Ceramic Thermocouple Junction Design for Gas Turbine Reliability
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Solution Overview
Problem
Ceramic thermocouples lack mechanical integrity, making them unsuitable for harsh environments such as gas turbines.
Innovation Solution
A thermocouple assembly comprising a silicon carbide rod and a molybdenum tube with a molybdenum disilicide coating, where the contact between the elements is limited to tapered portions to form a junction, eliminating the need for aluminium oxide washers and enhancing mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminium oxide washers are used to separate the ceramic elements, then electrical insulation is achieved, but mechanical integrity is reduced
Solution Approach 1:
The invention removes the aluminium oxide washers from the thermocouple structure, extracting the insulating function to the ceramic materials themselves. The silicon carbide tube and molybdenum disilicide rod are inherently insulating at their contact surfaces, eliminating the need for separate insulator components and improving mechanical integrity.
Solution Approach 2:
The ceramic elements serve dual functions: they provide both the thermocouple junction for temperature measurement and electrical insulation. The silicon carbide tube and molybdenum disilicide rod maintain electrical isolation through their material properties and geometric configuration, combining structural and insulating functions in single components.
2Reliability
If spring arrangements are used to press the ceramic elements together, then thermal contact is improved, but device complexity increases
Solution Approach 1:
The invention removes the spring arrangement from the thermocouple structure, extracting the contact function to the inherent elasticity of the ceramic materials. The silicon carbide tube and molybdenum disilicide rod maintain thermal contact through their material compliance and geometric design, eliminating complex mechanical pressing mechanisms.
3Reliability
If multiple aluminium oxide washers are ranged at intervals, then electrical insulation is maintained, but manufacturing complexity increases
Solution Approach 1:
The invention removes the multiple aluminium oxide washers from the assembly, extracting the insulating function to the ceramic elements themselves. The silicon carbide tube and molybdenum disilicide rod are manufactured with insulating surfaces and geometric features that maintain electrical isolation without requiring separate insulator components, significantly simplifying manufacturing.
4Reliability
If the ceramic elements are made rugged for harsh environments, then reliability in gas turbines improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention uses composite ceramic structures combining silicon carbide and molybdenum disilicide, which provide both environmental durability and manufacturing flexibility. These ceramic materials offer high strength, thermal stability, and fracture toughness, enabling rugged designs that can withstand gas turbine environments while maintaining reasonable manufacturing tolerances through their inherent material properties.
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 provides improved mechanical integrity and reduced manufacturing costs while maintaining temperature measurement functionality, suitable for demanding environments.
Implementation Method 1
The junction at the respective tapered end portions between the different semi-conducting elements defined by the silicon carbide rod and molybdenum disilicide coating produce an electromotive force dependent on the temperature of the junction and thereby form a thermocouple.
Implementation Method 2
The insulating aluminium oxide coating 6 on the non-tapered portion of the silicon carbide rod separates the remainder of the semi-conducting silicon carbide from the remainder of the molybdenum disilicide coating.
Data Source
AI summary
A ceramic thermocouple (10) in which the hot junction is defined by the junction between a first element (3) of molybdenum disilicide and a second element (2) of silicon carbide. The molybdenum disilicide element is formed by a layer of molybdenum disilicide on a molybdenum support.