Ceramic Spool Clearance Control via Phase-Change Paraffin
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining desired clearances between metallic and ceramic components due to differential thermal expansion, leading to parasitic performance losses and efficiency issues across varying operating temperatures and pressures.
Innovation Solution
An active clearance control system using an impingement-cooled conical arm and a sliding seal system allows the metallic volute to move independently of the ceramic shroud, maintaining a constant or controlled clearance gap between the ceramic rotor and shroud, minimizing gas flow leakage and optimizing engine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metallic and ceramic components are used in the gas turbine spool, then higher temperature operation and reduced component weight are achieved, but differential thermal expansion causes clearance control problems
Solution Approach 1:
The patent changes the physical state of the clearance control mechanism by using a phase-change material (paraffin) that transitions from solid to liquid at a specific temperature. This phase change allows the mechanism to automatically adjust and maintain the desired clearance between ceramic rotor and shroud across varying operating temperatures without requiring active control systems.
Solution Approach 2:
The clearance control system is designed to be self-regulating through the phase-change material that automatically expands or contracts based on temperature changes. The system serves itself by using the thermal energy from the engine operation to drive the clearance adjustment, eliminating the need for external power sources or complex control mechanisms.
2Loss of energy
If clearance gap between rotor and shroud is reduced to minimize leakage, then engine efficiency improves, but thermal expansion causes clearance variation under operating conditions
Solution Approach 1:
The patent utilizes the phase-change parameter of paraffin to dynamically adjust the clearance gap. As the paraffin transitions from solid to liquid, it changes volume and thereby adjusts the clearance between the rotor and shroud, maintaining optimal sealing while accommodating thermal expansion during engine operation.
Solution Approach 2:
The patent converts the harmful effect of thermal expansion into a beneficial self-regulating mechanism. The heat from the engine operation causes the paraffin to phase-change, which automatically adjusts the clearance to compensate for thermal expansion, turning the thermal energy that would normally cause clearance problems into the driving force for maintaining optimal clearance.
3Manufacturing precision
If active clearance control system is implemented, then clearance stability is maintained, but device complexity increases
Solution Approach 1:
The clearance control system is designed to be self-regulating through the phase-change material that automatically expands or contracts based on temperature changes. The system serves itself by using the thermal energy from the engine operation to drive the clearance adjustment, eliminating the need for external power sources or complex control mechanisms.
Solution Approach 2:
The patent replaces complex mechanical or electronic control systems with a passive thermal-mechanical system based on phase-change material. This substitution eliminates motors, sensors, actuators, and control electronics, reducing device complexity while maintaining effective clearance control through the natural physical properties of the paraffin.
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
The solution effectively maintains a stable clearance gap, reducing parasitic flow losses and enhancing overall engine efficiency by minimizing axial motion of the shroud at operating temperatures, thereby preventing a significant increase in leakage mass flow rate.
Implementation Method 1
accommodate the differential rates of thermal expansion between the ceramic rotor and metallic volute
Implementation Method 2
impingement-cooled conical arm
Implementation Method 3
sliding seal system that allows the metallic volute to expand and move independently of the ceramic shroud
Data Source
AI summary
A method and apparatus are disclosed for a gas turbine spool design combining metallic and ceramic components in a way that controls clearances between critical components over a range of engine operating temperatures and pressures. In a first embodiment, a ceramic turbine rotor rotates just inside a ceramic shroud and separated by a small clearance gap. The ceramic rotor is connected to a metallic volute. In order to accommodate the differential rates of thermal expansion between the ceramic rotor and metallic volute, an active clearance control system is used to maintain the desired axial clearance between ceramic rotor and the ceramic shroud over the range of engine operating temperatures. In a second embodiment, a ceramic turbine rotor rotates just inside a ceramic shroud which is part of a single piece ceramic volute/shroud assembly. As temperature increases, the ceramic volute expands at approximately the same rate as ceramic shroud and tends to increase the axial clearance gap between the ceramic rotor and ceramic shroud, but only by a small amount compared to a metallic volute attached to the shroud in the same way.