Brazed Metallic-Graphite Composite for Thermal Mismatch
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Solution Overview
Problem
Current graphite fiber and substrate structures face thermal mismatch issues and fragility due to the limited thickness and handling sensitivity of fibercore graphite, which affects their performance in heat exchanger systems.
Innovation Solution
A multi-layer fibercore graphite structure with longer graphite fibers and a sandwich configuration using BNi-2 filler and nickel-based metallic sheets, brazed to a substrate, enhances thermal compatibility and robustness, allowing for efficient brazing and shaping without damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fibercore graphite is used with limited thickness, then the structure can be handled and shaped, but thermal mismatch issues occur with metallic substrates
Solution Approach 1:
The patent uses a composite structure combining fibercore graphite layers with monolithic graphite layers. The fibercore graphite provides handling flexibility and machinability, while the monolithic graphite layer provides thermal compatibility with metallic substrates. This composite approach allows the structure to be both handleable and thermally reliable when brazed to aluminum or other metallic substrates.
2Reliability
If the thickness of fibercore is increased, then thermal mismatch is reduced, but the material becomes more fragile and difficult to handle
Solution Approach 1:
Instead of increasing fibercore thickness alone, the patent creates a composite where thin fibercore graphite layers (easy to handle) are combined with monolithic graphite layers (thermally compatible). This allows achieving thermal compatibility without making the fibercore itself thicker and more fragile.
Solution Approach 2:
Different regions of the graphite structure have different properties: the fibercore regions provide handling flexibility and machinability where needed, while the monolithic graphite regions provide thermal compatibility at the brazing interfaces with metallic substrates.
3Strength
If graphite fibers are joined to substrate via brazing, then strong bonding is achieved, but thermal mismatch causes stress during thermal processing
Solution Approach 1:
The patent addresses thermal expansion mismatch by using monolithic graphite layers with thermal expansion properties closer to metallic substrates at the brazing interface. This reduces thermal stress during processing while maintaining strong brazed bonds.
Solution Approach 2:
The composite structure allows the monolithic graphite layer to absorb thermal stresses at the interface, protecting the brazed joint from excessive stress while maintaining bonding strength.
4Reliability
If longer graphite fibers are used, then thermal compatibility improves, but the material becomes more fragile during handling
Solution Approach 1:
The patent combines long-fiber monolithic graphite (thermally compatible) with fibercore graphite (handleable) in a composite structure. This allows achieving thermal compatibility through the monolithic layer without making the entire structure fragile, as the fibercore portions remain easy to handle and shape.
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 a more robust and thermally compatible graphite fiber structure that reduces handling damage and improves thermal mismatch issues, enabling efficient heat dissipation and shaping for heat exchanger applications.
Implementation Method 1
securing the at least one metallic sheet to the one or more layers of graphite fiber material via brazing
Data Source
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AI summary
Disclosed is a method of assembling a metallic-graphite structure (10) including arranging one or more layers of graphite fiber material (12) and locating at least one metallic sheet (22) adjacent to the one or more layers of graphite fiber material (12). The at least one metallic sheet (22) is secured to the one or more layers of graphite fiber material (12) via brazing. Further disclosed is a metallic-graphite structure (10) including one or more layers of graphite fiber material (12) and at least one metallic sheet (22) located adjacent to the one or more layers of graphite fiber material (12). The at least one metallic sheet (22) is secured to the one or more layers of graphite fiber material (12) via brazing.