Leaf-Shaped Heat Exchanger Core for Vibration Mitigation
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Solution Overview
Problem
Aircraft heat exchangers face reduced service life due to thermal stresses from temperature mismatches and mechanical stresses from vibrations, particularly at interfaces between fluid inlets, outlets, and core sections, leading to potential resonance issues.
Innovation Solution
A heat exchanger core with a stacked, leaf-like geometry and additively manufactured core layers featuring concentric tubular flow paths and connecting vanes, allowing for tailored dimensions and increased stiffness to mitigate thermal and vibrational stresses, and independent core tubes that can bend under thermal loads to avoid resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If traditional heat exchanger core designs are used, then manufacturing is simpler, but thermal stresses from temperature mismatches and mechanical stresses from vibrations reduce service life
Solution Approach 1:
The core structure is divided into multiple independent core stages (first core stage, second core stage, etc.) with separate inlet/outlet continuations. Each stage can deform independently under thermal and vibrational loads, preventing stress concentration at single points and extending service life while maintaining manageable manufacturing complexity through modular design
Solution Approach 2:
Different regions of the core structure have different geometries and properties - core tubes have specific diameters and wall thicknesses, connecting vanes have varying thicknesses, and fluid intersections have optimized shapes. This local optimization allows each region to handle specific stress conditions appropriately, improving overall durability without requiring complete structural redesign
2Reliability
If rigid core structures are used, then manufacturing precision is easier to achieve, but natural frequencies coincide with engine operating frequencies causing resonance
Solution Approach 1:
The core structure transitions from a rigid design to a compliant design where core tubes and connecting vanes can flex under thermal and vibrational loads. This dynamic compliance changes the natural frequencies of the core structure away from engine operating frequencies, preventing resonance while the additively manufactured geometry maintains sufficient dimensional precision for functional requirements
3Productivity
If conventional core geometries are used, then manufacturing is more straightforward, but pressure drop is higher and thermal performance is reduced
Solution Approach 1:
Core tubes are designed with curved geometries rather than straight configurations, and fluid intersections have optimized curved shapes. This curvature improves flow distribution and reduces pressure drop across the core structure, enhancing thermal exchange efficiency. The complex curved geometries are efficiently manufactured using additive manufacturing technology
4Strength
If interfaces between inlets/outlets and core section are made robust, then mechanical strength is improved, but thermal stress concentration increases
Solution Approach 1:
Connecting vanes with optimized thicknesses and core tubes with specific wall thicknesses are used at interfaces between inlets/outlets and core sections. These flexible elements can deform under thermal expansion and contraction, maintaining mechanical strength while distributing thermal stresses to prevent concentration and failure at critical interface regions
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 design enhances thermal and mechanical performance by reducing pressure drop, improving compliance, and raising natural vibrational frequencies, thus extending the service life and preventing harmful resonance conditions.
Implementation Method 1
A plurality of first core tubes fluidly connect the first bifurcation to the first recombination
Implementation Method 2
Many aircraft heat exchangers operate at high temperatures and are subject to thermal stresses caused by thermal expansion, especially with thermal coefficient mismatch and uneven temperature distribution
Data Source
AI summary
A core arrangement for a heat exchanger includes a first core layer disposed along a first plane and having an inlet and outlet oriented along a first axis within the first plane and a first core stage disposed in fluid communication between the inlet and the outlet. The first core stage includes a first upstream fluid intersection downstream of and adjacent the inlet and having a first inlet continuation and a first bifurcation. The first core stage further includes a first downstream fluid intersection upstream of and adjacent the outlet and having a first outlet continuation and a first recombination. A plurality of first core tubes fluidly connect the first bifurcation to the first recombination. The first core layer further includes a second core stage disposed in fluid communication between the first inlet continuation and the first outlet continuation. The second core stage includes a second upstream fluid intersection downstream of the first inlet continuation and having a second bifurcation, and a second downstream fluid intersection upstream of the first outlet continuation and having a second recombination. A plurality of independent second core tubes fluidly connect the second bifurcation to the second recombination.