液膜空化热特性及微尺度效应对机械密封性能的影响研究

发布时间：2018-04-14 13:13

本文选题：机械密封 + 空化　；参考：《江苏大学》2017年硕士论文

【摘要】：动压型液体润滑机械密封间隙液膜的空化现象是其能够产生开启力的重要因素。由于空化一般发生在常温下,因此空化模型通常是在等温假设条件下建立的。但密封微间隙流体受到密封面结构形式和转速等因素导致粘性摩擦升温,间隙液膜各处并不是等温的,尤其是在高转速下,空化结构受温度的影响更加敏感且对密封性能的影响更加显著。同时由于密封微液膜间隙的微尺度效应,使密封润滑性能研究更加复杂。目前对于动压润滑机械密封的空化热特性以及微尺度效应等方面的研究仍然处于不断探索中。因此构建相关理论模型,分析空化热特性、微尺度效应对动压型机械密封摩擦润滑性能的影响,可为进一步了解机械密封失效机理和机械密封研究设计提供参考依据,具有理论和实际意义。本课题来源于国家自然科学基金资助项目《水力机械密封端面内部微尺度流动与密封润滑机理研究》(项目编号:51279067),主要研究工作及结论如下:(1)以上游泵送机械密封为例,在考虑粘温关系的基础上,采用计算流体动力学方法及Fluent二次开发功能(UDF),利用饱和蒸汽压力随温度的依变关系构建了基于质量输运方程的空化热特性模型,通过与一般性的粘温模型进行对比分析,研究了空化热特性模型对上游泵送机械密封润滑性能的影响。研究表明:在高转速下,空化热特性使上游泵送机械密封的高压区形成能力减弱,泵送量降低,开启力下降,因此在分析密封失效机理时,应考虑空化热特性的影响。(2)从微尺度效应理论出发阐述了表面润湿性对微流动及上游泵送机械密封的重要性,然后根据润湿性能的差异,分别建立上游泵送机械密封的亲水密封端面表观粘性模型及疏水密封端面的边界滑移模型,并分析其对密封液膜空化结构及性能的影响,最后做出相关试验验证。相关研究可为实际运行中液体润滑机械密封密封环材料性质的处理及选择提供一定的参考意见。研究表明:不同润湿性能端面的剪切应力均在槽区及空化区附近比较小,在坝区和堰区比较大;随着表面润湿性的增强,密封开启力增大,密封端面空化程度加深,摩擦扭矩增大。(3)针对水润滑动压型机械密封的开启力及稳定性较低,使密封使用场合受到限制的问题,利用边界滑移微尺度效应,采用人工手段在密封端面形成合理的滑移区和非滑移区,并基于粘温效应及空化热特性,建立上游泵送机械密封三维非均匀滑移模型,分析不同滑移量和转速对密封的开启力、空化区域、温度场和泄漏量等性能参数的影响。研究表明:通过螺旋槽表面处理而增大滑移量能够明显改善密封性能,且表面处理层处于槽底,可避免磨损破坏,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.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH136

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