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A Finite Element model for the noncontacting gas face seal is developed based on the modified Reynolds Equation developed by Fukui and Kaneko (4), (5) that considers the slip flow effects. Numerical studies of a representative spiral groove seal at the slow speed (≤, 500 rpm) and the low pressure (≤ .303 MPa) conditions showed that slip flow can significantly affect the seal performances such as the lift-off speed, leakage rate, load carrying capacities. Without the consideration of the slip flow effect, the lift-off speed and the corresponding leakage rate would be greatly underestimated, especially at near ambient pressure condition. By examining the F-h characteristic curves, it was found that under the parameters presented in the present study the slip flow could be significant for Knudsen number, Kn as small as .05, and the slip flow in effect reduces the viscous pumping resulting in a loss of load carrying capacities.
Bo Ruan (Sat,) studied this question.