flocculation process and high infrastructure costs. To research the reasons of the unsatisfactory hydraulic conditions of the reciprocating baffled flocculation tank, the flow field of the reciprocating baffled flocculation tank as the research objects, PIV experiment and numerical simulation method as the means, the influence of the hydraulic characteristics of the flow field on the flocculation is studied deeply and the ineffective energy consumption part of the fluid field can be found. And based on these, the improvement of the technological structure of the reciprocating baffled flocculation tank can be put forward to give reasonable suggestions for reference to the actual engineering design in the future. According to the research results of this paper, the following conclusions are drawn.(1) The computational results of the Standard k-e, RNG k-e and Realizable k-e models are generally the same as the results of the experiments. However,compared with the experimental data of PIV, the results of the Standard k-e model are more consistent with the experiment data.(2) Through the turbulent kinetic energy and the distribution of turbulent dissipation rate of the reciprocating baffled flocculation tank, we found that the turbulence of water flow are more intensive only in the entrance section and a section of the corridor after the turn. However, the turbulence intensity of water flow in about 2/3of the corridor is very small. This part of the corridor is considered as invalid section.Thus, the reasons for the low flocculation efficiency and the long flocculation time of the reciprocating separator flocculation tank are found in the angle of energy.(3) Through the research and comparison of the ratio of the area of water cross section at the turn of the corridor and the area of cross section of the corridor, we found that if the ratio of area A is about 1.2 to 1.5, the water flow can pass smoothly in theturning of the corridor. The big flocculation particles will not break because of the fast water flow. And large range of dead zone will not be formed.At the turn of the corridor,the dramatic change of the direction of water flow lead to the turbulence of water flow so intensively. And big velocity gradient exists in the water flow. These hydraulic characteristics make big improvement on the process of flocculation. At the same time, it can be found that “backwater zone” can be formed at the right angle turning. This part will make an adverse effect of flocculation. In this case,the paper puts forward to design the structure of the turning as circular arc as an improvement.(4) This paper sets up different angle V type baffles to improve the structure of the reciprocating baffle flocculation tank. Through the comparison of the velocity, the turbulent kinetic energy and the dissipation rate of turbulence, the V type baffle with 60 degrees to 90 degrees can effectively make the turbulence of water flow more intensively, and without excessive energy dissipation.