EGR Cooler Tubes With Compliant Regions for Thermal Stress Relief
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Solution Overview
Problem
EGR coolers fail due to high stress concentration at the connection points between cooling tubes and tube sheets, leading to degradation and leaks, caused by compressive forces and thermal gradients, especially at the leading edge closest to the exhaust inlet.
Innovation Solution
Incorporating a compliant region with corrugations on the leading cooling tubes near the exhaust inlet to allow expansion and reduce stress concentrations, while downstream tubes lack this feature to maintain structural integrity and prevent buckling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If cooling tubes are rigidly connected to tube sheets, then structural stability is improved, but stress concentration and connection degradation occur due to thermal expansion and compressive forces
Solution Approach 1:
The cooling tube is divided into three distinct segments: a rigid upstream section for structural stability, a compliant middle section with corrugations for stress absorption, and a downstream section for heat exchange. This segmentation allows each part to fulfill its specific function while resolving the contradiction between rigidity and flexibility.
Solution Approach 2:
Different sections of the cooling tube are given different mechanical properties - the upstream section near the exhaust inlet has higher rigidity to withstand compressive forces, while the middle compliant section has lower rigidity to absorb thermal expansion, and the downstream section has optimized properties for heat exchange efficiency.
2Duration of action of stationary object
If cooling tubes are made compliant to absorb thermal expansion, then connection durability is improved, but structural integrity and resistance to buckling deteriorate
Solution Approach 1:
The tube is segmented into rigid and compliant zones, where the rigid upstream section maintains structural integrity against buckling while the compliant middle section handles thermal expansion. This segmentation ensures that compliance is provided only where needed without compromising overall structural strength.
Solution Approach 2:
The corrugation geometry parameters (amplitude, wavelength, depth) are optimized to provide the exact amount of compliance needed for thermal expansion while maintaining sufficient structural rigidity to prevent buckling under compressive loads from the exhaust gas pressure.
3Stress or pressure
If corrugations are added to cooling tubes to allow expansion, then thermal stress is reduced, but manufacturing complexity increases
Solution Approach 1:
The corrugation geometry parameters (amplitude, wavelength, depth) are carefully selected and standardized to enable manufacturing using conventional tube forming equipment. The parameters are optimized to achieve the required compliance while remaining within the capabilities of standard manufacturing processes.
Solution Approach 2:
Corrugations are applied only to the middle compliant section of the tube where thermal expansion occurs, while the upstream and downstream sections remain smooth and rigid. This localized application reduces manufacturing complexity compared to corrugating the entire tube length.
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 compliant region absorbs thermal expansion and compressive forces, preventing degradation of the tube-tube sheet connection and reducing the risk of leaks and reduced cooling efficiency, thereby enhancing the durability and performance of the EGR cooler.
Implementation Method 1
the compliant region is shaped to enable expansion of the tube sheets toward and away from one another
Implementation Method 2
a compliant region including a plurality of corrugations
Data Source
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AI summary
Various methods and systems are provided for an exhaust gas recirculation cooler including a plurality of cooling tubes. In one example, an exhaust gas recirculation (EGR) cooler 134 includes a plurality of cooling tubes 204 positioned within a housing 202 of the EGR cooler, each cooling tube of the plurality of cooling tubes extending between and directly coupled to tube sheets 222 of the EGR cooler at ends of each cooling tube 204, where at least one end of one or more cooling tubes of a first portion of the plurality of cooling tubes, inward of a tube sheet coupled to the at least one end, includes a compliant region 306, where the first portion is positioned proximate to an exhaust inlet of the EGR cooler.