实际气体效应影响干气密封性能的机制研究

The behaviour of the gas is extremely different from that of the ideal gas when the pressure is high,and the real gas effect can not be ignored.The real gas effect on the influence of the dry gas seal has not been thoroughly investigated up to now.As to the widely used spiral groove and T-shape dry gas seal, the influence laws of the real gas effect on the dry gas seal will be investigated in this project in order to obtain the theory and methods to compare,to analyze,to evaluate,to investigate,to apply the feature of the real gas dry gas seal and the ideal gas dry gas seal. The main contents includes that the theory and the methods for the characterization of the real gas effect, the isothermal flow of the real gas film between the seal faces, the non-isothermal flow of the real gas film,the real gas flow in the seal chamber, the seal ring deformation by heat, the seal ring deformation by pressure, the coupling laws of the real gas effect,the thermal effects,the flow and the solid.The key is to establish,resolve,and validate the the related coupling equations of the real gas,the gas film flow,the heat transfer and the deformaton of the seal ring in order to obtain the theory and methods for determining the dry gas seal performance of the leakage,the open force,the gas film stiffness,and the gas film damp,and to set up the semi-analytica theory and numerical simulation methods for the coupling of the real gas,the heat,the flow and the solid. As to the experimental investigation, the high precision eddy current sensors will be used to measure the gas film thickness, and micro pressure sensors will be used to measure the pressure of the gas film, and thethermocouples will be used to measure the temperature.

压力较高时，实际气体行为明显偏离理想气体。实际气体效应不能忽略。迄今，实际气体效应影响干气密封性能的机制和规律还没有得到系统深入研究。本项目针对广泛应用的螺旋槽、T型槽等干气密封，开展实际气体效应影响干气密封行为规律研究，期望获得实际气体干气密封与理想气体干气密封性能对比、分析、评价、研究和应用的理论和方法。研究内容包括：实际气体效应表征理论和方法、实际气体在密封端面间的等温流动、非等温流动、实际气体在密封腔的流动、密封环的热变形、力变形，实际气体热流固耦合规律等。关键在于建立、求解及实验验证实际气体方程与端面气膜流动、端面传热、端面变形的耦合方程，获得确定实际气体效应影响干气密封泄漏率、开启力、气膜刚度、气膜阻尼等密封性能的理论和方法。建立起实际气体热流固耦合的近似解析理论和数值模拟方法。实验上采用高精度位移传感器测量端面气膜厚度，采用微型压力传感器测量端面压力，采用热电偶测量端面温度。

干气密封是离心式压缩机等流体机械常用的轴封形式，目前干气密封的应用压力越来越高。在高压情况下，干气密封润滑气体的性质明显不同于理想气体，干气密封实际气体行为影响干气密封性能的机制尚未查明。本项目以此为背景，研究实际气体效应影响干气密封的具体机制，对干气密封的设计、应用和稳定运行具有重要的理论意义和工程应用价值。通过该项目研究，针对干气密封工程应用中几种常用润滑气体（氮气、氢气、二氧化碳和水蒸气），获得了适用于表征其气体压缩因子Z的确定方法以及氮气实际气体的黏-温-压关系表达式。并获得了焦耳-汤姆逊效应的计算方法。针对等温假设下的螺旋槽干气密封（S-DGS），采用近似解析法获得了同时考虑实际气体效应和滑移流效应的S-DGS稳态性能，结果显示低压下滑移流效应起主导作用，高压下实际气体效应起主导作用；采用有限差分法和小扰动法，获得了高压工况中实际气体效应和阻塞流效应对S-DGS动态性能的影响规律，结果表明实际气体效应和阻塞流效应对动态气膜刚度的影响随压缩数、进口压力的增大而增强。选用合理的实际气体状态方程、黏度方程以及气体的热力学特性方程，通过Fluent三维数值模拟，对实际气体在S-DGS密封腔及端面间的非等温流动规律作了一系列的研究，结果表明与等温假设相比，温度对干气密封性能的影响不容忽视。在获得考虑实际气体效应的气膜压力的前提下，采用解析法和Ansys模拟分析了干气密封环的强度问题，两者结果对比显示切向应力远大于径向应力，强度校核时可主要考虑切向应力。联合Fluent软件和Mechanical软件对干气密封进行了流固耦合数值模拟研究，发现流固耦合界面在耦合前后的压力分布发生了明显的变化。项目研究成果为干气密封的研究、设计和应用，提供一套分析、预测、评估实际气体效应的完整理论和分析方法。