Comparison of Leakage Performance in Three Types of Gas Annular Seals Operating at a High Temperature (300°C)

Adequate sealing in rotating machinery reduces secondary leakage and results in more efficient and stable systems. Labyrinth seals are most common, although brush seals are popular in specialized applications. The hybrid brush seal (HBS) is a novel design that adds to the bristle brush matrix a number of cantilever pads that rest on the rotor surface. Upon shaft rotation the pads lift due to the generation of a hydrodynamic gas film, and the brushes effectively seal an upstream pressure. Hence, the HBS has no wear and no local thermal distortion effects. This article presents measurements of leakage versus pressure differential obtained in a three-tooth labyrinth, a conventional brush seal, and a hybrid brush seal for operation at high temperature (300 degrees C) and with shaft surface speeds to 26 m/s. The measurements demonstrate that the HBS leaks similar to 31% less than a standard brush seal and is significantly better (similar to 68%) than a similarly sized labyrinth seal. As temperature increases, the labyrinth seal leakage decreases because its clearance changes due to the thermal growth of the components. The HBS, on the other hand, shows leakage that is nearly insensitive to air inlet temperature. The measurements demonstrate HBS as a reliable seal technology for use in gas turbines, for example.