Spiral Zn Diffusion Layer for Corrosion-Resistant Heat Transfer Tubes
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Solution Overview
Problem
Heat transfer tubes in air conditioners face corrosion issues due to pitting corrosion, especially when made of aluminum alloys, leading to refrigerant leakage and reduced pressure resistance, particularly in harsh environments with salt and corrosive gases, where the thermal spraying of Zn has limitations in coverage and stability, resulting in unsprayed areas that compromise corrosion resistance.
Innovation Solution
A heat transfer tube with a spirally formed Zn diffusion layer covering 50% or more of the outer peripheral surface, having an average Zn concentration of 3% to 12%, a maximum concentration of 15% or less, and a diffusion depth of 80 μm to 285 μm, along with a lead angle of 8° or more, is used, combined with a manufacturing method involving thermal spraying, diffusion, and twisting to form spiral fins and Zn layers, ensuring comprehensive corrosion protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal spray guns are used to form Zn sprayed layer on heat transfer tube, then corrosion resistance is improved, but unsprayed portions remain on the outer peripheral surface compromising coverage
Solution Approach 1:
The patent transforms the linear sprayed layers from multiple thermal spray guns into a continuous spiral Zn diffusion layer wrapped around the heat transfer tube. This spiral configuration ensures complete circumferential coverage without unsprayed portions, while the curved spiral path allows uniform distribution of Zn along the entire tube surface, resolving the coverage gaps inherent in linear spraying approaches.
Solution Approach 2:
The patent transitions from forming Zn layers in the circumferential dimension only (using multiple spray guns positioned around the tube) to creating a spiral structure that extends into the longitudinal dimension. This three-dimensional spiral configuration ensures that every point on the tube surface is covered by the Zn diffusion layer, eliminating the unsprayed portions that occur when relying solely on circumferential spraying.
2Area of stationary object
If number of thermal spray guns is increased to improve sprayed layer coverage, then coverage increases, but equipment cost and Zn loss increase
Solution Approach 1:
The patent divides the Zn diffusion layer into sequential spiral segments that wrap around the heat transfer tube. This segmentation allows a single thermal spray gun to systematically cover the entire tube surface by moving along its length while the tube rotates, achieving complete coverage without requiring multiple simultaneous spray guns, thereby reducing equipment complexity and Zn material loss.
Solution Approach 2:
The patent implements continuous spiral wrapping of the Zn diffusion layer around the heat transfer tube, ensuring uninterrupted coverage. This continuous spiral approach allows a single spray gun to maintain constant useful action along the entire tube length, eliminating the need for multiple guns and their associated equipment costs while achieving complete surface coverage.
3Reliability
If Zn sprayed layer is formed by thermal spraying, then corrosion resistance is improved, but Zn concentration becomes non-uniform causing localized corrosion
Solution Approach 1:
The patent controls the thermal spray parameters (spray speed, rotation speed, Zn powder feed rate) to achieve uniform Zn deposition along the spiral path. By optimizing these parameters, the Zn concentration is maintained within a controlled range (3-12% average, maximum 15%), preventing localized high concentration areas that would cause accelerated corrosion while ensuring sufficient Zn content for corrosion protection throughout the diffusion layer.
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 excellent corrosion resistance, enabling the heat transfer tube to function effectively for an extended period in harsh environments by ensuring uniform Zn distribution and preventing pitting corrosion, even when rainwater or dew accumulates, thus enhancing the longevity and efficiency of the heat exchanger.
Implementation Method 1
The Zn diffusion layer is formed by thermally treating a Zn sprayed layer of an outer peripheral surface of a heat transfer tube and thermally diffusing Zn
Implementation Method 2
A Zn sprayed layer is formed by thermally spraying Zn to a heat transfer tube or an outer peripheral surface of a raw tube which becomes the heat transfer tube by a thermal spray gun
Data Source
AI summary
A heat transfer tube is made of aluminum and includes a streak-shaped Zn diffusion layer (6, 106) which is spirally formed on a circular outer peripheral surface in a length direction. According to this heat transfer tube, even in a case where rainwater or dew concentration water is intensively accumulated in a portion of the outer peripheral surface in a circumferential direction, it is possible to obtain a sufficient corrosion resistance.