【作者】 刘凤霞；

【导师】 刘志军； 周集体；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2009， 博士

【摘要】 本文借助Dantec FlowMap500 DPIV系统,对不同结构槽道内的涡旋波流动时空特性进行了实验研究。基于计算流体动力学对多种结构参数的槽道在多种操作参数条件下所形成的涡旋波流场进行了数值计算。对涡旋波膜生物反应器中氧体积传质系数及模拟废水COD降解状况进行了实验研究。研究的主要内容和成果如下:（1）从涡旋波流场PIV实验测试和数值模拟两方面入手,分析了涡旋波流动与卡门涡街的异同,定量地分析了槽道结构参数（槽道高度、宽度、扩张角度、扩张比例、折流间距等）和操作参数（St、Re、三种入流形式等）对涡旋波的流动形式、涡量、剪切力等的影响,给出了由于旋涡的产生、发展和消失的变化过程导致槽道壁面区域和中心区域流体对流混合的加剧程度,找出了涡旋波流动引起过程强化的根本原因。（2）根据边界层理论,分析了涡旋波流场中旋涡产生发展的机理,得到如下结论:流场中第一个旋涡的产生是由于槽道截面突扩致使流体产生了逆压梯度,后续的旋涡是由于入流减速阶段流体产生了逆压梯度而造成的,最后一个旋涡是由于面向来流的槽道壁面阻止了流体的流动致使流体产生了逆压梯度而造成的。（3）利用涡旋波流动的特点,设计了废水处理涡旋波膜生物反应器实验装置。以清水为介质进行了冷模实验,并以人工合成废水进行了活性污泥降解实验。实验结果表明:膜生物反应器中涡旋波流动与稳态流动相比,氧传递系数k_Lα值的增幅范围为8.8%～107.7%,COD去除率从77%提高到97%,表明涡旋波流动对强化传质和反应过程具有明显的效果。正交试验直观分析和方差分析结果表明,Re对试验指标k_Lα和COD去除率影响最大。本文也分析了Re、跨膜压差TMP、通气量Q_G和折流间距l等参数对k_Lα和COD去除率的影响。实验具有较好的重复性。（4）在实验研究的基础上,建立了底物降解一级反应动力学模型:C=C₀exp（—K₁t）。在COD的降解过程中,HRT=4.5h,达到排放标准。本文也研究了不同入口COD浓度、不同Re、TMP和Q_G下COD降解特性,通过实验数据的回归分析,得出了模型参数C₀和K₁。本文对涡旋波流动特性进行的理论研究、实验测试分析和模拟计算,以及涡旋波流动对膜生物反应器的传质和反应过程强化的实验研究,为涡旋波流动的理论研究和实际应用奠定了基础。更多还原

【Abstract】 It has been received much attention that the mass,momentum and heat transfer can be produced by unsteady flows in a channel during the past few decades because of their usages in chemical,biochemical and medical engineering.As the study of fluid mechanics has evolved from steady state investigations towards the reality of unsteady phenomena,it has become increasingly clear that instantaneous whole field non-intrusive flow measurement techniques are required.Vortex Wave Membrane Bioreactor（VWMBR） combines vortex wave flow with membrane aerated bioreactor for wastewater treatment,by which mass transfer is enhanced by the action of forced convective.Compared to traditional methods of enhancing mass transfer by using turbulent flow,the shearing stress and the power dissipation in VWMBR are rather lower.VWMBR increases survival rate of microorganism cells and can also solve some problems such as clogging and concentration polarization in the traditional MBR.The understanding of spatio-temporal characteristics of the fluid flow and the performance of the VWMBR are of great practical importance.To characterize the flow instability,digital particle image velocimetry（DPIV） （FlowMap500 from Dantec Inc.） is used to measure the near-instantaneous flow fields in 5 different channels with different structure respectively.To improve our understanding on the mixing processes,fluid flow in 2D asymmetric channels with different structure or different operating parameters are investigated via Computational Fluid Dynamics simulations.In this paper,performance of the VWMBR,such as volumetric oxygen transfer coefficient and the removal rates of COD,is investigated for artificial wastewater treatment.The main contributions of the study are included as follows:（1） System study shows that the flow regime is different from Karman Vortex Street. And quantitative analysis reveals the influence of geometric parameters（such as the channel height,width,transition angle,expand ratio,deflector distance） and operating parameters（St, Re,inlet velocity） on the size of vortex wave,the vorticity and the stress.The radical reason of mass transfer enhancement lies in the adequately convective mixture of the fluid particles in the central region and near the channel wall during vortices motions.（2） Quantitative analysis on mechanism of the vortices formation and motion based on boundary-layer theory indicates that the geneses of the vortices are different.The first and the last vortices are formed owing to the adverse pressure gradient caused by the channel enlargement and contraction in section,respectively.And the others were induced by the adverse pressure gradient attributed to inlet flow deceleration.（3） A set of experimental equipment of VWMBR in batch mode is established.The mass transfer experiments of water and wastewater are carded out for different channel structures. Results of synthesis wastewater treatment are evaluated by Chemical Oxygen Demand（COD） of influent and effluent.The comparison study of the k_La and COD removal rates shows that vortex wave can enhance convective mixing.The result of water experiment is consistent with that of wastewater treatment.Through orthogonal experiments,the factors affecting k_La and COD removal rates,such as Re,Tran-Membrane Pressure（TMP） and ventilation volumeQ_G were studied.The results showed that Re had strong effect on k_La and COD removal rates. The effects of four operation factors（Re,TMP,Q_G and deflector distance） on kLa and COD removal rates are investigated.The results show that the system is good for repetitiveness.（4） VWMBR can be treated as a batch continuous stirred tank reactor with the vortex wave flow regime.Based on the analysis of the laws of conservation of mass,the degradation is shown to follow a pseudo-first order reaction:C=C₀exp（-K₁t）。The water quality of the effluent could close to the national first discharge standard 100mg/L during experiment of 3h, and meet the standard after 4.5h.Using linear regressive analysis,approximate formulas are obtained which could be used to determine C₀ and K₁.This work presents quantitatively studies for the hydrodynamics and mass transfer characteristic of the vortex wave with low Reynolds number.It provides experimental and design foundation for further study and industrialization of the VWMBR.更多还原