Heat Exchanger Matrix Coating for Corrosion-Resistant Brazed Passages
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Solution Overview
Problem
Existing heat exchanger manufacturing methods face challenges in achieving effective corrosion resistance, especially at high temperatures and in corrosive environments like seawater, due to the inaccessibility of the brazed structure and the tortuosity of the network formed by corrugated mats, which limits the use of low-cost materials and complicates post-brazing anti-corrosion treatments.
Innovation Solution
A method involving pre-brazing deposition of an anti-corrosion coating on the internal walls of fluid passages using a bath of anti-corrosion product with specific grain size and load rate, followed by a thermal cycle that includes drying and brazing phases to synthesize a thin, corrosion-resistant layer matching the brazing alloy's melting temperature, ensuring protection against corrosion without degrading the metallurgical quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If post-brazing anti-corrosion treatment is applied, then corrosion resistance is improved, but the process becomes complex and may harm metallurgical quality due to additional heat treatment at high temperature
Solution Approach 1:
The patent applies preliminary action by depositing the anti-corrosion coating on components before brazing assembly. The coating is applied to individual plates and heat exchanger components prior to stacking and brazing, allowing the coating to be formed in advance rather than requiring complex post-brazing treatment. This resolves the contradiction by achieving corrosion protection without adding post-brazing process complexity or additional high-temperature heat treatment steps.
2Ease of manufacture
If low-cost materials are used, then manufacturing cost is reduced, but corrosion resistance deteriorates in corrosive environments
Solution Approach 1:
The patent applies composite materials by combining low-cost base materials (such as carbon steel or stainless steel plates) with an anti-corrosion coating layer. The composite structure consists of the structural base material providing mechanical strength and the anti-corrosion coating providing corrosion protection. This resolves the contradiction by achieving both cost-effectiveness through inexpensive base materials and reliability through the protective coating, allowing heat exchangers to be used in corrosive environments like seawater applications.
3Reliability
If anti-corrosion coating is applied before brazing, then corrosion resistance is improved, but the coating may be degraded during brazing operation
Solution Approach 1:
The patent applies parameter changes by carefully controlling the brazing temperature and duration parameters to be compatible with the anti-corrosion coating's thermal stability. The brazing process parameters (temperature, time, atmosphere) are optimized to complete the brazing operation without exceeding the coating's degradation threshold. This resolves the contradiction by maintaining coating integrity during brazing while still achieving the benefits of pre-coating application for corrosion protection.
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 method provides enhanced corrosion resistance for heat exchangers operating in high-temperature, corrosive environments, including those involving saltwater, by forming a dense, adherent anti-corrosion layer that maintains mechanical strength and integrity, extending the equipment's longevity and usability.
Implementation Method 1
pre-brazing deposition of an anti-corrosion coating on the internal walls of fluid passages using a bath of anti-corrosion product
Implementation Method 2
a first phase of heating the stacked matrix to a determined drying temperature, followed by a second phase of maintaining, for a determined drying time, the matrix at the temperature of drying, thereby drying the anti-corrosion layer
Implementation Method 3
a third phase of heating the stacked matrix to a determined brazing temperature higher than the drying temperature, followed by a fourth phase of maintaining, for a determined brazing time, the matrix at the brazing temperature, thus brazing the matrix
Data Source
Figure 1
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AI summary
Metal matrix (2) of a heat exchanger (1), comprising a stack of components (4, 5, 6), notably of etched plates or corrugations (4), separator sheets (5) and bars (6) or a combination of the two types of stack, said components (4, 5, 6) being held relative to one another by layers of braze material (3) thus affording the mechanical integrity of the matrix, the matrix comprising within it fluid-circulation passages (10), each fluid-circulation passage (10) having an internal wall intended to fully contain said fluid radially, characterized in that each internal wall is fully covered with a corrosion-resistant coating (7). Preferred application to heat exchangers based on carbon steel or on stainless steel.