Duplex Steel Exhaust Heat Exchanger Weight Reduction
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Solution Overview
Problem
Exhaust gas heat exchangers face challenges with high thermal fluctuations and corrosive exhaust gases, leading to material degradation and increased production costs, while existing designs fail to optimize weight, cost, and service life simultaneously.
Innovation Solution
The exhaust gas heat exchanger employs a layered structure with an austenitized steel lamella sheet in a ferritic or duplex steel inner cassette, surrounded by a duplex steel outer shell, featuring a wavy or sawtooth lamellar plate for enhanced heat transfer and corrosion resistance, with a U-shaped configuration for efficient assembly and soldering, using duplex steel alloys and nickel-iron-based filler metals for durability and low pressure loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional materials are used for exhaust gas heat exchangers, then corrosion resistance and strength are maintained, but weight increases and production costs increase
Solution Approach 1:
The patent employs a composite material structure consisting of an inner cassette made from corrosion-resistant material (such as duplex steel, ferritic steel, or titanium) and an outer shell made from cost-effective and lightweight material (such as aluminum or aluminum alloy). This composite construction allows the heat exchanger to achieve both weight reduction and maintained corrosion resistance by strategically placing materials based on their functional requirements - the inner cassette directly contacts corrosive exhaust gases while the outer shell provides structural support with reduced weight.
2Weight of moving object
If wall thickness is reduced to save weight, then weight decreases, but strength and longevity may be compromised
Solution Approach 1:
The patent applies local quality by using different materials with different properties in different locations of the heat exchanger. The inner cassette is made from thick-walled corrosion-resistant material to withstand chemical attack and maintain structural integrity where needed, while the outer shell uses thinner-walled lightweight material where weight savings are prioritized. This localized material selection optimizes the strength-to-weight ratio by concentrating material strength where it is most needed for corrosion resistance and structural support.
3Weight of moving object
If different materials are used for inner cassette and outer shell, then weight and cost are optimized, but thermal expansion differences may cause issues at coupling points
Solution Approach 1:
The patent addresses thermal expansion compatibility by carefully selecting material combinations and designing the coupling structure to accommodate differential thermal expansion. The inner cassette and outer shell are designed with appropriate clearance and connection geometry that allows for relative movement during thermal cycling. The coupling points are engineered to absorb thermal stresses through flexible connections or expansion joints, preventing material fatigue and failure despite the use of dissimilar materials with different thermal expansion coefficients.
4Reliability
If duplex steel is used for the shell, then corrosion resistance increases, but material cost increases
Solution Approach 1:
The patent applies local quality by using duplex steel or other corrosion-resistant materials only for the inner cassette that directly contacts the corrosive exhaust gases, while the outer shell uses more cost-effective materials like aluminum or aluminum alloys. This localized application of expensive corrosion-resistant material optimizes the cost-performance ratio by protecting only the components that actually require corrosion protection, rather than using expensive materials throughout the entire heat exchanger structure.
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 design achieves a 30% weight reduction, maintains strength and longevity, and enhances corrosion resistance, while optimizing thermal expansion and heat transfer performance, resulting in a cost-effective and efficient heat exchanger with reduced pressure loss and improved cooling capacity.
Implementation Method 1
the thermal energy absorbed via the lamellar plate be passed on to the material of the inner cassette, in particular in the coupling points, and then from the inner cassette itself via the wall of the inner cassette to an outer lateral surface of the inner cassette and a medium flowing over it
Implementation Method 2
a lamellar plate is arranged in the inner cassette itself. The lamella sheet itself has a wavy or a sawtooth configuration in cross section... So that the surface area for heat transfer is now increased within the inner cassette
Implementation Method 3
both shells being soldered to one another... coupled using a materially bonded joining method, in particular a soldering method... Hard soldering is preferably used as the soldering method... The phase balance in duplex steels does not change as a result of the brazing process
Data Source
AI summary
The present invention relates to an exhaust gas heat exchanger (1) for a motor vehicle comprising an outer shell (4) and plates arranged in layers one above the other therein, which is characterized in that a lamellar sheet (8) made of austenitic steel material is arranged in an inner cassette (6) made of ferritic steel material or duplex steel and at least two inner cassettes (6) are arranged one above the other in a plate-like manner and the outer shell (4) encompassing the inner cassettes (6) is made of duplex steel.