Adaptive trans-critical CO<sub>2 </sub>cooling systems for aerospace applications
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Solution Overview
Problem
Current cooling systems in aerospace applications are inefficient and bulky, particularly at high ambient temperatures, and often require redundant systems that exacerbate space constraints, limiting their effectiveness and design flexibility.
Innovation Solution
A cooling system with multiple evaporators and valve-controlled refrigerant flow paths that operate in trans-critical, sub-critical, or supercritical modes, using CO2 as a refrigerant to manage ambient conditions, and incorporating features like two-stage compression and ejectors to optimize performance across a wide range of temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a vapor compression cycle is used, then cooling efficiency is improved and system size is reduced, but the system cannot operate effectively at high ambient temperatures
Solution Approach 1:
The system dynamically switches between sub-critical and trans-critical operating modes based on ambient temperature conditions. A control system adjusts valve positions and refrigerant flow paths to optimize performance across varying ambient temperatures, allowing the system to adapt from efficient two-phase operation at lower temperatures to single-phase trans-critical operation at high temperatures
Solution Approach 2:
The system changes the thermodynamic operating parameters of the refrigerant by transitioning between sub-critical and trans-critical modes. This involves adjusting pressure and temperature parameters beyond the critical point of CO2, enabling the system to maintain efficiency across a wide ambient temperature range by optimizing refrigerant state at different operating conditions
2Adaptability or versatility
If a gas-based system is used to accommodate wide ambient conditions, then adaptability is improved, but system size and mass increase
Solution Approach 1:
The CO2-based system serves multiple functions by operating in both sub-critical two-phase mode and trans-critical single-phase mode. This multi-functionality allows a single system design to handle wide ambient temperature ranges without requiring separate systems, thereby reducing overall system mass while maintaining adaptability
Solution Approach 2:
By changing the operating parameters to trans-critical mode, the system achieves adaptability to wide ambient conditions without the mass penalty of a pure gas-based system. The liquid-like density of CO2 in trans-critical mode provides better thermal fluid properties compared to gas-based systems, reducing the mass required for duct passages and refrigerant volume
3Reliability
If redundant cooling systems are installed, then reliability is improved, but space requirements increase
Solution Approach 1:
The system uses dynamic control with adjustable valves and flow paths to provide redundancy. Instead of installing a complete duplicate system, the control system can dynamically redirect refrigerant flow and activate different portions of the system to compensate for failures, maintaining reliability while reducing space requirements through intelligent control rather than physical duplication
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
The system achieves efficient and compact cooling by dynamically adjusting refrigerant flow based on ambient conditions, reducing space requirements and improving efficiency across varying operational conditions, while maintaining redundancy for reliability.
Implementation Method 1
Vapor compression cycles pass a refrigerant through two-phase operation and can operate efficiently and take advantage of the thermal carrying capacity of a liquid, as opposed to a gas, as well as take advantage of the heat of vaporization of the liquid refrigerant
Implementation Method 2
Heat is rejected from the first and second cooling circuits, via a heat exchanger, from a respective cooling circuit to air passing into an engine of the aircraft
Implementation Method 3
a compressor configured to compress the CO2 refrigerant to a pressure above the critical pressure of the CO2 refrigerant
Implementation Method 4
an expansion device configured to expand the CO2 refrigerant from the high pressure to a low pressure
Data Source
AI summary
A cooling system for an aircraft includes a first cooling circuit having a first evaporator and a second evaporator, and a second cooling circuit having a third evaporator and a fourth evaporator. One of the first and second cooling circuits includes a first set of valves arranged to direct refrigerant through a first cooling sub-circuit, a second cooling sub-circuit, or both the first and second cooling sub-circuits based on ambient conditions. Two of the evaporators are installed on a first side of the aircraft, and the other two of the four evaporators are installed on a second side of the aircraft opposite the first side, and the first and second cooling circuits reject heat, via a heat exchanger, from their respective cooling circuit to air passing into an engine of the aircraft.