Low Speed Gas Film Face Seals Dynamic Characteristics Of Study

The gas face seal is an advanced non-contacting seal, which has been successfully used in high speed compressors, steam turbines, blowers and gas turbines due to its excellent performances. With the growing success of the non-contacting gas face seal, its application envelope is constantly being expanded. More and more non-contacting gas face seals are being used in the mixer and pump applications where slow speed conditions are likely.So far the performances of the gas face seal at the slow speed conditions have not been investigated enough, especially for its dynamic characteristics. The dynamic characteristics of the gas face seal at the slow speed conditions is one of the key factors that guarantee its stable and efficient operation. In order to obtain the dynamic characteristics of the T groove gas face seal at the slow speed conditions, the corresponding coefficients of the gas face seal was studied. In this paper, firstly, the iterative formulae of the gas pressure governing equation-the Reynolds Equation was obtained by adopting the control volume method, and the slip flow effects was taken into consideration, then the static characteristics of the gas face seal was calculated by the finite difference method. Secondly, the dynamic characteristics of the gas face seal was calculated by adopting a simplified algorithm of the axial gas film stiffness and the axial gas film damping coefficients with the finite difference method. Finally, the effects of the key geometric parameters and the operational parameters on the static and dynamic characteristics of the gas face seal (for instance, the opening force, the leakage rate, the axial stiffness, the ratio of the stiffness to the leakage rate and the axial damping coefficient) were also studied.By examining the results, it was found that the slip flow effects turned out to be significant at the slow speed and the thinner gas film conditions, the general effects of the slip flow basically made the hydrodynamic lift-off effect weaker, the leakage rate higher, it also made the gas film stiffness decreased, while the damping coefficients increased; the results also showed that the ratio of the groove depth to the gas film thickness, the ratio of the arc length of groove to the arc length of land, the ratio of the arc length of the smaller groove to the arc length of the larger groove and the ratio of the radial width of groove to the radial width of dam can greatly affect the gas face seal performances. The load capacity reached its maximum value when the ratio of the groove depth to the gas film thickness and the ratios mentioned above were 2.5,0.62,0.62 and 0.75 respectively, which however, came with the maximum value of the leakage rate. In this case, the ratio of the groove depth to the gas film thickness of 1.0 ensured relatively low leakage with good dynamic characteristics. The dynamic characteristics were getting worse while the ratio of the arc length of groove to the arc length of land and the ratio of the arc length of the smaller groove to the arc length of the larger groove increased. The dynamic force coefficients turned out to be fluctuating when the ratio of the radial width of groove to the radial width of dam rose, and the dynamic force coefficients reached a minimum value when the ratio approached 0.6. The dynamic force coefficients generally rose while the operational parameters increased.In conclusion, the effects of the slip flow turned out to be significant at the slow speed conditions; the effects of the ratio of the groove depth to the gas film thickness, the ratio of the arc length of groove to the arc length of land, the ratio of the arc length of the smaller groove to the arc length of the larger groove and the ratio of the radial width of groove to the radial width of dam on the gas face seal performances were comparatively significant, therefore the machining accuracy should be kept strictly. It was also found that, as for the operational parameters, they should be kept at a relatively high level to ensure the better performances of the gas face seal.