Steam Turbine Exhaust Diffuser with Inflection Point Inner Guide
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Solution Overview
Problem
Conventional exhaust diffuser systems for low-pressure steam turbines face inefficiencies due to flow separation and vortex formation, leading to reduced static pressure recovery and increased complexity, which affects the axial length and overall efficiency of the steam flow.
Innovation Solution
The design incorporates an inner guide with inclined walls featuring multiple inflection points and an outer guide with a curved wall and a controlled slit, optimizing the steam flow path to minimize flow separation and enhance efficiency, while maintaining a compact axial length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the outer guide surface has high curvature to redirect steam flow, then the axial length of the diffuser is reduced, but flow separation occurs leading to reduced static pressure recovery
Solution Approach 1:
The diffuser is divided into two independent guides (inner guide and outer guide) that can be optimized separately. The inner guide focuses on pressure recovery with appropriate curvature, while the outer guide handles flow redirection, allowing both functions to be performed efficiently without compromise
Solution Approach 2:
Different curvature characteristics are applied to different parts of the diffuser. The inner guide has optimized curvature for pressure recovery in the core flow region, while the outer guide has different curvature characteristics suitable for handling the outer flow and redirection requirements
2Ease of manufacture
If the inner guide has inflection points positioned far from the blade centerline to simplify construction, but this increases the axial length of the exhaust diffuser
Solution Approach 1:
The first inflection point is positioned early (close to the blade centerline) to preliminarily establish the flow direction and pressure distribution. This preliminary action allows the remaining guide sections to be shorter while still achieving proper flow control, thus reducing overall axial length without sacrificing manufacturability
3Reliability
If the diffuser design is optimized for efficiency with multiple inflection points and curved surfaces, then steam flow uniformity improves, but device complexity increases
Solution Approach 1:
The complex diffuser function is segmented into two independent guides, each with a specific number of inflection points optimized for its function. This segmentation allows the complexity to be distributed and managed separately, making the overall design more tractable while maintaining flow uniformity
Solution Approach 2:
Curved surfaces with optimized inflection points are used to guide steam flow smoothly through the diffuser. The curvature profiles are specifically designed to match the flow patterns from the turbine blades, ensuring uniform pressure distribution and minimizing flow separation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves the efficiency of the last stage blade by up to 6% compared to traditional designs, ensuring a smooth and uniform steam flow with reduced vortices and operational complexity.
Implementation Method 1
exhaust diffuser and through a discharge opening, typically to a condenser to be condensed
Implementation Method 2
higher curvature of the outer guide surface may lead to a flow separation from the outer guide surface, which in turn has negative effects on static pressure recovery
Implementation Method 3
discharge opening, typically to a condenser to be condensed and brought back into the system
Implementation Method 4
to a condenser to be condensed and brought back into the system
Data Source
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AI summary
The present invention relates to an exhaust diffuser for a steam turbine comprising an inlet area (S1) and an outlet area (S2), an inner guide (7) and an outer guide (6) having an endpoint (E), wherein the inner guide (7) comprises an inclined wall (70, 71, 72) with at least two inflection points (A, B, C, D), wherein the inclination of the inclined wall (70, 71, 72) with respect to the longitudinal axis of the steam turbine is given at the inflection points, wherein the inner guide (7) is adapted so that a ratio of the axial length (LAL) of the exhaust diffuser to the distance (L1) between the base (2) of the last stage blades (3) and the stator body above the tip of the last stage blade (3) is between 1,25 and 1,5, and wherein the outer guide (6) is adapted so that the ratio of the outlet area (S2) to the inlet area (S1) is between 1,45 and 1,85. The exhaust diffuser with the geometry as defined above provides for the improvement of efficiency of the exhaust diffuser assembly, while it allows keeping the axial length of the diffuser as short as possible.