油扩散泵结构对蒸汽射流场影响的数值研究

发布时间：2019-01-17 15:45

【摘要】：油扩散泵与其他种类真空泵相比,结构更为简单,无运动部件,没有振动与噪声,使用方便,寿命长,成本低,因此被广泛应用于各科学研究和工业生产领域中,如电子、冶金、化学、原子能等工业部门和空间技术等。扩散泵工作介质为扩散泵油,尽管在结构上采取了一些措施,但扩散泵油向高真空一侧返流造成的油污染问题一直是制约扩散泵应用的主要原因。提高抽气性能、抽气稳定性、降低返油率是扩散泵需要解决的主要问题,其中,低返油率扩散泵是当前科研、生产单位研发的重点。扩散泵的返油与一级喷嘴形状、尺寸、多级串联喷嘴间距、挡油帽形状、尺寸、挡油环设置位置等因素有关,这些因素决定了扩散泵油蒸汽的射流状态和流场结构。通过流场结构分析可以更好地理解扩散泵的抽气和返油机理,通过射流场控制可以有效地减少返流。由于扩散泵经典理论难以准确描述和定量反映扩散泵油蒸汽射流流动特性,本文在分析扩散泵抽气机理的基础上,运用计算流体力学软件Ansys-workbench,以K800扩散泵为计算原型,对其内部蒸汽射流场进行了数值模拟,得到了第一级喷嘴结构、挡油环位置、挡油帽尺寸、串联喷嘴级间距对扩散泵射流场的影响结果,对理解扩散泵抽气机理、改进扩散泵抽气性能、减少返油率均具有一定的指导意义。数值模拟结果表明,喷嘴出口速度受喉部尺寸的影响,喷嘴出口速度随喉部间隙减小而增大,随喷嘴张角增大而增大；挡油帽过长或者过短都不利于扩散泵抽气,存在与射流场匹配的最佳挡油帽结构尺寸,此时返油率较低；挡油环的位置影响蒸汽射流流场分布及涡旋的形成,决定扩散泵的返油率,挡油环位置的正确设置对减少返油率起到至关重要的作用；一二级喷嘴间距、二三级喷嘴间距存在的最佳值,且串联两级喷嘴距离越大,油蒸汽冷凝效果越好,但喷嘴间距离过大又影响扩散泵结构的紧凑性,而距离过小又会影响扩散泵的正常工作,合理的级间距设计要兼顾抽气稳定性和结构紧凑性。
[Abstract]:Compared with other types of vacuum pumps, oil diffuser pumps have simpler structure, no moving parts, no vibration and noise, easy to use, long life and low cost, so they are widely used in various fields of scientific research and industrial production, such as electronics, Metallurgical, chemical, atomic and other industrial sectors and space technology. The working medium of diffuser pump is diffusing pump oil. Although some measures have been taken in structure, oil pollution caused by reflux of diffusing pump oil to one side of high vacuum is the main reason that restricts the application of diffusive pump. Improving the pumping performance, pumping stability and reducing the oil return rate are the main problems to be solved in the diffuser pump, among which, the low return oil rate diffuser pump is the focus of R & D of the current scientific research and production units. The return oil of the diffuser pump is related to the shape of the first-order nozzle, the dimension, the space between the multi-stage series nozzles, the shape and size of the cap, the position of the oil retaining ring, and so on. These factors determine the jet state and the flow field structure of the oil vapor in the diffuser pump. The mechanism of pumping and returning oil of diffuser pump can be better understood by analyzing the flow field structure, and the reflux can be effectively reduced by the control of jet field. Because the classical theory of diffuser pump is difficult to accurately describe and quantitatively reflect the characteristics of oil-steam jet flow in diffuser pump, based on the analysis of pumping mechanism of diffuser pump, the K800 diffuser pump is used as the calculation prototype by using computational fluid dynamics software Ansys-workbench,. The influence of the structure of the first stage nozzle, the position of the oil retaining ring, the size of the oil retaining cap and the step spacing of the series nozzles on the jet field of the diffuser pump is obtained by numerical simulation, which is helpful to understand the pumping mechanism of the diffuser pump. Improving the pumping performance of the diffuser pump and reducing the oil return rate are of certain guiding significance. The numerical simulation results show that the nozzle exit velocity is affected by the throat size. The nozzle exit velocity increases with the decrease of throat clearance and increases with the increase of nozzle opening angle. If the cap is too long or too short, it is not conducive to the pumping of the diffuser pump, and there is the optimum structure size of the cap matching with the jet field, and the return rate of oil is low. The position of the oil retaining ring affects the distribution of the steam jet flow field and the formation of the vortex, and determines the oil return rate of the diffuser pump. The correct setting of the oil retaining ring position plays an important role in reducing the oil return rate. The best value of the distance between the first and second nozzles, the distance between the second and the third nozzles, and the larger the distance between the two stage nozzles in series, the better the condensing effect of the oil steam, but the larger the distance between the nozzles also affects the compactness of the structure of the diffuser pump. The distance is too small which will affect the normal operation of the diffuser pump. The reasonable design of stage spacing should take into account the pumping stability and structure compactness.
【学位授予单位】：东北大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB752

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