本文選題：機械密封 + 空化　； 參考：《江蘇大學》2017年碩士論文

【摘要】：動壓型液體潤滑機械密封間隙液膜的空化現(xiàn)象是其能夠產(chǎn)生開啟力的重要因素。由于空化一般發(fā)生在常溫下,因此空化模型通常是在等溫假設(shè)條件下建立的。但密封微間隙流體受到密封面結(jié)構(gòu)形式和轉(zhuǎn)速等因素導致粘性摩擦升溫,間隙液膜各處并不是等溫的,尤其是在高轉(zhuǎn)速下,空化結(jié)構(gòu)受溫度的影響更加敏感且對密封性能的影響更加顯著。同時由于密封微液膜間隙的微尺度效應,使密封潤滑性能研究更加復雜。目前對于動壓潤滑機械密封的空化熱特性以及微尺度效應等方面的研究仍然處于不斷探索中。因此構(gòu)建相關(guān)理論模型,分析空化熱特性、微尺度效應對動壓型機械密封摩擦潤滑性能的影響,可為進一步了解機械密封失效機理和機械密封研究設(shè)計提供參考依據(jù),具有理論和實際意義。本課題來源于國家自然科學基金資助項目《水力機械密封端面內(nèi)部微尺度流動與密封潤滑機理研究》(項目編號:51279067),主要研究工作及結(jié)論如下:(1)以上游泵送機械密封為例,在考慮粘溫關(guān)系的基礎(chǔ)上,采用計算流體動力學方法及Fluent二次開發(fā)功能(UDF),利用飽和蒸汽壓力隨溫度的依變關(guān)系構(gòu)建了基于質(zhì)量輸運方程的空化熱特性模型,通過與一般性的粘溫模型進行對比分析,研究了空化熱特性模型對上游泵送機械密封潤滑性能的影響。研究表明:在高轉(zhuǎn)速下,空化熱特性使上游泵送機械密封的高壓區(qū)形成能力減弱,泵送量降低,開啟力下降,因此在分析密封失效機理時,應考慮空化熱特性的影響。(2)從微尺度效應理論出發(fā)闡述了表面潤濕性對微流動及上游泵送機械密封的重要性,然后根據(jù)潤濕性能的差異,分別建立上游泵送機械密封的親水密封端面表觀粘性模型及疏水密封端面的邊界滑移模型,并分析其對密封液膜空化結(jié)構(gòu)及性能的影響,最后做出相關(guān)試驗驗證。相關(guān)研究可為實際運行中液體潤滑機械密封密封環(huán)材料性質(zhì)的處理及選擇提供一定的參考意見。研究表明:不同潤濕性能端面的剪切應力均在槽區(qū)及空化區(qū)附近比較小,在壩區(qū)和堰區(qū)比較大;隨著表面潤濕性的增強,密封開啟力增大,密封端面空化程度加深,摩擦扭矩增大。(3)針對水潤滑動壓型機械密封的開啟力及穩(wěn)定性較低,使密封使用場合受到限制的問題,利用邊界滑移微尺度效應,采用人工手段在密封端面形成合理的滑移區(qū)和非滑移區(qū),并基于粘溫效應及空化熱特性,建立上游泵送機械密封三維非均勻滑移模型,分析不同滑移量和轉(zhuǎn)速對密封的開啟力、空化區(qū)域、溫度場和泄漏量等性能參數(shù)的影響。研究表明:通過螺旋槽表面處理而增大滑移量能夠明顯改善密封性能,且表面處理層處于槽底,可避免磨損破壞,是有效、可行的方法。
[Abstract]:The cavitation of liquid film in the clearance of hydrodynamic liquid lubricated mechanical seal is an important factor to produce the opening force.Because cavitation usually occurs at room temperature, cavitation models are usually established under isothermal assumptions.However, due to the structure of sealing surface and the rotating speed of sealing surface, the fluid in the microgap is not isothermal, especially at high speed.Cavitation structure is more sensitive to temperature and has more significant effect on sealing performance.At the same time, the study of sealing lubrication performance is more complicated because of the microscale effect of sealing microliquid film clearance.At present, the research on cavitation heat characteristics and microscale effect of hydrodynamic lubrication mechanical seal is still in the process of exploration.Therefore, it can provide a reference for further understanding the failure mechanism of mechanical seals and the research and design of mechanical seals by constructing relevant theoretical models, analyzing the thermal characteristics of cavitation and the effect of micro-scale effect on the friction and lubrication performance of dynamic pressure mechanical seals.It has theoretical and practical significance.This subject comes from a project sponsored by the National Natural Science Foundation of China, "study on the Microflow and Lubrication Mechanism in the end face of hydraulic Machinery Seals" (Project No.: 51279067, the main research work and conclusions are as follows: 1) take upstream pumping mechanical seals as an example.On the basis of considering the relationship between viscosity and temperature, the cavitation heat characteristic model based on mass transport equation is constructed by using the computational fluid dynamics method and the Fluent secondary development function.The influence of cavitation heat characteristic model on lubrication performance of upstream pump mechanical seal was studied by comparing with general viscous temperature model.The results show that under high rotational speed, cavitation heat characteristic weakens the forming ability of the high pressure area of upstream pumping mechanical seal, decreases the pumping quantity and decreases the opening force. Therefore, when analyzing the failure mechanism of the seal,The effect of cavitation heat characteristics should be considered. (2) the importance of surface wettability to microflow and upstream pumping mechanical seal is expounded based on the theory of micro-scale effect, and then according to the difference of wetting performance,The apparent viscosity model of the hydrophilic seal end surface and the boundary slip model of the hydrophilic seal end face of the upstream pumping mechanical seal were established respectively. The influence of the model on the cavitation structure and performance of the sealing liquid film was analyzed.The relevant research can provide some reference for the treatment and selection of the material properties of liquid lubricating mechanical seal ring in practical operation.The results show that the shear stress of the end face of different wettability energy is smaller near the groove and cavitation area, and larger in the dam and Weir area, and with the increase of surface wettability, the sealing opening force increases and the cavitation degree of the seal end face deepens.In view of the problem that the opening force and stability of the hydrodynamic sliding press mechanical seal are low, the use of the seal is limited, and the boundary slip microscale effect is used.Based on the viscous temperature effect and cavitation heat characteristics, a three-dimensional non-uniform slip model of upstream pumping mechanical seal is established by artificial means to form a reasonable slip zone and a non-slip zone on the end face of the seal. The opening force of the seal with different slip amounts and rotational speeds is analyzed.Cavitation region, temperature field, leakage and other performance parameters.The results show that the sealing performance can be improved obviously by increasing the slip through the surface treatment of the spiral groove, and the surface treatment layer is at the bottom of the groove, which can avoid the wear and damage. It is an effective and feasible method.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TH136

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