【摘要】：油擴散泵與其他種類真空泵相比,結(jié)構(gòu)更為簡單,無運動部件,沒有振動與噪聲,使用方便,壽命長,成本低,因此被廣泛應用于各科學研究和工業(yè)生產(chǎn)領(lǐng)域中,如電子、冶金、化學、原子能等工業(yè)部門和空間技術(shù)等。擴散泵工作介質(zhì)為擴散泵油,盡管在結(jié)構(gòu)上采取了一些措施,但擴散泵油向高真空一側(cè)返流造成的油污染問題一直是制約擴散泵應用的主要原因。提高抽氣性能、抽氣穩(wěn)定性、降低返油率是擴散泵需要解決的主要問題,其中,低返油率擴散泵是當前科研、生產(chǎn)單位研發(fā)的重點。擴散泵的返油與一級噴嘴形狀、尺寸、多級串聯(lián)噴嘴間距、擋油帽形狀、尺寸、擋油環(huán)設置位置等因素有關(guān),這些因素決定了擴散泵油蒸汽的射流狀態(tài)和流場結(jié)構(gòu)。通過流場結(jié)構(gòu)分析可以更好地理解擴散泵的抽氣和返油機理,通過射流場控制可以有效地減少返流。由于擴散泵經(jīng)典理論難以準確描述和定量反映擴散泵油蒸汽射流流動特性,本文在分析擴散泵抽氣機理的基礎(chǔ)上,運用計算流體力學軟件Ansys-workbench,以K800擴散泵為計算原型,對其內(nèi)部蒸汽射流場進行了數(shù)值模擬,得到了第一級噴嘴結(jié)構(gòu)、擋油環(huán)位置、擋油帽尺寸、串聯(lián)噴嘴級間距對擴散泵射流場的影響結(jié)果,對理解擴散泵抽氣機理、改進擴散泵抽氣性能、減少返油率均具有一定的指導意義。數(shù)值模擬結(jié)果表明,噴嘴出口速度受喉部尺寸的影響,噴嘴出口速度隨喉部間隙減小而增大,隨噴嘴張角增大而增大；擋油帽過長或者過短都不利于擴散泵抽氣,存在與射流場匹配的最佳擋油帽結(jié)構(gòu)尺寸,此時返油率較低；擋油環(huán)的位置影響蒸汽射流流場分布及渦旋的形成,決定擴散泵的返油率,擋油環(huán)位置的正確設置對減少返油率起到至關(guān)重要的作用；一二級噴嘴間距、二三級噴嘴間距存在的最佳值,且串聯(lián)兩級噴嘴距離越大,油蒸汽冷凝效果越好,但噴嘴間距離過大又影響擴散泵結(jié)構(gòu)的緊湊性,而距離過小又會影響擴散泵的正常工作,合理的級間距設計要兼顧抽氣穩(wěn)定性和結(jié)構(gòu)緊湊性。
[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.
【學位授予單位】：東北大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB752

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