【作者】 李旻；

【导师】 周敬宣；

【作者基本信息】 华中科技大学 ， 环境工程， 2011， 博士

【摘要】 真空排水系统是一种具有潜在应用前景的生态污水收集系统。目前,国内外其基础理论及设计方法还停留在定性分析及经验计算的层次上。随着该系统的广泛应用,系统规模的扩大及对能耗问题的关心,其输送机理,设计方法及运行特性等研究还有待进一步深入。本文对真空排水系统终端、管网及真空站的建模及仿真方法进行了深入的研究,实现了系统层次的动态模拟,分析了系统能耗。给出了一种能细致刻画真空排水管道气-液两相流动的双流体模型及其求解方法。以真空排水系统中常见的情景为例,在更精细的尺度上实现了真空管道非恒定流动的数值模拟。以期为该系统的优化设计、运行与管理服务。建立了真空排水系统各子系统的数学模型：1.建立了真空排水系统的两种用户终端的数学模型。2.给出了基于连续性方程,一维气-液两相流稳态压降方程及节点压头方程的真空排水管网的水力模型。导出了动提升压降系数的物理意义,并利用Woldesemayat和Ghajar的Dix修正式给出了优化的计算方法。回顾及比较了四种理论或半经验摩擦压降计算方法(修正的海曾-威廉法、Averil-Heinke法,杜克勒Ⅱ法和段金明法)。为弥补现有方法不足,介绍了一种基于真空管道实验的实验二相系数方法。3.提出了真空站的数学模型,其包含三个控制方程,分别是气相质量方程、液相质量方程和容积方程。以系统的数学模型为基础,首次为真空排水系统定义了一个一维等温气-液两相流的物理域,并在Matlab\Simulink\Simscape软件环境下建立了其仿真模块库。以一个典型室外真空排水系统为例建立了其计算机模型,实现了系统层次的仿真,得到了各集水单元处的污水流量、管网水力特性、真空站的运行参数等重要信息。该平台特别适用于今后复杂的大规模真空排水系统。首次在理论上解答了在真空排水系统运行中备受关注的能耗问题。提出并讨论了三种基于不同假设的,用于描述真空排水系统能耗的数学模型(压力耦合-间歇模型、非耦合-间歇模型、非耦合-稳态模型),对室外系统的单位能耗,室内系统的单次能耗做了预测和比较。其中,压力耦合-间歇模型最接近真实系统,可用于设备的选型和控制策略的优化,但其求解需要在前述计算机平台上进行Monte Carlo模拟。提出了一种能更精细刻画真空管道内气-液两相非恒定流动的,基于等温假设的四方程双流体模型。给出了真空排水管道数值模拟常见边界条件的处理方法。通过将水平管道数值模拟的稳态压降与现有理论和半经验计算结果对比,在一定程度上验证了本研究双流体模型数值模拟的可靠性和精确性。首次对真空排水系统中几种典型的应用情境作了数值实验,其中包括：室外锯齿形管道铺设、室内U形提升管道铺设、室内系统中的上排式立管系统。观察到了气液两相在管内的非恒定流动过程,并讨论了其形成机理。本研究工作是真空排水系统研究由定性分析到定量计算的一个积极探索,以期为该系统的优化设计、运行与管理提供参考。更多还原

【Abstract】 Vacuum sewerage system (VSS) is a promising ecological wastewater collection system. However, its basic theories and design methods at home and abroad have still remain in the level of qualitative analysis and empirical calculation yet. With the extensive applications, scale enlargement and interest in the energy consumption of VSSs, a deeper insight into their transfer mechanisms, design methods and operating characteristics is needed. The modeling and simulation methods of user terminals, pipeline networks and vacuum stations in VSSs were investigated in this paper. A system-level dynamic simulation was achieved and the system energy consumptions were analyzed. A two-fluid gas-liquid model and its solution method dedicated to vacuum pipelines were presented. Some common scenarios in VSSs were chosen as examples here to illuminate the numerical simulation of unsteady two-phase flows in vacuum pipelines with a more delicate scale. This study would be a foundation for the follow-up study on optimization design, operation and management.Subsystem mathematic models of VSSs were established:1. Mathematical models of two types of user terminal in VSSs were built.2. A hydraulic model of vacuum pipeline networks based on continuity equations, pressure loss equations of one-dimension gas-liquid two phase flows, and point head equations was introduced. The physical meaning of the dynamic lift loss coefficient was deduced, of which an optimized calculation method was developed based on the improvement to the correlation of Dix made by Woldesemayat and Ghajar. Four theoretic or semi-empirical calculation methods of friction loss (e.g. modified Hazen-Williams formula, Averil-Heinke method, DuklerⅡmethod and Duan method) were reviewed and compared. To make up for their deficiencies, an experimental two-phase coefficient method for friction loss calculation based on vacuum pipeline experiments was introduced.3. The mathematic model of vacuum station was also built, which comprises three governing equations, e.g. the gas phase mass equation, liquid phase mass equation and volume equation.Based on the system mathematic model, a physical domain of one-dimension isothermal gas-liquid two-phase flow for VSS modeling was defined and a simulation block library was established in Matlab\Simulink\Simscape software environment for the first time. A typical outdoor VSS was taken as an example here to illuminate the modeling process. A system-level system-level dynamic simulation was achieved. Some important information, e.g. the sewage flow rates at each collection unit, hydraulic characteristics of the pipeline network and operation parameters of the vacuum station were obtained. This simulation platform is especially suitable for future large-scale VSSs.The concerned problem of energy consumption in VSSs was solved for the first time. Three energy consumption models (e.g., pressure-coupled intermittent model, uncoupled intermittent model and uncoupled continuous model) for VSSs based on different hypotheses were proposed and discussed. The specific energy demand in outdoor systems and energy demand per flush in indoor systems were predicted and compared. Among the three models, the pressure-coupled intermittent model turns out to be closest to the real system and can be used for equipment selection and control strategy optimization. However, its solution requires in the Monte Carlo simulation in computer platform.A four-equation two-fluid model for transient gas-liquid two-phase flows in vacuum pipelines based on an isothermal hypothesis was put forward. The treatment methods of common boundary conditions for the numerical simulation of vacuum pipelines were firstly presented. The steady pressure loss of horizontal pipe in this numerical simulation was compared with existing theoretic or semi-empirical calculation methods. The results verified the reliability and accuracy of the numerical simulation to a certain extent. Some typical scenarios were numerically investigated for the first time, e.g. saw-tooth pipelines in outdoor systems, U-shape transport-pocket pipelines and uphill-type risers in indoor systems. The transient phenomena of gas-liquid two-phase flows were observed, of which the mechanisms were discussed.This study is an active exploration of VSSs from the qualitative analysis to the quantitative calculation, which will provide a reference to system optimization design, operation and management.更多还原