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| Thermodynamic process of interfacial gas
film in spiral grooved dry gas seal |
| Song Pengyun, Chan Wen, Jiao Feng |
| Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650500, China |
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Abstract 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 spiral 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 (To), 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.
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Received: 10 March 2014
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