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高输运效率ESI离子聚集装置的数值仿真分析

Numerical Simulation of the High Transportation Efficiency Ion Focusing Equipment

作者: 专业:微机电工程 导师:邹赫麟 年度:2010 学位:硕士  院校: 大连理工大学

Keywords

ESI-MS, ANSYS, electrostatic, FLOTRAN, netual gas flow

        电喷雾电离质谱分析(ESI-MS)的灵敏度主要由电喷雾电离率和离子输运效率来决定。电喷雾电离效率通过控制流体流速、接口管鞘设计、以及对液态分析物的化学处理,能够有效地在大气条件下将液态分析物电离成气态离子。但是,由于电喷雾离子束中库伦空间电荷斥力造成的离子束扩展和质谱仪的取样限制孔径特征,仅有很少部分(0.01-0.1%)电离离子能够进入质谱分析仪被检测到。为了改善大气压环境下电喷雾电离源和质谱仪之间的离子输运效率,本文设计了一种新型电喷雾电离离子聚集装置模型。在电动力学和流场动力学的理论指导下,通过在聚集电极上施加电势产生静电场,以及高压干燥去溶中性气流来影响和改变离子的输运效率。本文对离子聚集电极影响下的静电场进行了仿真分析,得到了较好的仿真分析结果。为了有效减少仿真分析次数,电场分析时采用正交试验设计方法设计实验序列。利用Ansys有限元软件的电场数值分析模块,对这种基于电场的聚集离子装置进行有限元数值分析,提取数值分析结果写入文本文件,使用克里金插值法将这些文本文件中提取到的节点数据进行后处理,绘制等势线,定量分析模型中位于低压质谱入口附近的等势线形状,得到用于正交试验的响应数值。在分析信噪比和均值方差的基础上得到了影响显著性因子和最优化结果。电喷雾电离气态离子中的中性气流场则利用ANSYS/CFD模块FLOTRAN进行分析。在静电场优化分析的基础上,确定气流场的模型参数;通过设置流场属性、分析参数和边界条件,利用湍流标准κ-ε模型进行可压缩流场模型数值分析,结果显示气态离子所处的中性气流场为超音速场,具有自由射流的特征,与理论分析和实验观察到的现象相对应,具有带动分析物离子向低压区域聚集的趋势。
    The sensitivity of ESI-MS is decided mainly by electrospray ionization rates and ion transport efficiency. Electrospray ionization can be effectively generated in atmospheric pressure and turning liquid analyte ions into gaseous ion through controlling the flow velocity, interface design, as well as the tube scabbard liquid analyte chemical processing. However, due to the ion beam caused by expansion coulombic space charge, the ion beam electrospray repulsion and sampling limit aperture features, only a small fraction (0.01-0.1%) of the electrospray ionization ions can enter the mass spectrum analyzer and finally be detected.In order to improve the ion transport efficiency between ESI ion source in atmospheric pressure and mass spectrometer orifice inlet in low pressure, a new electrospray ionization ion ion focusing lens device prototype has been developed in this paper. Based on the electrostatic dynamics’and flow dynamics’theory, ion transport efficiency could be significantly influented by applyling potentials on electrodes in order to forming a accumulation electrostatic field, as well as the utilization of high pressure disovation neutral gas.In order to improving ion transmission efficiency from atmospheric pressure MEMS ion sources to mass spectrometry, a novel ion focusing device has been developed and simulated by ANSYS software with finite element numerical method (FEM). The ion focusing device consists of two electrodes with progressively smaller internal diameter to which electric field are applied. Taguchi DOE has been used in the process of optimization of the structure and diameters of the device. Postprocessing will be implemented by Kriging interpolation method. The shapes of equipotential lines are measured to obtain the response for Taguchi DOE by CAD software. The significance of each factor and optimized structure has been obtained by signal-to-noise ratio and means variance analysis.Neutral gas flow simulation which assist gaseous ion of desolvation is performed by ANSYS/CFD FLOTRAN module. Variables used to form the flow field model are based on mean variance of electrostatic field analysis. This includes defination of flow field attribute, determination of the analysis parameters and the boundary conditions, usage of standard turbulent modelκ-εof compressible model analysis. The results shows that the velocity of neutral flow is supersonic which is the feature of a free-jet phenomenon, corresponding to the theoretical analysis and experimental observing.
        

高输运效率ESI离子聚集装置的数值仿真分析

摘要5-6
Abstract6-7
1 绪论10-21
    1.1 电喷雾电离现象概述10
    1.2 电喷雾电离现象的机理10-13
        1.2.1 电喷雾现象机理10-12
        1.2.2 发生电喷雾的方法12-13
    1.3 电喷雾电离(ESI-MS)离子输运效率泊勺研究现状13-18
        1.3.1 低气压下的离子聚集装置13-14
        1.3.2 大气压下的离子聚集装置14-16
        1.3.3 离子聚集装置的数值分析进展16-18
    1.4 提高样品使用效率和离子输运效率的方法18-19
        1.4.1 使用纳升喷雾源18
        1.4.2 调整质谱仪取样限制孔径18-19
        1.4.3 改善喷雾离子的运动轨迹19
    1.5 课题研究主要内容19-21
2 ESI-MS过程中的离子输运机理21-31
    2.1 离子在离子锥透镜下的输运数学模型21-25
    2.2 质谱仪orifice-skimmer之间的离子输运数学模型25-30
        2.2.1 低压入射自由射流(Free Jet)现象25-27
        2.2.2 Five-Moment离子输运数学模型27-30
    2.3 总结30-31
3 离子聚集装置ANSYS电场分析及优化31-50
    3.1 ANSYS在电场仿真中的应用31-42
        3.1.1 电场基础理论31-33
        3.1.2 离子聚集装置的三维建模33-36
        3.1.3 APDL中使用循环数组进行参数化建模36-39
        3.1.4 参数化宏文件的建模分析过程39-42
    3.2 正交试验方法在电场仿真优化过程中的应用42-48
        3.2.1 静电场模型中因素及水平的确定42-43
        3.2.2 等势线的评价方法43-46
        3.2.3 静电场优化分析结果46-48
    3.3 小结48-50
4 离子聚集装置的ANSYS/CFD仿真50-61
    4.1 流场属性确定50-52
        4.1.1 雷诺数的判定50
        4.1.2 马赫数的判定50-51
        4.1.3 判断N-S方程的适用性51
        4.1.4 湍流模型的选择51-52
    4.2 ANSYS/CFD流场分析52-60
        4.2.1 单元选择和材料属性52
        4.2.2 模型建立和网格划分52-53
        4.2.3 边界条件53-54
        4.2.4 设置FLOTRAN分析参数54
        4.2.5 电极对流场分布的影响54-60
    4.3 总结60-61
结论61-63
参考文献63-66
附录A ANSYS静电场分析APDL命令流66-73
附录B ANSYS APDL宏文件73-79
攻读硕士学位期间发表学术论文情况79-80
致谢80-82
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