Abstract:

The dry gas seal working condition at the inlet of the supercritical CO₂ compressor is near the critical point. The strong nonlinear physical properties and high Reynolds number flow make the sealing characteristics different from conventional dry gas seals. Based on the steady-state film pressure calculation model considering the real gas effect, centrifugal inertia effect, turbulent effect and choked effect, a multi variables perturbation numerical model by considering perturbed film pressure, density, viscosity, Reynolds number, turbulence coefficient and inertia coefficient for calculating dynamic characteristics of dry gas seal is established based on perturbation method. The dynamic characteristics of supercritical CO₂ and N₂ dry gas seals were compared and analyzed. The influences of actual fluid effects and variable perturbation models on the axial and angular dynamic characteristics coefficients of supercritical CO₂ dry gas seals under different conditions were obtained. The results show that the stiffness and damping coefficient of supercritical CO₂ dry gas seal are reduced by more than 50% compared with N₂ dry gas seal under high frequency disturbance. Turbulent effect and real gas effect have significant influence on dynamic characteristics of dry gas seal. The calculation deviations of dynamic characteristics calculated by classical variable perturbation and ignoring turbulence coefficient perturbation are relative large under low frequency disturbance, while the prediction accuracy of the classical variable perturbation model is acceptable under high frequency disturbance.

Key words: supercritical carbon dioxide, dry gas seal, dynamic simulation, variable perturbation, turbulent flow, actual effect

摘要：

超临界CO₂压缩机进口端干气密封工况处于临界点附近，强非线性物性及高Reynolds数流动使其密封特性异于常规介质干气密封。在综合考虑四种实际流体效应的稳态膜压求解模型基础上，基于摄动法推导了包括膜压、密度、黏度、Reynolds数、湍流系数和惯性系数在内的多变量摄动干气密封动特性数值模型。对比分析了超临界CO₂和N₂干气密封的动态特性，研究了不同频率比下各实际流体效应和变量摄动形式对超临界CO₂干气密封动特性系数的影响规律，获得了不同条件下动态特性的关键影响因素。结果表明：高频下超临界CO₂干气密封的刚度和阻尼系数较N₂干气密封降幅超过50%，湍流效应和实际气体效应对干气密封动态特性影响显著，低频下采用经典变量摄动和忽略湍流系数摄动会使动特性系数计算偏差很大，而高频下经典变量摄动模型对刚度系数的预测精度可接受。

关键词: 超临界二氧化碳, 干气密封, 动态仿真, 变量摄动, 湍流, 实际效应