Bowed Heat Exchanger Core for Thermal Stress and Vibration
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Solution Overview
Problem
Heat exchangers used in aircraft engines experience short service lifetimes due to thermal and vibrational stresses, particularly at the interface of the heat exchanger inlet/outlet and core, where thermal expansion and material properties cause cracking and expansion issues.
Innovation Solution
A heat exchanger core design featuring compliant bowed conduits that reduce stiffness and accommodate thermal stress through bending deformation, with additively manufactured tubular dimensions tailored for specific operating environments, and varying wall thicknesses to balance compliance and stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the heat exchanger core uses rigid conduits to maintain structural strength, then the component can withstand mechanical loads, but thermal stress accumulates at the inlet/outlet interface causing cracking and reduced service life
Solution Approach 1:
The patent applies this principle by implementing compliant conduits with bowed geometries that can flex and deform under thermal stress. The conduits are designed with sufficient flexibility to accommodate thermal expansion and contraction while maintaining their structural integrity, thereby preventing cracking at the inlet/outlet interface and extending service life.
Solution Approach 2:
The patent applies this principle by varying the geometric parameters of the conduits, specifically introducing bowed shapes with controlled curvature radii and arc lengths. These parameter changes allow the conduits to have different compliance characteristics, enabling them to absorb thermal stress while maintaining the necessary structural strength for mechanical loads.
2Reliability
If the conduits are made compliant to reduce thermal stress, then thermal stress is reduced, but the component stiffness decreases potentially increasing vibrational response
Solution Approach 1:
The patent applies this principle by implementing varying wall thicknesses along the length of the conduits. The conduits have thicker walls at the inlet and outlet sections where they connect to rigid headers, providing local stiffness to reduce vibrational response. The mid-sections have thinner walls to provide compliance for thermal stress accommodation, thus achieving both thermal stress resistance and vibrational control.
Solution Approach 2:
The patent applies this principle by designing the conduits with bowed geometries rather than straight configurations. The curved paths naturally provide compliance for thermal expansion while the arc-shaped structure distributes stress more evenly, reducing peak stresses and improving resistance to both thermal and vibrational loads compared to straight rigid conduits.
3Ease of manufacture
If uniform wall thickness is used for simplicity of manufacture, then manufacturing is easier, but optimal balance between compliance and stiffness cannot be achieved
Solution Approach 1:
The patent applies this principle by specifying varying wall thicknesses at different locations along the conduits. The inlet and outlet sections have greater wall thicknesses to provide stiffness and reduce vibrational response, while the mid-sections have reduced wall thicknesses to provide compliance for thermal stress accommodation. This localized variation optimizes both thermal and vibrational performance while remaining manufacturable through additive processes.
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 thermal stress and vibrational response, allowing for improved heat transfer efficiency and extended service life.
Implementation Method 1
thermal stresses, which can cause expansion and cracking of the fluid conduits
Implementation Method 2
stresses due to vibration can arise when the natural frequencies of the component coincide significantly with engine operating frequencies
Data Source
Figure 1
Figure 2
AI summary
A core arrangement for a heat exchanger includes a plurality of inlets (34) arranged around an axis, a plurality of outlets (36) arranged around the axis, and a plurality of bowed conduits (18) arranged around the axis. The bowed conduits are structurally independent, connect the plurality of inlets to the plurality of outlets, bow outward from the axis between the plurality of inlets and the plurality of outlets, and provide thermal compliance to the core.