Integrating Mixing Tubes into Combustor Shroud Walls
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Solution Overview
Problem
Conventional micro-mixer nozzle designs in gas turbine engines face issues with temperature differentials causing uneven thermal expansion, leading to durability problems and pressure drop losses, which affect system efficiency and part life.
Innovation Solution
The design incorporates wall mixing tubes within the shroud wall and plenum walls, which integrate fuel ports to mix air and fuel uniformly, reducing temperature differentials and maintaining structural integrity while maximizing flow area for efficient mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional nozzle design with separate mixing tubes and plenum walls is used, then fuel-air mixing can be achieved, but temperature differentials cause uneven thermal expansion and high strain levels
Solution Approach 1:
The patent merges the mixing tube and plenum wall into a single integrated component. The mixing tubes are formed as integral parts of the plenum wall, eliminating the interface between separate components. This integration ensures uniform thermal expansion throughout the structure, reducing strain levels while maintaining effective fuel-air mixing functionality.
2Strength
If outer plenum walls are exposed to high temperatures without internal cooling, then structural strength is maintained, but thermal expansion differences cause cracking and deformation
Solution Approach 1:
The plenum wall mixing tubes serve dual functions: they provide structural support for the plenum wall while simultaneously acting as cooling passages. The fuel flowing through these tubes provides internal cooling to the plenum walls, reducing thermal gradients and preventing thermal fatigue cracking, thereby enhancing durability without compromising structural strength.
3Manufacturing precision
If mixing tube cross-sectional area is decreased to enhance fuel-air mixing, then mixing efficiency improves, but flow area is reduced and pressure drop increases
Solution Approach 1:
The patent utilizes the plenum wall dimension to accommodate mixing tubes, effectively adding vertical space for mixing functionality. By forming mixing tubes within the plenum wall thickness, the design provides additional mixing surface area without reducing the horizontal flow area, thus maintaining low pressure drop while enhancing mixing efficiency.
4Volume of moving object
If head end diameter is kept small for cooling and packaging requirements, then packaging efficiency improves, but flow area through the nozzle is limited
Solution Approach 1:
The patent concentrates the mixing functionality within the plenum wall region, creating localized mixing zones where fuel is injected and mixed with air before entering the main flow path. This localizes the mixing process to a specific dimension (the wall thickness) while keeping the overall head end diameter small, thus maintaining compact packaging while providing sufficient mixing area.
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 reduces thermal strains, maintains structural integrity, and enhances fuel-air mixing efficiency, thereby extending part life and improving system efficiency by minimizing pressure drop losses.
Implementation Method 1
The areas immediately surrounding the nozzle operate at different temperatures. For example, because the forward wall of the nozzle is positioned within the cap assembly, it is adjacent to a region having a much lower temperature than the aft portion of the nozzle, which borders the combustion zone.
Implementation Method 2
Significant temperature differentials develop across different areas within the nozzle during operation. This is problematic because of the uneven thermal expansion that results and the stresses the uneven expansions causes.
Implementation Method 3
as will be appreciated, the supply of air and fuel typically arrive at the nozzle at significantly different temperatures. Each flow also has different heat transfer characteristics due to the different properties and flow speed of each fluid.
Implementation Method 4
micro-mixer nozzle configurations results in a pressure drop across the nozzle, which is what drives the air through the mixing tubes at such high velocities.
Implementation Method 5
The air/fuel mixture is then ignited and combusted within the combustor, and the resulting highly energized flow or 'working fluid' is then expanded through the rotating blades of the turbine so work may be extracted therefrom.
Data Source
AI summary
A micro-mixer nozzle for use in a combustor of a combustion turbine engine, the micro-mixer nozzle including: a fuel plenum defined by a shroud wall connecting a periphery of a forward tube sheet to a periphery of an aft tubesheet; a plurality of mixing tubes extending across the fuel plenum for mixing a supply of compressed air and fuel, each of the mixing tubes forming a passageway between an inlet formed through the forward tubesheet and an outlet formed through the aft tubesheet; and a wall mixing tube formed in the shroud wall.