Rotary kinetic fluid motors or pumps – With lubricating – sealing – packing or bearing means having...
Reexamination Certificate
1999-05-24
2001-05-29
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With lubricating, sealing, packing or bearing means having...
C415S173500, C415S116000, C415S180000, C415S175000
Reexamination Certificate
active
06238179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a centrifugal compressor.
2. Discussion of Background
Contactless seals, in particular labyrinth seals, are widely used for sealing rotating systems in turbomachine construction. A high frictional loss occurs in the separating gap through which fluid flows between the rotating and stationary parts because of the boundary layers formed in the flow. This causes heating of the fluid in the separating gap and therefore produces heating of the components surrounding the separating gap. The high material temperatures cause a reduction in the life of the corresponding components.
A centrifugal compressor with a labyrinth seal arranged on the rear wall of the compressor impeller in the separating gap between the compressor casing and the compressor impeller is known from EP 0 518 027 B1. Because of the high pressure at the outlet of the compressor impeller, leakage air can penetrate into the annular space between the rotating wall and the stationary wall of the compressor casing. In order to avoid both this and also the associated heating of the components surrounding the separating gap, a cold gas at a higher pressure than that at the outlet of the compressor impeller is introduced into the separating gap. For this purpose, an additional annular space is arranged within the labyrinth seal and is connected to an external gas feed. The cold gas flows through the wall of the compressor casing into the labyrinth seal and then impinges on and cools the rear wall of the compressor impeller. When it impinges on the rear wall, the gas is divided and mainly flows radially inward and outward through the individual sealing elements of the labyrinth seal. The partial flow directed radially outward, in particular, is intended to prevent hot compressor air from the outlet of the compressor impeller from flowing through the separating gap.
Despite special ancillary components, which make the centrifugal compressor more expensive, the cooling effect of such a solution cannot be considered optimum. The fact is, rather, that during the feed of the cold gas, mixing initially occurs between the partial flow directed radially outward and the boundary layer forming on the rear wall of the compressor impeller. In addition, this partial flow has to do work against at least one sealing element of the contactless seal which, in addition to the worse cooling effect, also causes greater friction on the rear wall and therefore greater mechanical losses.
SUMMARY OF THE INVENTION
The invention attempts to avoid all these disadvantages. Accordingly, one object of the invention is to provide a novel centrifugal compressor with a cooling appliance which is simpler but more effective.
In accordance with the invention, this object is achieved for an appliance by the feed device for the gaseous medium opening into the separating gap upstream of the mainly radially extending gap region of the separating gap.
With this solution, it is possible to dispense with an additional annular space or additional feed spaces in the mainly radially extending gap region of the separating gap. This markedly simplifies the construction of the centrifugal compressor. In addition, the cooling medium employed can replace the hot leakage air which otherwise penetrates into the mainly radially extending gap region of the separating gap. Because of this, the boundary layer formed by the flow on the rear wall of the compressor impeller is formed from the outset mainly by the cooling medium supplied. In particular, an improved cooling effect can therefore be ensured in this particularly endangered region of the centrifugal compressor.
It is particularly useful for the supply duct of the feed device and the inlet region of the mainly radially extending gap region of the separating gap to be arranged so that they are radially aligned. In this way, both pressure losses in the entering cooling medium and its heating due to dissipation can be avoided. This in turn leads to an improved cooling effect. In addition, the cooling medium stops the hot leakage air penetrating into the mainly radially extending gap region either partially, or even completely.
It is, furthermore, advantageous for a plurality of feed ducts for the cooling medium directed in the direction of rotation of the compressor impeller to be arranged in the supply duct. For this purpose, the supply duct has a plurality of guide webs interrupted by recesses, the recesses simultaneously forming the feed ducts for the cooling medium. While using relatively simple components, this makes it possible to inject the cooling medium in the direction of rotation of the compressor impeller, which further reduces the frictional losses and, therefore, the heating of the compressor impeller.
Finally, a sealing element is advantageously arranged in the separating gap upstream of the inlet region of the mainly radially extending gap region. This makes it possible to reduce the pressure of the leakage flow arriving from the compressor impeller to such an extent that the cooling medium can also be fed in at a pressure which is less than that present at the compressor outlet.
A combination of the measures already mentioned above with a contactless seal downstream of the inlet region in the mainly radially extending gap region of the separating gap has been found to be particularly advantageous. By this means, the cooling medium arriving from a radially outward position reaches the individual sealing elements of the seal and there causes film cooling of the rear wall of the compressor impeller. In contrast to the prior art, the cooling medium does not flow radially outward but radially inward so that mixing with the boundary layer formed by the flow on the rear wall of the compressor impeller does not occur nor, likewise, does any increase in the friction on the rear wall. In consequence, the cooling effectiveness can be increased and the life of the compressor impeller can be further improved.
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Bothien Mihajlo
Bremer Joachim
Greber Jurg
Muller Ulf Christian
Wunderwald Dirk
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Look Edward K.
Woo Richard
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