端面微尺度效应和热黏效应对干气密封性能的影响

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Considering the effects of both surface micro-scale and gas film thermal viscosity,the expansion average Reynolds equation for compressible fluids was modified based on the theories of gas polytrophic process and gas lubrication.The modified Reynolds equation was solved with the finite element method.The effects of micro-scale and thermal viscosity on a spiral groove dry gas seal（S-DGS）performance were investigated with numerical solution of the modified Reynolds equation.When S-DGS was under normal running conditions,the couple effects of gas slip flow and surface roughness were lessened and even disappeared,and only the influence on leakage was at a fixed value with the pressure increased.The influence of surface roughness on sealing performance should be considered when the non-dimensional film thickness Hs3.5.If the inverse Knudsen number B≥21 or Knudsen number Kn≤0.0476,influence of gas slip flow could be ignored.Sealing dynamic pressure was increased,while leakage decreased due to the effects of surface roughness and thermal viscosity.On the contrary,the influence of gas slip flow increased leakage and reduced loading capacity of gas film.When the S-DGS was operating at low speed and high pressure,the influence of gas sliding flow on sealing performance was less than the influence of surface roughness.When po≥2.02 MPa,thermal viscosity effect dominated in affecting sealing performance.考虑干气密封环端面微尺度效应及气膜的热黏效应,基于气体多变过程理论和气体润滑理论,对可压缩流体条件下的扩展平均雷诺方程进行修正,并应用有限元法进行求解;通过改变密封的操作参数,分析研究了端面微尺度效应和热黏效应对干气密封性能的影响规律。结果表明,干气密封在正常工作状态下,压力的升高使气体滑移流和表面粗糙度之间的耦合效应减弱,对泄漏率有固定的影响。若量纲1膜厚Hs〈3.5,应考虑表面粗糙度对密封性能的影响;当逆Knudsen数B≥21或Knudsen数Kn≤0.0476时,可忽略气体滑移流效应的影响;热黏效应和表面粗糙度能提高密封动压效应,降低泄漏率,而气体滑移流效应却使泄漏率增大,端面承载能力降低;在低速高压下,表面粗糙度比滑移流效应对密封性能的影响大;当外压po≥2.02MPa时,热黏效应在对密封性能影响中占主导地位。