【作者】 杨非；

【导师】 楼上游；

【作者基本信息】 机械科学研究总院 ， 机械设计及理论， 2012， 博士

【摘要】 悬挂链移动曝气技术是近年来开发的一种新型曝气技术，因其具有效率高、投资少、可维护性强等优点，而迅速被世界各国众多污水处理厂所采用。目前，纵观国内外研究现状，对悬挂链摆动机理和摆动曝气后水力条件对传氧影响的研究仍然较少，深入研究悬挂链摆动机理、曝气流体力学行为，可以为优化曝气操作、设计高效曝气器结构以及拓展悬挂链曝气的应用范围提供依据。曝气的作用即是产生气泡，维持一定气液接触面积。气泡形成是复杂曝气过程中决定曝气效率的一个重要阶段。因此，本论文通过研究悬挂链柔性孔气泡生成特点和所建立的柔性孔气泡体积预测模型，对悬挂链气泡生成体积进行了分析，得出悬挂链采用柔性孔口与气泡尺寸、效率之间的关系。结果表明：柔性孔能产生更小气泡；增加曝气器开孔数将减小小孔流速，减小气泡尺寸。移动曝气是悬挂链区别于其他曝气形式的最大特点，对悬挂链摆动性质的理论分析有利于全面掌握悬挂链工作机理。本论文建立了悬挂链二维动力学模型。模型把悬挂链系统非线性性质与随机摆动建立起联系，分析出悬挂链随机摆动主要能量集中于低频区的特点。悬挂链的随机摆动有利于氧传质进行，使曝气效率提高。在曝气效率影响因素中，水力条件是影响氧传质进行和溶解氧扩散的重要因素。但是曝气流场状态复杂，气液两相间作用强烈，加之大量气泡的存在使得通过实验直接观察流场状态非常困难。近年来，随着计算流体力学、计算传质学的发展，数值模拟已逐渐成为流场研究的重要手段。本论文根据欧拉两相流方程与氧传质方程编制出OpenFOAM计算程序，对悬挂链曝气流场进行了计算流体力学模拟，移动曝气模拟揭示了悬挂链传氧效率高的原因。移动曝气气泡上升速度慢、液流均匀，涡漩流动易于出现在曝气池下部，增加水体总气含率的保有量，加快了溶解氧扩散，提高了氧总转移系数和充氧速度。所得结论为悬挂链改进设计提供了方向，即悬挂链曝气技术优化工作应从如何增加流场流动均匀性和如何增加曝气池中下部涡漩流动入手。更多还原

【Abstract】 Suspended chain moving aeration, as a new aeration technology both at home and abroad in the field of wastewater treatment, has lots of practical applications duo to its high efficiency, less investment, and flexible maintainability. However, the current domestic and international researches study little on suspended chain oscillation mechanism and effect of hydraulic condition on oxygen transfer. A fundamental investigation on oscillation mechanism and fluid dynamics of suspension chain moving aeration would be very beneficial to the optimization of aeration operation and to the design of high efficiency aerator structure and extension of their applications.The purpose of aeration is to maintain a certain gas‐liquid contact area by producing a large amount of bubbles. In the complex aeration process, bubble formation is one of the important stages in determining aeration efficiency. So the objective of the paper is to study the bubble formation generated from a flexible orifice and establish a flexible orifice bubble size prediction model. In this way, the size of the bubble generated from suspended chain aerator can be predicted and it can conclude how the orifice parameters, bubble size, and aeration efficiency are related to each other. The results show that flexible orifice can make smaller bubbles, and increasing the number of orifices will reduce gas velocity and bubble size.Moving aeration is the most distinguished characteristic that differentiates suspended chain aeration from others. Analysis of its movement is beneficial to grasping the working mechanism of suspended chain. A two‐dimension dynamic model of suspended chain has been established. With this model, the relationship between its nonlinear properties and random oscillation can be made and it can conclude that the energy in the oscillation mainly focuses on low frequency band. Moreover, the analysis suggests that the random oscillation is in favor of oxygen transfer and aeration efficiency improvement.As for the factors influencing aeration efficiency, hydraulic conditions, which influence the oxygen mass transfer and diffusion of dissolved oxygen, is one of the most important factors. But it is extremely difficult to experimentally study the details of flow patterns in aeration tank because there are the interaction and strong coupling between liquid and gas phases and the presence of a large amount of bubbles. In recent years, with the development of computational fluid dynamics and mass transfer, the numerical simulation has gradually become an important means for studying the flow field. Based on Eulerian‐Eulerian two fluid models and oxygen mass transfer model, numerical simulation of moving aeration flow field has been conducted through a compiled OpenFOAM program. The simulation results reveal the reasons for the higher oxygen transfer efficiency of suspended chain aeration. The results also show that moving aeration causes the slower rising bubbles, the more uniform flow, and the earlier and more frequent vortex flow in the lower part of aeration tank, which are the reasons for the increase in the total gas holdup, acceleration of diffusion of dissolve oxygen and improvement of volumetric oxygen transfer coefficient and oxygen transfer rate. In the future, it is a possible direction that suspended chain aerator design starts from optimizing uniform liquid flow and increasing vortex flow in the lower part of aeration tank.更多还原