Trans-Critical CO2 Cooling System for Wide Ambient Temperature Range
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Solution Overview
Problem
Current cooling systems for aerospace applications face limitations in efficiently operating over a wide range of ambient conditions, with vapor compression cycles being ineffective at high temperatures and gas-based systems being less efficient and bulkier.
Innovation Solution
A cooling system that operates in sub-critical, trans-critical, and super-critical modes using a refrigerant like CO2, with valve-controlled refrigerant flow paths and multiple compression stages, allowing for flexible operation and efficient heat management across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a vapor compression cycle is used, then cooling efficiency is improved through thermal carrying capacity and heat of vaporization, but the system becomes ineffective at high ambient temperatures
Solution Approach 1:
The system dynamically switches between sub-critical and trans-critical operating modes based on ambient temperature conditions. The refrigerant cycle adapts its pressure-temperature relationship to maintain efficiency across varying ambient temperatures, transitioning from conventional vapor compression at lower temperatures to trans-critical expansion at higher temperatures.
Solution Approach 2:
The system changes the operating parameters of the refrigerant cycle, specifically operating the CO2 refrigerant in trans-critical mode at high ambient temperatures where the refrigerant does not condense but rather undergoes a trans-critical expansion process, maintaining cooling efficiency beyond the limits of conventional vapor compression cycles.
2Adaptability or versatility
If a gas-based system using air as refrigerant is used, then the system can operate over a wide range of ambient conditions, but the system becomes less efficient and bulkier
Solution Approach 1:
The system uses CO2 refrigerant and changes its operating parameters to maintain high efficiency across wide ambient temperature ranges. By operating in trans-critical mode at high temperatures and sub-critical mode at lower temperatures, the system achieves both the adaptability of gas-based systems and the efficiency of vapor compression systems.
Solution Approach 2:
The system combines elements of both vapor compression and gas-based cycles into a hybrid trans-critical system. It integrates the high efficiency of liquid refrigerant thermal carrying capacity with the adaptability to operate across wide ambient temperature ranges, creating a composite cooling system that overcomes the limitations of either approach alone.
3Adaptability or versatility
If a gas-based system is used to cover a wide range of conditions, then the system can accommodate various ambient operating conditions, but the system size and mass increase
Solution Approach 1:
The system uses CO2 as a refrigerant with favorable thermodynamic properties that allow efficient operation across wide ambient temperature ranges. By utilizing trans-critical expansion and varying operating parameters, the system achieves wide adaptability without requiring the large mass and volume of traditional gas-based systems.
Solution Approach 2:
The trans-critical CO2 cooling system serves multiple functions: it operates efficiently at both high and low ambient temperatures, provides both sub-critical and trans-critical operating modes, and eliminates the need for separate systems for different temperature ranges. This multi-functionality reduces overall system mass compared to using separate optimized systems for different conditions.
4Use of energy by moving object
If a vapor compression cycle is used, then the system can provide efficient cooling through liquid thermal carrying capacity, but the system becomes limited to lower ambient temperature operation
Solution Approach 1:
The system changes the thermodynamic parameters of the refrigerant cycle by operating CO2 in trans-critical mode at high ambient temperatures. Instead of relying on condensation, the system uses trans-critical expansion where the refrigerant undergoes a phase transition without distinct liquid-vapor separation, maintaining high cooling efficiency at ambient temperatures where conventional vapor compression becomes ineffective.
Solution Approach 2:
The system dynamically adjusts its operating mode based on ambient temperature. At lower ambient temperatures, it operates in sub-critical vapor compression mode utilizing liquid thermal carrying capacity. At higher ambient temperatures, it transitions to trans-critical mode, dynamically adapting to maintain efficiency across the full temperature range.
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
Enables efficient cooling across a wide range of ambient conditions, reducing system size and weight while maintaining performance, by selectively directing refrigerant flow through different circuits based on ambient conditions and using CO2 as a refrigerant that spans the range of operating conditions.
Implementation Method 1
The evaporator is coupled to a thermal load of an aircraft and a receiver configured to accumulate reserve refrigerant to provide flexibility in system operation as the cooling system operates in sub-critical, trans-critical, and super-critical modes of operation
Implementation Method 2
A cooling system includes a first heat exchanger, an evaporator coupled to a thermal load of an aircraft
Data Source
AI summary
A cooling system includes a first heat exchanger, an evaporator coupled to a thermal load of an aircraft. first and second cooling circuits coupled to the heat exchanger, the first and second cooling circuits selectable via a set of cooling circuit valves that are arranged to direct a refrigerant through the first circuit, the second circuit, or both the first and second circuits based on air passing through the first heat exchanger at ambient conditions of the aircraft, and a receiver configured to accumulate reserve refrigerant to provide flexibility in system operation as the cooling system operates in sub-critical, trans-critical, and super-critical modes of operation.