Microchannel Heat Exchanger Fins Spaced From Headers for Fatigue Life
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Solution Overview
Problem
Conventional microchannel heat exchangers experience thermal stress and reduced fatigue life due to alternating tensile and compressive stresses at the joints between high-temperature headers and low-temperature tubes, leading to potential cracking and decreased performance.
Innovation Solution
The design includes a microchannel heat exchanger with fins shorter than the tubes, where at least one end of each fin is spaced away from the adjacent header, reducing stress and strain caused by expansion and contraction, and improving structural support with guard or 'dummy' tubes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fins are attached to heat exchanger tubes that connect to headers, then heat transfer efficiency is improved, but thermal stress and fatigue life are worsened due to alternating tensile and compressive stresses at the joints
Solution Approach 1:
The patent extracts the fin structure from extending to the header region, creating a gap between the fin and header. This removes the fin (disturbing element) from the high-stress joint area, eliminating the source of thermal stress concentration while preserving heat transfer functionality in the tube sections.
Solution Approach 2:
The patent introduces guard tubes as intermediary elements between the header and the finned tubes. These guard tubes act as a buffer zone that protects the joint area from direct thermal stress, mediating the thermal expansion forces and preventing stress concentration at the fin-to-tube joints.
2Area of stationary object
If fins extend to the header region, then heat transfer area is increased, but cracking and structural integrity are reduced due to high alternating stress
Solution Approach 1:
The fin structure is extracted from the header region, creating a gap that removes the vulnerable area where cracking would initiate. The finned tubes maintain adequate heat transfer area while eliminating the structural weakness at the fin-to-header interface.
Solution Approach 2:
Guard tubes are positioned beforehand at the header-to-tube transition zones to cushion and absorb thermal stress before it reaches the finned sections. This preventive measure protects the structural integrity of the joint areas from high alternating stresses.
3Ease of manufacture
If conventional fin-to-tube joints are used, then manufacturing simplicity is maintained, but stress concentration and fatigue failure increase
Solution Approach 1:
The fin structure is extracted from the header region, eliminating the complex stress concentration zone at the fin-to-header joint. This maintains the simple conventional brazing process for fin-to-tube joints while removing the reliability issue.
Solution Approach 2:
Guard tubes serve as intermediary protective elements that simplify the overall structure by providing a built-in stress relief mechanism, eliminating the need for complex stress-management designs while improving fatigue resistance.
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
This configuration significantly enhances the fatigue life and reliability of the heat exchanger by distributing stress and maintaining effective heat transfer.
Implementation Method 1
Fins are typically arranged to extend between the tubes to air in the transfer of thermal energy between the heating/cooling fluid and the surrounding environment
Implementation Method 2
Fins are typically arranged to extend between the tubes to air in the transfer of thermal energy between the heating/cooling fluid and the surrounding environment
Implementation Method 3
A plurality of heat exchanger tubes is arranged in a spaced parallel relationship. The heat exchanger tubes fluidly couple the first manifold and the second manifold
Implementation Method 4
This is because a header of the heat exchanger thermally expands by exposure to a high temperature, while the fins coupled to the heat exchanger tubes remain at a lower temperature
Data Source
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AI summary
A heat exchanger is provided including a first manifold and a second manifold. The first manifold and the second manifold are separated from one another. A plurality of heat exchanger tubes is arranged in a spaced parallel relationship. The heat exchanger tubes fluidly couple the first manifold and the second manifold. A plurality of fins is attached to the plurality of heat exchanger tubes such that a first end of each fin is spaced apart from the first manifold by a first distance.