螺旋槽干气密封端面气膜的热力过程

针对螺旋槽干气密封,仅考虑气体沿密封面流动经历压缩与膨胀的热力过程.利用萨特兰黏-温方程和气体过程方程表征气体黏度与压力的关系,将该方程代入Muijderman建立的螺旋槽流体膜压力控制方程,得到考虑多变指数m影响的端面气膜压力控制方程,对该方程求解获得气膜温度沿密封端面的变化规律.结果表明,随着m的增大,相应位置的气膜压力降低,但降低幅度不大.随着气体从外径流到内径,气膜温度沿密封环半径方向的分布规律反应出气膜的压缩膨胀特征.气体受到压缩时,气膜温度高于边界温度To,且m越大,温度越高;气体得到膨胀时,温度逐渐降低,且m越大,温度下降越迅速.

Thermodynamic process of interfacial gas film in spiral grooved dry gas seal

Dry gas seals have been extensively used in centrifugal compressors. Up to now, the process of gas flowing through the seal faces is generally considered isothermal. In fact, the gas temperature varies along with the gas flowing paths. In the flowing process, several effects, such as gas compression and expansion, viscous shear of interfacial film, convective heat transfer between the gas and the seal rings, and heat transfer between the rings and the ambient medium are involved. For a typical spi- ral grooved dry gas seal, it is considered that just compression and expansion thermodynamic processes are experienced when a gas flows through the gap between two end faces of the seal. A relationship between viscosity and pressure of gas in the gap is established by combining Sutherland＇s viscosity -temperature correlation and the process equations of ideal gas. Then the ordinary differential equations for film pressure with polytropic exponent （m） are deduced by substituting the relationship and the process equations into Muijderman＇s fluid film pressure equations in a dry gas seal with spiral grooves. The gas temperature profile along the radial direction in the film is figured out by solving the film pressure equations just obtained. The results show that the film pressure in a position decreases slightly with the increase of m. The variation of gas temperature along the radial direction in the seal rings clearly demonstrates that there are compression and expansion processes when the gas flows inside the gap. When the gas is compressed, the film temperature is higher than the ambient temperature （ T0 ） , and the film temperature rises with increasing m. When the gas expands, however, the film temperature decreases gradually; and the greater m is, the more rapidly the temperature drops.