Face Morphology Affect The Regularity Of The Gas Film Seal At Low Speed Performance

Non-contacting gas lubricated mechanical seal is one of the advanced mechanical seals, which has different kinds of hydrodynamic grooves on their faces such as spiral groove and keeps on non-contacting running. Because of the virtues of small leakage, endurable wear, longevity, a little energy consuming, good seal capability and low maintenance expense etc, non-contacting gas lubricated mechanical seal has been applied in high speed revolving services such as centrifugal compressors. The development trend is to use this kind of seal in some slow speed services such as mixers, agitators. At slow speed operation, there is a thin film between seal faces, so seal faces' shape would has important influence on seal's performance. An example is that this would make seal faces' micro protuberant body contact directly and shorten the using life of seal through excessive friction and serious heat. Because of above-mentioned reasons and the lack of research and analysis about this subject, this paper completely and detailedly analyzed the influence law of seal faces' shape (roughness, waviness and taper of seal faces) to spiral-grooved gas lubricated mechanical seal's performance in order to offer some theory and practice basis on its' design, production and industrial application.Because the hydrodynamic effects of gas lubricated mechanical seal is relatively weak at slow speed, the sticking point of these problems is how to make seal's face open and how to maintain continuous, steady gas film between them. Seal faces' shape is one of the important factors to affect gas film's stability and continuity, so it is necessary to take the effects of seal faces' shape into account when gas lubricated mechanical seal's operation performance is analyzed at slow speed. Few researches have been done on this aspect in china. According to the actual research status and the necessity of design and production, on the basis of the working having been done on this aspect, this paper established the control equation fit for the thin film lubrication at slow speed through modifying the Reynolds Equation, which took the influence seal faces' shape into consideration. According to the control equation and boundary condition, a finite element model for the spiral groove gas lubricated mechanical seal at slow speed has been developed based on the Galerkin weighted residual methodthat considers the seal face shape's effects. According to the above analysis and computation, a gas lubricated mechanical seal computation program has been developed in Visual C++ 6.0, which considered the effects of seal faces' roughness, waviness, taper and its' combination respectively. The program can be used to compute and analysis gas lubricated mechanical seal not only for consideration the effects of the seal faces' shape but also take no account the effects of seal faces' shape, not only for spiral groove but also for some other shape hydrodynamic groove gas face seal with some inheritance and overloading in a sort, not only in theory analysis but also in engineering design, and has great engineering value.With the developed program, the influence law of seal faces' shape to gas lubricated mechanical seal's performance parameters is researched and analyzed in detail through two computation models of consideration for the effects of seal faces' shape and taking no account for it, which shows that seal faces' shape has great influence on gas face seal's operation performance at slow speed. So the seal face shape's effects must be taken into account when this type of seal's performance is analyzed. Through abundant computation and analysis, the influence law of the seal faces' shape (seal faces' roughness, waviness, taper and its' combination) to seal's performance parameters is summarized in order to give some theory references for the seal's design, production and industrial application. The conclusions as follows: seal face's roughness has little influence on seal's performances and can be ignored when the ratio of film height to roughness is greater than 3-4, that is to say, seal face's roughness has no influence on seal's performances. Circumferential waviness is one of the important factors that make gas seal's leakage increase. Cosine waves have great influence on seal's performance with same amplitude. At certain origination angle, with the increase of amplitude, seal's performance parameters increase entirely except that the ratio of stiffness to leakage decreases. So, waviness has bad effects on seal's synthesis performance. Radial positive taper can enhance seal's instability but radial negative taper would reduce seal's open force and gas film stiffness. Both positive and negative taper would make seal's leakage increase.