Aircraft APU Muffler Vacuum Insulation
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Solution Overview
Problem
Current aircraft auxiliary power unit (APU) exhaust mufflers lack effective thermal insulation, leading to potential damage from high-temperature exhaust gases, and existing solutions are heavy, bulky, and inefficient in terms of weight and safety.
Innovation Solution
The use of a peripheral wall with multiple vacuum chambers, arranged to provide targeted thermal insulation, combined with a heat radiation protection layer and sensors for monitoring vacuum state, to minimize heat transfer and ensure safety and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If thermal blankets with foams and clothes are used for thermal insulation, then thermal insulation is provided, but weight increases significantly (up to 55% of exhaust weight)
Solution Approach 1:
The patent changes the physical state of the insulation medium from solid foam/cloth to vacuum (absence of matter). By creating vacuum chambers between the inner and outer walls, heat transfer by conduction and convection is eliminated, providing superior thermal insulation with minimal weight addition from the chamber structures themselves.
Solution Approach 2:
The patent uses vacuum as an inert environment between the inner and outer walls. This vacuum atmosphere prevents heat transfer and eliminates the need for heavy fire-resistant materials, while also preventing corrosion and chemical reactions that would require protective coatings.
2Temperature
If thermal blankets are used for thermal insulation, then thermal protection is provided, but the structure becomes bulky and occupies more space
Solution Approach 1:
The patent uses thin wall structures to enclose vacuum chambers, replacing bulky thermal blanket layers. The inner and outer walls are designed as thin shells that maintain structural integrity while minimizing volume, allowing the same thermal insulation performance in a more compact form factor.
3Reliability
If fire resistant thermal blankets are used, then fire resistance is achieved, but manufacturing complexity increases due to fluid tight requirements
Solution Approach 1:
The patent divides the exhaust muffler structure into separate vacuum chambers enclosed by inner and outer walls. This segmentation allows each chamber to be independently manufactured and sealed, reducing the overall manufacturing complexity compared to creating a single large fluid-tight thermal blanket assembly.
Solution Approach 2:
The patent replaces the mechanical thermal blanket system with vacuum-based thermal insulation. This substitution eliminates the need for fluid-tight sealing of porous materials and fire-resistant coatings, simplifying manufacturing while maintaining or improving fire resistance through the inherent properties of vacuum.
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 achieves high thermal insulation while being lightweight and compact, providing safety redundancy and efficient thermal protection with reduced weight and manufacturing complexity.
Implementation Method 1
The peripheral wall comprises at least two vacuum chambers arranged between an inner surface and an outer surface of the peripheral wall
Implementation Method 2
These foams and clothes need to be placed in fluid tight locations. In addition the thermal blankets need to be fire resistant.
Implementation Method 3
combined with a heat radiation protection layer and sensors for monitoring vacuum state, to minimize heat transfer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention relates to an exhaust muffler for an APU of an aircraft, comprising an exhaust gases inlet, an exhaust gases outlet, a peripheral wall adapted to guide a flow of exhaust gases between the inlet and the outlet, characterized in that said peripheral wall comprises at least one vacuum chamber to provide thermal insulation.