Centrifugal Impeller Eye Seal Design for Leakage Reduction
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Solution Overview
Problem
Centrifugal turbomachines face significant fluid leakage issues at the impeller eye, which reduces efficiency in both compressors and expanders, as existing sealing arrangements fail to effectively prevent fluid from leaking from high-pressure to low-pressure sides, leading to inefficient energy transfer and reduced mechanical work generation.
Innovation Solution
A labyrinth-type eye seal with a conical envelope profile is designed, featuring a first portion towards the inlet side and a last portion towards the outlet side, where the last portion is smaller in diameter, mounted on an inlet ring facing a stepped impeller eye region with matching conical steps, reducing the mean diameter of the impeller eye and seal without altering gas flow, thus minimizing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional eye seal with uniform diameter is used, then the sealing structure is simple, but fluid leakage from high-pressure to low-pressure sides is significant
Solution Approach 1:
The eye seal is segmented into multiple portions along its circumferential direction, with each portion having a different diameter. Specifically, the seal includes a first portion toward the inlet side and a last portion toward the outlet side, where the last portion has a smaller diameter than the first portion. This segmentation creates multiple sealing zones that progressively reduce leakage paths.
Solution Approach 2:
Different portions of the eye seal are given different local qualities in terms of diameter. The seal transitions from a larger diameter at the inlet side to a smaller diameter at the outlet side, creating localized sealing characteristics optimized for different pressure zones. This local variation in diameter enhances sealing effectiveness in high-leakage areas.
2Loss of energy
If the impeller eye diameter is reduced to minimize leakage, then sealing efficiency improves, but the inlet diameter and flow geometry are altered
Solution Approach 1:
The impeller eye is segmented into multiple stepped regions with different diameters along the radial direction. The first step has a larger diameter that maintains the inlet flow geometry, while subsequent steps have progressively smaller diameters that reduce the effective leakage area. This segmentation allows the inlet diameter to remain unchanged for proper flow while creating internal steps that reduce leakage paths.
Solution Approach 2:
The solution moves from a two-dimensional planar sealing approach to a three-dimensional stepped configuration. By adding the radial dimension with multiple steps at different heights, the seal creates a more complex leakage path that reduces fluid bypass without constraining the inlet flow area in the axial direction.
3Loss of energy
If a labyrinth-type eye seal with multiple teeth is used, then leakage prevention is enhanced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The labyrinth seal is segmented into a limited number of teeth (first tooth toward inlet side, last tooth toward outlet side, with intermediate teeth). Each tooth represents a discrete sealing element that can be manufactured and positioned independently, simplifying the overall manufacturing process while maintaining multiple sealing zones.
Solution Approach 2:
Instead of using a large number of teeth, the invention uses a partial number of teeth strategically positioned to provide sufficient sealing. The first and last teeth are positioned at critical locations, with intermediate teeth providing additional sealing where needed, achieving effective leakage prevention without excessive complexity.
Data Source
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AI summary
A centrifugal turbomachine (1) comprises a casing (2); a rotor assembly (3) including at least one centrifugal impeller (10) for a fluid flowing from an inlet side (11) to an outlet side (12) of the impeller (10 and an eye seal (20) extending between an impeller eye (15) of the centrifugal impeller (10) and the casing (2) for preventing the fluid from leaking between the casing (2) and the centrifugal impeller (10); wherein the eye seal (20) comprises at least a first portion (21a) toward the inlet side (11) and a last portion (21e) toward the outlet side (12) of the impeller (10), the last portion (21e) being smaller in diameter than the first portion (21a).