Reverse bootstrap air cycle machine
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Solution Overview
Problem
Reverse bootstrap air cycle machines on aircraft face challenges in providing adequate cooling when RAM air pressure is below ambient pressure, as insufficient power is available to drive the turbine and compressor, leading to inadequate vacuum for cooling electrical or electronic equipment.
Innovation Solution
Incorporating a motor connected to the shaft to drive the compressor when RAM air pressure is low, and using a control system with sensors to manage air flow through a turbine bypass valve and compressor bypass valve to optimize cooling based on RAM air pressure and temperature thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a reverse bootstrap air cycle machine uses only a turbine and compressor to cool equipment, then the device complexity is reduced, but the cooling performance deteriorates when RAM air pressure is below ambient pressure
Solution Approach 1:
The motor-compressor assembly serves multiple functions: it acts as a vacuum pump to draw air through the system when RAM pressure is low, and can be deactivated when RAM pressure is sufficient, allowing the turbine to drive the compressor. This multi-functionality resolves the contradiction by maintaining cooling performance across varying flight conditions without significantly increasing device complexity.
Solution Approach 2:
The system dynamically switches between motor-driven and turbine-driven operation based on RAM air pressure conditions. The control system activates or deactivates the motor depending on whether RAM pressure is below or above ambient pressure, optimizing cooling performance for each operational phase while avoiding unnecessary complexity.
2Reliability
If the motor is activated to drive the compressor when RAM air pressure is low, then the cooling performance is improved, but the energy consumption increases
Solution Approach 1:
The control system dynamically manages motor activation based on real-time RAM air pressure sensing. The motor is activated only when necessary (when RAM pressure is below ambient pressure and sufficient cooling is required), and deactivated when natural pressure differential is sufficient, thereby optimizing energy consumption while maintaining cooling performance.
Solution Approach 2:
The control system uses feedback from RAM air pressure sensors and temperature sensors to intelligently decide when to activate or deactivate the motor. This feedback mechanism ensures the motor operates only when truly necessary, balancing cooling performance requirements with energy consumption constraints.
3Reliability
If the turbine and compressor are always engaged, then the cooling capacity is maximized, but the device complexity and energy loss increase during high RAM air pressure conditions
Solution Approach 1:
The system employs bypass valves that allow air to partially bypass the turbine and compressor when RAM air pressure is sufficiently high. This partial action approach maintains adequate cooling capacity while avoiding the energy loss and mechanical wear that would result from continuously engaging all components, thus resolving the contradiction between cooling capacity and energy loss.
4Loss of energy
If bypass valves are added to direct air flow, then the energy efficiency is improved during high RAM pressure, but the device complexity increases
Solution Approach 1:
The bypass valves are integrated into the existing air cycle machine architecture, serving multiple functions: directing air flow to optimize energy efficiency during high RAM pressure, and maintaining proper system operation during various flight conditions. This multi-functional integration minimizes the increase in device complexity while achieving energy efficiency improvements.
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
Ensures effective cooling of heat loads by activating the motor to drive the compressor when necessary and bypassing components during high RAM air pressure conditions, enhancing the reverse bootstrap air cycle's performance and efficiency, including at ground static conditions.
Implementation Method 1
RAM air may be first expanded to a sub-ambient pressure and cooled in the turbine
Implementation Method 2
directed to a heat exchanger before being compressed back up to ambient pressure
Implementation Method 3
compressed back up to ambient pressure and expelled
Data Source
AI summary
Disclosed is a cooling circuit for cooling a heat load in an aircraft system, having: a compressor; a turbine connected to the compressor by a shaft, the turbine configured to drive the compressor via the shaft when RAM air pressure into a turbine inlet is above a first threshold; and a motor connected to the shaft configured to drive the compressor when RAM air pressure at the turbine inlet is below the first threshold to cause the compressor to draw air into the turbine inlet, through the turbine, a heat exchanger in fluid communication with the heat load, the compressor, and out of a compressor outlet.