Slip length in narrow sealing gaps – an experimental approach

For narrow sealing gaps in average smaller ca. 1 μm it is expected that the no-slip boundary condition does not yield anymore. As a consequence the friction is reduced and the leakage is increased compared to the no-slip design case. Though the concept of slip length was introduced by Navier and Maxwell already in the 19th century, it is up to now costly to measure the slip length. This is due to the required measurement precision. Today the slip length is measured in laboratories for glass, silicium or sapphire wafers while using fluorescence methods to determine the flow velocity and is thus far from sealing applications. The present paper introduces an alternative method to measure the slip length for typical materials that are used in sealing technologies. A key advantage of the presented method is that the slip length can be evaluated while measuring the physical quantities torque and gap setting.

Within the paper the design of the apparatus including the measurement equipment is discussed in detail.