【作者】 杨坤；

【导师】 袁一星；

【作者基本信息】 哈尔滨工业大学 ， 城市水资源， 2014， 博士

【摘要】 给水管网是重要的市政基础设施，是给水系统重要的组成部分。经过长年运行后的管道易产生腐蚀，沿管道内壁会逐渐形成不规则的生长环，它是给水管道内壁由沉淀物、锈蚀物、黏垢及生物膜相互结合而成的混合体。生长环不仅会造成水质的二次污染而且会使管道过水断面减小，阻力系数增加，直接影响管道的通水能力和供水压力。如何有效去除给水管道内壁上的生长环，成为困扰全国各大供水企业的一大难题，是必须要彻底解决的现实问题。气水脉冲管道清洗法是一种操作简单、适应性强、清洗效果较好、对环境无污染的生长环去除方法。但是，这种方法的应用现在还处在经验阶段，对其清洗理论和清洗规律的研究很少。本文利用试验和数值模拟两种手段，揭示了气水脉冲管道清洗过程中两相流的流动特性规律，分析了多个因素对管道壁面剪切力的影响。采用压力检测的方法对清洗过程中的压降进行测定，将试验结果与气液两相流均相流模型相结合，寻求气水脉冲管道清洗过程的压降变化规律。管道中的水流充入高压气体时，管道内的压降比不充气时增大了几十倍；每个清洗周期，管道内的压降具有相同的变化。通过设定不同的试验条件，揭示了供气压力、供水流量等参数对管内两相流压降变化的影响。在供水流量和脉冲频率一定的情况下，管内两相流压降与供气压力呈线性关系；在供气压力和脉冲频率一定的情况下，管内两相流压降与供水流量呈三次多项式关系。在大量试验基础上，对清洗过程中气液两相流流型及其转换进行分析，确定起主要清洗作用的流型为弹状流。基于对水平管内的气液两相流的理论研究，建立了气水脉冲管道清洗过程的数学模型，采用VOF (volume of fluid)方法进行CFD数值模拟，利用试验结果验证了模型的合理性，分别分析清洗过程中直管段和弯管段中流型、动压、湍流强度、壁面切应力等流动特性，为气水脉冲法清除管壁生长环的研究提供理论依据。气液两相流形成弹状流的过程中，水平管道内管道长度l>100D、弯管道内l>15D时弹单元趋于稳定。往管道水流中充入高压气体以后，管道内的动压比不充气时明显增大，并且随着充气时间的延长持续增大。管道内的湍流强度增大，水的紊动情况加剧，壁面剪切力增大，壁面剪切力沿管道长度的变化趋势与管道内气水两相流流态变化相符。通过数值模拟的方法计算不同管径、管道倾斜度、管内腐蚀情况、进气喷嘴尺寸和位置时管内流体与管道壁面的剪切力。条件相同的情况下，管径小于50mm时，管径的变化对流体与壁面间的剪切力值和沿管道的分布情况影响不大；当管径大于50mm时，管径对壁面剪切力的影响较大，随着管径的增大剪切力呈先增大后减小的趋势。向下倾斜管道和水平管的壁面剪切力大于向上倾斜管道的值。粗糙管的壁面剪切力大于光滑管。粗糙度较小时，随着粗糙度的增大，壁面剪切力增大。粗糙度大于0.3cm，随着粗糙度的增大剪切力变化不大。进气喷嘴位置相同时，尺寸小于0.5D（D为管径）的进气喷嘴，管道内流体与管壁的剪切力较小，进气喷嘴尺寸大于等于0.5D时，进气喷嘴尺寸的改变对壁面剪切力的影响不大。随着进气时间的增长，进气位置不同的管道内上壁面剪切力值相差不大。在大部分管段内，进气喷嘴在管道上部的管内流体与下壁面剪切力值最小。研究结果有助于提高气水脉冲管道清洗工程的清洗效果，有利于气水脉冲管道清洗技术的推广应用，有利于解决给水管网水质二次污染问题，降低供水能耗，为保障人民的身体健康、减少能源的消耗、减轻环境污染提供技术支持。更多还原

【Abstract】 Water supply network is the basic infrastructures in city and the component of water supply systems. The irregular growth rings gradually formed along the pipeline inwall because of the corrosion of longtime running. The growth ring is the mixture of the sediment, corrosion, contamination and biofilm, which not only causes the secondary pollution, but also reduces the water-crossing section and increases the resistance coefficient, directly affecting the water supply capacity and pressure. How to remove the growth ring has became the trouble of water suppliers. Air-water pulse washing method is an effective for removing growth ring, being simple to operate, highly adaptable, no environmental pollution. However, the application of barometric Pulse is still in the period of experience, the mechanisms and regulations of washing need to be studied thoroughly. In this study, combined experiments and numerical simulation was used to reveal the flow characteristics of two-phase flow in air-water pulse tube, simultaneously, various elements affecting wall shear stress was analyzed.The pressure drop in the process of washing was also analyzed by detecting the pressures, and the regulation of pressure drop in the process of air-water pulse tube was determined by combined the experimental results and homogeneous flow model of gas-liquid two phase flow. Compared with no air, the specific pressure drop in the pipes increased dozens of times when high pressure air was filled into flow, and the same changes of pressure drops was observed in every wash cycle. The effects of air pressure and water flow on pressure drops in the pipes was studied by setting different experimental conditions. When water flow and impulse frequency were constant, there was significant linear correction between the pressure drops and air pressure. When the air pressure and impulse frequency were constant, the relationship between pressure drops and flow can be expressed through a binary cubic polynomial. The conversion of flow pattern between air and water in the process of washing was observed by picture processing technology, and the slug flow was determined to be the main flow pattern playing the significant role in washing.Based on the study on the mechanisms about air-water two phase flow in the horizontal pipes, mathematical model in the washing process of water-air pulse flushing was established, CFD numerical simulation was conducted by VOF method, and the reasonability of model was verified by experimental results. The flow characteristics such as flow patterns, dynamic pressures, turbulence intensity and wall shear stress in the straight and bended pipes were respectively analyzed, which provided the theoretical basis for removing growth ring in air-water pulse method. In the formation of slug flow of air-water flow, when l>100D or l>15D in the horizontal or bended pipes, the elastic cells tended towards stability. After high pressure air was filled into flow, the dynamic pressure in the pipes was significantly increased, and continuously increased wit the extent of inflation time. It is observed that the turbulence intensity accelerated, the turbulent fluctuation aggravated, and the wall shear increased, simultaneously, the change trends of wall shear along the length of pipes was in accordance with the change of the air-water two phase flow regimes.The flow and wall shear stresses at different pipe diameters, inclinations, corrosion situation, inlet nozzle size and position were calculated by numerical simulation, which provided the guidance for determining the parameters in practical application. Other conditions being equal, when the pipe diameter was less than50mm, the effective of pipe diameter on flow and was small; when the pipe diameter was bigger than50mm, the wall shear stress was changed significantly and increased first and then decrease with the increase of pipe diameter. The wall shear stress in the downward upward inclined pipe and horizontal pipe was higher than that in the upward inclined pipe, and the wall shear stress in roughened tubes was bigger than that in the smooth pipe. When the roughness was lesser, the wall shear stress increased with the increase of roughness. With the roughness increased to a certain degree, the wall shear stress did not changed obviously. At the same position of nozzle of air supply, the flow and wall shear stress was smaller when the nozzle of air supply was less than0.5D (D is pipe diameter), while the wall shear stress was not affected when the nozzle of air supply was more than0.5D. With the extent of inlet time, the wall shear stress at different inlet position changed largely. In most of the section of pipe, the flow and wall shear stress values was the lowest.Research result can improve the cleaning effect of air-water pulse pipeline cleaning engineering, is advantageous to the application of air-water pulse pipe cleaning technology, solve the problem of network secondary pollution, reduce energy consumption of water supply, provide strong support of ensure people’s health, reduce energy consumption and environmental pollution.更多还原