【作者】 左小红；

【导师】 胡筱敏；

【作者基本信息】 东北大学 ， 环境工程， 2005， 硕士

【摘要】 旋转管式膜分离是强化十字流微滤的有效方法之一,它较好的解决了长期以来阻碍膜分离技术的膜污染和浓差极化问题。但是由于其内部为旋转剪切流、轴向剪切流和径向渗透流共同作用的三维流场,至今仍没有对其分离机理形成统一的认识。课题组于2001年采用PIV激光测试系统对旋转聚丙烯(PA)管式膜分离器环隙子午面的流场进行了实测,本研究将理论与测试结果结合进行分析,比较系统的研究了膜器环隙间的流场特征和膜器的过滤机理。 首先结合前人的研究成果,讨论了膜器环隙间的流动机制,分析了波涡、交错螺旋涡、交错螺旋波涡的涡动状态特征。推导出轴向流和渗透流同时存在时,流动从库特层流转化为层流涡以及从层流涡转化为波涡时临界Tavlor数的近似表达式,表达式较好地反映了轴向流和渗透流较小时的流态转变机制。 对课题组前期的测试结果进行分析发现:对于无轴向流和渗透流情形,在较低的内管转速下出现稳定的层流涡,涡的形状和位置基本不随测试时间的推移而改变,涡近似呈规则的正方形,大小与环隙宽度相当,流场近似活塞流,流场中的质量传递很小;随着内管转速的增大,环隙间的流体流动不稳定性增强,逐渐由层流涡向波涡、过渡涡甚至湍流涡发展。轴向流和渗透流同时存在时,环隙间仍会出现Taylor涡,并且涡在环隙间轴向漂移。在较宽的内管转速范围内均有波涡出现,波涡是比较适合实际过滤的一种流动形态。旁流伴随波涡的出现而产生,其流量随内管转速的增大逐渐减小,由于旁流对过滤速度和控制膜污染的影响相互矛盾,因此在实际过滤中应根据物料特性选择适当的内管转速。受底端进料的影响,垂直方向高位涡的轴向尺寸大于垂直方向低位涡的轴向尺寸。通过比较不同过滤压力和轴向流速下环隙间的流动发现:操作压力对环隙间的流动特征几乎没有影响;较大的轴向流会使环隙间的流动变得更加稳定,形成发育完全的稳定层流涡需要更大的内管转速。更多还原

【Abstract】 Rotary tubular membrane filtration is one of the most efficient methods to enhance cross-flow microfiltration. It can resolve the key problem of membrane fouling and concentration polarization that obstruct the development and application of the membrane separation technology for a long time. But its separating mechanism and the flow field characteristics in the annulus have been far from understanding, because the flow field is a combination of circular Couette flow, pressure-driven axial flow, and radial permeating flow at the inner cylinder. The flow field in the meridian plane of the apparatus was measured with Particle Image Velocimetry System (PIV) in 2001. In this paper, the flow field characteristics and filtration performance were investigated based on theoretic analysis and actual measurement.First, on the basis of previous research, transition law of the flow in the annulus and the characteristics of three vortex regimes (wavy vortices, alternating helical vortices and alternating helical wavy vortices) were discussed. When both axial flow and permeating flow existed, the formulae of critical Taylor number were deduced as flow transformed from Couette-Poiseuille flow (CP) into laminar vortices (LV) and from laminar vortices (LV) into wavy vortices (WV) respectively.Then, lots of velocity vector-graphs and streamlines of vortices in the meridian plane of the separator obtained in previous measurement were analyzed. In the absence of axial and permeating flow, when the rotational frequency of inner cylinder was 0.90rps, laminar vortices were observed. Laminar vortices are nearly sauare, and the dimension of vortices approximates to the width of annular gap. Laminar vortices are essentially更多还原