多相流系统中微颗粒的运动特性研究

发布时间：2018-02-25 00:04

本文关键词： 多相流 VOF模型 DPM离散相模型 PM2.5/PM10 气泡　出处：《西南交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着经济快速发展,世界各地的雾霾现象日益严重。雾霾中的PM2.5/PM10微颗粒对人体健康有着严重的危害性,因此对空气中PM2.5/PM10颗粒的浓度进行检测是非常有必要的。针对雾霾现象,本论文提出了一种基于石英晶体微天平和介电泳(Dielectrophoresis,DEP)原理的PM2.5/PM10浓度监测系统。为了提高PM2.5/PM10浓度监测系统的监测精度以及实现系统对PM2.5/PM10两种颗粒浓度分别监测,本论文采用离散相方法(Discrete Phase Model,DPM)与流体体积方法(Volume of Fluid,VOF)相耦合的方式对监测系统中PM2.5/PM10微颗粒的运动特性进行了数值模拟。为了便于描述微颗粒运动特性,本文将颗粒运动最接近检测池底部的位置称为颗粒的"沉降点"位置。在固-液两相流模型的微颗粒运动轨迹模拟中,分别研究了液体粘度、液体密度、入口速度因素对微颗粒运动轨迹的影响,结果表明:液体粘度由0.01Pa·s减小到1×10-Pa·s过程中,颗粒"沉降点"位置随着液体粘度的减小而下降,当液体粘度从1×10~(-4)Pa·s继续减小到1×10~(-6)Pa·s时,颗粒"沉降点"位置随着液体粘度的减小而略微上升;在液体密度从500kg/m~3增加到2500kg/m~3过程中,颗粒"沉降点"位置随着液体密度的减小而略微下降;入口速度由0.2m/s增加到10m/s的过程中,不同直径颗粒的运动轨迹分离程度变大且"沉降点"位置有所上升。在固-液两相流的基础上,利用VOF+DPM耦合模型模拟研究了气-液-固三相流中入口速度、液体粘度、液体密度、气液两相表面张力这些因素对微颗粒轨迹的影响,结果发现:入口速度由0.2m/s增大到2m/s过程中,不同直径微颗粒的运动轨迹分离程度不断增加,其中PM2.5颗粒"沉降点"位置随着入口速度增加而上升,PM10颗粒"沉降点"位置随着入口速度增加先降低随后上升;液体粘度从0.001Pa·s减小到1×10~(-6)Pa·s过程中,微颗粒"沉降点"位置不断下降;当液体密度500kg/m~3增大到2000kg/m~3过程中,颗粒的"沉降点"位置出现先下降后上升的趋势,在1500kg/m~3时,颗粒"沉降点"具有一个最低位置;气液两相表面张力的变化也对微颗粒的运动产生规律性影响,当表面张力为0.065N/m时,颗粒"沉降点"位置达到最低。通过模拟研究,得到优化的PM2.5/PM10检测系统物性参数,即入口速度设定为0.5m/s~(-1)m/s最为合适,并且可以利用高分子减阻剂将检测池中电解质溶液的液体粘度调整为1×10~(-5)Pa·s,液体密度调整为1500kg/m~3,表面张力调整为0.065N/m。
[Abstract]:With the rapid development of economy, the phenomenon of haze is becoming more and more serious all over the world. The PM2.5/PM10 microparticles in haze are harmful to human health, so it is necessary to detect the concentration of PM2.5/PM10 particles in air. In this paper, a PM2.5/PM10 concentration monitoring system based on quartz crystal microbalance and dielectrophoresisDep is proposed. In order to improve the monitoring accuracy of PM2.5/PM10 concentration monitoring system and realize the system to monitor the concentration of two kinds of PM2.5/PM10 particles separately. In this paper, the motion characteristics of PM2.5/PM10 microparticles in the monitoring system are numerically simulated by the coupling of discrete Phase Model (DPM) and fluid volume of fluid volume (VVF). In this paper, the position of particle movement closest to the bottom of the detection cell is called the "settlement point" of the particle. In the simulation of the motion trajectory of microparticles in the solid-liquid two-phase flow model, the viscosity and density of the liquid are studied, respectively. The effect of inlet velocity factor on the trajectory of microparticles shows that when the viscosity of the liquid decreases from 0.01 Pa 路s to 1 脳 10 ~ (-4) Pa 路s, the "settlement point" of the particles decreases with the decrease of the viscosity of the liquid, while the viscosity of the liquid decreases from 1 脳 10 ~ (-4) Pa 路s to 1 脳 10 ~ (-6) Pa 路s. The position of settling point increased slightly with the decrease of liquid viscosity, and decreased slightly with the decrease of liquid density during the increase of liquid density from 500 kg / m ~ (3) to 2 500 kg / m ~ (-3). In the process of increasing the inlet velocity from 0.2 m / s to 10 m / s, the moving trajectory of particles with different diameters became larger and the "settlement point" position increased. On the basis of solid-liquid two-phase flow, The effects of inlet velocity, liquid viscosity, liquid density and surface tension of gas-liquid two-phase in gas-liquid-solid three-phase flow were studied by VOF DPM coupling model. The results show that when the inlet velocity increases from 0.2 m / s to 2 m / s, the moving trajectory separation degree of different diameter microparticles increases continuously. The position of "settlement point" of PM2.5 particle increases with the increase of inlet velocity. The position of "settlement point" of PM10 particle decreases first and then rises with the increase of inlet velocity, while the viscosity of liquid decreases from 0.001 Pa 路s to 1 脳 10 ~ (-6) Pa 路s. When the liquid density increased from 500 kg / m ~ (3) to 2000 kg / m ~ (3), the position of "settling point" decreased first and then increased. At 1500 kg 路m ~ (-3) ~ 3:00, the "settlement point" had a lowest position. The variation of gas-liquid two-phase surface tension also has a regular effect on the movement of microparticles. When the surface tension is 0.065 N / m, the settlement point of the particles reaches the lowest. The physical parameters of the optimized PM2.5/PM10 detection system are obtained by simulation. That is to say, the inlet velocity of 0.5 m / s / s is the most suitable, and the viscosity of electrolyte solution in the cell can be adjusted to 1 脳 10 ~ (-5) Pa 路s, the density of liquid to 1 500 kg / m ~ (3) and the surface tension to 0.065 N / m ~ (-1) by using polymer drag reducing agent.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513

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