气水脉冲清洗给水管道两相流过程研究及其数值模拟

发布时间：2019-01-07 13:19

【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l100D、弯管道内l15D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。
[Abstract]:The water supply network is an important municipal infrastructure, which is an important part of the water supply system. the pipeline is easy to generate corrosion after the long-year operation, and an irregular growth ring is gradually formed along the inner wall of the pipeline, and the inner wall of the water supply pipe is a mixture formed by combining the sediment, the rust, the clay and the biological film. The growth ring can not only cause secondary pollution of water quality, but also reduce the cross-section of the pipe, increase the resistance coefficient, and directly influence the water supply capacity and the water supply pressure of the pipeline. How to effectively remove the growth ring on the inner wall of the water supply pipe becomes a difficult problem for the large-scale water supply enterprises in the whole country, and it is a real problem that must be thoroughly solved. The air-water pulse pipeline cleaning method is a method for removing the growth ring with the advantages of simple operation, strong adaptability, good cleaning effect and no pollution to the environment. However, the application of this method is still in the stage of experience, and has little research on its cleaning theory and cleaning rule. In this paper, the flow characteristics of two-phase flow in the process of gas-water pulse pipeline cleaning are revealed by means of experimental and numerical simulation, and the influence of several factors on the shear force of the wall surface is analyzed. The pressure drop in the cleaning process is measured by the method of pressure detection, the test result is combined with the gas-liquid two-phase flow homogeneous flow model, and the pressure drop variation rule of the gas-water pulse pipeline cleaning process is sought. law. When the water in the pipeline is filled into the high-pressure gas, the pressure drop in the pipeline is increased by dozens of times than when it is not inflated; and the pressure drop in the pipeline has the same change per cleaning cycle By setting different test conditions, the variation of pressure drop and pressure drop of two-phase flow in the tube is revealed by the parameters such as air supply pressure and water supply flow. In the event that the water supply flow and the pulse frequency are constant, the pressure drop of the two-phase flow in the pipe is in linear relation with the air supply pressure; in the case of the air supply pressure and the pulse frequency, the two-phase flow pressure drop and the water supply flow rate in the pipe are three times of polynomial on the basis of a large number of experiments, the two-phase flow type and the conversion of the gas liquid in the cleaning process are analyzed, the flow pattern of the main cleaning action is determined to be elastic, Based on the theoretical study of the two-phase flow of the gas liquid in the horizontal tube, the mathematical model of the gas-water pulse pipeline cleaning process is established, and the numerical simulation of the CFD is carried out by the volume of fluid method, and the model is validated by the results of the test. The flow characteristics of the flow type, the dynamic pressure, the turbulence intensity, the wall shear stress and the like in the straight pipe section and the bent pipe section during the cleaning process are analyzed respectively, and the study of the pipe wall growth ring is provided for the air-water pulse method. On the basis of the gas-liquid two-phase flow forming the elastic flow, the length of the pipe in the horizontal pipe is l100D, and the trend of the elastic unit in the curved pipe when the high-pressure gas is filled into the water flow of the pipeline, the dynamic pressure in the pipeline is obviously increased when the pressure in the pipeline is not inflated, and with the extension of the inflation time, The increase of the turbulence intensity in the pipeline, the increase of the turbulent flow of the water, the increase of the shear force of the wall, the change of the wall shear force along the length of the pipe and the flow state of the two-phase flow of the gas in the pipeline in accordance with that method of numerical simulation, the pipe wall and the pipe wall of the pipe are calculate by the method of numerical simulation, the pipe inclination, the corrosion condition in the pipe, the size and the position of the intake nozzle, The shear force of the surface is the same. When the pipe diameter is less than 50mm, the shear force value between the fluid and the wall surface and the distribution of the pipe are not affected by the change of the pipe diameter; when the pipe diameter is larger than 50mm, the influence of the pipe diameter on the shear force of the wall surface is large, The tendency to decrease. The wall shear force of the downward inclined pipe and the horizontal pipe is greater than the upward inclination The value of the inclined pipe. The shear force of the surface of the rough pipe It is larger than the smooth tube. The roughness is small, with the increase of the roughness, the wall surface The shear force is increased. The roughness is greater than 0. 3cm, and the shear force increases with the increase of the roughness. The force change is not large. When the position of the air inlet nozzle is the same, the air inlet nozzle with the size of less than 0.5D (D is the pipe diameter), the shearing force of the fluid in the pipeline and the pipe wall is small, the size of the air inlet nozzle is greater than or equal to 0.5D, and the change of the size of the air inlet nozzle is equal to the shear force of the wall surface. The influence of the air intake time is not large. With the increase of the air intake time, the shear force on the inner wall surface of the pipe with different air intake position The difference between the values is not large. In most of the pipe sections, the intake nozzle is cut from the pipe in the upper part of the pipe with the lower wall The method is beneficial to the popularization and application of the air-water pulse pipeline cleaning technology, is beneficial to solving the problem of secondary pollution of the water quality of the water supply pipe network, reduces the energy consumption of the water supply, and aims to ensure the health of the people, Reduce energy consumption and reduce environmental pollution
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU991.3

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