Exhaust Duct Closure for Heat Exchanger Reverse Flow Blocking
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Solution Overview
Problem
Aircraft engines with air-cooled heat exchangers are susceptible to temperature-related damage due to hot exhaust gases venting through the heat exchanger duct when the engine shuts down, as the airflow stops, potentially damaging temperature-sensitive materials like aluminum.
Innovation Solution
A movable cover mechanism, such as spring-loaded flaps or actuatable plates, is positioned between the heat exchanger and exhaust duct to prevent hot exhaust gases from flowing upstream by transitioning between open and closed positions based on airflow pressure differentials during engine operation and shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heat exchanger duct remains open to the exhaust duct, then cooling air can flow through the heat exchanger during engine operation, but hot exhaust gases can flow back into the heat exchanger during engine shutdown causing temperature damage
Solution Approach 1:
The closure is made movable between open and closed positions based on engine operational state. During operation, the closure is open to allow cooling air flow; during shutdown, the closure moves to the closed position to prevent hot exhaust gas ingress, adapting the system's configuration to different operational phases
Solution Approach 2:
The closure acts as an intermediary element between the heat exchanger duct and exhaust duct. It selectively opens or closes the flow path based on engine state, mediating between the need for cooling during operation and the need for protection during shutdown
2Reliability
If a closure mechanism is added to prevent exhaust gas reverse flow, then heat exchanger protection is improved, but device complexity increases
Solution Approach 1:
The closure system is designed to operate automatically based on engine operational state without requiring external control systems. The biasing member and pressure differential work together to self-actuate the closure, opening during operation and closing during shutdown, eliminating the need for complex control mechanisms
Solution Approach 2:
The system utilizes pneumatic pressure differentials between the heat exchanger duct and exhaust duct to drive the closure mechanism. The biasing member works in conjunction with these pressure differentials to achieve automatic opening and closing based on engine state, reducing mechanical complexity
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
Prevents heat-related damage to the air-cooled heat exchanger by blocking hot exhaust gases from entering the heat exchanger duct during engine shutdown, thereby protecting temperature-sensitive components.
Implementation Method 1
a biasing member operatively connected to the closure biasing the closure toward the closed position with a biasing force
Implementation Method 2
a first force generated on the closure by the source of pressurized fluid at the first pressure being greater than a second force generated on the closure by the source of pressurized fluid at the second pressure
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A cover (40) system selectively allows a gas flow through a heat exchanger duct upstream of an exhaust duct (30) in an aircraft engine (10). A fluid is at a first pressure during an engine (10) operating condition and a second pressure lower than the first during shutdown. A plate (42) extends across the heat exchanger duct with aperture(s) extending therethrough. A closure is movable between an open position with gas flowing through the apertures (44) into the exhaust duct (30), and a closed position with the closure closing the apertures (44). A biasing member operatively connected to the closure closes the closure with a biasing force. During the engine operating condition, the first pressure creates a first force acting against and greater than the biasing force to urge the closure open. At shutdown, the second pressure creates a second force acting against and lower than the biasing force, the biasing force biasing the closure closed.