网格絮凝池PIV测量及实验研究

发布时间：2018-03-09 15:32

本文选题：网格絮凝池　切入点：PIV测量　出处：《兰州交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文以网格絮凝池模型为试验研究对象,采用粒子成像速度场仪(PIV)对网格絮凝池流场进行测量,获得不同网孔尺寸网格板在不同进水流量条件下的流场信息。基于PIV测试结果,按变化规律信息将速度场划分区域,结合大涡PIV方法探求网格絮凝池内湍动能k及湍动耗散率ε的分布情况,找寻其与速度场划分区域间的联系。同时在相同的前提条件下,进行絮凝实验,深入的研究网格絮凝池流场的水力特性与絮凝效果之间的关系。通过对网格絮凝池模型进行流场PIV测量及絮凝实验研究,可以得出以下主要结论:1.对不同网格板后各向速度进行全面分析,得出水流过网格板后速度变化以纵向速度为主,距网格板越近,纵向速度与横向速度的比值越大;距网孔中心越近,纵向速度与横向速度的比值越大;距格挡中心越近,纵向速度与横向速度的比值越小。2.分析特定网格板(6×6mm)后各特征截面的各向速度,得出水流通过网格板后速度的变化规律基本呈现为三类:加速区、掺混区、稳定区,若改变水力条件,区域划分范围会有弱小的波动。本次试实验中1号网格板(4×4mm)和2号网格板(6×6mm)获取的流场中速度变化规律经历三个过程,加速区、掺混区、稳定区,3号网格板(10×10mm)获取的流场中速度变化规律只经历了加速区和掺混区。3.进水流量越大,水流过网格板后的流速越大,颗粒碰撞的几率随之增大,从而引起湍动能增大,湍动能耗散率增大。利用大涡PIV方法分析流场,距网格板距离一定,在相同进水流量条件下,不同网格板对应的湍动能及湍动能耗散率的波动幅度不同,分析得出,湍动能的波动幅度在加速区、掺混区较大,稳定区较小;湍动能耗散率的波动幅度在加速区较大,掺混区、稳定区较小。4.根据絮凝实验可以得出,改变水力条件对絮凝效果具有明显影响。网孔尺寸过小时,进水流量小,水流过网格板后的流速可以达到设计流速范围,絮凝效果较好;进水流量过大,水流过网格板后流速过大,对流场引起的紊动较大,会破坏已形成的絮体结构,使细小絮体的数量逐渐增加,絮凝效果反而变差。网孔尺寸过大时,随进水流量的改变,水流通过网格板后流速达不到设计流速范围,生成的絮体颗粒相互碰撞几率低,絮凝剂只会局部发生微团内高浓度反应,不能充分与更多悬浮物接触生成絮体并进行沉降,致使絮凝效果差。综合对比得出,2号网格板(6×6mm)的絮凝效果更好。
[Abstract]:In this paper, the flow field of grid flocculation tank is measured by particle imaging velocity field analyzer (PIV), and the flow field information of grid plate with different mesh size under different influent flow rate is obtained. Based on the results of PIV measurement, the flow field of the grid flocculating cell model is studied in this paper. The velocity field is divided into regions according to the changing law information, and the distribution of turbulent kinetic energy k and turbulent dissipation rate 蔚 in the grid flocculation cell is studied by using the large eddy PIV method, and the relation between the velocity field and the velocity field is found. At the same time, under the same premise, the distribution of turbulent kinetic energy k and turbulent dissipation rate 蔚 in the grid flocculation cell is studied. The relationship between hydraulic characteristics and flocculation effect of grid flocculation tank was studied in depth. The flow field PIV measurement and flocculation experiment were carried out on the model of grid flocculation tank. The main conclusions are as follows: 1. The following conclusions can be drawn: 1. The overall analysis of the velocity of different grid plates shows that the variation of water velocity after flowing through the grid plate is mainly the longitudinal velocity, the closer to the grid plate, the greater the ratio of longitudinal velocity to transverse velocity; The closer it is to the center of the mesh, the bigger the ratio of longitudinal velocity to transverse velocity is, and the closer it is to the center of the grid, the smaller the ratio of longitudinal velocity to transverse velocity is. It is concluded that the variation law of the flow velocity after passing through the grid plate is basically presented as three categories: acceleration zone, mixing zone, stable zone, if hydraulic conditions are changed, In this experiment, the velocity variation law in the flow field obtained from the 1 grid plate 4 脳 4 mm and 2 mesh plate 6 脳 6 mm) experienced three processes: acceleration zone, mixing zone, In the stable region, the velocity variation law in the flow field obtained by the No. 3 grid plate 10 脳 10mm only experienced the acceleration zone and the mixing zone .3.The larger the influent flow rate, the greater the velocity of water flowing through the grid plate, and the probability of particle collision increases, thus causing the increase of turbulent kinetic energy. The turbulent kinetic energy dissipation rate is increased. The large eddy PIV method is used to analyze the flow field with a constant distance from the grid plate. Under the same influent flow rate, the turbulence kinetic energy and turbulent kinetic energy dissipation rate of different grid plates are different. The fluctuation amplitude of turbulent kinetic energy is in the acceleration region, the mixing region is larger, the stable region is smaller, the fluctuation range of turbulent kinetic energy dissipation rate is larger in the acceleration zone, the mixing zone and the stable region are smaller. Changing hydraulic condition has obvious influence on flocculation effect. When the size of mesh hole is too small, the flow rate of water can reach the design velocity range, the flocculation effect is better, the influent flow rate is too large, the flow rate of water can reach the design velocity range after flowing through the grid plate, the flow rate of the inlet water is too large, When the velocity of water flows through the grid plate is too large, the turbulence caused by the flow field is larger, which will destroy the structure of the floc that has been formed, and make the quantity of the fine floc increase gradually, and the flocculation effect becomes worse. When the size of the mesh hole is too large, the flow rate changes with the influent. The velocity of flow through the grid plate can not reach the designed velocity range, and the probability of collision between the generated floc particles is low. The flocculant can only produce high concentration reaction in the micro-agglomeration, and can not fully contact with more suspensions to form the floc and make the floc settle. The result shows that the flocculation effect is better than that of No. 2 grid plate (6 脳 6 mm).
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU991.2

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