AN ALL-METAL COMPLIANT SEAL VERSUS A LABYRINTH SEAL: A COMPARISON OF GAS LEAKAGE AT HIGH TEMPERATURES
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Parasitic secondary flows (seals leakage) in centrifugal compressors and gas and steam turbines represent a substantial loss in efficiency and power delivery with an increase in specific fuel consumption. Labyrinth seals are the most common and inexpensive means of reducing secondary leakage, albeit wearing out with operation and thereby penalizing performance and even affecting rotordynamic stability. The novel Hydrostatic Advanced Low Leakage (HALO) seal is an all-metal seal with flexibly supported shoes that enable clearance self-control to effectively reduce leakage, in particular for operation with high pressure ratios and at high surface rotor speeds. This paper presents leakage tests with hot air (max. 300C) conducted in a test rig holding a labyrinth seal and a HALO seal, both of similar diameter, axial length and clearance. The novel seal leaks much less than the labyrinth seal as the supply/discharge pressure ratio (Ps/Pa) increases. The leakage reduction is 50% for (Ps/Pa) < 2 and continuously dropping to 70% for (Ps/Pa) > 3.0. Thus, the savings in leakage are maximized for operation with a high pressure differential. Leakage measurements with a rotor spinning to a maximum speed of 2,700 rpm (surface speed 24 m/s) produce a slight decrease in leakage for both seals. Characterization of seal leakage in terms of a flow factor removes the effect of temperature and supply pressure; the labyrinth seal showing a constant flow factor for (Ps/Pa) > 2. Application of the novel seal technology will aid to increase system efficiency by reducing leakage and will extend maintenance intervals since it eliminates wear of components.
