The Study On Optimal Design Of Energy Saving And Chlorine Disinfection In Clearwells

Along with rapid development of economy, pollution of water source and the power consumption of waterworks are day by day serious, disinfection process in the waterworks is more important. The article aims at enhancing the chlorine disinfection efficiency and lowering the energy consumption of clearwells, utilizes business software Fluent related to Computational Fluid Dynamics (CFD) as the calculation platform, with tracer experiments to research the structure and water-hydraulic characteristics of clearwells, the configuration of clearwells is optimized designed.The article establishes a model of energy saving in clearwells. That is, to enhance the water lever of clearwells, the pool of water distribution is set in clearwells. According to the annual average daily water energy consumption and annual average daily volume of the loss of water to make a mathematical model, and in accordance with the relationship between inlet and outlet of the pool of water distribution and the capacity of water pumping stations, it can analyse and calculate, and draw out the relationship between the electricity of the year and the year annual average of the daily water supply, to reach the purpose of optimizing the energy saving.The hydraulic characteristics and effective hydraulic residence time (t10) of round clearwells can be obtained by tracer experiments, t10 represents the true residence time in clearwells of disinfectants. According to the contrast results of round clearwells'tracer experiments and the CFD simulation, the flow fields and other hydraulic phenomena inside clearwells are visualized with versatile function of CFD method.It concentrates a method of adding User-defined scalar (UDS), programming User defined function (UDF), then uploads to the Fluent software, finally establishes 2-D mathematic model for clearwells. The mathematic model is applied to the simulation and the calculation of the velocity field of water flow, retention time distribution function of dye tracers, concentration field of chlorine for clear well with one baffle plate, two baffle plates, three baffle plates, four baffle plates and seven baffle plates respectively in rectangular (round) clearwells, and draw out the distribution function of the tracer resident timeand the loss of water. It can analyze the influence factors of disinfection efficiency of two baffle plates of rectangular (round) clearwells under increasing the perforated board, changing guiding wall shape, increasing inlet and outlet diameter and changing the length of plates.The CFD results indicate that, along with the number of baffle plates increasing, the distribution uniformity of flow field and chlorine concentration field are improved, the area of circumfluence is reduced, the flow field approaches the ideal plug flow, and the disinfection effect is enhanced. However, there is a limit of the number of plates, more than this value disinfection increase is not obvious, but a downward trend. Moreover, the guiding wall comer changes to arc, increase the baffle plates simultaneously increasing the perforated board and increase the length of plates, it is also helpful for the improvement of disinfection efficiency. The loss of water is not simply a linear relationship to the number of the baffle plates, but also need to consider the returning zones in clearwells. The loss of pressure is directly proportional to the area of the returing zones in clearwells.