Performance Research On A Spiral-Groove Dry Gas Seal With An Inner Annular Groove

Dry gas face seals (DGSs) have been successfully applied to rotating equipments with high speed such as compressors and gradually under slow speed conditions. But it's difficult to form a stable gas film between the two faces when starting up and at slow speeds and low pressures, which restricts the application widely. Therefore it's very important to perfect the basic theories of design and to improve start-up performances of DGSs at low and moderate speeds.Firstly, the finit element method (FEM) was used to solve the governing equations for compressible gases for a spiral-groove dry gas seal (S-DGS) with smooth surfaces. Comparisons of the sealing performances with a typical S-DGS proved the validity of the calculation. It is also found that a S-DGS with some converged groove depth has no advantages over the typical S-DGS under slow speed and low pressure conditions. Secondly, a mathematic model was built to analyze the sealing performances for a S-DGS with an inner annular groove connected to the spiral groove on the face and the micro-groove structure parameters were optimized based on the rule of getting larger film stiffness or opening force while maintaining lower leakage. Lastly, based on theory of lubrication, a model for gas film pressure considering slip flow was developed and the effects of slip flow on sealing performances were systematically studied at slow speeds and low pressures. It is suggested that when Knudsen number is larger than or equals 0.05 and less than 1.0, the effects of the slip flow on sealing performances are significant. Based on the same optimization rule, the principle for optimized face geometry parameters of such a DGS was presented, which provides theory guidance for improving start-up performances at slow speeds and low pressures and practical application and design.