| With the rapid development of the industrial technology and the needs of human production,water resources situation is severer and severer,and it is much concerned by human now.Water resources is insufficient with water pollution,it has seriously been affecting the production development and the improvement of life quality,and also restraining the sustainable development of Chinese economy and society.So the sewage treatment is becoming an urgent affair which should be implemented soon.Implementations of the water resource and sewage treatment measures,advanced treatment and reuse of treated wastewater have become the inevitable requirements of the sewage carcer development.Activated sludge process is an important method of treating sewage,and the aeration tank is the crucial equipment in an activated sludge wastewater treatment process.This article combines the Euler-Euler multiphase flow model with the RNG k-? turbulence model which was used numerically to simulate the typical plug-flow aeration,analyzes the different aeration tank's working conditions,including the air volume fraction,flow field structure,turbulent kinetic energy and its dissipation rate,and compares a number of physical quantities under the different inlet gas velocity to analyze a reasonable speed range,at the same time,compares the pros and cons of the two aeration tubes' arrangement position.Finally,compares and researches the aeration tube and uniform aeration holes,so that the users can select the reasonable aeration types which meet their requirements.The research mainly includes the following conclusions:(1)Through the validation of first model,it is known that the Euler-Euler multiphase flow model combined with the RNG k-? turbulence model was an effective way to simulate the gas-liquid two-phase flow in aeration tanks.Through the validation of second model we found that the selected solving method and degassing boundary conditions can reduce the number of grid,improve computational efficiency.Tlie validation of third model which use the selected solving method found that the simulation results and measured data of the vertical velocity along measured tines were analyzed and compared,and are in a good agreement,which verified that the adaptor of the calculation model and boundary conditions to simulating the fluid dynamics of two-phase flow in aeration tanks is good.(2)By comparing the air volume fraction,the gas-liquid two-phase velocity,the distribution of the turbulent kinetic energy and its dissipation rate,among different aeration speeds on the characteristic section of the aeration tank,it is obtained that the aeration speed of 6.25-7.813m/s could achieved a desired effect of aeration.(3)The distribution of the flow fields,the air volume fraction and turbulent kinetic energy of characteristic sections,non-uniform coefficient of velocity were compared when the aeration tube was arranged in the middle,at one side,respectively,of the aeration tank,which obtained that the mixture flow pattern is relatively stable when the aeration tube was arranged in the middle section of the aeration tank.And the air volume fractionis of characteristic sections is 2.8-5.4 times when arranged in the middle,turbulence is more intense,velocity distribution is more uniform which is conducive to the stability mixing of the mixture in the aeration tank,and the oxygen transferring between the gas and liquid.(4)The air volume fraction,turbulent kinetic energy and its dissipation rate,the average speed of gas and liquid were compared when the aeration tube was arranged in the middle and the uniform aeration,that found turbulence is more intense and has more air volume fraction,and the two-phase contact time is also longer under uniform aeration,that allows higher oxygen transfer efficiency between the gas and liquid,improve the utilization efficiency of oxygen.By studying the aeration rate and the arrangement mode of the aeration tank,some reference value has been provided for the designing and running of aeration tank. |
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