Aircraft Heat Exchanger Duct Reverse Flow Prevention
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Solution Overview
Problem
In aircraft engines, the venting of hot exhaust gas through the air-cooled heat exchanger duct during engine shutdown can cause temperature-related damage to temperature-sensitive materials like aluminum.
Innovation Solution
The implementation of a diverted airflow pathway and an evacuation valve in the heat exchanger duct assembly, which redirects hot exhaust gas away from the heat exchanger during shutdown and vents it to a safe location, preventing upstream flow and potential damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heat exchanger duct is directly connected to the exhaust duct, then the heat exchanger can effectively cool the exhaust gas during engine operation, but hot exhaust gas can flow back through the heat exchanger during engine shutdown causing temperature damage
Solution Approach 1:
The diversion pathway and valve are prepared in advance during engine operation but remain inactive. When shutdown is detected, the valve automatically activates the diversion pathway to redirect hot exhaust gas away from the heat exchanger, preventing temperature damage before it can occur
Solution Approach 2:
The harmful hot exhaust gas flow is extracted from the heat exchanger duct by introducing a separate diversion pathway. The evacuation valve selectively opens this alternative pathway during shutdown to channel exhaust gas away from the heat exchanger, separating the harmful flow from the temperature-sensitive components
2Reliability
If a valve is added to control exhaust gas flow, then reverse flow prevention is achieved, but the device complexity increases
Solution Approach 1:
The evacuation valve is designed to operate automatically based on engine operating conditions without requiring external control systems. The valve responds to pressure differentials and flow conditions itself, eliminating the need for complex control mechanisms while maintaining reliable reverse flow prevention
Solution Approach 2:
The diversion pathway acts as an intermediary channel that provides an alternative route for exhaust gas. By introducing this intermediate structure with a simple valve, the system achieves reliable flow control without directly modifying the main heat exchanger assembly, thereby limiting the increase in overall device 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
This solution effectively prevents hot exhaust gas from flowing upstream through the heat exchanger duct, thereby protecting temperature-sensitive components from damage during engine shutdown.
Implementation Method 1
an air-cooled heat exchanger disposed in the heat exchanger duct between the air inlet and the air outlet
Implementation Method 2
a valve in the duct wall of the heat exchanger duct between the first plate and the second plate, the valve selectively fluidly connecting the heat exchanger duct to an evacuation location
Data Source
AI summary
An aircraft engine has an exhaust duct receiving an engine gas flow and a heat exchanger duct having a wall extending from an inlet receiving a cooling air flow to an outlet connected to the exhaust duct. A heat exchanger is disposed in the heat exchanger duct between the inlet and outlet. A diverted airflow pathway in the heat exchanger duct includes first and second plates extending inwardly in the heat exchanger duct from first and second positions on an inner surface of the wall to plate distal ends, the plate distal ends extending past one another in a direction transverse to the wall. A valve in the wall selectively fluidly connects the heat exchanger duct to an evacuation location and is movable between closed and open positions during operating and shutdown conditions of the engine to fluidly disconnect and connect the heat exchanger duct to the evacuation location.