温差对辐流式沉淀池水力特性影响的数值模拟

Numerical simulation of influence of temperature difference on hydraulic characteristics in radial flow sedimentation tank

在同时考虑进水与池内水的污泥质量浓度差异及不同季节进水与池内水的温度差异的条件下,对城市污水处理厂中广泛应用的辐流式二沉池内的异重流现象进行数值模拟,重点研究冬夏季温差导致的异重流对池内流场、速度场及浓度场的影响,为提高沉淀池污水处理效率提供理论支持.选取Mixture模型和Realizable k-ε湍流模型,设初始时刻池内充满水,进水为含一定质量浓度污泥的污水(污泥密度为1 051kg/m3,污水密度为1 000.35kg/m3),并通过设置池内水与进水的不同温差,对沉淀池内冬季与夏季不同时刻各工况下异重流的演变规律进行数值模拟.结果表明:由于温度不同导致水流密度变化,使得夏季低温水进入池内产生下异重流,而冬季高温水进入时产生上异重流;冬夏季由温差导致的异重流的存在,均使沉淀池内产生较大的回流区,夏季沉淀池内形成较大的逆时针旋流,而冬季则在池中部形成逆时针旋流,池后部形成较大的顺时针旋流,异重流导致的旋流作用对沉淀池内水流流态及污水处理效率的影响不容忽视.

Considering the sludge concentration difference and the temperature difference between the inflow water and the water in pool in different seasons,the radial flow sedimentation tank is numerically simulated especially,the influence of temperature difference on the flow field,velocity field and sludge concentration distribution of density current in the radial flow sedimentation tank is studied in summer and in winter,to improve the efficiency of wastewater treatment.The mixture model with the realizable k-εmodel is used to simulate the property of density current by setting the different temperature differences between the inflow water and the water in the tank in summer and in winter.In initial time the sedimentation tank is filled with water and the inflow water is sewage which contains certain sediment mass concentration（sediment density is 1 051kg/m3,sewage density is 1 000.35kg/m3）.The results show that：water density changes with temperature difference,which makes the low temperature inflow water to strengthen the gravity flow in the bottom in summer;while the high temperature inflow water produces the gravity flow on the top in winter;the larger recirculation region in sedimentation tank is produced by the density current of temperature difference in summer and in winter;the counterclockwise vortex obviously forms in summer;while in winter the counterclockwise vortex forms in the middle of the tank and large clockwise vortex forms at the back of the tank,which influences the water flow property and the efficiencyof wastewater treatment in the sedimentation tank.