Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Reexamination Certificate
1999-11-29
2001-09-25
Mah, Chuck Y. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
Reexamination Certificate
active
06293554
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to seals, and more particularly to a brush seal segment.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular brush seal is made up of circumferentially-arrayed brush seal segments. Each brush seal segment is attached to the casing and includes a back (i.e., downstream) plate, a front (i.e., upstream) plate, and bristles which are positioned between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The bristles typically are canted at an angle of generally forty-five degrees in the direction of rotation of the rotor, and the free ends of the bristles are close to (and may even touch) the rotor. Typically, the front plate (and in some designs also portions of the back plate), near the free ends of the bristles, is spaced apart from the bristles to allow room for the bristles to flex and recover during transient encounters of the free ends of the bristles with the rotor. When the upstream gas flow is turbulent, some of the flow can swirl between the front plate and the bristles causing bristle flutter (i.e., instability) which quickly wears the bristles leading to premature brush seal failure. What is needed is a design for a brush seal segment which reduces bristle flutter in a turbulent-flow environment.
BRIEF SUMMARY OF THE INVENTION
In a first expression of an embodiment of the invention, a brush seal segment includes a back plate, a front plate, and bristles. The bristles are positioned between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The front plate has a portion extending to the edge of the front plate, such portion spaced apart from the bristles and having an array of through holes.
In a second expression of an embodiment of the invention, a brush seal segment includes a brush-seal holder having a shape of generally an annular segment of a circular ring. The holder has an annular back plate and an annular front plate each generally coaxially aligned with the longitudinal axis of the ring and each having an inner circumferential edge generally facing the axis. The brush seal segment also includes bristles positioned longitudinally between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The edge of the back plate extends closer to the axis than does the edge of the front plate. The front plate has a portion extending to the edge of the front plate, such portion longitudinally spaced apart from the bristles and having an array of through holes.
In a third expression of an embodiment of the invention, a brush seal segment includes a back plate, a front plate, and bristles. The bristles are positioned between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The front plate has a portion extending to the edge of the front plate, such portion spaced apart from the bristles and such portion at the edge of the front plate having a ledge projecting generally away from the bristles.
In a fourth expression of an embodiment of the invention, a brush seal segment includes a brush-seal holder having a shape of generally an annular segment of a circular ring. The holder has an annular back plate and an annular front plate each generally coaxially aligned with the longitudinal axis of the ring and each having an inner circumferential edge generally facing the axis. The brush seal segment also includes bristles positioned longitudinally between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The edge of the back plate extends closer to the axis than does the edge of the front plate. The front plate has a portion extending to the edge of the front plate, such portion longitudinally spaced apart from the bristles and such portion at the edge of the front plate having a ledge projecting generally longitudinally away from the bristles.
Several benefits and advantages are derived from the invention. In the first and second expressions of an embodiment of the invention, as shown by engineering analysis, the through holes in the front plate allow a subflow to pass therethrough and purge the space between the front plate and the bristles of turbulent flow otherwise entering the space near the free ends of the bristles such that the free ends of the bristles are damped since they experience a more stable flow resulting in less bristle flutter and hence increased brush-seal wear. In the third and fourth expressions of an embodiment of the invention, as shown by engineering analysis, the upstream-extending ledge of the front plate acts to channelize the turbulent flow such that the free ends of the bristles are damped since they experience a more stable flow resulting in less bristle flutter and hence increased brush-seal wear.
REFERENCES:
patent: 5066024 (1991-11-01), Reisinger et al.
patent: 5318309 (1994-06-01), Tseng et al.
patent: 5400952 (1995-03-01), Hetico et al.
patent: 5496045 (1996-03-01), Millener et al.
patent: 5961280 (1999-10-01), Turnquist et al.
patent: 5971400 (1999-10-01), Turnquist et al.
Albers Robert Joseph
Battle Michael Eugene
Dinc Osman Saim
Dogu Yahya
Proctor Robert
General Electric Company
Mah Chuck Y.
Patnode Patrick K.
Peavey Enoch E
Stoner Douglas E.
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