接触式机械密封界面的逾渗机制及泄漏流体流动特性研究

At requirements of resource conservation, production safety and environmental protection in the new century, contact mechanical seals have become the focus of scholars and engineers at home and abroad attention again. The two rough contact surfaces of the sealing rings are simplified to the seal porous interface in this study, and the seal porous interface percolation model will be established, which could be used to investigate the relationship between the percolation probability and the porosity, caulculate the threshold value when the percolation occurs and illustrate the cause of the seal interface leak channels. Then the motion equation of the average size of the micro-fluid flowing will be established to study the effect of the streamline tortuosity on the flow resistance of the fluid, and the flow characteristic of the micro-fluid in the leak channels combined with direct numerical simulations could be revealed. According to the section topography information of the seal interface on the different roughness depth, obtained by the laser scanning confocal microscopy, the three-dimensional digital samples of the seal porous interfaces could be established. And then, based on the time correlation and evolution of the the seal porous interface and its contact stress under conditions of wear and o-rings stress relaxation, the pore scale of the seal interface under percolation threshold will be studied and the leakage criterion of mechanical seals could be brought forth. In conclusion, the leakage mechanism of the contact mechanical seals will be illustrated based on theoretical analysis, numerical method and experimental research, and the method of the leakage prediction could be put forward, which can lay the foundation for the optimal design, further applications as well as the long-term safe operation of contact mechanical seals.

新世纪节约资源、安全生产和环境保护的要求，使得接触式机械密封再次成为国内外学者和工程技术人员关注的焦点。本项目将构成密封的两个粗糙接触表面简化为一密封多孔界面，研究建立密封多孔界面逾渗模型，探寻逾渗概率与孔隙率的关系，求解其发生逾渗的逾渗阈值，阐释泄漏通道的成因；研究建立微流体流动的体积平均化运动方程，探讨流体流线迂曲度对流动阻力的影响，并结合直接数值模拟，揭示逾渗通道内的微流体流动特性；再利用激光共焦显微镜获取密封多孔界面在不同粗糙度深度上的剖面形貌信息，建立三维数字样本；在探索密封多孔界面及其接触应力在摩擦磨损和O形圈应力松弛协同效应下的演化过程和时间相关规律后，确定密封多孔界面在逾渗阈值下的孔隙尺度，提出接触式机械密封的泄漏判据。从理论分析、数值计算、实验研究三个方面阐明泄漏机制，进而建立泄漏预测方法，为接触式机械密封的优化设计、应用范围的拓展和长周期安全运行奠定基础。

旋转机械装备的密封性能对生产过程的能耗、效率和环保具有重要影响。本项目针对接触式机械密封，开展了密封界面的逾渗机制及泄漏流体流动特性研究。基于粗糙表面轮廓分形维数D、尺度系数G和最大微凸体轮廓基底尺寸l，建立了新的粗糙表面接触分形模型，探讨了微凸体变形机制、粗糙表面的真实接触面积和接触载荷的关系，揭示了接触界面的孔隙率和真实接触面积随端面形貌、表面接触压力等参数变化的规律，给出了不同形貌界面被 压实的最大变形量。基于逾渗理论，分析了接触式机械密封界面空隙状态随动、静环表面分形参数和接触压力变化的规律，指出了密封界面在接触压力作用下表现的逾渗、逾渗点和非逾渗3种状态。根据液体毛细管力和气体克努森数，提出了微通道内流体流动判据，阐释了接触式机械密封界面泄漏机理。研究结果为接触机械密封优化设计和泄漏控制提供依据。.主要研究结论为：.（1）粗糙动、静环表面接触形成的密封界面存在空隙和接触点，表面分形参数及接触压力对空隙率具有重要影响。D增大，初始孔隙率0增大；接触压力pc增大，孔隙率减小，并随着D的增大和尺度系数G的减小，快速减小，直至填实。.（2）密封界面是否形成泄漏通道与界面空隙率相关。对于由磨削或研磨加工的动、静密封环表面构成的大空隙率密封界面，在正常表面接触压力下，可以简化为单层网格微通道结构模型。.（3）只要密封界面存在泄漏通道，被密封介质就会泄漏。当压差大于液体在泄漏微通道的毛细管力，或气体分子的平均自由程远小于泄漏微通道的特征尺寸时，泄漏表现为宏观泄漏；反之，表现为分子流泄漏。